Synergistic regulation at physiological, transcriptional and metabolic levels in tomato plants subjected to a combination of salt and heat stress.

With global warming and climate change, abiotic stresses often simultaneously occur. Combined salt and heat stress was a common phenomenon that was severe, particularly in arid/semi-arid lands. We aimed to reveal the systematic responsive mechanisms of tomato genotypes with different salt/heat susceptibilities to combined salt and heat stress. Morphological and physiological responses of salt-tolerant/sensitive and heat-tolerant/sensitive tomatoes at control, heat, salt and combined stress were investigated. Based on leaf Fv /Fm and H2 O2 content, samples from tolerant genotype at the four treatments for 36 h were taken for transcriptomics and metabolomics. We found that plant height, dry weight and net photosynthetic rate decreased while leaf Na+ concentration increased in all four genotypes under salt and combined stress than control. Changes in physiological indicators such as photosynthetic parameters and defence enzyme activities in tomato under combined stress were regulated by the expression of relevant genes and the accumulation of key metabolites. We screened five key pathways in tomato responding to a combination of salt and heat stress, such as oxidative phosphorylation (map00190). Synergistic regulation at morphological, physiological, transcriptional and metabolic levels in tomato plants was induced by combined stress. Heat stress was considered as a dominant stressor for tomato plants under the current combined stress. The oxidative phosphorylation pathway played a key role in tomato in response to combined stress, where tapped key genes (e.g. alternative oxidase, Aox1a) need further functional analysis. Our study will provide a valuable resource important for studying stress combination and improving tomato tolerance.

Stomatal effects and ABA metabolism mediate differential regulation of leaf and flower cooling in tomato cultivars exposed to heat and drought stress.

Co-occurring heat and drought stresses challenge crop performance. Stomata open to promote evaporative cooling during heat stress, but close to retain water during drought stress, which resulted in complex stomatal regulation under combined heat and drought. We aimed to investigate stomatal regulation in leaves and flowers of perennial, indeterminate cultivars of tomatoes subjected to individual and combined heat and drought stress followed by a recovery period, measuring morphological, physiological, and biochemical factors involved in stomatal regulation. Under stress, stomata of leaves were predominantly affected by drought, with lower stomatal density and stomatal closing, resulting in significantly decreased photosynthesis and higher leaf temperature. Conversely, stomata in sepals seemed affected mainly by heat during stress. The differential patterns in stomatal regulation in leaves and flowers persisted into the recovery phase as contrasting patterns in stomatal density. We show that flower transpiration is regulated by temperature, but leaf transpiration is regulated by soil water availability during stress. Organ-specific patterns of stomatal development and abscisic acid metabolism mediated this phenomenon. Our results throw light on the dual role of stomata in heat and drought tolerance of vegetative and generative organs, and demonstrate the importance of considering flower surfaces in the phenotyping of stomatal reactions to stress.

Salinity, waterlogging, and elevated [CO2] interact to induce complex responses in cultivated and wild tomato.

The effects of individual climatic factors on crops are well documented, whereas the interaction of such factors in combination has received less attention. The frequency of salinity and waterlogging stress is increasing with climate change, accompanied by elevated CO2 concentration (e[CO2]). This study explored how these three variables interacted and affected two tomato genotypes. Cultivated and wild tomato (Solanum lycopersicum and Solanum pimpinellifolium) were grown at ambient [CO2] and e[CO2], and subjected to salinity, waterlogging, and combined stress. Leaf photosynthesis, chlorophyll fluorescence, quenching analysis, pigment, and plant growth were analyzed. The response of tomatoes depended on both genotype and stress type. In cultivated tomato, photosynthesis was inhibited by salinity and combined stress, whereas in wild tomato, both salinity and waterlogging stress, alone and in combination, decreased photosynthesis. e[CO2] increased photosynthesis and biomass of cultivated tomato under salinity and combined stress compared with ambient [CO2]. Differences between tomato genotypes in response to individual and combined stress were observed in key photosynthetic and growth parameters. Hierarchical clustering and principal component analysis revealed genetic variations of tomatoes responding to the three climatic factors. Understanding the interacting effects of salinity and waterlogging with e[CO2] in tomato will facilitate improvement of crop resilience to climate change.

Dominant and Priming Role of Waterlogging in Tomato at e[CO2] by Multivariate Analysis.

