Antioxidant capacity in cultivated and wild Solanum species: the effect of wound stress

Phenoloxidases: catechol oxidase - the temporary employer and laccase - the rising star of vascular plants

Phenolics are vital for the adaptation of plants to terrestrial habitats and for species diversity. Phenoloxidases (catechol oxidases, COs, and laccases, LACs) are responsible for the oxidation and polymerization of phenolics. However, their origin, evolution, and differential roles during plant development and land colonization are unclear. We performed the phylogeny, domain, amino acids, compositional biases, and intron analyses to clarify the origin and evolution of COs and LACs, and analysed the structure, selective pressure, and chloroplast targeting to understand the species-dependent distribution of COs. We found that Streptophyta COs were not homologous to the Chlorophyta tyrosinases (TYRs), and might have been acquired by horizontal gene transfer from bacteria. COs expanded in bryophytes. Structural-functionality and selective pressure were partially responsible for the species-dependent retention of COs in embryophytes. LACs emerged in Zygnemaphyceae, having evolved from ascorbate oxidases (AAOs), and prevailed in the vascular plants and strongly expanded in seed plants. COs and LACs coevolved with the phenolic metabolism pathway genes. These results suggested that TYRs and AAOs were the first-stage phenoloxidases in Chlorophyta. COs might be the second key for the early land colonization. LACs were the third one (dominating in the vascular plants) and might be advantageous for diversified phenol substrates and the erect growth of plants. This work provided new insights into how phenoloxidases evolved and were devoted to plant evolution.

Early physiological consequences of fire as an abiotic stressor in metabolic source and sink of young Brutian pine (Pinus brutia Ten.)

Climatic change causes gradual deforestation, partly through forest fires. However, fire has not been seen as an oxidative stressor on surviving forest trees. In addition, discrimination of stress-induced responses from acclimation steps cannot be examined under prolonged stress. Thus, four young Brutian pine (Pinus brutia Ten.) trees, a fire-related species, were subjected to a simulation of a crown-fire event to evaluate its impact on the availability of soluble carbon (C) and nitrogen (N) and the redox status near fire-afflicted tissue. Total soluble sugars, amino acids and non-structural (NS) proteins in needles and phloem, the antioxidant ascorbic acid (AsA) and reactive oxygen species (ROS) in needles were investigated together with the phloem transport velocity. To examine the temporal progress of these parameters, samples were obtained prior to fire (pre-fire), 2 h after fire, the following day (Day 1) and the following week (Week 1). Findings were categorized into shock reactions (2 h) and acclimation steps. Phloem transport accelerated 2 h postfire by almost 30% and correlated negatively to phloem sugars. At the same time the phloem ratio of sugars/amino acids correlated negatively to needle ROS. The trees' main response at 2 h and particularly on Day 1 was a massive increase in phloem NS proteins. The acclimation process involved also significant increases in needle NS proteins and AsA, as well as significant depletion of phloem amino acids by 65% by Week 1. The highest availability of soluble C and N was recorded on Day 1 in the phloem. Regression models explained significantly the variability of most soluble compounds postfire. Our findings suggest sink control over the source and an advanced role of phloem transport in defense processes.