Showing papers in "Plant and Cell Physiology in 1991"

Astaxanthin Accumulation in the Green Alga Haematococcus pluvialis1

Abstract: Cells of the green microalga Haematococcus pluvialis were induced to accumulate the ketocarotenoid pigment, astaxanthin. This induction was achieved by the application of the following environmental conditions: light intensity (170//mol m~s~'), phosphate starvation and salt stress (NaCl 0.8%). These conditions retarded cell growth as reflected by a decrease in cell division rate, but led to an increase in astaxanthin content per cell. Accumulation of astaxanthin required nitrogen and was associated with a change in the cell stage from biflagellate vegetative green cells to non-motile and large resting cells. It is suggested that environmental or nutritional stresses, which interfere with cell division, trigger the accumulation of astaxanthin. Indeed, when a specific inhibitor of cell division was applied, a massive accumulation of astaxanthin occurred.

Inhibition of the Chloroplast Photochemical Reactions by Treatment of Wheat Seedlings with Low Concentrations of Cadmium: Analysis of Electron Transport Activities and Changes in Fluorescence Yield

Abstract: 2+ ions for 24 h in dark, and after this treatment the plants were grown in the light until the primary leaves were fully developed. Cd 2+ ions (30-120 fiu) induced a significant decrease in activities of both photosystem II and photosystem I. The extent of the decrease in PS II activity was much greater than that in the PS I activity. Analysis of changes in the fluorescence yield of chlorophyll a also indicated that Cd 2+ ions drastically affect the photochemistry of photosystem II. Cd 2+ ions induced decrease in the rates of photoreduction of 2,6-dichlorophenol indophenol even in the presence of the exogenous electron donor, hydroxylamine, both in Tris-treated and untreated chloroplasts. This result suggests that the site of inhibition is near the site of donation of electrons by hydroxylamine. Treatment with Cd 2+ ions impairs the electron transport system on the reducing side of PS II. The decrease in the fluorescence yield of Chi a is less than that in the evolution of O2 mediated by oxidized phenylenediamine. This difference may be a result of inhibition on the reducing side of PS II. In addition to inhibition on the reducing side, Cd 2+ ions may affect the oxidizing side of PS II. A comparative study of the rates of evolution of O2 with /7-benzoquinone and dichloro-^7-benzoquinone as electron acceptors was performed since the halogenated benzoquinones have been shown to accept electrons from both active and inactive centers of photosystem II while some of the benzoquinones accept electrons only from active centers. The results suggest that Cd 2+ ions induced a marginal increase in the number of inactive reaction centers in PS II. Analysis of light-saturation-kinetics of the evolution of O2 catalysed by PS II indicates a reduction in the size of the antennae as well as in the concentration of the active (a-type) reaction centers of PS II. Thus, the Cd 2+ -induced effects on the photochemistry of PS II involve changes on the reducing side of PS II as well as possible changes in the sizes of the populations of active and inactive centers. Thus, short-term exposure to Cd 2+ ions during establishment of seedlings has a severely detrimental effect on photochemical activities in chloroplasts.

Scavenging of Hydrogen Peroxide in Prokaryotic and Eukaryotic Algae: Acquisition of Ascorbate Peroxidase during the Evolution of Cyanobacteria

Abstract: Cyanobacteria can be divided into two groups, those that has and those that lacks AsA peroxidase. The first group scavenges hydrogen peroxide with the peroxidase using a photoreductant as the electron donor, and the second group only scavenges hydrogen peroxide with catalase

Brassinosteroids Act as Regulators of Tracheary-Element Differentiation in Isolated Zinnia Mesophyll Cells :

Abstract: Uniconazole [S-3307; (E)-l-(4-chlorophenyl)-4,4-dimethyl-2-(l,2,4-triazol-l-yl)-l-penten-3ol], a synthetic plant-growth retardant, inhibited the differentiation of isolated mesophyll cells of Zinnia elegans L. into tracheary elements (TEs) but had no effect on cell division when it was added to the culture medium at a concentration of 3.4 fiu. In the presence of uniconazole, none of the cytological events characteristic of the processes of TE differentiation, such as aggregation of actin filaments, bundling of microtubules or localized thickening and lignification of secondary walls, was observed. Uniconazole was effective when it was added to the medium within 36 h after the start of culture. Brassinosteroids (0.2 nM brassinolide or 2 (m homobrassinolide), but not gibberellin A3, counteracted the inhibitory effect of uniconazole on TE differentiation. Brassinosteroids were most effective when they were added to cultures between 24 and 30 h after the start of culture. Exogenously applied brassinosteroids promoted TE differentiation. It is suggested that the synthesis of brassinosteroids is essential for the differentiation of the cells into TEs and that uniconazole inhibits this differentiation through its inhibitory effect on the biosynthesis of brassinosteroids.

Resistance of Spirulina platensis to Ammonia at High pH Values

Abstract: Spirulina platensis is an alkalophilic cyanobacterium, exhibiting optimal growth at pH 9.0 to 10.0. It grows well at pH 11.5 but not at pH 7.0. Unlike many other photosynthetic microorganisms, it is capable of utilizing ammonia 3 even at high pH values, and is resistant to the ammoniamediated uncoupling of photosynthesis. The entry of ammonia into the cells is zlpH-dependent, and is limited by a relatively high average internal pH. This high pH value appears to be maintained predominantly by a high intrathylakoid pH.