The frequency of waterlogging episodes has increased due to unpredictable and intense rainfalls. However, less is known about waterlogging memory and its interaction with other climate change events, such as elevated CO2 concentration (e[CO2]). This study investigated the combined effects of e[CO2] and two rounds of waterlogging stress on the growth of cultivated tomato (Solanum lycopersicum) and wild tomato (S. pimpinellifolium). The aim is to elucidate the interaction between genotypes and environmental factors and thereby to improve crop resilience to climate change. We found that two rounds of treatments appeared to induce different acclimation strategies of the two tomato genotypes. S. pimpinellifolium responded more negatively to the first-time waterlogging than S. lycopersicum, as indicated by decreased photosynthesis and biomass loss. Nevertheless, the two genotypes respond similarly when waterlogging stress recurred, showing that they could maintain a higher leaf photosynthesis compared to single stress, especially for the wild genotype. This showed that waterlogging priming played a positive role in stress memory in both tomato genotypes. Multivariate analysis showed that waterlogging played a dominant role when combined with [CO2] for both the cultivated and wild tomato genotypes. This work will benefit agricultural production strategies by pinpointing the positive effects of e[CO2] and waterlogging memory.

Effects of UV radiation on transcript and metabolite accumulation are dependent on monochromatic light background in cucumber.

During recent years, we have advanced our understanding of plant molecular responses to ultraviolet radiation (UV, 280-400 nm); however, how plants respond to UV radiation under different spectral light qualities is poorly understood. In this study, cucumber plants (Cucumis sativus "Lausanna RZ F1") were grown under monochromatic blue, green, red, and broadband white light in combination with UV radiation. The effects of light quality and UV radiation on acclimatory responses were assessed by measuring transcript accumulation of ELONGATED HYPOCOTYL 5 (HY5), CHALCONE SYNTHASE 2 (CHS2), and LIGHT HARVESTING COMPLEX II (LHCII), and the accumulation of flavonoids and hydroxycinnamic acids in the leaves. The growth light backgrounds differentially regulated gene expression and metabolite accumulation. While HY5 and CHS2 transcripts were induced by blue and white light, LHCII was induced by white and red light. Furthermore, UV radiation antagonized the effects of blue, red, green, and white light on transcript accumulation in a gene-dependent manner. Plants grown under blue light with supplementary UV radiation increased phenylalanine, flavonol disaccharide I and caffeic acid contents compared to those exposed only to blue light. UV radiation also induced the accumulation of flavonol disaccharide I and II, ferulic acid hexose and coumaric acid hexose in plants grown under green light. Our findings provide a further understanding of plant responses to UV radiation in combination with different light spectra and contribute to the design of light recipes for horticultural practices that aim to modify plant metabolism and ultimately improve crop quality.

Unique miRNAs and their targets in tomato leaf responding to combined drought and heat stress.

BACKGROUND: Both drought and heat stress are serious global problems, leading to agricultural production loss. MicroRNAs (miRNAs) play important roles in plant species responding to individual drought and heat stress. However, the miRNAs and mRNAs in association with combined drought and heat in crops like tomato remains unclear. RESULTS: We studied the crosstalk of miRNAs and their target genes in tomato plants grown under simultaneous drought and heat stress that frequently happen in field conditions. In total, 335 known miRNAs representing 55 miRNA families and 430 potential novel miRNAs were identified in Solanum lycopersicum L. using small RNA deep sequencing. Through expression analysis, miRNAs in association with drought, heat and the combination of these were investigated. In total, 61, 74 and 37 miRNAs were differentially regulated for combination (of both stresses) vs control, combination vs drought and combination vs heat, respectively. Target genes with different expression levels were found using degradome sequencing, which were mainly involved in transcription factor activity, sequence-specific DNA binding, transcription, regulation of transcription, nucleus, DNA binding etc. The quantitative real-time polymerase chain reaction (qRT-PCR) results confirmed the accuracy of sequencing. CONCLUSIONS: Our study serves as valuable knowledge on how crop adapted to combined drought and heat stress by regulating miRNAs and mRNAs, which provide information for crop improvement to deal with future climate changes.

Interactive effects of elevated CO2 concentration and combined heat and drought stress on tomato photosynthesis.

