Characterising Biological and Physiological Drought Signals in Diverse Parents of a Wheat Mapping Population.

Water deficit affects the growth as well as physiological and biochemical processes in plants. The aim of this study was to determine differences in physiological and biochemical responses to drought stress in two wheat cultivars-Chinese Spring (CS) and SQ1 (which are parents of a mapping population of doubled haploid lines)-and to relate these responses to final yield and agronomic traits. Drought stress was induced by withholding water for 14 days, after which plants were re-watered and maintained until harvest. Instantaneous gas exchange parameters were evaluated on the 3rd, 5th, 10th, and 14th days of seedling growth under drought. After 14 days, water content and levels of chlorophyll a+b, carotenoids, malondialdehyde, soluble carbohydrates, phenolics, salicylic acid, abscisic acid (ABA), and polyamines were measured. At final maturity, yield components (grain number and weight), biomass, straw weight, and harvest index were evaluated. Physiological and biochemical parameters of CS responded more than those of SQ1 to the 14-day drought, reflected in a greater reduction in final biomass and yield in CS. Marked biochemical differences between responses of CS and SQ1 to the drought were found for soluble carbohydrates and polyamines. These would be good candidates for testing in the mapping population for the coincidence of the genetic control of these traits and final biomass and yield.

Measurements of Leaf Gas-Exchange Parameters Using Portable CIRAS-3 Infrared Gas Analyzer, with a Parkinson Leaf Chamber (PLC6).

Ranges of portable systems to measure leaf gas-exchange parameters are available. They allow real-time measurements of the photosynthesis rate (A), transpiration rate (E), stomatal conductance (gs), and intercellular CO2 concentration (Ci). Photosynthetic CO2 uptake is one of the most frequently studied plant physiological processes. The measurement is precise, simple, and noninvasive to perform in vivo. We describe the use of this method in environmental-controlled plant production systems at different temperatures on the growth and development of common buckwheat.

Variation Among Spring Wheat (Triticum aestivum L.) Genotypes in Response to the Drought Stress. II-Root System Structure.

(1) Background: The study analyzed wheat morphological traits to assess the role of roots structure in the tolerance of drought and to recognize the mechanisms of root structure adjustment to dry soil environment. (2) Methods: Root-box and root-basket methods were applied to maintain an intact root system for analysis. (3) Results: Phenotypic differences among six genotypes with variable drought susceptibility index were found. Under drought, the resistant genotypes lowered their shoot-to-root ratio. Dry matter, number, length, and diameter of nodal and lateral roots were higher in drought-tolerant genotypes than in sensitive ones. The differences in the surface area of the roots were greater in the upper parts of the root system (in the soil layer between 0 and 15 cm) and resulted from the growth of roots of the tolerant plant at an angle of 0-30° and 30-60°. (4) Conclusions: Regulation of root bending in a more downward direction can be important but is not a priority in avoiding drought effects by tolerant plants. If this trait is reduced and accompanied by restricted root development in the upper part of the soil, it becomes a critical factor promoting plant sensitivity to water-limiting conditions.

Diverse Stomatal Behaviors Mediating Photosynthetic Acclimation to Low Temperatures in Hordeum vulgare.

Photosynthetic acclimation to cold conditions is an important factor influencing freezing tolerance of plants. Photosynthetic enzyme activities increase as part of a photochemical mechanism underlying photosynthetic acclimation to low temperatures. Additionally, a non-photochemical mechanism may be activated to minimize photooxidative damage. The aim of this study was to test the hypothesis that differences in stomatal conductance in Hordeum vulgare plants with contrasting freezing tolerances induce various strategies for photosynthetic acclimation to cold stress. Different stomatal behaviors during the prehardening step resulted in diverse plant reactions to low-temperature stress. Plants with a relatively low freezing tolerance exhibited decreased stomatal conductance, resulting in decreased photochemical activity, faster induction of the non-photochemical mechanism, and downregulated expression of two Rubisco activase (RcaA) splicing variants. In contrast, plants with a relatively high freezing tolerance that underwent a prehardening step maintained the stomatal conductance at control level and exhibited delayed photochemical activity and RcaA expression decrease, and increased Rubisco activity, which increased net photosynthetic rate. Thus, in barley, the induction of photoinhibition avoidance (i.e., non-photochemical photoacclimation mechanism) is insufficient for an effective cold acclimation. An increase in cold-induced net photosynthetic rate due to open stomata is also necessary.

Enhanced expression of Rubisco activase splicing variants differentially affects Rubisco activity during low temperature treatment in Lolium perenne.

Alternative splicing of the Rubisco activase gene was shown to be a point for optimization of photosynthetic carbon assimilation. It can be expected to be a stress-regulated event that depends on plant freezing tolerance. The aim of the study was to examine the relationships among Rubisco activity, the expression of two Rubisco activase splicing variants and photoacclimation to low temperature. The experiment was performed on two Lolium perenne genotypes with contrasting levels of freezing tolerance. The study investigated the effect of pre-hardening (15°C) and cold acclimation (4°C) on net photosynthesis, photosystem II photochemical activity, Rubisco activity and the expression of two splicing variants of the Rubisco activase gene. The results showed an induction of Rubisco activity at both 15°C and 4°C only in a highly freezing-tolerant genotype. The enhanced Rubisco activity after pre-hardening corresponded to increased expression of the splicing variant representing the large isoform, while the increase in Rubisco activity during cold acclimation was due to the activation of both transcript variants. These boosts in Rubisco activity also corresponded to an activation of non-photochemical mechanism of photoacclimation induced at low temperature exclusively in the highly freezing-tolerant genotype. In conclusion, enhanced expression of Rubisco activase splicing variants caused an increase in Rubisco activity during pre-hardening and cold acclimation in the more freezing-tolerant Lolium perenne genotype. The induction of the transcript variant representing the large isoform may be an important element of increasing the carbon assimilation rate supporting the photochemical mechanism of photosynthetic acclimation to cold.

