Die invloed van droogtetoestande op die stikstofmetabolisme van twee mielielyne

MSc, North-West University, Potchefstroom CampusTwo maize lines, A281 and G556DT, were investigated to ascertain the effect of drought conditions on the following aspects of the water relations and nitrogen metabolism: relative percentage water deficit, total water soluble protein content rate of protein synthesis, chlorophyll content, total amount of water soluble protein fractions and qualitative and quantitative changes in the free protein amino acid content. During the drought period the relative percentage water deficit of A281 proves to be higher than that of G556DT. Total water soluble protein content is higher in G556DT than in A281. G556DT also exhibits a higher rate of protein synthesis under these conditions. A sharp decline in the chlorophyll content of both maize lines occurs under increasing water stress. The chlorophyll content of A281, however, decreases much faster than that of G556DT. The rate of protein synthesis and the chlorophyll content are apparently well correlated with each other during drought conditions. The RNase-activity of A281 increases from the first day of the drought period onwards. In the case of G556DT, the increase only begins after the third day of the drought period, and the rate of increase is lower than that of A281. The RNase evidently affects the rate of protein synthesis by destroying the mRNA linking the ribosomes. The most marked change in the protein fractions occurs in the molecular mass range of 50 000 u to 10 000 U• These changes in the protein fractions are less obvious in the case of G556DT than in that of A281. The free amino acid content of both maize lines initially increases under drought conditions, thereafter it decreases and this is followed by a slight increase at a very high relative percentage water deficit. The first accumulation is probably due to a higher synthesis rate of these amino acids and a partial interruption of the protein synthesis system. The decrease that follows is probably due to a decrease in amino acid synthesis and a higher utilization of certain amino acids as respiratory substrate. The ultimate slight increase in amino acid content under very high water stress is probably caused by the hydrolysis of proteins. Selection of drought resistant plants may be possible by determining the influence of drought conditions on: total water soluble protein content, changes in the protein fractions (especially the high molecular mass fraction), chlorophyll content, and proline content. Additionally, the elapsed time from the beginning of the drought period until the first changes in RNase-activity and free amino acid content are observed, may be significant.Master