Plant regeneration of NaCl-pretreated cells from long-term suspension culture of rice (Oryza sativa L.) in high saline conditions

Cells of a 2-year-old suspension culture of rice (Oryza sativa L.), grown under 1.5% NaCl stress for 3 months, gave rise to plants through embryogenesis in different saline conditions. The high regeneration potential (59.6%) on salt-free medium decreased rapidly with increasing concentration of salt in the regeneration medium. At 1.25% NaCl, healthy shoots were developed in 14.9% of the cultures. Under 1.5% salt stress, embryo formation and embryo germination (6.1%) was observed but further development into plants was inhibited. Cells not pretreated with salt produced plants at a low frequency (2.6–4.2%) both in salt-free and low saline condition (0.75–1% NaCl). Cells pretreated for 3 months with 0.75% salt did not give rise to plants on all tested media. Plants regenerated from the salt-stressed cultures were transferred to soil and grew to maturity in a greenhouse.Abbreviations BA 6-benzyladenine - CH casein hydrolysate - 2,4-D 2,4-dichlorophenoxyacetic acid - NAA 1-naphthaleneacetic acid     

NaCl-stress induced alteration in glutamine synthetase activity in excised senescing leaves of a salt-sensitive and a salt-tolerant rice cultivar in light and darkness

Alteration in glutamine synthetase activity was studied in excisedsenescing leaves of rice (Oryza sativa L.) of asalt-sensitive (Ratna) and a salt-tolerant (Getu) cultivar subjected toNaCl-stress. Glutamine synthetase activity declined during senescence indarkness, but increased initially and then decreased under light treatment,which is correlated with the degree of leaf senescence. In NaCl-stressed leavesthe declining trend of this enzyme activity was accelerated in the fastersenescing cv. Ratna in both light or darkness. However, it was partiallyretarded in the dark and fully in the light in the slower senescing cv. Getu.This probably indicates that the control mechanism of enzyme activities isdifferent in the sensitive and the tolerant cultivar under saline condition. Thehigher activity of glutamine synthetase and consequently higher syntheticactivity in the tolerant cultivar may be a biochemical adaptation for salttolerance in rice.     

Multiple stress and growth of barley: Effect of salinity and temperature shock

The effect of preconditioning to NaCl salinity (0 to 135 mmol L^-1) on the subsequent response of barley (Hordeum vulgare L.) to two days of low (5°C) temperature shock (LTS) was investigated. Both salinity and LTS reduced the final growth of barley tops and roots. The effect of LTS on growth of tops and roots depended on the level of salinity stress imposed. At salinity level of 45 mmol L^-1, for example, exposing the plants to LTS reduced top growth by an additional 34%; at 135 mmol L^-1 salinity, however, LTS reduced the top growth by only 2%. Salinity increased the concentration of Na, Cl, total P, PO₄, and Zn, reduced the concentration of K, Ca, total N, NO₃, and SO₄, but did not affect the concentration of total S in the barley tops. LTS increased the concentration of Ca and Zn in the tops; the concentrations of other elements (cations and anions) were not changed by the temperature treatment. In the tops of the control plants, NO₃, PO₄, and SO₄ accounted for 15%, 72% and 93% of the total N, P, and S, respectively. In the plants grown at 135 mmol L^-1 NaCl, however, the above values were 8%, 84%, and 70%, respectively, which indicates that salinity had altered the incorporation of N, P, and S into organic compounds. We suggest that salinity and low temperature affect growth and nutrient uptake and incorporation into organic matter by different mechanisms. Although barley subjected to low salinity becomes more sensitive to subsequent low temperature stress, preconditioning of barley to higher salinity stress seems to reduce the plant's sensitivity to subsequent low temperature.     

Growth and Protein Pattern in Cowpea Seedlings Subjected to Salinity

Cowpea (Vigna unguiculata) seeds were put to germinate on filter paper under control (distilled water) and salt stress (100 mM MaCl) conditions. Seeds and seedlings were classified in eight developmental stages (DS), according to their morphological traits. Under control conditions, 7 d after planting, 100 % of the seedlings reached DS VIII (seedlings with radicles measuring more than 5 cm, cotyledons leaving the filter paper, hypocotyls straight and cotyledonary leaves fully open) and under NaCl stress conditions, 11 d after planting only 68 % of the seedlings were at DS VIII. The length of the main root and of shoot has decreased 23 and 44 %, respectively. The two-dimensional electrophoretic patterns of the albumins isolated from stems and leaves were determined in seedlings at DS VIII. In stems 19 proteins (14.6 to 76.3 kDa) had their relative concentration increased by salinity, 8 (31.2 to 65.0 kDa) had their relative concentration decreased by salinity and 9 (16.3 to 39.8 kDa) were apparently synthesised de novo. In leaves, under salt conditions 9 proteins (18.2 to 33.2 kDa) increased in concentration, one (17.1 kDa) decreased in concentration and one (21.2 kDa) was apparently synthesised de novo. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of frost-hardening and salinity on glutathione and sulfhydryl levels and on glutathione reductase activity in spinach leaves

In frost-hardened spinach leaves ( Spinucea oleracea L. ev. Vroeg Reuzenblad ) an enhanced content of water-soluble non-protein sulfhydryl compounds was observed. The enhancement was due to higher levels of glutathione as well as to other non-protein-bound sulfhydryl compounds. In addition glutathione reductase activity was increased upon hardening. The affinity of the enzyme for oxidized glutathione was slightly lowered during hardening. The significance of glutathione accumulation during frost-hardening is discussed. Exposure of spinach to NaCl-stress did not affect the levels of glutathione and glutathione reductase of the leaves. In addition the kinetic properties of the enzyme remained unaltered by salinity. It is suggested that glutathione and glutathione reductase activity are not involved in adaptation of spinach to saline conditions.