Leaf Osmotic Potential Research Articles

Different drought-tolerance strategies of tree species to cope with increased water stress under climate change in a mixed forest.

Trees' functional strategies to cope with extreme drought are essential under climate change. In a mixed Mediterranean forest, we analyzed the functional strategy in response to drought of four co-occurring species (Pinus pinea, Pinus pinaster, Juniperus oxycedrus, and Quercus ilex) during two years. Specifically, we assessed functional traits related to tree water status, leaf water relations, and gas exchange. Different trait-syndrome metrics and the functional strategies under water stress observed suggested a species drought-tolerance differentiation, with the more anysohidric Q. ilex and J. oxycedrus showing a much higher drought tolerance than the more isohydric P. pinea and P. pinaster. All species recovered from negative leaf turgor reached during peak water stress in summer. Q. ilex and J. oxycedrus kept lower leaf osmotic potentials and lower sensitivity of leaf gas exchange and leaf photochemistry to water stress. In contrast, the pine species exhibited more drought-avoidant and water-conservative strategies, yet this behavior was less effective in mitigating water stress's impact on their physiology. The pine species were the most affected by drought, with prolonged near-zero net photosynthesis during summer. P. pinaster was more isohydric than P. pinea and exhibited a lower capacity to maintain leaf turgor. Physiological processes regulating leaf turgor under drought constitute a key functional strategy involved in the carbon and water-related mechanisms, ultimately inducing mortality under hot drought. The currently observed mortality dynamics for P. pinaster, and to a lower extent in P. pinea, may be exacerbated by loss of functional homeostasis.

Assessment of Drought Tolerance of Two Cultivars of Indian Mustard (Brassica juncea) Using Morphological and Physiological Parameters

Aims: Drought stress may affect the Morphology, biochemistry, growth, and physiology of Brassica juncea (Indian mustard), a low-cost, oil-yielding, and economically significant plant. In this paper assessing various growth, morphological, and physiological parameters under different irrigation regimes could offer some significant information for the selection of a suitable and appropriate genotype for breeding. Study Design: Two commonly grown cultivars (RH-725 and RH-749) of mustard in Haryana under four irrigation regimes were evaluated. The applied Irrigation regimes were: control (double irrigation: once at the 50% flowering and another at the 50% fruiting stages), early irrigation (at 50% flowering only), late irrigation (at 50% fruiting only), and stress (no irrigation). The plants were exposed to short-term water shortages during the vegetative and reproductive growth stages. Drought stress in both stages had a negative effect on the morphological and physiological parameters of mustard. Place and Duration of Study: An open field experiment was performed at the Nursery of Kurukshetra University, Kurukshetra, Haryana, India, located at the latitude of 290–95° north and longitude of 760–82° east, with a height of 258.4 m above sea level. Crop sown under field conditions from October to March for two consecutive years (2018-2019, 2019-2020) at a temperature of 30-32 °C (days) and 15-25 °C (nights). Methodology: Measured adaptability using 15 morphological, 4 physiological, and 7 different growth parameters. PCA data revealed that physiological and growth parameters are more sensitive than morphological parameters in distinguishing the control and drought treatments. Alterations in physiological parameters occurred at all three levels of water stress. Growth analysis and yield parameters decreased with the severity of stress. Drought-stress treatments gradually reduced the Morphological and physiological traits of mustard. Results: The study revealed a relationship between Brassica species' adaptation to drought stress and the rapidity, severity, and duration of the drought event. This highlights the importance of considering these factors while selecting genotypes for breeding programmes aimed at improving drought tolerance in B. juncea. Overall, the research provides valuable information for selecting suitable and appropriate genotypes for breeding drought-tolerant varieties of B. juncea. By understanding the specific physiological (relative water content, leaf osmotic potential, membrane stability index, electrolytic index) and growth parameters (plant height, root length, fresh and dry weight of leaves and roots, leaf area etc.) that are more sensitive to drought stress. Furthermore, this study revealed a relationship between Brassica species' adaptation to drought stress and the rapidity, severity, and duration of the drought event. Based on PCA values, the cultivar RH-749 performed better both morphologically and physiologically under all stress conditions compared to RH-725. This suggests that RH-749 is more adapted and tolerant to drought stress, making it a potential candidate for breeding and cultivation in water-limited environments.

