Progressive Water Stress Research Articles

Physiological efficiency of grapevine canopies having varying geometries: Seasonal and diurnal whole canopy gas exchange assessment under well-watered and water deficit conditions

Grapevine training systems should be thoroughly examined to contribute to vineyards more resilient to climate change. This study was conducted on 18 three-year-old fruiting Sangiovese vines grown in pots outdoors with canopies trained to a vertical shoot positioned (VSP) spur-pruned cordon, a single high wire (SHW), and a Pergola (P) training system. Whole-canopy net CO2 exchange rate (NCER) and transpiration (T) were monitored by an enclosure system on a 24/7 basis from DOY 179–249. All vines were kept well-watered (WW) from DOY 179 to DOY 199, and the water supply was first reduced to 50% (DOY200–204) and then to 35% (DOY 205–214) before final rewatering (DOY 215–217). Vegetative growth, yield components, and grape composition were also assessed. Seasonal gas exchange on a per vine basis reflected vine size given as total leaf area (LA) varying from 2.5 to 3.1 m2; however, when diurnal trends of NCER/LA and T/LA within the WW and rewatering periods were considered, the good correlations found with the modeled total canopy light interception (TCLI) in SHW and P, were not confirmed in VSP. In all canopy geometries, the best predictor of NCER/LA was the total direct light intensity, whereas T/LA was linearly and closely correlated with air VPD. In terms of NCER/LA during the WW period, SHW had 24% higher rates than VSP and P. Under progressive water stress, SHW again exhibited higher drought resilience, while NCER and T were severely reduced in VSP and P. Severe stress also caused lower light saturation points and quantum yield in VSP and P. Under similar yield levels, P reached the best fruit maturity. In terms of photosynthetic efficiency and adaptive response to increasing water stress, the SHW performed best. Results extrapolated at the field level indicate the P system as the most rewarding.

Sugar Beet Rooting Pattern Mediates Stomatal and Transpiration Responses to Progressive Water Stress

Water stress is the main risk facing sugar beet production in Europe and is expected to worsen with climate change. Therefore, future production essentially depends on the traits that sustain growth during water shortages. In this study, we investigated the interplay of stomatal conductance and transpiration rate as well as the root characteristics of six sugar beet cultivars in a climate chamber experiment under environmental conditions progressing from a non-stressed initial state toward high atmospheric water demand, followed by reduced soil water supply and then by a combination of high demand and low supply. Stomatal conductance quickly responded to changing conditions, dropping from 406.4 to 42.5 mmol m−2 s−1, one order of magnitude, with the transition to reduced soil water availability. The transpiration rate showed a slightly delayed response compared with stomatal conductance, while we observed an inverse influence on the subsequent stomatal behavior exerted by the depletion/conservation of available soil water. The rooting pattern substantially differed among genotypes, predominantly at depths between 60 and 80 cm, where 50.5% of the root length was allocated. Longer roots buffered the effects of the reduction in stomatal conductance at the onset of water supply limitation, with 5.4 mmol m−2 s−1 higher conductance per 100 cm of root length. Therefore, breeding and/or management measures targeting root system vigor are the key to the growth maintenance of sugar beet during dry periods.

Apricot water relation and fruit growth under progressive water stress conditions

Apricot water relation and fruit growth under progressive water stress conditions

Potassium fertilization for improving water relations, photosynthetic pigments and antioxidant defence system in intercropping system of Gossypium hirsutum L. and Cajanus cajan (L.) Millsp. under different irrigation regimes

The present study evaluated the impact of potassium chloride (KCl) on growth, physiology, photosynthetic pigments and antioxidant enzymes under intercropping system of Gossypium hirsutum L. (RCH-773 variety) and Cajanus cajan (L.) Millsp. (Manak variety). The intercropping was operated in randomised complete block design under different irrigation schedules. The treatments were given as control (full irrigation), early water stress (no irrigation at vegetative stage), late water stress (no irrigation at flowering stage) and stress (no irrigation) along with three potassium concentrations K0, K1 and K2 (0, 20, 60 kg/acre respectively).The sampling was done at flowering stage (120 days after sowing). A long progressive water stress significantly reduced plant height, fresh and dry weight, leaf area, leaf area index, relative water content, membrane stability index and photosynthetic pigments. But application of potassium fertilizer enhanced all these parameters at a great value. The other parameters i.e. electrolyte leakage, superoxide dismutase and catalase increased in stress conditions. However, under potassium application, electrolyte leakage showed a remarkable decrease while the activity of superoxide dismutase and catalase was increased in control as well as in water stressed plants. It clearly shows that potassium is a strong osmo-regulator, maintains cation-anion balance, acts as co-factor for enzymes and helps plant withstanding drought stress conditions.

