Water Relations Parameters Research Articles

Carbon nanoparticle exposure strengthens water-relation parameters by stimulating abscisic acid pathway and aquaporins genes in rice

Mechanism of action and molecular basis of positive growth effects including yield increase due to carbon nanoparticle (CNP) treatment in rice plants is dissected here. CNP at 500 -750 µg/mL were found to be the optimum dosages showing best seedling growth. CNP treatment resulted increase in stomata size, stomatal conductance and water use efficiency along with low relative humidity, decrease in stomata frequency and internal CO2 concentration. CNP-coupled with water uptake was found to be endocytosis mediated, although CNP uptake was not affected by endocytosis inhibitor application in roots. Genomic analysis resulted major involvement of ABA pathway and stomata size and frequency genes in Arabidopsis and rice. Elevated endogenous ABA in rice seedlings and flag leaves along with increased expression of ABA biosynthetic genes in Arabidopsis and rice AtNCED3, AtNCED6, OsNCED1 confirmed increased ABA synthesis. Negative regulators of ABA pathway, OsSNRK2 down-regulation and up-regulation of stomagen (OsEPFL9) reconfirmed ABA's involvement. CNP treatment exerted cold tolerance in seedlings and water stress tolerance in reproductive stage. CNP treatment under water withheld condition resulted water stress tolerance by maintaining lower stomatal conductance, transpiration rate and higher relative water content. Increased ABA (OsSNRK1, OsSNRK2) and aquaporin (OsPIP2–5 and OsPIP1–3) genes’ expressions could explain the better water stress tolerance in rice plants treated with CNP. Altogether, due to thermomorphogenesis, down-regulation of Phytochrome B transcript resulted altered the ABA pathway and stomatal distribution with size (Graphical Abstract). These changes resulted improved water relation parameters and water use efficiency (WUE) showing improvement in yield. Detailed mechanism of action of CNP in abiotic stress tolerance can be exploited using nano-agriculture at field level.

Water relations and photosystem II efficiency of the intertidal macroalga Fucus virsoides

Intertidal macroalgae are sessile poikilohydric organisms exposed to desiccation stress during emersion. Water relations parameters are useful tools to evaluate an organism's capacity to withstand water scarcity conditions, but such information on marine intertidal macroalgae is scarce. We assessed the water relations of the intertidal relict Fucus virsoides, the unique Fucus species endemic to the Mediterranean. We combined measurements of water potential (Ψ) parameters derived from pressure-volume curves and chlorophyll a fluorescence (Fv/Fm) in juvenile and adult thalli sampled in three different dates between March and April 2023. F. virsoides exhibited remarkable water stress tolerance, as evidenced by the low water potential at turgor loss point (Ψtlp, -7.0 MPa on average), and the maintenance of high Fv/Fm at low water potentials indicating a prolonged maintenance of healthy physiological status. While no differences were observed between growth stages, Ψtlp, capacitance (C) and the bulk modulus of elasticity (ε) varied significantly according to the sampling dates, whereas the osmotic potential at full turgor did not significantly change. Ψ measured on thalli collected after a typical prolonged emersion period was markedly lower (−12.3 MPa on average) than the estimated Ψtlp, suggesting that the population is frequently undergoing turgor loss. Further investigations are required to determine environmental tolerance ranges based on water status characteristics to enhance our understanding of F. virsoides responses and vulnerability to climate change, thus providing insight into the possible causes of its widespread decline.

Host Plant Modulated Physio-Biochemical Process Enhances Adaptive Response of Sandalwood (Santalum album L.) under Salinity Stress.

