Arsenic toxicity in soybean plants: Impact on chlorophyll fluorescence, mineral nutrition and phytohormones

Abstract

Arsenic (As) is naturally present in soils and groundwater in agricultural areas, mainly in the form of arsenate (AsV) and arsenite (AsIII). It can enter soybean plants and decrease their yield and growth, therefore posing a serious problem. Our aim was to evaluate its effects on physiological events closely related to plant growth and the possible signaling pathways involved. Photosynthesis related parameters, gas exchange, mineral concentration, phytohormone content, and the expression of genes related to abscisic acid (ABA) and jasmonic acid (JA), were analyzed in soybean leaves and roots exposed to AsV and AsIII. A reduction in the CO2 assimilation rate was associated with decreased stomatal conductance, transpiration rate and intercellular CO2 concentration in treated plants. The alterations observed in the photochemical phase of the photosynthesis (OJIP -test) suggest a reduction in electron transport, mainly under AsV treatment. Arsenic also induced changes in NH4+, NO3−, PO43−, Cl−, SO42− and Na+ content in roots, while the mineral status seemed to remain unchanged in leaves. Surprisingly, ABA content was significantly lower in As-treated plants and so was the expression of GmPYL1 and GmbZIP1, genes potentially involved in ABA signaling. However, treatment caused an increase in JA content and a decrease in its precursor, 12-oxo-phytodienoic acid (OPDA), which suggests that JA could play a key role in regulating the response to the metalloid. These results build on those of previous studies and contribute to elucidating the complexity of As-triggered responses in soybean.