BACKGROUND: Extreme weather events are predicted to increase, such as combined heat and drought. The CO2 concentration ([CO2]) is predicted to approximately double by 2100. We aim to explore how tomato physiology, especially photosynthesis, is affected by combined heat and drought under elevated [CO2] (e [CO2]). RESULTS: Two genotypes, 'OuBei' ('OB', Solanum lycopersicum) and 'LA2093' (S. pimpinellifolium) were grown at a [CO2] (atmospheric [CO2], 400 ppm) and e [CO2] (800 ppm), respectively. The 27-days-old seedlings were treated at 1) a [CO2], 2) a [CO2] + combined stress, 3) e [CO2] and 4) e [CO2] + combined stress, followed by recovery. The PN (net photosynthetic rate) increased at e [CO2] as compared with a [CO2] and combined stress inhibited the PN. Combined stress decreased the Fv/Fm (maximum quantum efficiency of photosystem II) of 'OB' at e [CO2] and that of 'LA2093' in regardless of [CO2]. Genotypic difference was observed in the e [CO2] effect on the gas exchange, carbohydrate accumulation, pigment content and dry matter accumulation. CONCLUSIONS: Short-term combined stress caused reversible damage on tomato while the e [CO2] alleviated the damage on photosynthesis. However, the e [CO2] cannot be always assumed have positive effects on plant growth during stress due to increased water consumption. This study provided insights into the physiological effects of e [CO2] on tomato growth under combined stress and contributed to tomato breeding and management under climate change.

Inherent trait differences explain wheat cultivar responses to climate factor interactions: New insights for more robust crop modelling.

Climate change predictions foresee a combination of rising CO2 , temperature and altered precipitation. Effects of single climatic variables are well defined, but the importance of combined variables and genotypic effects is less known, although pivotal for assessing climate change impacts, for example, with crop growth models. This study provides developmental and physiological data from combined climatic factors for two distinct wheat cultivars (Paragon and Gladius), as a basis to improve predictions for climate change scenarios. The two cultivars were grown in controlled climate chambers in a fully factorial setup of atmospheric CO2 concentration, growth temperature and watering regime. The cultivars differed considerably in their developmental rate, response pattern and the parameters responsible for most of their variation. The growth of Paragon was linked to climatic effects on photosynthesis and mainly affected by temperature. Paragon was overall more negatively affected by all treatment combinations compared to Gladius. Gladius was mostly affected by watering regime. The cultivars' acclimation strategies to climate factors varied significantly. Thus, considering a single factor is an oversimplification very likely impacting the accuracy of crop growth models. Intraspecific crop variation could help understanding genotype by environment variation. Cultivars with high phenotypic plasticity may have greater resilience against climatic variability.

The Alleviation of Photosynthetic Damage in Tomato under Drought and Cold Stress by High CO2 and Melatonin.

The atmospheric CO2 concentration (a[CO2]) is increasing at an unprecedented pace. Exogenous melatonin plays positive roles in the response of plants to abiotic stresses, including drought and cold. The effect of elevated CO2 concentration (e[CO2]) accompanied by exogenous melatonin on plants under drought and cold stresses remains unknown. Here, tomato plants were grown under a[CO2] and e[CO2], with half of the plants pre-treated with melatonin. The plants were subsequently treated with drought stress followed by cold stress. The results showed that a decreased net photosynthetic rate (PN) was aggravated by a prolonged water deficit. The PN was partially restored after recovery from drought but stayed low under a successive cold stress. Starch content was downregulated by drought but upregulated by cold. The e[CO2] enhanced PN of the plants under non-stressed conditions, and moderate drought and recovery but not severe drought. Stomatal conductance (gs) and the transpiration rate (E) was less inhibited by drought under e[CO2] than under a[CO2]. Tomato grown under e[CO2] had better leaf cooling than under a[CO2] when subjected to drought. Moreover, melatonin enhanced PN during recovery from drought and cold stress, and enhanced biomass accumulation in tomato under e[CO2]. The chlorophyll a content in plants treated with melatonin was higher than in non-treated plants under e[CO2] during cold stress. Our findings will improve the knowledge on plant responses to abiotic stresses in a future [CO2]-rich environment accompanied by exogenous melatonin.

Allopolyploidization in Cucumis contributes to delayed leaf maturation with repression of redundant homoeologous genes.

