Genes and salt tolerance: bringing them together
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Summary Salinity tolerance comes from genes that limit the rate of salt uptake from the soil and the transport of salt throughout the plant, adjust the ionic and osmotic balance of cells in roots and shoots, and regulate leaf development and the onset of senescence. This review lists some candidate genes for salinity tolerance, and draws together hypotheses about the functions of these genes and the specific tissues in which they might operate. Little has been revealed by gene expression studies so far, perhaps because the studies are not tissue‐specific, and because the treatments are often traumatic and unnatural. Suggestions are made to increase the value of molecular studies in identifying genes that are important for salinity tolerance. Contents Summary 645 I. Introduction 645 II. Physiological mechanisms of salt tolerance 646 III. Candidate genes for salt tolerance and results of transformation experiments 650 IV. Gene activity expected in roots, leaves and growing tissues of plants exposed to salinity, and results of gene expression studies 655 V. Conclusions 660 Acknowledgements 660 References 660Keywords:
Senescence
Salinity is one of most significant environmental stresses. Marigold is moderately tolerant to salinity stress. Therefore, in this study, the fresh weights of roots and shoots, rootFW/shootFW ratio, moisture content of shoots, micronutrient and macronutrient concentrations and ratios of K+/Na+ and Ca2+/Na+ in the roots and shoots of marigold were determined under salinity stress. Five salinity treatments (0, 50, 100, 150, and 200 mM NaCl) were maintained. In the current study, salinity affected the biomass of marigold. An increase of more than 100 mM in salt concentrations significantly reduced the shoot fresh weight. Increasing salinity stress increased the ratios of rootFW/shootFW, which were more significant under high salt levels (150 and 200 mM NaCl). Wet basis moisture contents of the shoots were reduced when salinity stress increased above 100 mM. In this study, salinity stress affected micronutrient and macronutrient uptake. Increases in the salt concentration and decreases in the concentration of Cu2+ and Zn2+ in the roots and Mn2+ and Fe2+ in the shoots were significant. Based on an increase in salinity stress, while the Ca2+, Mg2+, and Na+ concentrations increased, the K+ concentration decreased in the roots and shoots. Moreover, the K+/Na+ and Ca2+/Na+ ratios of the roots and shoots were significantly lower than those of the control in all of the salinity treatments. As a result, under increasing salinity stress, the Ca2+, Mg2+, K+, and Na+ uptakes in marigold were significant, revealing the effects of stress.
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The production of soybean (Glycine max L.) has doubled in the last two decades. It is now being grown on both traditional arable lands and on marginal soils, including saline soils, in various parts of the world. Most research on crop tolerance to salinity has been performed using soils with stable levels of salinity. However, there are soils that undergo sudden increases in topsoil salinity for short periods of time. The aim of this study was to compare the effect of stable salinity concentrations with peaks of salinity for their effects on soybean vegetative growth, grain yield, and the accumulation of chlorides. The response of soybean growth was evaluated in pot experiments with the following treatments: Control (non saline soil), soil salinity level of 0.4 S m-1 (0.4S) or 0.8 S m-1 (0.8S), and soil subjected to salinity peaks of 0.4 S m-1 (0.4P) and 0.8 S m-1 (0.8P). The salinity levels were obtained by application of saline irrigation water. Soybean responded differently to stable salinity levels versus peaks of salinity. When salinity was a permanent stress factor, regardless of the salinity level (i.e. 0.4 and 0.8 S m-1), biomass production and differentiation of reproductive organs was greatly affected. For 0.8S treated plants, they never reached the reproductive phase. Conversely, only small differences in growth data were found between 0.4P and Control treatments, although an 80% decrease in yield was associated with the 0.4P treatment. To obtain a reasonable soybean yield, a leaf chloride concentration of 1 mg g-1 of Cl- in dry matter should be considered a maximum threshold.
Topsoil
Saline water
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Shoots of naturally established, foliated red maple ( Acer rubrum L.) and persimmon ( Diospyros virginiana L.) growing in North Carolina were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) formulations following various shoot management procedures. Shoot management prior to treatment consisted of decapitating or not decapitating shoots at 2 inches above the ground line in May when the plants were 3 to 6 ft high. Herbicidal applications were made to uncut shoots and to resprouts of previously cut shoots at 30 and 60 days after decapitation. Responses measured 10, 14, and 22 months after treatment were percent control or original shoots, percent control of new shoots, shoot height, number of live stems/plant. The original shoot and new shoot values were averaged to provide a total shoot control index. Spraying of previously cut shoots at 30 or 60 days after cutting was more effective than spraying of uncut shoots except for 2,4,5-T applied to persimmon. The average total shoot control index for 2,4-D treated red maple, considering all rates, application dates, and evaluation dates was 82% for previously cut shoots and 56% for uncut shoots while the corresponding heights were 0.9 and 4.2 ft, respectively. For 2,4,5-T-treated red maple, the total shoot control indices were 92% and 78% for previously cut and uncut shoots, respectively, while the corresponding heights were 0.4 and 1.4 ft. For persimmon, there was a net advantage for treating previously cut shoots with 2,4-D, but the reverse was true for 2,4,5-T. The results are consistent with the theoretical behavior of 2,4-D and 2,4,5-T in woody plants outlined as a basis for conducting the study. Alternate explanations of results are proposed and practical implications described.