Salinity is one of the most significant abiotic stress that affects the growth and development of high-value tree species, including sandalwood, which can also be managed effectively on saline soils with the help of suitable host species. Therefore, the current investigation was conducted to understand the physiological processes and antioxidant mechanisms in sandalwood along the different salinity gradients to explore the host species that could support sandalwood growth in salt-affected agro-ecosystems. Sandalwood seedlings were grown with ten diverse host species with saline water irrigation gradients (ECiw~3, 6, and 9 dS m-1) and control (ECiw~0.82 dS m-1). Experimental findings indicate a decline in the chlorophyll content (13-33%), relative water content (3-23%), photosynthetic (27-61%) and transpiration rate (23-66%), water and osmotic potential (up to 137%), and ion dynamics (up to 61%) with increasing salinity levels. Conversely, the carotenoid content (23-43%), antioxidant activity (up to 285%), and membrane injury (82-205%) were enhanced with increasing salinity stress. Specifically, among the hosts, Dalbergia sissoo and Melia dubia showed a minimum reduction in chlorophyll content, relative water content, and plant water relation and gas exchange parameters of sandalwood plants. Surprisingly, most of the host tree species maintained K+/Na+ of sandalwood up to moderate water salinity of ECiw~6 dS m-1; however, a further increase in water salinity decreased the K+/Na+ ratio of sandalwood by many-fold. Salinity stress also enhanced the antioxidative enzyme activity, although the maximum increase was noted with host plants M. dubia, followed by D. sissoo and Azadirachta indica. Overall, the investigation concluded that sandalwood with the host D. sissoo can be successfully grown in nurseries using saline irrigation water and, with the host M. dubia, it can be grown using good quality irrigation water.

Responses of yield, fruit quality and water relations of sweet pepper in Mediterranean greenhouses to increasing salinity

Increasing salinization of groundwater used for irrigation is a current and growing problem for vegetable production in greenhouses in the Mediterranean Basin. Vegetable growers in this system require clear information of crop response to salinity, particularly of threshold values. For sweet pepper in Mediterranean greenhouses, this work (i) evaluated the effect of increasing salinity on various parameters of crop yield, fruit quality and plant water relations, and (ii) determined threshold and slope values for the Maas and Hoffman (M&H) model. Sweet pepper was grown with nutrient solutions (ns) with electrical conductivities (EC) of 2.5 (T1), 3.5 (T2), 4.5 (T3), 5.5 (T4), 6.5 (T5) and 7.5 (T6) dS m−1. There were substantial and statistically significant reductions in total and marketable yield, dry matter production (DMP) and average fruit weight, with increasing salinity. In treatment T4 (ns of 5.5 dS m−1), the respective reductions for these parameters, compared to T1 (ns of 2.5 dS m−1), were 37%, 37%, 47%, 52% and 30%. Applying the M&H model, soil solution EC threshold (ECsst) values for total and marketable yield were 4.8 and 5.0 dS m−1. The respective slope values were − 8.0 and − 12.0%/dS m−1. The more rapid decline in marketable yield was influenced by a large increase in the incidence of blossom end rot (BER) with increasing salinity. In treatment T1, 25% of discarded fruit had BER which increased to 70% in T6. Average fruit size was affected by salinity, but fruit number was not. Most fruit quality parameters were unaffected by increasing salinity. However, fruits were more red and more yellow. Leaf water potential (ΨW), leaf osmotic potential (ΨO), stomatal conductance (gS) and leaf turgor potential (ΨP) followed the Maas and Hoffman model, with ΨW, ΨO and gS declining and ΨP increasing after the EC threshold value. The ECsst value for ΨW was 5.0 dS m−1, and for ΨO, gS and ΨP was 5.6–5.8 dS m−1. Considering all data, an ECsst value of 5.0 dS m−1 is suggested for sweet pepper grown in Mediterranean greenhouses.

