连作苹果土壤酚酸对平邑甜茶幼苗的影响

为探讨连作(重茬)苹果土壤中酚酸类物质的积累与苹果连作障碍的关系,在砂培条件下,取连作果园土壤中实际浓度的酚酸类物质处理平邑甜茶幼苗,探讨了连作2a的果园土壤中实测浓度的根皮苷、间苯三酚、根皮素、对羟基苯甲酸和肉桂酸对平邑甜茶幼苗根系线粒体指标、抗氧化酶活性、膜过氧化程度及活性氧(ROS)含量的影响。结果表明:连作土壤中实际浓度的5种酚酸类物质均使平邑甜茶幼苗生长受到抑制,根系受影响程度高于地上部分,表现为根冠比降低;线粒体膜通透性转换孔(MPTP)开放程度增大,线粒体膜电位降低,细胞色素Cyt c/a比值下降;降低了幼苗根系中超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性,增加了过氧化氢(H2O2)、超氧阴离子自由基(O·-2)以及丙二醛(MDA)的含量。土壤浓度的5种酚酸类物质中,以根皮苷处理抑制效果最显著,间苯三酚处理抑制力最小。因此,根皮苷是引起苹果连作障碍的主要酚酸,实践中应重点考虑对根皮苷的降解以缓解苹果连作障碍。

Effects of five kinds of phenolic acid on the function of mitochondria and antioxidant systems in roots of Malus hupehensis Rehd. seedlings

Apple replant disease (ARD) is a biological syndrome that occurs in sites where the same or closely related tree species have been planted previously. It is common in all major apple-growing regions of the world. The problems caused by ARD are typically expressed as reductions in plant growth and development, inhibition of root system development, with a subsequent shortened productive life and reduced yields. Research suggests that ARD is complex and can be induced by many factors. Excessive accumulation of phenolic substances is one of the most important factors. Therefore, studying phenolic acid inhibition of apple trees would provide a scientific and theoretic basis for understanding ARD and enrich research on the continuous cultivation of apple trees. To understand the phytotoxic mechanisms induced by phenolic acids involved in this phenomenon, Malus hupehensis Rehd. seedlings were planted in sand and treated with five phenolic acids (phloridzin, phloretin, cinnamic acid, p-hydroxybenzoic acid, and phloroglucinol) at the same concentrations as found in orchard soils. The effects of these phenolic acids on the function of mitochondria and antioxidant systems of Malus hupehensis Rehd. seedlings were analyzed by measuring plant growth, activity of mitochondrial permeability transition pores (MPTPs), membrane electric potential and cytochrome c/a superoxidase (SOD), catalase (CAT) and peroxidase (POD) activity, along with malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide radical (O₂^{· -}) content. All five kinds of phenolic acids inhibited the growth of replanted seedlings, and reduced total root length and average root diameter. Phloridzin had more significant inhibitory effects than other phenolic acids, reducing under-ground dry weight, aboveground dry weight, total root length, and average root diameter by 56.5%, 32.9%, 31%, and 27.9%, respectively. Root/shoot ratios were significantly decreased, which indicates that the impact on roots was more serious than on shoots. The phenolic acids increased the opening of MPTPs, decreased membrane electric potential and cytochrome c/a. Furthermore, POD, SOD, and CAT activity declined, which could be responsible for H₂O₂, O₂^- and MDA accumulation under the phenolic acid stress. Phloridzin was more toxic to seedlings than the other four phenolic acids;it reduced SOD, POD, and CAT activity by 29.6%, 16.4%, and 27.5%, respectively, and increased MDA, H₂O₂, and O₂^·- content by approximately 6.3, 6.0, and 1.9-fold compared to the control. Based on the above results, it could be concluded that phenolic acids induce ROS generation, and reduce antioxidant enzyme activity, thereby inducing mitochondrial permeability transition (MPT), and releasing cytochrome c to the cytosol. Therefore, phloridzin is the main phenolic acid occurring in apple continuous cropping orchard soils, and the degradation of phloridzin is the key to alleviating ARD.