Alterations in the sugar metabolism and in the vacuolar system of mesophyll cells contribute to the desiccation tolerance of Haberlea rhodopensis ecotypes.

Haberlea rhodopensis belongs to the small group of resurrection plants having the unique ability to survive desiccation to air dry state retaining most of its chlorophyll content and then resume normal function upon rehydration. It prefers the shady valleys and northward facing slopes of limestone ridges in mountain zones with high average humidity. Nevertheless, it can be found rarely on rocks directly exposed to the sunlight, without the coverage of the canopy. In the present study, we follow the alterations in the subcellular organization of mesophyll cells and sugar metabolism upon desiccation of shade and sun H. rhodopensis plants. Composition and content of soluble carbohydrates during desiccation and rehydration were different in plants grown below the trees or on the sunny rocks. Sucrose, however, was dominating in both ecotypes. The amount of starch grains in chloroplasts was inversely related to that of sugars. Concomitantly with these changes, the number of vacuoles was multiplied in the cells. This can be explained by the development of small (secondary) vacuoles peripherally in the cytoplasm, rather than by the fragmentation of the single vacuole, proposed earlier in the literature. Accordingly, the centripetal movement of chloroplasts and other organelles may be a result of the dynamic changes in the vacuolar system. Upon rehydration, the inner vacuoles enlarged and the organelles returned to their normal position.

Cd-Fe interactions: comparison of the effects of iron deficiency and cadmium on growth and photosynthetic performance in poplar.

To check the importance of Cd-induced iron deficiency in Cd stress, symptoms of Cd stress were compared with those of iron deficiency or the combination of these two stresses. Poplar plants grown in hydroponics with Fe-EDTA (e) or Fe-citrate (c) up to four-leaf stage were treated for two weeks either by the withdrawal of iron (Fedef), or supplying 10 µM Cd(NO3)2 in the presence (Cad) or absence of an iron source (Fedef + Cad). Cadmium and iron content of leaves developing under the stress was in the order of cCad > eCad > cFedef + Cad and cCad ≈ eFedef ≈ cFedef + Cad < eCad < cFedef, respectively. Growth inhibition was much stronger in Cad than Fedef plants. The inhibitory effects on CO2 fixation, maximal and actual efficiency of PSII, chlorophyll synthesis, as well as the stimulation of the accumulation of violaxanthin cycle components and increase in non-photochemical quenching were the strongest in cFedef+Cad plants, otherwise these parameters changed parallel to the iron deficiency of leaves. Tendency of changes in thylakoid composition were similar under Cad treatments and strong iron deficiency: particularly PSI and LHCII decreased. Therefore, the development of the photosynthetic apparatus under Cd stress was mainly influenced by the Cd-induced strong iron deficiency, while leaf growth was affected primarily by the presence of Cd.