Cytopathological And Some Enzyme Activity Changes On Wheat Varietis Infected By Wheat Blue Dwarf Phytoplasma

Wheat Blue Dwarf (WBD) caused by phytoplasma was only reported from China, disseminated by Psammotettix striatus L. WBD is an important disease, which happened on winter wheat in northwestern China and reduced the wheat output seriously.In this research, activities of defendant enzymes peroxidase(POD), polyphemol oxidase(PPO)and phenylalanine ammonia lyase (PAL) in different wheat cultivars infected by wheat blue dwarf Phytoplasma were measures using spectrophotometer, the relation between the changes in activities of the three defendant enzymes and wheat variety resistance was analyzed and discussed.The cell ultrastructure alterations of wheat leaves infected by WBD were examined under transmission electron microscopy. WBD phytoplasmas were detected and identified by the fluorescence microscopic with DAPI and PCR with SecY gene in diseased wheat and viruliferous P.striatus The aim is to discuss and analyze the pathogenicity of wheat blue dwarf phytoplasma and resistant mechanisms of different wheat cultivars. The results are as follows:The results showed that the incubation period differred from cultivars, for resistant cultivar it is 12 days and susceptible ones is 18 days.About 1.3 kb fragment in protein translocation gene, SecY was amplified by PCR from the total DNA of diseased wheat sample with primer pair SecYF/SecYR.Phytoplasmas fluorescences were observed in the sieve tube and parenchyma cells of the infected phloem tissues and n sialoid gland of viruliferous P.striatus. There was no fluorescence in healthy leaf tissues and nonviruliferous P. striatus L., which showed that the stain was a specific and rapid method for phytoplasma.In transmission electron microscopy, a large number of phytoplasmas were observed to be present mainly as spherical,oval,inclusion in the sieve tube and parenchyma cells of the infected phloem tissues , Chloroplast became swell and monstrosity in shape, some chloroplast membranes has broken,depletion of chloroplast stroma, disruption of chloroplast grana, with starch grains and osmiphilis globules on them. Some nuclei of mesophyll cells were found disrupted as their nuclear membrane was broken, followed by loss of karyoplasm and dispersive disappearance of nucleoli. The amount of mitochondria increase, and discomposition of some mitochondria cristae were also observed associated with the pathological changes..The enzyme activities of PPO, POD, PAL in resistant cultivar markedly increased with increase of the time course of infection and the disease expansion, the peak of their activities appeared earlier than that in susceptible one. These results suggested that three enzyme activities might be used to serve as a valuable physiological indices for selecting wheat resistant cultivars to WBD.