Cuticular wax, the first protective layer of above ground tissues of many plant species, is a key evolutionary innovation in plants. Cuticular wax safeguards the evolution from certain green algae to flowering plants and the diversification of plant taxa during the eras of dry and adverse terrestrial living conditions and global climate changes. Cuticular wax plays significant roles in plant abiotic and biotic stress tolerance and has been implicated in defense mechanisms against excessive ultraviolet radiation, high temperature, bacterial and fungal pathogens, insects, high salinity and low temperature. As one of the most detrimental abiotic stresses, drought limits plant growth and productivity, which poses huge threats to global food security and health of terrestrial ecosystem. The composition, biochemistry, structure, biosynthesis and transport of plant cuticular wax have been reviewed extensively. However, the molecular and evolutionary mechanisms of cuticular wax in plants in response to drought stress are still lacking. In this review, we focus on potential mechanisms, from evolutionary, molecular, and physiological aspects, that control cuticular wax and its roles in plant drought tolerance. We also raise key research questions and propose important directions to be resolved in the future, leading to potential applications of cuticular wax for water use efficiency in agricultural and environmental sustainability.

New evidence for ABA-induced stomatal closure in fern and known evidence in earlier diverging lineages does not support the hypothesis that stomatal responsiven

Summary: Active removal of Na⁺ from the cytosol into the vacuole plays a critical role in salinity tissue tolerance, but another, often neglected component of this trait is Na⁺ retention in vacuoles. This retention is based on an efficient control of Na⁺‐permeable slow‐ and fast‐vacuolar channels that mediate the back‐leak of Na⁺ into cytosol and, if not regulated tightly, could result in a futile cycle. This Tansley insight summarizes our current knowledge of regulation of tonoplast Na⁺‐permeable channels and discusses the energy cost of vacuolar Na⁺ sequestration, under different scenarios. We also report on a phylogenetic and bioinformatic analysis of the plant two‐pore channel family and the difference in its structure and regulation between halophytes and glycophytes, in the context of salinity tolerance.

Nitrogen (N) is the most common limiting factor for crop productivity worldwide. An effective approach to solve N deficiency is to develop low N (LN) tolerant crop cultivars. Tibetan annual wild barley is well-known for its wide genetic diversity and high tolerance to poor soil fertility. Up to date, no study has been done to illustrate the mechanism of LN tolerance underlying the wild barley at transcriptional level. In this study, we employed Illumina RNA-Sequencing to determine the genotypic difference in transcriptome profile using two Tibetan wild barley genotypes differing in LN tolerance (XZ149, tolerant and XZ56, sensitive). A total of 1469 differentially expressed genes (DEGs) were identified in the two genotypes at 6 h and 48 h after LN treatment. Genetic difference existed in DEGs between XZ149 and XZ56, including transporters, transcription factors (TFs), kinases, antioxidant stress and hormone signaling related genes. Meanwhile, 695 LN tolerance-associated DEGs were mainly mapped to amino acid metabolism, starch and sucrose metabolism and secondary metabolism, and involved in transporter activity, antioxidant activities, and other gene ontology (GO). XZ149 had a higher capability of N absorption and use efficiency under LN stress than XZ56. The higher expression of nitrate transporters and energy-saving assimilation pattern could be attributed to its more N uptake and higher LN tolerance. In addition, auxin (IAA) and ethylene (ETH) response pathways may be also related to the genotypic difference in LN tolerance. The responses of XZ149 and XZ56 to LN stress differed dramatically at transcriptional level. The identified candidate genes related to LN tolerance may provide new insights into comprehensive understanding of the genotypic difference in N utilization and LN tolerance.

Stomata regulate photosynthesis and transpiration, and these processes are critical for plant responses to abiotic stresses such as salinity. A barley double haploid population with 108 lines derived from a cross between CM72 (salt-tolerant) and Gairdner (salt-sensitive) was used to detect quantitative trait loci (QTLs) associated with stomatal and photosynthetic traits related to salinity tolerance. A total of 11 significant QTLs (LOD > 3.0) and 11 tentative QTLs (2.5 < LOD < 3.0) were identified. These QTLs are distributed on all the seven chromosomes, except 5H and explain 9.5–17.3% of the phenotypic variation. QTLs for biomass, intercellular CO2 concentration, transpiration rate and stomatal conductance under control conditions co-localised together. A QTL for biomass also co-located with one for transpiration rate under salinity stress. A linkage was found between stomatal pore area and gas exchange. A QTL for salinity tolerance also co-localised with QTLs for grain yield and biomass on chromosome 3H. Based on the draft barley genome, the candidate genes for salinity tolerance at this locus are proposed. The lack of major QTLs for gas exchange and stomatal traits under control and saline conditions indicates a complex relationship between salinity and leaf gas exchange due to the fact that these complex quantitative traits are under the control of multiple genes.