Observation Of The Ultrastructure Of The Digestive Tract Of Chinese Honeybee And The Expression Of Aquaporin Gene

As a social insect,the honeybee's behaviors of foraging nectar,making honey,storing nectar and pollen play important roles in maintaining its social structure.In order to adapt to the changes in its behaviors,the structure and function of alimentary canal of honeybee have also undergone corresponding changes in the long-term evolution process.At the same time,the feeding habits of insects are closely related to the structural features of the alimentary canal.Therefore,It is shown that developing the research of honeybee alimentary canal structure provides a comprehensive understanding on the inherent mechanism of the adaptation between honeybee alimentary canal structure and its unique behavior,this research will also contribute to guide the development of modern apiculture.In our study,the morphology and ultrastructure of alimentary canal in Apis cerana cerana were observed using scanning electron microscope(SEM)and transmission electron microscope(TEM).We analysed the adaptation in the structure of alimentary canal and its function.At the same time,we studied the expression of aquaporin in different parts of the alimentary canal,head,and malpighian tubule of workers and drones based on the Real-time PCR,and illustrated the molecular mechanisms of their functional adaptation.The main results of our study were as following:1.The alimentary canal of Chinese bee can be divided into 3 parts:foregut(formed mainly by oesophagus,crop and proventriculus),midgut,hindgut(formed by ileum and rectum).There were two oesophageal nerves on the oesophagus.At the junction between the oesophagus and crop,each oesophageal nerve branched 2 or 3 times and innervated the crop.The crop comprised of circular muscle,longitudinal muscle and extremely folding epithelial layer.Proventriculus included a proventricular fold and stomach valve.Proventricular fold was formed by four thick lips of the proventricular wall with the cuticle coating external to the apex,presenting 8 types of hair,which functioned as feeling,capturing,separating and filtering the pollen and other particles from nectar.The midgut was relatively stubby,and the muscles of midgut were thinner than in foregut and hindgut.Ileum was curved and slender,and circular muscle was well-development.The epithelial layer of rectum specialized into 6 rectal pads.There were near hundred malpighian tubules located on the joint between the midgut and ileum.2.The results of the proventriculus comparison in worker and drone Apis cerana cerana showed that significant differences were found on the four lips of the proventriculus in worker and drone.(1)The length and width of the proventriculus lips in worker was larger than in drone;(2)The numbers and branches of structure trichodeum 1 in worker were more than in drone;(3)The strumae on the apex of lips was only found in worker Apis cerana cerana.It probably was related to that proventriculus lips separated and filtered pollen and particles from nectar in worker.3.The muscle and cuticle in foregut were thick,procuticle in crop were different from other parts of alimentary canal,and it consisted of four continuous cuticles,which was convenient to fold or stretch.Midgut lacked of cuticle.There were long microvilli,golgi,smooth endoplasmic reticulum(SER),abundant rough endoplasmic reticulum(RER),mitochondria,spherocrystals,infolding basal membrane in the epithelium of the midgut.All of these showed that digestion and absorption completed in midgut.The cuticle in hingut were also thick.Long infolding basal membrane and a few organelles were observed on the epithelium of hindgut.4.The results of Real-time PCR showed that AQPAe.a-like,AQPAn.G-like,AQPAn.G-like transcript variant X1 had expression in different tissues of worker and drone Apis cerana cerana.AQPAe.a-like gene was expressed highest on midgut in worker and on malpighian tubule in drone.It suggested that AQPAe.a-like was not only involved in the absorption of water in food by midgut,but also participated in the water reabsorption of malpighian tubule.The expression of AQPAn.G-like gene in the foregut and hindgut of worker and drone were higher than that of other tissues,and the expression levels of AQPAn.G-like gene in the hindgut and malpighian tubule of worker were significantly higher than those of drone.The AQPAn.G-like transcript variant X1 was expressed higher in malpighian tubule than other tissues both in worker and drone,and the expression levels of AQPAn.G-like transcript variant X1 gene in the midgut,hindgut and malpighian tubule of worker were significantly higher than those of drone.This difference may be related to the different feeding habits and metabolic capacities of worker and drone.