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Water stress may greatly limit plant functionality and growth. Stomatal closure and consequently reduced transpiration are considered as early and sensitive plant responses to drought and salinity stress. An important consequence of stomatal closure under water stress is the rise of leaf temperature (T leaf ), yet T leaf is not only fluctuating with stomatal closure. It is regulated by several plant parameters and environmental factors. Thermal imaging and different stress indices, incorporating actual leaf/crop temperature and reference temperatures, were developed in previous studies toward normalizing for effects unassociated to water stress on T leaf , aiming at a more efficient water stress assessment. The concept of stress indices has not been extensively studied on the model plant Arabidopsis thaliana. Therefore, the aim of this study was to examine the different indices employed in previous studies in assessing rosette transpiration rate (E) in Arabidopsis plants grown under two different light environments and subjected to salinity. After salinity imposition, E was gravimetrically quantified, and thermal imaging was employed to quantify rosette (T rosette ) and artificial reference temperature (T wet, T dry ). T rosette and several water stress indices were tested for their relation to E. Among the microclimatic growth conditions tested, RWSI 1 ([T rosette  - T wet ]/[T dry  - T wet ]) and RWSI 2 ([T dry  - T rosette ]/[T dry  - T wet ]) were well linearly-related to E, irrespective of the light environment, while the sole use of either T wet or T dry in different combinations with T rosette returned less accurate results. This study provides evidence that selected combinations of T rosette , T dry , and T wet can be utilized to assess E under water stress irrespective of the light environment., (© 2022 The Authors. Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

The development of technology, like the widely-used off-the-shelf portable photosynthesis systems, for the quantification of leaf gas exchange rates and chlorophyll fluorescence offered photosynthesis research a massive boost. Gas exchange parameters in such photosynthesis systems are calculated as gas exchange rates per unit leaf area. In small chambers (<10 cm 2 ), the leaf area used by the system for these calculations is actually the internal gasket area (A G ), provided that the leaf covers the entire A G . In this study, we present two inexpensive and non-destructive techniques that can be used to easily quantify the enclosed leaf area (A L ) of plant species with leaves of surface area much smaller than the A G , such as that of cereal crops. The A L of the cereal crop species studied has been measured using a standard image-based approach ( i A L ) and estimated using a leaf width-based approach ( w A L ). i A L and w A L did not show any significant differences between them in maize, barley, hard and soft wheat. Similar results were obtained when the w A L was tested in comparison with i A L in different positions along the leaf in all species studied. The quantification of A L and the subsequent correction of leaf gas exchange parameters for A L provided a precise quantification of net photosynthesis and stomatal conductance especially with decreasing A L . This study provides two practical, inexpensive and non-destructive solutions to researchers dealing with photosynthesis measurements on small-leaf plant species. The image-based technique can be widely used for quantifying A L in many plant species despite their leaf shape. The leaf width-based technique can be securely used for quantifying A L in cereal crop species such as maize, wheat and barley along the leaf. Both techniques can be used for a wide range of gasket shapes and sizes with minor technique-specific adjustments.

Main Conclusion: AM symbiosis did not strongly affect Arundo donax performances under salt stress, although differences in the plants inoculated with two different fungi were recorded. The mechanisms at the basis of the improved tolerance to abiotic stresses by arbuscular mycorrhizal (AM) fungi have been investigated mainly focusing on food crops. In this work, the potential impact of AM symbiosis on the performance of a bioenergy crop, Arundo donax, under saline conditions was considered. Specifically, we tried to understand whether AM symbiosis helps this fast-growing plant, often widespread in marginal soils, withstand salt. A combined approach, involving eco-physiological, morphometric and biochemical measurements, was used and the effects of two different AM fungal species (Funneliformis mosseae and Rhizophagus irregularis) were compared. Results indicate that potted A. donax plants do not suffer permanent damage induced by salt stress, but photosynthesis and growth are considerably reduced. Since A. donax is a high-yield biomass crop, reduction of biomass might be a serious agronomical problem in saline conditions. At least under the presently experienced growth conditions, and plant-AM combinations, the negative effect of salt on plant performance was not rescued by AM fungal colonization. However, some changes in plant metabolisms were observed following AM-inoculation, including a significant increase in proline accumulation and a trend toward higher isoprene emission and higher H 2 O 2 , especially in plants colonized by R. irregularis. This suggests that AM fungal symbiosis influences plant metabolism, and plant-AM fungus combination is an important factor for improving plant performance and productivity, in presence or absence of stress conditions.

Reactive oxygen, nitrogen and sulfur species are key signalling molecules involved in multiple physiological processes that can be examined in qualitative and quantitative manners. Here, we describe simple spectrophotometric assays that allow the quantification of hydrogen peroxide, nitrite-derived nitric oxide and hydrogen sulphide from plant tissues.

