COMPARATIVE PHYSIOLOGICAL-EFFECTS OF QUINCLORAC AND AUXINS, AND LIGHTINVOLVEMENT IN QUINCLORAC-INDUCED CHLOROSIS IN CORN LEAVES

The physiological effects of the herbicide quinclorac (3,7-dichloro-8- quinolinecarboxylic acid) in corn and the involvement of light on the herbicide-induced chlorosis were investigated. Quinclorac was highly i nhibitory to corn growth. However, different from the tested auxins, q uinclorac showed no promotion in an auxinic activity assay (corn coleo ptile elongation). Quinclorac induced significantly lower amounts of e thylene in corn coleoptile sections compared with IAA, NAA, and 2,4-D under darkness. Furthermore, quinclorac did not bind with a putative c orn membrane-bound auxin receptor. Quinclorac caused chlorotic discolo ration in the youngest leaf under light. When the quinclorac-treated c orn leaf disks were continuously exposed to light, a significant decre ase in total chlorophyll content was observed. No decrease in total ch lorophyll content of the herbicide-treated leaf disks under dark condi tions was detected. There was a significant correlation between light intensity and the reduction in total chlorophyll content of the leaf d isks induced by quinclorac. Moreover, quinclorac considerably increase d ethylene production in leaf disks under light conditions, whereas no enhancement of ethylene production in the dark was observed. 2,4-D sl ightly stimulated ethylene production under both the light and dark co nditions. There was a high negative correlation between quinclorac-ind uced ethylene production and total chlorophyll content in quinclorac-t reated leaf disks. These results suggest that the physiological action s of quinclorac applied to corn are not necessarily the same as 2,4-D and other auxins. Ethylene biosynthetic reaction may be closely relate d with the major herbicidal action of quinclorac, similar to that of 2 ,4-D. However, our data indicate that the quinclorac-enhanced ethylene biosynthetic reaction and the herbicide-induced chlorosis in corn lea ves are light dependent. (C) 1997 Academic Press.