Growth, proline accumulation and water relations of NaCl-selected and non-selected callus lines of Dactylis glomerata L

Foliar Pre-Treatment with Abscisic Acid Enhances Olive Tree Drought Adaptability

Water is the most widely limiting factor for plants distribution, survival and agricultural productivity, their responses to drought and recovery being critical for their success and productivity. Olea europaea L. is a well-adapted species to cyclic drought events, still at considerable expense of carbon reserves and CO2 supply. To study the role of abscisic acid (ABA) as a promoter of drought adaptability, young potted olive trees subjected to three drought-recovery cycles were pre-treated with ABA. The results demonstrated that ABA pre-treatment allowed the delay of the drought effects on stomatal conductance (gs) and net photosynthesis (An), and under severe drought, permitted the reduction of the non-stomatal limitations to An and the relative water content decline, the accumulation of compatible solutes and avoid the decline of photosynthetic pigments, soluble proteins and total thiols concentrations and the accumulation of ROS. Upon rewatering, ABA-sprayed plants showed an early recovery of An. The plant ionome was also changed by the addition of ABA, with special influence on root K, N and B concentrations. The improved physiological and biochemical functions of the ABA-treated plants attenuated the drought-induced decline in biomass accumulation and potentiated root growth and whole-plant water use efficiency after successive drought-rewatering cycles. These changes are likely to be of real adaptive significance, with important implications for olive tree growth and productivity.

Kaolin particle film modulates morphological, physiological and biochemical olive tree responses to drought and rewatering

Regarding the foreseeing climate change is reasonable to expect harmful consequences to olive tree (Olea europaea L.), an iconic species of Mediterranean region. Thus, the selection of practices that allow a better drought resistance and recovery capacity needs the immediate attention of scientific community. This study evaluates the strategies adopted by young potted olive trees, subjected to three cycles of drought and rewatering, in the presence of a reflective clay, kaolin (KL). The results demonstrated that KL induced shade-related leaf structural changes and was effective in keeping leaf water status during the most stressful periods. In general, photosynthetic activity of sprayed plants was improved by the alleviation of drought-induced stomatal and non-stomatal limitations. Moreover, during stress imposition sprayed leaves showed reduced oxidative damages, allowing lower investment in antioxidant defences. Furthermore, sprayed plants also had lower nighttime water losses due to inferior nighttime stomatal conductance, and are able to maintain higher respiration rates. Upon rewatering, the shaded effect conferred by KL limited gas exchange restauration, but improved the plants' capacity to restore the metabolic functions. In spite of the induced physiological and biochemical changes, no significant differences were found in whole-plant water use efficiency and plant biomass accumulation, possibly by the attenuation of photosynthesis restauration during the recovery events. In conclusion, the changes induced by KL might be beneficial under severe conditions, as on realistic Mediterranean field environments.

Salicylic acid modulates olive tree physiological and growth responses to drought and rewatering events in a dose dependent manner

The predicted accentuation of drought events highlights the importance of optimize plants capacity to tolerate drought, but also the capacity to recovery from it, especially in species, as olive tree (Olea europaea L.), that grows in particularly susceptible regions. Three different concentrations (10, 100 and 1000 μM) of salicylic acid (SA), a stress signaling phytohormone, was sprayed on 3-year-old potted olive trees subjected to three successive drought and rewatering events. Trees responses to SA application are concentration dependent, being 100 μM the most effective concentration to improve drought tolerance and recovery capacity. During drought events, this effectiveness was achieved by osmolytes accumulation, leaf water status maintenance, reduced photosynthetic systems drought-associated damages, and by optimizing shoot/root ratio. The better plant fitness during drought allowed a fast recovery of the physiological functions upon rewatering and reduced the necessity to invest in extra repair damages, allowing the regrowth. The intense abscisic acid (ABA) signal close to upper epidermis in stressed controls suggests a "memory" of the worst water status displayed by those plants. SA attenuated the limitation of total biomass accumulation imposed by drought, mainly in root system, increased water use efficiency and lead to a higher intense signal of indoleacetic acid (IAA) in leaves during recovery period. In summary, in a suitable concentration, SA demonstrate to be a promising tool to increase drought adaptability of olive trees.