Physiological responses of apricot and peach cultivars under progressive water shortage: Different crop signals for anisohydric and isohydric behaviours

The knowledge about the behaviour of different fruit tree species when subjected to water shortage is pivotal to pair correctly the species with the environment, as well as to choose the most reliable index for monitoring the plant water status. Net photosynthesis (Pn) and stomatal conductance (gs) are considered some of the most reliable variables describing the plant water status, functionality and potential productivity, but their measurement are actually time consuming, complex and expensive. The aims of the present study were to investigate the effect of a progressive water stress on leaf functioning and plant water status of two stone fruit trees species; to study the water relations within the Soil-Plant-Atmosphere Continuum; to assess a pool of indices for estimating Pn and gs by means of other variables quick to be measured, potentially through less expensive and user-friendly sensors. The trial was carried out on an early ripening apricot variety (Prunus armeniaca L. cv. Primius) and on a late ripening peach variety (Prunus persica (L.) Batsch cv. Calred) subjected to progressive dry down. Trees were monitored for stem water potential, leaf temperature, chlorophyl fluorescence, Pn and gs. “Primius” and “Calred” behaved as near anisohydric and near-isohydric plants, respectively. In “Primius” Pn and gs were more affected by soil water content than vapour pressure deficit (VPD) and the opposite occurred in “Calred”, suggesting a different approach to be used for managing water in the two cultivars. Chlorophyll fluorescence variables and leaf to air temperature difference (ΔT), combined properly by means of stepwise multiple regression analysis approach, were selected as good predictors of Pn for both the species. ΔT and VPD were selected to estimate gs, using the same approach. The prediction performance of the models resulted good suggesting their possible use for driving irrigation in a more sustainable and plant-based way.

Hormonal Balance, Photosynthesis, and Redox Reactions in the Leaves of Caragana korshinskii Kom. under Water Deficit.

To evaluate the physiological responses of Korshinsk peashrub (Caragana korshinskii Kom.) to water deficit, photosynthetic gas exchange, chlorophyll fluorescence, and the levels of superoxide anion (O2•-), hydrogen peroxide (H2O2), malondialdehyde (MDA), antioxidant enzymes, and endogenous hormones in its leaves were investigated under different irrigation strategies during the entire growth period. The results showed that leaf growth-promoting hormones were maintained at a higher level during the stages of leaf expansion and vigorous growth, and zeatin riboside (ZR) and gibberellic acid (GA) gradually decreased with an increase in water deficit. At the leaf-shedding stage, the concentration of abscisic acid (ABA) dramatically increased, and the ratio of ABA to growth-promoting hormones increased to a high level, which indicated that the rate of leaf senescence and shedding was accelerated. At the stages of leaf expansion and vigorous growth, the actual efficiency of photosystem II (PSII) (ΦPSii) was downregulated with an increment in non-photochemical quenching (NPQ) under moderate water deficit. Excess excitation energy was dissipated, and the maximal efficiency of PSII (Fv/Fm) was maintained. However, with progressive water stress, the photo-protective mechanism was inadequate to avoid photo-damage; Fv/Fm was decreased and photosynthesis was subject to non-stomatal inhibition under severe water deficit. At the leaf-shedding stage, non-stomatal factors became the major factors in limiting photosynthesis under moderate and severe water deficits. In addition, the generation of O2•- and H2O2 in the leaves of Caragana was accelerated under moderate and severe water deficits, which caused an enhancement of antioxidant enzyme activities to maintain the oxidation-reduction balance. However, when the protective enzymes were insufficient in eliminating excessive reactive oxygen species (ROS), the activity of catalase (CAT) was reduced at the leaf-shedding stage. Taken all together, Caragana has strong drought resistance at the leaf expansion and vigorous growth stages, but weak drought resistance at the leaf-shedding stage.

