The effect of the embryo axis and exogenous sucrose on lipolysis and glyoxysomal enzyme development in Ricinus communis (castor bean) endosperm and cotyledons

Publisher Website
Google Scholar
Abstract
Post‐germinative growth in castor bean (Ricinus communis L. cv. Hale) seedlings was investigated to determine whether lipolytic enzyme synthesis and lipid breakdown was a function of the embryo axis or simply based on a source‐sink mechanism connected with sucrose produced during mobilization of storage lipid. Endosperm and cotyledons were excised from the embryo axis at 24 h intervals and were then incubated in Petri dishes containing water or 0.1 M sucrose for 24 h. Excised endosperm showed similar or higher malate synthase (MS, EC 4.1.3.2) and isocitrate lyase (ICL, EC 4.1.3.1) activities and increased lipolysis when compared with endosperm obtained from similarly intact seedlings of the same age. In contrast, cotyledonary ICL and MS activity was up to 50% lower and lipolysis was only slightly affected in excised material when compared with cotyledons obtained from intact seedlings. Incubating endosperm in sucrose had no effect on the development of the above enzyme activities or lipid content, when compared with material incubated in water only. In contrast, cotyledonary MS and ICL activities were up to 70% lower in sucrose and lipolysis substantially inhibited. Lipid breakdown and the development of lipolytic enzyme activity in cotyledons seem to be dependent on the presence of the endosperm. It is concluded that enzyme regulation in castor bean seedlings cannot entirely be explained by axis control or source‐sink relationships.
Keywords