Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants

Stressful environments such as salinity, drought, and high temperature (heat) cause alterations in a wide range of physiological, biochemical, and molecular processes in plants. Photosynthesis, the most fundamental and intricate physiological process in all green plants, is also severely affected in all its phases by such stresses. Since the mechanism of photosynthesis involves various components, including photosynthetic pigments and photosystems, the electron transport system, and CO2 reduction pathways, any damage at any level caused by a stress may reduce the overall photosynthetic capacity of a green plant. Details of the stress-induced damage and adverse effects on different types of pigments, photosystems, components of electron transport system, alterations in the activities of enzymes involved in the mechanism of photosynthesis, and changes in various gas exchange characteristics, particularly of agricultural plants, are considered in this review. In addition, we discussed also progress made during the last two decades in producing transgenic lines of different C3 crops with enhanced photosynthetic performance, which was reached by either the overexpression of C3 enzymes or transcription factors or the incorporation of genes encoding C4 enzymes into C3 plants. We also discussed critically a current, worldwide effort to identify signaling components, such as transcription factors and protein kinases, particularly mitogen-activated protein kinases (MAPKs) involved in stress adaptation in agricultural plants.

Photosynthesis under stressful environments: An overview

High temperature (HT) stress is a major environmental stress that limits plant growth, metabolism, and productivity worldwide Plant growth and development involve numerous biochemical reactions that are sensitive to temperature Plant responses to HT vary with the degree and duration of HT and the plant type HT is now a major concern for crop production and approaches for sustaining high yields of crop plants under HT stress are important agricultural goals Plants possess a number of adaptive, avoidance, or acclimation mechanisms to cope with HT situations In addition, major tolerance mechanisms that employ ion transporters, proteins, osmoprotectants, antioxidants, and other factors involved in signaling cascades and transcriptional control are activated to offset stress-induced biochemical and physiological alterations Plant survival under HT stress depends on the ability to perceive the HT stimulus, generate and transmit the signal, and initiate appropriate physiological and biochemical changes HT-induced gene expression and metabolite synthesis also substantially improve tolerance The physiological and biochemical responses to heat stress are active research areas, and the molecular approaches are being adopted for developing HT tolerance in plants This article reviews the recent findings on responses, adaptation, and tolerance to HT at the cellular, organellar, and whole plant levels and describes various approaches being taken to enhance thermotolerance in plants

Physiological, biochemical, and molecular mechanisms of heat stress tolerance in plants

Contents
 	'Summary'	32	
I.	'Introduction'	32	
II.	'Effects of stress combination on growth, yield and physiological traits in plants and crops'	34	
III.	'The complexity of stress response signaling during stress combination'	38	
IV.	'Conclusions'	39	
 	'Acknowledgements'	41	
 	References	41	


Summary
Environmental stress conditions such as drought, heat, salinity, cold, or pathogen infection can have a devastating impact on plant growth and yield under field conditions. Nevertheless, the effects of these stresses on plants are typically being studied under controlled growth conditions in the laboratory. The field environment is very different from the controlled conditions used in laboratory studies, and often involves the simultaneous exposure of plants to more than one abiotic and/or biotic stress condition, such as a combination of drought and heat, drought and cold, salinity and heat, or any of the major abiotic stresses combined with pathogen infection. Recent studies have revealed that the response of plants to combinations of two or more stress conditions is unique and cannot be directly extrapolated from the response of plants to each of the different stresses applied individually. Moreover, the simultaneous occurrence of different stresses results in a high degree of complexity in plant responses, as the responses to the combined stresses are largely controlled by different, and sometimes opposing, signaling pathways that may interact and inhibit each other. In this review, we will provide an update on recent studies focusing on the response of plants to a combination of different stresses. In particular, we will address how different stress responses are integrated and how they impact plant growth and physiological traits.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.12797

Abiotic and biotic stress combinations

Photoinhibition of photosystem II under environmental stress.

Genetically engineered tobacco (Nicotiana tabacum L.) with the ability to accumulate glycinebetaine was established. The wild type and transgenic plants were exposed to heat treatment (25-50 degrees C) for 4 h in the dark and under growth light intensity (300 mumol m(-2) s(-1)). The analyses of oxygen-evolving activity and chlorophyll fluorescence demonstrated that photosystem II (PSII) in transgenic plants showed higher thermotolerance than in wild type plants in particular when heat stress was performed in the light, suggesting that the accumulation of glycinebetaine leads to increased tolerance to heat-enhanced photoinhibition. This increased tolerance was associated with an improvement on thermostability of the oxygen-evolving complex and the reaction center of PSII. The enhanced tolerance was caused by acceleration of the repair of PSII from heat-enhanced photoinhibition. Under heat stress, there was a significant accumulation of H(2)O(2), O (2) (-) and catalytic Fe in wild type plants but this accumulation was much less in transgenic plants. Heat stress significantly decreased the activities of catalase, ascorbate peroxidase, glutathione reductase, dehydroascorbate reductase, and monodehydroascorbate reductase in wild type plants whereas the activities of these enzymes either decreased much less or maintained or even increased in transgenic plants. In addition, heat stress increased the activity of superoxide dismutase in wild type plants but this increase was much greater in transgenic plants. Furthermore, transgenic plants also showed higher content of ascorbate and reduced glutathione than that of wild type plants under heat stress. The results suggest that the increased thermotolerance induced by accumulation of glycinebetaine in vivo was associated with the enhancement of the repair of PSII from heat-enhanced photo inhibition, which might be due to less accumulation of reactive oxygen species in transgenic plants.

