Physiological and molecular mechanisms of brassinosteroid-induced tolerance to high and low temperature in plants

Brassinosteroids (BRs) are plant hormones that were isolated for the first time in the 1970s. This group currently includes more than 70 compounds that differ in their structure and physiological activity. BRs are present in plants in a free form or in the form of conjugates. BRs are known as plant growth regulators, but they also play a role in the plant response to environmental stresses. In the case of plants that are exposed to low/high temperature, exogenous BRs can counteract growth inhibition and reduce biomass losses as well as increase plant survival. BRs show a multidirectional activity in regulating the metabolism of plants exposed to extreme temperatures. The following BRs actions can be distinguished: changes in membrane physicochemical properties, regulation of the expression of selected genes (including stress-responsive genes), as well as indirect effects on metabolism through other hormones or signalling molecules (such as hydrogen peroxide). This review summarizes the current knowledge about the effects of BRs on the physiological and biochemical processes that occur in plants during exposure to low or high temperatures.     

The Physiological,Biochemical and Molecular Roles of Brassinosteroids and Salicylic Acid in Plant Processes and Salt Tolerance

Plant hormones regulate plant growth and development by affecting an array of cellular, physiological, and developmental processes, including, but not limited to, cell division and elongation, stomatal regulation, photosynthesis, transpiration, ion uptake and transport, initiation of leaf, flower and fruit development, and senescence. Environmental factors such as salinity, drought, and extreme temperatures may cause a reduction in plant growth and productivity by altering the endogenous levels of plant hormones, sensitivity to plant hormones, and/or signaling pathways. Molecular and physiological studies have determined that plant hormones and abiotic stresses have interactive effects on a number of basic biochemical and physiological processes, leading to reduced plant growth and development. Various strategies have been considered or employed to maximize plant growth and productivity under environmental stresses such as salt-stress. A fundamental approach is to develop salt-tolerant plants through genetic means. Breeding for salt tolerance, however, is a long-term endeavor with its own complexities and inherent difficulties. The success of this approach depends, among others, on the availability of genetic sources of tolerance and reliable screening techniques, identification and successful transfer of genetic components of tolerance to desired genetic backgrounds, and development of elite breeding lines and cultivars with salt tolerance and other desirable agricultural characteristics. Such extensive processes have delayed development of successful salt-tolerant cultivars in most crop species. An alternative and technically simpler approach is to induce salt tolerance through exogenous application of certain plant growth–regulating compounds. This approach has gained significant interest during the past decade, when a wealth of new knowledge has become available on the beneficial roles of the six classes of plant hormones (auxins, gibberellins, cytokinins, abscisic acid, ethylene, and brassinosteroids) as well as several other plant growth–regulating substances (jasmonates, salicylates, polyamines, triacontanol, ascorbic acid, and tocopherols) on plant stress tolerance. Among these, brassinosteroids (BRs) and salicylic acid (SA) have been studied most extensively. Both BRs and SA are ubiquitous in the plant kingdom, affecting plant growth and development in many different ways, and are known to improve plant stress tolerance. In this article, we review and discuss the current knowledge and possible applications of BRs and SA that could be used to mitigate the harmful effects of salt-stress in plants. We also discuss the roles of exogenous applications of BRs and SA in the regulation of various biochemical and physiological processes leading to improved salt tolerance in plants.     

Salicylic acid and photosynthesis: signalling and effects

Salicylic acid (SA) is a well-known signalling molecule playing a role in local and systemic acquired resistance against pathogens as well as in acclimation to certain abiotic stressors. As a stress-related signalling compound, it may directly or indirectly affect various physiological processes, including photosynthesis. The effects of exogenously applied SA on plant physiological processes under optimal environmental conditions are controversial. Several studies suggest that SA may have a positive effect on germination or plant growth in various plant species. However, SA may also act as a stress factor, having a negative influence on various physiological processes. Its mode of action depends greatly on several factors, such as the plant species, the environmental conditions (light, temperature, etc.) and the concentration. Exogenous SA may also alleviate the damaging effects of various stress factors, and this protection may also be manifested as higher photosynthetic capacity. Unfavourable environmental conditions have also been shown to increase the endogenous SA level in plants. Recent results strongly suggest that controlled SA levels are important in plants for optimal photosynthetic performance and for acclimation to changing environmental stimuli. The present review discusses the effects of exogenous and endogenous SA on the photosynthetic processes under optimal and stress conditions.     

