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High temperatures seriously limit plant growth and productivity. Investigating heat-responsive molecular mechanisms is important for breeding heat-tolerant crops. In this study, heat-responsive mechanisms in leaves from a heat-sensitive spinach ( Spinacia oleracea L.) variety Sp73 were investigated using two-dimensional gel electrophoresis (2DE)-based and isobaric tags for relative and absolute quantification (iTRAQ)-based proteomics approaches. In total, 257 heat-responsive proteins were identified in the spinach leaves. The abundance patterns of these proteins indicated that the photosynthesis process was inhibited, reactive oxygen species (ROS) scavenging pathways were initiated, and protein synthesis and turnover, carbohydrate and amino acid metabolism were promoted in the spinach Sp73 in response to high temperature. By comparing this with our previous results in the heat-tolerant spinach variety Sp75, we found that heat inhibited photosynthesis, as well as heat-enhanced ROS scavenging, stress defense pathways, carbohydrate and energy metabolism, and protein folding and turnover constituting a conservative strategy for spinach in response to heat stress. However, the heat-decreased biosynthesis of chlorophyll and carotenoid as well as soluble sugar content in the variety Sp73 was quite different from that in the variety Sp75, leading to a lower capability for photosynthetic adaptation and osmotic homeostasis in Sp73 under heat stress. Moreover, the heat-reduced activities of SOD and other heat-activated antioxidant enzymes in the heat-sensitive variety Sp73 were also different from the heat-tolerant variety Sp75, implying that the ROS scavenging strategy is critical for heat tolerance.

Aims: Soil alkalization imposes severe ion toxicity, osmotic stress, and high pH stress to plants, inhibiting their growth and productivity. NaHCO3 is a main component of alkaline soil. However, knowledge of the NaHCO3-responsive proteomic pattern of alkaligrass is still lacking. Alkaligrass (Puccinellia tenuiflora) is a monocotyledonous halophyte pasture widely distributed in the Songnen Plain in Northeastern China. This study aims to investigate the NaHCO3-responsive molecular mechanisms in the alkaligrass plants. Methods: An integrative approach including photosynthetic and redox physiology, and comparative proteomics was used. Results: NaHCO3 decreased photosynthesis, but increased nonphotochemical quenching, increased membrane electrolyte leakage of alkaligrass, and increased proline and glycine betaine concentrations in leaves. In addition, the NaHCO3 stress increased Na+ concentration and decreased K+/Na+ ratio in leaves, while Ca2+ and Mg2+ concentrations were maintained, contributing to signaling and homeostasis of ion and enzyme activity. Furthermore, O2− generation rate and H2O2 concentration were increased, and the activities of ten antioxidant enzymes and antioxidant concentrations were changed in response to the NaHCO3 stress. Proteomics revealed 90 NaHCO3-responsive proteins, 54% of which were localized in chloroplasts. They were mainly involved in signaling, photosynthesis, stress and defense, carbohydrate and energy metabolism, as well as protein synthesis, processing and turnover. Some protein abundances did not correlate well with their activities, implying that the enzyme activities were affected by NaHCO3-induced post-translational modifications. Conclusions: To cope with the NaHCO3 stress, alkaligrass deployed multiple strategies, including triggering phospholipase D (PLD)-mediated Ca2+ signaling pathways, enhancing diverse reactive oxygen species (ROS) scavenging pathways, and regulating chloroplast protein synthesis and processing. [ABSTRACT FROM AUTHOR]

