Sugarcane genes differentially expressed during water deficit

Although regulated deficit irrigation may improve crop yields, little research has been conducted on the effects of water deficits on Isatis indigotica, a popular herbal medicine. Field experiments were conducted in 2016 and 2017 to study the effects of regulated deficit irrigation on the net photosynthetic rate, yield, water use efficiency (WUE), and quality of I. indigotica in northwest China. Plants at the vegetative and fleshy root growth stages were subjected to mild, moderate, and severe water deficits, and their photosynthetic physiological indexes, yield, and WUE were measured. Moderate and severe deficits, but not a mild deficit, significantly decreased the net photosynthetic rate and dry matter accumulation. The yield and WUE under mild deficit were markedly higher, reaching 8239.56 kg·ha−2 and 8390.80 kg·ha−2, respectively, in the vegetative stage and 24.11 kg·ha−2·mm−1 and 23.62 kg·ha−2·mm−1, respectively, in the fleshy root growth stage, while severe deficits significantly reduced yield and WUE. Mild and moderate deficits increased the content of (R,S)-goitrin, indirubin, and indigo, improving root quality, but severe deficits decreased these compounds. Therefore, a mild water deficit in the vegetative and fleshy root growth stages is optimal and can reduce water consumption and improve I. indigotica quality and WUE without reducing yield.

In arid regions, deficit irrigation stands as an efficacious strategy for augmenting agricultural water conservation and fostering sustainable crop production. The Hexi Oasis, an irrigation zone situated in Northwest China, serves as a pivotal area to produce grain and cash crops. Nonetheless, due to the predominant conditions of low rainfall and high evaporation, the scarcity of irrigation water has emerged as a critical constraint affecting crop growth and yield in the area. In order to evaluate the effects of deficit irrigation on photosynthetic characteristics, yield, quality, and water use efficiency of sunflower, a two-year field experiment with under-mulched drip irrigation was conducted in the cold and arid environment of the Hexi Oasis region. Water deficits were implemented at sunflower seedling and maturity and consisted of three deficit levels: mild deficit (65-75% field capacity, FC), moderate deficit (55-65% FC), and severe deficit (45-55% FC). A total of six combined water deficit treatments were applied, using full irrigation (75-85% FC) throughout the entire crop-growing season as the control (CK). The results illustrated that water deficit engendered a decrease in leaf net photosynthetic rate, transpiration rate, and stomatal conductance of sunflower compared to CK, with the decrease becoming significant with the water deficit increasing. A mild water deficit, both at the seedling and maturity phases, precipitated a significant enhancement (p< 0.05) in leaf water use efficiency. Under mild water deficit, stomatal limitation emerged as the predominant factor inducing a reduction in the photosynthetic capacity of sunflower leaves, while as the water deficit escalated, non-stomatal limitation progressively assumed dominance. Moreover, a mild/moderate water deficit at seedling and a mild water deficit at maturity (WD1 and WD3) significantly improved sunflower seed quality under consistent yield conditions and significantly increased irrigation water use efficiency, with an average increase of 15.3% and 18.5% over the two years, respectively. Evaluations utilizing principal component analysis and membership function methods revealed that WD1 attained the highest comprehensive score. Consequently, a mild water deficit at both seedling and maturity (WD1) is advocated as the optimal deficit irrigation strategy for sunflower production within the cold and arid environment of Northwest China.

