Effects of heat stress on growth,photosynthetic pigments,oxidative damage and competitive capacity of three submerged macrophytes

There is an information gap regarding heat stress-induced oxidative damage and the species-specific behavior of plants under stress conditions. The present study was designed with the hypothesis that heat stress may induce species-specific oxidative damage that determines the competitive capacity of common submerged macrophytes. We conducted two laboratory experiments to simulate mono- and mixed cultures of three submerged macrophytes with the application of two heat shock treatments. The results showed that both heat shocks had significant effects on growth, photosynthetic pigments and the ability to induce strong oxidative damage for all three species. The comparative results of mono- and mixed cultures showed that P. crispus had an advantage in both the control and high-temperature treatments over the other two species as a strong competitor in the mixed culture. Further, the competitive capacity of P. crispus increased in the moderately high-temperature condition compared to the control.     

AtHsfA2 modulates expression of stress responsive genes and enhances tolerance to heat and oxidative stress in Arabidopsis

In nature, plants are subject to changes of tempera-ture. Thus, like other organisms, plants have evolved strategies for preventing damage caused by rapid changes in temperature and for repairing what damage is unavoidable. Heat stress responses have been well documented in a wide range of organisms. In all spe-cies studied, the heat shock (HS) response is charac-terized by a rapid production and a transient accumu-lation of specific families of proteins known as heat shock proteins (Hsps) th…     

Overexpression of a chloroplast-localized small heat shock protein OsHSP26 confers enhanced tolerance against oxidative and heat stresses in tall fescue

Small heat shock proteins are involved in stress tolerance. We previously isolated and characterized a rice cDNA clone, Oshsp26, encoding a chloroplast-localized small heat shock protein that is expressed following oxidative or heat stress. In this study, we transferred this gene to tall fescue plants by an Agrobacterium-mediated transformation system. The integration and expression of the transgene was confirmed by PCR, Southern, northern, and immunoblot analyzes. Compared to the control plants, the transgenic plants had significantly lower electrolyte leakage and accumulation of thiobarbituric acid-reactive substances when exposed to heat or methyl viologen. The photochemical efficiency of photosystem II (PSII) (Fv/Fm) in the transgenic tall fescue plants was higher than that in the control plants during heat stress (42°C). These results suggest that the OsHSP26 protein plays an important role in the protection of PSII during heat and oxidative stress in vivo.     

Dynamics of heat-shock induced DNA damage and repair in senescent tobacco plants

Oxidative stress plays an important role in plant ageing and in response to different stresses. Oxidative DNA damage, unless repaired, may have detrimental consequences and increase genetic instability. Therefore, we determined the role of heat-shock induced oxidative stress on induction and repair of DNA damage in relation to oxidative stress tolerance in senescent tobacco plants. One-month-old (young) and three-month-old (senescent) plants were exposed to 42 °C for 2 and 4 h and left to recover at 26 °C for 24 and 72 h. The progression of senescence was characterized by the lower soluble protein and malondialdehyde content compared to young plants. Immediately after the heat shock, an increase in lipid peroxidation and guaiacol peroxidase activity, as well as DNA damage measured by the Comet assay were induced to higher extent in the young plants than in the senescent ones compared to their respective controls. Moreover, after 24-h recovery, the DNA damage further increased in the young plants whereas tendency of DNA repair was observed in the senescent plants. Upon 72-h recovery, no significant differences were noticed in all parameters studied (regardless of plant age) compared to the controls. The random amplified polymorphic DNA (RAPD) analysis confirmed genetic stability of the tobacco plants during the heat-shock exposures as well as the subsequent recovery periods.     

