Abstract
Summary A comparison of chlorophyll-a fluorescence in mesophyll and bundle sheath cells showed differences in the relative fluorescence intensities and induction time courses which correlated with electron transport capacity via photosystem II. The results reflect the low photosystem II activity in bundle sheath cells. Oxygen quenching effects of variable fluorescence were related to the electron transport system in both types of cells. The most intensive O2 quenching is found in mesophyll cells which possess the full complement of the various electron transport components, comparable to chloroplasts from C3 plants. Fluorescence spectra at 77 K of cells frozen after preillumination with 680 and 700 nm light in O2 at room temperature, showed decreased fluorescence at 735 nm. The ratios of the band peak at 735 nm (photosystem I fluorescence) to the peak at 695 nm (photosystem II fluorescence) decreased more by O2 addition in bundle sheath cells than in mesophyll cells. Cyclic electron flow in bundle sheath cells appears to be more susceptible to oxygen than linear flow in mesophyll cells.
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