Physiological, hormonal and metabolic alterations caused by selenium in rice seedlings
Selenium (Se) can alter the growth of some plant species and causes changes in levels of plant hormones, such as auxin and ethylene. However, the impact of Se supply on relationships between hormones biosynthesis and primary metabolism during growth of rice (Oryza sativa L.) seedlings is poorly understood. Thus, the hypothesis that Se induces changes in the interactions between auxin and ethylene to modulate primary metabolism and growth of rice seedlings was investigated. The application of selenite did not affect the of growth shoot of seedlings, but promoted the elongation of the primary root with reduction in the number and length of the lateral roots. There was a decrease in the concentrations of ethylene, 1- aminocyclopropane-1-carboxylic acid (ACC) and indole-3-acetic acid (IAA) in roots of rice seedlings treated with selenite as compared with the control. Selenite led to decreased expression of genes associated with the biosynthesis of auxin and ethylene, concomitantly with reduced production of these hormones by the roots. Moreover, selenite decreased the abundance of transcripts encoding auxin transport proteins. Treatment with IAA overrode the repressive effect of selenite on lateral root growth. The ethylene synthesis inhibitor L-α-(2- aminoethoxyvinyl)-glycine (AVG) increased elongation of primary root, whereas the ethylene precursor ACC resulted in the opposite effect. Moreover, soluble sugars accumulate in roots under selenite treatment. Together, these findings suggest that selenite affects primary and lateral root development by blocking ethylene and auxin biosynthesis, respectively. Experiments with organic Se showed that seleno-L-methionine (SeMet) at low concentration increased concentrations of hydrogen peroxide and superoxide anion production, inhibiting auxin biosynthesis and increasing ethylene production in both shoot and root. The effect of SeMet on seedlings was mediated by the inhibition of the abundance of transcripts encoding auxin transport and cell expansion proteins. Moreover, SeMet led to increased respiration, which was positively correlated with organic acids consumption, but negatively with sugars consumption, thereby decreasing seedling growth. In contrast with SeMet treatment, L- methionine did not affect reactive oxygen species production, hormone biosynthesis and growth of seedlings, indicating an exclusive Se effect. Treatment with 1,4-diazabicyclooctane (DABCO), a singlet oxygen scavenger, overrode the repressive effect of SeMet in seedling growth. It is concluded that Se regulates physiological and metabolic processes in rice seedlings are dependent on the form of Se supplied. Keywords: Cell expansion. Primary metabolism. Hormonal regulation. Oryza sativa L.
Hormônios vegetais, Controle hormonal, Metabolismo, Plântulas
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