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Enzymatic Changes During the Senescence of Field-grown Wheat¹

Senescence in the canopy of two field-grown hard red spring wheats (Triticum aestivum L. em Thell ‘Era’ and ‘Kitt’) was evaluated during the post-anthesis period. The upper three leaf blades and flag leaf sheath were measured for total and specific dry weights, RuBP-carboxylase (RuBPCase) activity, and glucose-6-phosphate dehydrogenase (G-6-PDH) activity. Leaf dry weights and specific leaf weights were relatively constant during most of the grain-filling period and declined slightly as maturity approached. RuBPCase activity was highest after anthesis, then declined for the rest of the post-anthesis period. G-6-PDH activity increased after anthesis, then remained constant during the remainder of the grain-filling period. Activities of both enzymes were not detectable at the end of the grain-filling period, thus providing an indication of leaf senescence. By evaluating senescence on the basis of functional leaf metabolic activity, it should be possible to screen wheat genotypes or chemical treatments for altered senescence patterns.

Key Words: RuBP-carboxylase • Glucose-6-phosphate dehydrogenase • Post-anthesis period • Grain-filling period

² Former graduate research assistant (present address: Boyce Thompson Institute for Plant Research, Ithaca, NY 14853); former professor of Agronomy (present address: Dep. of Agronomy and Crop Science, Oregon State Univ., Corvallis. OR 97331); and professor of Agronomy.

Received for publication April 19, 1979.