Coffea arabica seedlings genotypes are tolerant to high induced selenium stress: Evidence from physiological plant responses and antioxidative performance.

Selenium (Se) is considered a beneficial element to higher plants based on its regulation of antioxidative system under abiotic or biotic stresses. However, the limit of beneficial and toxic physiological effects of Se is very narrow. In the present study, the antioxidant performance, nutritional composition, long-distance transport of Se, photosynthetic pigments, and growth of Coffea arabica genotypes in response to Se concentration in solution were evaluated. Five Coffea arabica genotypes (Obatã, IPR99, IAC125, IPR100 and Catucaí) were used, which were grown in the absence and presence of Se (0 and 1.0 mmol L-1) in nutrient solution. The application of 1 mmol L-1 Se promoted root browning in all genotypes. There were no visual symptoms of leaf toxicity, but there was a reduction in the concentration of phosphorus and sulfur in the shoots of plants exposed to high Se concentration. Except for genotype Obatã, the coffee seedlings presented strategies for regulating Se uptake by reducing long-distance transport of Se from roots to shoots. The concentrations of total chlorophyll, total pheophytin, and carotenoids were negatively affected in genotypes Obatã, IPR99, and IAC125 upon exposure to Se at 1 mmol L-1. H2O2 production was reduced in genotypes IPR99, IPR100, and IAC125 upon exposure to Se, resulting in lower activity of superoxide dismutase (SOD), and catalase (CAT). These results suggest that antioxidant metabolism was effective in regulating oxidative stress in plants treated with Se. The increase in sucrose, and decrease in SOD, CAT and ascorbate peroxidase (APX) activities, as well as Se compartmentalization in the roots, were the main biochemical and physiological modulatory effects of coffee seedlings under stress conditions due to excess of Se.

Coffee seedlings growth under varied NO3-:NH4+ ratio: Consequences for nitrogen metabolism, amino acids profile, and regulation of plasma membrane H+-ATPase.

Root plasma membrane H+-ATPase electrochemical equilibrium for optimum coffee plant growth can be modulated by specific ammonium:nitrate (NO3-:NH4+) ratio supply. This study aimed to evaluate the coffee seedlings responses to varying ammonium:nitrate (NO3-:NH4+) ratio and to depict how much NO3- and NH4+ plants can use in terms of growth, nitrogen metabolism, amino acids profile and regulation of root plasma membrane H+-ATPase. Coffee plants were grown in nutrient solution with the following NO3-:NH4+ ratios (%): 100:0; 87.5:12.5; 50:50; 0:100. Plants were grown in nutrient solution for 90 days and evaluated for growth, nitrate reductase activity as well as the modulation of H+-ATPase activity in the plasma membrane of the roots, amino acids profile, chlorophyll a fluorescence parameters and estimated cations and anions taken up by plants. The plants treated with the 87.5:12.5 and 50:50 NO3-:NH4+ ratio showed higher ability to absorb nutrients maintaining balanced uptake and as a consequence, 6% and 29%, the highest dry mass yield as compared to the 0:100 NO3-:NH4+ ratio. In addition, plants supplied with the 87.5:12.5 and 50:50 NO3-:NH4+ ratio had respectively, 58% and 94%, greater photosynthetic capability. Those data suggest that farmers and plant nurseries could implement the 50:50 NO3-:NH4+ ratio of nitrogen sources at coffee plantations and seedlings.