Vergara - 1976 - Physiological and morphological adaptability of ri

‘WATER DEFiPiTS IN (TERI-KAI. creams 331
Table 1. Components of yield for the desiccated maize described in Fig. 243. Standard
deviations are shown beside means for Sto 10 plants. Most of the yield iossdue to desiccation
was caused by a decrease in the single-grain weight, although there was a slight decrease
in the number oi filled grains per ear. Note that the grain weight per shoot weight was
approximately the same for both treatments. This occurred despite the lack of new photosynthate
during most of the grain filling parted.-
Control
Desiccaled
Ears per plant 1010.0 1.0 1 0.0
Rows per ear 10.4 11.7 16.5 1 14
Florets per ear 7'46: 61 694 1 29
Filled grains per ear 461 1 B0 3T1 1 33
Single grain weight 0.297 1 0.036 g 0.109 1 0.01? g
Grain weight per plant 133: 21 g 62.2 1 44 g
Shoot weight per plant 311 1 24 g 154 1 i g
Grain weight per shoot weight 0.43 1 0.05 040 1 0.02
although a slight decrease in grain number may have occurred. The reduction in
grain weight is common in cereal grains that have been exposed to desiccation
after grain fill begins {Salter and (ioode, 1967). Apparently. maize fills most of
the grain that has begun to develop after pollination. but there is less photosynthate
to be transported and grain weight is reduced. It is probably significant
in this regard that the maturation of the grain of the desiccated plants
occurred much earlier than that of the well-\v'atered control. As was pointed out
earlier. the leaves of the desiccated plants senesced much more rapidly as well.
Since dry matter was being transported from the vegetative tissues. the early
senescence of the vegetative tissue may have been required for the completion of
grain fill because of photosynthate deprivation of one form or another.
NUTRITIONAL QUALITY OF
CEREAL GRAINS
Up to this point in our discussion, the effects of drought on grain production
have been explored largely in regard to total yield. Probably‘ just as important
from the human standpoint. however. are its effects on the nutritional quality’ of
the grain. In cereals. nutritional quality is related to the protein content and
amino acid composition of the grain as well as to a number of other factors.
Virtually nothing is known about the variation in these additional factors if
drought occurs during grain fill. However. as far as protein is concerned. Miller
(1938) points out that the bread-making quality of wheat (largely a function of
grain protein content) is affected by the dryfness of the growing season. For wheat
the percent protein increases during a drought. although total yield decreases.
Ex-‘identlfi’. the total protein production is inhibited. but total carbohydrate production
is inhibited even more.
In the vegetative portions of the plant, this order is reversed, and protein
synthesis appears to be reduced before photosynthesis decreases significantly’.
Recent studies of nitrate reductase synthesis illustrate the point. In vegetative
maize, nitrate reductase is an unstable enzyme that must be continually synthesized
(Beevers and I-Iageman, I969). Unfavorable temperature. CO, levels.