Defense Enzymes in Mycorrhizal Tomato Plants Exposed to Combined Drought and Heat Stresses

Abstract

As a result of climate change, drought and heat significantly reduced plant growth. Therefore, this study aims to explore and provide more insight into the effect of different arbuscular mycorrhizal fungi (AMF) strains (Rhizophagus irregularis, Funneliformis mosseae, and Funneliformis coronatum) on tomato plant tolerance against combined drought and heat stress, as well as combined drought and heat shock. A pot experiment was performed under controlled conditions in a growth chamber at 26/20 °C with a 16/8 h photoperiod. After six weeks of growth, one-third of plants were put in non-stress conditions, while another one-third were subjected to combined drought and heat stress (40% field capacity for two weeks and 38 °C/16 h and 30 °C/8 h for 5 days). The rest of the plants were exposed to combined drought and heat shock (40% of field capacity for two weeks and 45 °C for 6 h at the end of the drought period). All data were evaluated by one- and two-way analysis of variance (ANOVA). Means were compared by Duncan’s post hoc test at p < 0.05. The obtained results showed that combined drought and heat stresses had no significant impact on root colonization. Furthermore, stressed AMF plants exhibited a decrease in hydrogen peroxide and malondialdehyde content in the cells and showed changes in defense enzyme activities (peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and glutathione S-transferase (GST)) in leaves as well as in roots compared with their relative non-mycorrhizal plants.