THE NATURE OF STARCH ACCUMULATION AT THE RUST INFECTION SITE IN LEAVES OF PINTO BEAN PLANTS

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Abstract
The accumulation of radioactivity from carbon-14 dioxide assimilation at infection sites of Uromyces phaseoli was studied. The accumulated radioactivity was found to reside essentially in starch, which has been clearly demonstrated in this study to be the result of de novo synthesis from carbon-14 dioxide at the infection site and not due to an enhanced translocation of photosynthates from non-infected leaf areas and subsequent starch synthesis.It was also shown that U. phaseoli induced an increase in the chlorophyll content of the host tissue located at the periphery of the rust colony as it developed, and a concomitant increase in starch accumulation.Unlike the ‘green island' induced by powdery mildew in wheat leaves reported by Allen, the 'green island' induced by U. phaseoli in bean leaves is the result of pigment retention in the host tissue within the domain of influence of the parasite. The chlorophyll in the 'green island' was found to be photosynthetically active. Results from experiments of photosynthesis with 'green islands' provided the unequivocal evidence to support the idea of de novo synthesis of starch at the sites of rust infection.