Abscisic acid (ABA) plays a central role in the plant response to water deficit by inducing stomatal closure to conserve water when the soil dries. Exogenous ABA was applied at 45 days after sowing (DAS) as a soil drench, the physiological and seed yield response of soybean to exogenous ABA were examined as the soil was drying. Three experiments were conducted using the drought-tolerant soybean cultivar Jindou 19, grown in pots at the Yuzhong Experimental Station of Lanzhou University, China. In experiment 1, plants were exposed to progressive soil drying and leaf ABA concentration, leaf photosynthesis rate, leaf relative water content (RWC) and osmotic adjustment (OA) were measured. In experiment 2, plants were under progressive soil drying and lethal leaf water potential was measured. In experiment 3, flower production and abortion, and grain yield were measured in plants under well-watered (WW), moderate (MWD) and severe water deficits (SWD). Exogenous ABA application increased ABA accumulation in leaves and reduced the rate of soil drying. It also increased leaf photosynthetic rate, stomatal conductance and transpiration rate at 7–10 days after withholding water. The intrinsic and instantaneous water use efficiency (WUE) was consistently higher with exogenous ABA than without ABA as the soil dried. Exogenous ABA increased OA when the leaf relative water content (RWC) decreased at eight days after withholding water, lowering the lethal leaf water potential by 0.4 MPa. Exogenous ABA reduced water use, increased WUE for grain yield under WW and MWD, and had no effect on flower number, flower abortion or grain yield in any water treatment. We concluded that (1) exogenous ABA induced OA, improved leaf photosynthetic rate, leaf water relations and desiccant tolerance, but did not benefit grain yield in soybean under water deficits; (2) exogenous ABA improved the WUE at the leaf level as soil drying and WUE for grain yield under moderate water deficit.

To clarify the photoprotective mechanisms of cotton leaves under water deficit in the field, leaf gas exchange, chlorophyll a fluorescence as well as the corresponding physiological responses were examined in cotton (Gossypium hirsutum L.) to evaluate electron flux distribution. With increasing water deficit, net photosynthetic rate (Pn) significantly decreased, the total electron flux through PSII [Je(PSII)] gradually decreased and the fraction of electron flux required to sustain CO2 assimilation [Je(PCR)] markedly declined. Simultaneously, the ratio of quantum efficiency of PSII [Φ(PSII)] to the quantum efficiency of CO2 fixation [Φ(CO2)] increased, accompanied by an increase in the alternative electron flux (Ja). The enhanced alternative electron flux of O2-dependent Ja(O2-dependent) indicated that electrons had been transported to O2 in the Mehler-peroxide reaction (MPR) and that the remaining alternative electron flux Ja(O2-independent) had been used for nitrate reduction, as indicated by an increase in nitrate reductase (NR) and glutathinone reductase (GR) activities. In addition, mild water deficit increased the proportion of electron flux for the photorespiratory carbon oxidation [Je(PCO)]. Water deficit significantly increased surperoxide radical production rate (O2-•) and hydrogen peroxide content (H2O2), and the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and catalase (CAT) in cotton leaves also increased under water deficit. Therefore, the Mehler-peroxidation reaction, photorespiration and nitrate reduction helped to dissipated excess light energy, being important photoprotective mechanisms for adapting the photosynthetic apparatus to mild and moderate water deficit in cotton.

