Root zone temperature

In most desert ecosystems of the Arabian Peninsula Region (APRP), vegetable production is carried out under controlled environment structures covered with polycarbonate sheets and inbuilt evaporative cooling systems. The areas with mild winter, polycarbonate cover and evaporative cooling are not required. The former can be replaced by insect proof net and the latter with a root zone cooling system to maintain the root

Among the leafy vegetables, lettuce (Lactuca sativa L.) is the most widely grown species in the world. Wide ranges of physical properties of the products are used to assess the degree of maturity. In this study, different lettuce varieties were grown under an unheated plastic tunnel in springtime. We evaluated the agronomic properties of different lettuce varieties, evaluated the condition of the plants, and determined the bioactive substances. Larger head weight can be achieved by the 'King of May' butterhead (259.31 g) and 'Great Lakes 659'crisphead (220.40 g) genotypes. A very strong correlation (r = 0.995) was observed between the lettuce head index, and leaf index and both had a strong positive correlation (r = 0.828 and 0.760) with NDVI. The highest SPAD values were measured for cos lettuce 'Romaine lettuce' (44.01) and iceberg lettuce 'Great Lakes 659' (42.71). However, these genotypes showed the highest (9.52%; 8.74%) dry matter content, too. The red leaf variety 'Lollo Rosso' had the highest total polyphenol content (181.53 GAE/100 g FW). Among the evaluated properties, iceberg lettuce showed favorable morphology, plant condition, and good dry matter content. In addition, between the loose-leaf lettuces, the red leaf lollo type was outstanding with bioactive content.

Carbon dioxide (CO 2) concentration is reported to be the most important climate variable in greenhouse production with its effect on plant photosynthetic assimilation. A greenhouse study was conducted using a nutrient film technique (NFT) system to quantify the effect of two different levels of CO 2 (supplemented at an average of 800 ppm and ambient at~410 ppm) on growth and nutritional quality of basil (Ocimum basilicum L.) 'Cardinal', lettuce (Lactuca sativa L.) 'Auvona', and Swiss chard (Beta vulgaris L.) 'Magenta Sunset' cultivars. Two identical greenhouses were used: one with CO 2 supplementation and the other serving as the control with an ambient CO 2 concentration. The results indicate that supplemented CO 2 could significantly increase the height and width of hydroponically grown leafy greens. Supplemented CO 2 increased the fresh weight of basil 'Cardinal', lettuce 'Auvona', and Swiss chard 'Magenta Sunset' by 29%, 24.7%, and 39.5%, respectively, and dry weight by 34.4%, 21.4%, and 40.1%, respectively. These results correspond to a significant reduction in Soil Plant Analysis Development (SPAD) and atLEAF values, which represent a decrease in leaf chlorophyll content under supplemented CO 2 conditions. Chlorophyll, nitrogen (N), phosphorus (P), and magnesium (Mg) concentrations were generally lower in plants grown in supplemented CO 2 conditions, but the results were not consistent for each species. Supplemented CO 2 reduced tissue N concentration for basil 'Cardinal' and lettuce 'Auvona' but not Swiss chard, while Mg concentration was reduced in supplemented CO 2 for Swiss chard 'Magenta Sunset' only. In contrast, Fe concentration was increased under supplemented CO 2 for basil 'Cardinal' only. These findings suggest CO 2 supplementation could increase yield of leafy greens grown with hydroponics and have varying impact on different mineral concentrations among species.

Carbon dioxide (CO2) concentration is reported to be the most important climate variable in greenhouse production with its effect on plant photosynthetic assimilation. A greenhouse study was conducted using a nutrient film technique (NFT) system to quantify the effect of two different levels of CO2 (supplemented at an average of 800 ppm and ambient at ~410 ppm) on growth and nutritional quality of basil (Ocimum basilicum L.) ‘Cardinal’, lettuce (Lactuca sativa L.) ‘Auvona’, and Swiss chard (Beta vulgaris L.) ‘Magenta Sunset’ cultivars. Two identical greenhouses were used: one with CO2 supplementation and the other serving as the control with an ambient CO2 concentration. The results indicate that supplemented CO2 could significantly increase the height and width of hydroponically grown leafy greens. Supplemented CO2 increased the fresh weight of basil ‘Cardinal’, lettuce ‘Auvona’, and Swiss chard ‘Magenta Sunset’ by 29%, 24.7%, and 39.5%, respectively, and dry weight by 34.4%, 21.4%...