Plasticity and implications of water-use traits in contrasting tropical tree species under climate change.

Plants face a trade-off between hydraulic safety and growth, leading to a range of water-use strategies in different species. However, little is known about such strategies in tropical trees and whether different water-use traits can acclimate to warming. We studied five water-use traits in 20 tropical tree species grown at three different altitudes in Rwanda (RwandaTREE): stomatal conductance (gs), leaf minimum conductance (gmin), plant hydraulic conductance (Kplant), leaf osmotic potential (ψo) and net defoliation during drought. We also explored the links between these traits and growth and mortality data. Late successional (LS) species had low Kplant, gs and gmin and, thus, low water loss, while low ψo helped improve leaf water status during drought. Early successional (ES) species, on the contrary, used more water during both moist and dry conditions and exhibited pronounced drought defoliation. The ES strategy was associated with lower mortality and more pronounced growth enhancement at the warmer sites compared to LS species. While Kplant and gmin showed downward acclimation in warmer climates, ψo did not acclimate and gs measured at prevailing temperature did not change. Due to distinctly different water use strategies between successional groups, ES species may be better equipped for a warmer climate as long as defoliation can bridge drought periods.

Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis in hot conditions despite less drought-resistant leaves.

Many agricultural areas are expected to face hotter, drier conditions from climate change. Understanding the mechanisms that crops use to mitigate these stresses can guide breeding for more tolerant plant material. We tested relationships between traits, physiological function in hot conditions and historical climate associations to evaluate these mechanisms for winegrapes. We expected a more negative leaf osmotic potential at full hydration (πo), which reduces leaf turgor loss during drought, and either a metabolically cheaper or more osmoprotectant leaf chemical composition, to allow cultivars associated with hot, dry regions to maintain greater gas exchange in hot growing conditions. We measured πo, gas exchange and leaf chemistry for seven commercially important winegrape cultivars that vary widely in historical climate associations. Vines were grown in common-garden field conditions in a hot wine-growing region (Davis, CA, USA) and measured over the hottest period of the growing season (July-September). The value of πo varied significantly between cultivars, and all cultivars significantly reduced πo (osmotically adjusted) over the study period, although osmotic adjustment did not vary across cultivars. The value of πo was correlated with gas exchange and climate associations, but in the direction opposite to expected. Photosynthesis and πo were higher in the cultivars associated with hotter, less humid regions. Leaf chemical composition varied between cultivars but was not related to climate associations. These findings suggest that maintenance of leaf turgor is not a primary limitation on grapevine adaptation to hot or atmospherically dry growing conditions. Thus, selecting for a more negative πo or greater osmotic adjustment is not a promising strategy to develop more climate-resilient grape varieties, contrary to findings for other crops. Future work is needed to identify the mechanisms increasing photosynthesis in the cultivars associated with hot, dry regions.

Karık ve Damla Sulama Yöntemleriyle Kırmızı Biberde Farklı Sulama Stratejilerinin Yaprak Osmotik Potansiyeli ile K ve Ca İyon Konsantrasyonları Üzerine Etkilerinin Belirlenmesi

