Organization and activity of photosystems in the mesophyll and bundle sheath chloroplasts of maize

Photosystem I and Photosystem II activities, as well as polypeptide content of chlorophyll (Chl)-protein complexes were analyzed in mesophyll. (M) and bundle sheath (BS) chloroplasts of maize (Zea mays L.) growing under moderate and very low irradiance. This paper discusses the application of two techniques: mechanical and enzymatic, for separation of M and BS chloroplasts. The enzymatic isolation method resulted in depletion of potypeptides of oxygen evolving complex (OEC) and alpha CF1 subunit of coupling factor; D1 and D2 potypeptides of PSII were reduced by 50%, whereas light harvesting complex of photosystem II (LHCII) proteins were still detectable. Loss of PSII potypeptides correlated with the decreasing of Chl fluorescence measured at room temperature. Using mechanical isolation of chloroplasts from BS cells, all tested polypeptides could be detected. We found a total lack of O-2 evolution in BS chloroplasts, but dichlorophenolindophenol (DCPIP) was photoreduced. PSI activity of chloroplasts isolated from 14- and 28-day-old plants was similar in BS chloroplasts in moderate tight (ML), but in low light (LL) it was reduced by about 20%. PSI and PSII activities in M chtoroplasts of plants growing in ML decreased with aging of plants. In older LL-grown plants, activities of both photosystems were higher than those observed in chloroplasts from ML-grown plants.