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.

Differences in root functions during long-term drought adaptation: comparison of active gene sets of two wheat genotypes.

In an attempt to shed light on the role of root systems in differential responses of wheat genotypes to long-term water limitation, transcriptional differences between two wheat genotypes (Triticum aestivum L., cv. Plainsman V and landrace Kobomugi) were identified during adaptation to moderate water stress at the tillering stage. Differences in organ sizes, water-use efficiency and seed production were detected in plants grown in soil, and root functions were characterised by expression profiling. The molecular genetic background of the behaviour of the two genotypes during this stress was revealed using a cDNA macroarray for transcript profiling of the roots. During a 4-week period of moderate water deficit, a set of up-regulated genes displaying transiently increased expression was identified in young plantlets, mostly in the second week in the roots of Kobomugi, while transcript levels remained constantly high in roots of Plainsman V. These genes encode proteins with various functions, such as transport, protein metabolism, osmoprotectant biosynthesis, cell wall biogenesis and detoxification, and also regulatory proteins. Oxidoreductases, peroxidases and cell wall-related genes were induced significantly only in Plainsman V, while induction of stress- and defence-related genes was more pronounced in Kobomugi. Real-time qPCR analysis of selected members of the glutathione S-transferase gene family revealed differences in regulation of family members in the two genotypes and confirmed the macroarray results. The TaGSTZ gene was stress-activated only in the roots of Kobomugi.

Structural-functional changes in detached cucumber leaves, and modelling these by hormone-treated leaf discs.

Senescence and rejuvenation were investigated in detached cucumber (Cucumis sativus L.) leaves after cultivation in nutrient solution for one week or four weeks. Rooting of the petiole (visible generally from the 7th day) elicited a combination of different morphological, anatomical, and physiological changes in the lamina. Extensive growth in area and thickness, extreme regreening, changes of chloroplast structure and activity, as well as the pattern of Chl-protein complexes were observed and compared either to the corresponding parameters of young detached leaves or mature attached leaves. These responses could be provoked separately by treating excised leaf discs with kinetin, benzyladenine, or indolylacetic acid. The hormones showed mutuality in their effects, benzyladenine being responsible for the growth of cells, while indolylacetic acid and kinetin promoted an increase in chlorophyll content. However, none of the treatments resulted in the growth of the chloroplasts in the leaf discs, which was only prominent in the rooting leaves.

Effects of two iron sources on iron and cadmium allocation in poplar (Populus alba) plants exposed to cadmium.

Effects of 10 microM cadmium (supplied as Cd nitrate) on the utilization and allocation of iron (Fe) were investigated in poplar (Populus alba L.) plants grown in nutrient solution with Fe(III)-EDTA or Fe(III)-citrate as the Fe source. The effects of Cd were also compared with those of Fe deprivation. The accumulation of Fe in roots was 10-fold higher in plants grown with Fe-citrate than with Fe-EDTA. Cadmium decreased leaf chlorophyll concentrations and photosynthetic rates, and these decreases were more marked in plants grown with Fe-citrate than with Fe-EDTA. In both Fe treatments, addition of Cd caused large increases in root and shoot apoplasmic and non-apoplasmic Cd contents and increases in root Fe content; however, Cd decreased shoot Fe content, especially in plants grown with Fe-citrate. New leaves of plants grown with Fe-citrate had small cellular (non-apoplasmic) Fe pools, whereas these pools were large in new leaves of plants grown with Fe-EDTA. Non-apoplasmic Cd pools in new leaves were smaller in plants grown with Fe-citrate than with Fe-EDTA, indicating that inactivation of non-apoplasmic Cd pools is facilitated more by Fe-EDTA than by Fe-citrate. In the presence of Cd, Fe-EDTA was also superior to Fe-citrate in maintaining an adequate Fe supply to poplar shoots. Differences in plant responses to Fe-EDTA and Fe-citrate may reflect differences in long-distance transport of Fe rather than in acquisition of Fe by roots.

Rejuvenation of ageing bean leaves under the effect of low-dose stressors.

