Effects of sodium selenate and selenomethionine on reproductive growth, fruit quality, and 5-hydroxytryptophan metabolism of 'Qingcui' plum

Selenium (Se) is a beneficial element for plant growth and development. In this study, three-year-old potted 'Qingcui' plums were treated with Na2SeO4 (Se6+) or selenomethionine (SeMet Se2-) to explore the effect of Se on the plant growth, fruit quality, and 5-hydroxytryptophan (5-HTP) metabolism. Flower and fruit numbers, fruit quality and yield, Se content, and 5-HTP metabolites and enzymes were detected. The results showed that the flower and fruit numbers, and yield were significantly increased by the Se application. There were no significant differences in the fruit diameters, fruit mass, edible part ratio, titratable acids, water content, and solid acid ratio among the treatments. The total soluble solids, soluble protein, and malondialdehyde contents under the Se6+ treatment showed no significant difference compared to the Se2- treatment, but they were significantly higher than these under control by 16.71%, 39.13%, and 36.27%, respectively. The Se application markedly increased plant the Se content, and Se contents in the roots and leaves, or the fruits were significantly larger by the Se6+ treatments than the Se2- treatment. The leaves' pigment contents under the Se2- treatments were significantly larger than those under the control or Se6+ treatment. Tryptophan was not significantly influenced, the 5-HTP and 5-methoxytryptophan contents were reduced in the roots, and increased in the leaves, and the serotonin content was only significantly increased in the roots by the Se treatments. The tryptophan hydroxylase and hydroxyindole-O-methyltransferase levels were slightly influenced, and the tryptophan decarboxylase level in the roots or fruits was significantly increased by the Se treatments. The Se application had beneficial effects on the plant growth, fruit quality, and Se content, especially in the Se6+ treatment, and influenced the 5-HTP metabolism.