Effect Of Photosynthetic Inhibitors Research Articles

Effect of Photosynthetic Inhibitors on Induction of Tryptamine Pathway‐mediated Resistance in Lesion Mimic Mutant of Rice Infected with Magnaporthe grisea

AbstractRice cv. Sekiguchi‐asahi was identified as a lesion mimic mutant from cv. Asahi. This mutant showed light‐enhanced resistance to Magnaporthe grisea infection, inducing Sekiguchi lesion (sl) formation and tryptamine accumulation. To elucidate the role of chloroplasts on the activation of tryptamine pathway, the effect of some photosynthetic inhibitors on light‐dependant Sekiguchi lesion formation, tryptamine accumulation, and enzyme activities was investigated. When detached leaf blades which had been pretreated with Linuron, 1, 10‐Phenanthroline or Poly‐l‐lysine were inoculated with M. grisea, respectively, Sekiguchi lesion formation and typtamine accumulation were suppressed even under light, suppressing gene expression of tryptophan decarboxylase and monoamine oxidase activity. On the other hand, catalase activity was significantly inhibited in control leaves infected with M. grisea under light, but kept at high level in chemical‐pretreated leaves. These results suggested that photosynthetic activity in chloroplasts was involved in inhibition of antioxidant sysytem and activation of tryptamine pathway responsible for light‐enhanced resistance in sl mutant to M. grisea infection.

Fluorescence lifetime imaging microscopy of Chlamydomonas reinhardtii: non‐photochemical quenching mutants and the effect of photosynthetic inhibitors on the slow chlorophyll fluorescence transient

Fluorescence lifetime-resolved images of chlorophyll fluorescence were acquired at the maximum P-level and during the slower transient (up to 250 s, including P-S-M-T) in the green photosynthetic alga Chlamydomonas reinhardtii. At the P-level, wild type and the violaxanthin-accumulating mutant npq1 show similar fluorescence intensity and fluorescence lifetime-resolved images. The zeaxanthin-accumulating mutant npq2 displays reduced fluorescence intensity at the P-level (about 25-35% less) and corresponding lifetime-resolved frequency domain phase and modulation values compared to wild type/npq1. A two-component analysis of possible lifetime compositions shows that the reduction of the fluorescence intensity can be interpreted as an increase in the fraction of a short lifetime component. This supports the important photoprotection function of zeaxanthin in photosynthetic samples, and is consistent with the notion of a 'dimmer switch'. Similar, but quantitatively different, behaviour was observed in the intensity and fluorescence lifetime-resolved imaging measurements for cells that were treated with the electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, the efficient PSI electron acceptor methyl viologen and the protonophore nigericin and. Lower fluorescence intensities and lifetimes were observed for all npq2 mutant samples at the P-level and during the slow fluorescence transient, compared to wild type and the npq1 mutant. The fluorescence lifetime-resolved measurements during the slow fluorescence changes after the P level up to 250 s for the wild type and the two mutants, in the presence and absence of the above inhibitors, were analyzed with a graphical procedure (polar plots) to determine lifetime compositions. At higher illumination intensity, wild type and npq1 cells show a rise in fluorescence intensity and corresponding rise in the species concentration of the slow lifetime component after the initial decrease following the P level. This reversal is absent in the npq2 mutant, and for all samples in the presence of the inhibitors. Lifetime heterogeneities were observed in experiments averaged over multiple cells as well as within single cells, and these were followed over time. Cells in the resting state (induced by several hours of darkness), instead of the normal swimming state, show shortened lifetimes. The above results are discussed in terms of a superposition of effects on electron transfer and protonation rates, on the so-called 'State Transitions', and on non-photochemical quenching. Our data indicate two major populations of chlorophyll a molecules, defined by two 'lifetime pools' centred on slower and faster fluorescence lifetimes.

Distribution of Charasomes in Chara: Banding Pattern and Effect of Photosynthetic Inhibitors

Charasomes are structured elaborations of plasmalemma of some Charophytes which may be involved in enhanced transport of ions or inorganic carbon across the plasmalemma. They show a highly non-uniform distribution. We report here a novel method of quantifying charasome population density, using scanning electron microscopy of cell fragments removed from the cell wall. Consistent differences in density can occur in neighbouring regions of the membrane. The distribution of densities is not normal, but is skewed toward lower densities, with large areas of membrane showing no charasomes. Contrary to previous published reports, we found no correlation with acid and alkaline banding patterns. Inhibition of photosynthesis by either dark or DCMU (dichlorophenyl dimethyl urea, an inhibitor of photosystem II) results in a complete loss of charasomes in 1-3 weeks.