Analysis of oxidative events induced by expanded polyglutamine huntingtin exon 1 that are differentially restored by expression of heat shock proteins or treatment with an antioxidant

We recently reported that the transient expression of polyglutamine tracts of various size in exon 1 of the huntingtin polypeptide (httEx1) generated abnormally high levels of intracellular reactive oxygen species that directly contributed to cell death. Here, we compared the protection generated by heat shock proteins to that provided by the antioxidant agent N-acetyl-L-cysteine. In cells expressing httEx1 with 72 glutamine repeats (httEx1-72Q), the overexpression of Hsp27 or Hsp70 plus Hdj-1(Hsp40) or treatment of the cells with N-acetyl-L-cysteine inhibited not only mitochondrial membrane potential disruption but also the increase in reactive oxygen species, nitric oxide and protein oxidation. However, only heat shock proteins and not N-acetyl-L-cysteine reduced the size of the inclusion bodies formed by httEx1-72Q. In cells expressing httEx1 polypeptide with 103 glutamine repeats (httEx1-103Q), heat shock proteins neither decreased oxidative damage nor reduced the size of the inclusions. In contrast, N-acetyl-L-cysteine still efficiently decreased the oxidative damage induced by httEx1-103Q polypeptide without altering the inclusions. N-Acetyl-L-cysteine was inactive with regard to proteasome inhibition, whereas heat shock proteins partially restored the caspase-like activity of this protease. These observations suggest some relationships between the presence of inclusion bodies and the oxidative damage induced by httEx1-polyQ.     

Overexpression of heat shock protein gene PfHSP21.4 in Arabidopsis thaliana enhances heat tolerance

Nuclear-encoded chloroplast small heat shock proteins (Cp-sHSPs) play important roles in plant stress tolerance due to their abundance and diversity. Their functions in Primula under heat treatment are poorly characterized. Here, expression analysis showed that the Primula Cp-sHSP gene, PfHSP21.4, was highly induced by heat stress in all vegetative and generative tissues in addition to constitutive expression in certain development stages. PfHSP21.4 was introduced into Arabidopsis, and its function was analysed in transgenic plants. Under heat stress, the PfHSP21.4 transgenic plants showed increased heat tolerance as shown by preservation of hypocotyl elongation, membrane integrity, chlorophyll content and photosystem II activity (Fv/Fm), increased seedling survival and increase in proline content. Alleviation of oxidative damage was associated with increased activity of superoxide dismutase and peroxidase. In addition, the induced expression of HSP101, HSP70, ascorbate peroxidase and Δ1-pyrroline-5-carboxylate synthase under heat stress was more pronounced in transgenic plants than in wild-type plants. These results support the positive role of PfHSP21.4 in response to heat stress in plants.     

Role of oxidative stress in Drosophila aging.

We review the role that oxidative damage plays in regulating the lifespan of the fruit fly, Drosophila melanogaster. Results from our laboratory show that the lifespan of Drosophila is inversely correlated to its metabolic rate. The consumption of oxygen by adult insects is related to the rate of damage induced by oxygen radicals, which are purported to be generated as by-products of respiration. Moreover, products of activated oxygen species such as hydrogen peroxide and lipofuscin are higher in animals kept under conditions of increased metabolic rate. In order to understand the in vivo relationship between oxidative damage and the production of the superoxide radical, we generated transgenic strains of Drosophila melanogaster that synthesize excess levels of enzymatically active superoxide dismutase. This was accomplished by P-element transformation of Drosophila melanogaster with the bovine cDNA for CuZn superoxide dismutase, an enzyme that catalyzes the dismutation of the superoxide radical to hydrogen peroxide and water. Adult flies that express the bovine SOD in addition to native Drosophila SOD are more resistant to oxidative stresses and have a slight but significant increase in their mean lifespan. Thus, resistance to oxidative stress and lifespan of Drosophila can be manipulated by molecular genetic intervention. In addition, we have examined the ability of adult flies to respond to various environmental stresses during senescence. Resistance to oxidative stress, such as that induced by heat shock, is drastically reduced in senescent flies. This loss of resistance is correlated with the increase in protein damage generated in old flies by thermal stress and by the insufficient protection from cellular defense systems which includes the heat shock proteins as well as the oxygen radical scavenging enzymes. Collectively, results from our laboratory demonstrate that oxidative damage plays a role in governing the lifespan of Drosophila during normal metabolism and under conditions of environmental stress.     

