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Common bean is widely planted all over the world with a wide variety of ecological conditions. The photosynthesis of bean leaves varies remarkably under different ecological conditions which may be correlated to differing light quality and the light intensity. In order to study the effects of different intensities and qualities of the light on the photosynthesis of plant, bean(Phaseolus vulgaris) leaves were used as the material, and Pulse-Amplitude-Modulation chlorophyll fluorometer was used to record the changes of the chlorophyll fluorescence parameters with different light intensities of red or blue, primary leaves were offered to the treatments in the present work. The results showed that the maximum photochemical efficiency of light adaptation(Fv'/Fm', the efficiency of capture excitation energy in PSⅡ reaction center) decreased with the increase of light intensities of red or blue light, but the values of Fv'/Fm' under blue light were significantly (P<0.05) or very significantly (P<0.01)higher than those under the same intensities of red light. With the increase of light intensities of blue light, the actual photochemical efficiency of PS Ⅱ (Y(Ⅱ), the actual photochemical efficiency of PS Ⅱ under light)and the coefficient of photochemical fluorescence quenching (qP and qL, the proportion of reduction state of PS Ⅱ original electron acceptor-plastoquinone (QA) increased but became stable gradually, while the values of Y(Ⅱ), qP and qL decreased with the increase of red light intensities. These meant that the photosynthetic efficiency of bean leaves decreased with the increase of blue or red light intensities. Non-photochemical quenching coefficient(NPQ, the excess energy dissipation by PS Ⅱ antenna system), electronic transmission rate (ETR, ETR increases linearly with light intensity, until it reaches a maximum. This happens when the capacity of all electron sink is reached), and quantum yield of regulated energy dissipation [Y(NPQ), an important indicator of self protection and the ability of PS Ⅱ to deal with excess light energy] increased with the increase of blue light or red light intensity. Compared to under red light, the values of ETR under blue light were higher but the values of NPQ and Y(NPQ) were lower. Quantum yield of non-regulated energy dissipation [Y(NO), the proportion of excess light energy in the form of heat and fluorescence, one of the important indicators of light damage] increased with the increase of red light intensity but decreased with the increase of blue light intensity. These results showed that the photosynthetic efficiency of bean leaves decreased with the increase of light intensities, but the absorbing and utilizing efficiencies of blue light were higher than those of red lights. We believe that this work would be helpful in developing current understanding on the responses of plants to different light intensities and qualities. [ABSTRACT FROM AUTHOR]

Extracellular adenosine 5′-triphosphate (ATP) is a well-known signalling molecule in plants and plays important roles during plant stress response. In the present work, the treatment of tobacco cell suspension culture with exogenous hydrogen peroxide (H2O2) caused the decreases of respiratory O2 uptake, intracellular ATP production, extracellular ATP level, and reduction of cell viability. Combining this observation with the finding that the oxidative phosphorylation uncoupler or the respiratory inhibitor not only decreased intracellular ATP production but also decreased the extracellular ATP level and cell viability, it is suggested that the decrease of extracellular ATP level and cell viability under H2O2 stress could be a result of the suppressed production of intracellular ATP. Treatment with ATP-degrading enzyme, apyrase, also caused the decreases of cell viability, respiratory O2 uptake, and intracellular ATP production. More importantly, addition of exogenous ATP alleviated the H2O2-induced decreases of cell viability, respiratory O2 uptake, and production of intracellular ATP. These results indicate that extracellular ATP could be an important effector in regulating the cell viability, respiratory O2 uptake, and intracellular ATP production of tobacco cell suspension culture under H2O2 stress. [ABSTRACT FROM AUTHOR]

