RESYNTHESIS OF THYLAKOIDS AND FUNCTIONAL CHLOROPLASTS IN THE DESICCATED LEAVES OF THE POIKILOCHLOROPHYLLOUS PLANT XEROPHYTA-SCABRIDA UPON REHYDRATION

The ultrastructural changes in chloroplasts and other cell organelles in the desiccated, achlorophyllous leaves of Xerophyta scabrida, a poikilochlorophyllous desiccation tolerant (PDT) monocotyledonous plant, were examined during reconstitution of the photosynthetic apparatus after rehydration of air-dried leaves. In the desiccoplasts (the former chloroplasts) of the air-dried leaves no thylakoids were present, only osmiophilic lipid material in the place of former grana and stroma thylakoids and groups of translucent plastoglobuli. Ten to 12 h after the start of the rehydration of air-dried leaves the resynthesis of chlorophylls and thylakoids began, and fundamental structural changes occurred in desiccoplasts: the appearance of a small amount of starch, of primary thylakoids and of primary grana consisting of two appressed thylakoids, whereas the size of plastoglobuli descreased. At this stage the mitochondria appeared to be fully functional and to recover before the reconstitution of chloroplasts. Grana with 2-3 thylakoids were predominant 24 h after the start of rehydration; the degree of stacking and the ratio of appressed to non-appressed membranes increased. Translucent plastoglobuli were no longer seen, and only much smaller osmiophilic plastoglobuli were visible. At 72 h after rehydration of air-dried leaves, grana of up to 7 thylakoids appeared, the degree of stacking increased further, and starch granules became larger, as did the plastoglobuli, which also again turned translucent. The thylakoid system was then fully reconstituted and capable of ensuring the energy requirements of a normal rate of CO2 assimilation as well as synthesis and accumulation of excess lipids in the translucent plastoglobuli.