Sucrose and Malic Acid as the Compounds Exported to the Apical Bud of Pea following 14CO2 Labeling of the Fruit

Abstract

The G2 line of peas (Pisum sativum L.) displays senescence and death of the apical bud only in long days and in the presence of fruit. As the removal of fruit prevents senescence, one possible mechanism by which fruits induce senescence is that the fruits produce some ;senescence factor' under long day conditions, which is then transported to the apical bud. Allowing developing fruits to photosynthesize in the presence of (14)CO(2) results in the recovery of label in the apical bud. In order to determine the chemical nature of this radiolabeled material, fruits of G2 peas, growing under long days, were exposed to (14)CO(2) at the time when the first senescence symptoms start to appear. The radiolabeled material from apical buds was then extracted, purified, and identified. Using HPLC and GC-MS the major labeled compound found in the apical bud following exposure of pea fruits to (14)CO(2) was identified as sucrose, while malic acid was identified as the major ethyl acetate-soluble compound. These compounds accounted for about 73 and 16%, respectively, of the radioactivity in the apical bud. No other compounds were present in significant amounts. As neither of these chemicals is likely to have any kind of senescence effect, we report no evidence for a senescence factor.