Vergara - 1976 - Physiological and morphological adaptability of ri

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6. Dry weight distribution before and after grain till in the shoots ofthc maize
described in Fig. 2-5. The initial
treatment. Note that the vegetative portions of the shoot lost weight in desiccated
plants and that some grain was formed despite a virtual lack of photosynthesis
after the sixteenth day of grain fill (see Fig. 4). The vertical bars indicate : 1 standard
deviation for 9 l0 plants.
mechanism itself was relatively unaffected by desiccation, and that the effects of
desiccation on the source and sink accounted for most of the changes-in translocation.
However. Brevedan and Hodges (1973) suggest the reverse, that "C
translocation may be more severely affected than photosynthesis during drought
in the field.
This problem recently received further study with maize growing in soil at the
Climate Laboratory in New Zealand. The change in photosynthesis that occurred
during the desiccation experiment was enough to virtually stop photosynthesis
after l6 day's in the grain-filling period (Fig. 4). Nevertheless. grain
fill continued (Fig. 6). Figure 6 shows that much ofthc dry iveight of thc grain
was derived from the dry weight of thc \t'cgetati\-'c plant and therefore rcpresented
photosynthate that had accumulated in thc plant before desiccation
began. Curiously’. the dry matter transported to the grain represented a relatively
constant fraction of the total dry matter accumulated by the ShOOIS during the
growing season (Table 1). Therefore, it appears that the plant can utilize
prcviously' accumulated dry matter far translocation to thc grain. and studies
with recently supplied “C may not account for the total amount of translocation
that is occurring. This experiment suggests that thc photosynthetic activity’
before. as well as during the grai1i-t‘illing period, was the important determinant
of grain yicld during drought and that the translocation mechanism, while ltaving
less photosynthate available for transport. was itself relatively unaffected.
Table I also shows that the reduction in grain yield tvas caused largely by a
decrease in single grain weight rather than by a decrease in grain number.