Trehalose and NO work together to alleviate Cd toxicity in pepper (Capsicum annuum L.) plants by regulating cadmium sequestration and distribution within cells and the antioxidant defense system

The response of plants to trehalose (TR) and nitric oxide (NO) has been tested in different stressful conditions, but the contribution of endogenous TR to plant tolerance to cadmium stress (Cd-S) induced by NO is still unclear. Ten days after germination, among the pepper seedlings, half were immersed for 12 h in a solution containing 15.0 mM TR or 0.6 mM sodium citrate (SC), an inhibitor of trehalose-6-phosphate phosphatase (TPP). Then, the plants were exposed to control (no addition of Cd) or Cd-S (0.1 mM CdCl2) up to two additional weeks. Throughout the stress period, both treatments were combined with sodium nitroprusside (SNP; 0.1 mM), a NO donor, supplied through the nutrient solution. Plants exposed to Cd-S experienced a substantial reduction in plant growth, photosynthesis, and leaf water relation parameters, but an increase in oxidative stress parameters, free proline, phytochelatins (PCs), and the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione reductase (GR), and ascorbate peroxidase (APX). The detrimental effects of Cd-S on the afore-mentioned traits were reversed by the supplementation of SNP, which in turn significantly increased the endogenous NO and TR levels, and leaf calcium (Ca2+) and potassium (K+), and reduced the leaf H2O2, MDA, and Cd contents as well as membrane leakage. SNP raised the amounts of GSH and PCs in Cd-S- plants, thereby modulating Cd sequestration to render it nontoxic. The treatment of SNP encouraged Cd build-up in the cell walls of root and leaf in order to prevent Cd from being transported to other vital cell organelles to safeguard them from metal toxicity. The supplementation of SC, a scavenger of TPP, eliminated TR content, thereby reversing the positive effect of SNP on Cd-S plants. Exogenous application of TR together with SNP+SC reversed the negative effect of SC. This suggests that TR is necessary for NO to be effective in improving the pepper plant Cd-S tolerance.

Photosynthetic characteristics of the invasive weed Chromolaena odorata and other co‐occurring species in KwaZulu‐Natal

AbstractIn this study, we tested the hypothesis that photosynthetic characteristics contributed to the success and spread of the invasive, C3 perennial weed, Chromolaena odorata (L.) R. M. King & H. Rob. Measurements of gas exchange, chlorophyll fluorescence and water relations parameters were taken in summer and winter, as well as in sun and shade plants. Typically, diurnal CO2 exchange increased from dawn to a mid‐morning maximum between 10:00 h and 11:00 h, and thereafter decreased gradually for the rest of the day. Light response curves indicated saturation of CO2 uptake and electron transport rate (ETR) through Photosystem II (PSII) at a photosynthetic photon flux density (PPFD) ≥1800 μmol m−2 s−1. Maximal CO2 exchange was 15.64 ± 0.87 (±SE) in summer and 13.15 ± 0.26 μmol m−2 s−1 in winter. Leaf conductance (g), CO2 uptake (A) and transpiration (E) followed trends similar to those for PPFD. Leaf water potential (Ψ) and water use efficiency (WUE) declined from the predawn maximum values to a minimum at midday and thereafter recovered at dusk. Diurnal trends in actual quantum yield (ΦPSII) and maximum quantum yield (Fv/Fm) decreased from dawn to a minimum at midday, followed by complete recovery at dusk. The relationship between A and g, and A and ETR was linear. Trends in A, ΦPSII and ETR through PSII were tightly coupled to those of incident PPFD. Efficient light utilisation is achieved through modifying plastic traits such as leaf size, specific leaf area and chlorophyll content. Chromolaena is a facultative shade‐tolerant weed that exhibits superior light utilisation to maximise carbon gain, while efficient photoprotective mechanisms minimise photoinhibition and photodamage to the photosystems. These adaptive architectural and physiological strategies may probably confer competitive advantage over other species.

Leaf water relations and osmotic adjustment of Canada Western Red Spring wheat cultivars subjected to drought.

