Among the abiotic stresses high temperature stress is one of the most detrimental stresses threatening higher plant productivity and survival throughout the world. Each degree Celsius increase of average growing season temperature may decrease crop yield and affect plant distribution. On the other hand, global average temperatures are supposed to increase from 1.8 to 4.0 °C or higher by 2100 as compared to the 1980-2000 average. Plants are intimidated by adverse effects of high temperature stresses. Protein denaturation, inactivation of enzymes, production of reactive oxygen species, and disruption of membrane structure are some of the primary damage effects of high temperature that are also responsible for damage of ultrastructural cellular components. These anomalies hamper plant growth and development. Although higher plants develop their own defense strategies to overcome the high temperature stress effects, these often are not enough, therefore substantial damage is observed. The metabolism in plants is altered in response to high temperature stress. The antioxidants, secondary metabolites, hormones, osmoprotectants, and many other essential biomolecules are modulated, which help to defend against high temperature impacts. Moreover, numerous studies have proved that as protectants the exogenously applied hormones, osmoregulators, antioxidants, signaling molecules, polyamines, and trace elements confer high temperature stress tolerance in the organisms. This chapter presents the responses of plants to high temperature stress and evaluates the role of exogenous protectants under high temperature stress.
Salt stress is one of the most devastating abiotic stress which severely affects the agricultural productivity in various ways. A study was undertaken to investigate the tolerance and mitigation of salt stress in tomato by exogenous application of calcium (Ca 2+ ). The experimental results showed that salt stress significantly affects morphology, physiology and fruit weight of tomato. Plant height, leaf number and branch number/plant were decreased with increased levels of salinity mostly at 6 and 8 dS mG 1 . Salinity also adversely affected the shoot dry weight, leaf area, leaf chlorophyll content and also fruit weight/plant mostly at 8 dS mG 1 . Exogenous application of Ca 2+ significantly mitigates the adverse effects of salinity on plant biomass production or morphology, physiology and fruit production. The plant height, leaf number/plant, branch number/plant, dry weight of shoot/plant, leaf chlorophyll content, fruit weight/plant were increased with the application of calcium in saline condition compared to without calcium. The fruit weight of tomato is gradually decreased with the increased levels of salinity. In case of treatment combinations, the reduction rate of fruit weight of tomato was decreased with increased levels of Ca
Modulation of ion uptake in tomato (
INTRODUCTIONSalinity is one among the several environmental stresses causing drastic changes in the growth, physiology and metabolism of plants and threatening the cultivation of plants around the globe . Much salinity resulted from NaCl cause osmotic pressure of external solution become more than osmotic pressure of plant cells which is required for regulating osmotic pressure to prevent dehydration of plant cells. Uptake and transformation of nutrient ions such as potassium (k + ) and calcium (Ca 2+ ), or surplus of sodium (Na + ) can cause problems. high Na + and Clrates can cause direct toxic effects on enzymatic and membranous systems (Nazarbeygi et al., 2011). high salinity in soil disturbs intracellular ion homeostasis, leads to cell membrane damage, disrupts the metabolic activity, and thus finally causes growth inhibition and even plant death (Rains and Epstein, 1967). These phenomena were observed in agricultural and horticultural crops, including tomato (Lycopersicon esculentum L.) (Juan et al., 2005), which is considered as moderately sensitive or moderately tolerant to salinity depending on cultivar or growth stage (Santa-Cruz et al., 2002;Fernandez-Garcia et al., 2004;Estan et al., 2005).Once sodium enters the cytoplasm, it inhibits enzyme activity. This inhibition is also dependent on how much k + is present: a high Na + /k + ratio can cause a lot of damage. Ca 2+ is an important factor in the "battle" between Na + and k + ions. An increased Ca 2+ supply has a protective effect on plants under the Na stress. Calcium sustains k + transport and k + /Na + selectivity in Na-challenged plants. This beneficial effect of Ca is mediated by an intracellular signaling pathway that regulates the expression and activity of k + and Na + transporters. Calcium may also directly suppress sodium import mediated by nonselective cation channels (Davenport and Tester, 2000;Demidchik and Tester, 2002;Tester and Davenport, 2003;Zhu, 2003;Jouyban, 2012).Calcium is a crucial regulator of growth and development in plants. It is reported that Ca 2+ can alleviate the negative effects of salinity on root elongation
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