Changes in metabolism of cell wall polysaccharides in oat leaves during senescence: relevance to the senescence-promoting effect of methyl jasmonate

Abstract

Changes in cell wall polysaccharides in oat (Avena sativa L.) leaf segments during senescence promoted by methyl jasmonate (JA-Me) were studied. During the incubation with water at 25 °C in the dark, the loss of chlorophyll of the segments excised from the primary leaves of 8-day-old green seedlings was found dramatically just after leaf excision, and leaf color completely turned to yellow after the 3- to 4-day incubation in the dark. Application of 10 µM JA-Me substantially promoted the loss of chlorophyll corresponding with the chloroplast degradation. Cell wall polysaccharides in oat leaf segments mainly consisted of hemicellulosic and cellulosic ones. During the process of leaf senescence, the amount of hemicellulosic I and II, and cellulosic polysaccharides decreased, but little in pectic polysaccharides. JA-Me significantly enhanced the decrease in cellulosic polysaccharides, but little in hemicellulosic ones. Arabinose, xylose and glucose were identified as main constituents of neutral sugars of hemicellulosic polysaccharides. The neutral sugar compositions of hemicellulosic polysaccharides changed little during leaf senescence both in the presence or absence of JA-Me. These facts suggest that JA-Me affects sugar metabolism relating to cellulosic polysaccharides during leaf senescence.