Differential stress responses to NaCl salt application in early- and late-maturing diploid potato (Solanum sp.) clones

Cultivated tetraploid potatoes (Solanum tuberosum L.) are moderately salt sensitive but greater stress tolerance exists in diploid wild types. However, little work has been published on salt-tolerance in diploid potato. This study utilized sensitive and tolerant diploid potatoes as well as a commercially cultivated potato to investigate mechanisms of stress tolerance. Stem cuttings from salt-tolerant (T) and sensitive (S) clones of early-maturing (EM) and late-maturing (LM) diploid potato clones were stressed for 5 days at the tuber initiation stage with 150 mmol NaCl in a hydroponic sand culture under greenhouse conditions. The stress responses of the early- and late-maturing potato clones were distinctly different. Under stress, early-maturing clones accumulated Na⁺ in the leaf tissues while late-maturing clones generally excluded Na⁺ from the leaf tissues. Salt tolerant clones of both maturity types were able to tolerate high levels of Na⁺ in the leaf tissues. The lower leaves accumulated more Na⁺ than the upper leaves in both maturity types. The potassium to sodium ratio was significantly greater in the leaves of the late-maturing types, reflecting differences in Na⁺ accumulation rather than alterations in K⁺ levels. Proline levels increased upon salt exposure but were not clearly associated with salinity tolerance. Tolerance was manifested in maintenance of vegetative growth, tuber yield, and reduced leaf necrosis. These responses require efficient uptake of water and source–sink translocation. Maintenance of stomatal conductance under stress was not associated with these responses but tuber yield was related to lower-leaf osmotic potential (OP) in both early- and late-maturity types. Salt tolerant clones of both maturity types also had less negative tuber OP under salt stress than sensitive types. High yielding EMT and LMT clones either minimized tuber yield loss or even increased yield after exposure to salt stress. Mechanistic studies and screening experiments for salt tolerant clones should consider maturity type, leaf position and source–sink relationships enhancing tuber yield.     

Quantitative trait loci for agronomic and physiological traits for a bread wheat population grown in environments with a range of salinity levels

Worldwide, salinity is a major environmental stress affecting agricultural production. Sodium (Na⁺) exclusion has long been recognised as a mechanism of salinity tolerance (ST) in cereals and several molecular markers have been suggested for breeding. However, there have been no empirical studies to show that selection for Na⁺ exclusion markers could improve grain yield in bread wheat under dryland salinity. In six field trials, a bread wheat mapping population was grown to validate Na⁺ exclusion quantitative trait loci (QTL) identified earlier in hydroponics, to determine the impact of Na⁺ exclusion on grain yield, and to identify QTL for yield-related traits. The traits included grain yield, grain number per m², 1,000-grain weight, maturity, plant height, and leaf Na⁺ and K⁺ concentrations. The presence of numerous QTL with minor effects for most traits indicated the genetic complexity of these traits, and thus limited prospects for pyramiding at present. Considerable QTL-by-environment interactions were observed, with the stable QTL generally being co-located with maturity or early vigour/height genes, which demonstrates the importance of measuring major agronomic traits in order to discover genuine QTL for ST. Several QTL for seedling biomass and Na⁺ exclusion identified earlier in hydroponics were also detected in field trials but with marginal impact on grain yield. These results suggest that selection for Na⁺ exclusion and the use of hydroponics-based seedling assays may not necessarily result in improved ST. However, as this is the first report of its kind, there is an urgent need for testing other mapping populations in realistic environments to discover novel ST-QTL for breeding programs. In the meantime, grain yield QTL independent of maturity and height may offer potential to improve ST.     

