Physiological Responses Of Tobacco Caused By Bemisia Tabaci(Gennadius) B-Biotype Infestation

Bemisia tabaci (Gennadius) biotype B is a worldwide invasive pest. It has been a key pest of tobacco, and broke out in parts of tobacco-growing areas when it invades in China. B. tabaci biotype B feeding cause plant systemic or physiological disorders include silverleaf of squash, stem blanching of lettuce, white streaking of Brassica, and chlorosis of new foliage in numerous ornamental plants. Furthermore B. tabaci biotype B feeding caused reduction of net photosynthetic rate. Our previous studies showed that the feeding of B. tabaci biotype B directly inhibited the growth of tobacco and induced obviously white vein of tobacco leaves. It is indicated that the physiological response of tobacco was affected by B. tabaci biotype B. Photosynthesis is the most basic the physiological response of the plant. However, the influence mechanism of B. tabaci biotype B on the net photosynthetic rate (Pn) is also unknown. Meanwhile, the feeding of B. tabaci biotype B caused increase the activity of defense enzymes of tobacco leaves。Furthermore B. tabaci biotype B induces salicylic acid defenses and suppresses effectual jasmonic acid defenses. According to the above study results, we chose the model plant-tobacco as the host plant to investigate the effect and possible mechanism of Bemisia tabaci (Gennadius) B-biotype infestation on photosynthesis of tobacco plants. We also studied the temporal and spatial change of defense enzyme of phloem sap of tobacco plants induced by B. tabaci biotype B. We discussed the role of physiological and biochemical response of plants in the defense responses to other phloem feeder of tobacco plants induced by B. tabaci biotype B. This research had important academic meaning for showing the damage mechanism of B. tabaci biotype B to tobacco plants and scientifically assessing the ecological risk of B. tabaci biotype B. Major results as follows:1. There was temporal and spatial disadvantaged influence on photosynthesis of tobacco plants damaged by B. tabaci biotype B. While net photosynthetic rate (Pn) in infested leaves exhibited a dramatic decrease as time progressed, especially on15d and20d, the decrease was38.22%and54.2%; The Pn in systemic leaves of treatment displayed a decrease first and then an increase, but the level decreased by41.0%and18.5%than the control on15d and20d, respectively. This indicated that the inhibition to the photosynthesis caused by B. tabaci infestation is not only in the infested leaves, but also in the systemic leaves. The photosynthesis of tobacco leaves was affected only10days after B. tabaci infestation. The results show that the adverse effect of photosynthesis caused by B. tabaci infestation with time effect. B. tabaci infestation altered the content of chlorophyll, especially the chlorophyll a.2. B. tabaci infestation damaged the photosystem II (PS II) of tobacco leaves. Photosystem II is an important part of the photosynthese. It is the most sensitive part of photosynthetic apparatus to environmental change. The PS II is associated with the energy of light, absorption, energy conversion, electron transfer. B. tabaci infestation reduced the density of active reaction centers per excited cross-section (RC/CS) both in infested and systemic leaves (P<0.05). B. tabaci infestation caused the closure degree of the PS II reaction centers (1-qP) increase in infested and systemic leaves. B. tabaci infestation severely damaged the oxygenevolving complex (OEC). This indicated the structure of photosystem II was damaged. The reaction centers were damaged which decrease the rate of electron transporting. The inhibited points of the electron transporting included the OEC and the electron transporting from Qa to QB.Energy flux of PS Ⅱ was also affected by the B. tabaci infestation. B. tabaci infestation increased the energy dissipation per active reaction centers (DIo/RC) and decreased the energy utilization efficiency (cppo, Ψo and φpEo). It increased the excess excitation energy and the production of ROS, which could improve the salicylic acid defenses induced by B. tabaci. The effects caused by B. tabaci in tobacco leaves were systematically conductive.3. The proteins of tobacco leaves were assayed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The3rd instars of B. tabaci biotype B feeding induced the expression of nine proteins increase in systemic leaves. Four proteins of these were specific induced; and five of them were just induced. In infested leaves, there were only two proteins were just induced4. We investigated the temporal and spatial change of main defense enzyme activity and nutrition content of phloem sap of tobacco plants infested by B. tabaci. The phloem was the feeding sites for the phloem feeder. There are many proteins and secondary metabolisms that are related to defense response in the phloem sap. There was difference between the changes of the activity of polyphenol oxidase (PPO), β-1-3-glucanase and chitinase of phloem sap in local and systemic leaves. However, the increase rate of their activity of phloem sap in local leaves was lower than that in systemic leaves. The increase rate of their activity of peroxidase (POD) and phenylalanine ammonialyase (PAL) of phloem sap in systemic leaves was lower than that in local leaves. The activity of catalase (CAT) of phloem sap in systemic leaves was induced increase by B. tabaci infestation, however, in local leaves it decreased. The activity of ascorbate peroxidase (APX) and content of total phenol of phloem sap were not significantly changed by B. tabaci infestation in local leaves, which rarely increased in systemic leaves on20d and25d. This indicated that PPO, β-1-3-glucanase, chitinase and CAT of phloem sap are related to the defense response of tobacco plant to aphid.