Water stress protection by the arbuscular mycorrhizal fungus Rhizoglomus irregulare involves physiological and hormonal responses in an organ‐specific manner

Arbuscular mycorrhizal fungi may alleviate water stress in plants. Although several protection mechanisms have already been described, little information is available on how these fungi influence the hormonal response to water stress at an organ-specific level. In this study, we evaluated the physiological and hormonal responses to water stress in above and below-ground tissues of the legume grass Trifolium repens colonized by the arbuscular mycorrhizal fungus Rhizoglomus irregulare. Plants were subjected to progressive water stress and recovery. Different leaf and root physiological parameters, as well as phytohormone levels, were quantified. Water-stressed mycorrhizal plants showed an improved water status and no photoinhibition compared to uncolonized individuals, while some stress markers like α-tocopherol and malondialdehyde content, an indicator of the extent of lipid peroxidation, transiently increased in roots, but not in leaves. Water stress protection exerted by mycorrhiza appeared to be related to a differential root-to-shoot redox signaling, probably mediated by jasmonates, and mycorrhization enhanced the production of the cytokinin trans-zeatin in both roots and leaves. Overall, our results suggest that mycorrhization affects physiological, redox and hormonal responses to water stress at an organ-specific level, which may eventually modulate the final protection of the host from water stress.

Exploiting the drought tolerance of wild Elymus species for bread wheat improvement.

Crop wild resources are excellent sources of new genetic variation for resilience against climate extremes. However, detailed characterization of the desirable phenotypes is essential before using these crop wild resources in breeding programs. This current study was, therefore, conducted to investigate the water stress responses of eight wild Elymus species and two wheat cultivars. The experiment was carried out under varying levels of osmotic stress induced by polyethylene glycol and progressive water stress through different field capacities. Water stress significantly reduced both physiological and biochemical traits compared to control, ranging from 7.1% (protein content) to 34.5% (chlorophyll) under moderate stress and 9.1–45.8% under severe stress. The anatomical features were also affected under progressive water stress, including a reduction in xylem vessel diameter (7.92 and 16.50%), phloem length (4.36 and 7.18%), vascular bundle length (3.09 and 6.04%), and ground tissue thickness (2.36 and 5.52%), respectively. Conclusively, Elymus borianus (endemic to Swat, Pakistan), E. russelli, E. caninus, E. longioristatus, and E. dauhuricus outperformed the check wheat cultivar, Pirsabak 2005, which is a rainfed variety. The results revealed that Elymus species belonging to the tertiary gene pool of bread wheat could be an excellent drought tolerance source for use in a breeding program.

Morpho-Anatomical Traits and Soluble Sugar Concentration Largely Explain the Responses of Three Deciduous Tree Species to Progressive Water Stress.

A better understanding of plant drought responses is essential to improve plant water use efficiency, productivity, and resilience to ever-changing climatic conditions. Here, we investigated the growth, morpho-anatomical, physiological, and biochemical responses of Quercus acutissima Carruth., Quercus serrata Murray, and Betula schmidtii Regel to progressive water-stress. Seedlings were subjected to well-watered (WW) and water-stressed (WS) conditions while regularly monitoring the soil volumetric water content, stem diameter (SD), height, biomass, stomatal conductance (gs), intercellular CO2 concentration (Ci), and leaf relative water content (RWC). We also investigated the variation in stomatal pore (SP) area, specific leaf area (SLA), root xylem vessel diameter (VD), and total soluble sugar (TSS) concentration between treatments. After 2 months, WS significantly suppressed SD growth of Q. acutissima and B. schmidtii but had no impact on Q. serrata. Total biomass significantly declined at WS-treated seedlings in all species. WS resulted in a smaller SLA than WW in all species. The SP of WS-treated seedlings of Q. acutissima and B. schmidtii significantly decreased, whereas it increased significantly with time in Q. serrata. Larger vessels (i.e., >100 to ≤ 130) were more frequent at WS for Q. acutissima and B. schmidtii, whereas smaller vessels (i.e., >40 to ≤ 90) were more frequent at WS than at WW for Q. serrata after 8 weeks. Tylosis was more frequent at WS than WW for Q. serrata and B. schmidtii at eighth week. WS seedlings showed lower gs, Ci, and RWC compared with WW-treated ones in Q. acutissima and B. schmidtii. TSS concentration was also higher at WS-treated seedlings in two Quercus species. Overall, principal component analysis (PCA) showed that SLA and SP are associated with WS seedlings of Q. serrata and B. schmidtii and the tylosis frequency, TSS, and VD are associated with WS seedlings of Q. acutissima. Therefore, water-stressed plants from all species responded positively to water stress with increasing experimental duration and stress intensity, and that is largely explained by morpho-anatomical traits and soluble sugar concentration. The present study should enhance our understanding of drought-induced tree growth and short-term tree-seedling responses to drought.