Physiology and proteome responses of two contrasting rice mutants and their wild type parent under salt stress conditions at the vegetative stage

Salinity is one of the major environmental limiting factors that affects growth and productivity of rice (Oryza sativa L.) worldwide. Rice is among the most sensitive crops to salinity, especially at early vegetative stages. In order to get a better understanding of molecular pathways affected in rice mutants showing contrasting responses to salinity, we exploited the power of 2-DE based proteomics to explore the proteome changes associated with salt stress response. Our physiological observations showed that standard evaluation system (SES) scores, Na⁺ and K⁺ concentrations in shoots and Na⁺/K⁺ ratio were significantly different in contrasting mutants under salt stress condition. Proteomics analysis showed that, out of 854 protein spots which were reproducibly detected, 67 protein spots showed significant responses to salt stress. The tandem mass spectrometry analysis of these significantly differentially accumulated proteins resulted in identification of 34 unique proteins. These proteins are involved in various molecular processes including defense to oxidative stresses, metabolisms, photosynthesis, protein synthesis and processing, signal transduction. Several of the identified proteins were emerged as key participants in salt stress tolerance. The possible implication of salt responsive proteins in plant adaptation to salt stress is discussed.     

Comparative physiological analysis in the tolerance to salinity and drought individual and combination in two cotton genotypes with contrasting salt tolerance

Soil salinity and drought are the two most common and frequently co‐occurring abiotic stresses limiting cotton growth and productivity. However, physiological mechanisms of tolerance to such condition remain elusive. Greenhouse pot experiments were performed to study genotypic differences in response to single drought (4% soil moisture; D) and salinity (200 mM NaCl; S) stress and combined stresses (D + S) using two cotton genotypes Zhongmian 23 (salt‐tolerant) and Zhongmian 41 (salt‐sensitive). Our results showed that drought and salinity stresses, alone or in combination, caused significant reduction in plant growth, chlorophyll content and photosynthesis in the two cotton genotypes, with the largest impact visible under combined stress. Interestingly, Zhongmian 23 was more tolerant than Zhongmian 41 under the three stresses and displayed higher plant dry weight, photosynthesis and antioxidant enzymes activities such as superoxide dismutase (SOD), peroxidase (POD) catalase (CAT) and ascorbate peroxidase (APX) activities compared to control, while those parameters were significantly decreased in salt‐stresses Zhongmian 41 compared to control. Moreover, Na⁺/K⁺‐ATPase activity was more enhanced in Zhongmian 23 than in Zhongmian 41 under salinity stress. However, under single drought stress and D + S stress no significant differences were observed between the two genotypes. No significant differences were detected in Ca²⁺/Mg²⁺‐ATPase activity in Zhongmian 41, while in Zhongmian 23 it was increased under salinity stress. Furthermore, Zhongmian 23 accumulated more soluble sugar, glycine‐betaine and K⁺, but less Na⁺ under the three stresses compared with Zhongmian 41. Obvious changes in leaf and root tips cell ultrastructure was observed in the two cotton genotypes. However, Zhongmian 23 was less affected than Zhongmian 41 especially under salinity stress. These results give a novel insight into the mechanisms of single and combined effects of drought and salinity stresses on cotton genotypes.     

Physiological and biochemical parameters for evaluation and clustering of rice cultivars differing in salt tolerance at seedling stage

Salinity tolerance levels and physiological changes were evaluated for twelve rice cultivars, including four white rice and eight black glutinous rice cultivars, during their seedling stage in response to salinity stress at 100 mM NaCl. All the rice cultivars evaluated showed an apparent decrease in growth characteristics and chlorophyll accumulation under salinity stress. By contrast an increase in proline, hydrogen peroxide, peroxidase (POX) activity and anthocyanins were observed for all cultivars. The K⁺/Na⁺ ratios evaluated for all rice cultivars were noted to be highly correlated with the salinity scores thus indicating that the K⁺/Na⁺ ratio serves as a reliable indicator of salt stress tolerance in rice. Principal component analysis (PCA) based on physiological salt tolerance indexes could clearly distinguish rice cultivars into 4 salt tolerance clusters. Noteworthy, in comparison to the salt-sensitive ones, rice cultivars that possessed higher degrees of salt tolerance displayed more enhanced activity of catalase (CAT), a smaller increase in anthocyanin, hydrogen peroxide and proline content but a smaller drop in the K⁺/Na⁺ ratio and chlorophyll accumulation.     