A study was managed to identify the water stress effect on marketable yield, osmatic potential, and potassium (K) and calcium (Ca) ions for drip and furrow irrigated processing red pepper in the 2010 and 2011 growing seasons in Tarsus, Turkey. The treatments for drip irrigation; comprise full irrigation (DFI1.0), deficit irrigation DDI0.75, DPRD0.5, DFPRD0.5, and DDI0.5; for furrow irrigation; full irrigation (FFI1.0), fix alternative furrow (FAF0.5) and PRD furrow (FPRD0.5). FAF0.5 and FPRD0.5 received 50 % of the water applied to FFI1.0. In FAF0.5 the same furrows were irrigated while in FPRD0.5 irrigated alternately. Irrigation methods and irrigation levels had a remarkable effect on the total yield of red pepper in both experimental years. Drip irrigation treatments manufactured higher red pepper yields than the furrow irrigation treatments. The maximum yield in the drip irrigation system was acquired from the DFI1.0 treatment followed by DDI0.75, DDI0.5, and DFPRD0.5 treatments. Though DPRD0.5, DFPRD0.5, and DDI0.5 applied the same amount of water, DPRD0.5 resulted in a higher yield. In furrow treatments, FFI1.0 resulted in the highest yield followed by FPRD0.5 and FAF0.5. Water use efficiency (WUE) diminished with increasing the water amount for drip and furrow irrigation methods. While lower osmotic potential values were measured in full irrigation treatments in furrow and drip irrigation plots, higher osmotic potential values were determined in treatments where water stress was determined in both years. In both drip and furrow irrigation, the lowest Ca (%) values were obtained in full irrigation, while the highest Ca values were obtained in limited irrigation with water stress in the 2010 and 2011 years. K ion values were generally similar in the first and fourth pepper harvests in drip and furrow irrigation.

Exogenous glycine betaine alleviates water-deficit stress in Indian pennywort (Centella asiatica) under greenhouse conditions.

Centella asiatica (Indian pennywort) is a green leafy vegetable containing centelloside' (triterpenoid), a key phytochemical component in traditional medicine. Being a glycophytic species, they exhibit decline in growth performance and yield traits when subjected to water-deficit (WD) conditions. Glycine betaine (GB) is a low molecular-weight organic metabolite that plays a crucial role in abiotic stress conditions in higher plants. The objective of this study was to investigate the potential of GB in alleviating water-deficit stress (in terms of morphological and physiological responses) in two different genotypes of Indian pennywort, "Nakhon Pathom" (NP; high centelloside-yielding genotype) and "Pathum Thani" (PT; low centelloside-yielding genotype). The genotypes of Indian pennywort were propagated by stolon cutting and transplanted into plastic bags containing 2kg of garden soil. At the flower-initiation stage (30days after transplantation), uniform plant material was treated exogenously with 0 (control), 25, and 50mMGB at 100mL per plant (one-time foliar spray) and then divided into two groups, 1) well watered (WW; irrigated daily with 400mL fresh water; 98% field capacity) and 2) water deficit (WD; withheld water for 14days; 72% field capacity). Foliar application of GB (25mM) significantly improved leaf osmotic potential in NP under WD conditions via osmotic adjustment by free proline and fructose. Differences in leaf temperature (Tleaf) between WD and WW in NP were maximized (+ 1.93°C) and the gap of Tleaf was reduced in the case of 25-50mMGB application. Similarly, crop water stress index (CWSI) in NP and PT plants under WD condition was significantly increased by 1.95- and 1.86-fold over the control, respectively; however, it was significantly decreased by exogenous GB application. Increasing Tleaf and CWSI in drought-stressed plants was closely related to stomatal closure, leading to reduced gas exchange parameters, i.e., stomatal conductance (gs), transpiration rate (E), net photosynthetic rate (Pn), and intercellular CO2 concentration (Ci), and consequently decreased plant biomass and total centelloside yield. Overall physiological, morphological, and secondary metabolite traits were enhanced in NP under WD conditions using 25mMGB exogenous application compared with the control. The study highlights the significance of GB in Indian pennywort production under limited water irrigation (water deficit) with higher vegetable yield and phytochemical stabilization.