Ozone affects gas exchange, growth and reproductive development in Brassica campestris (Wisconsin fast plants)

Exposure to ozone (O(3)) may affect vegetative and reproductive development, although the consequences for yield depend on the effectiveness of the compensatory processes induced. This study examined the impact on reproductive development of exposing Brassica campestris (Wisconsin Fast Plants) to ozone during vegetative growth. Plants were exposed to 70 ppb ozone for 2 d during late vegetative growth or 10 d spanning most of the vegetative phase. Effects on gas exchange, vegetative growth, reproductive development and seed yield were determined. Impacts on gas exchange and foliar injury were related to pre-exposure stomatal conductance. Exposure for 2 d had no effect on growth or reproductive characteristics, whereas 10-d exposure reduced vegetative growth and reproductive site number on the terminal raceme. Mature seed number and weight per pod and per plant were unaffected because seed abortion was reduced. The observation that mature seed yield per plant was unaffected by exposure during the vegetative phase, despite adverse effects on physiological, vegetative and reproductive processes, shows that indeterminate species such as B. campestris possess sufficient compensatory flexibility to avoid reductions in seed production.     

Abnormal leaf formation in soybean: genetic and environmental effects

Soybean is trifoliolate, but 4-, 5-, or 6-foliolate leaves have been reported and expression of such multi-foliolate (MF) leaf forms has been shown to be heritable. Here we analyze the genetic complexity of the MF phenotype and the dependence of its expression on the environment. Recombinant inbred (RI) segregants of soybean were grown in different environments. The frequency of plants expressing the MF phenotype as well as the frequency of nodes exhibiting MF leaves varied with both the environment and the RI segregant genotype. Growth chamber experiments supported field observations suggesting that environment (day length, temperature, etc.) at emergence influenced expression of MF during subsequent growth. Marker facilitated analyses of three RI segregant populations identified quantitative trait loci (QTLs) in 17 regions of the soybean genome. These either directly regulated MF phenotype expression, or were involved in interactions with such loci. Loci, identified in one RI population also were identifiable in another, different, RI population. Most of the loci affected both the frequency of plants expressing MF, and the number of nodes on MF plants that expressed the phenotype. However, a few loci differentiated between these two effects. Many loci affected plants in both field experiments, however, a few differentiated between the two environments. Similar patterns were observed for interactions between loci. QTLs regulating the MF phenotype were located in genome regions that also contained QTLs regulating major agronomic traits—e.g. yield, lodging, etc. This suggests that the loci involved regulate plant growth at some over-arching level, controlling multiple phenotypes or traits.     

Regulation in Plant Stress Tolerance by a Potential Plant Growth Regulator, 5-Aminolevulinic Acid

Exogenous application of different plant growth regulators is a well-recognized strategy to alleviate stress-induced adverse effects on different crop plants by regulating a variety of physiobiochemical processes such as photosynthesis, chlorophyll biosynthesis, nutrient uptake, antioxidant metabolism, and protein synthesis, which are directly or indirectly involved in the mechanism of stress tolerance. Of various environmental factors, salinity, drought, and extreme temperature (low or high) considerably diminish plant growth and yield by modulating endogenous levels as well as signaling pathways of plant hormones. Of various plant hormones/regulators, a potential plant growth regulator, 5-aminolevulinic acid (ALA), is known to be effective in counteracting the injurious effects of various abiotic stresses in plants. Until now the mechanisms behind ALA regulation of growth under stress have not been fully elucidated. It is also not yet clear how far growth and yield in different crops can be promoted by exogenous application of ALA and whether this ALA-induced growth and yield promotion is cost-effective. Thus, in this review we discuss at length the effects of ALA in regulating growth and development in plants under a variety of abiotic stress conditions, including salinity, drought, and temperature stress. Furthermore, advances in the functional and regulatory interactions of this plant growth regulator with plant stress tolerance, as well as the effective mode of exogenous application of ALA in inducing stress tolerance in plants are also comprehensively discussed in this review. In the future, overaccumulation of ALA in plants through manipulation of gene(s) could enhance plant stress tolerance. Thus, genetic manipulation of plants with the goal of attaining increased synthesis/accumulation of ALA and hence improved stress tolerance under stress conditions is an important area for research.     