For wheat (Triticum aestivum ), sustained crop yield at limited soil water availability has been linked to osmotic adjustment (OA) - a physiological mechanism that aids maintenance of leaf hydration status, turgor (P ) and growth. 'Canada Western Red Spring' (CWRS) wheat cultivars are typically grown in rainfed areas with milder climates, but ongoing climate change is increasesing the frequency and intensity of drought events. The overarching goal of this study was to elucidate if commercially used CWRS cultivars ('Superb', 'Stettler', 'AAC Viewfield') have the ability for leaf OA. Measurements of leaf water relation parameters (water potential, Ψ ; solute potential, Ψ s ; stomatal conductance, g s ; relative water content, RWC) showed that all three cultivars reached zero P (= Ψ - Ψ s ) at a leaf Ψ of -1.1MPa. Prior to that, P maintenance in 'Superb' and 'AAC Viewfield' was associated with a significant reduction in leaf Ψ s and OA contributed 0.53MPa ('Superb') and 0.73MPa ('AAC Viewfield'). Our data analyses provided no support for the existence of OA in 'Stettler'. Under water deficit, leaf g s was significantly higher in 'AAC Viewfield' compared to 'Stettler'; it was intermediate in 'Superb'. Together, drought tolerance in CWRS wheat cultivars is most likely linked to the degree of OA.

Comparative study of leaf physiological and biochemical characteristics in commercial and traditional Prunus dulcis (Mill.) Rchb. cultivars under rain-fed conditions

ABSTRACT Drought is the major abiotic stress in agriculture, and enhancement of plant characteristics under this stress is one of the major goals behind plant breeding. Almond is a drought-tolerant species, but, when water supply is not limited, it presents increased performance. To overcome the lack of water availability, the correct selection of cultivars is of great importance, as different responses of various almond genotypes have been reported in relation to drought stress. Hence, the present work aims to characterize leaf traits of several Portuguese traditional almond cultivars (‘Bonita’, ‘Casanova’, ‘Parada’, ‘Pegarinhos’ and ‘Verdeal’), comparing them to two foreign cultivars (‘Ferragnès’ and ‘Glorieta’). For this, leaf gas exchange, sclerophylly, leaf water relations parameters, photosynthetic pigments and total phenolic content were studied in 2017 and 2018, years that presented contrasting weather conditions. Several significant differences on leaf traits were found, particularly in relative water content, leaf mass per area, photosynthetic rate or stomatal conductance. Besides a clear effect of the cultivar, the sampling year also significantly influenced results, although not in all the parameters under study. The results obtained show a complex behavior of almond trees under rainfed conditions, but highlight some potential drought resistance in Portuguese cultivars, namely ‘Casanova’ and ‘Parada’ that should be further studied.

The Use of Soil Conditioners to Ensure a Sustainable Wheat Yield under Water Deficit Conditions by Enhancing the Physiological and Antioxidant Potentials

Traditional mulch material (farmyard manure) has long been used in agriculture. However, recent developments have also introduced the scientific community and farmers to advanced chemicals such as potassium polyacrylamide (KPAM), which has revolutionised the concept of the soil water-holding capacity to many compared with other materials being used. To compare the effect of different organic and inorganic soil amendment materials under water stress conditions, a two-year (2018 and 2019) field study was conducted. The main plots consisted of irrigation treatments, i.e., I0 (control irrigation), I1 (drought-induced by skipping irrigation at the 4th leaf stage), and I2 (drought-induced by skipping irrigation at the anthesis stage). The subplots included a control treatment and soil amended with different conditioners such as potassium polyacrylamide (KPAM, 30 kg/ha), farmyard manure (FYM, 4 tons/ha), and biochar (10 tons/ha); these were mixed thoroughly with the soil before sowing. The results showed a significant reduction in the water relation parameters (water potential up to 35.77% and relative water content up to 21%), gas exchange parameters (net CO2 assimilation rate up to 28.85%, stomatal conductance up to 43.18%, and transpiration rate up to 49.07%), and yield attributes (biological yield up to 8.45% and grain yield up to 32.22%) under drought stress conditions. In addition, water stress also induced an increase in the synthesis of osmoprotectants (proline up to 77.74%, total soluble sugars up to 27.43%, and total free amino acids up to 11.73%). Among all the soil conditioners used, KPAM significantly reduced the negative effects of drought stress on the wheat plants. Thus, it could be concluded that the use of soil conditioners is a promising method for dealing with the negative consequences of drought stress for achieving sustainable crop yields.

