Starch Accumulation and Photosynthetic Activity in Primary Leaves of Bean (Phaseolus vulgaris L.)

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Abstract
The effects of starch accumulation on photosynthesis and chloroplast ultrastructure were studied in primary leaves of bean (Phaseolus vulgaris L. cv. Bulgarian). De-topping the shoot above the primary leaf node, caused over an 8-day period, a considerable increase in the photosynthetic activity of the primary leaves, despite the fact that a large quantity of starch had accumulated in their chloroplasts. The accumulation of starch was greater in the chloroplasts of spongy cells in comparison with that of the palisade cells. Initiation of starch grains was observed mainly in the peripheral part of the chloroplast, distant from the cell wall. As a result, most of the starch was accumulated close to the inner part of the cell, leaving a considerable mass of the chloroplast near the cell wall free of starch. The accumulation of starch was accompanied by the destruction, deformation and disorientation of grana and thylakoids. It is concluded that the accumulation of starch is not inevitably a limiting factor in photosynthesis and the results cast doubt on the hypothesis that starch accumulation or dissipation is the main factor involved in the regulation of photosynthesis.

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