Two long-term effects of light that control the stability of proteins related to photosynthesis during senescence of rice [Oryza sativa] leaves
1998
Okada, K. (Tokyo Univ. (Japan)) | Katoh. S.
Rate of light-saturated photosynthesis (Pmax) decreased during senescence, with no or small changes in the initial slope of the light-response curve (Phi-i), an index of light-harvesting and light-utilization capacity. Senescence of rice leaves was associated with shading of the leaves by upper younger leaves and evidence indicated that a major modulator of the light-response curve during senescence is the light environment of leaves. Chl and proteins in leaves were largely degraded during several days in darkness, and proteins that are related to Pmax and Phi-i were stabilized by light at different intensities. A decline in Pmax during senescence was related to degradation of Rubisco Cytf and the beta subunit of ATPase that was completely suppressed only= at about 300 mu-mol quanta m(-1)s(-1) and, hence, proceeded in the darkened environments caused by shading. By contrast, Phi-i remained relatively constant during senescence because Chl and proteins related to the light-harvesting Chl proteins and the reaction center complexes were effectively stabilized by very weak light. Evidence was obtained indicating that phytochrome is involved in the stabilization of Chl, whereas the photoprotection of Rubisco is a complex reaction involving photosynthesis and a signal function(s) of light. Physiological or ecophysiological significance of the two long-term effects of light that differentially stabilize the two groups of proteins are discussed
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