Qualitative and Quantitative Differences in Osmolytes Accumulation and Antioxidant Activities in Response to Water Deficit in Four Mediterranean Limonium Species

Abstract

Limonium is a genus represented in the Iberian Peninsula by numerous halophytic species that are affected in nature by salinity, and often by prolonged drought episodes. Responses to water deficit have been studied in four Mediterranean Limonium species, previously investigated regarding salt tolerance mechanisms. The levels of biochemical markers, associated with specific responses—photosynthetic pigments, mono- and divalent ions, osmolytes, antioxidant compounds and enzymes—were determined in the control and water-stressed plants, and correlated with their relative degree of stress-induced growth inhibition. All the tested Limonium taxa are relatively resistant to drought on the basis of both the constitutive presence of high leaf ion levels that contribute to osmotic adjustment, and the stress-induced accumulation of osmolytes and increased activity of antioxidant enzymes, albeit with different qualitative and quantitative induction patterns. Limonium santapolense activated the strongest responses and clearly differed from Limonium virgatum, Limonium girardianum, and Limonium narbonense, as indicated by cluster and principal component analysis (PCA) analyses in agreement with its drier natural habitat, and compared to that of the other plants. Somewhat surprisingly, however, L. santapolense was the species most affected by water deficit in growth inhibition terms, which suggests the existence of additional mechanisms of defense operating in the field that cannot be mimicked in greenhouses.

Optimal Duration of Drought Stress Near Harvest for Promoting Bioactive Compounds and Antioxidant Capacity in Kale with or without UV-B Radiation in Plant Factories

“…The results were in agreement with a previous report by Oh et al, which showed that the drought stress induced by withholding water for 4 days improved the TPC and TAC in lettuce [15]. Furthermore, numerous studies have shown that drought stress enhances one or both enzymatic and nonenzymatic antioxidants in a wide range of plants [31][32][33][34][35]. Moderate drought stress can improve plant drought tolerance, and enhance the antioxidant system [30,36].…”

“…The changes in antioxidant capacity under drought stress are different among plant species. The DPPH free radical scavenging activity was not changed in Limonium species, despite water deficit stress for 1 month [34]. However, the same activity was significantly increased in St. John's wort plants after water stress for 12 days [8].…”

Strategies to Apply Water-Deficit Stress: Similarities and Disparities at the Whole Plant Metabolism Level in Medicago truncatula

“…This phenomenon was also observed in wheat leaves subjected to PEG stress [ 41 , 42 ]. However, water withholding did not alter leaf ion content in Limonium species either [ 43 ], suggesting a lack of nutrient deficiency under these conditions. Maintaining appropriate nutrient levels is key for plant function and growth, and it is of special relevance under drought stress, where the decrease in transpiration and water uptake can lower K + influx to the roots [ 44 ].…”

Responses to Increased Salinity and Severe Drought in the Eastern Iberian Endemic Species Thalictrum maritimum (Ranunculaceae), Threatened by Climate Change

“…Therefore, Ca 2+ uptake and accumulation may contribute to tolerance to stress in T. maritimum , not only to high salinity but also to water deficit. Indeed, increased concentrations of Ca 2+ have been reported in several typical halophytes, such as species of the genus Limonium , both under salt stress [ 30 ] and under water stress [ 42 ]. As observed for the other analysed ions, higher Ca 2+ concentrations have been measured in the aboveground organs of the plants than in the roots, under high salinity conditions (but not in response to water stress).…”

“…In the present study, however, MDA contents did now show any significant change in response to water deficit or high salinity, indicating that, under the specific conditions of our experiments, high levels of oxidative stress were not generated. The lack of secondary oxidative stress associated with salt and water stress is not common in stress-sensitive plants but has been previously reported in many halophytes, both in their natural habitats [ 51 , 64 , 65 ] and under controlled greenhouse conditions [ 42 ]. In T. maritimum , redox equilibrium seemed to be maintained by a slight increase in the specific activity of SOD, under conditions of water deficit and high salinity, whereas activation of CAT and GR, also weak, was only detected in the presence of high salt concentrations.…”