Exogenous salicylic acid alleviates the negative impacts on production components, biomass and gas exchange in tomato plants under water deficit improving redox status and anatomical responses.

Salicylic acid (SA) is an interesting messenger in plant metabolism that modulates multiple pathways, including the antioxidant defence pathway, and stimulates anatomical structures essential to carbon dioxide fixation during the photosynthetic process. The aim of this research was to determine whether pre-treatment with exogenous SA can alleviate the deleterious effects induced by water deficit on production components, biomass and gas exchange, measuring reactive oxygen species, antioxidant enzymes, variables connected to photosynthetic machinery, anatomical responses, and agro-morphological traits in tomato plants under water deficit. The experiment used a factorial design with four treatments, including two water conditions (control and water deficit) and two salicylic acid concentrations (0 and 0.1 mM salicylic acid). Water deficit negatively impacted the biomass and fruit number of tomato plants. Pre-treatment using 0.1 mM SA in plants submitted to water restriction induced increments in fruit number, weight, and biomass. These results were related to the protective role triggered by this substance, stimulating superoxide dismutase (27.07%), catalase (17.81%), ascorbate peroxidase (50.52%), and peroxidase (10.81%) as well as reducing the cell damage (malondialdehyde and electrolyte leakage) caused by superoxide and hydrogen peroxide. Simultaneously, application of SA improved the net photosynthetic rate (84.55%) and water-use efficiency (65.00%) of stressed plants in which these factors are connected to anatomical benefits, as verified by stomatal density, palisade and spongy parenchyma, combined with improved performance linked to photosystem II.

Down Regulation and Loss of Auxin Response Factor 4 Function Using CRISPR/Cas9 Alters Plant Growth, Stomatal Function and Improves Tomato Tolerance to Salinity and Osmotic Stress.

Auxin controls multiple aspects of plant growth and development. However, its role in stress responses remains poorly understood. Auxin acts on the transcriptional regulation of target genes, mainly through Auxin Response Factors (ARF). This study focuses on the involvement of SlARF4 in tomato tolerance to salinity and osmotic stress. Using a reverse genetic approach, we found that the antisense down-regulation of SlARF4 promotes root development and density, increases soluble sugars content and maintains chlorophyll content at high levels under stress conditions. Furthermore, ARF4-as displayed higher tolerance to salt and osmotic stress through reduced stomatal conductance coupled with increased leaf relative water content and Abscisic acid (ABA) content under normal and stressful conditions. This increase in ABA content was correlated with the activation of ABA biosynthesis genes and the repression of ABA catabolism genes. Cu/ZnSOD and mdhar genes were up-regulated in ARF4-as plants which can result in a better tolerance to salt and osmotic stress. A CRISPR/Cas9 induced SlARF4 mutant showed similar growth and stomatal responses as ARF4-as plants, which suggest that arf4-cr can tolerate salt and osmotic stresses. Our data support the involvement of ARF4 as a key factor in tomato tolerance to salt and osmotic stresses and confirm the use of CRISPR technology as an efficient tool for functional reverse genetics studies.