The important role of polyploidy in plant evolution is widely recognized. However, many questions remain to be explored to address how polyploidy affects the phenotype of the plant. To shed light on the phenotypic and molecular impacts of allopolyploidy, we investigated the leaf development of a synthesized allotetraploid (Cucumis × hytivus), with an emphasis on chlorophyll development. Delayed leaf maturation was identified in C. × hytivus, based on delayed leaf expansion, initial chlorophyll deficiency in the leaves and disordered sink-source transition. Anatomical observations also revealed disturbed chloroplast development in C. ×hytivus. The determination of chlorophyll biosynthesis intermediates suggested that the chlorophyll biosynthesis pathway of C. × hytivus is blocked at the site at which uroporphyrinogen III is catalysed to coproporphyrinogen III. Three chlorophyll biosynthesis-related genes, HEMA1, HEME2 and POR, were significantly repressed in C. × hytivus. Sequence alignment showed both synonymous and non-synonymous substitutions in the HEMA1, HEME2 and POR genes of the parents. Cloning of the chlorophyll biosynthetic genes suggested the retention of homoeologs. In addition, a chimeric clone of the HEMA1 gene that consisted of homologous genes from the parents was identified in C. × hytivus. Overall, our results showed that allopolyploidization in Cucumis has resulted in disturbed chloroplast development and reduced chlorophyll biosynthesis caused by the repressed expression of duplicated homologous genes, which further led to delayed leaf maturation in the allotetraploid, C. × hytivus. The preferential retention/loss of certain types of genes and non-reciprocal homoeologous recombination were also supported in the present study, which provides new insights into the impact of allopolyploidy.

Physiological analysis and transcriptome sequencing reveal the effects of combined cold and drought on tomato leaf.

BACKGROUND: Co-occurrence of cold and drought stress can alter the response of plants at morphological, physiological and molecular levels, which finally affect crop production, more than individual stress. Understanding the responses of crop to combined stress is necessary to improve tolerance and maintain crop production especially in the field where combined stress frequently occurs. We aimed to clarify the underlying leaf physiological and molecular mechanisms of tomato by imposing combining cold and drought on one popular tomato cultivar 'Jinlingmeiyu' as an example. RESULTS: The physiological and genetic responses were identified in tomatoes after 42 h exposure to control, cold, drought and combined treatments. As compared with control, water loss rate at the three stresses including cold, drought and combined stress significantly decreased until 40 min after taking samples from the plants. The content of H2O2, zeatin riboside (ZR) and melatonin in all stress treatments were significantly higher than the control. Drought stress alone and combined stress induced the accumulation of abscisic acid (ABA) and auxin (IAA) as compared with control. The individual cold and combined stress significantly decreased the maximum quantum efficiency of PSII (Fv/Fm), quantum yield of PSII (Fq'/Fm') and electron transport rate (ETR). In total, 7141, 1850 and 7841 genes were involved in the stress response to cold, drought and their combination. Functional analysis of the stress-inducible genes provided more insights concerning the complex regulatory mechanisms that were involved in combined stress. The expression level of 12 genes were validated by quantitative real-time PCR (qRT-PCR). CONCLUSIONS: We found that the expression of stress-specific genes changed with physiological variation, indicating the close crosstalk between physiological and genetic response especially under combined stress. This study provides new knowledge on the complex regulatory mechanism genes in tomato ('Jinlingmeiyu') leaf to abiotic stresses.

Physiological response of tomatoes at drought, heat and their combination followed by recovery.

In nature, crops encounter a combination of abiotic stresses that severely limit yield. Our aim was to dynamically expose the changes of tomatoes' physiological parameters to drought, heat and their combination and thereby clarify the relationship between the responses to single and combined stress. We studied the effect of single and combined drought and heat stresses on the shoot and root of two tomato cultivars (Sufen No.14 as CV1; Jinlingmeiyu as CV2). After being exposed to combined stress for 6 days, the dry weight of shoot and root significantly decreased. The Fq '/Fm ' (quantum yield of photosystem II) was significantly lower in CV1 upon drought and combined stress and in CV2 subjected to combined stress (between days 4 and 6) compared to control. The relative water content during combined stress was significantly lower than control from day 4 to recovery day 2. On days 3 and 6, the water loss rate significantly increased under heat stress and decreased at drought and combined stress, respectively. The combined stress caused severe damages on photosystem II and chloroplast ultrastructure. The root activity after stress recovered even though drought significantly increased the activity from day 2 to day 6. Combined stress result in complex responses during tomato growth. The CV1 was more heat tolerant than CV2, but there was no varietal difference at drought and combined stress. This study contributes to the understanding of the underlying physiological response mechanism of plant to combined stress and crop improvement by providing valuable information for abiotic stress-tolerant tomato breeding.