Differential of three fields grown Juniperus species summer drought and cold hardening

Background: Understanding species’ reactions to environmental stressors (cold and drought) and characterizing drought tolerance can help us understand their ecosystem responses related to global change. This study aimed to understand and compare the drought and cold tolerance strategies of Juniperus excelsa, Juniperus foetidissima, and Juniperus oxycedrus, which are found in the Western Mediterranean Region. Water relation parameters [ΨTLP (osmotic potential at turgor loss point), Ψ100 (osmotic potential at full turgor), Ɛmax (bulk modulus of elasticity), V0/DW (symplastic water at the saturated point per dry weight of the shoot), RWC (relative water content)] in summer and winter were determined. Total soluble sugar and photosynthetic pigment content were identified in spring, summer, autumn, and winter. Results: J. foetidissima had lower Ψ TLP and higher Ɛmax in summer than other species. The species had similar Ψ TLP 1 Ψ 100 1 Ɛmax, V0/DW, and RWC in winter. A seasonal change was observed in total soluble sugar and photosynthetic pigment content. Total soluble sugar and photosynthetic pigment contents were related to mean air temperature and total precipitation. Conclusion: J. foetidissima was more tolerant to water deficit in the summer, whereas the three species reacted similarly to the cold in the winter.

Water Relations, Gas Exchange, Chlorophyll Fluorescence and Electrolyte Leakage of Ectomycorrhizal Pinus halepensis Seedlings in Response to Multi-Heavy Metal Stresses (Pb, Zn, Cd).

The success of mine site restoration programs in arid and semi-arid areas poses a significant challenge and requires the use of high-quality seedlings capable of tolerating heavy metal stresses. The effect of ectomycorrhizal fungi on different physiological traits was investigated in Pinus halepensis seedlings grown in soil contaminated with heavy metals (Pb-Zn-Cd). Ectomycorrhizal (M) and non-ectomycorrhizal (NM) seedlings were subjected to heavy metals stress (C: contaminated, NC: control or non-contaminated) soils conditions for 12 months. Gas exchange, chlorophyll fluorescence, water relations parameters derived from pressure–volume curves and electrolyte leakage were evaluated at 4, 8 and 12 months. Ectomycorrhizal symbiosis promoted stronger resistance to heavy metals and improved gas exchange parameters and water-use efficiency compared to the non-ectomycorrhizal seedlings. The decrease in leaf osmotic potentials (Ψπ100: osmotic potential at saturation and Ψπ0: osmotic potential with loss of turgor) was higher for M-C seedling than NM-C ones, indicating that the ectomycorrhizal symbiosis promotes cellular osmotic adjustment and protects leaf membrane cell against leakage induced by Pb, Zn and Cd. Our results suggest that the use of ectomycorrhizal symbiosis is among the promising practices to improve the morphophysiological quality of seedlings produced in forest nurseries, their performance and their tolerance to multi-heavy metal stresses.

Enhancement of drought tolerance in diverse Vicia faba cultivars by inoculation with plant growth-promoting rhizobacteria under newly reclaimed soil conditions

Water deficit has devastating impacts on legume production, particularly with the current abrupt climate changes in arid environments. The application of plant growth-promoting rhizobacteria (PGPR) is an effective approach for producing natural nitrogen and attenuating the detrimental effects of drought stress. This study investigated the influence of inoculation with the PGPR Rhizobium leguminosarum biovar viciae (USDA 2435) and Pseudomonas putida (RA MTCC5279) solely or in combination on the physio-biochemical and agronomic traits of five diverse Vicia faba cultivars under well-watered (100% crop evapotranspiration [ETc]), moderate drought (75% ETc), and severe drought (50% ETc) conditions in newly reclaimed poor-fertility sandy soil. Drought stress substantially reduced the expression of photosynthetic pigments and water relation parameters. In contrast, antioxidant enzyme activities and osmoprotectants were considerably increased in plants under drought stress compared with those in well-watered plants. These adverse effects of drought stress reduced crop water productivity (CWP) and seed yield‐related traits. However, the application of PGPR, particularly a consortium of both strains, improved these parameters and increased seed yield and CWP. The evaluated cultivars displayed varied tolerance to drought stress: Giza-843 and Giza-716 had the highest tolerance under well-watered and moderate drought conditions, whereas Giza-843 and Sakha-4 were more tolerant under severe drought conditions. Thus, co-inoculation of drought-tolerant cultivars with R. leguminosarum and P. putida enhanced their tolerance and increased their yield and CWP under water-deficit stress conditions. This study showed for the first time that the combined use of R. leguminosarum and P. putida is a promising and ecofriendly strategy for increasing drought tolerance in legume crops.