Genetic engineering of the biosynthesis of glycinebetaine enhances thermotolerance of photosystem II in tobacco plants

Genetically engineered tobacco (Nicotiana tabacum L.) with the ability to synthesis glycinebetaine (GB) in chloroplasts was established by introducing the BADH gene for betaine aldehyde dehydrogenase from spinach (Spinacia oleracea L.). The genetic engineering resulted in enhanced tolerance of growth of young seedlings to salt stress. This increased tolerance was not due to improved water status, since there were no significant differences in accumulation of sodium and chloride, leaf water potential, and relative water content between wild type and transgenic plants under salt stress. Salt stress resulted in a decrease in CO2 assimilation and such a decrease was much greater in wild type plants than in transgenic plants. Though salt stress showed no damage to PSII, there were a decrease in the maximal PSII electron transport rate in vivo and an increase in non-photochemical quenching (NPQ) and these changes were greater in wild type plants than in transgenic plants. In addition, salt stress inhibited the activities of ribulose 1,5-bisphosphate carboxylase/oxygenase, chloroplastic fructose-1,6-bisphosphatase, fructose-1,6-bisphosphate aldolase, and phosphoribulokinase and such a decrease was also greater in wild type plants than in transgenic plants, suggesting that GB protects these enzymes against salt stress. However, there were no significant changes in the activities of phosphoglycerate kinase, triose phosphate isomerase, ribulose-5-phosphate isomerase, transketolase, and sedoheptulose-1,7-bisphosphatase in both wild type and transgenic plants. The results in this study suggest that enhanced tolerance of CO2 assimilation to salt stress may be one of physiological bases for increased tolerance of growth of transgenic plants to salt stress.

http://chglib.icp.ac.ru/subjex/2011/pdf/Plant%20Molecular%20Biology/Plant%20Molecular%20Biology.2008,%20V.66,%20N%201-2,p.73-86.pdf

Genetic engineering of the biosynthesis of glycinebetaine leads to increased tolerance of photosynthesis to salt stress in transgenic tobacco plants

Compared with small heat shock proteins (sHSPs) in other organisms, those in plants are the most abundant and diverse. However, the molecular mechanisms by which sHSPs are involved in cell protection remain unknown. Here, we characterized the role of HSP21, a plastid nucleoid-localized sHSP, in chloroplast development under heat stress. We show that an Arabidopsis thaliana knockout mutant of HSP21 had an ivory phenotype under heat stress. Quantitative real-time RT-PCR, run-on transcription, RNA gel blot, and polysome association analyses demonstrated that HSP21 is involved in plastid-encoded RNA polymerase (PEP)–dependent transcription. We found that the plastid nucleoid protein pTAC5 was an HSP21 target. pTAC5 has a C4-type zinc finger similar to that of Escherichia coli DnaJ and zinc-dependent disulfide isomerase activity. Reduction of pTAC5 expression by RNA interference led to similar phenotypic effects as observed in hsp21. HSP21 and pTAC5 formed a complex that was associated mainly with the PEP complex. HSP21 and pTAC5 were associated with the PEP complex not only during transcription initiation, but also during elongation and termination. Our results suggest that HSP21 and pTAC5 are required for chloroplast development under heat stress by maintaining PEP function.

/pdf/chloroplast-small-heat-shock-protein-hsp21-interacts-with-26hfuglikj.pdf

Chloroplast Small Heat Shock Protein HSP21 Interacts with Plastid Nucleoid Protein pTAC5 and Is Essential for Chloroplast Development in Arabidopsis under Heat Stress

Whole spinach (Spinacia oleracea) plants were subjected to heat stress (25°C–50°C) in the dark for 30 min. At temperatures higher than 35°C, CO2 assimilation rate decreased significantly. The maximal efficiency of photosystem II (PSII) photochemistry remained unchanged until 45°C and decreased only slightly at 50°C. Nonphotochemical quenching increased significantly either in the absence or presence of dithiothreitol. There was an appearance of the characteristic band at around 698 nm in 77 K fluorescence emission spectra of leaves. Native green gel of thylakoid membranes isolated immediately from heat-stressed leaves showed that many pigment-protein complexes remained aggregated in the stacking gel. The analyses of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting demonstrated that the aggregates were composed of the main light-harvesting complex of PSII (LHCIIb). To characterize the aggregates, isolated PSII core complexes were incubated at 25°C to 50°C in the dark for 10 min. At temperatures over 35°C, many pigment-protein complexes remained aggregated in the stacking gel of native green gel, and immunoblotting analyses showed that the aggregates were composed of LHCIIb. In addition, isolated LHCII was also incubated at 25°C to 50°C in the dark for 10 min. LHCII remained aggregated in the stacking gel of native green gel at temperatures over 35°C. Massive aggregation of LHCII was clearly observed by using microscope images, which was accompanied by a significant increase in fluorescence quenching. There was a linear relationship between the formation of LHCII aggregates and nonphotochemical quenching in vivo. The results in this study suggest that LHCII aggregates may represent a protective mechanism to dissipate excess excitation energy in heat-stressed plants.

Heat Stress Induces an Aggregation of the Light-Harvesting Complex of Photosystem II in Spinach Plants

http://sourcedb.ib.cas.cn/cn/ibthesis/201112/P020111205345116981052.pdf

Xiaogang Wen

Papers

Genetic engineering of the biosynthesis of glycinebetaine enhances thermotolerance of photosystem II in tobacco plants

Genetic engineering of the biosynthesis of glycinebetaine leads to increased tolerance of photosynthesis to salt stress in transgenic tobacco plants

Chloroplast Small Heat Shock Protein HSP21 Interacts with Plastid Nucleoid Protein pTAC5 and Is Essential for Chloroplast Development in Arabidopsis under Heat Stress

Heat Stress Induces an Aggregation of the Light-Harvesting Complex of Photosystem II in Spinach Plants

The combined effect of salt stress and heat shock on proteome profiling in Suaeda salsa.