Soybean (Glycine max) response to phosphate deficiency

Phosphorus is one of the principal mineral nutrients required by plants, but it is also one of the least available nutrients in soils. The form of P readily accessed by plants is as orthophosphate ions H2PO4-, HPO42- (Pi), but its concentration rarely exceeds 10 mu M; therefore, the plants are continually exposed to phosphate deficiency. Reports describing the changes induced during phosphate deficiency in soybean (Glycine max) plants were not found. Therefore, the objective of this study was to evaluate the response of soybean to Pi defficiency. Root growth was not modified in soybean, var. Tapachula 86, grown under phosphate sufficiency or under different phosphate deficiencies, whereas shoot growth was stopped. Secreted acid phosphatase activity increased almost ten fold in plants grown under Pi absence, whereas the activity of these enzymes only increased between four and five times in the other Pi deficiency treatments. Amount of Pi was higher in phytic acid and in aluminum phosphate treatments, indicating that soybean plants also produce phytases and organic acids which help Pi mobilization. However, these adaptations were insufficient to promote normal plant growth.