Drought stress had a predominant effect over heat stress on three tomato cultivars subjected to combined stress.

BACKGROUND: Abiotic stresses due to environmental factors could adversely affect the growth and development of crops. Among the abiotic stresses, drought and heat stress are two critical threats to crop growth and sustainable agriculture worldwide. Considering global climate change, incidence of combined drought and heat stress is likely to increase. The aim of this study was to shed light on plant growth performance and leaf physiology of three tomatoes cultivars ('Arvento', 'LA1994' and 'LA2093') under control, drought, heat and combined stress. RESULTS: Shoot fresh and dry weight, leaf area and relative water content of all cultivars significantly decreased under drought and combined stress as compared to control. The net photosynthesis and starch content were significantly lower under drought and combined stress than control in the three cultivars. Stomata and pore length of the three cultivars significantly decreased under drought and combined stress as compared to control. The tomato 'Arvento' was more affected by heat stress than 'LA1994' and 'LA2093' due to significant decreases in shoot dry weight, chlorophyll a and carotenoid content, starch content and NPQ (non-photochemical quenching) only in 'Arvento' under heat treatment. By comparison, the two heat-tolerant tomatoes were more affected by drought stress compared to 'Arvento' as shown by small stomatal and pore area, decreased sucrose content, ΦPSII (quantum yield of photosystem II), ETR (electron transport rate) and qL (fraction of open PSII centers) in 'LA1994' and 'LA2093'. The three cultivars showed similar response when subjected to the combination of drought and heat stress as shown by most physiological parameters, even though only 'LA1994' and 'LA2093' showed decreased Fv/Fm (maximum potential quantum efficiency of photosystem II), ΦPSII, ETR and qL under combined stress. CONCLUSIONS: The cultivars differing in heat sensitivity did not show difference in the combined stress sensitivity, indicating that selection for tomatoes with combined stress tolerance might not be correlated with the single stress tolerance. In this study, drought stress had a predominant effect on tomato over heat stress, which explained why simultaneous application of heat and drought revealed similar physiological responses to the drought stress. These results will uncover the difference and linkage between the physiological response of tomatoes to drought, heat and combined stress and be important for the selection and breeding of tolerant tomato cultivars under single and combine stress.

Pore size regulates operating stomatal conductance, while stomatal densities drive the partitioning of conductance between leaf sides.

BACKGROUND AND AIMS: Leaf gas exchange is influenced by stomatal size, density, distribution between the leaf adaxial and abaxial sides, as well as by pore dimensions. This study aims to quantify which of these traits mainly underlie genetic differences in operating stomatal conductance (gs) and addresses possible links between anatomical traits and regulation of pore width. METHODS: Stomatal responsiveness to desiccation, gs-related anatomical traits of each leaf side and estimated gs (based on these traits) were determined for 54 introgression lines (ILs) generated by introgressing segments of Solanum pennelli into the S. lycopersicum 'M82'. A quantitative trait locus (QTL) analysis for stomatal traits was also performed. KEY RESULTS: A wide genetic variation in stomatal responsiveness to desiccation was observed, a large part of which was explained by stomatal length. Operating gs ranged over a factor of five between ILs. The pore area per stomatal area varied 8-fold among ILs (2-16 %), and was the main determinant of differences in operating gs between ILs. Operating gs was primarily positioned on the abaxial surface (60-83 %), due to higher abaxial stomatal density and, secondarily, to larger abaxial pore area. An analysis revealed 64 QTLs for stomatal traits in the ILs, most of which were in the direction of S. pennellii. CONCLUSIONS: The data indicate that operating and maximum gs of non-stressed leaves maintained under stable conditions deviate considerably (by 45-91 %), because stomatal size inadequately reflects operating pore area (R(2) = 0·46). Furthermore, it was found that variation between ILs in both stomatal sensitivity to desiccation and operating gs is associated with features of individual stoma. In contrast, genotypic variation in gs partitioning depends on the distribution of stomata between the leaf adaxial and abaxial epidermis.

Spectral effects of LEDs on chlorophyll fluorescence and pigmentation in Phalaenopsis 'Vivien' and 'Purple Star'.

