Development and evaluation of novel salt‐tolerant Eucalyptus trees by molecular breeding using an RNA‐Binding‐Protein gene derived from common ice plant (Mesembryanthemum crystallinum L.)

The breeding of plantation forestry trees for the possible afforestation of marginal land would be one approach to addressing global warming issues. Here, we developed novel transgenic Eucalyptus trees (Eucalyptus camaldulensis Dehnh.) harbouring an RNA‐Binding‐Protein (McRBP) gene derived from a halophyte plant, common ice plant (Mesembryanthemum crystallinum L.). We conducted screened‐house trials of the transgenic Eucalyptus using two different stringency salinity stress conditions to evaluate the plants’ acute and chronic salt stress tolerances. Treatment with 400 mM NaCl, as the high‐stringency salinity stress, resulted in soil electrical conductivity (EC) levels >20 mS/cm within 4 weeks. With the 400 mM NaCl treatment, >70% of the transgenic plants were intact, whereas >40% of the non‐transgenic plants were withered. Treatment with 70 mM NaCl, as the moderate‐stringency salinity stress, resulted in soil EC levels of approx. 9 mS/cm after 2 months, and these salinity levels were maintained for the next 4 months. All plants regardless of transgenic or non‐transgenic status survived the 70 mM NaCl treatment, but after 6‐month treatment the transgenic plants showed significantly higher growth and quantum yield of photosynthesis levels compared to the non‐transgenic plants. In addition, the salt accumulation in the leaves of the transgenic plants was 30% lower than that of non‐transgenic plants after 15‐week moderate salt stress treatment. There results suggest that McRBP expression in the transgenic Eucalyptus enhances their salt tolerance both acutely and chronically.     

Post‐flowering night respiration and altered sink activity account for high night temperature‐induced grain yield and quality loss in rice (Oryza sativa L.)

High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT‐induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field‐based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post‐flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post‐flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn‐mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT‐induced damage under future warming scenarios.     

OsSUV3 dual helicase functions in salinity stress tolerance by maintaining photosynthesis and antioxidant machinery in rice (Oryza sativa L. cv. IR64)

To overcome the salinity‐induced loss of crop yield, a salinity‐tolerant trait is required. The SUV3 helicase is involved in the regulation of RNA surveillance and turnover in mitochondria, but the helicase activity of plant SUV3 and its role in abiotic stress tolerance have not been reported so far. Here we report that the Oryza sativa (rice) SUV3 protein exhibits DNA and RNA helicase, and ATPase activities. Furthermore, we report that SUV3 is induced in rice seedlings in response to high levels of salt. Its expression, driven by a constitutive cauliflower mosaic virus 35S promoter in IR64 transgenic rice plants, confers salinity tolerance. The T₁ and T₂ sense transgenic lines showed tolerance to high salinity and fully matured without any loss in yields. The T₂ transgenic lines also showed tolerance to drought stress. These results suggest that the introduced trait is functional and stable in transgenic rice plants. The rice SUV3 sense transgenic lines showed lesser lipid peroxidation, electrolyte leakage and H₂O₂ production, along with higher activities of antioxidant enzymes under salinity stress, as compared with wild type, vector control and antisense transgenic lines. These results suggest the existence of an efficient antioxidant defence system to cope with salinity‐induced oxidative damage. Overall, this study reports that plant SUV3 exhibits DNA and RNA helicase and ATPase activities, and provides direct evidence of its function in imparting salinity stress tolerance without yield loss. The possible mechanism could be that OsSUV3 helicase functions in salinity stress tolerance by improving photosynthesis and antioxidant machinery in transgenic rice.     

Leaf cell membrane stability‐based mechanisms of zinc nutrition in mitigating salinity stress in rice