Background Nitrogen (N), phosphorus (P), and potassium (K) are the three major fertilizer nutrients, and adequate fertilization is one of the most important factors in plant production (Mengel and Kirkby 2001). Fertilization may affect the availability of elements other than those applied to soils. For example, the application of ammonium sulfate may increase the availability of some heavy metals in soils by lowering soil pH (Murányi et al. 1994). The effects of fertilization on soils are more obvious in a long-term fertilizer experiment

Under the impact of new cultivation and socioeconomic trends, and the aspiration for agricultural sustainability, a research study was conducted under Cyprus conditions. Lettuce (Lactuca sativa cvs. 'Paris island', 'Lollo rosa', and 'Oakleaf') and strawberry (Fragaria x ananassa cv. 'Camarosa') plants were used to evaluate horizontal and vertical growing setups in a 'closed' soilless system. For lettuce, the vertical system provided more marketable lettuce per system's surface area compared to the horizontal setup. However, the horizontal system provided greater lettuce mass and higher percentage marketable yield than the vertical one. The nitrate content of all lettuce cultivars was not signifi cantly different between the two systems and remained lower than the European standards all over the experiment. For strawberry, the vertical setup offered higher yield compared to the horizontal one. The quality characteristics were not different between the two systems. These results suggest that the studied setups and the 'closed' soilless system can be used as a tool for the improvement of Cyprus greenhouse production, water use effi ciency and prevention of environmental damage from regular` disposal of hydroponics solution. The possibility of an improved greenhouse production system could be considered as technique of choice under semi-arid Cyprus and E. Mediterranean conditions using such materials.

One of the main limiting factors of plant yield is drought, and while the physiological responses to this environmental stress have been broadly described, research addressing its impact on mineral nutrition is scarce. Brassica napus and Triticum aestivum were subjected to moderate or severe water deficit, and their responses to drought were assessed by functional ionomic analysis, and derived calculation of the net uptake of 20 nutrients. While the uptake of most mineral nutrients decreased, Fe, Zn, Mn, and Mo uptake were impacted earlier and at a larger scale than most physiological parameters assessed (growth, ABA concentration, gas exchanges and photosynthetic activity). Additionally, in B. napus, the patterns of 183 differentially expressed genes in leaves related to the ionome (known ionomic genes, KIGs) or assumed to be involved in transport of a given nutrient were analyzed. This revealed three patterns of gene expression under drought consisting of up (transport of Cl and Co), down (transport of N, P, B, Mo, and Ni), or mixed levels (transport of S, Mg, K, Zn, Fe, Cu, or Mn) of regulation. The three patterns of gene regulations are discussed in relation to specific gene functions, changes of leaf ionomic composition and with consideration of the crosstalks that have been established between elements. It is suggested that the observed reduction in Fe uptake occurred via a specific response to drought, leading indirectly to reduced uptake of Zn and Mn, and these may be taken up by common transporters encoded by genes that were downregulated. Highlight In wheat and rapeseed, drought downregulates the uptake of Fe, Mo, Zn, and Mn before reduction of growth, and this was associated with differential expressions of transport-related genes.

We investigated the performance of six Intermountain West (IMW) native herbaceous perennial species grown in a pot-in-pot (PIP) or conventional above-ground (CAG) production system for two years. Three different species were grown for two production cycles each year. Root zone temperature (RZT), plant and container water loss, stomatal conductance, plant height, and final biomass were measured. The RZT of plants in the PIP system were as much as 7C cooler than the CAG system, with temperature differences greater at the edge than at the center of the container. Water loss was approximately 10% lower for PIP plants on five of eight measured dates despite higher stomatal conductance on five of seven dates. Higher RZT and lower gas exchange reduced top growth more than root growth for CAG produced plants, but results varied with species and season. Conventional above-ground plants showed no visible damage but had slower growth rates compared to PIP plants. Lower elevation species were m...

The aim of this research was to develop an effective protocol for the application of nonthermal plasma (NTP) technology to the hydroponic nutrient solution, and to investigate its effects on the growth and quality of baby leaf lettuce (Lactuca sativa var. acephala Alef.) grown in a hydroponic growing system (HGS) specifically designed for indoor home cultivation. Four HGSs were placed in separate growth chambers with temperature of 24 ± 1 °C and relative humidity of 70 ± 5%). Lettuce plants were grown for nine days in nutrient solutions treated with NTP for 0 (control) to 120 s every hour. Results of the first experiments showed that the optimal operating time of NTP was 120 s h−1. Fresh leaf biomass was increased by the 60 and 120 s NTP treatments compared to the control. Treating the nutrient solution with NTP also resulted in greater leaf content of total chlorophylls, carotenoids, total phenols, and total antioxidant capacity. NTP also positively influenced chlorophyll a fluores...

Bacterial leaf spot (BLS) caused by Xanthomonas campestris pv. vitians (Xcv) places a major constraint on lettuce production worldwide. The most sustainable strategy known to date for controlling BLS is the use of resistant cultivars. The nutrient elemental signature (ionome) of ten lettuce cultivars with three levels of resistance was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine which nutrient balances are linked to resistance to BLS, and to assess the effect of Xcv infection on the ionome. The elemental concentrations were preprocessed with isometric log-ratios to define nutrient balances. Using this approach, 4 out of 11 univariate nutrient balances were found to significantly influence the resistance of lettuce cultivars to BLS (P < 0.05). These significant balances were the overall nutritional status balancing all measured nutrients with their complementary in the dry mass, as well as balances [Mn | Zn,Cu], [Zn | Cu], and [S,N | P]. Moreover, the infection of lettuce cultivars mostly affected the lettuce ionome on the [N,S | P] balance, where infection tended to lean the balance toward the N,S part relatively to P. This study shows that nutrient uptake in lettuce can be affected by BLS infection and that nutrient status influences resistance to BLS infection.

