ACTIVATION OF PLANT FOLIAR OXIDASES BY INSECT FEEDING REDUCES NUTRITIVE QUALITY OF FOLIAGE FOR NOCTUID HERBIVORES
ACTIVATION OF PLANT FOLIAR OXIDASES BY INSECT FEEDING REDUCES NUTRITIVE QUALITY OF FOLIAGE FOR NOCTUID HERBIVORES
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DOI：
10.1007/bf01014725
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发表时间：
1989-12-01
影响因子：
2.3
通讯作者：
DUFFEY, SS
中科院分区：
文献类型：
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作者：
FELTON, GW;DONATO, K;DUFFEY, SS
番茄植物 Lycopersicon esculentum 的叶子和果实含有多酚氧化酶 (PPO) 和过氧化物酶 (POD)，它们与邻二羟基酚底物原位分离。然而，当叶子组织因昆虫取食而受损时，酶和酚类物质接触，导致酚类物质快速氧化为邻醌。当番茄果虫Heliothis zea或甜菜夜蛾Spodoptera exigua以番茄叶子为食时，摄入的大量绿原酸在昆虫肠道中被PPO氧化成绿原醌。此外，果虫的消化酶有可能进一步激活肠道中的叶氧化酶活性。氯原醌是一种高反应性亲电子分子，很容易与氨基酸和蛋白质的亲核基团共价结合。特别是，氨基酸的-SH和-NH2基团易于结合或烷基化。在番茄叶子实验中，果虫的相对生长速率与 PPO 活性呈负相关。随着番茄植株的成熟，叶面PPO活性可能增加近10倍，而果虫的生长速度却严重下降。在番茄果实中，未成熟的小果实中 PPO 的含量最高，但成熟果实中的含量基本上可以忽略不计。幼虫在果实上的生长速度也与PPO活性呈负相关，当幼虫取食成熟果实时，幼虫生长速度最快。幼虫生长的减少被认为是由于邻醌对氨基酸/蛋白质的烷基化以及随后叶子营养质量的降低造成的。这种烷基化降低了膳食蛋白质的消化率和氨基酸的生物利用度。我们认为，这种消化率降低的机制可能可以推广到其他植物-昆虫系统，因为多酚氧化酶和酚类底物在维管植物物种中普遍存在。
The foliage and fruit of the tomato plant Lycopersicon esculentum contains polyphenol oxidases (PPO) and peroxidases (POD) that are compartmentally separated from orthodihydroxyphenolic substrates in situ. However, when leaf tissue is damaged by insect feeding, the enzyme and phenolic sustrates come in contact, resulting in the rapid oxidation of phenolics to orthoquinones. When the tomato fruitworm Heliothis zea or the beet armyworm Spodoptera exigua feed on tomato foliage, a substantial amount of the ingested chlorogenic acid is oxidized to chlorogenoquinone by PPO in the insect gut. Additionally, the digestive enzymes of the fruitworm have the potential to further activate foliar oxidase activity in the gut. Chlorogenoquinone is a highly reactive electrophilic molecule that readily binds covalently to nucleophilic groups of amino acids and proteins. In particular, the -SH and -NH2 groups of amino acids are susceptible to binding or alkylation. In experiments, with tomato foliage, the relative growth rate of the fruitworm was negatively correlated with PPO activity. As the tomato plant matures, foliar PPO activity may increase nearly 10-fold while the growth rate of the fruitworm is severely depressed. In tomato fruit, the levels of PPO are highest in small immature fruit but are essentially negligible in mature fruit. The growth rate of larvae on fruit was also negatively correlated with PPO activity, with the fastest larval growth rate occurring when larvae fed on mature fruit. The reduction in larval growth is proposed to result from the alkylation of amino acids/protein by o-quinones, and the subsequent reduction in the nutritive quality of foliage. This alkylation reduces the digestibility of dietary protein and the bioavailability of amino acids. We believe that this mechanism of digestibility reduction may be extrapolatable to other plant-insect systems because of the ubiquitous cooccurrence of PPO and phenolic substrates among vascular plant species.