DETERMINATION OF THE EFFECT OF DIFFERENT DOSES OF JASMONIC ACID APPLICATIONS ON ALLEVIATING SALT STRESS IN TOMATO PLANTS WITH PHYSIOLOGICAL PARAMETERS

Salt stress is one of the most important abiotic stress factors that limit productivity in crop production due to climate change, whose effects have been felt more clearly in the world in recent years, and incorrect applications in agricultural soils. Research in plant production in saline soils, based on alleviating the effects of stress through applications to plants or soil, has gained momentum in recent years. In our study, we aimed to demonstrate that foliar jasmonic acid application to tomato plants alleviates the effects of salt stress with physiological parameters. Two tomato genotypes, sensitive to salt stress (TOM 106) and tolerant (TOM 23), determined in previous studies on abiotic stress, were used as plant materials. These two genotype selections were chosen to determine how close jasmonic acid brings the sensitive genotype to the tolerant genotype in salt stress. Salt dose is 100 mM and Control (0mM), jasmonic acid doses are; It was applied as 0, 20, 30 and 40 μM. The experiment carried out in pots was carried out under controlled conditions. Plant growth parameters (plant fresh and dry weight, stem diameter and plant length) and physiological parameters (such as leaf water potential, leaf osmotic potential, photosynthetic rate, transpiration rate, internal CO2, stomatal conductivity, chlorophyll) were measured at regular intervals. Jasmonic acid applications created a statistically significant difference. As a result, it was determined that 20 and 30 μM jasmonic acid applications were more effective in reducing salt stress damage.

ESTIMATING THE PHOTOSYSTEM’S EFFICIENCY, ANTIOXIDANTS ACTIVITY AND PLANT WATER RELATIONS OF TOMATO UNDER WATER DEFICIT CONDITIONS

Due to physiological repercussions, the tomato crop has decreased productivity caused by drought throughout its entire life cycle. The tomato harvest has exceeded expectations due to a worldwide water resource limitation. The objective of subjecting the tomato cultivars Flanto and Sahel, to a self-imposed drought was to investigate the interrelationships among biochemical, physiological, enzymatic, and water-related factors. Five varying levels of moisture strongly impacted all plant attributes: 100%, 80%, 60%, 40%, and 20% when subjected to drought stress. The lack of water resulted in notable improvements in some metrics. Some examples of these traits include linear electron flow (LEF), photosynthetic efficiency (PSE), inward light dissipation ratio (qP), catalase activity (CAT), ascorbate peroxidase activity (APX), and leaf water potential (LEWP). Consider, for example, the intriguing discoveries concerning photosystem II, non-photochemical quenching, chlorophyll levels, leaf osmotic potential, and leaf turgor potential.

Leaf nitrogen and phosphorus resorption efficiencies are related to drought resistance across woody species in a Chinese savanna.

Leaf nutrient resorption and drought resistance are crucial for the growth and survival of plants. However, our understanding of the relationships between leaf nutrient resorption and plant drought resistance is still limited. In this study, we investigated the nitrogen and phosphorus resorption efficiencies (NRE and PRE), leaf structural traits, leaf osmotic potential at full hydration (Ψosm), xylem water potential at 50% loss of xylem-specific hydraulic conductivity (P50) and seasonal minimum water potential (Ψmin) for 18 shrub and tree species in a semiarid savanna ecosystem, in Southwest China. Our results showed that NRE and PRE exhibited trade-off against drought resistance traits (Ψosm and P50) across woody species. Moreover, this relationship was modulated by leaf structural investment. Species with low structural investment (e.g., leaf mass per area, leaf dry mass content and leaf construction cost [LCC]) tend to have high NRE and PRE, while those with high LCCs show high drought resistance, showing more negative Ψosm and P50.These results indicate that species with a lower leaf structural investment may have a greater need to recycle their nutrients, thus exhibiting higher nutrient resorption efficiencies, and vice versa. In conclusion, nutrient resorption efficiency may be a crucial adaptation strategy for coexisting plants in semiarid ecosystems, highlighting the importance of understanding the complex relationships between nutrient cycling and plant survival strategies.

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.

