AMITROLE EFFECTS ON CHLOROPLASTS OF BARLEY PLANTS GROWN AT DIFFERENT TEMPERATURES

The effects of amitrole, a bleaching herbicide affecting carotenogenes is, were studied in barley plants grown in light at 20 degrees C and a t 30 degrees C. At the lower temperature the herbicide caused dramatic damage to the leaf chloroplasts, compared with control plants. The sy nthesis of protective carotenoids was drastically impaired, with some accumulation of lycopene and a very low production of beta-carotene an d xanthophylls. In chloroplasts this effect of amitrole was related to a fall in chlorophyll content, reduction of the thylakoid system and destruction of most 70S ribosomes. Though the damaged organelles maint ained a certain ability to synthesize proteins, chlorophyll-binding po lypeptides encoded by plastid DNA were not found in the altered thylak oids which, however, contained chlorophyll-binding proteins and other polypeptides encoded by the nuclear DNA. Amitrole appeared to be less effective in plants grown at 30 degrees C. The synthesis of the protec tive carotenoids was greatly increased and the chloroplasts exhibited structure and composition almost similar to those of control organelle s. The possible existence in the carotenoid biosynthetic pathway of al ternative thermo-modulated steps, with different amitrole sensitivity, is suggested.