COMPARATIVE ULTRASTRUCTURAL AND FLUORESCENCE STUDIES OF GRAPEVINE (VITIS-VINIFERA L) CHLOROPLASTS ISOLATED FROM STEM AND LEAF TISSUES

Ultrastructural observations of chlorophyll-containing stem tissues (woody shoots) of Vitis vinifera L. show that the chloroplasts in mature sieve elements (phloem and xylem) contain preferentially a large number of appressed (granal) thylakoids. This finding is in close relation with the extremely low chlorophyll a/b ratios in the stem tissues, which characterizes the photosystem II (PSII)-containing granal membranes. These structural differences are accompanied also by differences in the properties of the low temperature (77K) chlorophyll fluorescence emission. In both phloem and xylem chloroplasts the peak at 735 nm originating from photosystem I (PSI) is strongly reduced and the F735 F695 ratio is much more lower than in leaf chloroplasts. Furthermore, the value of the F735 F695 ratio in stem tissues depends to a lower extent on the presence of Mg2+, i.e.,the cation control of excitation energy distribution between PSII and PSI (spillover) is considerably restricted in both phloem and xylem thylakoid membranes. © 1990.