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The considerable drought tolerance of wild cereal crop progenitors has diminished during domestication in the pursuit of higher productivity. Regaining this trait in cereal crops is essential for global food security but requires novel genetic insight. Here, we assessed the molecular evidence for natural variation of drought tolerance in wild barley (Hordeum spontaneum), wild emmer wheat (Triticum dicoccoides), and Brachypodium species collected from dry and moist habitats at Evolution Canyon, Israel (ECI). We report that prevailing moist vs dry conditions have differentially shaped the stomatal and photosynthetic traits of these wild cereals in their respective habitats. We present the genomic and transcriptomic evidence accounting for differences, including co-expression gene modules, correlated with physiological traits, and selective sweeps, driven by the xeric site conditions on the African Slope (AS) at ECI. Co-expression gene module 'circadian rhythm' was linked to significant drought-induced delay in flowering time in Brachypodium stacei genotypes. African Slope-specific differentially expressed genes are important in barley drought tolerance, verified by silencing Disease-Related Nonspecific Lipid Transfer 1 (DRN1), Nonphotochemical Quenching 4 (NPQ4), and Brassinosteroid-Responsive Ring-H1 (BRH1). Our results provide new genetic information for the breeding of resilient wheat and barley in a changing global climate with increasingly frequent drought events.

This study aimed to reveal the mechanistic basis of the melatonin-mediated amelioration of salinity stress in plants. Electrophysiological experiments revealed that melatonin decreased salt-induced K+ efflux (a critical determinant of plant salt tolerance) in a dose- and time-dependent manner and reduced sensitivity of the plasma membrane K+-permeable channels to hydroxyl radicals. These beneficial effects of melatonin were abolished by NADPH oxidase blocker DPI. Transcriptome analyses revealed that melatonin induced 585 (448 up- and 137 down-regulated) and 59 (54 up- and 5 down-regulated) differentially expressed genes (DEGs) in the root tip and mature zone, respectively. The most noticeable changes in the root tip were melatonin-induced increase in the expression of several DEGs encoding respiratory burst NADPH oxidases (OsRBOHA and OsRBOHF), calcineurin B-like/calcineurin B-like-interacting protein kinase (OsCBL/OsCIPK), and calcium-dependent protein kinase (OsCDPK) under salt stress. Melatonin also enhanced the expression of potassium transporter genes (OsAKT1, OsHAK1, and OsHAK5). Taken together, these results indicate that melatonin improves salt tolerance in rice by enabling K+ retention in roots, and that the latter process is conferred by melatonin scavenging of hydroxyl radicals and a concurrent OsRBOHF-dependent ROS signalling required to activate stress-responsive genes and increase the expression of K+ uptake transporters in the root tip.

Efforts to breed salt tolerant crops could benefit from investigating previously unexplored traits. One of them is a tissue succulency. In this work, we have undertaken an electrophysiological and biochemical comparison of properties of mesophyll and storage parenchyma leaf tissues of a succulent halophyte species Carpobrotus rosii ("pigface"). We show that storage parenchyma cells of C . rossii act as Na + sink and possessed both higher Na + sequestration (298 vs. 215 mM NaCl in mesophyll) and better K + retention ability. The latter traits was determined by the higher rate of H + ‐ATPase operation and higher nonenzymatic antioxidant activity in this tissue. Na + uptake in both tissues was insensitive to either Gd 3+ or elevated Ca 2+ ruling out involvement of nonselective cation channels as a major path for Na + entry. Patch‐clamp experiments have revealed that Caprobrotus plants were capable to downregulate activity of fast vacuolar channels when exposed to saline environment; this ability was higher in the storage parenchyma cells compared with mesophyll. Also, storage parenchyma cells have constitutively lower number of open slow vacuolar channels, whereas in mesophyll, this suppression was inducible by salt. Taken together, these results provide a mechanistic basis for efficient Na + sequestration in the succulent leaf tissues.

Aphid, a short germband insect, displays an embryogenesis different from that of long germband insect species. Furthermore, the development of its parthenogenetic and viviparous embryo is different from that of the embryo resulting from sexual reproduction. To better understand the genetic regulation of this type of embryogenesis, the functions of hunchback in asexual Acyrthosiphon pisum were investigated by parental RNAi. Microinjection of Aphb double-stranded RNA yielded several defective phenotypes. Quantitative real-time PCR analysis revealed that these defects resulted from reduction of Aphb mRNA level in injected aphids. All these results suggested that the hb gene in parthenogenetic and viviparous Acyrthosiphon pisum was involved in abdominal identity suppression and germband growth as its homologue does in sexual insects.

Salt sensitive (pea) and salt tolerant (barley) species were used to understand the physiological basis of differential salinity tolerance in crops. Pea plants were much more efficient in restoring otherwise depolarized membrane potential thereby effectively decreasing K+ efflux through depolarization-activated outward rectifying potassium channels. At the same time, pea root apex was 10-fold more sensitive to physiologically relevant H2O2 concentration and accumulated larger amounts of H2O2 under saline conditions. This resulted in a rapid loss of cell viability in the pea root apex. Barley plants rapidly loaded Na+ into the xylem; this increase was only transient, and xylem and leaf Na+ concentration remained at a steady level for weeks. On the contrary, pea plants restricted xylem Na+ loading during the first few days of treatment but failed to prevent shoot Na+ elevation in the long term. It is concluded that superior salinity tolerance of barley plants compared with pea is conferred by at least three different mechanisms: (1) efficient control of xylem Na+ loading; (2) efficient control of H2O2 accumulation and reduced sensitivity of non-selective cation channels to H2O2 in the root apex; and (3) higher energy saving efficiency, with less ATP spent to maintain membrane potential under saline conditions.

