Changes in photosynthetic performance and ABA levels under osmotic stress in drought tolerant and sensitive wheat genotypes

We investigated the effect of osmotic stress induced by 400 mOsm PEG 6000 on the photosynthetic parameters and the abscisic acid (ABA) levels in drought tolerant (Triticum aestivum L. cv. MV Emese) and sensitive (cv. GK Élet) wheat cultivars in seedling stage. Our aim was to find fast and sensitive laboratory methods for screening drought sensitivity of the genotypes. The water potential (Ψw) values, net CO2 assimilation, chlorophyll a (chla) fluorescence and ABA levels in leaves and roots were determined a function of increasing osmotic stress. Although the decline of Ψw was more significant in the leaves of the sensitive cultivar (cv. Élet), the effect of water stress on the PSII photochemistry was not more pronounced. The ABA levels increased earlier, from day 9 under osmotic stress in the sensitive cultivar, but the hormone contents of the leaves were higher in the tolerant cv. MV Emese. This suggests that the accumulation of the stress hormone, ABA is a first line of defence to osmotic stress

Chlorophyll a fluorescence induction parameters of flag leaves characterize genotypes and not the drought tolerance of wheat during grain filling under water deficit

Chlorophyll a fluorescence induction parameters of two drought tolerant (MV Emese and Plainsman V) and two sensitive (GK Élet and Cappelle Desprez) wheat cultivars were compared on the day 16 post anthesis (DPA) under control and water stressed conditions. It was found that under drought stress the chlorophyll a (Chl ) content declined earlier in the sensitive genotypes, but the rate of Chl loss was much higher in the tolerant cultivars and also in the controls of cv. Plainsman after 12 DPA. The transzeatin content, a transport form of cytokinins also significantly declined to 16 DPA in the sensitive GK Élet. Because cytokinins prevent Chl loss, it may be a cause of the decreased Chl level in this cv. under drought. Neither net CO2 assimilation rate (PN) nor other Chl a fluorescence induction parameters such as Fv/Fm or φ PSII, qP and NPQ as a function of increasing photon flux densities (PFD) exhibited a special change which could characterize only tolerant or sensitive cultivars. Instead, these changes characterized the genotypes. In cvs MV Emese and Plainsman the flag leaf senescence could result in faster and better remobilization of the pre-stored carbon from vegetative tissues, and ultimately betteryield than in GK Élet and Cappelle Desprez under drought

The roleS of ABA, reactive oxygen species and Nitric Oxide in root growth during osmotic stress in wheat: comparison of a tolerant and a sensitive variety

The effects of PEG 6000-induced osmotic stress (−0.976 MPa) on the root growth of young plants, and the changes in abscisic acid (ABA), reactive oxygen species (ROS) and NO contents were investigated in the root tips of a drought-tolerant and a drought-sensitive wheat cultivar (Triticum aestivum L. cvs. MV Emese and GK Élet, respectively). The root length of cv. MV Emese was more effectively reduced than that of GK Élet by osmotic stress. Concomitantly, the ABA content of the 15-mm apical zone of the roots remained at the control level in GK Élet cultivar, but in MV Emese it decreased significantly after the early phase of the experiment, indicating that the accumulation of ABA is necessary for the maintenance of root growth under osmotic stress. The extent of ROS accumulation relative to the respective control was more pronounced in the elongation zone of roots in MV Emese in the later stages of the experiment, while NO concentrations increased significantly early after PEG exposure, suggesting that high concentrations of ROS and NO were unfavourable for root expansion. In contrast, in cv. Élet, the high NO content in the elongation zone declined to the control level under osmotic stress within 4 days. The changes in root growth due to osmotic stress did not exhibit a correlation with the drought tolerance of the genotypes defined on the basis of the crop yield

Metabolic indicators of drought stress tolerance in wheat: Glutamine synthetase isoenzymes and Rubisco

Drought stress has a considerable impact on the ecosystem and agriculture. Continuous water deficit induces early leaf senescence in plants. During this process, chloroplasts are degraded and photosynthesis drastically drops. The objective of this investigation was to look into the regulation of nitrogen and carbon metabolism during water deficit. Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase; EC 4.1.1.39) and the total protein contents inform us of the sink-source relation in plants. Glutamine synthetase (GS, EC 6.3.1.2) isoenzymes are good markers of plastid status (GS2) and the nitrogen metabolism (GS1). Tolerant and sensitive wheat (Triticum aestivum L.) genotypes were tested, which are widely used in agriculture. The amount of protein, Rubisco and GS isoforms in leaves were measured during the grain filling period, as indicative traits that ultimately determine the onset and stage of senescence. The symptoms of senescence first appeared on the oldest and finally on the youngest leaves. Drought stress disrupted the sequentiality of senescence in the sensitive varieties. An untimely senescence appeared in flag leaves, earlier than in the older leaves. Total protein and Rubisco contents decreased and the GS2 isoenzyme declined considerably in the youngest leaves. In the tolerant varieties, however, these physiological parameters did not change under drought, only the sequential senescence of leaf levels accelerated in some cases compared to the control, well-watered plants. Our results revealed that GS is a good indicator of drought stress, which can be applied for the characterization of wheat cultivars in terms of drought stress tolerance