• Excess salt affects about 955 million ha of arable land worldwide, and 49% of agricultural land is Zn‐deficient. Soil salinity and zinc deficiency can intensify plant abiotic stress. The mechanisms by which Zn can mitigate salinity effects on plant functions are not well understood.
• We conducted an experiment to determine how Zn and salinity effects on rice plant retention of Zn, K⁺ and the salt ion Na⁺ affect chlorophyll formation, leaf cell membrane stability and grain yield. We examined the mechanisms of Zn nutrition in mitigating salinity stress by examining plant physiology and nutrition. We used native Zn‐deficient soils (control), four salinity (EC ) and Zn treatments – Zn 10 mg·kg^?1 (Zn₁₀), EC 5 dS ·m^?1 (EC ₅), Zn₁₀+EC ₅ and Zn₁₅+EC ₅, a coarse rice (KS ‐282) and a fine rice (Basmati‐515) in the study.
• Our results showed that Zn alone (Zn₁₀) significantly increased rice tolerance to salinity stress by promoting Zn/K⁺ retention, inhibiting plant Na⁺ uptake and enhancing leaf cell membrane stability and chlorophyll formation in both rice cultivars in native alkaline, Zn‐deficient soils (P  <  0.05). Further, under the salinity treatment (EC ₅), Zn inputs (10–15 mg·kg^?1) could also significantly promote rice plant Zn/K⁺ retention and reduce plant Na⁺ uptake, and thus increased leaf cell membrane stability and grain yield. Coarse rice was more salinity‐tolerant than fine rice, having significantly higher Zn/K⁺ nutrient retention.
• The mechanistic basis of Zn nutrition in mitigating salinity impacts was through promoting plant Zn/K⁺ uptake and inhibiting plant Na⁺ uptake, which could result in increased plant physiological vigour, leaf cell membrane stability and rice productivity.

     

Susceptibility and tolerance in hybrid and pure‐line rice varieties to herbivore attack: biomass partitioning and resource‐based compensation in response to damage

Hybrid rice has been noted for its susceptibility to insects and diseases compared to pure‐line (conventional) rice varieties. We investigated herbivory by Nilaparvata lugens, Sogatella furcifera and Scirpophaga incertulas on replicated three‐line hybrid sets (parental and hybrid lines) in field and greenhouse experiments. In a field experiment, caterpillar densities and stemborer damage was similar among hybrid and parental lines. In field and greenhouse experiments, the cytoplasmic male sterile (CMS)‐lines and maintainer lines had higher densities of planthoppers (including N. lugens and S. furcifera) than restorer or hybrid lines likely because of their wild abortive CMS‐lineage. High nitrogen levels increased plant mortality due to N. lugens, but often reduced mortality from S. furcifera and S. incertulas: this was similar between hybrid and pure‐line varieties. The hybrids were generally more tolerant of herbivory (lower biomass reductions per unit weight of insect) than the inbred parental lines. The addition of nitrogen to both the hybrid and pure‐line varieties had contrasting effects on tolerance depending on the nature of the attacking insect: fertiliser increased tolerance to S. furcifera (lower losses of yield and shoot biomass per mg insect) and S. incertulas (lower yield, shoot and root biomass loss) but fertiliser reduced tolerance to N. lugens (higher loss of root biomass and no effects on yield and shoot biomass loss). Our results indicate that hybrid rice is not physiologically more susceptible to herbivores than are pure‐line varieties even under high nitrogen conditions, but does have higher tolerance to insect damage.     

Diversity and salt tolerance of native Acacia rhizobia isolated from saline and non‐saline soils

Re‐establishing native vegetation in stressed soils is of considerable importance in many parts of the world, leading to significant interest in using plant–soil symbiont interactions to increase the cost‐effectiveness of large‐scale restoration. However, effective use of soil microbes in revegetation requires knowledge of how microbe communities vary along environmental stress gradients, as well as how such variation relates to symbiont effectiveness. In Australia, shrubby legumes dominate many ecosystems where dryland salinity is a major issue, and improving plant establishment in saline soils is a priority of regional management agencies. In this study, strains of rhizobial bacteria were isolated from a range of Acacia spp. growing in saline and non‐saline soils. Replicates of each strain were grown under several salinity levels in liquid culture and characterized for growth and salt tolerance. Genetic characterization of rhizobia showed considerable variation among strains, with salt tolerance and growth generally higher in rhizobial populations derived from more saline soils. These strains showed markedly different genetic profiles and generic affiliations to those from more temperate soils, suggesting community differentiation in relation to salt stress. The identification of novel genomic species from saline soils suggests that the diversity of rhizobia associated with Australian Acacia spp. is significantly greater than previously described. Overall, the ability of some symbiotically effective strains to tolerate high salinity is promising with regard to improving host plant re‐establishment in these soils.     

