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Anthropogenic activities in the past and present eras have created global warming and consequently a storm of drought stress, affecting both plants and animals. Being sessile, plants are more vulnerable to drought stress and consequently reduce plant growth and yield. To mitigate the effects of drought stress on plants, it is very crucial to determine the plant response mechanisms against drought stress. Drought response mechanism includes morph-physiological, biochemical, cellular and molecular processes takes place in plants underlying drought stress. These processes include improvement in root system, leaf structure, osmotic adjustment, relative water content and stomata regulation. In addition, calcium and phytohormone (Abscisic acid, Jasmonic acid, Salicylic acid, Auxins, Gibberellins, Ethylene etc.) signaling pathways and scavenging of reactive oxygen species are the key mechanisms to cope with drought stress. Moreover, microorganisms such as bacteria and fungi also have an important role in drought tolerance enhancement. To further elucidate and improve drought tolerance in plants, quantitative trait loci, transgenic approach and application of exogenous substances (nitric oxide, 24-epibrassinoide, glycine betaine and proline) are very crucial. Hereby, the present study integrates various mechanisms of drought tolerance in plants. [ABSTRACT FROM AUTHOR]

Key message: This study shows mitigating effects achieved by exogenously applied melatonin in drought-stressed Davidia involucrata seedlings and demonstrates the reprogramming of gene networks related to melatonin-mediated drought stress response. Drought stress can have adverse effects on endangered plant species such as the dove tree (Davidia involucrata Baill.). Despite significant advances in uncovering the roles of melatonin in abiotic stress tolerance, the function of melatonin in the dove tree during drought stress is unknown. Here, we show the effects of exogenously applied melatonin on drought damage to D. involucrata seedlings. Melatonin pretreatment of dove tree seedlings was correlated with reduced membrane lipid peroxidation, suppressed production of drought-induced reactive oxygen species (ROS), and improved antioxidant capacity. Comparative RNA-Seq-based transcriptome profiling was employed to dissect the mechanistic basis of melatonin in drought response. We found that melatonin pretreatment resulted in differential expression of 2737 genes (1849 up-regulated and 888 down-regulated) under drought stress. Further detailed analysis suggested that melatonin modulates D. involucrata response to drought through fine-tuning of multiple phytohormone signaling and synthesis pathways, including transcriptional stimulation of auxin signaling-related genes and brassinosteroid biosynthetic genes. Moreover, phenylpropanoid biosynthesis and glutathione metabolism pathways were activated by melatonin, which could be linked to the observed enhancement of ROS scavenging capacity in melatonin-pretreated D. involucrata seedlings under drought condition. Additionally, melatonin-mediated drought stress response may involve activation of calcium signaling via up-regulating gene expressions of CNGC, CaM/CML, and CDPK family members. Collectively, this study yields insights into transcriptionally regulatory mechanisms of melatonin action under drought stress and provides a potential strategy for ex situ cultivation and landscape application of endangered ornamental tree species particularly in the context of global climate change. [ABSTRACT FROM AUTHOR]

An experiment was conducted to evaluate the effects of irrigation regimes (irrigation after 40 and 75% depletion of available soil water) and nitrogen levels (0 and 85 mg N kg−1 soil) on millet cultivars (Bastan and Pishahang) under two atmospheric CO2 concentrations (390 ± 50 and 700 ± 50 µmol mol−1). Evaluation of different biochemical traits at 50% flowering stage and measurement of dry matter weight at milk stage revealed that water shortage reduced shoot dry weight as the consequence of decreasing chlorophyll and carotenoid contents, leaf area, membrane stability index, and root dry weight but it increased not only the production of H2O2 but also MDA and antioxidant enzyme activities. Drought conditions with elevated levels of CO2 and nitrogen supply, however, partly relaxed limitations observed under water shortage conditions so that H2O2 and MDA production decreased but chlorophyll content and leaf area increased, leading to reduced loss of shoot dry weight. Increased CO2 had a greater effect on the reduction of ascorbate peroxidase and catalase in Bastan, while in Pishahang it had more effect on the reduction of malondialdehyde. Results showed that elevated CO2 and nitrogen supply depended for their effects on both irrigation regime and the genotype grown. [ABSTRACT FROM AUTHOR]

RD26 has ability of drought tolerance in dicotyledonous plants, but it is unknown if there are homologs of RD26s in monocotyledonous plants, and if they have ability of drought responses. Here we identified nine homologs of RD26s in maize, each harboring a conserved domain as signature of NAC-family genes. Phylogenetic analyses resulted in three distinct classes, namely Classes I, II and III, respectively. The maize RD26 genes show high divergence in expression, with Zm00001d043094_T001 and Zm00001d034601_T001 dominating expression among Class II genes, and Zm00001d042609_T001 highly were expressed in normal conditions among Class III genes. Three genes in Class II showed significant induction by BR, PEG and NaCl, among which Zm00001d012527_T001 was the most evident with 6.77-fold increase of expression 3 h after induction by PEG. The divergent expression under stresses in different classes of phylogeny suggests functional divergence of the RD26 genes in maize, with genes in Class II only likely be involved in positive response to abiotic stresses, and function as potential targets for future manipulation of maize capability to overcome adverse conditions of drought and salinity. [ABSTRACT FROM AUTHOR]

