The production of cassava, the most important staple root crop in the world, is constrained by th... more The production of cassava, the most important staple root crop in the world, is constrained by the short shelf life of the cassava storage roots that are undergoing post-harvest physiological deterioration (PPD) shortly after harvest. PPD reduces starch quality and renders the roots unpalatable and unmarketable. PPD is a complex process involving enzymatic stress responses to wounding, changes in gene expression and protein synthesis as well as accumulation of secondary metabolites. PPD can be strongly influenced by environmental factors making the identification of genotypes with delayed PPD trait difficult. In the present review, we propose an integrative presentation of PPD phenomenon based on a comprehensive analysis of several key PPD studies. We discuss recent progress in the standardization of methods to assess and score PPD tolerance in cassava roots. Traditional and improved storage techniques to extend cassava shelf-life are presented and prospects of transgenic approaches to delay PPD are discussed.
The use of the root crop Cassava (Manihot esculenta Crantz) is constrained by its rapid deteriora... more The use of the root crop Cassava (Manihot esculenta Crantz) is constrained by its rapid deterioration after harvest. Chemical and spectroscopic examination revealed the accumulation of four hydroxycoumarins (esculin, esculetin, scopolin and scopoletin), compounds derived from the phenylpropanoid pathway, during the time course of post-harvest deterioration. Fluorescence-microscopy revealed their localization in the apoplast of the parenchyma. Scopoletin and scopolin showed the most dramatic increases in concentration, peaking by day 2 after harvesting. A smaller secondary peak of scopoletin tended to be more pronounced in cultivars showing lower susceptibility to deterioration. Evidence for the metabolism of scopoletin to an insoluble coloured product by means of a peroxidase is presented. This product may be the cause of the discolouration of the vascular tissue during storage.
Cassava (Manihot esculenta Crantz) is a major world crop, whose storage roots provide food for ov... more Cassava (Manihot esculenta Crantz) is a major world crop, whose storage roots provide food for over 800Â million throughout the humid tropics. Despite many advantages as a crop, the development of cassava is seriously constrained by the rapid post-harvest physiological deterioration (PPD) of its roots that occurs within 24-72Â h of harvest, rendering the roots unpalatable and unmarketable. PPD limits cassava's marketing possibilities in countries that are undergoing increased development and urbanisation due to growing distances between farms and consumers. The inevitable wounding of the roots caused by harvesting triggers an oxidative burst that spreads throughout the cassava root, together with the accumulation of secondary metabolites including phenolic compounds, of which the coumarin scopoletin (7-hydroxy-6-methoxy-2H-1-benzopyran-2-one) is the most abundant. Scopoletin oxidation yields a blue-black colour, which suggests its involvement in the discoloration observed during P...
Randomly amplified polymorphic DNA (RAPD) markers combined with the Simple Matching index for cal... more Randomly amplified polymorphic DNA (RAPD) markers combined with the Simple Matching index for calculating the distance matrix were used to determine the genetic diversity of African cassava clones. A preliminary study of three Manihot species using 20 primers clearly showed that RAPD markers were relevant for analyzing their genetic diversity. DNAs from 19 cultivars of Mariihot escuIenta Crantz (cassava) were amplified using 8 primers. Cultivars were well discriminated and coherently distributed, comparing to previous results from isozymes and RFLP studies. Genetic diversity analysis, characterization of collections and study of introgression are the domains that RAPD markers can contribute to the improvement of cassava.
Detection of a novel restriction fragment polymorphism type in Naegleria fowleri (free-living amoeba) isolates from electricity power stations in England and France
A phytochemical analysis of cassava (Manihot esculenta Crantz) fresh roots and roots suffering fr... more A phytochemical analysis of cassava (Manihot esculenta Crantz) fresh roots and roots suffering from postharvest physiological deterioration (PPD) has been carried out. The first isolation and identification of galactosyl diacylglycerides from fresh cassava roots is reported, as well as b-carotene, linamarin, and b-sitosterol glucopyranoside. The hydroxycoumarin scopoletin and its glucoside scopolin were identified from cassava roots during PPD, as well as trace quantities of esculetin and its glucoside esculin. There is no isoscopoletin in cassava roots during PPD.
