Soybean seed phenol, lignin, and isoflavones and sugars composition are altered by Foliar Boron application in soybean under water stress

Authors: Bellaloui, Nacer

Submitted to: Food and Nutrition Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2012
Publication Date: 4/18/2012
Citation: Bellaloui, N. 2012. Soybean seed phenol, lignin, and isoflavones and sugars composition are altered by Foliar Boron application in soybean under water stress. Food and Nutrition Sciences. 3:579-590.

Interpretive Summary: Boron is a micronutrient essential for crop growth, productivity, and seed quality. Boron has been reported to be involved in structural support of plant tissues and involved in production of phenolic compounds, natural products present in plant leaves, roots, and seed that have been reported to have a significant role in plant disease resistance and to have health benefits for humans because of their antioxidant properties. Therefore, suboptimal levels of boron concentration in plants due to water stress/drought would compromise disease resistance. This research investigating the effects of foliar boron fertilizer on seed phenolics (phenol, lignin, and isoflavones) in a greenhouse experiment with well-watered and water-stressed soybean showed higher total phenol and lignin concentrations in seed from the water-stressed plants. Application of foliar boron fertilizer resulted in higher concentrations of seed boron, sucrose and isoflavones in both watered and water-stressed plants; however, seed raffinose and stachyose were higher in water-stressed plants. Higher seed sucrose is desirable for soybean seed flavor, but higher stachyose is undesirable because it is indigestible by human and monogastric animals. Higher concentration of seed phenol, lignin, and isoflavones is desirable because of the involvement of these compounds in disease resistance and their benefit to human health. Soybean breeders may be able to select for higher phenolic compounds and desirable sugars to increase disease resistance and seed quality under drought conditions.

Technical Abstract: Previous research showed that foliar boron (B) fertilizer at flowering or seed-fill growth stages altered seed protein, oil, and fatty acids. The objective of this research was to investigate the effects of foliar B fertilizer on seed phenolics (phenol, lignin, and isoflavones) and sugars concentrations. A repeated greenhouse experiment was conducted on soybean [(Glycine max(L.) Merr.)] under watered and water-stressed conditions. Soybean plants were divided into different sets, and each set was subjected to one of the following treatments: W= plants were watered with no foliar B; WB= Plants were watered and received foliar B; WS=plants were water-stressed with no foliar B; WSB=plants were water-stressed and received foliar B. Foliar B was applied at rate of 0.45 kg/ha twice at flowering and twice at seed-fill stages. The results showed that total phenol and lignin concentrations were higher in seed collected from water-stressed plants compared with those collected from watered plants whether B was applied or not, suggesting that higher phenol and lignin concentrations were due to B-deficiency in plant tissues. Application of B resulted in higher concentrations of total seed B and isoflavones under watered and water-stressed plants. Higher cell wall B was higher in water-stressed plants than in watered plants, having an opposite trend to total B. Application of B resulted in higher seed sucrose in watered and water-stressed plants, but raffinose and stachyose were significantly higher under water-stressed plants. The research demonstrated that foliar B fertilizer altered seed phenol, lignin, isoflavones, and sugars, and suggested that B involved in phenolics and sugar metabolism. The higher cell wall B in water-stressed plants than in watered plants supports previous research that B has mainly a structural role. The higher sucrose resulting from foliar B in watered plants is desirable as sucrose contributes to seed quality. The increase of raffinose and stachyose concentrations in seed of water-stressed plants is undesirable, but raffinose, and especially stachyose may be involved in water stress/drought tolerance. The current knowledge would help soybean breeders select for higher phenolic compounds and desirable sugars for higher seed qualities under drought conditions.