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Trichoderma species are widely known for their antagonistic properties, but plant growth promotion and abiotic stress tolerance have also been reported. Mechanisms of abiotic stress tolerance, such as drought in plants in interaction with Trichoderma spp., remain unclear. In this work, the results about the influence of Trichoderma brevicompactum on the physiological parameters and abscisic acid (ABA) content in leaves and roots of tomato, as well as the Trichoderma‐modulated plant response to drought are presented. Both in optimally watered plants and droughted plants treated with Trichoderma, the relative water content (RWC) was 17% higher than in untreated plants. Drought lowered RWC by 25% in both Trichoderma‐untreated and ‐treated plants. Under drought conditions, the better water status of plants treated with Trichoderma is connected with lower stomatal conductance and closure of stomata. The lower increase of root ABA content in Trichoderma‐treated plants that we observed could be an adaptive advantage in sense of smaller inhibition of plant growth induced by drought. Trichoderma modulation of the salicylic acid (SA) marker genes response to drought was observed in leaves. Our results suggest that signalling pathways of jasmonic acid (JA), SA and ABA are involved in response to both drought and Trichoderma. The mutual effect of the tested treatments leads to the modification of gene expression in comparison to the reaction to a single stress. The upregulation of SA marker genes in leaves and JA marker genes in the roots 2 weeks after the interaction with T. brevicompactum indicates that it could be promising biocontrol agent. [ABSTRACT FROM AUTHOR]

Metal contamination represents a strong selective pressure favoring tolerant genotypes and leading to differentiation between plant populations. We investigated the adaptive capacity of early-colonizer species of Verbascum recently exposed to Zn- and Cu-contaminated soils (10-20 years). Two Verbascum thapsus L. populations from uncontaminated sites (NMET1, NMET2), one V. thapsus from a zinc-contaminated site (MET1), and a Verbascum lychnitis population from an open-cast copper mine (MET2) were exposed to elevated Zn or Cu in hydroponic culture under glasshouse conditions. MET populations showed considerably higher tolerance to both Zn and Cu than NMET populations as assessed by measurements of growth and net photosynthesis, yet they accumulated higher tissue Zn concentrations in the shoot. Abscisic acid (ABA) concentration increased with Zn and Cu treatment in the NMET populations, which was correlated to stomatal closure, decrease of net photosynthesis, and nutritional imbalance, indicative of interference with xylem loading and divalent-cation homeostasis. At the cellular level, the sensitivity of NMET2 to Zn and Cu was reflected in significant metal-induced ROS accumulation and ion leakage from roots as well as strong induction of peroxidase activity (POD, EC 1.11.1.7), while Zn had no significant effect on ABA concentration and POD activity in MET1. Interestingly, MET2 had constitutively higher root ABA concentration and POD activity. We propose that ABA distribution between shoots and roots could represent an adaptive mechanism for maintaining low ABA levels and unaffected stomatal conductance. The results show that metal tolerance can occur in Verbascum populations after relatively short time of exposure to metal-contaminated soil, indicating their potential use for phytostabilization. [ABSTRACT FROM AUTHOR]