Isolation and characterisation of an ACC oxidase gene from cassava. IVth Scientific Meeting of Cassava Biotechnology Network, Salvador, Brazil. 5-13 November
A Comparative Study of Willaertia magna (Free-Living Amoeba) from Different Geographic Areas Using Whole-cell and Small-subunit rDNA Restriction Fragment Length Polymorphisms
The use of PCR has enabled the survey of transposable elements in many plants; thereby making the... more The use of PCR has enabled the survey of transposable elements in many plants; thereby making the study of their diversity and applications possible in species where the full genome sequence data are not yet available. In the present study, we used PCR primers anchored on the conserved domain of reverse transcriptase and endonuclease to amplify the Ty3/Gypsy-like polyprotein fragment from the genome of cassava (Manihot esculenta Crantz). The PCR product was cloned and sequenced. Sequence analysis of individual clones clearly identified the conserved domain of the polyprotein enzymes and showed the cassava Ty3/Gypsy-like retrotransposon, Megyp (for Manihot esculenta gypsy-like), sequences to be highly heterogeneous. Some Megyps clustered with other plants' Ty3/Gypsy-like retrotransposons, while some clustered with Gypsy of Drosophila melanogaster and Ty3-2 of Saccharomyces cerevisiae in the comparative multiple sequence analysis. This suggests that the later belong to the retrovi...
A complementary-DNA library to mRNA from castor-bean endosperm has been prepared. Three clones ha... more A complementary-DNA library to mRNA from castor-bean endosperm has been prepared. Three clones have been examined in detail. One of these is complementary to isocitrate-lyase mRNA. The other two clones code for proteins with M r 42000 and 38000. All three clones have been used to measure levels of transcripts during seed germination. The three transcripts all increased during germination and the rate of their appearance is stimulated by exogenous GA 3. The data strongly support the view that the action of GA 3 in these seeds is to stimulate non-specifically the rate of transcription and, in turn, protein synthesis. Possible mechanisms for the action of the growth regulator are discussed.
Naegleria fowleri is a small free-living amoeboflagellate found in warm water habitats worldwide.... more Naegleria fowleri is a small free-living amoeboflagellate found in warm water habitats worldwide. The organism is pathogenic to humans, causing fatal primary amoebic meningoencephalitis. When monitoring the environment for the presence of N. fowleri, it is important to reliably differentiate the organism from other closely related but nonpathogenic species. To this end, we have developed species-specific DNA probes for use in the rapid identification of N. fowleri from the environment. Samples were taken from the thermal springs in Bath, England, and cultured for amoebae. Of 84 isolates of thermophilic Naegleria spp., 10 were identified as N. fowleri by probe hybridization. The identity of these isolates was subsequently confirmed by their specific whole-cell DNA restriction fragment length polymorphisms (RFLPs). One DNA clone was found to contain a repeated element that detected chromosomal RFLPs that were not directly visible on agarose gels. This enabled the further differentiati...
High sequence conservation between isocitrate lyase from Escherichia coli and Ricinus communis
Protein sequences & data analysis, 1989
The deduced amino acid sequences of isocitrate lyase (EC 4.1.3.1) from Escherichia coli and Ricin... more The deduced amino acid sequences of isocitrate lyase (EC 4.1.3.1) from Escherichia coli and Ricinus communis (castor bean) were compared and regions of high homology between the two enzymes were identified. The castor-bean enzyme had a 14 amino acid amino-terminal, and a 25 amino acid carboxy-terminal extension and a 102 amino acid central insertion compared to the E. coli enzyme. Enzymatic data were used to attempt to identify specific amino acids in the active site. Comparisons with putative peroxisomal/gloxysomal targeting sequences were made and a region including part of the central insertion of the castor bean enzyme was tentatively identified.
Restriction endonuclease digestion of Acanthamoeba whole-cell DNA was used to study the relations... more Restriction endonuclease digestion of Acanthamoeba whole-cell DNA was used to study the relationship between 33 morphologically identical strains from keratitis cases (30 strains), contact lens storage containers (2 strains), and soil (1 strain). Samples digested with BglII, EcoRI, or HindIII and separated by agarose gel electrophoresis contained detectable mitochondrial DNA restriction fragment length polymorphisms (RFLPs). By comparing RFLPs, the strains could be assigned to seven multiple-strain and three single-strain groups. The largest of these contained nine strains, eight of which were isolated in keratitis cases in various locations worldwide and may indicate a group particularly associated with keratitis. Restriction endonuclease analysis of whole-cell DNA is proposed as a valuable technique for detecting mitochondrial DNA RFLPs in the differentiation of morphologically identical Acanthamoeba strains and may therefore be useful in resolving the complex taxonomy of the genu...
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