THICKNESS AND STRUCTURE OF THE CELL-WALLS IN DEVELOPING RYE COLEOPTILES

Expansive growth of intact, etiolated rye coleoptiles (Secale cereale L.) is accompanied by a corresponding accumulation of cell-wall materi al. Determination of wall mass per unit length indicated that the aver age wall thickness remained constant during coleoptile elongation (2-7 days after sowing). Upon irradiation with continuous white light cole optile growth ceased, but wall accumulation continued for 2 further da ys at the same rate as in darkness. Hence, net wall accumulation and c ell elongation are independent processes. The thickness of the longitu dinal cell. walls, measured by electron microscopy, was maintained dur ing growth of the etiolated and irradiated coleoptiles. At the thick, expansion-limiting outer epidermal wall of growing coleoptiles electro n-dense (osmiophilic) particles were observed. In coleoptiles that had ceased to elongate no such particles were detected. In the basal (gro wing), but not in the apical (non-growing) region of the primary leaf we likewise observed electron-dense secretion products. The particles were only found at the thick outer walls of the two epidermises of the leaf. We suggest that these osmiophilic deposits are causally linked to the growth process of the peripheral cell walls in coleoptile and p rimary leaf of the rye seedling.