Vigor and salt tolerance in 3 lines of tall wheatgrass

The F₁ progeny of the cross of two salt-tolerant lines of Thinopyrum elongatum [Host] D. R. Dewey grew better than either parent under non-saline and saline growth conditions. Under non-saline conditions, the hybrid produced 1.8 times as much vegetative tissue as one parent and 3.2 times more than the other parent in the same length of time. The relative growth rates of the 2 parental lines decreased equally as media osmotic potentials decreased. The relative growth rate of the hybrid did not decrease as rapidly as that of the parents; therefore, it was concluded that the greater growth of the hybrid was due to increased salt tolerance. Carbohydrate reserves and water-soluble solutes believed to be involved in osmotic adjustment were assayed to determine if there were any differences between the hybrid and its parents in their abilities to accumulate these compounds. The concentrations of these constituents were measured at dawn and at dusk of the same day in plants grown in media at osmotic potentials ranging from –0.1 to –1.2 MPa. There were no differences in pool sizes of the organic compounds in the 3 lines. Starch increased 10–40 fold in leaves from dawn to dusk and sucrose increased 100-fold. However, this pattern was unaffected by salinity. Conversely, betaine concentrations increased with increasing salinity but were the same at dawn and dusk. Na⁺ and K⁺ were affected by both light and salinity. Cl was one-half (Na⁺+ K⁺) on a molar basis under all conditions. Proline accumulated when (Na⁺+ K⁺) exceeded 200 μmol (g fresh weight)^?1. Since this amount of (Na⁺+ K⁺) existed only in tissues harvested at dusk from severely saline-stressed plants, only leaves from such plants harvested at dusk contained proline.     

New perspective on the mechanism of alleviating salt stress by spermidine in barley seedlings

Salt stress is considered to be a major limiting factor for plant growth and crop productivity. Salt injuries in plants are mostly due to excess Na⁺ entry. A possible survival strategy of plants under saline environments is the effective compartmentation of excess Na⁺ by sequestering Na⁺ in roots and inhibiting transport of Na⁺ from roots to shoots. Our previous study showed that exogenous application of polyamines (PAs) could attenuate salt injuries in barley plants. In order to further understand such protective roles of PAs against salt stress, the effects of spermidine (Spd) on sodium and potassium distribution in barley (Hordeum vulgare L.) seedlings under saline conditions were investigated. The results showed that exogenous application of Spd induced reductions in Na⁺ levels in roots and shoots with comparison of NaCl-treated plants, while no significant changes in K⁺ levels were observed. Correspondingly, the plants treated with Spd exogenously maintained high values of [K⁺]/[Na⁺] as compared with salt-stressed plants. Moreover, it was shown by X-ray microanalysis that K⁺ and Na⁺ accumulated mainly in the exodermal intercellular space and cortical cells of roots under salinity stress, and low accumulation was observed in endodermal cells and stelar parenchyma, indicating Casparian bands possibly act as ion transport barriers. Most importantly, Spd treatment further strengthened this barrier effects, leading to inhibition of Na⁺ transport into shoots. These results suggest that, by reinforcing barrier effects of Casparian bands, exogenous Spd inhibits Na⁺ transport from roots to shoots under conditions of high salinity which are beneficial for attenuating salt injuries in barley seedlings.     

