Characterization of Growth, Water Relations, and Proline Accumulation in Sodium Sulfate Tolerant Callus of Brassica napus L. cv Westar (Canola)

Treatment with spermidine protects chrysanthemum seedlings against salinity stress damage

Salinity-stressed plants of salinity sensitive ('Qx096') and tolerant ('Qx097') chrysanthemum cultivar were treated with a range of concentrations of spermidine (Spd). Plant performance, as indicated by various parameters associated with growth, was improved by the treatment, as was the tissue content of soluble protein and proline. The extent of both Na(+) accumulation and K(+) loss was reduced. Activity levels of the stress-related enzymes SOD, POD, APX and CAT were significantly increased and the production of malondialdehyde (MDA) decreased. The suggestion was that treatment with 1.5 mM Spd would be an effective means alleviating salinity-stress induced injury through its positive effect on photosynthetic efficiency, reactive oxygen species scavenging ability and the control of ionic balance and osmotic potential. Its protective capacity was more apparent in 'Qx096' than in 'Qx097'.

Prediction of the maximum temperature for life based on the stability of metabolites to decomposition in water

The components of life must survive in a cell long enough to perform their function in that cell. Because the rate of attack by water increases with temperature, we can, in principle, predict a maximum temperature above which an active terrestrial metabolism cannot function by analysis of the decomposition rates of the components of life, and comparison of those rates with the metabolites' minimum metabolic half-lives. The present study is a first step in this direction, providing an analytical framework and method, and analyzing the stability of 63 small molecule metabolites based on literature data. Assuming that attack by water follows a first order rate equation, we extracted decomposition rate constants from literature data and estimated their statistical reliability. The resulting rate equations were then used to give a measure of confidence in the half-life of the metabolite concerned at different temperatures. There is little reliable data on metabolite decomposition or hydrolysis rates in the literature, the data is mostly confined to a small number of classes of chemicals, and the data available are sometimes mutually contradictory because of varying reaction conditions. However, a preliminary analysis suggests that terrestrial biochemistry is limited to environments below ~150-180 °C. We comment briefly on why pressure is likely to have a small effect on this.

Enhancement of spermidine content and antioxidant capacity in transgenic pear shoots overexpressing apple spermidine synthase in response to salinity and hyperosmosis

In our previous work, an apple spermidine synthase (SPDS)-overexpressing transgenic European pear (Pyrus communis L. 'Ballad'), line no. 32 (#32), demonstrated attenuated susceptibility to stress treatment. In the current paper, changes in enzymatic and non-enzymatic antioxidant capacity of the transgenic pear (line #32) were investigated in response to NaCl or mannitol stress. Under non-stressed conditions (before stress treatment), spermidine (Spd) contents and SPDS activity of line #32 were higher than those of the non-transformant (wild type). However, no significant differences were detected between line #32 and the wild type as regards contents of malondialdehyde (MDA) and H2O2, and activities of antioxidant enzymes like superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR). When exposed to NaCl or mannitol stress, both the wild type and line #32 exhibited accumulation of Spd with the latter accumulating more. The transgenic line contained higher antioxidant enzyme activities, less MDA and H2O2 than the wild, implying it suffered from less injury. These results suggested that increase of Spd content in the transgenic line could, at least in part, lead to enhancing enzymatic and non-enzymatic antioxidant capacity.

Potassium transport and plant salt tolerance

Salinity is a major abiotic stress affecting approximately 7% of the world's total land area resulting in billion dollar losses in crop production around the globe. Recent progress in molecular genetics and plant electrophysiology suggests that the ability of a plant to maintain a high cytosolic K+/Na+ ratio appears to be critical to plant salt tolerance. So far, the major efforts of plant breeders have been aimed at improving this ratio by minimizing Na+ uptake and transport to shoot. In this paper, we discuss an alternative approach, reviewing the molecular and ionic mechanisms contributing to potassium homeostasis in salinized plant tissues and discussing prospects for breeding for salt tolerance by targeting this trait. Major K+ transporters and their functional expression under saline conditions are reviewed and the multiple modes of their control are evaluated, including ameliorative effects of compatible solutes, polyamines and supplemental calcium. Subsequently, the genetic aspects of inheritance of K+ transport 'markers' are discussed in the general context of salt tolerance as a polygenic trait. The molecular identity of 'salt tolerance' genes is analysed, and prospects for future research and breeding are examined.

Rubidium chloride tolerant callus cultures of rice (Oryza sativa L.) accumulate more potassium and cross tolerate to other salts

Callus cultures from salt tolerant (CSR-10) and susceptible (Swarnadhan) varieties of Oryza sativa L. were established in Murashige and Skoog's (MS) medium containing lethal concentrations (50 mM) of rubidium chloride (RbCl) as a selective agent. While 95-100% cells were viable in callus cultures grown without RbCl, viability was 75% in 50 mM RbCl selected cultures. Growth of RbCl selected calli in presence of salt was comparable to that of callus grown without it. Cells tolerant to RbCl showed more vacuoles and accumulated more K(+) in comparison with their corresponding controls. Suspension cultures were established and uptake of (86)Rb(+) was measured at 10 and 20 min intervals, which revealed a linear relationship between the absorption of K(+) and time. Callus cultures (560-day-old) tolerant to 50 mM RbCl regenerated shoots with 35-40% frequencies in both the varieties, but the same age-old callus grown in the medium devoid of RbCl did not show any organogenesis. Callus cultures that are tolerant to 50 mM RbCl when exposed to 25 mM LiCl, 50 mM NaCl, 50 mM KCl and 25 mM CsCl also exhibited cross tolerance in both the varieties. This is the first time that a callus line of rice resistant to RbCl was raised and shown to accumulate a major cation K(+ )and also an increased influx of it.

