Abstract: Polyamines (PAs) have been suggested to play roles in plant salt stress adaptation . In this study , alteration of free, conjugated and bound PAs [ putrescine (Put ) , cadaverine (Cad) , spermidine (Spd) and spermine (Spm) ] in roots and leaves of vetiver grass ( Vetiveria zizanioides) seedlings in response to salt stress were investigated. Under moderate salt stresses (100 and 200mmol L ^{- 1} NaCl) for 9 days, vetiver grass grew at similar vigor compared with seedlings under normal growth conditions . However , growth was severely arrested when plants were treated with severe salt stress (300 mmol L^{- 1}NaCl). Under three different concentrations of NaCl stress mentioned above, the contents of free Put , Cad , Spd , Spm and total free PA substantially decreased in roots and leaves , and more severe loss of free PAs was observed under higher NaCl concentration. Conjugated Put , Cad , Spd , Spm, and total conjugated PAs remarkably increased, and the extent of the increase after 300mmol L^{- 1} NaCl treatment was smaller than those after 100 or 200mmol L- 1 NaCl treatments . Bound Put, Cad and total bound PAs decreased in both roots and leaves under salt stress , moreover , bound Spd and Spm decreased in leaves while increased in roots in response to salt treatments, and the more obvious rise was displayed under moderate salt stresses. With the exception of the significant decreases of free (Spd + Spm )/Put ratio in roots and leaves after 300 mmol L^{- 1} NaCl treatment , other ratios of free , conjugated , bound and the total (Spd + Spm )􊄯Put increased in roots and leaves of vetiver grass seedlings after different salt treatments, and especially under moderate salt stress . These results indicated that maintaining homeostasis of total PAs content and high (Spd + Spm )/Put ratios could be an adaptation mechanism in vetiver grass to moderate saline environment .

Key words: 多胺