Current forest planting in Queensland, Australia, is concentrated in the humid coastal zone with mean annual rainfall greater that 1000 mm. However, further expansion will be concentrated in a lower rainfall (600 to 1000 mm) zone, for which Eucalyptus cloeziana F.Muell. and Eucalyptus argophloia Blakely are favoured native species. This study investigated ecophysiological characteristics of E. argophloia (dry inland), and dry inland and coastal (humid) provenances of E. cloeziana in response to changes in soil water availability, temperature, photon flux density and vapour pressure deficit as an aid to site-species matching for this plantation enterprise. Effects of water stress duration and intensity on gas exchange, leaf water relations, water use efficiency and biomass production were investigated in potted seven-month-old seedlings supplied with 100% (W100), 70% (W70), 50% (W50) of water required daily to restore field capacity or were watered when they were wilted at dawn (W0). At W100, E. argophloia had the highest midday net photosynthetic rate (A), stomatal conductance (gs), stomatal density and predawn leaf water potential (Ppd). The E. cloeziana provenances did not differ in these attributes. The W70 and W50 treatments reduced A by 30% in E. argophloia argophloia, and by 55% in the E. cloeziana provenances. Following stress relief both A and gs recovered more quickly in E. argophloia and in the inland provenance of E. cloeziana than in the humid provenance. Leaf water relations analyses revealed lower relative water content at turgid loss point, apoplastic water content, ratio of dry weight to turgid weight and bulk modulus of elasticity in both the dry and humid provenances of E. cloeziana than in E. argophloia. The E. cloeziana provenances maintained turgor at moderate water deficits by a combination of osmotic and elastic adjustments whereas E. argophloia had more rigid cell walls and reached lower water potentials at a higher relative water content. Eucalyptus argophloia produced twice as much biomass at W100, more than three times as much at W70 and W50, and allocated 10% more biomass to roots than did either E. cloeziana provenance. The humid provenance of E. cloeziana had a greater leaf area at W100 than the dry provenance but both suffered extensive leaf loss under severe water deficits. Biomass allocation patterns were significantly affected by genotype but not by soil water availability. Transpiration efficiency (dry weight gain/transpiration, WUET) did not differ between provenances at W100, but was significantly higher in E. argophloia than in either E. cloeziana provenance as available soil moisture decreased. Midday instantaneous water use efficiency (net assimilation/transpiration, WUEi) was lowest in E. argophloia. Carbon isotope composition (d13C) values for E. argophloia in all three water regimes were significantly lower than those of E. cloeziana provenances, which did not differ significantly. For all three provenances, d13C was not correlated with WUEi or WUET. Acclimation of gas exchange to temperature and light was determined in 18-month-old potted plants grown at day/night temperatures of 18/13, 23/18, 28/23 and 33/28 dC in controlled-temperature glasshouses for four months. There were no significant differences in the shape and quantum yield parameters of light response curves among provenances at 23, 28 and 33 dC day temperatures. Average values of dark respiration for the three provenances ranged from 0.61 to 1.86 mmol -2 s-1. The optimum temperatures for net photosynthesis increased from 23 to 32 dC for the humid and 25 to 33 dC for the dry provenances of E. cloeziana and from 21 to 33 dC for E. argophloia as daytime temperature of the growth environment increased from 18 to 33 dC. Physiological responses to diurnal and seasonal changes in soil water availability, leaf temperature and leaf-to-air vapour pressure deficit (VPD) were investigated in four-year-old trees in field plantings in southeast Queensland. Water relations of Eucalyptus argophloia and the Hungry Hills provenance of E. cloeziana suggested possible access to water at depth. Prediction models for net photosynthesis and phenomenological models of stomatal conductance explained 60 to 80% of observed variation in A and gs. E. argophloia has potential for plantation forestry in the humid and subhumid tropics, shown by high dry matter production rates under both high and low soil water availability in the glasshouse environment. Leaf water relations suggested that the relatively low cell wall elasticity, the maintenance of high relative water content and development of a large soil-plant water potential gradient were important characteristics in maintaining a large foliage mass under water limiting conditions in E. argophloia. E. cloeziana has considerable potential for use in plantations in humid conditions, but has limited potential under moderate and severe water deficit conditions. This is demonstrated by the ability of the species to produce large leaf area and high ratio of above to below ground biomass allocation under moist conditions but an inability to maintain that leaf area under water deficit conditions.n

Water scarcity is the most significant factor limiting coffee production, although some cultivars can still have important drought tolerance. This study analyzed leaf transcriptomes of two coffee cultivars with contrasting physiological responses, Coffea canephora cv. CL153 and Coffea. arabica cv. Icatu, subjected to moderate (MWD) or severe water deficits (SWD). We found that MWD had a low impact compared with SWD, where 10% of all genes in Icatu and 17% in CL153 reacted to drought, being mainly down-regulated upon stress. Drought triggered a genotype-specific response involving the up-regulation of reticuline oxidase genes in CL153 and heat shock proteins in Icatu. Responsiveness to drought also included desiccation protectant genes, but primarily, aspartic proteases, especially in CL153. A total of 83 Transcription Factors were found engaged in response to drought, mainly up-regulated, especially under SWD. Together with the enrollment of 49 phosphatases and 272 protein kinases, results suggest the involvement of ABA-signaling processes in drought acclimation. The integration of these findings with complementing physiological and biochemical studies reveals that both genotypes are more resilient to moderate drought than previously thought and suggests the existence of post-transcriptional mechanisms modulating the response to drought.

