THE EFFECTS OF CARBON STARVATION ON CELLULAR-METABOLISM AND PROTEIN AND RNA-SYNTHESIS IN GERBERA CALLUS-CULTURES

Gerbera jamesonii H. Bolus var. hybrida callus cultures subjected to carbon starvation show alteration in some physiological parameters and protein synthesis. Five days of continuous starvation induce a decrease of protein and carbohydrate contents to, respectively, 27% and 12% of the values of the control, while specific activities of glutamate dehydrogenase and proteases reached levels about 5-fold and 2-fold higher than the control ones. Electrophoresis of proteins labelled by in vivo and in vitro translation showed the appearance of several starvation-related proteins (STP). At day 5 from the onset of starvation the induction of STPs was related with levels of in vitro translatable mRNAs, whereas at day 1 the synthesis of STPs depended upon translational regulation. The induction of STPs was also analyzed under conditions of specific protein synthesis inhibition by heat-shock. Protein synthesis in heat-shocked starved cells showed (i) the induction of heat-shock proteins (HSPs), and (ii) the disappearance of all but three STPs of molecular mass 70, 69 and 36 kDa. A similarity between one HSP and one STP is hypothesized on the basis of comigration on two-dimensional gels (70 kDa). During recovery from heat-shock starved cells showed the reappearance of all the STPs and the simultaneous maintenance of most of the HSPs. The data presented support a role of STPs in starvation and the existence of interactions between heat-shock and nutrient deprivation.