BACKGROUND: Aphids are insect pests with significant importance worldwide for agricultural and horticultural crops. The chemical pesticides used to control aphids could result in pesticide residues in agricultural and horticultural products as well as in negative effects on the environment. Therefore, alternative control methods are urgently needed. This study identified a new gene from strain BJFS526 of the symbiotic bacterium Xenorhabdus bovienii and expressed the protease inhibitor protein encoded by the gene. The effects of the protein on the pea aphids, Acyrthosiphon pisum, were also investigated. RESULTS: The gene PIN1 encoding the protease inhibitor protein against aphids was successfully cloned from BJFS526. The study demonstrated that the protein had adverse effects on pea aphid survival, and that the activity of aphid aminopeptidase was significantly inhibited by the protein. CONCLUSION: The results from this study suggest that this gene and the protease inhibitor protein encoded may offer an alternative method to control aphids in the future. Copyright © 2012 Society of Chemical Industry

The subcellular distribution and chemical forms of different heavy metals in rice are correlated with their bio-toxicity. An experiment was conducted to investigate the subcellular distribution and chemical forms of chromium (Cr) in two rice genotypes (Oryza sativa L. cv. Xiushui 113 and cv. Dan K5) differing in Cr accumulation, to understand the mechanisms of Cr toxicity and resistance in rice plants. The results show that Cr in the roots of rice plants exposed to Cr stress was mainly localized in cell walls, whereas Cr in leaves and stems was mainly present in both cell walls and vacuoles, suggesting that both compartments act as important protective barriers against Cr toxicity in rice plants. Although Cr ions in all plant tissues exist predominantly in the forms extracted by 80% ethanol and distilled water, the amount of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues was significantly increased under the highest Cr level (100 μM Cr) compared to the plants grown under lower Cr levels. These results indicate that excess Cr accumulated in rice plants under Cr stress is bound to undissolved or low-bioavailable compounds, such as undissolved phosphate and oxalate, being beneficial for rice plants to alleviate Cr toxicity. In addition, under the highest Cr level (100 μM), Dan K5 had a higher percentage of Cr in the chemical forms extracted by 2% HAc, 0.6 M HCl, and in residues compared to Xiushui 113 in both stems and leaves, indicating that more Cr ions in shoots of Dan K5 were bound to undissolved or low-bioavailable compounds, in comparison with those of Xiushui 113. It is evident that the low bioavailability of Cr in the shoots of Dan K5 is related to a high Cr accumulation.

A hydroponic experiment was carried out to study effects of chromium (Cr) stress on the subcellular distribution and chemical form of Ca, Mg, Fe, and Zn in two rice genotypes differing in Cr accumulation. The results showed that Ca, Mg, Fe, and Zn ions were mainly located in cell walls and vacuoles in roots. However, large amounts of metal ions were transferred from the vacuole to the nucleus and to other functional organelles in shoots. Chromium concentrations in the nutrient solution of 50 lM and above significantly decreased Ca concentrations in the chloroplast/trophoplast, the nucleus, and in mitochondria. It further increased Mg concentrations in the nucleus and in mitochondria, as well as Zn and Fe concentrations in the chloroplast/trophoplast. These Cr-induced changes in ion concentrations were associated with a significant reduction in plant biomass. It is suggested that Cr stress interferes with the functions of mineral nutrients in rice plants, thus causing a serious inhibition of plant growth. The chemical forms of the four nutrients were determined by successive extraction. Except for Ca, which was mainly chelated with insoluble phosphate and oxalic acid, Mg, Zn, and Fe were extractable by 80% ethanol, d-H2O, and 1lM NaCl. The results indicated that these low–molecular weight compounds, such as organic acids and amino acids, may play an important role in deposition and translocation of Mg, Zn, and Fe in the xylem system of rice plants.

Oxygen deprivation is a key determinant of root growth and functioning under waterlogging. In this work, changes in net K+ flux and membrane potential (MP) of root cells were measured from elongation and mature zones of two barley varieties under hypoxia and anoxia conditions in the medium, and as influenced by ability to transport O2 from the shoot. We show that O2 deprivation results in an immediate K+ loss from roots, in a tissue- and time-specific manner, affecting root K+ homeostasis. Both anoxia and hypoxia induced transient membrane depolarization; the extent of this depolarization varied depending on severity of O2 stress and was less pronounced in a waterlogging-tolerant variety. Intact roots of barley were capable of maintaining H+-pumping activity under hypoxic conditions while disrupting O2 transport from shoot to root resulted in more pronounced membrane depolarization under O2-limited conditions and in anoxia a rapid loss of the cell viability. It is concluded that the ability of root cells to maintain MP and cytosolic K+ homeostasis is central to plant performance under waterlogging, and efficient O2 transport from the shoot may enable operation of the plasma membrane H+-ATPase in roots even under conditions of severe O2 limitation in the soil solution.