Foliar Application of Boron Nanoencapsulated in Almond Trees Allows B Movement Within Tree and Implements Water Uptake and Transport Involving Aquaporins.

Nanotechnology brings to agriculture new forms of fertilizer applications, which could be used to reduce environmental contamination and increase efficiency. In this study, foliar fertilization with nanoencapsulated boron (B) was studied in comparison to an ionic B (non-encapsulated) application in young B-deficient almond trees grown under a controlled environment. B movement within the plant in relation to the leaf gas exchange, water relations parameters, and root hydraulic conductance was measured. Also, the expression of aquaporins (AQPs) [plasma membrane intrinsic protein (PIP) and tonoplast intrinsic protein (TIP)] was studied in relation to water uptake and transport parameters to establish the effectiveness of the different B treatments. The obtained results were associated with a high concentration of observed B with nanoencapsulated B, provided by the higher permeability of carrier nanovesicles, which allowed B to reach the cell wall more efficiently. The increases in water uptake and transport obtained in these plants could be related to the role that this element played in the cell wall and the relationship that it could have in the regulation of the expression of AQPs and their involvement in water relations. Also, an increase in the expression of PIPs (mainly PIP2.2) to the applied nanoencapsulated B could be related to the need for B and water transport, and fine regulation of TIP1.1 in relation to B concentration in tissues provides an important feature in the remobilization of B within the cell.

More sensitive to drought of young tissues with weak water potential adjustment capacity in two desert shrubs

Water is the main limiting factor for survival and growth for desert plants, and plants can alleviate water deficits under drought by adjusting water potential (Ψ). However, the water potential adjustment capacity and water-sensitivity at the tissue level among shrub species remains unclear. The objective of this study was to evaluate water potential adjustment capacity and water-sensitivity of different tissues in Artemisia ordosica and Caragana korshinskii through calculating the water relation parameters from pressure-volume (P-V) curves. The present study found that the sensitivity coefficients, −1/β and −1/b, were gradually decreased with increasing degree of lignification in A. ordosica and C. korshinskii, suggesting that younger tissues with low lignification are more sensitive to water deficit. Additionally, the younger tissues with more negative osmotic potential at full turgor (Ψπ, sat), water potential at turgor loss point (Ψtlp), and lower the bulk modulus of elasticity (ε), the relative water deficit at turgor loss point (RWDtlp), apoplastic water fraction (AWF) and total hydraulic capacitance (Ctotal), which indicated that younger tissues have stronger turgor adjustment capacity compared to osmotic adjustment capacity and them were more easily lose water during times of decreased water potential because of higher cell wall elasticity and weaker water storage capacity. Collectively, the present study highlighted that younger tissues are more sensitive to drought due to their weaker water potential adjustment capacity and provided critical insight into water physiological mechanism or sensitivity of species to drought.