Effects of Soil Amendment With Wood Ash on Transpiration, Growth, and Metal Uptake in Two Contrasting Maize (Zea mays L.) Hybrids to Drought Tolerance.

Wood ash as a soil amendment has gained wide spread acceptance in the recent years as a sustainable alternative to chemical fertilizers, although information regarding the effects of its application on maize growth and yield in the context of climate change and increasing drought severity is lacking till date. In the present study, field and pot trials were carried out at the experimental farm of the University of Padova at Legnaro (NE Italy) in a silty-loam soil in order to investigate the effects of soil amendment with wood ash (0.1% w/w, incorporated into the 0.2-m top soil) on the bioavailability of mineral elements and their uptake by maize. Characteristics analyzed included plant growth, leaf transpiration dynamics, and productivity in two contrasting hybrids, P1921 (drought sensitive) and D24 (drought tolerant). Wood ash contained relevant amounts of Ca, K, Mg, P, and S, and hazardous levels of Zn (732 mg kg−1), Pb (527 mg kg−1), and Cu (129 mg kg−1), although no significant changes in total soil element concentration, pH, and electrical conductivity were detected in open field. Ash application led to a general increasing trend of diethylene triamine penta-acetic acid (DTPA)-extractable of various elements, bringing to higher grain P in D24 hybrid, and Zn and Ni reductions in P1921 hybrid. Here, the results demonstrated that ash amendment enhanced shoot growth and the number of leaves, causing a reduction of harvest index, without affecting grain yield in both hybrids. The most relevant result was a retarded inhibition of leaf transpiration under artificial progressive water stress, particularly in the drought-tolerant D24 hybrid that could be sustained by root growth improvements in the field across the whole 0–1.5 m soil profile in D24, and in the amended top soil in P1921. It is concluded that woody ash can be profitably exploited in maize fertilization for enhancing shoot and root growth and drought tolerance, thanks to morphological and physiological improvements, although major benefits are expected to be achieved in drought tolerant hybrids. Attention should be payed when using ash derived by metal contaminated wood stocks to avoid any health risk in food uses.

Effects of plant growth-promoting rhizobacteria strains producing ACC deaminase on photosynthesis, isoprene emission, ethylene formation and growth of Mucuna pruriens (L.) DC. in response to water deficit

Agricultural sustainability is an increasing need considering the challenges posed by climate change and rapid human population growth. The use of plant growth-promoting rhizobacteria (PGPR) may represent an excellent, new agriculture practice to improve soil quality while promoting growth and yield of important crop species subjected to water stress conditions. In this study, two PGPR strains with 1-Aminocyclopropane-1-Carboxylate (ACC) deaminase activity were co-inoculated in velvet bean plants to verify the physiological, biochemical and molecular responses to progressive water stress. The results of our study show that the total biomass and the water use efficiency of inoculated plants were higher than uninoculated plants at the end of the water stress period. These positive effects may be derived from a lower root ACC content (−45 %) in water-stressed inoculated plants than in uninoculated ones resulting in lower root ethylene emission. Furthermore, the ability of inoculated plants to maintain higher levels of both isoprene emission, a priming compound that may help to protect leaves from oxidative damage, and carbon assimilation during water stress progression may indicate the underlining metabolic processes conferring water stress tolerance. Overall, the experimental results show that co-inoculation with ACC deaminase PGPR positively affects tolerance to water deficit, confirming the potential for biotechnological applications in water-stressed agricultural areas.