Wounding increased the extracellular Adenosine 5ʹ-triphosphate (eATP) level of kidney bean leaves. Treatment with wounding or exogenous ATP increased the hydrogen peroxide (H2O2) content, activities of catalase and polyphenol oxidase, and malondialdehyde content in both the treated and systemic leaves. Pre-treatment with ATP-degrading enzyme, apyrase, to the wounded leaves reduced the wound-induced local and systemic increases in H2O2 content, activities of catalase and polyphenol oxidase, and malondialdehyde content. Application of dimethylthiourea (DMTU) and diphenylene iodonium (DPI) to the wounded and ATP-treated leaves, respectively, reduced the wound- and ATP-induced local and systemic increases in H2O2 content, activities of catalase and polyphenol oxidase, and malondialdehyde content. Moreover, the wound- and ATP-induced systemic increases of these physiological parameters were suppressed when DMTU or DPI applied to leaf petiole of the wounded and ATP-treated leaves. These results suggest that eATP at wounded sites could mediate the wound-induced local and systemic responses by H2O2-dependent signal transduction. [ABSTRACT FROM AUTHOR]

In the present work, by using tobacco cell suspension and wheat seedlings, we studied that eATP (extracellular ATP) released by copper (Cu) stress could act as diffusible signal in alleviating the Cu stress-induced cell death. A semipermeable membrane was fixed in the middle of a plastic box to divide the box into two equal compartments (A and B, respectively). This semipermeable membrane can prevent direct cell-to-cell (or seedling-to-seedling) contact and the diffusion of the macromolecules [such as ATPase (adenosine 5′-triphosphatase)] between these two compartments. The cell suspension directly stressed with CuCl2 was placed in compartment A and was incubated with the untreated cell suspension in compartment B. Such treatment significantly increased the levels of cell death and eATP content of the cell suspension in these two compartments. In contrast, addition of ATPase into the cell suspension directly stressed with CuCl2 decreased the eATP level in these two compartments but further increased the level of cell death in compartment B, compared to no addition of ATPase. Similar results were obtained when tobacco cell suspension was replaced by wheat seedlings. These observations indicate that when Cu stress from compartment A induced the plant cell death in compartment B, ATP transferred from compartment A could play a role in alleviating this cell death. Thus, it is suggested that eATP released by copper stress could act as diffusible signal in alleviating the Cu stress-induced cell death. [ABSTRACT FROM AUTHOR]

Although excess excitation energy (EEE) can damage the photosynthetic apparatus and deregulate many cellular processes, some studies have reported that EEE can be used by plants to optimize the resistance to pathogen infection. Here, we investigated whether the EEE-induced resistance to pathogen infection might be mediated by mitochondrial alternative oxidase (AOX). The present work showed that exposure of Arabidopsis (Arabidopsis thaliana) leaves to short-term excess light or treatment of Arabidopsis leaves with the electron transport inhibitor, DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone), restricted the growth of virulent biotrophic bacteria, Pseudomonas syringae pv tomato (Pst) DC3000. Exposure to short-term excess light or DBMIB treatment also enhanced the level of the capacity of the cyanide-resistant respiration of the infected leaves. The lack of AOX1a gene in the AtAOX1a anti-sense line attenuated the excess light- or DBMIB-induced resistance toward Pst DC3000. These results indicate that AOX may play a role in regulating the EEE-induced resistance to virulent pathogen infection. [ABSTRACT FROM AUTHOR]

Hypertonic salt stress with different concentrations of NaCl increased the levels of extracellular ATP of Arabidopsis leaves. And, hypertonic salt stress decreased the levels of Fv/Fm (the maximal efficiency of photosystem II), ΦPSII (the photosystem II operating efficiency), qP (photochemical quenching), and intracellular ATP (iATP) production. The treatment with β,γ-methyleneadenosine 5′-triphosphate (AMP-PCP), which can exclude extracellular ATP from its binding sites of extracellular ATP receptors, caused a further decrease in the levels of Fv/Fm, ΦPSII,qP, and iATP production of the salt-stressed Arabidopsis leaves, while the addition of exogenous ATP rescued the inhibitory effects of AMP-PCP on ΦPSII, qP, and iATP production under hypertonic salt stress. Under hypertonic salt stress, the values of Fv/Fm, ΦPSII, qP, and iATP production were lower in the dorn 1–3 mutant than in the wild-type plants. These results indicate that the responses of photosystem II and intracellular ATP production to salt stress could be affected by extracellular ATP. [ABSTRACT FROM AUTHOR]