Positive and negative biotic interactions and invasive Triadica sebifera tolerance to salinity: a cross‐continent comparative study

Exotic plant species may exhibit abiotic niche expansions that enable them to persist in a greater variety of habitat types in their introduced ranges than in their native ranges. This may reflect variation in limitation by different abiotic niche dimensions (realized niche shift) or phenotypic effects of biotic interactions that vary among ranges (realized niche expansion). Novel abiotic and biotic environments in the introduced range may also lead to genetic changes in exotic plant traits that enhance their abiotic stress tolerance (fundamental niche expansion). Here, we investigated how biotic interactions (aboveground herbivory and soil organisms) affect plant salinity tolerance using the invasive species Triadica sebifera from China (native range) and US (introduced range) populations grown in common gardens in both ranges. Simulated herbivory significantly reduced survival in saline treatments with reductions especially large at low salinity. Soil sterilization had a negative effect on survival at low salinity in China but had a positive effect on survival at low salinity in the US. Triadica survival and biomass were higher for US populations than for China populations, particularly in China but salinity tolerance did not depend on population origin. On average, arbuscular mycorrhizal (AM) colonization was higher for US populations, US soils and low salinity. These factors had a significant, positive, non‐additive interaction so that clipped seedlings from US populations in low saline US soils had high levels of AM colonization. Overall, our results show that phenotypic biotic interactions shape Triadica's salinity tolerance. Positive and negative biotic interactions together affected plant performance at intermediate stress levels. However, only aboveground damage consistently affected salinity tolerance, suggesting an important role for enemy release in expanding stress tolerance.     

Opportunities of marker‐assisted selection for rice fragrance through marker–trait association analysis of microsatellites and gene‐based markers

Developing fragrant rice through marker‐assisted/aided selection (MAS) is an economical and profitable approach worldwide for the enrichment of an elite genetic background with a pleasant aroma. The PCR‐based DNA markers that distinguish the alleles of major fragrance genes in rice have been synthesised to develop rice scent biofortification through MAS. Thus, the present study examined the aroma biofortification potential of these co‐dominant markers in a germplasm panel of 189 F₂ progeny developed from crosses between a non‐aromatic variety (MR84) and a highly aromatic but low‐yielding variety (MRQ74) to determine the most influential diagnostic markers for fragrance biofortification. The SSRs and functional DNA markers RM5633 (on chromosome 4), RM515, RM223, L06, NKSbad2, FMbadh2‐E7, BADEX7‐5, Aro7 and SCU015RM (on chromosome 8) were highly associated with the 2AP (2‐acetyl‐1‐pyrroline) content across the population. The alleles traced via these markers were also in high linkage disequilibrium (R² > 0.70) and explained approximately 12.1, 27.05, 27.05, 27.05, 25.42, 25.42, 20.53, 20.43 and 20.18% of the total phenotypic variation observed for these biomarkers, respectively. F₂ plants harbouring the favourable alleles of these effective markers produced higher levels of fragrance. Hence, these rice plants can be used as donor parents to increase the development of fragrance‐biofortified tropical rice varieties adapted to growing conditions and consumer preferences, thus contributing to the global rice market.     

Ethylenediamine‐N,N′‐disuccinic acid mitigates salt‐stress damages in strawberry by interfering with effects on the plant ionome

This study evaluated the hypothesis that the organic chelant ethylenediamine‐N,N′‐disuccinic acid (EDDS) mitigates plant damage under salinity, and that this is accomplished by EDDS‐induced effects on cation uptake. Damaging effects of salinity on plants often involve inhibited uptake of nutritional cations, such as K and Ca, and excessive accumulation of Na. Therefore, mechanisms that improve uptake of K and Ca, or reduce Na uptake, have a potential for ameliorating salinity damages. Organic chelants increase heavy‐metal cation availability at the site of uptake and increase their uptake by the roots or in planta transport. Although organic chelants are routinely used in agriculture to enhance uptake of heavy‐metal cations into plants, and for soil bioremediation, their effect on uptake of cation‐macronutrients is not known, and neither is their impact on plant function under salinity. In this study, we evaluated the response of strawberry plants to EDDS application (0, 1, 3 and 5 mmol kg soil^?1), under six levels of NaCl (0, 3, 6, 9, 12 and 15 mmol L^?1). EDDS application under salinity improved vegetative development, as well as reproductive growth and chlorophyll content, with statistically significant interaction between chelant dosage and level of salinity. The mitigation of salinity damage by EDDS occurred at high salinity treatments (from 9 mM NaCl). Application rates of 1–3 mmol EDDS kg^?1 were optimal for mitigating salinity effects on reproductive development, but in accordance with the extent of chelant‐induced accumulation of the macronutrients K, Ca and P in the leaves, higher application rates (3–5 mmol EDDS kg^?1) were required for optimal improvement of vegetative development. These results suggest that EDDS improves plant function under mild salinities by interfering with salinity effects on the plant ionome.     

