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Repression of isocitrate lyase synthesis in seeds germinated in the presence of glucose

1968; Elsevier BV; Volume: 157; Issue: 1 Linguagem: Inglês

10.1016/0005-2787(68)90272-4

1879-3002

P. Lado, M. Schwendimann, E. Marrè,

Lipid metabolism and biosynthesis

1. In the castor bean endosperm, isocitrate lyase activity is almost undetectable throughout seed maturation, while it rapidly increases during the early period of germination. Also in the cotyledons isolated from the seeds germinated 37 h (at 27°) isocitrate lyase activity, initially very low, rapidly increases when the cotyledons are incubated in water. 2. In the isolated cotyledons actinomycin D almost completely inhibits the development of isocitrate lyase as well as that of glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase and isocitrate dehydrogenase. In endosperm slices the drug inhibits by only 30–40 % the increase of the enzyme; in this case also the inhibition of RNA synthesis is far from complete. These results support the evidence that most if not all of the increase of isocitrate lyase in cotyledons, and presumably also in the endosperm of the castor bean, depends on de novo RNA and protein synthesis. 3. The presence of glucose in the incubation medium inhibits the rise of isocitrate lyase in the isolated cotyledons by about 86 %. The development increase of the other enzyme activities investigated is not inhibited by glucose; this indicates that the repressing effect of glucose on isocitrate lyase synthesis is fairly specific. In the endosperms of germinating seeds the development of isocitrate lyase is significantly, even if only partially, repressed by glucose. These data support the view that, in higher plants too, glucose, or some of its derivatives, represses isocitrate lyase development by preventing the synthesis of its specific messenger RNA (mRNA).