New research on plant-water relations examines the molecular, structural, and physiological mechanisms of plant responses to their environment

Current Scenario and Future Prospects of Endophytic Microbes: Promising Candidates for Abiotic and Biotic Stress Management for Agricultural and Environmental Sustainability

Globally, substantial research into endophytic microbes is being conducted to increase agricultural and environmental sustainability. Endophytic microbes such as bacteria, actinomycetes, and fungi inhabit ubiquitously within the tissues of all plant species without causing any harm or disease. Endophytes form symbiotic relationships with diverse plant species and can regulate numerous host functions, including resistance to abiotic and biotic stresses, growth and development, and stimulating immune systems. Moreover, plant endophytes play a dominant role in nutrient cycling, biodegradation, and bioremediation, and are widely used in many industries. Endophytes have a stronger predisposition for enhancing mineral and metal solubility by cells through the secretion of organic acids with low molecular weight and metal-specific ligands (such as siderophores) that alter soil pH and boost binding activity. Finally, endophytes synthesize various bioactive compounds with high competence that are promising candidates for new drugs, antibiotics, and medicines. Bioprospecting of endophytic novel secondary metabolites has given momentum to sustainable agriculture for combating environmental stresses. Biotechnological interventions with the aid of endophytes played a pivotal role in crop improvement to mitigate biotic and abiotic stress conditions like drought, salinity, xenobiotic compounds, and heavy metals. Identification of putative genes from endophytes conferring resistance and tolerance to crop diseases, apart from those involved in the accumulation and degradation of contaminants, could open new avenues in agricultural research and development. Furthermore, a detailed molecular and biochemical understanding of endophyte entry and colonization strategy in the host would better help in manipulating crop productivity under changing climatic conditions. Therefore, the present review highlights current research trends based on the SCOPUS database, potential biotechnological interventions of endophytic microorganisms in combating environmental stresses influencing crop productivity, future opportunities of endophytes in improving plant stress tolerance, and their contribution to sustainable remediation of hazardous environmental contaminants.

SlERF52 regulates SlTIP1;1 expression to accelerate tomato pedicel abscission

Abscission of plant organs is induced by developmental signals and diverse environmental stimuli and involves multiple regulatory networks, including biotic or abiotic stress-impaired auxin flux in the abscission zone (AZ). Depletion of auxin activates AZ ethylene (ETH) production and triggers acceleration of abscission, a process that requires hydrogen peroxide (H2O2). However, the interaction between these networks and the underlying mechanisms that control abscission are poorly understood. Here, we found that expression of tonoplast intrinsic proteins, which belong to the aquaporin (AQP) family in the AZ was important for tomato (Solanum lycopersicum) pedicel abscission. Liquid chromatography-tandem mass spectrometry and in situ hybridization revealed that SlTIP1;1 was most abundant and specifically present in the tomato pedicel AZ. SlTIP1;1 localized in the plasma membrane and tonoplast. Knockout of SlTIP1;1 resulted in delayed abscission, whereas overexpression of SlTIP1;1 accelerated abscission. Further analysis indicated that SlTIP1;1 mediated abscission via gating of cytoplasmic H2O2 concentrations and osmotic water permeability (Pf). Elevated cytoplasmic levels of H2O2 caused a suppressed auxin signal in the early abscission stage and enhanced ETH production during abscission. Furthermore, we found that increasing Pf was required to enhance the turgor pressure to supply the break force for AZ cell separation. Moreover, we observed that SlERF52 bound directly to the SlTIP1;1 promoter to regulate its expression, demonstrating a positive loop in which cytoplasmic H2O2 activates ETH production, which activates SlERF52. This, in turn, induces SlTIP1;1, which leads to elevated cytoplasmic H2O2 and water influx.

Preferential Root Tropisms in 2D Wet Granular Media with Structural Inhomogeneities

We investigate certain aspects of the physical mechanisms of root growth in a granular medium and how these roots adapt to changes in water distribution induced by the presence of structural inhomogeneities in the form of solid intrusions. Physical intrusions such as a square rod added into the 2D granular medium maintain robust capillary action, pumping water from the more saturated areas at the bottom of the cell towards the less saturated areas near the top of the cell while the rest of the medium is slowly devoid of water via evaporation. The intrusion induces "preferential tropism" of roots by first generating a humidity gradient that attracts the root to grow towards it. Then it guides the roots and permits them to grow deeper into more saturated regions in the soil. This further allows more efficient access to available water in the deeper sections of the medium thereby resulting to increased plant lifetime.

