Physiological and biochemical mechanism of allelopathy of secalonic acid Fon higher plants

Our previous work indicated that secalonic acid F (SAF) was the major allel ochemical produced by Aspergillus japonicus. Studies showed that SAF marked ly inhibited the seedling growth of sorghum (Sorghum vulgare Pers.), hairy beggarticks (Bidens pilosa L.), and barnyardgrass (Echinochloa crus-galli ( L.) Beauv.), It significantly reduced the activities of superoxide dismutas e (SOD) and peroxidase (POD) at a concentration of 0.3 mM, Secalonic acid F enhanced malondialdehyde (MDA) contents, but it lowered the content of chl orophyll (CHL) a and b as well as the photosynthetic rates of tested plants . Respiration, membrane permeability, and abscisic acid (ABA) content incre ased after treatment with SAF, but the reduction activity of the root syste m was lowered. There is no remarkable change in the soluble proteins of pla nts that are treated with SAF, Transmission electron microscope (TEM) obser vations showed that treated plants exhibited amorphous mitochondria without integral membranes and swelling chloroplasts without membranes in a disord erly arrangement. The SAF treatment also damaged the stratiform structure o f the chloroplasts and the membranes and structure of the nuclei. These res ults suggest that SAF may weaken the protective ability of plant tissues ag ainst membrane lipid peroxidation and damage the whole membrane system of p lants, resulting in the ultrastructure destruction of chloroplasts, mitocho ndria, and nuclei. Cell ultrastructure destruction causes a reduction of ph otosynthesis and root activities and an increase in respiration. These abno rmal physiological processes contribute to the inhibition of plant growth.