Physiological and biochemical characterization of NERICA‐L‐44: a novel source of heat tolerance at the vegetative and reproductive stages in rice

The predicted increase in the frequency and magnitude of extreme heat spikes under future climate can reduce rice yields significantly. Rice sensitivity to high temperatures during the reproductive stage is well documented while the same during the vegetative stage is more speculative. Hence, to identify and characterize novel heat‐tolerant donors for both the vegetative and reproductive stages, 71 rice accessions, including approximately 75% New Rice for Africa (NERICAs), were phenotyped across field experiments during summer seasons in Delhi, India, and in a controlled environment study at International Rice Research Institute , Philippines. NERICA‐L‐44 (NL‐44) recorded high seedling survival (52%) and superior growth and greater reproductive success exposed to 42.2°C (sd ± 2.3) under field conditions. NL‐44 and the heat‐tolerant check N22 consistently displayed lower membrane damage and higher antioxidant enzymes activity across leaves and spikelets. NL‐44 recorded 50–60% spikelet fertility, while N22 recorded 67–79% under controlled environment temperature of 38°C (sd ±1.17), although both had about 87% fertility under extremely hot field conditions. N22 and NL‐44, exposed to heat stress (38°C), had similar pollen germination percent and number of pollen tubes reaching the ovary. NL‐44 maintained low hydrogen peroxide production and non‐photochemical quenching (NPQ) with high photosynthesis while N22 avoided photosystem II damage through high NPQ under high‐temperature stress. NL‐44 with its reproductive stage resilience to extreme heat stress, better antioxidant scavenging ability in both vegetative tissue and spikelets and superior yield and grain quality is identified as a novel donor for increasing heat tolerance at both the vegetative and reproductive stages in rice.     

Predicted effects of climate change on potential sources of non‐indigenous marine species

Aim

We compare the present‐day global ocean climate with future climatologies based on Intergovernmental Panel on Climate Change (IPCC) models and examine whether changes in global ocean climate will affect the environmental similarity of New Zealand's (NZ) coastal environments to those of the rest of the world. Our underlying rationale is that environmental changes to source and recipient regions may result in changes to the risk of non‐indigenous species survival and establishment.

Location

Coastlines of global continents and islands.

Methods

We determined the environmental similarity (Euclidean distance) between global coastlines and north‐east NZ for 2005 and 2050 using data on coastal seawater surface temperature and salinity. Anticipated climate models from the SRES A1B scenario family were used to derive coastal climatologies for 2050.

Results

During the next decades, most global regions will experience an increase in coastal seawater surface temperatures and a decline or increase in salinity. This will result in changes in the similarity of other coastal environments to north‐east NZ's coastal areas. Global regions that presently have high environmental similarity to north‐east NZ will variously retain this level of similarity, become more similar or decrease in environmental similarity. Some regions that presently have a low level of similarity will become more similar to NZ. Our models predict a widespread decrease in the seasonal variation in environmental similarity to NZ.

Main conclusions

Anticipated changes in the global ocean climate have the potential to change the risk of survival and establishment of non‐indigenous marine species arriving to NZ from some global regions. Predicted changes to global human transport networks over the coming decades highlight the importance of incorporating climate change into conservation planning and modelling.

     

Influence of sudden salinity variation on the physiology and domoic acid production by two strains of Pseudo‐nitzschia australis

Several coastal countries including France have experienced serious and increasing problems related to Pseudo‐nitzschia toxic blooms. These toxic blooms occur in estuarine and coastal waters potentially subject to fluctuations in salinity. In this study, we document for the first time the viability, growth, photosynthetic efficiency, and toxin production of two strains of Pseudo‐nitzschia australis grown under conditions with sudden salinity changes. Following salinity variation, the two strains survived over a restricted salinity range of 30–35, with favorable physiological responses, as the growth, effective quantum yield and toxin content were high compared to the other conditions. In addition, high cellular quotas of domoic acid (DA) were observed at a salinity of 40 for the strain IFR‐PAU‐16.1 in comparison with the other strain IFR‐PAU‐16.2 where the cell DA content was directly released into the medium. On the other hand, the osmotic stress imposed at lower salinities, 20 and 10, resulted in cell lysis and a sudden DA leakage in the medium. Intra‐specific variability was observed in growth and toxin production, with the strain IFR‐PAU‐16.1 apparently able to withstand higher salinities than the strain IFR‐PAU‐16.2. On the whole, DA does not appear to act as an osmolyte in response to sudden salinity changes. Since most of the shellfish harvesting areas of bivalve molluscs in France are located in areas where the salinity generally varies between 30 and 35, Pseudo‐nitzschia australis blooms might potentially impact public health and commercial shellfish resources in these places.     

