Effects of phytotoxic extracts from peach root bark and benzoic acid on peach seedlings growth, photosynthesis, antioxidance and ultrastructure properties

- The water- or ethanol-extracts of peach root bark and benzoic acid caused retarded growth of peach seedlings.
- Root bark extracts and BA triggered lipid peroxidation and activity of antioxidative enzymes;.
- Root bark extracts and BA reduced photosynthesis and pigment (chlorophylls and carotenoids) levels;.
- Root bark extracts and BA changed the root ultrastructure in varying degrees;.
- GC-MS identified 49 chemicals in peach root bark, among which, four potent allelopathic compounds occurred in higher amounts.

During growth cycle, the accumulation of autotoxins released from peach root into soil strongly restrains the perennial tree growth in the same soil plot. However, the toxication syndrome on plant developmental physiology and the identities of toxic substances from peach root are still elusive to date. In this study, we used pot trials to investigate the influence of peach root bark extracts (extracted either in water or ethanol) and benzoic acid (a major allelopathic agent in most plant species)on seedling performance. Subsequently, the chemical compounds from peach root extracts were characterized by Gas Chromatography-Mass. Interestingly, in our study, the major toxic cyanide was only detected in the water extracts of root bark not in the root wood part and more cyanide could be detected in the presence of β-glucosidase. After applying exogenous root extracts and benzoic acid, the seedlings physiological growth was inhibited as expected, and lipid peroxidation and the antioxidant enzymes were increased as well. The photosynthetic parameters, including net photosynthetic rate, stomatal conductance and intercellular CO2 concentration, were all significantly reduced by the exogenous root extracts application. At cellular level, transmission electron microscopy showed that most of the organelles were lost in the root tip cells treated by ethanol-based peach root extracts, while the irregular nuclei, amorphous mitochondria in root tip cells, dissolved middle lamella and elongated plastids were observed in benzoic acid treatment. Furthermore, for the first time we identified 49 chemicals from ethanol-based peach root extracts, among which, 2, 4-bis (1, 1-dimethylethyl) -phenol (10.40%), benzoic acid (8.65%) and palmitic acid (7.12%) occurred in the highest amounts. Altogether our comprehensive physiological profile by toxication analysis and the determined major toxins from the root bark extracts could provide critical clues for peach allelopathic studies.