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Under the water temperature that ranges between 28.6 and 29.5℃ and pH 8.2,the growth and survival of Hemifusus tuba juveniles [shells high(19.5±1.23) mm,weight(661.4±48.6) mg] at different salinity were studied.The goal is to find out the range of optimal survival salinity and optimal growth salinity to H.tuba juveniles by two-point method.The results show that the suitable survival salinity and optimal survival salinity are 17.7‰ 40.8‰ and 25.1‰ 35.9‰,and that the growth suitable salinity and growth optimal salinity were 17.5 39.9‰ and 27.8 33.2‰,respectively.In the range of growth optimal salinity,the average daily growth rate of shells and weight were 0.358 0.397 mm.d 1 and 44.64 49.09 mg.d 1,respectively.The survival rate and the average daily growth rate of shells fell obviously when the range of salinity optimal survival salinity was exceeded.Moreover,the tolerance of salinity by H.tuba Juvenile was related to the original environmental salinity.The survival rate was 84.0% in 72h when the juveniles were adapted for 20d in the salinity of 17.0‰ and then transported to the salinity of 14.0‰,and the survival rate was 96.0% when the juveniles were adapted for 20d in the salinity of then transported to the salinity of 45.0‰.However,the survival rates were 8.0% and zero in 72h when the juveniles were transported from the salinity of 30.5‰ to 14.0‰ and 45.0‰,respectively.Both the suitable range and the tolerance of salinity can be increased when the juvenile was domesticated in gradually changing conditions.
Temperature salinity diagrams
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Canopies of heterophyllous trees expand by production of long shoots. We have previously shown in mountain birch ( Betula pubescens ssp. czerepanovii ) that damage to internode leaves within long shoots does not impede shoot growth, indicating that long‐shoot elongation occurs by means of external resources. To study to what extent leaves other than true long‐shoot leaves are necessary for the normal growth of mountain birch long shoots, we simulated herbivore damage to the two basal leaves of shoots (which flush simultaneously with short‐shoot leaves) and the short‐shoot leaves nearest to the long shoot within the branch. Damage to the two basal long‐shoot leaves significantly reduced long‐shoot growth. Additional damage to short‐shoot leaves, situated proximally to the long shoot, did not retard long‐shoot growth any more than damage to basal leaves alone. To determine the extent to which short‐shoot leaves within a large branch are responsible for the pooled long‐shoot production of the branch, we clipped differing proportions of short‐shoot leaves from such branches. We found small but significant reduction in the pooled length of the long shoots of the branch, presumably indicating a limited role in long‐shoot elongation of current photosynthates within the branch. Our experiments indicate that long shoots are not independent modular units in their carbon economy.
Elongation
Betulaceae
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Plant productivity is limited on an estimated one third of the irrigated land in the
world or approximately 4 x 10? ha by soluble salt accumulations in the soil, often
referred to as soil salinity or salinity. As irrigated agriculture expands, more salinity
problems will develop because there are millions of hectares of potentially irrigable
land that could become saline. Every year new salinity problem areas develop and are
identified. Salinity is the most important problem facing irrigated agriculture, and
solving salinity problems is one of the greatest challenges to agricultural scientists.
Much research has been conducted during the past 30 to 40 years to determine the
relative tolerance of crops to salinity. Most of the salinity tolerance data available
through the early 1960s was compiled into useful relationships by Bernstein in 1964,
and these data have been cited and applied throughout the world. Since then, many
new salinity tolerance studies have been conducted, and many new management practices
have been proposed, evaluated, and some of them practiced to reclaim salt-affected
soils for improved crop production. Recently, Maas and Hoffman evaluated
existing salinity tolerance data for agricultural crops and presented the data graphically
so that the relative tolerance among crops could be easily compared.
Dryland salinity
Hectare
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Temperature salinity diagrams
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Abstract This study was undertaken to examine the effects of NaCl and Na 2 SO 4 salinity on the growth of carrot ( Daucus carota L.) and the concentrations of essential and nonessential elements in the shoots and storage roots determined by polarized energy dispersive x‐ray fluorescence (PEDXRF). Both types of salinity reduced plant growth, but growth reduction in NaCl salinity was more pronounced. Na concentrations in shoots and roots were increased by salinity treatment. The concentration of Cl was also increased by NaCl salinity. Salinity treatments decreased K concentrations in the shoots and storage roots, and Ca concentrations in the shoots. Concentration of P in shoots and roots, and S, Mg, and Si in roots were not significantly affected by salinity treatments, while the NaCl salinity reduced S and Si and increased Mg concentrations in the shoots. Fe, Zn, Mn and Mo concentrations in the shoots were not significantly affected by salinity treatments. In the storage roots, the concentration of Fe was significantly increased by NaCl salinity, while Na 2 SO 4 salinity significantly increased Zn and Mn concentrations in storage roots. Concentration of Al in the storage roots was significantly higher with NaCl treatment than with Na 2 SO 4 treatment. Ni concentrations in the shoots were strongly increased by NaCl salinity, while concentrations of Br in the shoots and storage roots were significantly reduced by NaCl salinity. Rb concentrations in shoots and storage roots were significantly reduced by Na 2 SO 4 salinity, but not by NaCl salinity. Concentration of Cs in the shoots was increased by both types of salinity, but Cs concentration of the roots was increased by Na 2 SO 4 . Concentration of Ba in the shoots was lowered by Na 2 SO 4 treatment, while it was increased in the roots by Na 2 SO 4 salinity. Salinity did not affect the Ce concentration in the shoots but increased it in the storage root, and NaCl salinity increased U concentration in the roots of the carrot plants. Copyright © 2008 John Wiley & Sons, Ltd.
Daucus carota
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Senescence
Cellular senescence
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