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Photosynthesis under drought and salt stress…

Salinity Stress and Salt Tolerance | InTechOpen

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04/01/2018 · Figure 4

Molecular mechanism of salt tolerance revealed in the model plants will facilitate identification of candidate genes and development of transgenic plants with salt tolerance in crops. Overexpression of genes encoding enzymes related to abiotic stresses enhanced crop salt tolerance. Transgenic spp. plants expressing a choline oxidase () gene from showed a significantly higher net photosynthetic rate and a higher photosynthetic rate under high salinity conditions than wild-type plants (). proved that plays a crucial role in salt stress tolerance during the vegetative stage of and that transgenic plants overexpressing have enhanced tolerance to salt stress. Glutathione (GSH) plays an important role in cell function and metabolism as an antioxidant. developed transgenic plants by introducing the γ ( ) gene from () into rice. Overexpression of confers plants with significantly enhanced tolerance to salinity by sustaining a cellular GSH redox state to avoid attacks from reactive oxygen species produced by salt. Furthermore, the transgenic rice plants also exhibited a 15–18% increase in grain yield under general paddy field conditions.

Signalling pathways responsible for Na+ extrusion in Arabidopsis under salt stress

Although QTL mapping and MAS in crops has great potential for developing varieties with high yield and quality, very few drought- or salt-tolerant cultivars and lines have been developed, which is mainly due to the quantitative nature of stress tolerance, difficulty of transferring stress-tolerant traits from interspecific and intergeneric sources and the linkage drag between desirable and undesirable genes. Moreover, plants tend to be exposed to multiple stresses (i.e., drought and salinity), which makes the breeding of stress-tolerant lines more difficult using conversional strategies. Fortunately, the transgenic approach promises a substantial improvement in desired traits. Understanding the molecular mechanisms of drought and salt tolerance may lead to a generalized master mechanism for stress tolerance. This will be possible because there were many common features between the two stresses. For example, there is cross-talk between drought and salt stress, since both stresses will finally result in dehydration of the cell and osmotic imbalance. Engineered genes encoding organic osmolytes, plant growth regulators, antioxidants, late embryo-genesis abundant proteins, and transcription factors have been introduced into transgenic lines which performed well under controlled stress conditions (). In the future, it is desirable to use multiple tolerance mechanisms of drought and salt stresses to achieve high levels of tolerance for commercial exploitation in crops. There already exists an example for this target. The cis-acting dehydration response element (DRE) plays an important role in regulating gene expression in response to these stresses. showed that overexpression of cDNA encoding DREB1A (DRE binding protein) in transgenic plants activated the expression of many stress-tolerant genes and resulted in improved tolerance to drought, salt and freezing. Under field conditions, plants are often subjected to multiple stresses. Transgenic approaches should be integrated with conventional breeding and molecular breeding as well as more recent innovative strategies. It is also imperative to note that most drought- and salt-tolerant transgenic lines have been developed using a single gene transformation, which may not be as productive as using transformation of many genes. Thus, it is considered to be a more logical approach to enhance crop stress tolerance by transferring a number of target genes.


Glycinebetaine improves salt tolerance in vinal (Prosopis ruscifolia Griesbach) seedlings

Recently, studies of salt tolerance in plants have covered genetic mapping to molecular characterization of salt-induced genes. Increasing the understanding of biochemical pathways and mechanisms that participate in plant stress responses has made it possible to genetically improve the salinity performance of new varieties through various routes. Currently, transgenic plants have been used to test the effect of overexpression of specific plant genes that are known to be up-regulated by salt stress (). Great progress of salt tolerance has been made in major crops, such as rice, wheat and tomatoes. A number of QTLs have been mapped () and some important genes have been cloned (, , , , , , ). However, studies on QTLs or genes controlling salt tolerance in oil crops are still very limited. To date, the breeding practice of salt tolerance in crops has been largely unsuccessful, although some salt-tolerant cultivars of have been developed in India, e.g., ‘CS56’. Researchers and breeders endeavor to understand the mechanisms of salt tolerance and screen for stable salt-tolerant genotypes to use in breeding programs. Attempts have also been made to develop salt-tolerant transgenic crops with candidate genes with proven roles in ion homeostasis and osmolytes accumulation ().