SummaryThe degree of drought tolerance exhibited by a plant is related to its ability to respond to adverse conditions. To determine if it is possible to alter this capacity in potted miniature roses (Rosa x hybrida), plants were produced with reduced water availability during the six weeks prior to flowering. The response of two rose cultivars to a cyclic non-lethal water deficit treatment (moderate water deficit with 5.d stress and 5.d recovery) and two long-term steady-state water deficit treatments at 60% (severe water deficit) and 75% (moderate water deficit) water availability, were compared. All plants produced with water deficit were more compact than control plants and the cyclic-grown plants most closely resembled commercially produced plants. Whilst all drought treatments significantly reduced the number of buds at flowering, time to flowering was not influenced by the treatments. Moderately stressed plants maintained leaf numbers but reduced the size of the individual leaves by 20%. In contrast the severely drought stressed plants reduced both leaf number and total leaf area by 40%; consequently individual leaf size was maintained. Total daily water consumption per unit leaf area was reduced only under severe stress. However, all plants grown with reduced water availability significantly reduced dark transpiration rates as a percentage of light transpiration, with the cyclic-grown plants being the most efficient. During recovery the cyclic plants restored stomatal conductance and photosynthesis to rates comparable with control plants. All plants produced with reduced water availability were more efficient in dry-matter production per volume of water consumed as compared with controls. The response of potted miniature roses to steady-state versus cyclic water-deficit treatments is discussed.

Water deficit limits the establishment of sugarcane plants from pre-sprouted seedlings (PSS). Silicon (Si) can mitigate such stress, and your supply in plants with the active absorption mechanism is carried out through roots. However, foliar spraying has been practiced to supply Si in PSS production nurseries. Althought it is known that Si via roots can alter C: N: P ratios, nothing has been reported about its supply via foliar spraying, nor whether such changes interfere with structural nutrient use efficiency and with plant physiological responses. Thus, this study aimes to asses whether Si foliar spraying changes C: N: P ratios and increases the nutritional efficiency of PSS, as well as whether water deficiency interferes with such a relationships. For these purposes, three experiments were carried out. In experiment I, treatments consisted of two sugarcane cultivars (CTC 4 and RB 966928) and three Si supply forms (in nutrient solution via roots [SiR], via foliar spraying [SiL], and one control with the absence of Si [-Si]). The same Si supply forms were used in the other two experiments. In experiment II, a short-term water deficit was induced by polyethylene glycol addition to nutrient solution (-0.6 MPa) for three days. In experiment III, a long-term water deficit was imposed using levels of soil water retention capacity (70% [no water deficit], 50% [moderate water deficit], and 30% [severe water deficit] for 30 days. Our findings revealed that Si supply decreased C concentrations regardless of water conditions and that N and P concentrations varied with Si supply form and water deficit level. Moreover, root- and foliar-applied Si modified the C: N: P stoichiometry and increased C use efficiency in PSS, which thus increased N and P use efficiencies. Such an increased nutritional performance helped adjust physiological parameters and increase dry matter yield in PSS, both under water stress and non-stress conditions. Further, Si foliar spraying promoted structural effects on PSS regardless of water conditions, even if sugarcane has an active absorption via roots. In conclusion, foliar spraying can be used to supply Si in PSS production nurseries.

Grapefruit mint, Mentha suaveolens × M. piperita, belonging to the Lamiaceae family, is an important medicinal plant with applications in the cosmetic, pharmaceutical, food, and nutraceutical industries. Environmental factors such as cold, salinity, and water deficit significantly impact the quantity and quality of the active compounds of medicinal plants. To examine the effects of drought stress and β-aminobutyric acid (BABA) as an elicitor on the biochemical characteristics and essential oil (EO) profile of grapefruit mint, a factorial experiment was conducted in a completely randomized design (CRD) with two factor and three replications under greenhouse conditions. The first factor included field moisture capacity (FC) as the control (100% FC), mild (75% FC), moderate (55% FC), and severe water deficit stress (35% FC), while the second factor consisted of 0 (control plants without BABA), 0.8, 1.6, and 2.4 mM of BABA foliar application. Water stress and BABA application significantly affected the EO content and composition of grapefruit mint. The highest content of EO was observed in mild drought stress and BABA spraying at 1.6 to 2.4 mM, which increased by about 140% compared with the control condition. The EO components were identified using GC-FID and GC-MS analysis. Linalool (33.7–47.3%) and linalool acetate (31.2–52%) were the most abundant compounds. The highest content of linalool acetate was observed in severe drought stress (35% FC) with foliar application of BABA (1.6 mM), which increased by 33.86% compared with the control condition. However, the highest content of linalool was observed under normal irrigation with foliar application of 0.8 to 1.6 mM BABA. Based on the results, severe drought stress reduced the total chlorophyll and carotenoids by 81.76 and 64.6% compared with the control condition, respectively. Water stress and the foliar application of BABA significantly affected the activity of antioxidant enzymes (ascorbate peroxidase, APX; guaiacol peroxides, GPX; and superoxide dismutase, SOD). The application of 1.6 mM BABA significantly increased the activity of antioxidant enzymes under water stress conditions. Finally, our results showed that the application of BABA (mainly at 1.6 mM) can improve the grapefruit mint yield and EO profile under water stress conditions.

