The Biochemical and Functional Properties of Thylakoid Protein Complexes from Mesophyll and Bundle Sheath Chloroplasts of Three Types of C4 Plants

Leaves of C 4 plants contain two distinct types of photosynthetic cells, mesophyll (M) and bundle sheath (BS) which are quite different organized both structurally and functionally. There are three C 4 subgroups based on differences in decarboxylating mechanisms: NADP-ME, NAD-ME and PEP-CK type [1]. The BS chloroplasts in NADP-ME subtype are agranal with structures like stroma lamellae of C 3 chloroplasts. The BS and M chloroplasts in both NAD-ME and PEP-CK subtypes are granal but is unknown if the structural and functional heterogeneities in PSI and PSII exist. In NADP-ME species, BS thylakoids exhibit only PSI activity and little is known about the amount, composition, and the function of the PSII centers. Because the conflicting data on PSII activity has been reported, the degree of PSII deficiency in bundle-sheath chloroplasts of NADP-ME species has always been a matter of debate. Discrepancy could be due either to different experimental assay conditions or to cross-contamination of the bundle-sheath with the mesophyll chloroplasts. Pfündel et al. [2] using flow cytometry method for sorting the chloroplasts showed, that PSII light absorption in BS chloroplasts contributes significantly to the functional antenna of PSI despite their relatively low concentration. This agree with observation of Bassi et al. [3] who found that LHCII acts as an antenna of PSI in bundle sheath maize chloroplasts. PSII in BS cells of young seedlings of maize is active but it is progressively reduced during leaf differentiation. A loss of activity was caused by reduced rates of synthesis of polipeptydes of oxygen evolving complex (OEC); D1, D2, CP47 polypeptides [4]. The appearance of M and BS chloroplasts is very similar in NAD-ME and PEP-CK types of C4 plants, but PSII concentration in bundle sheath cells is elevated in NAD-ME species [2]. Information about the organization of chlorophyll-protein complexes and photochemical activity of PSI and PSII in both types of chloroplasts are very limited. Dynamic and reversible changes of composition in thylakoids membranes have great importance to sustain of photosynthetic activities of plants under changing conditions. We have investigated the PSI and PSII activity, the relative amounts of individual thylakoid proteins, composition of Chl-P complexes in M and BS chloroplsts of Zea mays (NADP-ME), Panicum