Abstract

Aluminum and manganese toxicity have been described as the most important growth-limiting factor for plants in many acid soils around the world. Under acidic pH conditions, the Al3+ and Mn2+ concentrations increase, becoming potentially phytotoxic for plants. As an essential micronutrient, Mn takes place in several metabolic processes, such as photosynthesis by forming part of the structure of proteins in the oxygen-evolving complex, participating in the H2O photolysis, electron transport and also as an enzyme antioxidant-cofactor. However, Mn excess can lead to damages of the photosynthetic machinery, specifically PSII subunits. On the other hand, Al3+ toxicity results in root growth reduction, inducing chloroplast malformations, decreases in total chlorophyll content and photosynthetic rates accompanied by partial inhibition of photosynthetic electron transport in photosystem II (PSII). There is a need to evaluate new strategies to counteract the negative effects of these elements in crop plants growing under acid soils. The exogenous application of Methyl jasmonate (MeJA) has shown to be a promising tool to improve the harmful effects of different stress factors such as Al, Cd, among others. Therefore, we aimed to evaluate the contribution of an exogenously applied MeJA on the performance of two Vaccinium corymbosum cultivars under Al and Mn toxicity. Two contrasting blueberry cultivars (Camellia, resistant and Star, sensitive to Al) were conditioned in nutrient solution at pH 4.8 with and without MeJA (0.01 mM) application under toxic Mn (1000 μM) and Al (200μM) for 21 days as following: Control, MeJA, Al, Mn, Al+Mn, Al+MeJA, Mn+MeJA and Al+Mn+MeJA. Photosynthetic parameters were evaluated in vivo, and leaves were collected to evaluate photosynthetic pigments (PP) by HPLC-DAD and total hormones (TH) as IAA equivalents. Besides, leaves were fixed with Glutaraldehyde 2.5% to evaluate stomata density (SD) by VP-SEM microscopy. The results showed a differential response between cultivars with MeJA application under Al and Mn stress and their combinations. Similar SD is shown in the non-stressed condition in both genotypes. However, MeJA alone regulates the number of stomata negatively in both cultivars, decreasing significantly in Star (48%). Despite SD decline, A (net photosynthesis), gs (stomatal conductance) and E (transpiration) did not change with MeJA treatment in Star and Camellia. However, Star photosynthetic performance, total chlorophylls, chlorophyll ratio, and β-carotene showed ahigh decrease (until 70%) under Al and Mn treatments (showing sensitivity to both treatments), recovering with the exogenous MeJA application. Regarding TH, Camellia and Star showed similar behavior under control and MeJA; however, when exposed to Al alone, both cultivars increased its values. Star cultivar appears to be sensitive to Al and Mn toxicity, improving its performance with MeJA treatment. Interestingly, MeJA alone negatively regulates the SD without changing the photosynthetic parameters in both cultivars. However, in the presence of stress conditions, the MeJA application improves the performance of the sensitive cultivar Star. Acknowledgments: FONDECYT-1171286