Sodium exclusion QTL associated with improved seedling growth in bread wheat under salinity stress

Worldwide, dryland salinity is a major limitation to crop production. Breeding for salinity tolerance could be an effective way of improving yield and yield stability on saline-sodic soils of dryland agriculture. However, this requires a good understanding of inheritance of this quantitative trait. In the present study, a doubled-haploid bread wheat population (Berkut/Krichauff) was grown in supported hydroponics to identify quantitative trait loci (QTL) associated with salinity tolerance traits commonly reported in the literature (leaf symptoms, tiller number, seedling biomass, chlorophyll content, and shoot Na⁺ and K⁺ concentrations), understand the relationships amongst these traits, and determine their genetic value for marker-assisted selection. There was considerable segregation within the population for all traits measured. With a genetic map of 527 SSR-, DArT- and gene-based markers, a total of 40 QTL were detected for all seven traits. For the first time in a cereal species, a QTL interval for Na⁺ exclusion (wPt-3114-wmc170) was associated with an increase (10%) in seedling biomass. Of the five QTL identified for Na⁺ exclusion, two were co-located with seedling biomass (2A and 6A). The 2A QTL appears to coincide with the previously reported Na⁺ exclusion locus in durum wheat that hosts one active HKT1;4 (Nax1) and one inactive HKT1;4 gene. Using these sequences as template for primer design enabled mapping of at least three HKT1;4 genes onto chromosome 2AL in bread wheat, suggesting that bread wheat carries more HKT1;4 gene family members than durum wheat. However, the combined effects of all Na⁺ exclusion loci only accounted for 18% of the variation in seedling biomass under salinity stress indicating that there were other mechanisms of salinity tolerance operative at the seedling stage in this population. Na⁺ and K⁺ accumulation appear under separate genetic control. The molecular markers wmc170 (2A) and cfd080 (6A) are expected to facilitate breeding for salinity tolerance in bread wheat, the latter being associated with seedling vigour.     

Dynamics of Na+, K+, and Proline Accumulation in Salttreated Vigna sinensis (L) and Phaseolus aureus (L)

The dynamics of Na⁺, K⁺, and proline accumulation in various organs of non nodulated Vigna sinensis and Phaseolus aureus was followed during their acclimation to two levels of salinities for a period of 35 days and was correlated to the vegetative growth of the two species. The rate of Na⁺ and K⁺ absorption is at a maximum during the first 15 to 20 days of culture. K⁺ absorption is not completely inhibited even at 100 mM NaCl although the endogenous Na⁺ largely surpasses that of K⁺ in certain organs. Low salinity rather accelerates K⁺ absorption in both species. The relative growth rates (RGR) correlate with the rate of Na⁺ and K⁺ accumulation. At low salinity (10 mM NaCl), the RGR of V. sinensis is greater than that of P. aureus. However, at high salinity (100 mM NaCl) the RGR is the same for both species. The growth of the younger parts of the two species is not arrested by salt treatment. Very high accumulation of Na⁺ is avoided in organs with less vacuolated tissues. At no time does the endogenous K : Na ratio in these organs fall below 1.0. Certain organs, especially the roots, hypocotyls, and the lower parts of the stems are capable of storing large quantities of Na⁺. In V. sinensis, the accumulated Na⁺ and K⁺ are evenly distributed among the various organs while in P. aureus they are rather concentrated in the roots. External salinity creates water deficiency in the younger plant parts and as a consequence, proline accumulates especially in the youngest aerial organs - more in P. aureus than in V. sinensis. The accumulation of this amino acid in both the species is dependent on time and correlates directly, not only with the water deficit, but also with the K⁺ contents. In contrast, it does not seem to depend directly on the endogenous Na⁺ content. The relative salt tolerance of the two species and the possible role of K⁺, Na⁺ and proline in the osmotic adjustments of the two species under saline conditions are discussed.     

Co-expression of the Arabidopsis SOS genes enhances salt tolerance in transgenic tall fescue (Festuca arundinacea Schreb.)