Main conclusion: Hydrogen peroxide-responsive pathways in roots of alkaligrass analyzed by proteomic studies and PutGLP enhance the plant tolerance to saline-, alkali- and cadmium-induced oxidative stresses.Oxidative stress adaptation is critical for plants in response to various stress environments. The halophyte alkaligrass (Puccinellia tenuiflora) is an outstanding pasture with strong tolerance to salt and alkali stresses. In this study, iTRAQ- and 2DE-based proteomics approaches, as well as qRT-PCR and molecular genetics, were employed to investigate H2O2-responsive mechanisms in alkaligrass roots. The evaluation of membrane integrity and reactive oxygen species (ROS)-scavenging systems, as well as abundance patterns of H2O2-responsive proteins/genes indicated that Ca2+-mediated kinase signaling pathways, ROS homeostasis, osmotic modulation, and transcriptional regulation were pivotal for oxidative adaptation in alkaligrass roots. Overexpressing a P. tenuiflora germin-like protein (PutGLP) gene in Arabidopsis seedlings revealed that the apoplastic PutGLP with activities of oxalate oxidase and superoxide dismutase was predominantly expressed in roots and played important roles in ROS scavenging in response to salinity-, alkali-, and CdCl2-induced oxidative stresses. The results provide insights into the fine-tuned redox-responsive networks in halophyte roots. [ABSTRACT FROM AUTHOR]

Elevated temperatures limit plant growth and reproduction and pose a growing threat to agriculture. Plant heat stress response is highly conserved and fine-tuned in multiple pathways. Spinach (Spinacia oleracea L.) is a cold tolerant but heat sensitive green leafy vegetable. In this study, heat adaptation mechanisms in a spinach sibling inbred heat-tolerant line Sp75 were investigated using physiological, proteomic, and phosphoproteomic approaches. The abundance patterns of 911 heat stress-responsive proteins, and phosphorylation level changes of 45 phosphoproteins indicated heat-induced calcium-mediated signaling, ROS homeostasis, endomembrane trafficking, and cross-membrane transport pathways, as well as more than 15 transcription regulation factors. Although photosynthesis was inhibited, diverse primary and secondary metabolic pathways were employed for defense against heat stress, such as glycolysis, pentose phosphate pathway, amino acid metabolism, fatty acid metabolism, nucleotide metabolism, vitamin metabolism, and isoprenoid biosynthesis. These data constitute a heat stress-responsive metabolic atlas in spinach, which will springboard further investigations into the sophisticated molecular mechanisms of plant heat adaptation and inform spinach molecular breeding initiatives. [ABSTRACT FROM AUTHOR]

Significance: Plant chloroplasts generate reactive oxygen species (ROS) during photosynthesis, especially under stresses. The sulfhydryl groups of protein cysteine residues are susceptible to redox modifications, which regulate protein structure and function, and thus different signaling and metabolic processes. The ROS-governed protein thiol redox switches play important roles in chloroplasts. Recent Advances: Various high-throughput thiol redox proteomic approaches have been developed, and they have enabled the improved understanding of redox regulatory mechanisms in chloroplasts. For example, the thioredoxin-modulated antioxidant enzymes help to maintain cellular ROS homeostasis. The light- and dark-dependent redox regulation of photosynthetic electron transport, the Calvin/Benson cycle, and starch biosynthesis ensures metabolic coordination and efficient energy utilization. In addition, redox cascades link the light with the dynamic changes of metabolites in nitrate and sulfur assimilation, shikimate pathway, and biosynthesis of fatty acid hormone as well as purine, pyrimidine, and thiamine. Importantly, redox regulation of tetrapyrrole and chlorophyll biosynthesis is critical to balance the photodynamic tetrapyrrole intermediates and prevent oxidative damage. Moreover, redox regulation of diverse elongation factors, chaperones, and kinases plays an important role in the modulation of gene expression, protein conformation, and posttranslational modification that contribute to photosystem II (PSII) repair, state transition, and signaling in chloroplasts. Critical Issues: This review focuses on recent advances in plant thiol redox proteomics and redox protein networks toward understanding plant chloroplast signaling, metabolism, and stress responses. Future Directions: Using redox proteomics integrated with biochemical and molecular genetic approaches, detailed studies of cysteine residues, their redox states, cross talk with other modifications, and the functional implications will yield a holistic understanding of chloroplast stress responses. [ABSTRACT FROM AUTHOR]