GABACULINE IMPAIRED ACCUMULATION OF PIGMENTS AND APOPROTEINS IN LIGHT-HARVESTING COMPLEXES AND REACTION CENTERS OF WHEAT THYLAKOIDS

We have examined the effect of gabaculine (3-amino-2,3-dihydrobenzoic acid) on chlorophyll (Chl) binding photosystem (PS) apoproteins in thy lakoid membranes relative to the effect on pigment accumulations and g rana thylakoid stacking in wheat (Triticum aestivum L.) seedling leave s. The accumulations of critical PS1, PS2, light-harvesting complex (L HC1 and LHC2) apoproteins differed in response to gabaculine treatment . The reaction center proteins, D1 of PS2 and the 68 kDa PS 1, were no t detected in either primary or secondary leaf chloroplasts of treated etiolated seedlings after greening or secondary leaf chloroplasts of treated green seedlings. However, the LHC apoproteins accumulated at r educed levels relative to the controls and LHC1 was more sensitive to treatment than LHC2. Gabaculine decreased plastid pigment levels in pr imary leaf chloroplasts of treated etiolated seedlings by only 50 % an d in secondary leaf chloroplasts by more than 85 % of that in the cont rols. The accumulations of Chl a, Chl b, and die carotenoids, neoxanth in and B-carotene, were most sensitive to treatment and were decreased in a similar manner. Granal thylakoid development was more sensitive to treatment than stroma thylakoid development and LHC2 apoprotein acc umulations enriched stroma thylakoids in some treatments. The lack of starch and critical reaction center apoproteins in these chloroplasts suggest a loss of photosynthetic competency.