Exogenous application of glycine betaine improved water use efficiency in winter wheat(Triticum aestivum L.) via modulating photosynthetic efficiency and antioxidative capacity under conventional and limited irrigation conditions

Improving water use efficiency(WUE)is an important subject in agricultural irrigation for alleviating the scarcity of water resources in semiarid regions of the North China Plain.Moreover,glycine betaine(GB)is one of the most effective compatible solutes synthesized naturally in plants for enhancing stress tolerance under abiotic stress,but little information is available on the involvement of GB in regulating crop WUE under field conditions.This study was conducted to explore the role of exogenously applied GB in improving WUE and plant physiological and biochemical responses inwinterwheat subjected to conventional or limited irrigation during the 2015–2016 and 2016–2017 growing seasons.Exogenous application of GB significantly enhanced antioxidant enzyme activities and reduced the accumulation ofmalondialdehyde and hydrogen peroxide under limited irrigation conditions.Furthermore,GB-treated plantsmaintained higher leaf relative water content andmembrane stability,which led to higher chlorophyll content and gas exchange attributes for better intrinsic and instantaneouswater use efficiencies compared to control plants under limited irrigation conditions.GB-treated plants had higher indole-acetic acid and zeatin riboside levels but lower ABA levels compared to control plants under conventional and limited irrigation conditions.Additionally,GB enhanced the grain filling rate and duration,grain number per spike,and final grainweight,which resulted in higher grain yield compared to the control.Interestingly,GB significantly improved the integrative and photosynthetic WUE under conventional and limited irrigation conditions,although GB treatment did not markedly affect total water consumption.These results suggest the involvement of GB in improving WUEs in winter wheat by modulating hormonal balance,membrane stability,photosynthetic performance and antioxidant systems to maintain higher grain yield under conventional and limited irrigation conditions.

Increase in root density induced by coronatine improves maize drought resistance in North China

Drought stress caused by insufficient irrigation or precipitation impairs agricultural production worldwide.In this study,a two-year field experiment was conducted to investigate the effect of coronatine(COR),a functional analog of jasmonic acid(JA),on maize drought resistance.The experiment included two water treatments(rainfed and irrigation),four COR concentrations(mock,0μmol L^(-1);A1,0.1μmol L^(-1);A2,1μmol L^(-1);A3,10μmol L^(-1))and two maize genotypes(Fumin 985(FM985),a drought-resistant cultivar and Xianyu 335(XY335),a drought-sensitive cultivar).Spraying 1μmol L^(-1)COR at seedling stage increased surface root density and size,including root dry matter by 12.6%,projected root area by 19.0%,average root density by 51.9%,and thus root bleeding sap by 28.2%under drought conditions.COR application also increased leaf area and SPAD values,a result attributed to improvement of the root system and increases in abscisic acid(ABA),JA,and salicylic acid(SA)contents.The improvement of leaves and roots laid the foundation for increasing plant height and dry matter accumulation.COR application reduced anthesis and silking interval,increasing kernel number per ear.COR treatment at 1μmol L^(-1)increased the yield of XY335 and FM985 by 7.9%and 11.0%,respectively.Correlation and path analysis showed that grain yields were correlated with root dry weight and projected root area,increasing maize drought resistance mainly via leaf area index and dry matter accumulation.Overall,COR increased maize drought resistance mainly by increasing root dry weight and root area,with 1μmol L-^(-1)COR as an optimal concentration.

Coronatine promotes maize water uptake by directly binding to the aquaporin ZmPIP2;5 and enhancing its activity

Water uptake is crucial for crop growth and development and drought stress tolerance. The water channel aquaporins(AQP) play important roles in plant water uptake. Here, we discovered that a jasmonic acid analog, coronatine(COR), enhanced maize(Zea mays) root water uptake capacity under artificial water deficiency conditions. COR treatment induced the expression of the AQP gene Plasma membrane intrinsic protein 2;5(ZmPIP2;5).In vivo and in vitro experiments indicated that COR also directly acts on ZmPIP2;5 to improve water uptake in maize and Xenopus oocytes. The leaf water potential and hydraulic conductivity of roots growing under hyperosmotic conditions were higher in ZmPIP2;5-overexpression lines and lower in the zmpip2;5 knockout mutant, compared to wild-type plants. Based on a comparison between ZmPIP2;5 and other PIP2s, we predicted that COR may bind to the functional site in loop E of ZmPIP2;5. We confirmed this prediction by surface plasmon resonance technology and a microscale thermophoresis assay, and showed that deleting the binding motif greatly reduced COR binding. We identified the N241 residue as the COR-specific binding site, which may activate the channel of the AQP tetramer and increase water transport activity,which may facilitate water uptake under hyperosmotic stress.