The aim of this research was to develop an effective protocol for the application of nonthermal plasma (NTP) technology to the hydroponic nutrient solution, and to investigate its effects on the growth and quality of baby leaf lettuce (Lactuca sativa var. acephala Alef.) grown in a hydroponic growing system (HGS) specifically designed for indoor home cultivation. Four HGSs were placed in separate growth chambers with temperature of 24 ± 1 °C and relative humidity of 70 ± 5%). Lettuce plants were grown for nine days in nutrient solutions treated with NTP for 0 (control) to 120 s every hour. Results of the first experiments showed that the optimal operating time of NTP was 120 s h−1. Fresh leaf biomass was increased by the 60 and 120 s NTP treatments compared to the control. Treating the nutrient solution with NTP also resulted in greater leaf content of total chlorophylls, carotenoids, total phenols, and total antioxidant capacity. NTP also positively influenced chlorophyll a fluores...

In this study, phosphorus (P) strength [(full strength: 1×-P, half strength: 0.5×-P and zero strength: 0×-P)] and root zone temperature (10 and 15 °C RZT) were investigated in red romaine lettuce to determine their effects on anthocyanin content. This experiment was conducted using a deep-flow technique (DFT) hydroponic system in a greenhouse during the winter in Gangwon province in the Korea Republic. The treatments were 1×-P (15 and 10 °C RZT), 0.5×-P (15 and 10 °C RZT) and 0×-P (15 and 10 °C RZT). The results showed that the P (phosphorus), K (potassium) and Ca (calcium) accumulation contents were lower in the 0×-P -treated red romaine lettuce leaves than in the other treatments. The maximum red romaine lettuce yields per plant, leaf number and leaf length were exhibited during the 1×-P at 15 °C RZT treatment. In 0×-P at 10 °C, RZT treatment showed lower leaf color values of L*, b*, chrome, ºh and higher leaf color a* values. Moreover, in the 0×-P treatment at 10 °C RZT, the leaf...

In this study, phosphorus (P) strength [(full strength: 1×-P, half strength: 0.5×-P and zero strength: 0×-P)] and root zone temperature (10 and 15 °C RZT) were investigated in red romaine lettuce to determine their effects on anthocyanin content. This experiment was conducted using a deep-flow technique (DFT) hydroponic system in a greenhouse during the winter in Gangwon province in the Korea Republic. The treatments were 1×-P (15 and 10 °C RZT), 0.5×-P (15 and 10 °C RZT) and 0×-P (15 and 10 °C RZT). The results showed that the P (phosphorus), K (potassium) and Ca (calcium) accumulation contents were lower in the 0×-P -treated red romaine lettuce leaves than in the other treatments. The maximum red romaine lettuce yields per plant, leaf number and leaf length were exhibited during the 1×-P at 15 °C RZT treatment. In 0×-P at 10 °C, RZT treatment showed lower leaf color values of L*, b*, chrome, ºh and higher leaf color a* values. Moreover, in the 0×-P treatment at 10 °C RZT, the leaf...

The aim of this research was to develop an effective protocol for the application of nonthermal plasma (NTP) technology to the hydroponic nutrient solution, and to investigate its effects on the growth and quality of baby leaf lettuce (Lactuca sativa var. acephala Alef.) grown in a hydroponic growing system (HGS) specifically designed for indoor home cultivation. Four HGSs were placed in separate growth chambers with temperature of 24 ± 1 °C and relative humidity of 70 ± 5%). Lettuce plants were grown for nine days in nutrient solutions treated with NTP for 0 (control) to 120 s every hour. Results of the first experiments showed that the optimal operating time of NTP was 120 s h−1. Fresh leaf biomass was increased by the 60 and 120 s NTP treatments compared to the control. Treating the nutrient solution with NTP also resulted in greater leaf content of total chlorophylls, carotenoids, total phenols, and total antioxidant capacity. NTP also positively influenced chlorophyll a fluores...

Lettuce (Lactuca sativa L.) is a winter-spring leafy vegetable, but the high demand for fresh products available year-round requires off-season production. However, the warm climate of the Mediterranean areas can impair the summer production of lettuce, thus requiring the adoption of genotypes tolerant to high irradiance as well as useful agronomic strategies like shading net installations. The aim of our research was to assess the leaf morpho-physiological and anatomical changes, in addition to productive responses, of four lettuce cultivars (‘Ballerina’, ‘Maravilla De Verano Canasta’, ‘Opalix’, and ‘Integral’) grown under shading and non-shading conditions to unveil the adaptive mechanisms of this crop in response to sub-optimal microclimate (high irradiance and temperature) in a protected environment. Growth and yield parameters, leaf gas exchanges, chlorophyll fluorescence and morpho-anatomical leaf traits (i.e., leaf mass area, stomatal density and epidermal cell density) were ...

