| dc.description.abstract | Two 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. | en_US |
