Cotton Induced Aphid Resistance And Related Defense Gene Expression

Studies on the Induced Resistance to Aphids and the Expression of Defence-related Gene in Cotton Plants Abstract Base on the interaction between aphids (Aphis gossypii Glover) and cotton (Gossypium hirsutum) plants, and our previous study on induced resistance against aphids including primary and secondary metabolisms, the experiments were carried out to study the induced defence mechanism of cotton seedlings L expression by analysis of defence-related gene against cotton aphids.The results were as follows: Under the continuous suppression of aphid feeding, the expression of induced resistance of 4-leaf stage seedlings was a rapid, discontinuous and repeatly self-regulated process. The activities of four isozymes following aphid feeding showed periodic changes as increase?decrease-+increase more, etc. The change patterns of periodicity were different for different cotton varieties. 2 days after a single leaf (3 rd leaf) of a 4-leaf stage cotton seedling was subjected to aphid feeding suppression, the induced resistance was produced throughout the whole-plant system, which persisite at least 15 days. However, enzyme activity assays associated with defense genes revealed that in different leaves (e.g. different position relative to 3 rd leaf), there were different putative defenses and their changed patterns, which had different effects on the biology of subsequent aphids such as fecundity, survival and winged-aphid rates.This temporal and spatial heterogeneity of induced phytochernicals might be served as an important component of plant induced resistance to herbivory. Mechanical wounding on one leaf of 4-leaf cotton plants and spraying leaves with salicylic acid (SA) solution also caused the plants to induce resistance. These two methods can be further utilized as technology to activate a series of defence genes expression and enhance cotton plants resistance against aphids. Northerm blot and Dot blot analyses of defence gene in cotton plants indicated that after aphid feeding suppression, the velocity of expression, accumulated volume and temporal changes of CAT, POD and PAL gene were different in different cotton varieties. The strength of gene expression was greater in resistant cotton varieties than in susceptible ones. The expression and accumulation of anionic POD isozymes cDNAs (cotapl niRNA) were regulated at transcriptional level, and possessed induced expression characteristics. After 1.5 days of localized feeding suppression to cotton seedlings by aphids, the induced cotapl was expressed in leaves and stem systemically. And the expression of cotapl mRNA was enhanced during the second suppression. These result shown that the induced expression of cotapl mRNA played an important role in cotton plant defence against aphids. The change patterns of CAT, SOD, PAL and their gene expression characteristics between prior and post-aphid feeding can be used in the idetification and breeding of cotton cultivars resistant to aphids.