Lethal and sublethal effect of heat shock on Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

Temperature is an important abiotic environmental factor, and is responsible for various kinds of behavioral and physiological changes in living organisms. Induced heat shock is associated with feeding behaviour, reproduction and reactive oxygen species (ROS) generation that causes oxidative damage. In this experiment, we examined the lethal and sublethal effects of heat shock on reproduction, feeding behaviour and antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and peroxidases (POD) in P. solenopsis. Results showed that males were highly susceptible to heat shock treatments than females, as LTemp₅₀ values were 43.8 °C for males and 45.11 °C for females. Heat shock events non-significantly affected the fecundity in female only treated adults and significantly affected the both sexes heat treated adults, it increased the xylem feeding duration, percentage of xylem feeding adults and reduce the phloem feeding duration and percentage of phloem feeding adults. Similarly it alter the antioxidant enzymes activities, an increase of CAT, SOD and POD activities were noticed in response to highest intensity of heat shock while a reduction of CAT and SOD activity were noticed in response to lowest intensity of heat shock compared to control (30 °C). These results suggest that heat shock may result in loss of body water and induce oxidative stress in P. solenopsis. However, antioxidant enzymes play a significant role in overcoming the oxidative damage.     

Sensitization of U937 cells to heat shock by oxalomalate, a competitive inhibitor of NADP+-dependent isocitrate dehydrogenase

Heat shock may increase oxidative stress due to increased production of reactive oxygen species (ROS) and/or the promotion of cellular oxidation events. Cytosolic NADP

+

-dependent isocitrate dehydrogenase (ICDH) in U937 cells produces NADPH, an essential reducing equivalent for the antioxidant system. The protective role of ICDH against heat shock in U937 cells was investigated in control and cells treated with oxlalomalate, a competitive inhibitor of ICDH. Upon exposure to heat shock, the viability was lower and the protein oxidation, lipid peroxidation and oxidative DNA damage were higher in oxalomalate-treated cells as compared to control cells. We also observed the significant increase in the endogenous production of ROS, as measured by the oxidation of 2'7'-dichlorodihydrofluorescin in U937 cells treated with oxalomalate. These results suggest that ICDH plays an important role as an antioxidant defense enzyme in cellular defense against heat shock through the removal of ROS.     

The Arabidopsis J-protein AtDjB1 facilitates thermotolerance by protecting cells against heat-induced oxidative damage

AtDjB1 belongs to the J-protein family in Arabidopsis thaliana. Its biological functions in plants are largely unknown. In this study, we examined the roles of AtDjB1 in resisting heat and oxidative stresses in A. thaliana using reverse genetic analysis. AtDjB1 knockout plants (atj1-1) were more sensitive to heat stress than wildtype plants, and displayed decreased concentrations of ascorbate (ASC), and increased concentrations of hydrogen peroxide (H(2)O(2)) and oxidative products after heat shock. Application of H(2)O(2) accelerated cell death and decreased seedling viability in atj1-1. Exogenous ASC conferred much greater thermotolerance in atj1-1 than in wildtype plants, suggesting that a lower concentration of ASC in atj1-1 could be responsible for the increased concentration of H(2)O(2) and decreased thermotolerance. Furthermore, AtDjB1 was found to localize to mitochondria, directly interact with a mitochondrial heat-shock protein 70 (mtHSC70-1), and stimulate ATPase activity of mtHSC70-1. AtDjB1 knockout led to the accumulation of cellular ATP and decreased seedling respiration, indicating that AtDjB1 modulated the ASC concentration probably through affecting the function of mitochondria. Taken together, these results suggest that AtDjB1 plays a crucial role in maintaining redox homeostasis, and facilitates thermotolerance by protecting cells against heat-induced oxidative damage.     

Protection against heat stress-induced oxidative damage in Arabidopsis involves calcium, abscisic acid, ethylene, and salicylic acid