We examined the effect of light emitting diode (LED) lighting in greenhouse facilities on growth, chlorophyll fluorescence and pigmentation in Phalaenopsis 'Vivien' and 'Purple Star' under purpose-built LED arrays yielding c. 200 µmol m(-2) s(-1) at plant height for 14 h per day and 24/18°C day/night temperature, respectively, from January to April 2013. The light treatments were (1) 40% blue in 60% red (40% B/R), (2) 0% blue in 100% red (0% B/R) and (3) white LEDs with 32% blue in white (32% B/W, control), with background daylight under shade screens. The plants were harvested twice for leaf growth and pigmentation. There was no clear pattern in the spectral effect on growth since the order of leaf size differed between harvests in March and April. Fv /Fm was in the range of 0.52-0.72, but overall slightly higher in the control, which indicated a permanent downregulation of PSII in the colored treatments. The fluorescence quenching showed no acclimation to color in 'Purple Star', while 'Vivien' had lower ETR and higher NPQ in the 40% B/R, resembling low light acclimation. The pigmentation showed corresponding spectral response with increasing concentration of lutein while increasing the fraction of blue light, which increased the light absorption in the green/yellow part of the spectrum. The permanent downregulation of PSII moved a substantial part of the thermal dissipation from the light regulated NPQ to non-regulated energy losses estimated by ΦNPQ and ΦNO and the difference found in the balance between ΦPSII and ΦNPQ in 'Vivien' disappeared when ΦNO was included in the thermal dissipation.

Wheat cultivars selected for high Fv /Fm under heat stress maintain high photosynthesis, total chlorophyll, stomatal conductance, transpiration and dry matter.

The chlorophyll fluorescence parameter Fv /Fm reflects the maximum quantum efficiency of photosystem II (PSII) photochemistry and has been widely used for early stress detection in plants. Previously, we have used a three-tiered approach of phenotyping by Fv /Fm to identify naturally existing genetic variation for tolerance to severe heat stress (3 days at 40°C in controlled conditions) in wheat (Triticum aestivum L.). Here we investigated the performance of the previously selected cultivars (high and low group based on Fv /Fm value) in terms of growth and photosynthetic traits under moderate heat stress (1 week at 36/30°C day/night temperature in greenhouse) closer to natural heat waves in North-Western Europe. Dry matter accumulation after 7 days of heat stress was positively correlated to Fv /Fm . The high Fv /Fm group maintained significantly higher total chlorophyll and net photosynthetic rate (PN ) than the low group, accompanied by higher stomatal conductance (gs ), transpiration rate (E) and evaporative cooling of the leaf (ΔT). The difference in PN between the groups was not caused by differences in PSII capacity or gs as the variation in Fv /Fm and intracellular CO2 (Ci ) was non-significant under the given heat stress. This study validated that our three-tiered approach of phenotyping by Fv /Fm performed under increasing severity of heat was successful in identifying wheat cultivars differing in photosynthesis under moderate and agronomically more relevant heat stress. The identified cultivars may serve as a valuable resource for further studies to understand the physiological mechanisms underlying the genetic variability in heat sensitivity of photosynthesis.

3D Laser Triangulation for Plant Phenotyping in Challenging Environments.

To increase the understanding of how the plant phenotype is formed by genotype and environmental interactions, simple and robust high-throughput plant phenotyping methods should be developed and considered. This would not only broaden the application range of phenotyping in the plant research community, but also increase the ability for researchers to study plants in their natural environments. By studying plants in their natural environment in high temporal resolution, more knowledge on how multiple stresses interact in defining the plant phenotype could lead to a better understanding of the interaction between plant responses and epigenetic regulation. In the present paper, we evaluate a commercial 3D NIR-laser scanner (PlantEye, Phenospex B.V., Herleen, The Netherlands) to track daily changes in plant growth with high precision in challenging environments. Firstly, we demonstrate that the NIR laser beam of the scanner does not affect plant photosynthetic performance. Secondly, we demonstrate that it is possible to estimate phenotypic variation amongst the growth pattern of ten genotypes of Brassica napus L. (rapeseed), using a simple linear correlation between scanned parameters and destructive growth measurements. Our results demonstrate the high potential of 3D laser triangulation for simple measurements of phenotypic variation in challenging environments and in a high temporal resolution.

Threshold response of stomatal closing ability to leaf abscisic acid concentration during growth.

