南美斑潜蝇为害对黄瓜体内4种防御酶活性的影响

植物对昆虫取食产生的防御反应,在昆虫与植物相互作用关系中起着重要的作用。为明确南美斑潜蝇Liriomyza huidobrensis(Blanchard)取食与植物防御之间的作用关系,本文分别测定了南美斑潜蝇幼虫持续为害1、3、5、7及9d后黄瓜叶片中苯丙氨酸解氨酶(PAL)、多酚氧化酶(PPO)、过氧化物酶(POD)及超氧化物歧化酶(SOD)活性的变化。结果表明：在南美斑潜蝇幼虫持续取食下,PAL、PPO、POD和SOD等4种酶活性显著上升；PAL、PPO和POD等3种酶活性随受害程度的加重而上升幅度加大,即重度受害>轻度受害>系统对照>健康对照,而SOD活性变化没有规律。在系统对照黄瓜叶片中,PAL、PPO、POD和SOD等4种酶活性最大值分别在第5、1、5和5d；在轻度受害黄瓜叶片中,PAL、PPO、POD和SOD等4种酶活性最大值分别在第5、9、5和9d；在重度受害黄瓜叶片中,PAL、PPO、POD和SOD等4种酶活性最大值分别在第7、7、5和5d。黄瓜叶片受害后,POD和PPO活性上升幅度较大,PAL和SOD活性上升幅度较小,说明POD和PPO对取食胁迫响应比PAL和SOD更灵敏。

Effects of Liriomyza huidobrensis infestation on the activities of four defensive enzymes in the leaves of cucumber plants

The pea leafminer, Liriomyza huidobrensis(Blanchard), is a widely distributed pest of ornamental and vegetable crops from subtropical to temperate regions and can cause economic losses to host plants by both adult and larval infestations. Larval mining in palisade parenchyma tissue reduces the photosynthetic capacity of plants up to 62%, and severely infested leaves may fall. A further damage to leaves is caused by females, which use the ovipositor to make holes in the surfaces of the leaves promoting the production of leaf exudates on which both females and males feed. The defensive responses of plants to insect herbivory play an important part in the interactive relationship between insects and plants. Insects obtain their nourishment from plants. The nutritional quality of plants and the limited availability of various plant parts deter many insects from using plants as a food source. Insects can be prevented from feeding by plant defenses, ranging from physical barriers to toxins and antifeedants. Plants produce a considerable variety of chemicals with roles in defense against herbivory. These chemicals include secondary plant metabolites and some proteins. Plants can produce proteins that play a critical role in defense by targeting the digestive system of insects, thus impairing the ability of the insect to digest and absorb food. These proteins include protease inhibitors and defensive enzymes which are widespread in plants and are inducible by wounding and herbivory. Four main defensive enzymes, including phenylalanine ammonialyase(PAL), polyphenol oxidase(PPO), peroxidase(POD) and superoxide dismutase(SOD), are key enzymes in the generating process of secondary plant metabolites. However, the interactions between the leafminer and its host plants have been studied mainly on the relationship between host preference of adults and trichomes, volitales, primary and secondary metabolites in host plants. In order to explore the interaction between L. huidobrensis herbivory and plant defense, we investigated the changes in the active levels of these four defensive enzymes in the leaves of cucumber plants that had been continuously feeding by the larvae for 1, 3, 5, 7 and 9 days, respectively.The results indicated that the activities of four enzymes in the leaves of cucumber plants, which had been feeding by the larvae, rose significantly. The magnitude of activity rising of PAL, PPO and POD increased with the increase of damaged levels, i.e. damaged heavily > lightly > systemically > undamaged, but the change of SOD activity were not regular. The maximum activities of PAL, PPO, POD and SOD appeared on the 5th, 1st, 5th and 5th day, respectively, in the systemic controls. They were on the 5th, 9th, 5th and 9th day, respectively, in the damaged-lightly leaves, and on the 7th, 7th, 5th and 5th day, respectively, in the damaged-heavily leaves. The magnitudes of activity increasing of POP and PPO were more than those of PAL and SOD after the leaves had been feeding, which suggests the responses of POP and PPO to insect herbivory are more sensitive than those of PAL and SOD.