GENE-EXPRESSION INDUCED BY SPERMINE IN ISOLATED EMBRYONIC AXES OF CHICKPEA SEEDS

Nuclei and mRNA obtained from the embryonic axes of chick-pea (Cicer a rietinum) seeds grown in the presence of spermine (Spm) have been used to study certain characteristics of gene expression induced by this p olyamine. In the embryonic axes, free Spm varied between 100 and 300 m ug (g fresh weight)-1, whereas Spm bound to macromolecules varied betw een 6 and 30 mug (g fresh weight)-1. Isolated nuclei of the controls s ynthesized RNA at a rate of 1.1 nmol (H-3)-UTP (mg DNA)-1 min-1, and R NA polymerase activity increased concomitantly with growth, although t his activity was inhibited by alpha-amanitin (5 mg l-1). Isolated nucl ei from axes grown in a medium with Spm had a lesser transcriptional a ctivity than the controls; this activity was weaker still when abscisi c acid (ABA) was present. Nevertheless, Spm stimulated RNA synthesis i n vivo [measured as incorporated (H-3)-uridine into trichloroacetic ac id-insoluble material]. These results suggest a cytoplasmic control of transcription by Spm. Gene expression at the mRNA level was studied b y analyzing its in vitro translated products (one- and two-dimensional PAGE). Some mRNA species were enhanced by Spm whereas others were sup pressed or only weakly expressed. A polypeptide of 26-27 kDa, absent i n the control, appeared strongly with Spm or ABA, and very weakly in t he presence of Spm plus ABA. In presence of Spm the mRNA encoding this protein was not expressed in vivo. The mode of action of Spm in our s ystem is discussed in view of these findings.