The aim of this research was to develop an effective protocol for the application of nonthermal plasma (NTP) technology to the hydroponic nutrient solution, and to investigate its effects on the growth and quality of baby leaf lettuce (Lactuca sativa var. acephala Alef.) grown in a hydroponic growing system (HGS) specifically designed for indoor home cultivation. Four HGSs were placed in separate growth chambers with temperature of 24 ± 1 °C and relative humidity of 70 ± 5%). Lettuce plants were grown for nine days in nutrient solutions treated with NTP for 0 (control) to 120 s every hour. Results of the first experiments showed that the optimal operating time of NTP was 120 s h−1. Fresh leaf biomass was increased by the 60 and 120 s NTP treatments compared to the control. Treating the nutrient solution with NTP also resulted in greater leaf content of total chlorophylls, carotenoids, total phenols, and total antioxidant capacity. NTP also positively influenced chlorophyll a fluores...

Soilless growing systems can improve water-use efficiency, especially in closed soilless growing systems. The main purpose of this study was to evaluate the effects of different transplanting conditions, and determine how supplying H2O2 as an oxygen source to the rhizosphere of strawberry plants in a soilless growing system affects plant growth, fruit yield and fruit quality. Strawberry plants (Fragaria x ananassa Duch.) cv. ‘Fortuna’ were cultivated in 12 L pots filled with peat substrate, and maintained under conditions of natural light and temperature. Treated plants were supplied with hydrogen peroxide (H2O2) (H1) and control plants did not receive H2O2 (H0). In terms of the transplanting conditions, the plants were transplanted in October (T1), and either maintained in a culture chamber (T2), or refrigerated (T3), for one month, before being transplanted. A completely randomized block design with two treatment factors (transplanting conditions, and H2O2 treatment) and five repl...

The goal of this research was to investigate the effect of electrical conductivity (EC) levels of the nutrient solution on the fresh weight, chlorophyll, and nitrate content of hydroponic-system-grown lettuce. The selected cultivars are the most representative commercial varieties grown for European markets. Seven cultivars (‘Sintia,’ ‘Limeira,’ ‘Corentine,’ ‘Cencibel,’ ‘Kiber,’ ‘Attiraï,’ and ‘Rouxaï’) of three Lactuca sativa L. types’ (butterhead, loose leaf, and oak leaf) were grown in a phytotron in rockwool, meanwhile the EC level of the nutrient solutions were different: normal (&lt;1.3 dS/m) and high (10 dS/m). The plants in the saline condition had a lower yield but elevated chlorophyll content and nitrate level, although the ‘Limeira’ and ‘Cencibel’ cultivars had reduced nitrate levels. The results and the special characteristic of the lollo-type cultivars showed that the nitrate level could be very different due to salinity (‘Limeira’ had the lowest (684 µg/g fresh weight ...

Soilless growing systems can improve water-use efficiency, especially in closed soilless growing systems. The main purpose of this study was to evaluate the effects of different transplanting conditions, and determine how supplying H2O2 as an oxygen source to the rhizosphere of strawberry plants in a soilless growing system affects plant growth, fruit yield and fruit quality. Strawberry plants (Fragaria x ananassa Duch.) cv. ‘Fortuna’ were cultivated in 12 L pots filled with peat substrate, and maintained under conditions of natural light and temperature. Treated plants were supplied with hydrogen peroxide (H2O2) (H1) and control plants did not receive H2O2 (H0). In terms of the transplanting conditions, the plants were transplanted in October (T1), and either maintained in a culture chamber (T2), or refrigerated (T3), for one month, before being transplanted. A completely randomized block design with two treatment factors (transplanting conditions, and H2O2 treatment) and five repl...

Over-fertilization is one of important environmental problems, but also affects plant nutritional status. To investigate the influence of over-fertilization on leaf mineral content, lettuce was hydroponically grown at higher nutrients concentrations. The experiment revealed no significant differences in leaf mineral content and root length between treatments, but we have observed much bigger variability of data at the lowest concentration. Similar trend has been observed comparing mobilities: more nutrients there are in a solution, significantly smaller the variability between plants is. Obviously, plants need to compete between each other at lower nutrients availability for their uptake, which increases variability, but not at higher.

Three consecutive years of field experiments were conducted to investigate how different root-zone temperatures, manipulated by using different mulches, affect the phytoextraction of Ba, Cl, Sn, Pt and Rb in different organs of potato plants (roots, tubers, stems and leaves). Four different plastic covers were used (T1: transparent polyethylene; T2: white polyethylene; T3: white and black coextruded polyethylene, and T4: black polyethylene), using uncovered plants as control (T0). The different treatments had a significant effect on mean root zone temperatures (T0 ¼ 16 C, T1 ¼ 20 C, T2 ¼ 23 C, T3 ¼ 27 C and T4 ¼ 30 C) and induced a significantly different response in Ba, Cl, Sn, Pt and Rb concentration and accumulation. The T3 treatment gave rise to the greatest phytoextraction of Ba, Pt, Cl and Sn in the roots, leaflets and tubers.