Influence of density and salinity on larval development of salt‐adapted and salt‐naïve frog populations

Environmental change and habitat fragmentation will affect population densities for many species. For those species that have locally adapted to persist in changed or stressful habitats, it is uncertain how density dependence will affect adaptive responses. Anurans (frogs and toads) are typically freshwater organisms, but some coastal populations of green treefrogs (Hyla cinerea) have adapted to brackish, coastal wetlands. Tadpoles from coastal populations metamorphose sooner and demonstrate faster growth rates than inland populations when reared solitarily. Although saltwater exposure has adaptively reduced the duration of the larval period for coastal populations, increases in densities during larval development typically increase time to metamorphosis and reduce rates of growth and survival. We test how combined stressors of density and salinity affect larval development between salt‐adapted (“coastal”) and nonsalt‐adapted (“inland”) populations by measuring various developmental and metamorphic phenotypes. We found that increased tadpole density strongly affected coastal and inland tadpole populations similarly. In high‐density treatments, both coastal and inland populations had reduced growth rates, greater exponential decay of growth, a smaller size at metamorphosis, took longer to reach metamorphosis, and had lower survivorship at metamorphosis. Salinity only exaggerated the effects of density on the time to reach metamorphosis and exponential decay of growth. Location of origin affected length at metamorphosis, with coastal tadpoles metamorphosing slightly longer than inland tadpoles across densities and salinities. These findings confirm that density has a strong and central influence on larval development even across divergent populations and habitat types and may mitigate the expression (and therefore detection) of locally adapted phenotypes.     

盐度对滨海土壤细菌多样性和群落构建过程的影响

滨海盐土是重要的农业土地后备资源。微生物是土壤中物质循环的关键动力,然而盐度对土壤微生物群落特征影响的研究还很缺乏。本研究采集滨海地区的土壤样品,研究非盐、轻盐和高盐3组不同盐度对土壤细菌数量、多样性和群落构建的影响。结果表明: 与非盐和轻盐土壤相比,高盐土壤的脱氢酶活性和细菌数量显著降低,而细菌α多样性没有变化,细菌群落结构发生分异。利用零模型反演群落构建过程,发现盐度是细菌群落构建过程的主控因子,盐度主导的高确定性过程控制了滨海盐土细菌的群落结构。说明在现有的盐度范围内,高盐土壤中同样含有丰富的微生物种质资源,具有盐土改良的生物学基础,然而由于高确定性的群落构建机制,外源物种很难定殖于滨海盐土。因此,在利用微生物技术改良滨海盐土时,应尽可能筛选耐盐的土著菌种,提高定殖效率。     

Salinity tolerance of japonica and indica rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) at the seedling stage

In order to identify the degree of salinity tolerance of the indica and japonica rice groups, 10 varieties were tested under saline and non-saline conditions. Twelve-day-old seedlings were grown in normal culture solution, then initially salinized at an electrical conductivity (EC) of 6 dS/m for 4 days, and finally salinized at an EC of 12 dS/m for the next 14 days. The growth parameters, and Na and K absorption in the shoot were measured to characterize the tolerance level of the two rice groups. Reduction in all growth parameters of tolerant varieties was significantly lower in indica varieties than in japonica varieties. Tolerant indica varieties were good Na excluders, absorbed high amounts of K, and maintained a low Na/K ratio in the shoot. Tolerant japonica varieties also absorbed less Na but were not as good excluders as indica varieties. Shoot K concentration alone did not show any relationship to salinity tolerance. These results indicate that, for all parameters measured, the tolerance level of indica was higher than that of japonica.     

