Life Sciences

This study examined the effects of season-long exposure to elevated carbon dioxide (CO 2 ) and/or ozone (O 3 ) on tuber quality in potato (Solanum tuberosum L. cv. 'Bintje'). Stands of potato were grown to maturity in open-top chambers (OTCs) in 1998 and 1999 under a factorial combination of three CO 2 (ambient, 550 and 680 mol mol −1 ) and two O 3 levels (ambient and elevated; 8 h per day seasonal means of 50 and 65 nmol mol −1 in 1998 and 1999, respectively). The intermediate CO 2 concentration was omitted from analysis of tuber quality. In 1999, the starch content of tubers and the viscosity of the resulting paste were increased by elevated CO 2 (P < 0.05). Tuber nitrogen content was reduced by elevated CO 2 in both years (P < 0.05), but nitrate content was decreased only in 1999 (P < 0.05). Elevated CO 2 reduced citric acid content in 1998 (P < 0.05) and increased Vitamin C content in 1999 (P < 0.05). Elevated CO 2 also tended to decrease the total glycoalkaloid content of tubers (P < 0.08) by decreasing their ␣-chaconine content. Elevated O 3 had less marked effects on tuber quality even though AOT40 values (accumulated O 3 exposure above a threshold of 40 nmol mol −1 ) of 12,461 and 27,113 nmol mol −1 h were applied in 1998 and 1999, respectively. In 1998 the paste produced from tubers produced under elevated O 3 was more viscous (P < 0.05) and in 1999 the starch granules were less resistant to swelling (P < 0.05) than in tubers produced under ambient O 3 . Total glycoalkaloid content was increased in 1999 because of an increase in ␣-solanine content (P < 0.05). No CO 2 × O 3 interactions were detected for any of the quality parameters examined. The results are discussed in the context of the likely effects of predicted changes in climatic conditions on tuber quality.

The use of the 2H/1H composition of terrestrial plants in climate and ecology studies depends on fundamental understanding of the processes within the plant that control fractionation of these two isotopes. Little is currently known about the extent of 2H/1H fractionation at different steps of biosynthesis, after the initial H uptake following leaf water photolysis. Knowing this effect is particularly important when seeking to interpret the 2H/1H composition of leaf wax biomarkers from plants that differ in the amount and type of individual compound classes in their leaf waxes. The purpose of this study was to investigate the link between the quantity and distribution of n-alkyl lipids in leaf waxes and their isotopic composition.

The perennial species Rhazya stricta (R. stricta) grows in arid zones and carries out typical C 3 photosynthesis under daily extremes of heat, light intensity and low humidity. In order to identify processes attributable to its adaptation to this harsh environment, we profiled the foliar transcriptome of apical and mature leaves harvested from the field at three time periods of the same day.

Arabidopsis thaliana ecotype Columbia was used for all experiments. The A. thaliana chloroplast division mutants arc6, arc10, and arc11 obtained from the Nottingham Arabidopsis Stock Centre, University of Nottingham, UK, were also used for localization experiments. All plants were propagated in an identical manner. Surface sterilized seeds were sown on MS medium, placed at 4ЊC in darkness for 2-4 days, and germinated under continuous white light at 22ЊC. Seedlings were then transferred to 8 hr light/16 hr dark cycles at 22ЊC or transferred to soil and grown under standard green house conditions. For transmission electron microscopy, plants were grown as described above and intact leaves were prepared from 2-week-old seedlings by using standard fixation procedures.

index of stomatal conductance; IRGA, infrared gas analysis; IWUE i , imaged intrinsic water use efficiency; PPFD, photosynthetic flux density; r aw , leaf boundary layer resistance to water vapour; r HR , parallel resistance to heat and radiative transfer; r w , leaf resistance to water vapour; s, slope of the curve relating saturation vapour pressure to temperature; T Dry , mean temperature of the dry standard; T Leaf , mean temperature of the leaf surface; T Wet , mean temperature of the wet standard; VPD, vapour pressure deficit, WUE, water use efficiency; WUE i , intrinsic WUE; γ, psychrometric constant; θ, temperature phrase normalizing leaf temperature with the wet and dry standards.

Potato plants (Solanum tuberosum L. cv. Bintje) were grown in open-top chambers (OTCs) under three CO 2 levels (ambient and 24 h d À1 seasonal mean concentrations of 550 and 680 mmol mol À1 ) and two O 3 levels (ambient and a seasonal mean 8 h d À1 concentration of 50 nmol mol À1 ). The objectives were to determine the effects of season-long exposure to these key climate change gases on gas exchange, leaf thickness and epidermal characteristics. The experimental design also provided an ideal opportunity to examine within-leaf variation in epidermal characteristics at the whole-leaf level. Stomatal and epidermal cell density and stomatal index were measured at specific locations on the youngest fully expanded leaf (centre of lamina, mid-way between tip and base) and representative whole leaves from each treatment. Effects on leaf conductance, assimilation rate and instantaneous transpiration efficiency were determined by infrared gas analysis, while anatomical characteristics were examined using a combination of leaf impressions and thin sections. Exposure to elevated CO 2 or O 3 generally increased leaf thickness, leaf area, stomatal density, and assimilation rate, but reduced leaf conductance. The irregular stomatal distribution within leaves resulted from a combination of uneven differentiation and expansion of the epidermal cells. The results are discussed with reference to sampling protocols and the need to account for within-leaf variation when examining the impact of climate change or other environmental factors on epidermal characteristics.

