Effect of Head Removal on Leaf Senescence of Sunflower

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Abstract
Greenhouse and field studies examined the effect of flower or seedhead removal on leaf senescence and associated changes in sunflower (Helianthus annuus L.) plants. At intervals during seed development, selected leaves (leaves 6 through 8 from the top in the greenhouse and leaf 7 from the top in the field) were harvested and analyzed for chlorophyll, specific leaf weight, N, P, soluble protein, and electrophoretic gel profiles of soluble polypeptides. In both the greenhouse and the field, the leaves of headless plants retained or accumulated more N, P, soluble protein, and dry weight than leaves of plants with heads. Obviously, head removal affected the partitioning of these metabolites during seed development. None of the treatments resulted in the formation of new polypeptides (electrophoretic gel profiles). Comparisons of the rates and extent of loss of chlorophyll, soluble protein, and polypeptide bands (especially ribulose 1,5-bisphosphate carboxylase) from the leaves of headed and deheaded plants showed that head removal delayed the rate of development of leaf senescence for the greenhouse-grown but had much less effect on field-grown plants. These findings illustrate the variability in different parameters commonly associated with the leaf senescence processes of headed and deheaded sunflower plants grown under different environments.