Auxin stimulates the synthesis but not the loosening of cell walls in isolated outer tissue of dark-grown squash (Cucurbita maxima duch.) hypocotyls

Indole-3-acetic acid (IAA) promoted elongation and cell wall loosening of o uter tissue of intact segments from squash (Cucurbita maxima Duch.) hypocot yls. On the other hand, when the segment was separated into the outer and i nner tissues and then incubated, the isolated outer tissue slightly shrank and did not elongate, while the isolated inner one rapidly elongated. IAA d id nor affect either growth or the mechanical properties of cell walls of i solated outer and inner tissues. In intact segments, IAA significantly prom oted the incorporation of radioactivity from [C-14] glucose into cell wall fractions of outer tissue without affecting uptake into the intact: segment s but it did not: promote that of inner tissue. In isolated outer tissue, I AA substantially inhibited the uptake but significantly promoted the distri bution of the incorporated radioactivity into cell wall fractions. IAA, how ever, barely affected the uptake and incorporation of radioactivity into ce ll wall fractions in isolated inner tissue. These results suggest that IAA primarily stimulates the synthesis of certain cell wall polysaccharides in outer tissue, irrespective of being intact or isolated, but the stimulation to that extent is not directly involved in the processes of cell wall loos ening in outer tissue.