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Pathogen recognition is linked to the perception of microbe/pathogen-associated molecular patterns triggering a specific and transient accumulation of reactive oxygen species (ROS) at the pathogen attack site. The apoplastic oxidative "burst" generated at the pathogen attack site depends on the ROS-generator systems including enzymes such as plasma membrane NADP (H) oxidases, cell wall peroxidases and lipoxygenase. ROS are cytotoxic molecules that inhibit invading pathogens or signalling molecules that control the local and systemic induction of defence genes. Post-translational modifications induced by ROS are considered as a potential signalling mechanism that can modify protein structure and/or function, localisation and cellular stability. Thus, this review focuses on how ROS are essential molecules regulating the function of proteins involved in the plant response to a pathogen attack through post-translational modifications. • The impact of reactive oxygen species (ROS) on proteins through the post-translational modifications (PTMs). • Role of ROS controlling signalling pathways during plant pathogen interactions. • Plant perceive the pathogen invasion and trigger resistance response using ROS as signal molecules. • ROS largely signal through PTMs, providing strict spatial and temporal control of protein conformation to fine-tune activity. [ABSTRACT FROM AUTHOR]

Alfalfa is a model plant defined as less sensitive than others to iron (Fe) deficiency. In the present work, some mechanisms induced in low Fe availability conditions were studied, including the effect of inoculation of alfalfa seeds with Pseudomonas putida. The effect of different Fe contents in the nutrient solution on the growth parameters was evaluated at 3 and 10 days, observing that low Fe conditions promoted biomass accumulation. Activation in the mechanisms of Fe acquisition, through acidification of the media and an increase in the ferric chelate reductase (FCR) activity, was observed in the absence of Fe at 10 days. The presence of P. putida KT2442 in the rhizosphere eliminated FCR activation through the excretion of siderophores. The effect of the siderophores on the modulation of FCR activity was demonstrated using a ppsD mutant strain, unable to segregate them, observing an activation of the activity similar to that observed in the absence of the bacteria. This, together with the demonstrated mechanisms to increase Fe availability, contributed to the conclusion that alfalfa can be used for recovery programmes of soils with low Fe availability. [ABSTRACT FROM PUBLISHER]

Measurements of leaf stomatal conductance, leaf CO2 assimilation rate, leaf chlorophyll fluorescence, and a previously published biochemical model have been used to evaluate the thermo-tolerance of the photosynthetic apparatus in two tomato genotypes ('Amalia' and 'Nagcarlang'). The study was carried out as two experiments. In Experiment 1, a brief (20 min) increase in leaf temperature to 35°C reduced the photosynthetic rate of 'Amalia' leaves grown at 25°C, but stimulated photosynthesis in 'Nagcarlang', due to an increase in the maximum rate of carboxylation of ribulose-1,5- bisphosphate-carboxylase/oxygenase (VCmax). The heat-sensitive step in 'Amalia' seemed to be the maximum rate of electron transport (Jmax). However, in Experiment 2, there was no significant difference between Jmax at 25°C and 35°C when plants had been acclimatised to these temperatures. [ABSTRACT FROM AUTHOR]

Purification and characterisation of pepper ( Capsicum annuum L) chloroplasts and chromoplasts isolated from commercial green, red and yellow mature fruits were undertaken. Induction of the synthesis of several antioxidants in organelles isolated from mature fruits was found. The ultrastructure of organelles and the presence and activity of SOD isozymes and enzymes involved in the ASC-GSH cycle, together with the non-enzymatic antioxidant content and some oxidative parameters, were analysed. It was found that lipids, rather than proteins, seem to be a target for oxidation in the chromoplasts. The ascorbate and glutathione contents were elicited during differentiation of chloroplasts into chromoplasts in both red and yellow fruits. The activity of SOD and of components of the ASC-GSH cycle was up-regulated, suggesting that these enzymes may play a role in the protection of plastids and could act as modulators of signal molecules such as O2˙− and H2O2 during fruit maturation. The presence of an Mn-SOD in chromoplasts isolated from yellow pepper fruits was also investigated in terms of structural and antioxidant differences between the two cultivars. [ABSTRACT FROM AUTHOR]