Many studies investigated temperature effects on leaf initiation and expansion by relating these processes to air temperature or the temperature of a specific organ (e.g. leaf temperature). In reality plant temperature is hardly ever equal to air temperature or spatially uniform. Apical bud temperature (T bud ), for example, may greatly differ from the temperature of the rest of the plant (T plant ) dependent on the environment. Recent research in Cucumis sativus showed that T bud influences leaf initiation independent of T plant . These findings trigger the question if such spatial temperature differences also influence leaf expansion and plant phenotype. In a 28 day study, we maintained temperature differences between T bud and T plant ranging from -7 to +8 °C using a custom-made bud temperature control system. Leaf expansion did not only depend on leaf temperature but also on the difference between bud and leaf temperature. Differences between T bud and T plant considerably influenced vertical leaf area distribution over the shoot: increasing T bud beyond T plant resulted in more and smaller leaves, while decreasing T bud below T plant resulted in less and larger leaves. The trade-off between leaf number and leaf area resulted in phenotypic alterations that cannot be predicted, for example, by crop models, when assuming plant temperature uniformity., (© 2016 The Authors Plant, Cell & Environment Published by John Wiley & Sons Ltd.)

Abiotic stresses severely limit crop yield and their detrimental effects are aggravated by climate change. Chemical priming is an emerging field in crop stress management. The exogenous application of specific chemical agents before stress events results in tolerance enhancement and reduction of stress impacts on plant physiology and growth. However, the molecular mechanisms underlying the remarkable effects of chemical priming on plant physiology remain to be elucidated. Reactive oxygen, nitrogen and sulfur species (RONSS) are molecules playing a vital role in the stress acclimation of plants. When applied as priming agents, RONSS improve stress tolerance. This review summarizes the recent knowledge on the role of RONSS in cell signalling and gene regulation contributing to abiotic stress tolerance enhancement., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Main Conclusion: Leaf initiation rate is largely determined by the apical bud temperature even when apical bud temperature largely deviates from the temperature of other plant organs. We have long known that the rate of leaf initiation (LIR) is highly sensitive to temperature, but previous studies in dicots have not rigorously demonstrated that apical bud temperature controls LIR independent of other plant organs temperature. Many models assume that apical bud and leaf temperature are the same. In some environments, the temperature of the apical bud, where leaf initiation occurs, may differ by several degrees Celsius from the temperature of other plant organs. In a 28-days study, we maintained temperature differences between the apical bud and the rest of the individual Cucumis sativus plants from -7 to +8 °C by enclosing the apical buds in transparent, temperature-controlled, flow-through, spheres. Our results demonstrate that LIR was completely determined by apical bud temperature independent of other plant organs temperature. These results emphasize the need to measure or model apical bud temperatures in dicots to improve the prediction of crop development rates in simulation models.

Crop plants are subjected to multiple abiotic stresses during their lifespan that greatly reduce productivity and threaten global food security. Recent research suggests that plants can be primed by chemical compounds to better tolerate different abiotic stresses. Chemical priming is a promising field in plant stress physiology and crop stress management. We review here promising chemical agents such as sodium nitroprusside, hydrogen peroxide, sodium hydrosulfide, melatonin, and polyamines that can potentially confer enhanced tolerance when plants are exposed to multiple abiotic stresses. The challenges and opportunities of chemical priming are addressed, with the aim to boost future research towards effective application in crop stress management., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Long-term effects of light quality on leaf hydraulic conductance (K(leaf)) and stomatal conductance (g(s)) were studied in cucumber, and their joint impact on leaf photosynthesis in response to osmotic-induced water stress was assessed. Plants were grown under low intensity monochromatic red (R, 640 nm), blue (B, 420 nm) or combined red and blue (R:B, 70:30) light. K(leaf) and g(s) were much lower in leaves that developed without blue light. Differences in g(s) were caused by differences in stomatal aperture and stomatal density, of which the latter was largely due to differences in epidermal cell size and hardly due to stomatal development. Net photosynthesis (A(N)) was lowest in R-, intermediate in B-, and highest in RB- grown leaves. The low A(N) in R-grown leaves correlated with a low leaf internal CO(2) concentration and reduced PSII operating efficiency. In response to osmotic stress, all leaves showed similar degrees of stomatal closure, but the reduction in A(N) was larger in R- than in B- and RB-grown leaves. This was probably due to damage of the photosynthetic apparatus, which only occurred in R-grown leaves. The present study shows the co-ordination of K(leaf) and g(s) across different light qualities, while the presence of blue in the light spectrum seems to drive both K(leaf) and g(s) towards high, sun-type leaf values, as was previously reported for maximal photosynthetic capacity and leaf morphology. The present results suggest the involvement of blue light receptors in the usually harmonized development of leaf characteristics related to water relations and photosynthesis under different light environments.