Physiological traits for crop yield improvement in low N and P environments

Nitrogen and phosphorus are recognized as essential elements in crop production, but the full extent of the requirement for these elements in the physiological processes leading to crop growth seems not to be always fully appreciated. Virtually all the biochemical compounds in plants that support development and growth contain N and/or P. Deficiencies in either element lead to a lost ability for plant growth such that there is a quantitative relationship between crop yield and accumulation by plants of each of these elements. Few options appear to exist to greatly diminish the requirement for either element in crop growth and the formation of seed yield. Consequently, crop yields cannot be increased without increased acquisition of N and P by plants. If the soil environment does not offer these elements, then crop yield will necessarily be restricted. While little opportunity exists to increase N recovery under low nutrient environments, several options can be investigated for increasing P accumulation by the crop. Ultimately, however, the rigid limitation on yields of inadequate N means that without external supplies of N for the cropping system, biological fixation of N must be enhanced to increase N input. In particular, it appears that considerable research needs to be focused on whole-plant processes in legumes that lead to enhanced symbiotic N fixation. A critical aspect of increased legume production will be improved management of P to allow legumes to achieve high N fixation rates and yields.     

Colonization with arbuscular mycorrhizal fungus affects growth,drought tolerance and expression of stress-responsive genes in <Emphasis Type="Italic">Poncirus trifoliata</Emphasis>

The objective of this study was to investigate the effects of arbuscular mycorrhizal fungus (AMF) inoculation on growth and drought tolerance of Poncirus trifoliata seedlings. The seedlings were inoculated with or without Glomus mosseae before exposure to a short-term (3 days) water depletion, and relevant physiological and biochemical parameters (plant height, chlorophyll content, relative water content, activity of antioxidant enzymes) and expression patterns of several stress-responsive genes were examined. Inoculation with G. mosseae led to growth promotion of the seedlings, as revealed by larger plant height and higher relative water and chlorophyll contents. When subjected to drought treatment, the AMF-inoculated (AM) plants showed better tolerance than the nonmycorrhizal (NAM) plants. Under drought, the AM plants exhibited higher level of proline and activity of two antioxidant enzymes, superoxide dismutase (SOD) and peroxidase (POD). In addition, mRNA abundance of four genes involved in reactive oxygen species homeostasis and oxidative stress battling was higher in the AM plants when compared with the NAM plants. These results indicate that AMF inoculation stimulated growth and enhanced drought tolerance of the seedlings, which may be due to activation of an arsenal of physiological, biochemical and molecular alterations.     

The Role of Salicylic Acid Signal in Plant Growth,Development and Abiotic Stress

In nature, plants are constantly affected by adverse conditions. Unlike animals, plants can resist these adverse stresses only by insisting on their original positions. Stress can be divided into biological stress and abiotic stress, abiotic stress directly affects the growth, development and yield of plants, it spans all developmental stages from seed germination to senescence. In order to adapt to changing environment, plants have evolved well-developed mechanisms that help to perceive the stress signals and enable optimal growth response. Salicylic acid (SA) is an important endogenous signal molecule in plants, which not only regulate some plant growth and development processes, but also plays an important part in plant stress resistance. Much work about salicylic acid has been done on the immunity of plants to pathogens, and the synthesis and signal transduction of SA are clearly understood, its function in plant growth, development and abiotic stress is also well learned, we systemically summarized the multiple function of SA signal in non-pathogen-related response, such review should help us understand the common but essential function of SA signal in modulating plant growth, development and abiotic stress.     

植物中的气体信号分子硫化氢：无香而立，其臭如兰

硫化氢（H₂S）一直被认为是一种有毒气体,作为第三种气体信号分子,H₂S在生物体中的生理功能逐渐被揭示。植物中H2S信号研究在不到10年时间已取得了长足进步。植物体内H2S的生成酶比动物细胞丰富,定位于细胞质、线粒体和叶绿体等多个亚细胞部位,表达具有时空性。目前,植物领域H₂S的功能研究主要采用药理学方法。随着研究的深入,遗传学证据不断加强。内源H₂S的研究手段也在不断进步,从亚甲基蓝间接测定,发展到气/液相色谱、荧光探针、活体电极等直接检测手段。植物中H₂S的生理功能研究主要集中在对干旱、重金属等环境非生物胁迫的缓解作用及机理,也有一些植物生长发育调控方面的报道。目前了解到,H₂S可通过与植物激素、其它气体信号分子、活性氧等相互作用以及蛋白质巯基化修饰等方式发挥生理功能。虽然植物气体信号的研究有其特殊性,也遇到很多困难,但是H₂S信号的广泛而特殊的生理功能是一个具有重要科学意义和应用前景的研究领域。     

