CHLOROPLAST THYLAKOID PROTEIN-CHANGES INDUCED BY LOW GROWTH TEMPERATURE IN MAIZE REVEALED BY IMMUNOCYTOLOGY

Tissue-specific effects of low growth temperature on maize chloroplast thylakoid protein accumulation were analysed using immunocytology. Sections of leaves from plants grown at 25 and 14-degrees-C were probed with antibodies to specific chloroplast thylakoid proteins from the four major protein multisubunit complexes of the thylakoid membrane followed by fluorescein-conjugated goat anti-rabbit antibodies. At a normal growth temperature of 25-degrees-C, the 32 kDa D1 protein of the photosystem II reaction centre and the 33 kDa protein of the extrinsic oxygen-evolving complex of photosystem II are both accumulated to a greater degree in the mesophyll than in the bundle sheath chloroplasts. In contrast, subunit II of photosystem I, cytochrome f and the is-proportional-to- and beta-subunits of ATP synthetase are predominant in the bundle sheath thylakoids at 25-degrees-C. A striking difference between the 25-degrees-C-grown and the 14-degrees-C-grown leaf tissue was the presence in the latter of (20-30%) cells whose chloroplasts apparently completely lack several of the thylakoid proteins. In plants grown at 14-degrees-C, the accumulation of the 33 kDa protein of the extrinsic oxygen-evolving complex of photosystem II was apparently unchanged, but other thylakoid proteins showed a significant reduction. The uneven distribution of proteins between the bundle sheath and mesophyll chloroplasts observed at 25-degrees-C was also maintained at 14-degrees-C. Reduction in the fluorescence at 14-degrees-C was manifested either as an overall reduction in the diffuse fluorescence across the chloroplast profiles or less frequently as a reduction to small discrete bodies of intense fluorescence. The significance of these results to low-temperature-induced reduction in the photosynthetic productivity of maize is discussed.