Endogenous Regulation of Photosynthetic Rate in Primary Leaves of Bean (Phaseolus vulgaris L.)

Abstract

The rate of photosynthesis and/or dry matter production was studied in fully-expanded primary leaves of bean ( Phaseolus vulgaris cv. Bulgarian) plants which had been subjected to various surgical and hormonal treatments. Between 30 and 40 per cent of the assimilates produced by the primary leaves, over a 4-day period starting with expansion of the first trifoliate leaf, were diverted to the growing shoot above the insertion of the primary leaves. In detopped plants (i.e. lacking all leaves, stem and buds above insertion of primary leaves), both the rate of net photosynthesis (NP) of the primary leaves 4 days after detopping, and the mean net assimilation rate (NAR) over this interval, did not differ significantly from those of intact plants. The assimilate normally diverted to the top in intact plants was distributed between the remaining organs of the detopped plant. When translocation of assimilates from the primary leaves was stopped by girdling their petioles, both NAR and NP were as in untreated control plants after a 2^-day period. The assimilates produced during that period accumulated in the mesophyll chlorenchyma in the form of starch granules. Intact plants supplied with GA3, or IAA, through the primary leaves as well as detopped plants supplied with IAA through the stump, differed from untreated control plants in the pattern of distribution of the assimilates produced: IAA favoured dry-matter accumulation in the roots, while GA3 favoured the tops. Nevertheless, neither NP, nor NAR differed significantly from the corresponding controls.