Effects of in vitro exposure to power frequency magnetic fields on UV-induced DNA damage of rat lymphocytes

The mechanisms of biological effects of 50/60 Hz (power frequency) magnetic fields (MF) are still poorly understood. There are a number of studies indicating that MF affect biochemical processes in which free radicals are involved, such as the biological objects' response to ultraviolet radiation (UVA). Therefore, the present study was aimed to assess the effect of 50 Hz MFs on the oxidative deterioration of DNA in rat lymphocytes irradiated in vitro by UVA. UVA radiation (150 J/m2) was applied for 5 min for all groups and 50 Hz MF (40 microT rms) exposure was applied for some of the groups for 5 or 60 min. The level of DNA damage was assessed using the alkaline comet assay, the fluorescence microscope, and image analysis. It has been found that the 1 h exposure to MF caused an evident increase in all parameters consistent with damaged DNA. This suggest that MF affects the radical pairs generated during the oxidative or enzymatic processes of DNA repair.     

Structural,physiological, and biochemical aspects of salinity tolerance of halophytes

Modern concepts on structural, physiological, and biochemical aspects of salt tolerance of higher plants were considered. Integral physiological processes, such as growth and photosynthesis of glycophytes and halophytes in the context of their ecological plasticity, variety of their adaptive strategies developed in the course of their evolution, and natural selection, were discussed. Analysis of the known anatomical and morphological adaptations of halophytes (succulence, special salt-excreting structures, features associated with special tissues growth, leaf kranz-anatomy and mesostructure) providing their salt tolerance was conducted. The most important physiological and biochemical adaptations of such plants to salinity related to uptake, accumulation and excretion of Na⁺ and Cl^–, peculiarities of membrane composition and the pigment system, and protection against osmotic and oxidative stresses were described. The association of physiological and biochemical peculiarities of halophytes with ecological salt tolerance strategy was discussed.     

Selenium uptake,translocation, assimilation and metabolic fate in plants

The chemical and physical resemblance between selenium (Se) and sulfur (S) establishes that both these elements share common metabolic pathways in plants. The presence of isologous Se and S compounds indicates that these elements compete in biochemical processes that affect uptake, translocation and assimilation throughout plant development. Yet, minor but crucial differences in reactivity and other metabolic interactions infer that some biochemical processes involving Se may be excluded from those relating to S. This review examines the current understanding of physiological and biochemical relationships between S and Se metabolism by highlighting their similarities and differences in relation to uptake, transport and assimilation pathways as observed in Se hyperaccumulator and non-accumulator plant species. The exploitation of genetic resources used in bioengineering strategies of plants is illuminating the function of sulfate transporters and key enzymes of the S assimilatory pathway in relation to Se accumulation and final metabolic fate. These strategies are providing the basic framework by which to resolve questions relating to the essentiality of Se in plants and the mechanisms utilized by Se hyperaccumulators to circumvent toxicity. In addition, such approaches may assist in the future application of genetically engineered Se accumulating plants for environmental renewal and human health objectives.     

The Mechanism of Yield Increasing Bacteria and Plant Ecological Engineering

Yield-Increasing-Bacteria (YIB) increased crop yields by two ways: 1) Ecological effect. The YIB produced the effect for rapid reproduction and resistance to extreme environmental conditions and the function of regulating the microflora on plant surfaces(including rhizosphere and phyllosphere).The improved microflora promoted plant growth and inhibited the plant pathogens and deleterioui rhizobzcteria(DRB.II) physiological effect.YIB produced growth rogulating substances,such as gibberellin and zeatin which increased the growth and yield of crops Based on related research in the past 20 years and current expleration of YIB,the concept of Plant Ecological Engineering was elucidated,i.e.changing the microflora artificially in and on plants so as to promote the exprossion of fine characteristies of plants and the prduction potantial, restraning the activity of plant pathogens and DRB,thus making the crop healthy.     

微生物肥料及其生产应用中的问题

微生物肥料和微生物制剂是新世纪实行绿色农业的重要技术保障,关键是因其中含有大量的有效微生物的生命活动产生特定的肥效或其他生理功能,导致增产,微生物肥料包括根瘤菌肥,解磷菌肥、解钾菌肥、5406菌肥,植物根际促生菌,VA菌根等等,有机肥料堆制剂中含有多种降解农业有机废料的菌种,可缩短堆肥周期,提高养份利用率,由于微生物本身的特殊性,相关市场监督机制不健全,微生物肥料的生产,应用领域存在很多问题,甚至出现明显的伪科学,科研、生产、行政各有关部门应加强基础研究,提高全民科普水平,健全市场监督机制,依靠专家设计严格试验,优选可靠技术,保证良好的经济效益和社会效益。     

Genome instability and epigenetic modification--heritable responses to environmental stress?

