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 proteinglycosylation 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 detectableeffect on growth at 100µg ml^–1. DOG impaired growthat concentrations larger than 1 mM. Total inhibition of growthoccurred at a concentration of 20 mM. Similar effects were observedwith mannose and glucosamine. The effect on wall-synthetic processesin the growth-limiting epidermis was analysed by tracer incorporationstudies. Within 30 min hemicellulose and cellulose synthesis,measured as ³H-glucose incorporation, was not affected by DOG,indicating that inhibition of growth is not causally relatedto synthesis of both wall components. In contrast, protein synthesisand secretion into the walls, measured as incorporation of ³H-leucineinto the TCA-precipitable protoplasmic and wall-bound protein,was rapidly inhibited by DOG. Concomitant with the effect ongrowth, DOG as well as mannose inhibited the occurrence of osmiophilicparticles (OPs) which specifically occur at the growth-limitingepidermis during IAA-induced growth. The results provide evidencethat IAA-induced wall loosening underlying elongation growthis dependent on O-glycosylation of proteins and their subsequentsecretion into the epidermal walls. It appears that interferencewith these processes is responsible for inhibition of IAA inducedgrowth by hexoses acting as anti-glucose antimetabolites. Key words: Auxin-induced growth, cell-wall synthesis, 2-deoxy-D-glucose, mannose, osmiophilic particles, tunicamycin