Capability of leaf water content and its threshold values in reflection of soil–plant water status in maize during prolonged drought

Leaves play an important role in plant growth and development through photosynthesis and transpiration. Many studies have explored the effects of short-term drought stress on leaf water status; however, few studies have focused on the leaf water content capacity as an indicator of soil–plant water status during prolonged droughts. The results of a field experiment with various irrigation regimes that was conducted during two consecutive maize growing seasons from 2013 to 2014, indicated that the water content of the first fully expanded leaf (LWCtop1) was representative of the soil–plant water status with the development of drought. LWCtop1 was closely linked to the water condition of other leaves and different plant parts in response to progressive water stress. LWCtop1 shared a quadratic relationship with the photosynthetic rate (Pn), and Pn peaked when LWCtop1 approached 84.11% and decreased to zero when LWCtop1 dropped to 68.26%. Moreover, three stages (slow-fast-slow) were observed as leaf water content responded to soil drying, and two important threshold values (minimum: 70.86 ± 0.80%, maximum: 84.58 ± 1.10%) of the leaf water content were determined. The results of this study may provide a physiological and ecological basis for the identification and monitoring of crop drought.

Characterization of Eucalyptus camaldulensis clones with contrasting response to short-term water stress response

The intra-specific diversity of adaptive traits in tree species is a key factor determining their survivability under stress conditions. In vitro screening under controlled environmental conditions to evaluate the whole-tree response to drought condition is routinely employed to select tolerant genotypes for breeding and conservation programs. The present study demonstrates the response of two Eucalyptus camaldulensis clones to progressive short-term water stress condition at morphological, physiological, biochemical, molecular and metabolite levels. Distinct differential response was recorded in root: shoot, specific leaf area, relative water content and leaf phenol content across the clones. The biochemical changes were significant in root tissues of both genotypes after stress imposition when compared to leaf. Metabolite profiling revealed accumulation of α-limonene, fenchyl alcohol, borneol, 4-terpineol, 4-thujanol, aromadendrene, α-eudesmol and eicosyl acetate in tolerant clone under water stress condition. Molecular profiling documented up-regulation of germin (GER3) in leaf and several transcription factors like DREB, CBF2 and CBF1c in root tissues of tolerant clone. This study has presented several parameters with distinct variation across the tolerant and susceptible clone like root carbohydrate content, stomatal density and root phytohormone level, which can be used for nursery screening of Eucalyptus clones for water stress tolerance.

Carbon Isotope Composition and the NDVI as Phenotyping Approaches for Drought Adaptation in Durum Wheat: Beyond Trait Selection

High-throughput phenotyping platforms provide valuable opportunities to investigate biomass and drought-adaptive traits. We explored the capacity of traits associated with drought adaptation such as aerial measurements of the Normalized Difference Vegetation Index (NDVI) and carbon isotope composition (δ13C) determined at the leaf level to predict genetic variation in biomass. A panel of 248 elite durum wheat accessions was grown at the Maricopa Phenotyping platform (US) under well-watered conditions until anthesis, and then irrigation was stopped and plot biomass was harvested about three weeks later. Globally, the δ13C values increased from the first to the second sampling date, in keeping with the imposition of progressive water stress. Additionally, δ13C was negatively correlated with final biomass, and the correlation increased at the second sampling, suggesting that accessions with lower water-use efficiency maintained better water status and, thus, performed better. Flowering time affected NDVI predictions of biomass, revealing the importance of developmental stage when measuring the NDVI and the effect that phenology has on its accuracy when monitoring genotypic adaptation to specific environments. The results indicate that in addition to choosing the optimal phenotypic traits, the time at which they are assessed, and avoiding a wide genotypic range in phenology is crucial.

Diversity of bacterial endophyte in Eucalyptus clones and their implications in water stress tolerance

