Physiological, biochemical and phytohormone responses of to -pinene-induced allelopathy.

The -pinene is the main allelochemical of many weeds that inhibit the growth of , an important forage and ecological restoration herbage. However, the response changes of -pinene-induced allelopathy to is still unclear. Here, we investigated the physiological, biochemical and phytohormone changes of exposed to different -pinene concentrations. The -pinene-stress had no significant effect on height and fresh weight (FW) of seedlings. The water-soluble proteins, the soluble sugars and proline (Pro) strengthened seedlings immunity at 5 and 10 µL L -pinene. Superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased at 5 µL L -pinene to resist stress. APX reduced the membrane lipid peroxidation quickly at 10 µL L -pinene. The high-activity of peroxidase (POD), APX along with the high level of GSH contributed to the cellular redox equilibrium at 15 µL L -pinene. The POD, glutathione reductase (GR) activity and glutathione (GSH) level remained stable at 20 µL L -pinene. The changes in antioxidant enzymes and antioxidants indicated that was effective in counteracting the harmful effects generated by hydrogen peroxide (HO). The -pinene caused severe phytotoxic effects in seedlings at 15 and 20 µL L. Endogenous signal nitric oxide (NO) and cell membrane damage product Pro accumulated in leaves of seedlings at 15 and 20 µL L -pinene, while lipid peroxidation product malondialdehyde (MDA) accumulated. The chlorophylls (Chls), chlorophyll a (Chl a), chlorophyll b (Chl b) content decreased, and biomass of seedlings was severely inhibited at 20 µL L -pinene. The -pinene caused phytotoxic effects on seedlings mainly through breaking the balance of the membrane system rather than with reactive oxygen species (ROS) productionat 15 and 20 µL L -pinene. Additionally, phytohormone levels were altered by -pinene-stress. Abscisic acid (ABA) and indole acetic acid (IAA) of seedlings were sensitive to -pinene. As for the degree of -pinene stress, salicylic acid (SA) and jasmonic acid (JA) played an important role in resisting allelopathic effects at 15 µL L -pinene. The ABA, Zeatin, SA, gibberellin 7 (GA7), JA and IAA levels increased at 20 µL L -pinene. The -pinene had a greatest impact on ABA and IAA levels. Collectively, our results suggest that seedlings were effective in counteracting the harmful effects at 5 and 10 µL L -pinene, and they were severely stressed at 15 and 20 µL L -pinene. Our findings provided references for understanding the allelopathic mechanism about allelochemicals to plants.