Response of a plurispecific permanent grassland to border irrigation regulated by tensiometers

The effect of postveraison water deficit on the phenolic composition and concentration of the Kékfrankos (Vitis vinifera L.) berry

This study evaluates physiological aspects of two peanut cultivars ( Arachis hypogaea L. IAPAR 25 Tição and IAC Tatu ST) grown under water regimes in order to verify drought tolerance. The randomized block experi­mental design was used in a 2 x 3 factorial design (two cultivars and three water regimes). The water regimes were, namely: control, in which plants were maintained at field capacity conditions (FC - without water deficit); moderate water deficit (MD - 50% of water deficit); and severe water deficit (SD - 75% of water deficit) in relation to control. Relative water content, gas exchange, dry matter, and leaf proline content were analyzed. Both cultivars developed physiological mechanisms of acclimatization to water deficit, such as reducing leaf relative water content, CO 2 assimilation rate, stomatal conductance, and transpiration in the initial period of water deficit, besides increasing proline production. Such physiological changes negatively affected dry matter accumulation in the grains and the number of grains, as well as dry matter accumulation in shoots and roots.

The implementation of phytoremediation strategies under arid and semiarid climates requires the use of appropriate plant species capable of withstanding multiple abiotic stresses. In this study, we assessed the combined effects of organo-mineral amendments and microbial inoculants on the chemical and biological properties of mine tailings, as well as on the growth of native plant species under drought stress conditions. Plants were cultivated in pots containing 1 kg of a mixture of mine tailings and topsoil (i.e., pre-mined superficial soil) in a 60:40 ratio, 6% marble sludge, and 10% sheep manure. Moreover, a consortium of four drought-resistant plant growth-promoting rhizobacteria (PGPR) was inoculated. Three irrigation levels were applied: well-watered, moderate water deficit, and severe water deficit, corresponding to 80%, 45%, and 30% of field capacity, respectively. The addition of topsoil and organo-mineral amendments to mine tailings significantly improved their chemical and biological properties, which were further enhanced by bacterial inoculation and plants’ establishment. Water stress negatively impacted enzymatic activities in amended tailings, resulting in a significant decrease in acid and alkaline phosphatases, urease, and dehydrogenase activities. Similar results were obtained for bacteria, fungi, and actinomycete abundance. PGPR inoculation positively influenced the availability of phosphorus, total nitrogen, and organic carbon, while it increased alkaline phosphatase, urease (by about 10%), and dehydrogenase activity (by 50%). The rhizosphere of Peganum harmala showed the highest enzymatic activity and number of culturable microorganisms, especially in inoculated treatments. Severe water deficit negatively affected plant growth, leading to a 40% reduction in the shoot biomass of both Atriplex halimus and Pennisetum setaceum compared to well-watered plants. P. harmala showed greater tolerance to water stress, evidenced by lower decreases observed in root and shoot length and dry weight compared to well-watered plants. The use of bioinoculants mitigated the negative effects of drought on P. harmala shoot biomass, resulting in an increase of up to 75% in the aerial biomass in plants exposed to severe water deficit. In conclusion, the results suggest that the combination of organo-mineral amendments, PGPR inoculation, and P. harmala represents a promising approach to enhance the phytoremediation of metal-polluted soils under semiarid conditions.

Chapter 7 - Drought stress memory and subsequent drought stress tolerance in plants

Predictive models of drought tolerance indices based on physiological, morphological and biochemical markers for the selection of cotton (Gossypium hirsutum L.) varieties