Combined Drought and Heat Activates Protective Responses in Eucalyptus globulus That Are Not Activated When Subjected to Drought or Heat Stress Alone

Abstract

Aiming to mimic a more realistic field condition and to determine convergent and divergent responses of individual stresses in relation to their combination, we explored physiological, biochemical, and metabolomic alterations after drought and heat stress imposition (alone and combined) and recovery, using a drought-tolerant Eucalyptus globulus clone. When plants were exposed to drought alone, the main responses included reduced pre-dawn water potential (Ψpd) and gas exchange. This was accompanied by increases in malondialdehyde (MDA) and total glutathione, indicative of oxidative stress. Abscisic acid (ABA) levels increased while the content of jasmonic acid (JA) fell. Metabolic alterations included reductions in the levels of sugar phosphates accompanied by increases in starch and non-structural carbohydrates. Levels of α-glycerophosphate and shikimate were also reduced while free amino acids increased. On the other hand, heat alone triggered an increase in relative water content (RWC) and Ψpd. Photosynthetic rate and pigments were reduced accompanied by a reduction in water use efficiency. Heat-induced a reduction of salicylic acid (SA) and JA content. Sugar alcohols and several amino acids were enhanced by the heat treatment while starch, fructose-6-phosphate, glucose-6-phosphate, and α-glycerophosphate were reduced. Contrary to what was observed under drought, heat stress activated the shikimic acid pathway. Drought-stressed plants subject to a heat shock exhibited a sharp decrease in gas exchange, Ψpd and JA, no alterations in electrolyte leakage, MDA, starch, and pigments and increased glutathione pool in relation to control. Comparing this with drought stress alone, subjecting drought stressed plants to an additional heat stress alleviated Ψpd and MDA, maintained an increased glutathione pool and reduced starch content and non-structural carbohydrates. A novel response triggered by the combined stress was the accumulation of cinnamate. Regarding recovery, most of the parameters affected by each stress condition reversed after re-establishment of control growing conditions. These results highlight that the combination of drought and heat provides significant protection from more detrimental effects of drought-stressed eucalypts, confirming that combined stress alter plant metabolism in a novel manner that cannot be extrapolated by the sum of the different stresses applied individually.

Impacts of warming and water deficit on antioxidant responses in Panicum maximum Jacq

“…However, the environmental factors evaluated (water stress and + 2°C in the canopy temperature) had a significant influence on the characterisation of stress. MDA is a by‐product of lipid peroxidation and is used to quantify the damage caused by ROS to cell membranes (Correia et al ). In this work, independent of treatment, the MDA content was low at 06:00 h and high at 12:00 h, as a result of the elevated level of solar radiation commonly observed at noon.…”

Experimental Design and Sample Preparation in Forest Tree Metabolomics

“…In addition to the direct economic benefits provided by tree species, i.e., timber and non-timber products, gaming and tourism, forests have an immensurable ecological value, being the major determinants for water, oxygen, carbon, and energy balance and can be seen as a major opportunity to mitigate climate change effects [12], i.e., continued drought, increased soil and water salinization and acidification, and intensification of extreme temperatures [13]. In forest tree metabolomics research, most biological questions are indeed related to the responses towards the acclimation and adaptation to a permanently changing environment [14][15][16][17][18][19][20][21][22][23][24][25][26] as well as to the identification of potentially active components in tree species of pharmacological, agricultural, environmental, or industrial importance [27][28][29][30][31][32][33].…”

“…In forest tree research, LC-MS instruments have also been used for untargeted secondary metabolite profiling and phytohormone quantification studies. The focus of these studies was related with abiotic stress responses [19][20][21][22][23][24]67,88,89]; and to a smaller extent to biotic stress responses [90,91] and plant growth and developmental processes [77,92,93].…”

Impact on physiology and malting quality of barley exposed to heat, drought and their combination during different growth stages under controlled environment

“…Among these co‐occurring stresses, the impacts of heat and drought stress combination are the most devastating (Mittler ) and have become the subject of considerable research in the recent years (Mahalingam , Lawas et al ). Research on combined heat and drought stress in model plants (Rizhsky et al , Iyer et al ) as well as in plants of agronomic importance have been reported (Simon‐Sarkadi et al , Prasad et al , Zhao et al , Templer et al , Correia et al , Sehgal et al ).…”

“…Lawas et al 2018). Research on combined heat and drought stress in model plants (Rizhsky et al 2004, Iyer et al 2013 as well as in plants of agronomic importance have been reported (Simon-Sarkadi et al 2005, Prasad et al 2011, Zhao et al 2016, Templer et al 2017, Correia et al 2018, Sehgal et al 2018.…”