伤害和挥发物对棉花花外蜜的诱导效应

植物花外蜜的分泌是一种植物间接防御反应。为了明确植食性昆虫、机械伤和机械伤诱导的挥发性气体在植物花外蜜诱导分泌中的作用,分析了咀嚼式口器昆虫棉铃虫Helicoverpa armigera(Hübner)、刺吸式口器昆虫棉蚜Aphis gossypii Glover取食、剪刀机械伤、剪刀机械伤+棉铃虫反吐物、针刺机械伤以及机械伤诱导挥发物、顺式-茉莉酮对棉花Gossypium hirsutum L.叶片花外蜜分泌量的影响。结果表明,棉铃虫取食、剪刀机械伤、剪刀机械伤+棉铃虫反吐物处理均显著增加了被处理叶片花外蜜的分泌量。棉花花外蜜的诱导效应在处理叶片上表现明显,并且在较幼嫩的第3片真叶上也有系统性增长。顺式-茉莉酮和机械伤挥发物处理1 d对棉花较幼嫩的第4、5片真叶花外蜜有诱导效应。棉花叶片花外蜜的诱导主要与植物组织损伤有关;不同口器类型的昆虫对棉花叶片花外蜜的诱导量不同,咀嚼式口器的棉铃虫对棉花花外蜜的诱导强度显著高于刺吸式口器的棉蚜;顺式-茉莉酮和机械伤诱导的挥发物能作为棉花植株间交流的信息物质诱导棉花幼嫩叶片花外蜜的分泌。

The effects of damage and volatiles on extrafloral nectar production in cotton plants

The production of extrafloral nectar is believed to be an indirect plant defense that allows plants to recruit predators and parasitoids. Although damage and herbivory by various leaf-chewing insects induces secretion of plant extrafloral nectar, the relative impact of different damage patterns and herbivory by different feeding guilds is not well understood. In this study, we investigated the differential production of foliar extrafloral nectar in cotton plants (Gossypium hirsutum L.) in response to herbivory by different feeding guilds and by mechanical damage and mechanical damage-induced volatiles. To compare the levels of cotton extrafloral nectar induced by these factors, we subjected cotton plants having three to four true leaves (first to third fully expanded leaves) to herbivory by the chewing herbivore Helicoverpa armigera (Hübner) and the sap-sucking aphid Aphis gossypii Glover, and mechanically damaged the second leaves by using scissors, by punching a needle through the leaves, and by exposure to the regurgitates of H. armigera. We also exposed whole cotton plants having five to six true leaves (first to fifth fully expanded leaves) to (Z)-jasmone and mechanically damage-induced volatiles. Extrafloral nectar levels were assessed every 24 h. Because extrafloral nectar in the single nectary of the leaf mid-vein was viscous and could not be collected by capillaries, extrafloral nectar droplets were absorbed on Whatman filter paper weighed on an electronic balance prior to and after extrafloral nectar collection. Pre- and post-leaf damage over seven consecutive days as well as extrafloral nectar induction was analyzed by repeated measures analysis of variance. The analysis revealed that herbivory by H. armigera, mechanical damage caused by scissors, and mechanical damage with regurgitate of H. armigera significantly increased extrafloral nectar production in comparison to undamaged cotton plants. After 1 d of treatment, damage from A. gossypii and needle-punched leaves showed significantly higher levels of extrafloral nectar production. No difference in extrafloral nectar production was found between cotton plants damaged by A. gossypii and those damaged with a needle. While treated leaves were significantly affected, an additional systemic increase was also observed on young leaves (third leaves). The effect was stronger on treated leaves than on untreated leaves, and no significant changes in extrafloral nectar production occurred on old leaves (first leaves). After 1 d of treatment, (Z)-jasmone and mechanical damage-induced volatiles increased extrafloral nectar production by young leaves (fourth and fifth leaves), whereas no significant changes in extrafloral nectar production were recorded on old leaves (first to third leaves). We conclude that the induction of extrafloral nectar secretion in cotton is primarily a generalized response to tissue damage. Damage from different herbivores with different mouthpart types generated different levels of extrafloral nectar induction. Damage from the leaf-chewing caterpillar H. armigera resulted in stronger induction than that caused by the sap-sucking aphid A. gossypii. Treatment with (Z)-jasmone and mechanical damage-induced volatiles stimulated extrafloral nectar secretion in young leaves; these compounds serve as airborne cues to mediate communication between cotton plants.