Nutritional eustress such as salinity or nutrient stress applied in soilless systems, is a convenient pre-harvest factor efficient in modulating the phytochemical components of horticultural crops, by triggering defensive mechanisms and accumulating plant secondary metabolites in plants tissues. Nevertheless, genetic material (cultivars with different pigmentation) dictates lettuce metabolites and physiological response to extrinsic eustress, with red leaf cultivars being highly nutrient packed notwithstanding the stress. Product quality can be meliorated equally by applying several cuts, a practice proven to increase bioactive compounds accumulation. In this study, we analyzed the effects of four salinity levels (1, 10, 20 and 30 mM NaCl) on green and red pigmented Salad Bowl lettuce (Lactuca sativa L. var. acephala) in two successive harvests cultivated in a floating raft system. The morphological parameters, mineral composition, leaf gas exchanges, bioactive compounds, and antiox...

Nutritional eustress such as salinity or nutrient stress applied in soilless systems, is a convenient pre-harvest factor efficient in modulating the phytochemical components of horticultural crops, by triggering defensive mechanisms and accumulating plant secondary metabolites in plants tissues. Nevertheless, genetic material (cultivars with different pigmentation) dictates lettuce metabolites and physiological response to extrinsic eustress, with red leaf cultivars being highly nutrient packed notwithstanding the stress. Product quality can be meliorated equally by applying several cuts, a practice proven to increase bioactive compounds accumulation. In this study, we analyzed the effects of four salinity levels (1, 10, 20 and 30 mM NaCl) on green and red pigmented Salad Bowl lettuce (Lactuca sativa L. var. acephala) in two successive harvests cultivated in a floating raft system. The morphological parameters, mineral composition, leaf gas exchanges, bioactive compounds, and antiox...

We hypothesized that sub-optimal root zone temperature (RZT) will cause a reduction in the bioactive components contents, adversely affect PS II and hinder uptake/partitioning of mineral elements in the ''Light Green Variant'' of the African snake tomato (Trichosanthes cucumerina L.). Three RZT temperatures (20, 25 and 30°C) were evaluated in a digitally controlled growth chamber. Results showed that for all the mineral nutrients analyzed (Ca, Mg, P, K, Fe and Mn), the amounts absorbed by the plant increase as RZT increases with each nutrient displaying different characteristics with respect to the quantity partitioned into root, stem and leaf at the different RZT. At sub-optimal RZT (20°C), significantly higher amounts of Ca and K were found in the root, whereas at normal RZT (25 and 30°C) higher amounts of Ca were recorded in the stem, and about 50% of the amounts in the stem were found in the leaves. For all the RZT, the amounts of Mg in the leaves were significantly higher than in the root and stem, while the amounts in the stems were also significantly higher than the amounts in the roots. At normal RZT (25 and 30°C) almost equal amounts of P were present in the root, stem and leaf. The amounts of phenolics, ascorbic acid, chlorophyll a and b and total chlorophyll increase as the RZT increases. Photosystem analyses showed that at 30°C the F v /F m (relative photochemical efficiency) was 0.76, while at 20 and 25°C the values were 0.35 and 0.60, respectively. The F v /F m value (0.35) obtained at 20°C confirmed the adverse effects of suboptimal RZT on the photosystem II (PS II). Photosynthetic measurements showed that as the RZT increased, A (net photosynthetic efficiency), E (transpiration rate), C i (intercellular carbon dioxide concentration) and g 1 (stomata conductance) also increased. We postulate that the higher E and g 1 at high RZT have a great physiological implication on plant performance, because transpiration cooling would be improved, especially during the summer; but the lost water must be complemented by adequate irrigation. The totality of the results confirm our hypothesis that sub-optimal RZT will cause a reduction in the bioactive components contents, adversely affect PS II and hinder uptake/partitioning of mineral elements in T. cucumerina.

Nutritional eustress such as salinity or nutrient stress applied in soilless systems, is a convenient pre-harvest factor efficient in modulating the phytochemical components of horticultural crops, by triggering defensive mechanisms and accumulating plant secondary metabolites in plants tissues. Nevertheless, genetic material (cultivars with different pigmentation) dictates lettuce metabolites and physiological response to extrinsic eustress, with red leaf cultivars being highly nutrient packed notwithstanding the stress. Product quality can be meliorated equally by applying several cuts, a practice proven to increase bioactive compounds accumulation. In this study, we analyzed the effects of four salinity levels (1, 10, 20 and 30 mM NaCl) on green and red pigmented Salad Bowl lettuce (Lactuca sativa L. var. acephala) in two successive harvests cultivated in a floating raft system. The morphological parameters, mineral composition, leaf gas exchanges, bioactive compounds, and antiox...

