Polyamines in humic acid and their effect on radical growth of lettuce seedlings

Humic acids have been shown to contain many types of nitrogen compounds. Previous research has indicated that polyamines which function as plant growth regulators may be present in soils. A high performance liquid chromatography (HPLC) method was used for separation of polyamines from soils and different sources of humic acids. The results demonstrated that the purified humic acid significantly affected the radicle growth of lettuce seedlings, but not the shoot as noted for polyamines authentic. The optimum concentrations of polyamines which affected the radicle growth of lettuce seedlings were between 10(-6)-10(-12) M. The content of polyamines, putrescine, spermidine, and spermine in different sources of humic acid ranged between 1.54-7.00, 0.39-3.88, 0.48-4.79 nM g(-1), respectively. Polyamines may explain the hormone-like activity of humic substances.