Browsing by Author "Bangu, Nicholas T. A"

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    Effect of sulphur and other protein metabolism influencing factors on cyanogenesis in cassava
    (University of Dar es Salaam, 1988) Bangu, Nicholas T. A
    The effect of sulphur and other environmental factors on cyanogenic glucosides (CNG) and protein concentrations in different parts of cassava plants grown in pots or in field was studied. At low N level, increasing S level decreased CNG concentration but increased that of protein. The decrease in CNG concentration as a result of increasing the level of S was also observed in tubers of cassava plants grown under field conditions and in another cyanophoric plant Linum usitatissimum. The reduction in CNG concentration in tubers was > 50%. Inhibition of protein synthesis in Linum usitatissimum by cycloheximide resulted in increased CNG concentration. At medium and higher N levels, increasing S level increased both CNG and protein concentrations. Reduction of light intensity from 16 to 4 MJ m-2 day-1 had little or no effect on the pattern of changes in CNG and protein concentrations as influenced by increasing levels of S but decreased the overall mean CNG concentrations in the aerial parts and increased that in roots. The overall mean CNG concentration in the aerial parts was significantly increased by drought. Exogenous application of cysteine and/or methionine to cassava seedlings resulted in large increases in CNG concentrations. Feeding roots of cassava seedlings with L-valine-U-14C gave rise to a labelled compound with characteristics other than those reported in similar feeding investigations. The observed changes in CNG and protein concentrations are discussed in terms of events at molecular level and agronomic implications. The results are suggestive that there exists a competition for the precursor amino acids between CNG and protein synthesis, that in the course of competition protein synthesis excels over CNG synthesis, that as long as the availability of the precursor amino acids is nonlimiting the concentrations of CNG and proteins are independent of each other, that application of sulphur at low N can be used as an agronomic technique to minimize accumulation of cyanogenic glucosides in tubers of cassava.