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 poi kilochlorophyllous desiccation tolerant (PDT) monocotyledonous plant, were examined during reconstitution of the photosynthetic apparatus af ter 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 th ylakoids and groups of translucent plastoglobuli. Ten to 12 h after th e start of the rehydration of air-dried leaves the resynthesis of chlo rophylls and thylakoids began, and fundamental structural changes occu rred in desiccoplasts: the appearance of a small amount of starch, of primary thylakoids and of primary grana consisting of two appressed th ylakoids, 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 pr edominant 24 h after the start of rehydration; the degree of stacking and the ratio of appressed to non-appressed membranes increased. Trans lucent plastoglobuli were no longer seen, and only much smaller osmiop hilic plastoglobuli were visible. At 72 h after rehydration of air-dri ed leaves, grana of up to 7 thylakoids appeared, the degree of stackin g increased further, and starch granules became larger, as did the pla stoglobuli, which also again turned translucent. The thylakoid system was then fully reconstituted and capable of ensuring the energy requir ements of a normal rate of CO2 assimilation as well as synthesis and a ccumulation of excess lipids in the translucent plastoglobuli.