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

Global warming is predicted to have a general negative effect on plant growth due to the damaging effect of high temperatures on plant development. The increasing threat of climatological extremes including very high temperatures might lead to catastrophic loss of crop productivity and result in wide spread famine. In this review, we assess the impact of global climate change on the agricultural crop production. There is a differential effect of climate change both in terms of geographic location and the crops that will likely show the most extreme reductions in yield as a result of expected extreme fluctuations in temperature and global warming in general. High temperature stress has a wide range of effects on plants in terms of physiology, biochemistry and gene regulation pathways. However, strategies exist to crop improvement for heat stress tolerance. In this review, we present recent advances of research on all these levels of investigation and focus on potential leads that may help to understand more fully the mechanisms that make plants tolerant or susceptible to heat stress. Finally, we review possible procedures and methods which could lead to the generation of new varieties with sustainable yield production, in a world likely to be challenged both by increasing population, higher average temperatures and larger temperature fluctuations.

Plant tolerance to high temperature in a changing environment: scientific fundamentals and production of heat stress-tolerant crops

https://www.cell.com/trends/biochemical-sciences/pdf/S0968-0004(11)00201-5.pdf

How do plants feel the heat

During the course of their ontogenesis plants are continuously exposed to a large variety of abiotic stress factors which can damage tissues and jeopardize the survival of the organism unless properly countered. While animals can simply escape and thus evade stressors, plants as sessile organisms have developed complex strategies to withstand them. When the intensity of a detrimental factor is high, one of the defense programs employed by plants is the induction of programmed cell death (PCD). This is an active, genetically controlled process which is initiated to isolate and remove damaged tissues thereby ensuring the survival of the organism. The mechanism of PCD induction usually includes an increase in the levels of reactive oxygen species (ROS) which are utilized as mediators of the stress signal. Abiotic stress-induced PCD is not only a process of fundamental biological importance, but also of considerable interest to agricultural practice as it has the potential to significantly influence crop yield. Therefore, numerous scientific enterprises have focused on elucidating the mechanisms leading to and controlling PCD in response to adverse conditions in plants. This knowledge may help develop novel strategies to obtain more resilient crop varieties with improved tolerance and enhanced productivity. The aim of the present review is to summarize the recent advances in research on ROS-induced PCD related to abiotic stress and the role of the organelles in the process.

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ROS-mediated abiotic stress-induced programmed cell death in plants.

Due to the present scenario of climate change, plants have to evolve strategies to survive and perform under a plethora of biotic and abiotic stresses, which restrict plant productivity. Maintenance of plant protein functional conformation and preventing non-native proteins from aggregation, which leads to metabolic disruption, are of prime importance. Plant heat shock proteins (HSPs), as chaperones, play a pivotal role in conferring biotic and abiotic stress tolerance. Moreover, HSP also enhances membrane stability and detoxifies the reactive oxygen species (ROS) by positively regulating the antioxidant enzymes system. Additionally, it uses ROS as a signal to molecules to induce HSP production. HSP also enhances plant immunity by the accumulation and stability of pathogenesis-related (PR) proteins under various biotic stresses. Thus, to unravel the entire plant defense system, the role of HSPs are discussed with a special focus on plant response to biotic and abiotic stresses, which will be helpful in the development of stress tolerance in plant crops.

Heat Shock Proteins: Dynamic Biomolecules to Counter Plant Biotic and Abiotic Stresses.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/j.febslet.2010.11.051

Over-expression of mitochondrial heat shock protein 70 suppresses programmed cell death in rice.

Maize is a major economic crop worldwide, with substantial crop loss attributed to flooding. During a stress response, programmed cell death (PCD) can be an effective way for plants better adapt. To identify flooding stress related PCD proteins in maize leaves, proteomic analysis was performed using two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) and mass spectrometry. Comparative proteomics was combined with physiological and biochemical analysis of maize leaves under flooding stress. Fv/Fm, qP, qN and relative water content (RWC) were found to be altered in response to flooding stress, with an increase in H2O2 content noted in vivo. Furthermore, DNA ladder detection indicated that PCD had occurred under flooding treatment. The maize leaf proteome was analyzed via 2D-DIGE gel, with a total of 32 differentially expressed spots isolated, 31 spots were successfully identified via MALDI-TOF/TOF MS which represent 28 proteins. The identified proteins were related to energy metabolism and photosynthesis, PCD, phytohormones and polyamines. To better characterize the role of translationally controlled tumor protein (TCTP) in PCD during a stress response, mRNA expression was examined in different plants by stress-induced PCD. These included heat stress induced rice protoplasts, Tobacco Mosaic Virus infected tobacco leaves and dark induced rice and Arabidopsis thaliana leaves, all of which showed active PCD, and TCTP expression was increased in different degrees. Moreover, S-adenosylmethionine synthase 2 (SAMS2) and S-adenosylmethionine decarboxylase (SAMDC) mRNA expression were also increased, but ACC synthase (ACS) and ACC oxidase (ACO) mRNA expression were not found in maize leaves following flooding. Lastly, ethylene and polyamine concentrations were increased in response to flooding treatment in maize leaves. Following flooding stress, the photosynthetic systems were damaged, resulting in a disruption in energy metabolism, with the noted photosynthetic decline also possibly attributed to ROS production. The observed PCD could be regulated by TCTP with a possible role for H2O2 in TCTP induction under flooding stress. Additionally, increased SAMS2 expression was closely associated with an increased polyamine synthesis during flooding treatment.

