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Development and Growth Regulation

Expression of Three RNase Activities during Natural and Dark-Induced Senescence of Wheat Leaves ¹

U.S. Department of Agriculture, Agricultural Research Service, Western Regional Research Center, 800 Buchanan St., Albany, California 94710

We have monitored the activities of RNases WL_A, WL_B, and WL_C (A Blank, TA McKeon [1991] Plant Physiol 97: 1402-1408) during leaf senescence in wheat (Triticum aestivum L. cv Chinese Spring). When seedlings were induced to senesce in darkness, protein loss from primary leaves began immediately. RNase WL_B activity was unchanged for 2 days and then rose linearly, reaching a sixfold elevation in 7 days. RNase WL_C activity declined for 2 days and then rose linearly, reaching a twofold elevation in 7 days. RNase WL_A activity declined in the first 2 days and was unchanged thereafter. Although differentially expressed, these RNase activities may respond to a common regulatory mechanism(s) which, at 2 days of darkness, signals progression into a more advanced stage of senescence. The RNase activities were also differentially expressed during light-induced recovery, returning to normal levels in dissimilar patterns. In flag leaves of greenhouse-grown wheat, the three RNase activities increased during the early postanthesis period when protein content was stable and underwent further, accelerated accumulation during senescence. RNase WL_B activity showed the largest overall senescence-associated elevation (sixfold), followed by RNase WL_C (fourfold) and RNase WL_A (threefold).

¹ Research supported in part by the T. W. Edminster Award from the Agricultural Research Service, U.S. Department of Agriculture.

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