Saline Tolerance in Hybrids of Lycopersicon Esculentum X Solanum Penellii and Selected Breeeding Lines

162

Cells of Nicotiana tabacum L. var Wisconsin 38 adapted to NaCi (up to 428 millimolar) which have undergone extensive osmotic adjustment accumulated Na' and a-as principal solutes for this adjustment. Although the intracellular concentrations of Na' and a-correlated well with the level of adaptation, these ions apparently did not contribute to the osmotic adjustment which occurred during a culture growth cycle, because the concentrations of Na' and a-did not increase during the period of most active osmotic adjustment. The average intracellular concentrations of soluble sugars and total free amino acids increased as a function of the level of adaptation; however, the levels of these solutes did not approach those observed for Na' and a-. The concentration of proline was positively correlated with cell osmotic potential, accumulating to an average concentration of 129 millimolar in cells adapted to 428 millimolar Naa and representing about 80% of the total free amino acid pool as compared to an average of 0.29 millimolar and about 4% of the pool in unadapted cells. These results indicate that although Na' and aare principal components of osmotic adjustment, organic solutes also may make significant contributions.Osmotic adjustment is a fundamental adaptive response of plant cells which are exposed to salinity (8,11,26) and is necessary for survival and growth under saline conditions. Osmotic adjustment in response to salinity is a result of solute accumulation which occurs through the uptake of solutes, the synthesis of organic compounds, or both. The identification of solutes which accumulate in response to salinity is an initial step toward elucidating the biochemical and physiological mechanisms which are responsible for and regulate osmotic adjustment. Halophytes typically utilize Na+ and Cl-as principal osmotica (8,11,26), although organic solutes apparently serve an important role in balancing the osmotic pressure ofthe cytoplasm with that of the vacuole, into which much of the Na+ and Cl-is thought to be compartmentalized (8,26,28). In response to moderate levels of salinity, many glycophytic plants appear to exclude Na+ and Cl-as a mechanism of tolerance (21), using instead the synthesis and accumulation of organic compounds for osmotic adjustment (1 1, 28). However, the ability of glycophytic plants to accumulate Na+ and Cl-and survive high levels of salinity has not been investigated thoroughly.The in vitro isolation ofcells ofglycophytes with enhanced salt tolerance has helped facilitate the study of cellular responses to salinity ( 1-3, 15, 24). These salt tolerant cells are especially useful

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Solute Accumulation in Tobacco Cells Adapted to NaCl

Binzel¹,

Hasegawa²,

Rhodes³

et al. 1987

162

“…L. pennellii is a genetically compatible distant relative of tomato and is a potential source of improved salt tolerance (1,16,17,21,22,24,25). Comparing closely related L. esculentum x L. pennellii breeding lines, we have found that regulation of foliar sodium, such that the sodium level in salt-treated plants exceeds that of control plants by no more than a 2-to 3-fold increase, is a necessary but not sufficient factor in determining a genotype's salt tolerance (21,22). Approximately 60% of the differences in salt tolerance within this group ofinterspecific breeding lines was accountable to differences in degrees of sodium regulation.…”

Section: Introductionmentioning

confidence: 99%

Inositol and Sugars in Adaptation of Tomato to Salt

Sacher¹,

Staples²

1985

Tomato (Lycopersicon esculentum Mill. cv New Yorker) plants subjected to 100 millimolar NaCl plus Hoagland nutrients exhibited a pattern of wilting, recovery of turgor, and finally recovery of growth at a reduced level, which required 3 days. During the nongrowing, adaptation phase there were immediate increases in free hexoses and sucrose which declined to near control levels as growth resumed. There was a steady increase in myo-inositol content which reached its maximal level at the time of growth resumption. The myo-inositol level then remained elevated for the remainder of the experiment. Myo-inositol constituted two-thirds of the soluble carbohydrate in leaves and three-fourths of the soluble carbohydrate in roots of salt-adapted plants. Plants which were alternated daily between salt and control solutions accumulated less myo-inositol and exhibited less growth than the continuously salt-treated plants. In tolerance, including salt (18, 19). Differences between species, with regard to salt accumulation, are pronounced and associated with salt tolerance (20). Genetic improvements in the salt tolerance of many crop plants are feasible approaches to overcoming the productivity limitations imposed by salinity in irrigated and dryland situations (2, 3).The tomato is a crop of worldwide importance with further untapped potential for genetic improvement (17, 18). L. pennellii is a genetically compatible distant relative of tomato and is a potential source of improved salt tolerance (1,16,17,21,22,24,25). Comparing closely related L. esculentum x L. pennellii breeding lines, we have found that regulation of foliar sodium, such that the sodium level in salt-treated plants exceeds that of control plants by no more than a 2-to 3-fold increase, is a necessary but not sufficient factor in determining a genotype's salt tolerance (21,22). Approximately 60% of the differences in salt tolerance within this group ofinterspecific breeding lines was accountable to differences in degrees of sodium regulation.The regulation of foliar sodium is not by complete exclusion, however, and large increases in sodium and chloride must still be dealt with by each cell. How a cell copes with an elevated external ionic content is an important question. It Osmoregulation in plants has been found to follow principles which are general across a very wide spectrum of life forms (6,26,27). The ionic content of the cytosol is regulated relative to the external medium and relative to the vacuole (5) such that an acceptable ionic concentration range is maintained. Organic solutes are synthesized to offset the steep osmotic gradients which arise as ions are segregated. In animals, higher plants, algae, fungi and lichens, the organic osmoregulant solutes have been found to be either nitrogenous species such as amino acids and betaines or various carbohydrates and polyols. Nitrogenous materials predominate in grasses and certain halophytic dicots while carbohydrates are most common in glycophytes (4,8,26).We report here the occurrence of ...

“…Despite indications of negative correlations between ion accumulation and salt tolerance in glycophytes, such as tomato (22), rice (29), wheat (27), and maize (12), examination of the data reveals that, even in tolerant genotypes, the accumulated levels of Na+ and Clare substantial. In some instances whole cell Na+ and Cl-accumulation was similar for both tolerant and sensitive genotypes (22,27,29). Thus, the ability to compartmentalize Na+ and Clmay be an underlying determinant of the tolerance not only of halophytes but also of many crop species.…”

mentioning

confidence: 99%

Intracellular Compartmentation of Ions in Salt Adapted Tobacco Cells

Binzel¹,

Hess²,

Bressan³

et al. 1988

246

129

Na+ and Cl-are the principal solutes utilized for osmotic adjustment in cells of Nicotiana tabacum L. var Wisconsin 38 (tobacco) adapted to NaCi, accumulating to levels of 472 and 386 millimolar, respectively, in cells adapted to 428 millimolar NaCI. X-ray microanalysis of unetched frozen-hydrated cells adapted to salt indicated that Na+ and Cl-were compartmentalized in the vacuole, at concentrations of 780 and 624 millimolar, respectively, while cytoplasmic concentrations of the ions were maintained at 96 millimolar. The morphometric differences which existed between unadapted and salt adapted cells, (cytoplasmic volume of 22 and 45% of the cell, respectively), facilitated containment of the excited volume of the x-ray signal in the cytoplasm of the adapted cells. Confirmation of ion compartmentation in salt adapted cells was obtained based on kinetic analyses of 22NaI and 36CI-efflux from cells in steady state. These data provide evidence that ion compartmentation is a component of salt adaptation of glycophyte ceUs.A typical response of many plants to saline environments, particularly halophytes, is to accumulate high intracellular concentrations of Na+ and Cl- (9,11,23,26,28). Since the in vitro activities of enzymes isolated from glycophytes or halophytes are inhibited equally by NaCl (9, 11), it has been generally accepted that the accumulated ions are sequestered in the vacuole and 'compatible solutes,' such as sugars, proline, and glycinebetaine, function to balance the osmotic pressure of the cytoplasm (9,11,26). This ability to compartmentalize Na+ and Cl-has been considered to be a mechanism of tolerance of halophytes (26).Although salt tolerance of glycophytes, particularly agronomic species, is usually attributed to the ability to exclude Na+ and Cl-, especially from the shoot (8, 11), intracellular ion compartmentation also may occur in these species. Despite indications of negative correlations between ion accumulation and salt tolerance in glycophytes, such as tomato (22), rice (29), wheat (27), and maize (12), examination of the data reveals that, even in tolerant genotypes, the accumulated levels of Na+ and Clare substantial. In some instances whole cell Na+ and Cl-accumulation was similar for both tolerant and sensitive genotypes (22,27,29). Thus, the ability to compartmentalize Na+ and Clmay be an underlying determinant of the tolerance not only of halophytes but also of many crop species.Verification of ion compartmentation has been restricted by the difficulty in obtaining reliable measurements of subcellular ion concentrations (7,15,23,30). Despite this, cytoplasmic Na + concentration in leaf cells of Suaeda maritima was determined to be 165 mm by efflux analysis when the whole cell concentration was about 600 mM (28). Data obtained by x-ray microanalysis of frozen hydrated leaves of Atriplex spongiosa (23) revealed that cytoplasmic ion concentrations were considerably lower than those in the vacuole.Results from investigations of glycophytes exposed to salinity have been less conc...