Proteomic response of barley leaves to salinity

Drought and salinity stresses are adverse environmental factors that affect crop growth and yield. Proteomic analysis offers a new approach to identify a broad spectrum of genes that are expressed in living system. We applied this technique to investigate protein changes that were induced by salinity in barley genotypes (Hordeum vulgare L.), Afzal, as a salt-tolerant genotype and L-527, as a salt-sensitive genotype. The seeds of two genotypes were sown in pot under controlled condition of greenhouse, using a factorial experiment based on a randomized complete block design with three replications. Salt stress was imposed at seedling stage and leaves were collected from control and salt-stressed plant. The Na⁺ and K⁺ concentrations in leaves changed significantly in response to short-term stress. About 850 spots were reproducibly detected and analyzed on 2-DE gels. Of these, 117 proteins showed significant change under salinity condition in at least one of the genotypes. Mass spectrometry analysis using MALDI-TOF/TOF led to the identification some proteins involved in several salt responsive mechanisms which may increase plant adaptation to salt stress including higher constitutive expression level and upregulation of antioxidant, upregulation of protein involved in signal transduction, protein biosynthesis, ATP generation and photosynthesis. These findings may enhance our understanding of plant molecular response to salinity.     

Proteome analysis of sugar beet (Beta vulgaris L.) elucidates constitutive adaptation during the first phase of salt stress

Salinity is one of the major stress factors responsible for growth reduction of most of the higher plants. In this study, the effect of salt stress on protein pattern in shoots and roots of sugar beet (Beta vulgaris L.) was examined. Sugar beet plants were grown in hydroponics under control and 125 mM salt treatments. A significant growth reduction of shoots and roots was observed. The changes in protein expression, caused by salinity, were monitored using two-dimensional gel-electrophoresis. Most of the detected proteins in sugar beet showed stability under salt stress. The statistical analysis of detected proteins showed that the expression of only six proteins from shoots and three proteins from roots were significantly altered. At this stage, the significantly changed protein expressions we detected could not be attributed to sugar beet adaptation under salt stress. However, unchanged membrane bound proteins under salt stress did reveal the constitutive adaptation of sugar beet to salt stress at the plasma membrane level.     

PGPR regulate caspase-like activity,programmed cell death,and antioxidant enzyme activity in paddy under salinity

The response of two root associated bacteria Pseudomonas pseudoalcaligenes and Bacillus pumilus were studied in the (salt-sensitive) rice GJ17 cultivar to salinity under controlled environmental growth conditions for protection of plant from adverse effect of salinity. Salinity affects the growth of salt-sensitive cultivar, but inoculation of plant growth promoting rhizobacteria (PGPR) reduces the harmful effect of salinity. The present study states that PGPR helps to reduce lipid peroxidation and superoxide dismutase activity in salt-sensitive GJ17 cultivar under salinity and play an important role in the growth regulation for positive adaptation of plants to salt stress. This study shows that inoculation of paddy (Oryza sativa) with such bacteria could provide salt-tolerant ability by reducing the toxicity of reactive oxygen species by reducing plant cell membrane index, cell caspase-like protease activity, and programmed cell death and hence resulted in increase cell viability. As these isolates remain associated with the roots, the effects of tolerance against salinity are observed here. Results also indicate that isolated PGPR strain help in alleviating up to 1.5 % salinity stress as well as improve tolerance.     

Soil bacteria confer plant salt tolerance by tissue-specific regulation of the sodium transporter HKT1

Elevated sodium (Na(+)) decreases plant growth and, thereby, agricultural productivity. The ion transporter high-affinity K(+) transporter (HKT)1 controls Na(+) import in roots, yet dysfunction or overexpression of HKT1 fails to increase salt tolerance, raising questions as to HKT1's role in regulating Na(+) homeostasis. Here, we report that tissue-specific regulation of HKT1 by the soil bacterium Bacillus subtilis GB03 confers salt tolerance in Arabidopsis thaliana. Under salt stress (100 mM NaCl), GB03 concurrently down- and upregulates HKT1 expression in roots and shoots, respectively, resulting in lower Na(+) accumulation throughout the plant compared with controls. Consistent with HKT1 participation in GB03-induced salt tolerance, GB03 fails to rescue salt-stressed athkt1 mutants from stunted foliar growth and elevated total Na(+) whereas salt-stressed Na(+) export mutants sos3 show GB03-induced salt tolerance with enhanced shoot and root growth as well as reduced total Na(+). These results demonstrate that tissue-specific regulation of HKT1 is critical for managing Na(+) homeostasis in salt-stressed plants, as well as underscore the breadth and sophistication of plant-microbe interactions.     

Differential responses of antioxidative enzymes and lipid peroxidation to salt stress in salt-tolerant Plantago maritima and salt-sensitive Plantago media

The changes in plant growth, relative water content (RWC), stomatal conductance, lipid peroxidation and antioxidant system in relation to the tolerance to salt stress were investigated in salt-tolerant Plantago maritima and salt-sensitive Plantago media. The 60 days old P. maritima and P. media seedlings were subjected to 0, 100 and 200 mM NaCl for 7 days. Reduction in shoot length was higher in P. media than in P. maritima after exposure to 200 mM NaCl, but 100 mM NaCl treatment did not show any effect on shoot length of P. maritima. Shoot dry weight decreased in P. media and did not change in P. maritima. Two hundred millimolar NaCl treatment had no effect on leaf RWC in P. maritima, but it was reduced in P. media. Salt stress caused reduction in stomatal conductance being more pronounced in P. media than in P. maritima. Activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), glutathione reductase (GR; EC 1.6.4.2) decreased in P. media with increasing salinity. Ascorbate peroxidase (APX; EC 1.11.1.11) activity in leaves of P. media was increased and showed no change under 100 and 200 mM NaCl, respectively. However, activities of CAT, APX and GR increased under 200 mM NaCl while their activities did not change under 100 mM NaCl in P. maritima. SOD activity in leaves of P. maritima increased with increasing salinity. Concomitant with this, four SOD activity bands were identified in leaves of P. maritima, two bands only were observed in P. media. Peroxidase (POX; EC 1.11.1.7) activity increased under both salt concentrations in P. maritima, but only under 200 mM NaCl in P. media. Confirming this, five POX activity bands were identified in leaves of P. maritima, but only two bands were determined in P. media. Malondialdehyde levels in the leaves increased under salt stress in P. media but showed no change and decreased in P. maritima at 100 and 200 mM NaCl, respectively. These results suggest that the salt-tolerant P. maritima showed a better protection mechanism against oxidative damage caused by salt stress by its higher induced activities of antioxidant enzymes than the salt-sensitive P. media.