Reactions of three European oak species (Q. robur, Q. petraea and Q. ilex) to repetitive summer drought in sandy soil

Young trees of deciduous Quercus robur and Q. petraea and evergreen Q. ilex were grown together in a competition lysimeter experiment to assess i) – whether the observed growth differences between evergreen Q. ilex and the deciduous Q. robur and Q. petraea on sandy soil in the field and ii) – whether the different natural distribution of Q. robur and Q. petraea could be attributed to physiological differences between the species under experimental drought stress (DS). Half of the plants were subjected to long-term DS in two consecutive years and monitored for physiological and growth parameters. In the first year, water withholding for more than three months did not lead to significant drought stress, probably because of a sufficient residual water volume in the lysimeter for the relatively small plants. However, in the second year, 2018, which was warmer, the bigger plants now competed for the residual water and clear drought stress symptoms developed for more than two months in all trees in the DS lysimeter basin. Growth was only moderately (and mostly not significantly) affected by the DS in the second year, except for a smaller total leaf area in DS Q. ilex as compared to DS Q. robur and Q. petraea and smaller root collar diameter in DS Q. ilex compared to DS Q. robur. Under DS, the deciduous species revealed significant decreases in ΔVIP, indicating a negative effect on electron transport through PS I. Pn, PIabs and water relations parameters (ΨPD and LWC) all decreased to various extents under DS in all three species, leading to clear separation of the deciduous from the evergreen species by PCA. However, PCA did not separate the two deciduous species from each other. It is concluded that longer root growth in the two deciduous species as compared to Q. ilex ameliorates DS effects in Q. robur and Q. petraea and may be the key to understand the better performance of deciduous oaks on sandy soil in the field.

Responses of Mungbean to Water Deficit, Water use Efficiency and Drought Resistance

Backround: Legumes are the second important agricultural crop of great prominence to humans. Among 20000 legume species the mungbean is one of the most important grain cultivated in India. Drought is a major environmental stress that affects mungbean in the sub-humid, dry and intermediate zones of India. The present study records the response of mung bean varieties to water stress during its growth stage.Methods: The impact of drought stress imposed on the crop was evaluated by measuring the water relation parameters and the biochemical progresses like osmolyte accumulation, nitrate assimilation and antioxidant system in Mung bean during 2017-2018 in Avinashilingam Institute for Home Science and Higher Education for Women, Coimbatore.Result: Drought stress altered the water status of the crop by reducing the RWC, which was enhanced in drought susceptible varieties. Increased amount of proline denotes the osmoregulatory mechanism in the crop to bring about resistance and the elevated levels of antioxidant enzymes shows the protective mechanism in the crop at cellular level.

The Effect of Irrigation Rate on the Water Relations of Young Citrus Trees in High-Density Planting

The availability and proper irrigation scheduling of water are some of the most significant limitations on citrus production in Florida. The proper volume of citrus water demand is vital in evaluating sustainable irrigation approaches. The current study aims to determine the amount of irrigation required to grow citrus trees at higher planting densities without detrimental impacts on trees’ water relation parameters. The study was conducted between November 2017 and September 2020 on young sweet orange (Citrus sinensis) trees budded on the ‘US-897’ (Cleopatra mandarin x Flying Dragon trifoliate orange) citrus rootstock transplanted in sandy soil at the Southwest Florida Research and Education Center (SWFREC) demonstration grove, near Immokalee, Florida. The experiment contained six planting densities, including 447, 598, and 745 trees per ha replicated four times, and 512, 717, and 897 trees per ha replicated six times. Each density treatment was irrigated at 62% or 100% during the first 15 months between 2017 and 2019 or one of the four irrigation rates (26.5, 40.5, 53, or 81%) based on the calculated crop water supplied (ETc) during the last 17 months of 2019–2020. Tree water relations, including soil moisture, stem water potential, and water supplied, were collected periodically. In addition, soil salinity was determined. During the first year (2018), a higher irrigation rate (100% ETc) represented higher soil water contents; however, the soil water content for the lower irrigation rate (62% ETc) did not represent biological stress. One emitter per tree regardless of planting density supported stem water potential (Ψstem) values between −0.80 and −0.79 MPa for lower and full irrigation rates, respectively. However, when treatments were adjusted from April 2019 through September 2020, the results substantially changed. The higher irrigation rate (81% ETc) represented higher soil water contents during the remainder of the study, the lower irrigation rate (26.5% ETc) represents biological stress as a result of stem water potential (Ψstem) values between −1.05 and −0.91 MPa for lower and higher irrigation rates, respectively. Besides this, increasing the irrigation rate from 26.5% to 81%ETc decreased the soil salinity by 33%. Although increasing the planting density from 717 to 897 trees per hectare reduced the water supplied on average by 37% when one irrigation emitter was used to irrigate two trees instead of one, applying an 81% ETc irrigation rate in citrus is more efficient and could be managed in commercial groves.