Development of NaCl-tolerant line in Chrysanthemum morifolium Ramat. through shoot organogenesis of selected callus line

Plants were regenerated successfully through shoot organogenesis of a NaCl-selected callus line of Chrysanthemum morifolium Ramat. cv. Maghi Yellow (a salt sensitive cultivar), developed through stepwise increase in NaCl concentration (0-100mM) in the MS medium. The stepwise increase in NaCl concentration from a relatively low level to cytotoxic level was found to be a better way to isolate NaCl-tolerant callus line, since direct transfer of callus to high saline medium was detrimental to callus survival and growth. The selected callus line exhibited significant increase in superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) activities compared to control callus (grown in medium devoid of NaCl). Stability of salt tolerance character of the selected callus line was checked by growing the calli in NaCl-free medium for 3 consecutive months followed by re-exposure to higher salinity stress (120mM NaCl). Among different growth regulator treatments, a combination of 5mgl(-1) TDZ (Thidiazuron) along with 0.25mgl(-1) NAA and 0.5mgl(-1) GA(3) was found to be the most effective for shoot organogenesis in selected callus line. The regeneration potential of the NaCl-tolerant callus ranged from 20.8% to 0% against 62.4% to 0% in control callus line. Under elevated stress condition (medium supplemented with 250mM NaCl), selected calli derived regenerants (S1 plants) exhibited significantly higher SOD and APX activities over both PC (positive control: control callus derived plants grown on MS medium devoid of NaCl) and NC (negative control: control callus derived plants subjected to 250mM NaCl stress) plants. In addition, the NC plants showed stunted growth, delayed root initiation, and had lesser number of roots as compared to S1 plants. Based on growth performance and antioxidant capacity, the S1 plants could be considered as NaCl-tolerant line showing all positive adaptive features towards the salinity stress. Further study on agronomic performance of these S1 plants under saline soil condition need to be undertaken to check the genetic stability of the induced salt-tolerance.

Isolation of a NaCl-tolerant mutant of Chrysanthemum morifolium by gamma radiation: in vitro mutagenesis and selection by salt stress

A stable NaCl-tolerant mutant (R1) of Chrysanthemum morifolium Ramat has been developed by in vitro mutagenesis with gamma radiation (5 gray; Gy). Salt tolerance was evaluated by the capacity of the plant to maintain both flower quality and yield under NaCl stress. Enhanced salt tolerance of the R1 mutant was attributed to increased activities of reactive oxygen species (ROS)-scavenging enzymes, namely superoxide dismutase (SOD), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), and to reduced membrane damage, higher relative water content (RWC), chlorophyll and carotenoids contents. RAPD analysis revealed two polymorphic bands (956 and 1093 bp) for the R1 mutant that might be considered as specific RAPD markers associated with salt tolerance. Better performance of the R1 progeny under identical salinity stress conditions, even in the second year, confirmed the genetic stability of the induced salt tolerance character. The R1 mutant developed by gamma ray treatment can be considered a salt-tolerant mutant showing all the positive characteristics of tolerance to NaCl stress.

Growth, proline accumulation and water relations of NaCl-selected and non-selected callus lines of Dactylis glomerata L

Sodium chloride-tolerant calli were selected from leaf-derived embryogenic calli of Dactylis glomerata L. on agar solidified medium supplemented with 200 mM NaCl, a concentration lethal to non-selected calli. Growth characteristics, water relations and proline accumulation pattern were compared in selected and non-selected lines. The objective was to gain an understanding of the mechanism(s) of tolerance in the NaCl-tolerant line. Growth in the selected line, as expressed in terms of tolerance index (ratio of fresh wt. on NaCl medium:fresh wt. on NaCl free medium x 100), was greater than that of the non-selected line at all levels of NaCl between 50 and 300 mM. There was no significant difference in proline accumulation in the selected and non-selected lines. Maintenance of turgor by osmotic adjustment was observed in the non-selected line despite decreased growth. In contrast, the selected line lost either the need or the ability to adjust osmotically. There was little or no increase in symplastic osmolality in the selected line when exposed to NaCl. Presumably, selection was made for a salt-excluding tissue that has lost the ability to accumulate solutes and adjust turgor with NaCl stress.

Salt tolerant sugarbeet progeny from tissue cultures challenged with multiple salts

Lines of sugarbeet (Beta vulgaris L.) tolerant of multiple salts was accomplished by an in vitro multiple salt challenge. Petioles were placed on RV medium amended with 5 different salts along with Murashige and Skoog base salts for one month. Surviving shoots were cultured on RV medium to obtain petioles for subsequent challenges. During the first, second and third challenges, organogenically regenerated shoots developed from 5%, 46%, and 80% of the petioles, respectively. After the third multiple salt challenge, tolerant shoots were rooted and transplanted in soil. Salt was added to this soil at 1.0% by weight and plants were observed for 2 months. The ten most salt tolerant plants were vernalized to obtain seed. The R1 seed and controls were planted in soil containing 0%, 0.61% or 0.77% multiple salts per dry soil weight. Emergence of R1 seedlings was significantly greater than the controls under salt stress. Multiple salt tolerant R1 plants were maintained in salt amended soil to the 8-10 leaf stage and appeared as healthy and vigorous as the control growing in salt free soil.

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

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(7) cells, one of which was reestablished as a cell suspension. This cell line, JL5, was also resistant to the other group IA cations- Li(+), 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(max), but there was no alteration in its K(m). 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.