The genus Eucalyptus with over 747 species occurs in wide ecological range and is preferred for bioenergy plantations due to their short rotation, rapid growth and superior wood properties. They are planted in 22 million ha area and India is third largest planter of Eucalyptus. In the present study, the bacterial endophyte community in leaves of six Eucalyptus clones belonging to E. tereticornis and E. camaldulensis was assessed by sequencing the V3–V4 region of the bacterial 16S rRNA gene. The clones were selected based on their response to progressive water stress. A total of 4947 operational taxonomic units (OTUs) were obtained and the dominant phyla were Proteobacteria, Bacteroidetes and Firmicutes. Escherichia coli was enriched in all samples at species level. Comparison of endophyte diversity was conducted between the two species and across the water stress tolerant and susceptible clones. The alpha-diversity analysis revealed that species richness and diversity was high in E. camaldulensis and water stress susceptible clones. LefSe analysis predicted 69 and 54 significantly enriched taxonomic biomarkers between species and stress response groups respectively. A maximum of 49 taxonomic biomarkers were recorded in susceptible group and the significantly enriched species were Bacteroides thetaiotaomicron and Turicibacter sanguinis, while the tolerant group documented 5 biomarkers including oscillibacter sp. The presence of functional biomarkers was also assessed in both the groups. The findings of the present study provides an insight into the diversity of bacterial endophyte in Eucalyptus leaves and to our knowledge this is the first report on documenting the endophyte abundance in water stress responsive Eucalyptus clones.

Grafting cv. Grechetto Gentile Vines to New M4 Rootstock Improves Leaf Gas Exchange and Water Status as Compared to Commercial 1103P Rootstock

M4 is a relatively new rootstock that was selected for increased resilience of vineyards across hot regions where meteorological drought is often coupled to water scarcity. However, M4 has thus far been tested only against water-stress sensitive rootstocks. Against this backdrop, the aim of the present work is to examine the water status and gas exchange performances of vines grafted to M4 in comparison to those of vines grafted to a commercial stock that is drought-tolerant, 1103 Paulsen (1103P), under a progressive water deficit followed by re-watering. This study was undertaken on Grechetto Gentile, a cultivar that is renowned for its rather conservative water use (near-isohydric behavior). While fifty percent of both grafts were fully irrigated (WW), the remaining underwent progressive water stress by means of suspending irrigation (WS). Soil and leaf water status, as well as leaf gas exchanges, along with chlorophyll fluorescence, were followed daily from 1 day pre-stress (DOY 176) until re-watering (DOY 184). Final leaf area per vine, divided in main and lateral contribution, was also assessed. While 1103P grafted vines manifested higher water use under WW conditions, progressive stress evidenced a faster water depletion by 1103P, which also maintained slightly more negative midday leaf water potential (Ψleaf) as compared to M4 grafted plants. Daily gas exchange readings, as well as diurnal assessment performed at the peak of stress (DOY 183), also showed increased leaf assimilation rates (A) and water use efficiency (WUE) in vines grafted on M4, which were also less susceptible to photosynthetic downregulation. Dynamic of stomatal closure targeted at 90% reduction of leaf stomatal conductance showed a similar behavior among rootstocks since the above threshold was reached by both at Ψleaf of about −1.11 MPa. The same fractional reduction in leaf A was reached by vines grafted on M4 at a Ψleaf of −1.28 MPa vs. −1.10 MPa measured in 1103P, meaning that using M4 as a rootstock will postpone full stomatal closure. While mechanisms involved in improved CO2 uptake in M4-grafted vines under moderate-to-severe stress are still unclear, our data support the hypothesis that M4 might outscore the performance of a commercial drought-tolerant genotype (1103P) and can be profitably used as a tool to improve the resilience of vines to summer drought.

Protein hydrolysates modulate leaf proteome and metabolome in water-stressed grapevines

Biostimulants are innovative tools for the modern vineyard management, especially in relation to the new challenges posed by climate change. These products can modulate vine physiology and improve biotic/abiotic stress tolerance, but their mechanisms of action are still unclear. The present work aims at investigating the effects of two vegetal-derived protein hydrolysates on water-stressed vines, clarifying the involved mechanisms of action.Potted vines of Vitis vinifera L. cv. Montepulciano were subjected to a progressive water-stress. Vines sprayed pre-veraison with ‘Trainer’ (PH1) and ‘Stimtide’ (PH2) were compared with untreated vines. Leaves were sampled to perform non-target analysis of leaf proteome and metabolome. Gas exchanges performances were measured after re-watering and, at harvest, vine productivity and fruit composition were evaluated.PH1 significantly up-regulated metabolites involved in plant growth regulations and promoted the delay of senescence. At leaf Ψ= −1.4 MPa, both biostimulants up-regulated 6 and 7 photosynthesis-related proteins, respectively. However, 5 days past re-watering, no effects were found on assimilation rates, but leaf transpiration was improved by both treatments, as compared to control. The two formulates did not change vine yield and bunch morphology, but significantly reduced grapes total soluble solids (−3.5°Brix) and pH (−6%). PH2 significantly increased grapes TA (+1.87 g/L). The two biostimulants did not significantly affect the grapes total anthocyanins or their phenolic profile.In conclusion, PH1 and PH2 produced deep changes in leaf proteome and metabolome that delayed physiological maturity and maintained higher acidity, with no negative effects on anthocyanins and phenolics. Considering the negative effects of warming trends, today affecting most of traditional and modern wine regions, protein hydrolysates can be considered valuable tools to improve fruit quality and vineyard sustainability.

