Senescence in Detached Oat Leaves I. Changes in Free Amino Acid Levels

Changes in the levels of free amino acids have been measuredduring light and dark senescence of oat leaf segments. Leaveswere aged either on water, 5 ppm kinetin or 30 ppm abscisicacid. The patterns with which levels of individual amino acidschange differ a great deal in leaves senescing either in darkor light, signifying that different mechanisms may regulateoat leaf senescence in light and dark. Levels of serine andmost of the other amino acids that increase substantially duringdark senescence of oat leaves change parallel to mitochondrialrespiration. Kinetin depresses the rise in amino acids justas it does with respiration in the dark. The synthesis of serineproteases does not seem to be limited by the availability ofendogenous serine. The levels of glutamine increase dramaticallyin leaves kept in light (ca. 2,200% of initial value within7 days) but only a little in the dark, which may reflect a possiblerole of photorespiration during the senescence of oat leavesin the light. Abscisic acid enhances the release of amino acidsmore strongly in the light than dark. The senescence promotingeffect of abscisic acid in the light seems to bring about changesin amino acid levels similar to those that appear in leavessenescing on water in the dark. ¹ Present address: C.F. Kettering Research Laboratory, 150 EastSouth College Street, Yellow Springs, Ohio 45387, U.S.A. (Received June 24, 1981; Accepted October 30, 1981)