High resolution chlorophyll a¯uorescence imaging was used to compare the photosynthetic ef®ciency of PSII electron transport (estimated by F q ¢/F m ¢) in guard cell chloroplasts and the underlying mesophyll in intact leaves of six different species: Commelina communis, Vicia faba, Amaranthus caudatus, Polypodium vulgare, Nicotiana tabacum, and Tradescantia albifora. While photosynthetic ef®ciency varied between the species, the ef®ciencies of guard cells and mesophyll cells were always closely matched. As measurement light intensity was increased, guard cells from the lower leaf surfaces of C. communis and V. faba showed larger reductions in photosynthetic ef®ciency than those from the upper surfaces. In these two species, guard cell photosynthetic ef®ciency responded similarly to that of the mesophyll when either light intensity or CO 2 concentration during either measurement or growth was changed. In all six species, reducing the O 2 concentration from 21% to 2% reduced guard cell photosynthetic ef®ciency, even for the C 4 species A. caudatus, although the mesophyll of the C 4 species did not show any O 2 modulation of photosynthetic ef®ciency. This suggests that Rubisco activity is sig-ni®cant in the guard cells of these six species. When C. communis plants were water-stressed, the guard cell photosynthetic ef®ciency declined in parallel with that of the mesophyll. It was concluded that the photosynthetic ef®ciency in guard cells is determined by the same factors that determine it in the mesophyll. Abbreviations: C a , ambient CO 2 concentration; F¢, chlorophyll¯uorescence in the light-adapted state; F m ¢, chlorophyll¯uorescence when PSII centres are maximally closed in the light-adapted state; F o ¢, chlorophyll¯uorescence when PSII centres are maximally open in the light-adapted state; F q ¢, difference between F¢ and F m ¢; F q ¢/F m ¢,¯uorescence parameter that provides an estimate of the operating ef®ciency of PSII photochemistry; F q ¢/F v ¢, factor relating the operating and maximum ef®ciencies of PSII photochemistry; F v ¢, variable chlorophyll¯uorescence (F m ¢±F o ¢); F v ¢/F m ¢,¯uorescence parameter that provides an estimate of the maximum ef®ciency of PSII photochemistry (when all PSII centres are open); PPFD, photosynthetic photon¯ux density; Rubisco, ribulose 1,5-bisphosphate carboxylase oxygenase; VPD, vapour pressure de®cit.

Concentrations of heme b, the ironcontaining prosthetic group of many hemoproteins, were measured in 6 species of marine phytoplankton (Dunaliella tertiolecta, Emiliania huxleyi, Thalassiosira weissflogii, T. oceanica, Phaeodactylum tricornutum and Synechococcus sp. WH7803) that were subjected to variations in iron concentration. Changes in heme b in response to reduced light and nitrate were also ex amined for E. huxleyi and T. oceanica. Results from laboratory cultures were compared with heme b determined in particulate material in the North Atlantic. In cultures, heme b made up 18 ± 14% (SE) of the total iron pool. Reduced iron and nitrate concentrations resulted in a decreased intracellular heme b concentration, expressed as per mole carbon. Chlorophyll a (chl a) to heme b ratios in E. huxleyi and D. tertiolecta in creased in response to limited light and nutrient availability, but slightly decreased or did not change in the diatoms and the cyanophyte Synechococcus sp. WH7803. The heme b:particulate organic carbon (POC) and chl a:heme b ratios in the North Atlantic were within the range observed in phytoplankton cultures. In the surface mixed layer, decreases in heme b:POC ratios were linked to decreases in nutrient concentrations. Chl a:heme b ratios increased with depth and were thus primarily affected by light availability. Relative relationships between heme b, chl a and POC in the North Atlantic likely represented a change in the ability of cells to undertake cellular processes driven by chl a (light harvesting) and heme b (e.g. electron transport) according to ambient light and nutrient conditions. KEY WORDS: Hemoprotein · Iron · Electron transport · Cytochrome · Nutrient limitation · Celtic Sea Resale or republication not permitted without written consent of the publisher In heme b, the central iron atom (orange) is bound to four nitrogen atoms (blue) of a tetrapyrrole ring composed of carbon (grey), hydrogen (white) and oxygen (red) atoms.

Variation in stomatal development and physiology of mature leaves from Alnus glutinosa plants grown under reference (current ambient, 360 µmol mol −" CO # ) and double ambient (720 µmol mol −" CO # ) carbon dioxide (CO # ) mole fractions is assessed in terms of relative plant growth, stomatal characters (i.e. stomatal index and density) and leaf photosynthetic characters. This is the first study to consider the effects of elevated CO # concentration on the distribution of stomata and epidermal cells across the whole leaf and to try to ascertain the cause of intraleaf variation. In general, a doubling of the atmospheric CO # concentration enhanced plant growth and significantly increased stomatal index. However, there was no significant change in relative stomatal density. Under elevated CO # concentration there was a significant decrease in stomatal conductance and an increase in assimilation rate. However, no significant differences were found for the maximum rate of carboxylation (V cmax ) and the light saturated rate of electron transport (J max ) between the control and elevated CO # treatment.