Searching for a deficit irrigation strategy to save water and improve fruit quality without compromising pomegranate production

Deficit irrigation (DI) strategies have frequently studied in drought resistant crops to optimise water-use-efficiency and save water. Four different DI strategies were studied in fifteen-year-old pomegranate trees (Punica granatum (L.) cv. Mollar de Elche) during the season of 2021: irrigation at 120 % of ETc during the whole season (control, C); irrigation at 50 % of ETc during the whole season (SDI); irrigation at 50 % of ETc during the linear fruit growth phase (RDIfg) and irrigation at 25 % of ETc during the ripening phase (RDIr). The effects of DI treatments on water relations, gas exchange, canopy temperature, yield and fruit quality were analysed. Water status of pomegranate responded closely to changes in soil water content. The reduction of leaf osmotic potential and leaf osmotic potential at full turgor to SDI, RDIfg and RDIr treatments indicated an osmotic adjustment. The stem water potential and the crop water stress index were more sensitive to water stress than gas exchange. SDI treatment increased non-marketable fruit weight and number. Nevertheless, RDIfg treatment could be considered a non-critical period because of the low sensitivity to water stress of trees, yield maintenance and the increase of nutritional organic compounds in fruits, saving 27 % of irrigation water. The application of RDIr produced the highest content of bioactive compounds, saving 8 % of water saving with a slight increase of non-marketable fruit number and weight. This suggests that the intensity and duration in which the deficit irrigation was applied could set the threshold irrigation conditions above which pomegranate production could be negatively affected.

A comparative analysis of agronomic water-use efficiency and its proxy measures as derived from key morpho-physiological and supportive quantitative genetics attributes of perennial ryegrass under imposed drought.

Water-use efficiency (WUE) is an under-researched but very important drought tolerance trait in forage breeding. This research estimated quantitative genetic parameters of morpho-physiological traits linked to agronomic water-use efficiency (WUEA) and its proxy measures based on δ13C (WUEi) or gas exchange (evapotranspiration, WUEAET, or stomatal conductance WUEASC) of genotypes from half-sib families of Lolium perenne L. (PRG) in a simulated summer drought cycle. Principal component analysis (PCA) of trait data distinguished a group of PRG genotypes where high WUEA and dry matter yield was associated with deep rooting, leaf hydration at more negative leaf osmotic and water potential, and reduced soil moisture depletion. Plants with this trait association sustained net assimilation and postdefoliation regrowth in drought. However, WUEi, WUEASC, and WUEAET were poorly correlated with most traits of interest at p < .05. Another PCA revealed a weak association between WUEA and its proxy measures under conditions tested. Quantitative genetic parameters including high estimates of narrow-sense heritability () of WUEA and related traits emphasized the genetic potential of the key trait combination for selecting PRG for improved drought tolerance. Research findings highlight the relative importance of WUEA and its proxy measures in the broad definition of PRG drought tolerance for breeding purposes.

Investigating high throughput phenotyping based morpho-physiological and biochemical adaptations of indian pennywort (Centella asiatica L. urban) in response to different irrigation regimes

Indian pennywort (Centella asiatica L. Urban; Apiaceae) is a herbaceous plant used as traditional medicine in several regions worldwide. An adequate supply of fresh water in accordance with crop requirements is an important tool for maintaining the productivity and quality of medicinal plants. The objective of this study was to find a suitable irrigation schedule for improving the morphological and physiological characteristics, and crop productivity of Indian pennywort using high-throughput phenotyping. Four treatments were considered based on irrigation schedules (100, 75, 50, and 25% of field capacity denoted by I100 [control], I75, I50, and I25, respectively). The number of leaves, plant perimeter, plant volume, and shoot dry weight were sustained in I75 irrigated plants, whereas adverse effects on plant growth parameters were observed when plants were subjected to I25 irrigation for 21 days. Leaf temperature (Tleaf) was also retained in I75 irrigated plants, when compared with control. An increase of 2.0 °C temperature was detected in the Tleaf of plants under I25 irrigation treatment when compared with control. The increase in Tleaf was attributed to a decreased transpiration rate (R2 = 0.93), leading to an elevated crop water stress index. Green reflectance and leaf greenness remained unchanged in plants under I75 irrigation, while significantly decreased under I50 and I25 irrigation. These decreases were attributed to declined leaf osmotic potential, increased non-photochemical quenching, and inhibition of net photosynthetic rate (Pn). The asiatic acid and total centellosides in the leaf tissues, and centellosides yield of plants under I75 irrigation were retained when compared with control, while these parameters were regulated to maximal when exposed to I50 irrigation. Based on the results, I75 irrigation treatment was identified as the optimum irrigation schedule for Indian pennywort in terms of sustained biomass and a stable total centellosides. However, further validation in the field trials at multiple locations and involving different crop rotations is recommended to confirm these findings.