Involvement of Ethylene in Physiological Processes Determining the Vase Life of Various Hybrids of Mokara Orchid Cut Flowers

There is limited information about the postharvest performance and physiology of Mokara orchid cut flowers, which are a special group of artificially created trigenetic hybrids of Vanda × Arachnis × Ascocentrum. Therefore, we first characterized the patterns of various physiological parameters during vase life of five Mokara hybrids, which differ in their longevity. Then, we examined the effects of ethephon and ethylene inhibitors on these physiological parameters, and on parameters of the ethylene biosynthesis pathway, during vase life of two selected Mokara hybrids, “Moo-deang” and “Dao-lai”, which showed significant differences in their vase life duration and senescence symptoms. The results demonstrate that the differences in vase life longevity among the five Mokara hybrids are due to differences in their ethylene production rates, which regulate flower development processes expressed in bud opening and floret senescence. The results clearly show that ethylene is involved in the regulation of the Mokara flower senescence, and pretreatment with ethylene inhibitors significantly improved their vase life longevity. Thus, ethylene seems to be the main factor that determines the longevity differences of the Mokara hybrids, rather than their water relations parameters. This study can serve as a research tool for developing effective postharvest treatments for Mokara hybrids.

Non-invasive measurement of leaf water content and pressure\u2013volume curves using terahertz radiation

In this paper we describe a non-invasive method of measuring leaf water content using THz radiation and combine this with psychrometry for determination of leaf pressure–volume relationships. In contrast to prior investigations using THz radiation to measure plant water status, the reported method exploits the differential absorption characteristic of THz radiation at multiple frequencies within plant leaves to determine absolute water content in real-time. By combining the THz system with a psychrometer, pressure–volume curves were generated in a completely automated fashion for the determination of leaf tissue water relations parameters including water potential at turgor loss, osmotic potential at full turgor and the relative water content at the turgor loss point. This novel methodology provides for repeated, non-destructive measurement of leaf water content and greatly increased efficiency in generation of leaf PV curves by reducing user handling time.

Chemical priming agents controlling drought stress in Physalis angulata plants

Despite the use of chemical priming as a promising tool for the study of plant stress physiology and the management of field crops, little is known of its importance when studying adult plants, especially in unexploited species. The aim of this work was to evaluate the use of sodium nitroprusside (SNP), hydrogen peroxide (H2O2) and proline (Pro) as possible chemical priming inducing agents in Physalis angulata plants exposed to water deficit. For this, plants in well-watered conditions were sprayed with different concentrations of SNP (25 and 50 μM), H2O2 (10 and 20 Mm) and Pro (10 and 20 mM) and evaluated after exposure to water deficit. Although the parameters of water relations, gas exchange, growth and dry matter accumulation were reduced with the imposition of water deficit, pretreated plants showed significant improvements in the same variables. Plants sensitized with Pro and SNP doses showed improvement in relative water content and water leaf potential, contributing to the maintenance of plant water status when exposed to water deficit. The attenuation of the effects of reduced water availability on gas exchange was significantly promoted with SNP spraying, notably carbon assimilation, stomatal conductance and transpiration, parallel to an increasing in the photosynthetic pigment content. The pretreatment also influenced the growth (with Pro 10 and 20 mM; SNP 50 μM) and biomass accumulation of plants exposed to water deficit (especially with SNP 50 μM), contributing to tolerance increase to this abiotic stress. Pretreatment with hydrogen peroxide had a reduced priming effect. The pretreatment of plants with sodium nitroprusside and proline contribute to the attenuation of water deficit effects in Physalis angulata plants, acting as potential chemical priming.