Crop productivity is greatly affected by soil salinity; therefore, improvement in salinity tolerance of crops is a major goal in salt-tolerant breeding. The Salt Overly Sensitive (SOS) signal-transduction pathway plays a key role in ion homeostasis and salt tolerance in plants. Here, we report that overexpression of Arabidopsis thaliana SOS1+SOS2+SOS3 genes enhanced salt tolerance in tall fescue. The transgenic plants displayed superior growth and accumulated less Na⁺ and more K⁺ in roots after 350 mM NaCl treatment. Moreover, Na⁺ enflux, K⁺ influx, and Ca²⁺ influx were higher in the transgenic plants than in the wild-type plants. The activities of the enzyme superoxide dismutase, peroxidase, catalase, and proline content in the transgenic plants were significantly increased; however, the malondialdehyde content decreased in transgenic plants compared to the controls. These results suggested that co-expression of A. thaliana SOS1+SOS2+SOS3 genes enhanced the salt tolerance in transgenic tall fescue.     

Comparison of salt tolerance and osmotic adjustment of low-sodium and high-sodium subspecies of the C4 halophyte, Atriplex canescens

The relationship between Na⁺ accumulation and salt tolerance was tested by comparing subspecies of the halophyte, Atriplex canescens (fourwing saltbush), that differed markedly in Na⁺ content and Na:K ratios. Above ground tissues of one low-sodium and two high-sodium subspecies were compared with respect to cation accumulation, osmotic adjustment and growth along a salinity gradient in greenhouse trials. Plants of each subspecies were grown for 80 d on 2.2, 180, 540 and 720 mol m^?3 NaCl. At harvest, A. canescens ssp. canescens had significantly lower Na⁺ levels, higher K⁺ levels and lower Na:K ratios in leaf and stem tissues than A. canescens ssp. macropoda and linearis over the salinity range (P < 0.05 or 0.01). Na:K ratios in leaves of the latter two, high-sodium, subspecies were approximately 2 on the lowest salinity treatment and ranged from 5 to 10 on the more saline solutions. By contrast, Na:K ratios in leaves of the low-sodium subspecies canescens, were only 0.4 on the lowest salinity and ranged narrowly from 1.7 to 2.3 at higher salinities. However, despite different patterns of Na⁺ and K⁺ accumulation, all three subspecies exhibited equally high salt tolerance and had similar osmotic pressures in their leaves or stems over the salinity range. Contrary to expectations, high salt tolerance was not necessarily dependent on high levels of Na⁺ accumulation in this species.     

短期NaCl胁迫对不同小麦品种幼苗K+吸收和Na+、K+积累的影响

为研究盐胁迫下小麦幼苗生长及Na⁺、K⁺的吸收和积累规律,以中国春、洲元9369和长武134等3种耐盐性不同小麦品种为材料,采用非损伤微测技术检测盐胁迫2 d后的根系K⁺离子流变化,并对植株体内的Na⁺、K⁺含量进行测定。结果表明:短期(2d)盐胁迫对小麦生长有抑制作用,且对根系的抑制大于地上部,耐盐品种下降幅度小于盐敏感品种。盐胁迫下,小麦根际的 K⁺大量外流,盐敏感品种中国春K⁺流速显著高于耐盐品种长武134,最高可达15倍。小麦幼苗地上部分和根系均表现为Na⁺积累增加,K⁺积累减少,Na⁺/K⁺比随盐浓度增加而上升。中国春限Na⁺能力显著低于长武134,Na⁺/K⁺则显著高于长武134。综上所述,盐胁迫下造成小麦组织器官中Na⁺/K⁺比上升的主要原因是根系K⁺大量外流和Na⁺的过量积累,耐盐性不同的小麦品种间差异显著,并认为根系对K⁺的保有能力可能是作物耐盐性评价的一个重要指标。     

Different mechanisms of ion homeostasis are dominant in the recretohalophyte <Emphasis Type="Italic">Tamarix ramosissima</Emphasis> under different soil salinity