Phytoaccumulation is a technique to extract metals from soil utilising ability of plants. Cesium is a valuable metal while radioactive isotopes of cesium can be hazardous. In order to establish a more efficient phytoaccumulation system, small molecules which promote plants to accumulate cesium were investigated. Through chemical library screening, 14 chemicals were isolated as 'cesium accumulators' in Arabidopsis thaliana. Of those, methyl cysteinate, a derivative of cysteine, was found to function within the plant to accumulate externally supplemented cesium. Moreover, metabolite profiling demonstrated that cesium treatment increased cysteine levels in Arabidopsis. The cesium accumulation effect was not observed for other cysteine derivatives or amino acids on the cysteine metabolic pathway tested. Our results suggest that methyl cysteinate, potentially metabolised from cysteine, binds with cesium on the surface of the roots or inside plant cells and improve phytoaccumulation. The recovery of high-value or toxic metals from soil and water attracts considerable attention from engineers, economists and environmentalists. Biological methods especially, which are generally cost effective and eco-friendly, have recently gained in popularity as an alternative to the conventional physical and chemical approaches to capture metals from soil or water. Biological methods can be divided largely into two categories: biosorption and bioaccumulation (or bioextraction). Biosorption uses materials of a biological origin which is generally pre-treated with chemicals to optimise the surface physicochemical properties for adsorption whereas bioaccumulation uses the ability of living organisms to naturally absorb the metal of interest 1. Bioaccumulation by plants, more specifically termed as phytoaccumulation, is extremely useful where a valuable/toxic metal is to be directly extracted from soil without disrupting the soil structure but the most common downside with phytoaccumulation is low uptake efficiency. Therefore, it would be beneficial to develop methods which enable improved efficiency in phytoaccumulation of the target metal. Of the many commercial and high-value metals, cesium exists at relatively low levels of approximately 3 ppm in the Earth's crust 2. Cesium is utilised widely industrially for example in the production of drilling fluids and in the manufacture of atomic clocks. Radiocesium-137 also has medical, hydrological and industrial applications. Currently, mining of pollucite ore is the major source of cesium production but mining is conducted in only very few places and only on a small scale. Although cesium reserves are said to be sufficient for consumption at the present rate, since cesium is not recycled, it is vulnerable to depletion in the long term 3. Additionally, cesium-137, the radioactive isotope derived from nuclear waste and fallout, presents a serious health risk and environmental threat such that improved phytoaccumulation efficiency of cesium offers advantages in the light of phytoremediation also. Many plant species have been tested in the search for 'hyperaccumulator plants' of cesium, however most of the species tested suffer low absorption efficiency for practical application in the soil 4-12. Various factors have been investigated and suggested as positive regulators of cesium accumulation in plants. For example, inoculation with root-associated microorganisms has been

Three consecutive years of field experiments were carried out to investigate the effect of root temperatures induced by the application of mulches for phytoextraction of As, Ag, Cr and Sb using potato plants (roots, tubers, stems and leaflets). Four different plastic covers were used (T1: transparent polyethylene; T2: white polyethylene; T3: white and black coextruded polyethylene; and T4: black polyethylene), taking uncovered plants as control (T0). The different treatments had a significant effect on mean root temperatures (T0 ¼ 16 C, T1 ¼ 20 C, T2 ¼ 23 C, T3 ¼ 27 C and T4 ¼ 30 C) and induced a significantly different response in the As, Ag, Cr and Sb phytoaccumulation. The T3 treatment gave rise to the greatest phytoaccumulation of As, Ag, Cr and Sb in the roots, leaflets and tubers. In terms of the relative distribution of the phytoaccumulated metals (with respect to the total of the plant), As accumulated mainly in the roots and leaflets whereas Ag, Cr and Sb accumulated primarily in the tubers, establishing a close relationship between biomass development of each 1389

Phytoaccumulation is a technique to extract metals from soil utilising ability of plants. Cesium is a valuable metal while radioactive isotopes of cesium can be hazardous. In order to establish a more efficient phytoaccumulation system, small molecules which promote plants to accumulate cesium were investigated. Through chemical library screening, 14 chemicals were isolated as 'cesium accumulators' in Arabidopsis thaliana. Of those, methyl cysteinate, a derivative of cysteine, was found to function within the plant to accumulate externally supplemented cesium. Moreover, metabolite profiling demonstrated that cesium treatment increased cysteine levels in Arabidopsis. The cesium accumulation effect was not observed for other cysteine derivatives or amino acids on the cysteine metabolic pathway tested. Our results suggest that methyl cysteinate, potentially metabolised from cysteine, binds with cesium on the surface of the roots or inside plant cells and improve phytoaccumulation.