Leaf abscisic acid concentration ([ABA]) during growth influences morpho-physiological traits associated with the plant's ability to cope with stress. A dose-response curve between [ABA] during growth and the leaf's ability to regulate water loss during desiccation or rehydrate upon re-watering was obtained. Rosa hybrida plants were grown at two relative air humidities (RHs, 60% or 90%) under different soil water potentials (-0.01, -0.06, or -0.08MPa) or upon grafting onto the rootstock of a cultivar sustaining [ABA] at elevated RH. Measurements included [ABA], stomatal anatomical features, stomatal responsiveness to desiccation, and the ability of leaves, desiccated to varying degrees, to recover their weight (rehydrate) following re-watering. Transpiration efficiency (plant mass per transpired water) was also determined. Soil water deficit resulted in a lower transpiration rate and higher transpiration efficiency at both RHs. The lowest [ABA] was observed in well-watered plants grown at high RH. [ABA] was increased by soil water deficit or grafting, at both RHs. The growth environment-induced changes in stomatal size were mediated by [ABA]. When [ABA] was increased from the level of (well-watered) high RH-grown plants to the value of (well-watered) plants grown at moderate RH, stomatal responsiveness was proportionally improved. A further increase in [ABA] did not affect stomatal responsiveness to desiccation. [ABA] was positively related to the ability of dehydrated leaves to rehydrate. The data indicate a growth [ABA]-related threshold for stomatal sensitivity to desiccation, which was not apparent either for stomatal size or for recovery (rehydration) upon re-watering.

Plant responses to co-occurring heat and water deficit stress: A comparative study of tolerance mechanisms in old and modern wheat genotypes.

Global climate change increases the likelihood of co-occurrence of hot and dry spells with increased intensity, frequency, and duration. Studying the impact of the two stresses provide a better understanding of tolerance mechanisms in wheat, and our study was focused on revealing plant stress responses to different severities of combined stress at two phenophases in old and modern wheat genotypes. During the stem elongation and anthesis stages, plants were exposed to four treatments: control, deficit irrigation, combined heat, and deficit irrigation at 31 °C (HD31) and 37 °C (HD37). The modern genotypes were less affected by deficit irrigation at stem elongation as they maintained higher photosynthesis, stomatal conductance, and leaf cooling than old genotypes. When the HD37 stress was imposed during anthesis, the modern genotypes exhibited superior performance compared to the old, which was due to their higher photosynthetic rates resulting from improved biochemical regulation and a higher chlorophyll content. The plant responses varied during two phenophases under the combined stress exposure. Genotypes subjected to HD37 stress during stem elongation, photosynthesis was mainly controlled by stomatal regulation, whereas at anthesis it was predominated by biochemical regulation. These findings contribute to a deeper comprehension of plant tolerance mechanisms in response to different intensities of co-occurring hot and dry weather conditions.

Elevated CO2 induce alterations in the hormonal regulation of stomata in drought stressed tomato seedlings.

The atmospheric CO2 level is rising, and the consequent climate change is causing an increase in drought events. Furthermore, the CO2 level is known to induce changes in the physiological responses to stress in plants. Exogenous melatonin is suggested to play roles in the response of plants to abiotic stresses, including drought. We investigated physiological drought stress responses at ambient and elevated CO2 levels (aCO2 and eCO2) of melatonin-treated and untreated tomato plants, aiming to link effects of water use efficiency of photosynthesis at (WUELeaf) and stomatal conductance (gs) with the hormonal regulation of stomata. Tomatoes grown at eCO2 had reduced water use of both irrigated and drought stressed plants during the progression of drought at the whole plant level. This was also reflected in a CO2-affected increase in WUELeaf at eCO2 across irrigated and drought-stressed plants. These CO2-induced effects were mediated through stomatal closing and reductions in stomatal pore area rather than stomatal density or size. Abscisic acid (ABA) and its conjugated form, ABA glucose ester (ABA-GE), increased at drought stress in aCO2, while only ABA-GE increased at eCO2. Contrary, salicylic acid (SA) increased to a greater magnitude at drought stress in eCO2 than aCO2. Melatonin treatment showed no effects on the stomatal regulation. Our findings imply that eCO2 changes in the balance of hormonal effectors in stomatal regulation during drought, shifting from it ABA to SA regulation, suggesting to consider stomatal reactions at eCO2 in a perspective of a hormonal interplay rather than only ABA.