Total ion (Na⁺, K⁺, Ca²⁺, SO₄ ^2? and Cl^?) accumulation by plants, ion contents in plant tissues and ion secretion by salt glands on the surface of shoots of Tamarix ramosissima adapted to different soil salinity, namely low (0.06 mmol Na⁺/g soil), moderate (3.14–4.85 mmol Na⁺/g soil) and strong (7.56 mmol Na⁺/g soil) were analyzed. There are two stages of interrelated and complementary regulation of ion homeostasis in whole T. ramosissima plants: (1) regulation of ion influx into the plant from the soil and (2) changing the secretion efficiency of salt glands on shoots. The secretion efficiency of salt glands was appraised by the ratio of ion secretion to tissue ion content. Independent of soil salinity, the accumulation of K⁺ and Ca²⁺ was higher than the contents of these ions in the soil. Furthermore, the accumulation of K⁺, Ca²⁺ and SO₄ ^2? ions by plants was maintained within a narrow range of values. Under low soil salinity, Na⁺ was accumulated, whereas under moderate and strong salinity, the influxes of Na⁺ were limited. However, under strong salinity, the accumulation of Na⁺ was threefold higher than that under low soil salinity. This led to a change in the Na⁺/K⁺ ratio (tenfold), an increase in the activity of salt glands (tenfold) and a reduction in plant growth (fivefold). An apparently high Na⁺/K⁺ ratio was the main factor determining over-active functioning of salt glands under strong salinity. Principal component analysis showed that K⁺ ions played a key role in ion homeostasis at all levels of salinity. Ca²⁺ played a significant role at low salinity, whereas Cl^? and interrelated regulatory components (K⁺ and proline) played a role under strong salinity. Proline, despite its low concentration under strong salinity, was involved in the regulation of secretion by salt glands. Different stages and mechanisms of ion homeostasis were dominant in T. ramosissima plants adapted to different levels of salinity. These mechanisms facilitated the accumulation of Na⁺ in plants under low soil salinity, the limitation of Na⁺ under moderate salinity and the over-activation of Na⁺ secretion by salt glands under strong salinity, which are all necessary for maintaining ion homeostasis and water potential in the whole plant.     

Multi-locus genome-wide association studies reveal novel genomic regions associated with vegetative stage salt tolerance in bread wheat (Triticum aestivum L.)

Soil salinity is one of the typical abiotic stresses affecting sustainability of wheat production worldwide. In the present study, we performed a 35 K SNP genotyping assay on association panel of 135 diverse wheat genotypes evaluated for vegetative stage tolerance in hydroponics. Association analyses using five multi-locus GWAS models revealed 42 reliable QTNs for 10 salt tolerance associated traits. Among these 42 reliable QTNs, 9, 17 and 16 QTNs were associated with physiological, biomass and shoot ionic traits respectively. Novel major QTNs were identified for chlorophyll content, shoot fresh weight, seedling total biomass, Na⁺ and K⁺ concentration and Na⁺/K⁺ ratio in shoots. Further, 10 major QTNs showed significant effect on the corresponding salt tolerance traits. Gene ontology analysis of the associated genomic regions identified 58 candidate genes. The information generated in this study will be of potential value for improvement of salt tolerance of wheat cultivars using marker assisted selection.     

Differences in physiological and biochemical characteristics in response to single and combined drought and salinity stresses between wheat genotypes differing in salt tolerance

