| (1) Tobacco is a poor host plant for both the invasive B biotype and indigenous ZHJ1 of Bemisia tabaci. However, the B biotype has been shown to increase its fecundity and longevity significantly when feeding on tobacco plants infected with Tomato yellow leaf curl China virus (TYLCCNV) or Tobacco curly shoot virus (TbCSV) compared to its performance on healthy plants. In contrast, ZHJ1 has been shown to perform similarly on healthy or virus-infected plants. To investigate the physiological mechanisms behind the differences between the B and ZHJ1 of B. tabaci with regard to their interactions with the viruses and host plants, we measured the activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in the B and ZHJ1 feeding on healthy, TYLCCNV-infected or TbCSV-infected tobacco plants. We also measured the quantity and composition of free amino acids in phloem sap in healthy and virus-infected plants as well as the profiles of free amino acids in the honeydew excreted by B and ZHJ1 feeding on healthy or virus-infected plants.(2) When adults of the B biotype fed on healthy or virus-infected tobacco after transfer from cotton, their SOD activity was increased. And after one day of feeding, the SOD activity in the whiteflies feeding on the virus-infected plants was significantly higher than that of the whiteflies on the healthy plants. In contrast, the SOD activity in ZHJ1 whiteflies feeding on healthy or virus-infected plants was decreased after transfer from cotton. Although the SOD activity of ZHJ1 whiteflies feeding on virus-infected plants was higher than that feeding on healthy plants, it was still lower than the activity feeding on cotton. The activity of both CAT and POD in the B biotype whiteflies was activated after transfer from cotton to healthy or virus-infected tobacco, and this effect was more significant in the whiteflies feeding on the virus-infected plants. The changes of CAT and POD activity in ZHJ1 whiteflies was similar to those in the B biotype whiteflies, and feeding on virus-infected plants was shown to activate the enzyme activity; but the higher CAT and POD activity did not increase the insects' survival and longevity, probably due to the simultaneous low activity of SOD. The differences in activity of SOD, CAT and POD between the B and ZHJ1 whiteflies was speculated as a mechanism for the different performance of the two biotypes feeding on healthy and virus-infected tobacco plants.(3) The nitrogen concentration in the phloem sap of TYLCCNV-infected tobacco was higher than that in healthy tobacco. In contrast, the nitrogen concentration of TbCSV-infected tobacco was lower than that in healthy tobacco. However, compared to the profiles of the free amino acids in healthy tobacco, the changes in the proportions of free amino acids in the phloem sap were similar in TYLCCNV-infected and TbCSV-infected plants. It is suggested that, the performance of the whiteflies was more related to the proportion of various free amino acids than to the N concentration. Concentrations of valine, methionine, and lysine increased in both TYLCCNV-infected and TbCSV-infected tobacco compared to those in healthy plants, indicating that these essential amino acids might be important to the performance of the whiteflies.(4) The total quantity of free amino acids in TYLCCNV-infected tobacco was higher than that in healthy plants, but the total quantity of free amino acids in the honeydew secreted by the B biotype feeding on TYLCCNV-infected tobacco was lower than that feeding healthy plants, and in contrast, the total quantity of free amino acids in the honeydew secreted by the ZHJ1 biotype feeding on TYLCCNV-infected tobacco was similar to that feeding on healthy plants. The total quantity of free amino acids in TbCSV-infected tobacco was lower than that in healthy plants; the total quantity of free amino acids in the honeydew secreted by both the B biotype and ZHJ1 biotype feeding on TbCSV-infected tobacco was lower than that feeding healthy plants, and the reduction was more substantial in the B biotype than in the ZHJ1 biotype. These results suggest that infections of the plants with viruses enable the B biotype to more effectively utilize the free amino acids in the hosts, but the infection did not enable ZHJ1 to do so and more nutrients taken by ZHJ1 were not well-utilized but secreted as honeydew.(5) These results may help to elucidate the physiological mechanisms for the indirect mutualism between TYLCCNY, TbCSV and B biotype whitefly as well as the lack of such mutualism between these viruses and the ZHJ1 whitefly.
|
PDF Full Text Request