Key hydraulic traits control the dynamics of plant dehydration in four contrasting tree species during drought.

Trees are at risk of mortality during extreme drought, yet our understanding of the traits that govern the timing of drought-induced hydraulic failure remains limited. To address this, we tested SurEau, a trait-based soil-plant-atmosphere model designed to predict the dynamics of plant dehydration as represented by changes in water potential, against those observed in potted trees of four contrasting species (Pinus halepensis, Populus nigra, Quercus ilex, and Cedrus atlantica) exposed to drought. SurEau was parameterised with a range of plant hydraulic and allometric traits, soil, and climatic variables. We found close correspondence between predicted and observed plant water potential (MPa) dynamics during early phase drought leading to stomatal closure, as well as during latter phase drought leading to hydraulic failure in all four species. A global model's sensitivity analysis revealed that for a common plant size (leaf area) and soil volume, dehydration times from full hydration to stomatal closure (Tclose) was most strongly controlled by leaf osmotic potential (Pi0) and its influence on stomatal closure, in all four species, while maximum stomatal conductance (gsmax) also contributed to Tclose in Q. ilex and C. atlantica. Dehydration times from stomatal closure to hydraulic failure (Tcav) was most strongly controlled by Pi0, the branch residual conductance (gres), and Q10a sensitivity of gres in the three evergreen species, while xylem embolism resistance (P50) was most influential in the deciduous species Populus nigra. Our findings point to SurEau as a highly useful model for predicting changes in plant water status during drought and suggest adjustments made in key hydraulic traits are potentially beneficial to delaying the onset of drought-induced hydraulic failure in trees.

African savanna grasses outperform trees across the full spectrum of soil moisture availability.

Models of tree-grass coexistence in savannas make different assumptions about the relative performance of trees and grasses under wet vs dry conditions. We quantified transpiration and drought tolerance traits in 26 tree and 19 grass species from the African savanna biome across a gradient of soil water potentials to test for a trade-off between water use under wet conditions and drought tolerance. We measured whole-plant hourly transpiration in a growth chamber and quantified drought tolerance using leaf osmotic potential (Ψosm ). We also quantified whole-plant water-use efficiency (WUE) and relative growth rate (RGR) under well-watered conditions. Grasses transpired twice as much as trees on a leaf-mass basis across all soil water potentials. Grasses also had a lower Ψosm than trees, indicating higher drought tolerance in the former. Higher grass transpiration and WUE combined to largely explain the threefold RGR advantage in grasses. Our results suggest that grasses outperform trees under a wide range of conditions, and that there is no evidence for a trade-off in water-use patterns in wet vs dry soils. This work will help inform mechanistic models of water use in savanna ecosystems, providing much-needed whole-plant parameter estimates for African species.

Testing the suitability for coastal green areas of three ornamental shrub species through physiological responses to the saline nebulization