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Examination of the leaf proteome during flooding stress and the induction of programmed cell death in maize.

It has been known that the process of leaf senescence is accompanied by programmed cell death (PCD), and the previous study indicated that dark-induced senescence in detached leaves from rice led to the release of cytochrome f (Cyt f) from chloroplast into the cytoplasm. In this study, the effects of Cyt f on PCD were studied both in vitro and in vivo. In a cell-free system, purified Cyt f activated caspase-3-like protease and endonuclease OsNuc37, and induced DNA fragmentation. Furthermore, Cyt f-induced caspase-3-like activity could be inhibited by MG132, which suggests that the activity was attributed to the 26S proteasome. Conditional expression of Cyt f in the cytoplasm could also activate caspase-3-like activity and DNA fragmentation. Fluorescein diacetate staining and annexin V-FITC/PI double staining demonstrated that Cyt f expression in cytoplasm significantly increased the percentage of PCD protoplasts. Yeast two-hybrid screening showed that Cyt f might interact with E3-ubiquitin ligase and RPN9b, the subunits of the ubiquitin proteasome system (UPS), and other PCD-related proteins. Taken together, these results suggest that the released Cyt f from the chloroplast into the cytoplasm might activate or rescue caspase-3-like activity by interacting with the UPS, ultimately leading to the induction of PCD.

/pdf/induction-of-caspase-3-like-activity-in-rice-following-1997ducgzo.pdf

Induction of Caspase-3-like activity in Rice following release of cytochrome-f from the chloroplast and subsequent interaction with the Ubiquitin-Proteasome System

Endoplasmic reticulum (ER) stress activates unfolded protein response (UPR) and autophagy. However, prolonged, severe stresses activate programmed cell death (PCD) in both animal and plant cells. Compared to the well-studied UPR pathway, the molecular mechanisms of ER-stress-induced PCD are less understood. Here, we report the identification of Gas2, the glucosidase II β subunit in the ER, as a potential switch between PCD and autophagy in rice. MS analysis identified Gas2, GRP94, and HSP40 protein in a purified caspase-3-like activity from heat stressed rice cell suspensions. The three corresponding genes were down-regulated under DTT-induced ER stress. Gas2 and GRP94 were localized to the ER, while HSP40 localized to the cytoplasm. Compared to wild-type, a Gas2 RNAi cell line was much sensitive to DTT treatment and had high levels of autophagy. Both caspase-3 and heat-stressed cell suspension lysate could cleave Gas2, producing a 14 kDa N-terminal fragment. Conditional expression of corresponding C-terminal fragment resulted in enhanced caspase-3-like activity in the protoplasts under heat stress. We proposed that mild ER stress causes down-regulation of Gas2 and induces autophagy, while severe stress results in Gas2 cleavage by caspase-3-like activity and the cleavage product amplifies this activity, possibly participating in the initiation of PCD.

/pdf/glucosidase-ii-b-subunit-a-novel-substrate-for-caspase-3-1udbqpet78.pdf

Glucosidase II β-subunit, a novel substrate for caspase-3-like activity in rice, plays as a molecular switch between autophagy and programmed cell death

The application of organic fertilizer has been one of the most important agricultural practices to increase tea plant productivity. However, a single organic fertilizer alone could not match the nutrient requirements of tea plant. According to the nutrient demand of tea plant, tea-specific fertilizer with an appropriate nutrient ratio in combination with organic fertilizer would be an appropriate way. A four-year field experiment was conducted to characterize the sensory quality of green tea subjected to four different fertilization treatments, i.e., tea-specific fertilizer (N-P2O5-K2O: 18-8-12) + urea + colza cake, tea-specific fertilizer + urea + livestock waste compost, and tea-specific fertilizer + urea, combined tea-specific fertilizer (referred to as M1, M2, and M3, respectively); nonfertilizing (CK) served as control. The fertilizer formulated specifically for tea could enhance the taste qualities of green tea, such as water extract, caffeine, tea polyphenol, EGCG, and ECG. However, the effect of this fertilizer on enhancing the aroma level of green tea was weaker than that of the application of tea-specific fertilizer combined with organic fertilizer, whereby this combined fertilization significantly improved the concentration of green tea aroma compounds, such as D-limonene, cis-jasmone, nonanal, linalool, cis-3-hexenyl hexanoate, and cis-3-hexenyl benzoate. This study provides a theoretical basis for judicious fertilization by combining tea-specific fertilizer and organic fertilizer in tea orchards.

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Hongjuan Wang

Papers

Over-expression of mitochondrial heat shock protein 70 suppresses programmed cell death in rice.

Examination of the leaf proteome during flooding stress and the induction of programmed cell death in maize.

Induction of Caspase-3-like activity in Rice following release of cytochrome-f from the chloroplast and subsequent interaction with the Ubiquitin-Proteasome System

Glucosidase II β-subunit, a novel substrate for caspase-3-like activity in rice, plays as a molecular switch between autophagy and programmed cell death

Application of Tea-Specific Fertilizer Combined with Organic Fertilizer Improves Aroma of Green Tea