Patterns of starch accumulation in alfalfa, Medicago sativa L., were studied in response to injury caused by potato leafhopper, Empoasca fabae (Harris). Using image analysis of iodine-stained leaf tissues, we compared lightness scores of leaves from leafhopper-injured and healthy plants sampled at early morning and mid-afternoon. In addition, we related lightness scores to standard chemical analyses for starch and sugar. The lightness scores were significantly related to starch concentrations but not to sugar concentrations. In the morning samples, all fully developed and developing leaves above the site of feeding indicated higher starch concentrations than comparable leaves on healthy plants. In contrast, all leaves from mid-afternoon samples and leaves below the site of feeding from morning samples did not significantly differ between injured and healthy plants. The observation that the lack of starch degradation during the night occurs in all tissues distal to the feeding site, and especially in developing leaves, suggests that the mechanism of starch accumulation is not just feedback from phloem blockage caused by leafhopper feeding but also a change in starch degradation in all chloroplasts without regard to source-sink status.
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