Plants, in common with all organisms, have evolved mechanisms to cope with the problems caused by high temperatures. We examined specifically the involvement of calcium, abscisic acid (ABA), ethylene, and salicylic acid (SA) in the protection against heat-induced oxidative damage in Arabidopsis. Heat caused increased thiobarbituric acid reactive substance levels (an indicator of oxidative damage to membranes) and reduced survival. Both effects required light and were reduced in plants that had acquired thermotolerance through a mild heat pretreatment. Calcium channel blockers and calmodulin inhibitors increased these effects of heating and added calcium reversed them, implying that protection against heat-induced oxidative damage in Arabidopsis requires calcium and calmodulin. Similar to calcium, SA, 1-aminocyclopropane-1-carboxylic acid (a precursor to ethylene), and ABA added to plants protected them from heat-induced oxidative damage. In addition, the ethylene-insensitive mutant etr-1, the ABA-insensitive mutant abi-1, and a transgenic line expressing nahG (consequently inhibited in SA production) showed increased susceptibility to heat. These data suggest that protection against heat-induced oxidative damage in Arabidopsis also involves ethylene, ABA, and SA. Real time measurements of cytosolic calcium levels during heating in Arabidopsis detected no increases in response to heat per se, but showed transient elevations in response to recovery from heating. The magnitude of these calcium peaks was greater in thermotolerant plants, implying that these calcium signals might play a role in mediating the effects of acquired thermotolerance. Calcium channel blockers and calmodulin inhibitors added solely during the recovery phase suggest that this role for calcium is in protecting against oxidative damage specifically during/after recovery.     

Oxalomalate, a competitive inhibitor of NADP+-dependent isocitrate dehydrogenase, regulates heat shock-induced apoptosis

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Recently, we demonstrated that the control of cytosolic and mitochondrial redox balance and the cellular defense against oxidative damage is one of the primary functions of NADP(+)-dependent isocitrate dehydrogenase (ICDH) by supplying NADPH for antioxidant systems. The protective role of ICDH against heat shock-induced apoptosis in U937 cells was investigated in the control and the cells pre-treated with oxalomalate, a competitive inhibitor of ICDH. Upon exposure to heat shock, there was a distinct difference between the control cells and the cells pre-treated with 3mM oxalomalate for 3h in regard to apoptotic parameters, cellular redox status, and mitochondrial function. The oxalomalate pre-treated cells showed significant enhancement of apoptotic features such as activation of caspase-3, up-regulation of Bax, and down-regulation of Bcl-2 compared to the control cells upon exposure to heat shock. This study indicates that ICDH may play an important role in regulating the apoptosis induced by heat shock presumably through maintaining the cellular redox status.     

Cellular defense against heat shock-induced oxidative damage by mitochondrial NADP+ -dependent isocitrate dehydrogenase

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Mitochondrial NADP+ -dependent isocitrate dehydrogenase (IDPm) produces NADPH, an essential reducing equivalent for the antioxidant system. The protective role of IDPm against heat shock in HEK293 cells, an embryonic kidney cell line, was investigated in control and cells transfected with the cDNA for IDPm, where IDPm activity was 6-7 fold higher than that in the control cells carrying the vector alone. Upon exposure to heat shock, the viability was lower and the protein oxidation, lipid peroxidation and oxidative DNA damage were higher in control cells as compared to HEK293 cells in which IDPm was over-expressed. We also observed the significant difference in the cellular redox status reflected by the endogenous production of reactive oxygen species, NADPH pool and GSH recycling between two cells. The results suggest that IDPm plays an important role as an antioxidant defense enzyme in cellular defense against heat shock through the removal of reactive oxygen species.     

Proteomic study of β-aminobutyric acid-mediated cadmium stress alleviation in soybean

The present study highlights the protective role of β-aminobutyric acid (BABA) in alleviating cadmium (Cd) stress in soybean. Proteomic analyses revealed that out of 66 differentially abundant protein spots in response to Cd challenge, 17 were common in the leaves of BABA-primed and non-primed plants. Oxygen-evolving enhancer protein 1 and ribulose bisphosphate carboxylase small chain 1 were detected in increase abundance in both groups of leaves. Among the 15 commonly decreased protein spots, the relative intensity levels of heat shock cognate 70-kDa protein, carbonic anhydrase, methionine synthase, and glycine dehydrogenase were partially restored after BABA treatment. Moreover, BABA priming significantly enhanced the abundance of the defense-related protein peroxiredoxin and glycolytic enzymes in response to Cd exposure. Additionally, the impact of Cd on the physiological state of BABA-primed and non-primed plants was analyzed using a biophoton technique. The finding of comparatively low biophoton emission in BABA-primed leaves under Cd stress indicates that these plants experienced less oxidative damage than that of non-primed plants. Proteomic study coupled with biophoton analysis reveals that BABA pretreatment helps the plants to combat Cd stress by modulating plants' defence mechanism as well as activating cellular detoxification system to protect the cells from Cd induced oxidative stress damages.