RELEASE OF UV-ABSORBING SUBSTANCES FROM MAIZE COLEOPTILES DURING AUXIN-MEDIATED, FUSICOCCIN-MEDIATED AND ACID-MEDIATED ELONGATION GROWTH

Isolated cell walls from maize coleoptiles prepared under conditions t hat preserve the ability fdr enzymatic hemicellulose autolysis release UV-absorbing substances into dhe incubation medium in a time-dependen t reaction with an optimal rate at pH 6-7. The reaction can be inhibit ed by low temperature and protein-denaturing treatments, indicating an enzymatic process. Spectroscopic and chromatographic analyses showed that the liberated substances represent a complex mixture of free and bound (alkali-hydrolyzable) phenolic compounds with similar absorption spectra restricted to the range below 300 nm and thus excluding hydro xycinnamic acids from cell-wall esters. A spectroscopically and chroma tographically similar mixture of soluble UV-absorbing substances is re leased if living (abraded) maize coleoptiles or coleoptile segments ar e incubated in water or buffer, suggesting that insoluble phenolic mat erials in the cell wall are metabolized also in vivo. This reaction ca n be promoted by anaerobic conditions and application of fusicoccin wh ereas auxin had a slightly inhibitory effect. No clear relationship to elongation growth could be demonstrated. We conclude from these resul ts that polymeric phenolic constituents of the cell wall are subject t o enzymatic degradation in mure similar to polysaccharide autolysis an d that this process is under metabolic control.