Physiological and Dry Matter Characteristics of Spring Maize in Northeast China under Drought Stress

This paper examined impacts of drought on both physiological and dry matter characteristics of spring maize grown in Liaoning, China in 2016. We compared responses of dry matters of various parts, yield components, leaf photosynthesis, and transpiration to four drought levels: RD (no drought treatment), D1 (drought treatment between the 38th and 65th day after sowing), D2 (drought treatment between the 38th and 79th day after sowing), and D3 (drought treatment between the 53rd and 93rd day after sowing). Results indicate that the long-term drought in either jointing period or tasseling period had a severer impact on the dry matters and yield components than the short-term drought in jointing period. Moreover, the dry matters and the corresponding partitioning coefficients of different parts were distinct. The yield reduction was caused by the decreases of ear length and bald tip ratio during the short-term drought at jointing period, while it was caused by the reductions of ear length, ear diameter, and grain number per spike during the long-term drought in jointing and tasseling periods. Responses of leaf photosynthesis and transpiration to drought were lagging, but reactions of tasseling drought were faster. Leaf photosynthesis and transpiration after a short-term drought in jointing period could recover to an average level but that after the long-term drought in either jointing or tasseling period could not, after irrigation.

Plant hydraulics as a central hub integrating plant and ecosystem function: meeting report for 'Emerging Frontiers in Plant Hydraulics' (Washington, DC, May 2015)

Water plays a central role in plant biology and the efficiency of water transport throughout the plant affects both photosynthetic rate and growth, an influence that scales up deterministically to the productivity of terrestrial ecosystems. Moreover, hydraulic traits mediate the ways in which plants interact with their abiotic and biotic environment. At landscape to global scale, plant hydraulic traits are important in describing the function of ecological communities and ecosystems. Plant hydraulics is increasingly recognized as a central hub within a network by which plant biology is connected to palaeobiology, agronomy, climatology, forestry, community and ecosystem ecology and earth-system science. Such grand challenges as anticipating and mitigating the impacts of climate change, and improving the security and sustainability of our food supply rely on our fundamental knowledge of how water behaves in the cells, tissues, organs, bodies and diverse communities of plants. A workshop, 'Emerging Frontiers in Plant Hydraulics' supported by the National Science Foundation, was held in Washington DC, 2015 to promote open discussion of new ideas, controversies regarding measurements and analyses, and especially, the potential for expansion of up-scaled and down-scaled inter-disciplinary research, and the strengthening of connections between plant hydraulic research, allied fields and global modelling efforts.

Transpirational demand affects aquaporin expression in poplar roots

Isohydric plants tend to maintain a water potential homeostasis primarily by controlling water loss via stomatal conductance. However, there is accumulating evidence that plants can also modulate water uptake in a dynamic manner. The dynamics of water uptake are influenced by aquaporin-mediated changes in root hydraulics. Most studies in this area have been conducted on herbaceous plants, and less is known about responses of woody plants. Here a study was conducted to determine how roots of hybrid poplar plants (Populus trichocarpa×deltoides) respond to a step change in transpirational demand. The main objective was to measure the expression of selected aquaporin genes and to assess how transcriptional responses correspond to changes in root water flow (Q R) and other parameters of water relations. A subset of plants was grown in shade and was subsequently exposed to a 5-fold increase in light level. Another group of plants was grown at ~95% relative humidity (RH) and was then subjected to lower RH while the light level remained unchanged. Both plant groups experienced a transient drop in stem water potentials. At 28h after the increase in transpirational demand, water potentials recovered. This recovery was associated with changes in the expression of PIP1 and PIP2 subfamily genes and an increase in Q R. Stomata of plants growing at high RH were larger and showed incomplete closure after application of abscisic acid. Since stomatal conductance remained high and unchanged in these plants, it is suggested that the recovery in water potential in these plants was largely driven by the increase in Q R.