EFFECT OF INHIBITION OF PROTEIN GLYCOSYLATION ON AUXIN-INDUCED GROWTH AND THE OCCURRENCE OF OSMIOPHILIC PARTICLES IN MAIZE (ZEA-MAYS L) COLEOPTILES

The dependence of auxin (IAA)-induced elongation growth on protein glycosylation was investigated in abraded maize (Zea mays L.) coleoptile segments, employing 2-deoxy-D-glucose (DOG) and tunicamycin (TUM) as inhibitors of protein glycosylation. TUM had no detectable effect on growth at 100 mu g ml(-1). DOG impaired growth at concentrations larger than 1 mM. Total inhibition of growth occurred at a concentration of 20 mM. Similar effects were observed with mannose and glucosamine. The effect on wall-synthetic processes in the growth-limiting epidermis was analysed by tracer incorporation studies. Within 30 min hemicellulose and cellulose synthesis, measured as H-3-glucose incorporation, was not affected by DOG, indicating that inhibition of growth is not causally related to synthesis of both wall components, In contrast, protein synthesis and secretion into the walls, measured as incorporation of H-3-leucine into the TCA-precipitable protoplasmic and wall-bound protein, was rapidly inhibited by DOG. Concomitant with the effect on growth, DOG as well as mannose inhibited the occurrence of osmiophilic particles (OPs) which specifically occur at the growth-limiting epidermis during IAA-induced growth. The results provide evidence that IAA-induced wall loosening underlying elongation growth is dependent on O-glycosylation of proteins and their subsequent secretion into the epidermal walls. It appears that interference with these processes is responsible for inhibition of IAA-induced growth by hexoses acting as anti-glucose antimetabolites.