The Preliminary Study On The Mechanism For Small Brown Planthopper Resistance In Rice Varieties

The small brown planthopper (SBPH), Laodelphax striatellus Fallen (Homoptera:Delphacide), is an economically important pest in rice (Oryza sativa L.) and distributes widely in China. It not only does great harm to rice by transmiting several viral diseases such as rice stripe, virus (RSV) and rice black-streaked dwarf virus (RB SDV), but also causes direct damage by sucking plant sap. For proving up the mechanism of the small brown planthopper attacked to the seedling, results are as follows.1. SBPH-resistant (ASD7) and susceptible (Kittake) rice varieties were subjected to SBPH nymph infestation at densities of 20 nymphs per hill for 3 and 6 days, the changes of physiology and biochemistry in leaves were analyzed.The contents of chlorophyll, soluble sugar and soluble protein in leaves are all decreased significantly in Kittake after the SBPH infestation, and the decline rate of those them was 45.76%,43.25% and 32.48% compared to control respectly, while the content of these substance in ASD7 showed no significant diffrernce compared to control.The contents of free proline and malondialdehyde in leaves are all increased both in SMPH-resistant and susceptible varieties after the SBPH infestation. The content of free proline in ASD7 was increased significantly compared to control, the growth rate of free proline was 15.83% compared to control, on the contrary the content of free proline in Kittake showed no significant change. The content of malondialdehyde in Kittake was increased significantly compared to control, the growth rate of malondialdehyde was 54.88% compared to control, while the content of malondialdehyde in ASD7 showed no significant difference compared to control.Changes of the activity of defense enzyme POD and CAT both in resistance and susceptible rice varieties showed significant difference compared to control, but the SBPH infestation caused a more drastic changes for ASD7.We also detected the concentration of H2O2 both in resistance and susceptible rice varieties after the SBPH infestation through the detection method DAB staining, the results showed that, H2O2 was detected in ASD7 at 3 days, so it has a earlier response to the stress than Kittake. The concentration of H2O2 in ASD7 decreased as time goes on, till there is no evidence of H2O2 can be detected, on the contrary in Kittake was just the opposite. 2. Results of transmission electron microscopic (TEM) indicate that chloroplast in both SBPH-resistant and susceptible rice varieties are all rising a expansion after the SBPH infestation for 3 days, the linage direction of internal layers has changed in Kittake. After the SBPH infestation for 6 days, the membrane of chloroplast in both rice varieties are disintegrated, but the internal layers of ASD7 were still existed and well sorted.3. Upon SBPH treatments, we measured expression changes of 8 relevant genes of metabolic system in leaves of both SBPH-resistant and susceptible rice varieties by real-time PCR. We measured the expression levels of gene encoding glutamate decarboxylase (GAD5) and 4-aminobutyrate aminotransferase (GABA-T) acting as the key enzymes of theγ-aminobutyric acid shunt (GABA shunt). The results indicated that SBPH infestation induced up-regulation of about 10-fold in GAD5 expression level for ASD7, whereas such up regulation was about 3-fold for Kittake. GABA-T expression for ASD7 showed significant up-regulation after SBPH treatment for 3 days, whereas its expression level in Kittake did not change significantly during the whole treatment period. SBPH infestation caused more marked up-regulation for key genes regulating GABA shunt, such observation indicated that activation of GABA shunt was vital for rice plants to resist SBPH infestation.