Besides abiotic constraints, plants along the coastal urban areas must face additional cues such as saline aerosol, which impact net plant CO2 assimilation (Pn), reducing biomass and influencing their aesthetic features. In this study, three species (Photinia × fraseri, P; Escallonia rubra, E; and Feijoa sellowiana, F) were subjected to saline nebulization (SN) with a 100 mM NaCl solution. Analyses were performed at 0, 10, and 20 days by monitoring the ion accumulation in plant organs, leaf osmotic potentials, gas exchange, chlorophyll a fluorescence parameters, and chlorophyll contents. Overall, E-SN plants absorbed more Na+ and Cl− in leaves than P-SN and F-SN ones. This phenomenon was influenced by leaf ‘wettability’ features such as the contact angle of water droplets, droplet retention, and water storage capacity, and the effectiveness of translocating these ions on twig tissues. SN increased the leaf osmotic potential (regardless of species). At 10 days (i.e., moderate stress conditions), Pn declined in all SN species, but more severely (−82 %) in E-SN plants. The observed Pn reductions were due to different limiting factors according to the plant species: Pn was reduced by non-stomatal limitations in P-SN plants, stomatal closure in F-SN, and a combination of both in E-SN individuals. At 20 days (i.e., severe stress conditions), in all SN-plants, lower values in all the physiological parameters than controls were observed, indicating a low tolerance to prolonged SN. The work shows that non-destructive physiological measurements provide a reliable assessment of plant tolerance to SN, which can help growers to select ornamental species suitable for coastal green areas.

Deciphering salt tolerance in tetraploid honeysuckle (Lonicera japonica Thunb.) from ion homeostasis, water balance and antioxidant defense

Polyploid plants are usually salt tolerant, but the underlying mechanisms remain fragmental. This study aimed to dissect salt resistance of tetraploid honeysuckle (Lonicera japonica Thunb.) from ion balance, osmotic adjustment and antioxidant defense by contrasting with its autodiploid through pot experiments. Less salt-induced reduction in leaf and root biomass confirmed higher tolerance in tetraploid honeysuckle, and moreover, its greater stability of photosynthetic apparatus was verified by mild influence on delayed chlorophyll fluorescence transients. Compared with the diploid, greater root Na+ exclusion helped alleviate salt-induced decrease in leaf K+/Na+ for maintaining ion balance in tetraploid honeysuckle, and relied on Na+/H+ antiporter activity, because their difference of root Na+ exclusion disappeared after applying a specific inhibitor of Na+/H+ antiporter. Lower reduction in leaf relative water content suggested higher tolerance to osmotic pressure in tetraploid honeysuckle under salt stress, which hardly resulted from osmotic adjustment given the similar decrease extent of leaf osmotic potential with that in the diploid. In contrast to significant elevated leaf lipid peroxidation and superoxide dismutase and ascorbate peroxidase activities in the diploid, no obvious changes in them suggested that tetraploid honeysuckle never suffered salt-induced oxidative stress. According to more accumulated leaf chlorogenic acid and phenolics and greater elevated leaf phenylalanine ammonia-lyase activity and transcription, leaf phenolic synthesis was enhanced greater in tetraploid honeysuckle upon salt stress, which might serve to prevent oxidative threat by consuming reducing power. In conclusion, polyploidy enhanced salt tolerance in honeysuckle by maintaining ion homeostasis and water balance and preventing oxidative stress.

Ectopic expression of a grapevine alkaline α-galactosidase seed imbibition protein VvSIP enhanced salinity tolerance in transgenic tobacco plants.

Alpha-galactosidase seed imbibition protein (VvSIP) isolated from Vitis vinifera is up-regulated upon salt stress and mediates osmotic stress responses in a tolerant grapevine cultivar. So far, little is known about the putative role of this stress-responsive gene. In the present study, VvSIP function was investigated in model tobacco plants via Agrobacterium-mediated genetic transformation. Our results showed that overexpression of VvSIP exhibited increased tolerance to salinity at germination and late vegetative stage in transgenic Nicotiana benthamiana compared to the nontransgenic plants based on the measurement of the germination rate and biomass production. High salt concentrations of 200 and 400mM NaCl in greenhouse-grown pot assay resulted in better relative water content, higher leaf osmotic potential, and leaf water potential in transgenic lines when compared to the wild-type (WT) plants. These physiological changes attributed to efficient osmotic adjustment improved plant performance and tolerance to salinity compared to the WT. Moreover, the VvSIP-expressing lines SIP1 and SIP2 showed elevated amounts of chlorophyll with lower malondialdehyde content indicating a reduced lipid peroxidation required to maintain membrane stability. When subjected to high salinity conditions, the transgenic tobacco VvSIP exhibited higher soluble sugar content, which may suggest an enhancement of the carbohydrate metabolism. Our findings indicate that the VvSIP is involved in plant salt tolerance by functioning as a positive regulator of osmotic adjustment and sugar metabolism, both of which are responsible for stress mitigation. Such a candidate gene is highly suitable to alleviate environmental stresses and thus could be a promising candidate for crop improvement.

