chlorophyll-a and 2-phenyl-4-4-5-5-tetramethylimidazoline-1-oxyl-3-oxide

NO-mediated alternative pathway plays an important role in protecting wheat seedlings against drought stress through dissipating excessive reducing equivalents generated by photosynthesis. Alternative pathway (AP) has been proven to be involved in responses to various stresses. However, the mechanisms of AP in defense response to drought stress are still lacking. The aims of this work are to investigate the role of AP in drought tolerance and how AP is induced under drought stress using two wheat cultivars with different drought tolerance. Our results showed that Longchun22 cultivar is more tolerant to drought than 98SN146 cultivar. Seedlings exposed to drought led to a significant increase in AP, and it increased more in Longchun22. Furthermore, chlorophyll fluorescence parameters (Fv/Fm, ΦPSII, qP) decreased significantly in drought-treated seedlings, especially in 98SN146, indicating that photoinhibition occurred under drought stress. Pretreatment with SHAM, the malate-oxaloacetate shuttle activity and photosynthetic efficiency were further inhibited in drought-treated seedlings, resulting in more serious oxidative damage as indicated by higher levels of malondialdehyde and hydrogen peroxide. Moreover, NO modulated AP under drought stress by increasing AOX1a expression and pyruvate content. Taken together, these results indicate that NO-mediated AP is involved in optimizing photosynthesis under drought stress by avoiding the over-reduction of photosynthetic electron transport chain, thus reducing reactive oxygen species production and oxidative damage in wheat leaves.

Topics: Adaptation, Physiological; Cell Respiration; Chlorophyll; Cyclic N-Oxides; Droughts; Fluorescence; Gene Expression Regulation, Plant; Hydrogen Peroxide; Imidazoles; Malondialdehyde; Nitric Oxide; Nitroprusside; Photosynthesis; Plant Leaves; Signal Transduction; Stress, Physiological; Triticum; Water

When seedlings are grown in the dark, proplastids of the developing leaf differentiate into etioplasts. Greening of etiolated plastids is stimulated by light, which is sensed by various types of photoreceptors. Nitric oxide (NO) has been shown to be a bioactive molecule that could take part in this light-mediated process in plants. In this paper, we show that emission of NO in barley seedlings increased concomitantly with increasing activities of nitric oxide synthase (NOS) during the greening. Treatment with sodium nitroprusside (SNP), a NO donor, increased the accumulation of chlorophyll contents, enhanced the accumulation of thylakoid membrane proteins, such as light harvesting complex of photosystem II (LHCII) and PSIA/B, and then improved the effective quantum yield of photosystem II (PSII) (Phi(PSII)) in the light. Instead, treatment with either NO scavenger 2-phenyl-4,4,5,5-tetramentylimidazoline-1-oxyl-3-xide (PTIO) or NOS inhibitor N(omega)-nitro-l-arginine (l-NNA) retarded the greening of etiolated-seedlings. Moreover, sodium ferrocyanide, an analog of SNP, nitrite and nitrate, two NO-decomposition products did not have any effect on the greening process. These results indicated that NO, as an endogenous signaling molecule, participates in light-mediated greening of barley seedlings, and exogenous NO accelerates this process.

Topics: Blotting, Western; Chlorophyll; Cyclic N-Oxides; Electron Transport; Ferrocyanides; Hordeum; Imidazoles; Light; Light-Harvesting Protein Complexes; Membrane Proteins; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Nitroprusside; Photosynthesis; Photosystem I Protein Complex; Plant Proteins; Plastids; Seedlings; Signal Transduction; Thylakoids

A concentration-dependent toxicity of hydrogen peroxide (H(2)O(2)) was observed on growth yield, chlorophyll a content and chlorophyll fluorescence characteristics of the green microalga Scenedesmus obliquus under laboratory batch culture conditions. The addition of sodium nitroprusside, a nitric oxide (NO) donor, in combination with H(2)O(2) prevented chlorophyll losses, and the inhibition level of growth yield, maximum quantum yield of photosystem II (PSII) and the light-adapted quantum yield of PSII were significantly reduced. The antioxidant compounds, penicillamine and thiourea also reduced the damage caused by H(2)O(2) exposure. The protective actions of sodium nitroprusside were, however, arrested in cultures where sodium nitroprusside was supplemented in combination with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), a specific scavenger of NO. The NO(3)(-)-grown Scenedesmus depicted less sensitivity to H(2)O(2) toxicity with respect to the quantum yields of PSII as compared to its NH(4)(1)-grown counterpart. The role of NO in providing protection against H(2)O(2) toxicity to the processes under study was discussed.

Topics: Animals; Antioxidants; Chlorophyll; Chlorophyll A; Chlorophyta; Cyclic N-Oxides; Free Radical Scavengers; Hydrogen Peroxide; Imidazoles; Light-Harvesting Protein Complexes; Nitric Oxide; Nitric Oxide Donors; Nitroprusside; Penicillamine; Photosynthetic Reaction Center Complex Proteins; Photosystem II Protein Complex; Thiourea