Contrasting leaf porometer and infra-red gas analyser methodologies: an old paradigm about the stomatal conductance measurement

Here we compare the stomatal conductance (gs) values obtained with leaf porometer and infra-red gas analyzer (IRGA) in different species subjected to different water availability and evaluated in two different environmental conditions. Sunflower, maize, bean, and grapevine were subjected to two treatments of water availability: well-watered and progressive water stress for 3 days and evaluated in two different times with contrasting environmental conditions. The gs was determined both on the abaxial and adaxial side of leaves using a leaf porometer and an IRGA. The measured gs strongly differed between IRGA and porometer, in a way that depended on the species, as well as water availability and environmental conditions. Under maximum water stress, gs measured with leaf porometer was higher than those measured with IRGA in the four species studied. The present results question the use of usual methodologies for the estimation of gs, suggesting that gs would not only depend on the environmental conditions and the water status of the plants, but also on the method used to measure it.

Parthenium avoids drought: Understanding the morphological and physiological responses of the invasive herb Parthenium hysterophorus to progressive water stress

Parthenium hysterophorus L. is a noxious annual invasive herb which threatens biodiversity, food security and human and animal health in various tropical and sub-tropical regions globally. Given that these regions, including South Africa, experience frequent drought events, it is important that the invasive potential of this weed be better understood in the context of water stress. This study aimed to assess the physiological and morphological responses of P. hysterophorus to water stress. To elicit these responses, juvenile and adult plants were progressively water stressed over a six-week period. Despite significant reductions in leaf water potential, relative leaf water content and stomatal conductance from severe soil water stress, plants maintained positive net photosynthesis, albeit at a severely reduced rate. Concomitantly, water-use efficiency of P. hysterophorus increased by more than 300 %. Morphologically, water-stressed plants exhibited reductions in leaf area and leaf number, with adults accelerating flower production when compared to well-watered plants. Linked to this, were alterations in biomass, with juveniles and adults reducing above-ground biomass by 75 % and 35 %, respectively. Overall, many of the physiological and morphological responses are indicative of a largely drought avoidance strategy, allowing P. hysterophorus to persist during periods of water-stress as leafy basal rosettes (juveniles) or as reproductive herbs (adults). This research yielded valuable insights into the underlying water relations of P. hysterophorus, and how these may relate to the potential spread, detriment and management of the weed in various sub-tropical environments.

Transcriptomic analysis of a Sorghum bicolor landrace identifies a role for beta-alanine betaine biosynthesis in drought tolerance

Sorghum is indigenous to Africa and a remarkably drought tolerant cereal crop. In this study, the genetic response mechanisms involved in sorghum's tolerance to progressive water deficit and re-watering were investigated in a South African landrace (designated LR6), using cDNA microarrays comprising 35,899 transcript probes. Significant differential expression of 902 transcripts, including 128 transcripts with currently unknown functions, was altered in response to progressive water stress and re-watering. The modulated sorghum genes had homology to proteins involved in growth, regulation, and protection. Gene Ontology (GO) analysis identified significant enrichment of 26 genes involved in the ‘response to abiotic stimulus’ GO category during severe stress. The expression of two genes associated with beta(β)-alanine betaine biosynthesis was validated with quantitative RT-PCR. Importantly, the detection of β-alanine betaine in sorghum leaf extracts using NMR spectroscopy, and the significant increase in relative abundance during severe stress supports the microarray and qRT-PCR findings, thereby highlighting a role for β-alanine betaine biosynthesis in drought tolerance of sorghum. In future, crop improvement initiatives that consider metabolic engineering of the β-alanine betaine biosynthesis pathway should be explored.