Although studies on the molecular mechanism of stress tolerance in crops have not advanced much, there is an advantage to studies in that information obtained on , which belongs to the family Brassicaceae, may be directly applied to the breeding of crops. In this review, we first highlight the recent achievements in physiological mechanisms and genetic improvement for drought stress in crops. Second, a new understanding of salt tolerance in these crops is presented. Third, the challenges and perspectives of breeding drought- and/or salt-tolerant crop varieties are also discussed.

Biotechnology for the Development of Drought Tolerant Crops

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Cotton is important fiber-yielding crop plant grown worldwide. Abiotic stresses such as drought, salinity, heat, mineral deficiency, hot climate have adverse effects on the plant growth and its total fiber yield (fiber quality and its length). One of the fundamental properties of a plant to survive under stressed environment is its adaptive mechanisms where a gene must be inducible in response toa stress (Bray 1997).To understand drought induced regulatory mechanism in cotton, in our previous work we identified several stress related genes induced by water deficit condition (Ranjan et al. 2012a; Trivedi et al. 2012). One such gene is cyclophilin, also known as peptidyl-prolyl isomerases (PPIaes: EC peptidyl-prolyl isomeraseshasability to catalyze the inter-conversion of cis and trans isomers of proline. The physiological function of cyclophilinPPIase has been described as a chaperone or foldase(Gothel and Marahiel 1999), which helps in the folding of some proteins by rearrangements of disulfide bonds by isomerization of peptide bonds by PPIases(Galat and Metcalfe 1995). PPIases are present in a wide range of organisms, (Chou and Gasser 1997) and in organelles such as mitochondria (Anderson et al. 1993) and chloroplasts (Fulgosi et al. 1998). When plants are exposed to various environmental stresses, the heat-shock protein genesor chaperonsof different families are induced(Cui et al. 2017; Lee et al. 2016). Chaperons prevent protein aggregation, misfolding and also helps in proteolytic degradation of proteins (Hayes and Dice 1996; Mainali et al. 2014). Cyclophilins are also known to have role in diverse signaling pathways, including mitochondrial apoptosis (Leung and Halestrap 2008), RNA splicing (Teigelkamp et al. 1998) and adaptive immunity (Anderson et al. 1993). Furthermore, cyclophilin expression gets induced by both biotic and abiotic stresses including HgCl2,salicylic acid and salt stress, (Lee et al. 2015; Marivet et al. 1995; Marivet et al. 1994) heat, cold shock (Scholze et al. 1999), light (Chou and Gasser 1997) and drought stress (Sharma and Singh 2003). The cyclophilins proteins are involved in various functions viz, cell signaling, protein biogenesis and trafficking, cell cycle control, abiotic and biotic responses and regulation of membrane receptors, channels and pores (Schiene-Fischer and Yu 2001).

Obviously, there are some common features between drought and salinity stresses in plants. Both stresses impose cellular dehydration, which causes osmotic stress and removal of water from the cytoplasm into the intercellular space. Early responses to drought and salt stress are also similar to each other, except for the ionic component in the cells of plants under salt stress. Thus, it seems that a salinity-tolerant species could also be drought-tolerant, and has largely identical mechanisms to deal with these stresses (, ). In the recent decade, great progresses have been made in the understanding of genetic control of drought and salt tolerance in major crops, such as maize (), rice () and the model plant (), which can certainly shed some light on the mechanisms underlining drought and salt tolerance in crops and also directly contribute to agronomic-trait improvement (, ). Since the 1980s, with the aid of newly developed genetic experimental tools (, ), a number of physiological and genetic studies on drought and salt tolerance have been reported.

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XIX International Botanical Congress

The tolerant varieties maintained lower Na concentrations besides maintaining K concentrations under high salt concentration. On the other hand, the sensitive rice varieties were unable to effectively prevent accumulation of Na as well as the depletion of K. The success of the tolerant varieties in gaining higher fresh and dry weights at all the stages widens the differences in their Na concentrations still further by dilution. Tolerant genotypes like CSR 1 showed regulation over distribution and accumulation of Na taken up by the plants i.e. the delicate and vital organs like young and photosynthetically active leaves as well as the reproductive organs like panicles are kept relatively free of Na, beside having an assured supply of K even under higher salt concentration.

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Beneficial roles of melatonin on redox regulation of photosynthetic electron transport and synthesis of D1 protein in tomato seedlings under salt stress.

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