Vergara - 1976 - Physiological and morphological adaptability of ri

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5. Net photosynthesis in maize at various leaf water potentials and two ages.
The GS-dzrv-old plants were those described in Fig. 2-4 (Dekalb XL-t-S) and were
in the early portion of the grain filling period. The SO-dayold plants were grown
under similar conditions but are those shonsn in Fig. l (GSC 50 single cross). The
younger plants had not tasselcd. Note that photosynthesis appears to he more
sensitive to desiccation in the younger plants than in the older plants.
photosjrnthetic apparatus, including the stomata. may remain unaffected by
drought over a wider range of leaf water potentials as plants become older.
TRANSLOCATION
Photosynthetic products must be transported to the grain of cereal crops for a
hart-‘estable yield to be produced. In maize, about half of the shoot dry matter
ultimately moves into the grain. The transport task is a large one. and any
inhibition of it will result in a reduction in yield.
It is generally agreed that drought results in a diminution of dry matter
transported to developing grain. Wardlaw (1967, 1969. 1971) has ShOWt] that
the rate of transloeation of recently fixed “C W35 reduced in wheat growing
under desiccating conditions. Translocatitm in maize growing in the field shows
a similar behavior (Brevedan and Hodges. 1973).
Reduced rates of translocation are to be expected during drought since there
is a reduction in the amount of photosynthate available for transport. 1n
addition. however. there could be a direct inhibition of the translocation process.
Wardlaw (1969) attempted to distinguish between these possibilities by manipulating
the amount of photosynthetic tissue (the source) relative to the amount
of utilizing tissue (the sink) in wheat. When the sink strength in the desiccated
plants was increased, the velocity of transport was the same as in the controls.
although the total quantity of “C transported was less than in the controls.
Wardlaw (1969) interpreted these results to indicate that the translocation