The root transcriptome dynamics reveals new valuable insights in the salt-resilience mechanism of wild grapevine (Vitis vinifera subsp. sylvestris).

Most of elite cultivated grapevine varieties (Vitis vinifera L.), conventionally grafted on rootstocks, are becoming more and more affected by climate changes, such as increase of salinity. Therefore, we revisited the valuable genetic resources of wild grapevines (V. sylvestris) to elaborate strategies for a sustainable viticulture. Here, we compared physiological and biochemical responses of two salt-tolerant species: a wild grapevine genotype "Tebaba" from our previous studies and the conventional rootstock "1103 Paulsen". Interestingly, our physio-biochemical results showed that under 150mM NaCl, "Tebaba" maintains higher leaf osmotic potential, lower Na+/K+ ratio and a significant peaked increase of polyphenol content at the first 8h of salinity stress. This behavior allowed to hypothesis a drastic repatterning of metabolism in "Tebaba's" roots following a biphasic response. In order to deepen our understanding on the "Tebaba" salt tolerance mechanism, we investigated a time-dependent transcriptomic analysis covering three sampling times, 8h, 24h and 48h. The dynamic analysis indicated that "Tebaba" root cells detect and respond on a large scale within 8h to an accumulation of ROS by enhancing a translational reprogramming process and inducing the transcripts of glycolytic metabolism and flavonoids biosynthesis as a predominate non-enzymatic scavenging process. Afterwards, there is a transition to a largely gluconeogenic stage followed by a combined response mechanism based on cell wall remodeling and lignin biosynthesis with an efficient osmoregulation between 24 and 48 h. This investigation explored for the first time in depth the established cross-talk between the physiological, biochemical and transcriptional regulators contributing to propose a hypothetical model of the dynamic salt mechanism tolerance of wild grapevines. In summary, these findings allowed further understanding of the genetic regulation mechanism of salt-tolerance in V. sylvestris and identified specific candidate genes valuable for appropriate breeding strategies.

Seed priming with ascorbic acid improves response of Medicago polymorpha L. seedlings to osmotic stress induced by NaCl and PEG solutions

This study assessed to which extent seed priming with ascorbic acid (0.2 mM) may improve Medicago polymorpha L. performance under water shortage induced by irrigation with either 50 mM NaCl or 100 g/L polyethylene glycol (PEG). Parameters related to plant morphology, CO2/H2O leaf gas exchanges, osmotic adjustment, pigment content, and proline accumulation were specifically determined. Both NaCl and PEG solutions induced osmotic stress and reduced plant biomass (−30% and −40%, respectively), number of leaves and ramifications, stem length, net CO2 assimilation (−31% and 63%, respectively), and leaf water content. However, both treatments and especially PEG led to increased root/shoot ratios and leaf proline content. Interestingly, seed priming using ascorbic acid improved CO2/H2O gas exchange and plant biomass production (+66%, +100%, and +92% in control, NaCl-, and PEG-treated plants, respectively). It also improved the water relations as reflected by the decrease of leaf osmotic potential and higher leaf proline accumulation (+67% and +120% in PEG- and NaCl-treated plants, respectively) and water content (especially under PEG treatment). Besides, seed priming with ascorbic acid increased leaf carotenoid and chlorophyll contents (+65 and +45%, respectively, for chlorophyll a and chlorophyll b), thereby contributing to the better photosynthetic activity, and hence plant performance under salinity. We conclude that seed priming with ascorbic acid is an easy, cost-effective and promising approach to mitigate the impact of osmotic stresses like drought and salinity, by especially improving plant water relations and photosynthetic activity.