Production of Indole-3-Acetic Acid by Bradyrhizobium japonicum: A Correlation with Genotype Grouping and Rhizobitoxine Production

Abstract: Bioassays show that rhizobitoxine-producing strains of Bradyrhizobium japonicum excreted another phytotoxic compound into their culture fluid. This compound was purified and identified by HPLC and mass spectrometry as indole-3-acetic acid (IAA). The levels of IAA produced by the different strains of B. japonicum, for which the genotype groups have been determined with respect to the degree of base substitution in and around nifDKE, were quantified using gas chromatography/mass spectrometry and a deuterated internal standard. Genotype II strains, which produce rhizobitoxine, excreted more than 20fits of IAA into their culture fluid. However, no IAA was detected in the culture supernatants of genotype I strains, which do not produce rhizobitoxine. This was true even when tryptophan was added to the medium. Moreover, cells of genotypes I and II strains, which were grown under our culture conditions, did not show IAA degradation activity. These results suggest that, in wild-type B. japonicum strains, complete IAA biosynthesis is confined exclusively to genotype II strains that produce rhizobitoxine.

Formation of Chlorophyll-Protein Complexes during Greening. 2. Redistribution of Chlorophyll among Apoproteins

Abstract: The formation of Chl-protein complexes (CPs) in cucumber cotyledons during a dark period after a brief illumination was studied. SDS-PAGE analysis showed that the P700-Chl a-protein complex (CPl) and Chi a-protein complex of the PS II core (CPa) increased, with a concomitant decrease in the light-harvesting Chi a/6-protein complex of PS II (LHCII), during 24-h dark incubation of cotyledons after 6h of continuous illumination. In agreement with these results, curve analysis revealed that spectral components characteristic of CPl and CPa increased while those of Chi b decreased during the dark incubation. Since Chi is not synthesized in the dark, Chi must be released from LHCII and re-incorporated into CPl and CPa. The amounts of apoproteins of CPl and 43 kDa protein (one of the apoproteins of CPa) increased during the dark incubation, and the increase could be inhibited by chloramphenicol (CAP). CPl did not increase in the dark when tissues were incubated with CAP which inhibited the synthesis of apoproteins of CPl, indicating that CP formation by Chi redistribution needs newly synthesized apoproteins. The decrease in LHCII apoproteins during dark incubation was inhibited by CAP probably because Chi was not removed from LHCII by apoproteins of CPl and CPa, whose synthesis was blocked by the presence of CAP. When intermittently-illuminated cotyledons containing a little LHCII were incubated with CaCl 2 in the dark, Chi b and LHCII apoproteins accumulated with the disappearance of 43 kDa protein; Chi of 43 kDa protein may be utilized for LHCII formation. We concluded that Chi molecules once bound with their apoproteins are redistributed among the apoproteins.

Enzymatic degradation of chlorophyll in chenopodium album

Abstract: We describe here the breakdown of Chl in crude extracts of Chenopodium album in complete darkness. The results show that the degradation of Chl was the result of enzymatic reactions and suggest the possible existence of a Mg-releasing enzyme, «Mg-dechelatase». The possibility of the inhibitory accumulation of pheophorbide species is discussed

Effects of the Introduction of Agrobacterium tumefaciens T-DNA ipt Gene in Nicotiana tabacum L. cv. Petit Havana SR1 Plant Cells

Abstract: LIMBURGS UNIV CENTRUM,DEPT SBM,B-3590 DIEPENBEEK,BELGIUM. STATE UNIV GHENT,GENET LAB,B-9000 GHENT,BELGIUM.BEINSBERGER, SEI, UNIV INSTELLING ANTWERP,DEPT BIOL,B-2610 WILRIJK,BELGIUM.

Do Microtubules Control Growth in Tropism? Experiments with Maize Coleoptiles :

Abstract: A recently proposed hypothesis [Nick et al. (1990) Planta 181: 162] suggests that, in maize coleoptiles, tropistic curvature might be caused by a stimulus-induced trans-organ gradient over the orientation of cortical microtubules adjacent to the outer cell wall of the outer epidermis. This gradient, in turn, is controlled by a light-induced redistribution of auxin. The hypothesis was tested by following the behaviour of microtubules for various light stimuli using indirect immunofluorescence in epidermal strips as assay. Analysis of gravitropic straightening, nastic curvature on the horizontal clinostat, effects of .tonic irradiation with red and/or blue light, and experiments involving opposing light pulses demonstrate that bending direction and microtubule orientation gradients are not as closely linked as predicted: Considerable bending can be produced without detectable gradients of microtubule orientation, and conspicuous gradients of microtubule orientation are not necessarily expressed as corresponding curvature. Thus, a monocausal relationship between microtubules and tropism is excluded. Furthermore, a comparison of tonic light effects on microtubules to earlier studies into the impact of light upon auxin content indicate that the relationship between auxin and microtubules might be more complex than hitherto assumed. It is concluded that, at least in maize coleoptiles, growth can be regulated by various mechanisms, and that microtubules, although somehow related to tropism, are probably not the cause of the fast tropistic responses.