[Allelopathic effect of p- and m-hydroxy-phenylacetic acid on soybean (Glycine max L.) germination]

In present work the p-hydroxy-phenylacetic acid (PHPA) and m-hydroxy-phenylacetic acid(MHPA) in rhizospheric soil solutions and decomposed root residues were detected by High Performance Liquid Chromatography (HPLC), and their effects on soybean germination at the level of 0, 30, 60, 150, 300 and 600 mg.kg-1, on melting temperature of DNA at the level of 600 mg.kg-1 and on cytoplasm protein patterns at the level of 0, 30, 150, 300 mg.kg-1 were also studied. PHPA and MHPA were detected in decomposed products of root residue and soil solutions collected from rhizosphere in which soil sickness was occurred, but not detected in soil on which soybean rotated with wheat. The standard samples of PHPA and MHPA were used for bioassay in Petri dish. The main root length and lateral root number of soybean were seriously reduced, even at the level of 30 mg.L-1. Soybean germination and root growth were retarded seriously by MHPA, in contrast with PHPA. At the level of 600 mg.kg-1, the melting temperature (Tm) of soybean DNA was increased sharply from 77 degrees C to 84.5 degrees C with PHPA, and from 77 degrees C to 88.5 degrees C with MHPA. Tm was affected markedly by MHPA, compared to PHPA, and the result was consistent with that of bioassay. The cytoplasm protein patterns of soybean leaves were obtained from SDS-PAGE, showing several low weight molecular proteins were affected, especially on 16. 1 kD and 20.2 kD. The results implied that PHPA and MHPA had allelopathic effect on soybean, and might have a role in soil-sickness of soybean.