Artificial tripartite symbiosis involving a green alga (Chlamydomonas), a bacterium (Azotobacter) and a fungus (Alternaria): morphological and physiological characterization.

A long-living artificial tripartite symbiosis involving a green alga (Chlamydomonas), a bacterium (Azotobacter) and a fungus (Alternaria) was established on carbon- and nitrogen-free medium. The basis of the interdependence is the complementation of photosynthetic CO2 assimilation and atmospheric nitrogen fixation. Green color of the colonies indicated that the algal cells had enough nitrogen to synthesize chlorophylls. The chlorophyll content was nearly 40% of the control cells. The relatively high rate of photosynthetic oxygen evolution proved that nitrogen was effectively used for building up a well functioning photosynthetic apparatus. This was supported by the analysis of photosystems and ultrastructural investigations. In comparison with degreened algae cultured on nitrogen-free medium, the chloroplasts in the symbiont algal cells contained a well-developed, stacked thylakoid membrane system without extreme starch or lipid accumulation. The occurrence of the fungus in the association greatly increased the chlorophyll content. Far fewer types of amino acids were excreted by the tripartite cultures than by pure cultures. Cystathionine, which is a common intermediate in the sulfur-containing amino acid metabolism, was produced in high quantities by the tripartite symbiosis. This can mostly be attributed to the activity of the fungus.

On the mechanism of rejuvenation of ageing detached bean leaves by low-concentration stressors.

The effect of low concentrations of some stress-inducing compounds of different toxicity and chemical nature, such as Cd and Pb salts or DCMU, was investigated on the senescence of chloroplasts in detached primary leaves of bean (Phaseolus vulgaris L.). After 1 week of senescence followed by root development from the petiole, these agents stimulated chlorophyll accumulation and photosynthetic activity ((14)CO(2) fixation) as compared to the control, thus inducing rejuvenation. Low-concentration stressors increased the level of active cytokinins in roots and leaves during the treatment, as monitored by the Amaranthus betacyanin bioassay and high-pressure liquid chromatography. The lithium ion, an inhibitor of the PIP(2)-IP(3)/DAG signal transduction pathway, abolished the stimulating effect of stressors, both in roots (retarding cytokinin synthesis) and consequently also in leaves (reducing cytokinin-dependent chlorophyll accumulation). This suggests the involvement of the PIP(2)-IP(3)/DAG signal transduction pathway in generation of these consecutive organ-specific responses.

Involvement of the phosphoinositide signaling pathway in the anti-senescence effect of low-concentration stressors on detached barley leaves.

The effect of low concentration of some stress-inducing compounds of different toxicity and chemical nature like Pb and Ti salts or DCMU on the senescence of chloroplasts was investigated in detached primary leaves of barley (Hordeum vulgare cv. Omega). These agents stimulated chlorophyll accumulation, photosynthetic activity ((14)CO (2) fixation), and decreased the number of plastoglobuli in chloroplasts compared to the control, thus delaying senescence. Low-concentration stressors did not increase the level of active cytokinins of leaves during the treatment. Lithium and stearoylcarnitine chloride inhibited the stimulating effect of stressors. This points to the involvement of the PIP (2)-IP (3)/DAG signal transduction pathway in generation of the specific responses.

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.

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.