Alleviation of osmotic stress effects by exogenous application of salicylic or abscisic acid on wheat seedlings.

The aim of the study was to assess the role of salicylic acid (SA) and abscisic acid (ABA) in osmotic stress tolerance of wheat seedlings. This was accomplished by determining the impact of the acids applied exogenously on seedlings grown under osmotic stress in hydroponics. The investigation was unique in its comprehensiveness, examining changes under osmotic stress and other conditions, and testing a number of parameters simultaneously. In both drought susceptible (SQ1) and drought resistant (CS) wheat cultivars, significant physiological and biochemical changes were observed upon the addition of SA (0.05 mM) or ABA (0.1 µM) to solutions containing half-strength Hoagland medium and PEG 6000 (-0.75 MPa). The most noticeable result of supplementing SA or ABA to the medium (PEG + SA and PEG + ABA) was a decrease in the length of leaves and roots in both cultivars. While PEG treatment reduced gas exchange parameters, chlorophyll content in CS, and osmotic potential, and conversely, increased lipid peroxidation, soluble carbohydrates in SQ1, proline content in both cultivars and total antioxidants activity in SQ1, PEG + SA or PEG + ABA did not change the values of these parameters. Furthermore, PEG caused a two-fold increase of endogenous ABA content in SQ1 and a four-fold increase in CS. PEG + ABA increased endogenous ABA only in SQ1, whereas PEG + SA caused a greater increase of ABA content in both cultivars compared to PEG. In PEG-treated plants growing until the harvest, a greater decrease of yield components was observed in SQ1 than in CS. PEG + SA, and particularly PEG + ABA, caused a greater increase of these yield parameters in CS compared to SQ1. In conclusion, SA and ABA ameliorate, particularly in the tolerant wheat cultivar, the harmful effects and after effects of osmotic stress induced by PEG in hydroponics through better osmotic adjustment achieved by an increase in proline and carbohydrate content as well as by an increase in antioxidant activity.

An increase in the content of cell wall-bound phenolics correlates with the productivity of triticale under soil drought.

The objective of this study was to investigate whether the content of cell wall-bound phenolics can simultaneously influence both the productivity and the water status of triticale under soil drought conditions. Two parallel treatments were carried out. The T1 treatment involved plants being subjected to soil drought twice, during the tillering phase and then during the flowering phase. The T2 treatment included drought only during the flowering phase. After T1 treatment, the majority of cultivars exhibited better PSII functioning at the flowering phase in comparison to T2, which could be related to better adaptation of the photosynthetic apparatus to leaf dehydration. Simultaneously, the higher activity of the photosynthetic apparatus of flag leaves for T1 was significantly correlated with the higher content of cell wall-bound phenolics. The dry mass of plants was markedly lower in the T1 treatment and was correlated with a higher content of cell wall-bound phenolics. Moreover, cultivars subjected to the T1 treatment showed a significantly higher water content in comparison to the T2 treatment. The delay in the leaf rolling and the ageing of plants in the T1 treatment, which induced a higher level of cell wall-bound phenolics, was visual proof of the improvement in the water status of plants. Phenolic compounds that form cross-bridges with carbohydrates of the cell wall can be considered a more effective biochemical protective mechanism than free phenolics during the dehydration of leaves. This potentially higher level of effectiveness is likely the result of the double action of phenolic compounds, both as photoprotectors of the photosynthetic apparatus and hydrophobic stabilizers, preventing water loss from the apoplast.

Early stage de-etiolation increases the ferulic acid content in winter triticale seedlings under full sunlight conditions.

In the presented work an attempt has been made to estimate the phenolics content and its implication for the protection of the photosynthetic apparatus in course of a plant's de-etiolation. The experiments were carried out on two genotypes of winter triticale varying in their resistance to drought. The activity of the photosynthetic apparatus was monitored by taking measurements of chlorophyll fluorescence and chlorophyll/carotenoids content. Analyses of the total pool of phenolic compounds and ferulic acid as well as l-phenylalanine ammonia lyase activity were completed. The first illuminations of etiolated seedlings induced a chlorophyll synthesis, which was followed by the increasing activity of the photosynthetic apparatus in both studied genotypes. Piano exhibited a higher values of the maximum quantum efficiency of photosystem II primary photochemistry during de-etiolation than Imperial. These results may just indicate that for Imperial, the delivery of photons to the reaction centres exceeded the capacity of the photosynthetic apparatus to transduce this energy via electron transport. An increase in the content of ferulic acid was more noticeable for Piano and seems to be a consequence of adaptation to the new light conditions. It should be taken into account, that an increase of ferulic acid content during early stage of de-etiolation, may limit the photoinhibition of photosynthesis whenever radiation is excessive for the photosynthetic apparatus.