Photoorientation in the freshwater dinoflagellate,Peridinium gatunense Nygaard

The photoorientation of Peridinium gatunense, which causes massive algal blooms each year in Lake Kinneret (Israel), is characterized using a microcomputer-controlled video immage system. The cells show positive phototaxis under a wide light irradiance range from 1 lx up to about 18 klx, i.e., to about fifth of the natural solar radiation measured on the water surface. Above 20 klx diaphototactic movement of the cells is observed. The action spectrum of photoorientation based on fluence rate-response curves shows little activity below 520 nm and a peak of 640 nm. No obvious effect of photosynthetic inhibitors (DCMU and DBMIB) was found on phototaxis, although motility of the cells is drastically affected in the presence of high concentrations of these inhibitors. The results suggest that the photsynthetic mechanism is not involved in photoperception of phototactically active radiation. The ecological significance of photoorientation of the cells is discussed in this paper.

Effect of Photosynthetic Inhibitors and Uncouplers of Oxidative Phosphorylation on Nitrate and Nitrite Reduction in Barley Leaves

The effects of several photosynthetic inhibitors and uncouplers of oxidative phosphorylation on NO(3) (-) and NO(2) (-) assimilation were studied using detached barley (Hordeum vulgare L. cv Numar) leaves in which only endogenous NO(3) (-) or NO(2) (-) were available for reduction. Uncouplers of oxidative phosphorylation greatly increased NO(3) (-) reduction in both light and darkness, while photosynthetic inhibitors did not.The NO(2) (-) concentration in the control leaves was very low in both light and darkness; 98% or more of the NO(2) (-) formed from NO(3) (-) was further assimilated in control leaves. More NO(2) (-) accumulated in the leaves in light and darkness in the presence of photosynthetic inhibitors. Of this NO(2) (-), 94% or more was further assimilated. It appears that metabolites, either external or internal to the chloroplast, capable of reducing NADP (which, in turn, could reduce ferredoxin via NADP reductase) might support NO(2) (-) reduction in darkness and light when photosynthetic electron flow is inhibited by photosynthetic inhibitors.NITRITE ASSIMILATION WAS MUCH MORE SENSITIVE TO UNCOUPLERS IN DARKNESS THAN IN LIGHT: in darkness, 74% or more of NO(2) (-) formed from NO(3) (-) was further assimilated, whereas in light, 95% or more of the NO(2) (-) was further assimilated.

Effects of photosynthetic inhibitors and light-dark regimes on the replication of cyanophage SM-2

The effects of photosynthetic inhibitors and light-dark regimes on the replication of cyanophage SM-2 in its host cyanobacteria (Synechococcus elongatus UTEX 563 and Microcystis aeruginosa NRC-1, Synechococcus NRC-1 UTEX 1937) have been investigated. Photoassimilation of CO2 by infected cells was enhanced and remained elevated until late in the infection cycle. Photosynthetic inhibitors and the removal of light suppressed viral replication. SM-2, like other cyanophage of unicellular cyanobacteria, is highly dependent on host photosynthetic metabolism for the energy required in replication.

Effect of Light on Lesion Development in Cucumber Downy Mildew

The present paper deals with experiments on the effect of light on lesion development in cucumber downy mildew, caused by Pseudoperonospora cubensis (Berk. et Curt.) Rostow.1. Infected cucumber leaves kept in darkness for 5 to 8 days after inoculation showed a marked decrease in lesion development. Dark treatment for 2 days befor inoculation, however, gave no effect to lesion development.2. As the period of darkness during which infected leaves were kept after inoculation was prolonged, the lesion development was proportionately checked. Especially, the lesion development was remarkably suppressed when kept in darkness for 3 or more days after inoculation.3. Lesion development was affected by the light intensity of from 0 to 0.35cal/cm2/min, provided by mercury lamps, when exposed after inoculation. Lesion area decreased with the decrease of light intensity. The rate of decrease was more conspicuous in the light intensity range below the light compensation point of cucumber leaf, 0.05cal/cm2/min.4. Effect of photosynthetic inhibitors on lesion development was examined. Solutions of photosynthetic inhibitors linuron (3-(3, 4-dichlorophenyl)-1-methoxy-1-methylurea) and simazine (2-chloro-4, 6-bisethylamino-1, 3, 5-triazine) were sprayed onto the upper surface of infected leaves 2 days after inoculation, or of healthy leaves.By the application of linuron, conspicuous decrease in lesion area in infected leaf and also conspicuous reduction of photosynthesis in healthy leaf were observed. As the concentration of linuron was increased from 10 to 50ppm, the inhibition of lesion development and of photosynthesis increased, the inhibition being more pronounced at 30ppm and above. Linuron showed no effect on conidial germination at the concentration of 30ppm. Simazine inhibited neither lesion development in infected leaf nor photosynthesis in healthy leaf.From these results it was concluded that the lesion development in cucumber downy mildew is closely dependent on the photosynthesis of the host plant.