As sessile organisms, plants need to continuously adjust their responses to external stimuli to cope with changing growth conditions. Since the seed dispersal range is often rather limited, exposure of progeny to the growth conditions of parents is very probable. The plasticity of plant phenotypes cannot be simply explained by genetic changes such as point mutations, deletions, insertions and gross chromosomal rearrangements. Since many environmental stresses persist for only one or several plant generations, other mechanisms of adaptation must exist. The heritability of reversible epigenetic modifications that regulate gene expression without changing DNA sequence makes them an attractive alternative mechanism. In this review, we discuss recent advances in understanding how changes in genome stability and epigenetically mediated changes in gene expression could contribute to plant adaptation. We provide examples of environmentally induced transgenerational epigenetic effects that include the appearance of new phenotypes in successive generations of stressed plants. We also describe several cases in which exposure to stress leads to nonrandom heritable but reversible changes in stress tolerance in the progeny of stressed plants.     

Molecular approaches for designing heat tolerant wheat

Global warming is causing changes in temperature rapidly for over two decades. The increased temperature during reproductive phase of plant growth has emerged as a serious problem all over the world. Constant or transitory high temperatures may affect the plant growth and development which may lead to diverse morphological, physiological and biochemical changes in plants ultimately decrease in yield. Genetic approaches leading to improved thermo-tolerance can mitigate the reduction in yield. In this backdrop, several indirect traits or parameters have been developed for identification of heat tolerant plants/lines. The traits like stay green/delayed senescence are reported to contribute toward capability of plants to tolerate heat stress. In addition, understanding of biochemical and molecular basis of thermo-tolerance in combination with genetic approaches like identification and mapping of heat tolerant QTLs will not only assist conventional breeders to develop heat tolerant cultivars but also help molecular biologists to clone and characterize genes associated with heat tolerance, which could be used in genetically modified heat tolerant plants. Therefore, overviews of different strategies for developing heat tolerant wheat are discussed in this review.     

Exogenously applied spermidine confers protection against cinnamic acid-mediated oxidative stress in Pisum sativum

This study investigated the stress responses of cinnamic acid (CA) in pea plants and explored the protective role of spermidine (SPD) against CA-induced adverse effects. Pea seedlings exposed to CA had reduced length, biomass, moisture, chlorophyll, sugar, and protein contents and reduced nitrate reductase activity. These parameters increased when SPD was applied alone and in combination with CA. Electrolyte leakage and malondialdehyde content were high in seedlings treated with CA but decreased when the SPD + CA treatment was applied. Foliar exposure to SPD partially mitigated CA-induced stress effects by strengthening the antioxidant defense system, which helped preserve the integrity of biochemical processes. These results indicate that SPD (1 mM) could mitigate the adverse effects of CA and enhance plant defense system. Hence, SPD can be used as a growth regulator for the maintenance of physiological functions in pea plants in response to the pernicious consequences of CA stress.     

Seed pretreatment with magnetic field alters the storage proteins and lipid profiles in harvested soybean seeds

The increase in crop productivity is an urgent need of the time to reduce scarcity of food in underdeveloped countries. Several biological, chemical and physical methods have been applied to promote crop yield. Application of magnetic field (MF) is an emerging physical method used to increase plant growth and yield. The reports on MF pretreatment-induced nutritional changes in harvested seeds are scarce. We previously identified the optimal frequency of MF to improve plant growth and yield as 1500 nT at 10.0 Hz. This study was aimed to investigate the effect of MF treatment on storage proteins and fatty acids in harvested soybean seeds. The results showed that MF triggered globulin production and suppressed prolamin production. However, lipid content in seeds increased, because MF exposure caused an elevation of several fatty acids including caprylic acid, palmitic acid, heptadecanoic acid, linoleic acid, lignoceric acid and eicosapentaenoic acid. This is the first report to reveal the seed pretreated MF on nutritional values of harvested seeds. This study suggests that MF treatment improves seed quality by regulating the metabolism of storage proteins and fatty acids.