Effects of three allelopathic phenolics on chlorophyll accumulation of rice (Oryza sativa) seedlings: I. Inhibition of supply-orientation

Abstract

The effects of three allelopathic chemicals, o-hydroxyphenyl acetic, ferulic, and p-coumaric acids, on the chlorophyll (Chl) supply-orientation in the rice leaf (Oryza sativa cul. TN67) were investigated. Two-week-old eti- olated seedlings of rice were cultured in growth chamber in one-tenth Kimura's culture solution, with or without 25, 50 or 100 ppm of the phenolic compounds. The photoperiod, light intensity, and relative humidity were 12 h, 300 µmol/m 2 s, and 70%, respectively. Leaves were harvested at 1, 3, 6, 12, 24 and 48 h after treatment with phenolics. The concentrations of Chl and its three biosynthetic porphyrin precursors--i.e. protoporphyrin IX (Proto), Mg- protoporphyrin IX (Mg-Proto), and protochlorophyllide (Pchlide)--were determined, and the mole percent of total porphyrins was calculated. Accumulation of Chl and porphyrin contents were more inhibited as the phenolic concen- trations increased. While the mole percent of Mg-Proto affected by the three allelochemical phenolics exhibited the same pattern, those of Proto and Pchlide showed quite different patterns of change in concentration. The data strongly suggest that Mg-chelatase may be the major target of the three phenolics. The order of inhibition strength is ferulic acid>p-coumaric acid>o-hydroxyphenyl acetic acid. It is concluded that the supply-orientation of Chl is significantly inhibited by the exogenous phenolics, causing the shortage of Chl.