In this study, phosphorus (P) strength [(full strength: 1×-P, half strength: 0.5×-P and zero strength: 0×-P)] and root zone temperature (10 and 15 • C RZT) were investigated in red romaine lettuce to determine their effects on anthocyanin content. This experiment was conducted using a deep-flow technique (DFT) hydroponic system in a greenhouse during the winter in Gangwon province in the Korea Republic. The treatments were 1×-P (15 and 10 • C RZT), 0.5×-P (15 and 10 • C RZT) and 0×-P (15 and 10 • C RZT). The results showed that the P (phosphorus), K (potassium) and Ca (calcium) accumulation contents were lower in the 0×-P-treated red romaine lettuce leaves than in the other treatments. The maximum red romaine lettuce yields per plant, leaf number and leaf length were exhibited during the 1×-P at 15 • C RZT treatment. In 0×-P at 10 • C, RZT treatment showed lower leaf color values of L*, b*, chrome, ºh and higher leaf color a* values. Moreover, in the 0×-P treatment at 10 • C RZT, the leaf chlorophyll content (SPAD), chlorophyll a, chlorophyll b and chlorophyll total were the lowest. Anthocyanin content was the highest in the 0×-P treatment, followed by 0.5×-P and 1×-P treatments at both 15 and 10 • C RZT. Regardless of the P intensity treatment, anthocyanin content was higher at 10 • C RZT than at 15 • C RZT. In summary, the 1×-P at 15 • C RZT treatment is the best for red romaine lettuce leaf yield, and the 0×-P at 10 • C RZT treatment is the best for lettuce leaf anthocyanin content.

—Manganese (Mn) and zinc (Zn) interact with iron (Fe) and this interaction can result in impacts on the yield of corn plants. This research was conducted to examine the effect of different levels of Mn and Zn on the Fe concentration in roots and shoots of sweet corn plants. Sweet corn was grown in nutrient culture containing all combinations of Zn and Mn at levels of 0.0, 0.1, 1.0, and 10.0 mg L-1 as ZnSO 4 .7H 2 O and MnSO 4 .H 2 O, respectively and harvested at 28 days after transplanting. Fe concentration in shoots reduced with increasing Mn levels, but Fe concentration in roots did not show any correlation with Mn concentration in nutrient solution. Fe concentration in roots of corn plants increased with increasing Zn levels but different levels of Zn in nutrient solution did not show any significant effect on Fe concentration in the shoots (P>0.05).

In previous studies with tropical plant species, low root zone temperature (RZT) induced boron (B) deficiency, but it is not known if the same response to RZT will be expressed in temperate species, like oilseed rape, that are more tolerant of low temperature. The present experiments investigated the effect of RZT (10 and 20 C) on oilseed rape (Brassica napus L. cv. Hyola 42) response to B in solution culture, in summer and winter. Regardless of canopy growth conditions, low RZT (10 C) promoted the partitioning of shoot B to the actively growing leaves, especially when B supply was low. However, low RZT did not significantly alter net B uptake rates or plant biomass. Low RZT decreased the shoot-to-root ratio, countering the effects of low B which increased it, leading to a decreased demand for B in the shoot at low RZT. At low B supply, B-deficiency symptoms appeared later at 10 than at 20 C, corresponding with higher B concentrations in the youngest fully opened leaves (YOLs) at 10 C RZT. Thus 10 C RZT increased the tolerance to low B supply. As a result, it is concluded that the effect of decreasing RZT on the responses of the temperate species, oilseed rape, to low B supply depends on whether the low RZT is above or below the optimal root temperature for growth.

Lotus japonicus was used to study the distribution and interconnections of 15 elements in plant tissues, including essential and non-essential elements: boron (B), sodium (Na), magnesium (Mg), potassium (K), calcium (Ca), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), strontium (Sr), molybdenum (Mo), cadmium (Cd) and cesium (Cs). Large amounts of B and Ca accumulated in plant leaves, while Fe, Na, Ni, As and Cd tended to mainly occur in the roots, and Mo was the only element to accumulate in the stems. The elemental compositions within plants were severely disturbed by treatment with toxic elements. Competition between element pairs in the same group (e.g. K and Cs; Ca and Sr) was not found. Iron, Cu and Zn accumulation were induced by Cd and Ni addition. When natural variants grew in a nutrition solution with subtoxic levels of As, Cd, Cs, Ni, Mo and Sr, intriguing relationships between the elements (such as Fe, As and K; Mg and Ni; Mn and Ca) were revealed using principalcomponent analysis. This study on the plant ionome offers detailed information of element interactions and indicates that chemically different elements might be closely linked in uptake or translocation systems.