The effect of low concentrations of some stress-inducing compounds like Cd, Pb, Ni, and Ti salts and DCMU on the senescence of chloroplasts was investigated in detached primary leaves of bean. After the petioles of ageing leaves had developed roots, these low-dose stressors stimulated chlorophyll synthesis and photosynthetic activity, as compared to the control, thus causing rejuvenation in treated leaves. The amount of photosystem I (lowest in DCMU-treated leaves) and light-harvesting complex II increased, while that of photosystem II decreased or remained unchanged. Fluorescence induction parameters indicated unchanged electron transport (except for DCMU treatment). CO2 fixation and, in some cases, starch accumulation was stimulated. In parallel, the occurrence of large plastoglobuli seemed to decrease in plastids of heavy metal-treated leaves. A cytokinin bioassay of leaf extracts confirmed the cytokinin-mediated effect of low-dose stressors, as the slopes of Chl and cytokinin curves were similar during the rejuvenation process. It is assumed that these stressors generate non-specific alarm reactions, which involve changes in the hormonal balance by increasing the synthesis of cytokinins.

Separation of chlorophyll-protein complexes by Deriphat polyacrylamide gradient gel electrophoresis.

An improved Deriphat polyacrylamide gradient gel electrophoresis system was developed for the separation of chlorophyll-protein complexes. The relatively good resolution of the starting discontinuous gel system was further improved by using glycerol in gels and an acrylamide gradient with high acrylamide-to-N,N'-methylenebisacrylamide ratio in the separating gel. By applying mild but efficient glycosidic detergents for solubilization, and Deriphat to gels and buffers, the stability of complexes was increased, and only a low amount of pigment was removed. The advantage of our system is the better resolution of larger-size complexes, especially those of photosystem I. In addition, it makes possible an easier interpretation of results due to less overlapping of photosystem I and photosystem II bands when different plant species or the effects of different treatments are compared using whole thylakoid membranes.

Partial characterization of a minor chlorophyll-protein found in primary thylakoids of intermittently illuminated maize.

A mild solubilization with sodium dodecyl sulphate of intermittently illuminated maize (Zea mays L. Mvsc 429) thylakoids allows the separation of a minor chlorophyll-protein in the position of the light harvesting chlorophyll-protein monomer of green plants by polyacrylamide gel electrophoresis. It contains mainly chlorophyll a, its chlorophyll b content may come from the slightly contaminating light harvesting chlorophyll a/b-protein. It represents about 15% of the chlorophyll in protochloroplasts. The new chlorophyll-protein has an absorption maximum at 672 nm, and only one fluorescence emission peak at 680 nm. A 34 kD polypeptide is the most abundant one in the polypeptide pattern of the complex. The function of the new chlorophyll-protein is unknown at present. Its relationship to other chlorophyll-proteins is discussed.

Effect of lincomycin on the dimorphic chloroplasts of Zea mays L. leaves.

The effect of lincomycin treatment on the ultrastructure, and on the absorption and fluorescence emission spectra, of mesophyll and bundle sheath chloroplasts of maize was investigated. The ultrastructural and absorption changes affected mainly the unstacked lamellae (photosystem 1) in the treated mesophyll and bundle sheath plastids, while the fluorescence emission spectra reflect a changed energy transfer between the chlorophyll a forms. The results provide additional evidence for the compositional and developmental similarity of the intergranal lamellae of mesophyll chloroplasts to the membranes of the nearly agranal bundle sheath chloroplasts.

Light-induced fluorescence decay during the greening of normal and lincomycin-treated maize leaves.

Light-induced fluorescence decay was examined during the greening of control and lincomycintreated maize (Zea mays L.) leaves. Assuming that this decay to a first approximation is the result of two parallel first-order reactions, the fluorescence induction curves were linearized on the logarithm plot and the parameters were determined. The variable fluorescence increased, and the parameters of the two linear sections of the fluorescence decay-that is, the kinetics of the induction curves-changed during the greening of the control leaves. Lincomycin treatment caused some chlorophyll deficiency and the lowering of the chlorophyll a/b ratio, changed the fluorescence emission spectra and the effect of Mg(2+) on the regulation of the excitation energy distribution. The structure of the thylakoids and the kinetics of the fluorescence decay were also changed in the treated leaves. The possible relationship between the change of the kinetics of the fluorescence decay and the change of spillover during greening and after lincomycin treatment is discussed.