Salt‐stress induced modulation of chlorophyll biosynthesis during de‐etiolation of rice seedlings

Chlorophyll biosynthesis in plants is subjected to modulation by various environmental factors. To understand the modulation of the chlorophyll (Chl) biosynthesis during greening process by salt, 100–200 mM NaCl was applied to the roots of etiolated rice seedlings 12 h prior to the transfer to light. Application of 200 mM NaCl to rice seedlings that were grown in light for further 72 h resulted in reduced dry matter production (–58%) and Chl accumulation (–66%). Ionic imbalance due to salinity stress resulted in additional downregulation (41–45%) of seedling dry weight, Chl and carotenoid contents over and above that of similar osmotic stress induced by polyethylene glycol. Downregulation of Chl biosynthesis may be attributed to decreased activities of Chl biosynthetic pathway enzymes, i.e. 5‐aminolevulinic acid (ALA) dehydratase (EC‐2.4.1.24), porphobilinogen deaminase (EC‐4.3.1.8), coproporphyrinogen III oxidase (EC‐1.3.3.3), protoporphyrinogen IX oxidase (EC‐1.3.3.4), Mg‐protoporphyrin IX chelatase (EC‐6.6.1.1) and protochlorophyllide oxidoreductase (EC‐1.3.33.1). Reduced enzymatic activities were due to downregulation of their protein abundance and/or gene expression in salt‐stressed seedlings. The extent of downregulation of ALA biosynthesis nearly matched with that of protochlorophyllide and Chl to prevent the accumulation of highly photosensitive photodynamic tetrapyrroles that generates singlet oxygen under stress conditions. Although, ALA synthesis decreased, the gene/protein expression of glutamyl‐tRNA reductase (EC‐1.2.1.70) increased suggesting it may play a role in acclimation to salt stress. The similar downregulation of both early and late Chl biosynthesis intermediates in salt‐stressed seedlings suggests a regulatory network of genes involved in tetrapyrrole biosynthesis.     

Salinity and crop yield

Thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity. Securing and augmenting agricultural yield in times of global warming and population increase is urgent and should, aside from ameliorating saline soils, include attempts to increase crop plant salt tolerance. This short review provides an overview of the processes that limit growth and yield in saline conditions. Yield is reduced if soil salinity surpasses crop‐specific thresholds, with cotton, barley and sugar beet being highly tolerant, while sweet potato, wheat and maize display high sensitivity. Apart from Na⁺, also Cl^?, Mg²⁺, SO₄^2‐ or HCO₃^‐ contribute to salt toxicity. The inhibition of biochemical or physiological processes cause imbalance in metabolism and cell signalling and enhance the production of reactive oxygen species interfering with cell redox and energy state. Plant development and root patterning is disturbed, and this response depends on redox and reactive oxygen species signalling, calcium and plant hormones. The interlink of the physiological understanding of tolerance processes from molecular processes as well as the agronomical techniques for stabilizing growth and yield and their interlinks might help improving our crops for future demand and will provide improvement for cultivating crops in saline environment.     

Expression of the Arabidopsis vacuolar H+‐pyrophosphatase gene (AVP1) improves the shoot biomass of transgenic barley and increases grain yield in a saline field

Cereal varieties with improved salinity tolerance are needed to achieve profitable grain yields in saline soils. The expression of AVP1, an Arabidopsis gene encoding a vacuolar proton pumping pyrophosphatase (H⁺‐PPase), has been shown to improve the salinity tolerance of transgenic plants in greenhouse conditions. However, the potential for this gene to improve the grain yield of cereal crops in a saline field has yet to be evaluated. Recent advances in high‐throughput nondestructive phenotyping technologies also offer an opportunity to quantitatively evaluate the growth of transgenic plants under abiotic stress through time. In this study, the growth of transgenic barley expressing AVP1 was evaluated under saline conditions in a pot experiment using nondestructive plant imaging and in a saline field trial. Greenhouse‐grown transgenic barley expressing AVP1 produced a larger shoot biomass compared to null segregants, as determined by an increase in projected shoot area, when grown in soil with 150 mm NaCl. This increase in shoot biomass of transgenic AVP1 barley occurred from an early growth stage and also in nonsaline conditions. In a saline field, the transgenic barley expressing AVP1 also showed an increase in shoot biomass and, importantly, produced a greater grain yield per plant compared to wild‐type plants. Interestingly, the expression of AVP1 did not alter barley leaf sodium concentrations in either greenhouse‐ or field‐grown plants. This study validates our greenhouse‐based experiments and indicates that transgenic barley expressing AVP1 is a promising option for increasing cereal crop productivity in saline fields.     

Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata

Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice.