Relation between Ion Accumulation of Salt-Sensitive and Isolated Stable Salt-Tolerant Cell Lines of Citrus aurantium

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%

Solute Accumulation in Tobacco Cells Adapted to NaCl

Binzel¹,

Hasegawa²,

Rhodes³

et al. 1987

162

“…It has been shown that both stresses cause inhibition ofgrowth ofvarious calli (2)(3)(4)6) and in some cultured plant systems both stresses result in accumulation of proline (10,16,26). Salt-tolerant cells have been isolated from tobacco (8,22,23,26), alfalfa (7), and Citrus (3,4,18,24). Cells PEG-induced water stress have been isolated from tomato (6, 12) and mannitol-adapted carrot cell line was described by Harms and Oertli (11).…”

mentioning

confidence: 99%

“…Thus, in this study, cells of two species of Citrus, isolated for better tolerance to NaCl, were examined for their response to PEG-induced water stress. These two species seem to vary in their mechanism for salt tolerance (3,4) and their performance under water stress may give useful information on the role of osmotic adaptation occurring during selection for NaCl tolerance.…”

mentioning

confidence: 99%

Relationship between Salt Tolerance and Resistance to Polyethylene Glycol-Induced Water Stress in Cultured Citrus Cells

Ben–Hayyim¹

1987

Self Cite

Salt-tolerant selected cells of Shamouti orange (Citrus sixensis) arilSour orange (Citrus aurantiwm) grew considerably better than nonselected cells at any NaCl concentration tested up to 200 millimolar. Also, the growth response of each treatment was identical in the two species. However, the performance of cells ofthe two species under osmotic stress induced by polyethylene glycol (PEG), which is presumably a nonabsorbed osmoticum, was significantly different. The nonselected Shamouti cell lines were significantly more sensitive to osmotic stress than the selected cells. The salt adapted Shamouti cells were apparently also adapted to osmotic stress induced by PEG. In Sour orange, however, the selected lines had no advantage over the nonselected line in response to osmotic stress induced by PEG. This response was also similar quantitatively to the response of the selected salt-tolerant Shamouti cell line. It seems that the tolerance to salt in Shamouti, a partial salt excluder, involves an osmotic adaptation, whereas in Sour orange, a salt accumulator, such an adaptation apparently does not occur. PEG-induced osmotic stress causes an increase in the percent dry weight of salt-sensitive and salt-tolerant cells of both species. No (2)(3)(4)6) and in some cultured plant systems both stresses result in accumulation of proline (10,16,26). Salt-tolerant cells have been isolated from tobacco (8,22,23,26), alfalfa (7), and Citrus (3,4,18,24).

“…Chloride toxicity was implicated in this effect. Na-resistant cell lines of sour orange took up greater amounts of Na than sensitive cells and, although their growth correlated with cellular K+ contents, they remained very sensitive to the K+ concentration in the medium (2). In these cells it may be that the cytoplasm became overloaded with K+ as a result of insufficient vacuolar compartmentation.…”

Section: Kmmentioning

confidence: 91%

Increased Potassium Absorption Confers Resistance to Group IA Cations in Rubidium-Selected Suspension Cells of Brassica napus

Lefebvre

1989

Cell lines of suspension cultures of Brassica napus cv. Jet Neuf were identified for their ability to tolerate 100 millimolar Rb+, a level which was double the normally lethal concentration. Ten spontaneous isolates were obtained from approximately 5 x 10' cells, one of which was reestablished as a cell suspension. This cell line, JL5, was also resistant to the other group IA cationsLi, Na+, K+, and Cs+-and this trait was stable for at least 30 cell generations in the absence of Rb+ selection pressure. The growth characteristics were similar to those of sensitive cells under nonselective conditions. The selected JL5 cells were shown by analysis to have effected more net accumulation of K and Rb+ and less of Na+ than did the unselected cells. JL5 and unselected cells after 14 days of culture in basal medium contained 597.2 and 258.2 micromoles of K per gram dry weight, respectively. Michaelis-Menten kinetic analysis of K+ influx showed that JL5 possessed an elevated phase 1 V,,,e, but there was no alteration in its Km. This is the first time that a plant mutation has been shown to have both increased influx and net absorption of a major essential cation.Salt-tolerant cultures have been isolated from a number of plant species (1-3, 15, 21) including Brassica napus (7). Selections that have employed sodium salts often resulted in the isolates being resistant to water stress where the tolerance mechanism appears to have a broader physiological basis than that involved solely in the membrane transport and cellular compartmentation of Na+. This study was specifically designed to identify cells possessing alterations in K+ absorption. It