Lettuce production in re-circulating hydroponic systems is done on a limited scale in South Africa with conflicting information on the recommended spacing for optimal yield and quality in such systems. The development and yield of four lettuce (Lactuca sativa L.) cultivars 'NIZ 44-675', 'Nougatine', 'Tango' and 'Natividad' at five different inter-and intra-row spacings namely: 10x20 (50 plants m -2 ), 10x25 (40 plants m -2 ), 15x20 (30 plants m -2 ), 20x20 (25 plants m -2 ) and 20x25 (20 plants m -2 ) cm were evaluated during May/June 2008. The experimental layout was a randomized complete block design and each treatment combination was replicated three times. There was a significant interaction between spacing and cultivar regarding leaf fresh and dry mass while all cultivars reacted similarly to different spacings on other yield parameters. Plant population significantly affected plant height, fresh and dry leaf mass, leaf area and leaf number m -2 , with significantly higher values of all variables at the closest spacing (50 plants m -2 ). The results indicate that an increase in plant population results in a significant increase in yield and yield components of leafy lettuce, with all cultivars producing the highest yield at a spacing of 50 plants m -2 during winter production. Cultivar differences observed showed that 'NIZ 44-675' and 'Tango' performed better than 'Nougatine' and 'Natividad', mostly due to higher leaf area, fresh mass, plant height and leaf number.

We hypothesized that sub-optimal root zone temperature (RZT) will cause a reduction in the bioactive components contents, adversely affect PS II and hinder uptake/partitioning of mineral elements in the ''Light Green Variant'' of the African snake tomato (Trichosanthes cucumerina L.). Three RZT temperatures (20, 25 and 30°C) were evaluated in a digitally controlled growth chamber. Results showed that for all the mineral nutrients analyzed (Ca, Mg, P, K, Fe and Mn), the amounts absorbed by the plant increase as RZT increases with each nutrient displaying different characteristics with respect to the quantity partitioned into root, stem and leaf at the different RZT. At sub-optimal RZT (20°C), significantly higher amounts of Ca and K were found in the root, whereas at normal RZT (25 and 30°C) higher amounts of Ca were recorded in the stem, and about 50% of the amounts in the stem were found in the leaves. For all the RZT, the amounts of Mg in the leaves were significantly higher than in the root and stem, while the amounts in the stems were also significantly higher than the amounts in the roots. At normal RZT (25 and 30°C) almost equal amounts of P were present in the root, stem and leaf. The amounts of phenolics, ascorbic acid, chlorophyll a and b and total chlorophyll increase as the RZT increases. Photosystem analyses showed that at 30°C the F v /F m (relative photochemical efficiency) was 0.76, while at 20 and 25°C the values were 0.35 and 0.60, respectively. The F v /F m value (0.35) obtained at 20°C confirmed the adverse effects of suboptimal RZT on the photosystem II (PS II). Photosynthetic measurements showed that as the RZT increased, A (net photosynthetic efficiency), E (transpiration rate), C i (intercellular carbon dioxide concentration) and g 1 (stomata conductance) also increased. We postulate that the higher E and g 1 at high RZT have a great physiological implication on plant performance, because transpiration cooling would be improved, especially during the summer; but the lost water must be complemented by adequate irrigation. The totality of the results confirm our hypothesis that sub-optimal RZT will cause a reduction in the bioactive components contents, adversely affect PS II and hinder uptake/partitioning of mineral elements in T. cucumerina.

The effects of root-zone temperature (RZT) on the ion uptake, distribution and interactions of 21 (11 essential and 10 non-essential) elements using Lotus japonicus were studied. After acclimation in hydroponics at ambient (25 C) RZT for three weeks, seedlings were exposed to sub-optimal (15 C and 20 C) and ambient RZTs. After one week, plants were harvested and then growth and mineral elements were analyzed. The highest shoot and root biomass was at 25 C and lowest at 15 C RZT. In shoots, the highest concentrations of all elements, except for nickel (Ni), were at 25 C RZT. At lower RZTs, the reductions in concentrations were more evident especially for trace elements and heavy metals. Except for magnesium (Mg), the highest root concentrations were at 15 C RZT for all essential elements. Unlike other non-essential elements, the highest cadmium (Cd) and cobalt (Co) concentrations in roots were at 25 C RZT. The shoot/root ratios of almost all elements were affected by sub-optimal RZTs. Only manganese (Mn) and Co showed increased shoot/root ratio at sub-optimal RZTs; and this ratio decreased for other elements. Nickel in shoots and Mn, Co and Cd in roots tended to be negatively correlated with most other elements (either, essential or non-essential) in each respective organ. The present study showed that RZT significantly changed the ion profile of L. japonicus and suggests possible connection between global warming and phytoaccumulation of heavy metals, especially in temperate regions, since most metals tended to accumulate in shoots at higher RZT.

Colocacia indica (Colocacia esculenta Linn) is a herbaceous perennial 0.5-2 m tall, with an underground starchy corm which produces at its apex a whorl of large leaves with long robust petioles. The leaves are heart-shaped, 20 -50 cm long, with rounded basal lobes; the leaf stalk joins the blade some distance inward from the notch between the lobes (ie the leaf is peltate -a feature which distinguishes the plant from the rather similar Xanthosoma). The inflorescence is on a stout peduncle, shorter than the leaf stalks, with a pale yellow spathe about 20 cm long: seeds are extremely rare. The corms vary greatly in size and are round/cylindrical, up to 35 cm long and 15 cm in diameter, and are surrounded by a number of secondary corms (cormels); the root system is superficial and fibrous.