The combined drought and salinity stresses pose a serious challenge for crop production, but the physiological mechanisms behind the stresses responses in wheat remains poorly understood. Greenhouse pot experiment was performed to study differences in genotype response to the single and combined (D + S) stresses of drought (4% soil moisture, D) and salinity (100 mM NaCl, S) using two wheat genotypes: Jimai22 (salt tolerant) and Yangmai20 (salt‐sensitive). Results showed that salinity, drought and/or D + S severely reduces plant growth, biomass and net photosynthetic rate, with a greater effect observed in Yangmai20 than Jimai22. A notable improvement in water use efficiency (WUE) by 239, 77 and 103% under drought, salinity and D + S, respectively, was observed in Jimai22. Moreover, Jimai22 recorded higher root K⁺ concentration in drought and salinity stressed condition and shoot K⁺ under salinity alone than that of Yangmai20. Jimai22 showed lower increase in malondialdehyde (MDA) accumulation, but higher activities of superoxide dismutase (SOD, EC 1.15.1.1) and guaicol peroxidase (POD, EC 1.11.1.7), under single and combined stresses, and catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) under single stress. Our results suggest that high tolerance of Jimai22 in both drought and D + S stresses is closely associated with larger root length, higher Fv/Fm and less MDA contents and improved capacity of SOD and POD. Moreover, under drought Jimai22 tolerance is firmly related to higher root K⁺ concentration level and low level of Na⁺, high‐net photosynthetic rate and WUE as well as increased CAT and APX activities to scavenge reactive oxygen species.     

Agronomical and physiological characterization of salinity tolerance in a commercial tomato hybrid

The salt tolerance of the commercial F1 tomato hybrid (Lycopersicon esculentum Mill) Radja (GC-793) has been agronomically and physiologically evaluated under greenhouse conditions, using a control (nutrient solution), a moderate (70 mM NaCl added to the nutrient solution) and a high salt level (140 mM NaCl), applied for 130 days. The results show that Radja is a Na⁺-excluder genotype, tolerant to moderate salinity. Fruit yield was reduced by 16% and 60% and the shoot biomass by 30% and more than 75% under moderate and high salinities, respectively. At 90 days of salt treatment (DST), the mature leaves feeding the 4th truss at fruiting accumulated little Na⁺ (178 mmol kg^-1 DW). At this time, the sucrose concentration in these leaves even increased with moderate salinity and the amino acid proline was not accumulated under salt conditions as compared to control. At 130 DST, Na⁺ was accumulated mainly by the roots in proportion to the salt level applied, while in leaves appreciable amounts were found only at high salinity (452 mmol kg^-1 DW). In the leaves, Cl^- was always accumulated in proportion to the salt level and in a very much greater amounts than Na⁺ (until 1640 mmol kg^-1 DW). The sucrose content was reduced in all plants by salinity, and was distributed preferentially toward the distal stem and peduncle of a truss at fruiting under moderate salinity, and toward the basal stem and root at high salinity. Moreover, proline was accumulated in different organs of the plant only at high salinity, coinciding with Na⁺ accumulation in leaves. Attempts are made to find a clear relationship between physiological behaviour triggered by stress and the agronomical behaviour, in order to assess the validity of physiological traits used for salt-tolerance selection and breeding in tomato.     

Ectopic expression of PgRab7 in rice plants (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) results in differential tolerance at the vegetative and seed setting stage during salinity and drought stress

In this work, we have overexpressed a vesicle trafficking protein, Rab7, from a stress-tolerant plant, Pennisetum glaucum, in a high-yielding but stress-sensitive rice variety Pusa Basmati-1 (PB-1). The transgenic rice plants were tested for tolerance against salinity and drought stress. The transgenic plants showed considerable tolerance at the vegetative stage against both salinity (200 mM NaCl) and drought stress (up to 12 days after withdrawing water). The protection against salt and drought stress may be by regulating Na⁺ ion homeostasis, as the transgenic plants showed altered expression of multiple transporter genes, including OsNHX1, OsNHX2, OsSOS1, OsVHA, and OsGLRs. In addition, decreased generation and maintenance of lesser reactive oxygen species (ROS), with maintenance of chloroplast grana and photosynthetic machinery was observed. When evaluated for reproductive growth, 89–96 % of seed setting was maintained in transgenic plants during drought stress; however, under salt stress, a 33–53 % decrease in seed setting was observed. These results indicate that PgRab7 overexpression in rice confers differential tolerance at the seed setting stage during salinity and drought stress and could be a favored target for raising drought-tolerant crops.