In this investigation, pot culture experiment was carried out to estimate the ameliorating effect of triazole compounds, namely Triadimefon (TDM), Tebuconazole (TBZ), and Propiconazole (PCZ) on drought stress, photosynthetic pigments, and biochemical constituents of Zea mays L. (Maize). From 30 days after sowing (DAS), the plants were subjected to 4 days interval drought (DID) stress and drought with TDM at 15 mg l, TBZ at 10 mg l, and PCZ at 15 mg l. Irrigation at 1-day interval was kept as control. Irrigation performed on alternative day. The plant samples were collected on 40, 50, and 60 DAS and separated into root, stem, and leaf for estimating the photosynthetic pigments and biochemical constituents. Drought and drought with triazole compounds treatment increased the biochemical glycine betaine content, whereas the protein and the pigments contents chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid, and anthocyanin decreased when compared to control. The triazole treatment mitigated the adverse effects of drought stress by increasing the biochemical potentials and paved the way to overcome drought stress in corn plant. [ABSTRACT FROM AUTHOR]

To understand the molecular responses of PC (Overexpressing the maize C4- pepc gene, which encodes phosphoenolpyruvate carboxylase (PEPC)), to drought stress at cell level, we analyzed changes in the levels of signaling molecules (hydrogen peroxide (H2O2), calcium ion (Ca2+), and nitric oxide (NO)) in suspension-cultured PC and wild-type (WT) rice ( Oryza sativa L.) cell under drought stress induced by 20% polyethylene glycol 6000 (PEG-6000). Results demonstrated that PC improved drought tolerance by enhancing antioxidant defense, retaining higher relative water content, survival percentages, and dry weight of cells. In addition, PEPC activity in PC under PEG treatment was strengthened by addition of H2O2 inhibitor, dimethylthiourea (DMTU) and NO synthesis inhibitor, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), respectively, while that in PC was weakened by addition of free calcium chelator, ethylene glycol-bis(b-aminoethylether)- N, N, N′, N′-tetraacetic acid (EGTA) + calcium channel outflow inhibitor, ruthenium red (RR) + plasma membrane channel blocker La(NO3)3, but EGTA + RR did not. Results also showed that NO and Ca2+ was lying downstream of H2O2 in drought-induced signaling. Calcium ion was also involved in the expression of C 4 -pepc in PC. These results suggested that PC could improve oxidative tolerance in suspension-cultured cells and the acquisition of this tolerance required downregulation of H2O2 and the entry of extracellular Ca2+ into cells across the plasma membrane for regulation of PEPC activity and C 4 -pepc expression. [ABSTRACT FROM AUTHOR]

The highly coordinated, dynamic nature of growth requires plants to perceive and react to various environmental signals in an interactive manner. Elaborate signaling networks mediate this plasticity in growth and the ability to adapt to changing environmental conditions. The fluctuations of stress-responsive hormones help alter the cellular dynamics and hence play a central role in coordinately regulating the growth responses under stress. Recent experimental data unequivocally demonstrated that interactions among various phytohormones are the rule rather than exception in integrating the diverse input signals and readjusting growth as well as acquiring stress tolerance. The presence of multiple and often redundant signaling intermediates for each phytohormone appears to help in such crosstalk. Furthermore, there are several examples of similar developmental changes occurring in response to distinct abiotic stress signals, which can be explained by the crosstalk in phytohormone signaling. Therefore, in this brief review, we have highlighted the major phytohormone crosstalks with a focus on the response of plants to abiotic stresses. The recent findings have made it increasingly apparent that such crosstalk will also explain the extreme pleiotropic responses elicited by various phytohormones. Indeed, it would not be presumptuous to expect that in the coming years this paradigm will take a central role in explaining developmental regulation. [ABSTRACT FROM AUTHOR]

Background: ERECTA (ER) is a leucine-rich repeat-receptor-like kinase gene (LRR-RLK) encoding a protein isolated from Arabidopsis. Although the regulatory functions of ER genes have been widely explored in plant development and disease resistance, their roles in drought stress responses remain to be clarified. Results: In this study, we cloned and characterized two ER genes, SbER1–1 and SbER2–1, from the drought-tolerant model plant sorghum (Sorghum bicolor L.). Under drought stress, the two genes were expressed in the leaves and stems but not in the roots, and SbER2–1 transcript accumulation in the stem was increased. SbER2–1 was localized both on the plasma membrane and in the chloroplast. Moreover, SbER2–1 expression in Arabidopsis and maize conferred increased drought tolerance, especially in regard to water-use efficiency, increasing the net photosynthetic rate in maize under drought stress. Based on RNA-Seq analysis together with the physiological data, we conclude that the transgenic maize plants have upregulated phenylpropanoid metabolism and increased lignin accumulation under drought stress. Conclusions: Our results demonstrate that SbER2–1 plays an important role in response to drought stress. Furthermore, photosynthetic systems and phenylpropanoid metabolism are implicated in SbER2–1-mediated drought stress tolerance mechanisms. The use of genetic engineering to regulate SbER2–1 expression in plants and to breed new varieties tolerant to drought is a research field full of potential. [ABSTRACT FROM AUTHOR]