Nitrogen Metabolism And Inset-Pest Resistance Of Transgenic Bt Rice Under Elevated CO₂

Transgenic Bt rice can alleviate the damage caused by target Lepidoptera pests. It can also influence the harm of non-target insects (e.g., brown planthoppers). Many documents have indicated that the introduction of alien Bt genes into rice can change plant nitrogen metabolism. Nitrogen is the essential ingredient of nucleic acids, proteins and alkaloids, and even Bt toxins for transgenic Bt rice. And the growth and population occurrence of Chilo suppreddalis and brown planthoppers are closely related with the nitrogen nutrition of host plants. The amino acid synthesis, gs (GS) and other key enzyme activity during the nitrogen metabolism can be improved by the optimized fertilizer N management, thereby promoting protein's synthesis and Bt toxins expressing. However, to date, there are few studies on this topic.In recent years, global environmental change, especially the rise in atmospheric CO2 concentration, has been an item of great concern for the scientific community. Elevated atmospheric CO2 concentrations benefit to improve crop photosynthesis and prolificacy, and then to change plant allocation of the photosynthates. It has proved that the Bt toxin of transgenic Bt rice grown in elevated CO2 will be reduced. It is obvious that the nitrogen nutrition and insect resistance will be affected by elevated CO2. So clarifying the mechanism of these changes will contribute to give full play on the ecological and sustainable usage of transgenic Bt rice in the future.In this paper, transgenic Bt rice (KMD) and non-transgenic rice (XSD), C. suppreddalis and brown planthoppers were studied in closed-dynamics CO2 chamber (CDCC) and in open-top chamber (OTC), by controlling CO2 levels experiments. The effects of elevated CO2 and nitrogen fertilizer on the plant physiological indexes (including plant growth and nitrogen metabolism) and change of enzyme activity in target insects and non-target insects, in order to ascertain the arget-resistance and non-target-resistance mechanism of transgenic Bt rice. The main results were as follows:1. Effects of double-atmospheric CO2 (750 vs.375μl/L) on the metabolism enzyme of acetylcholinesterase (AChE) and three protective enzymes of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the larvae of stem borer,Chilo suppreddalis were studied as they fed on transgenic Bt rice (cv. KMD expressing pure CrylAb) and nontransgenic rice (cv. XSD; i.e., the parental line) in open-top chambers. The results indicated that:(1) CO2 level significantly affected the AChE activity, and significant decreases were found as C. suppreddalis fed on transgenic Bt rice or nontransgenic rice in elevated CO2 relative to ambient CO2. (2) Elevated CO2 and Bt rice both markedly enhanced the activities of POD and SOD. POD activity decreased sharply while SOD activity increased only at the beginning, and obvious increase in CAT activity was observed at the beginning while declined after a period. (3) There were significant interactions on the activity of metabolism and protective enzymes among CO2 level, rice variety and sampling time. It is presumed that some short-term adverse effects from elevated CO2 and transgenic Bt rice can be alleviated through the physiological regulation of stem borer C. suppreddalis based on the metabolism and protective enzymes, while the regulation mechanism in physiology and metabolism of C. suppreddalis maybe loses the efficiency in response to the environmental suppression, which is, in turn, to reduce the population performance of stem borers.2. The effects of elevated CO2 (750 vs.375μl/L) on population abundances and metabolism enzyme of AChE and protective enzymes of SOD, POD and CAT in brown planthoppers (BPH) Nilaparvata lugens, and on size and abundances of yeast-like endosymbiotes (YLES) were studied as BPH fed Bt rice expressing pure Cry1Ab after successively two generations in open-top chambers. The results indicated that:(1) Elevated CO2 only significantly inhibited AChE activity as brachypterous-BPH fed nontransgenic rice. Significant increases in POD and SOD, and significant decrease in CAT were found as brachypterous-BPH fed Bt rice, while significant increases in CAT and significant decrease in POD were also observed as fed nontransgenic rice in elevated CO2 relative to ambient CO2. (2) Bt rice significantly inhibited POD and SOD activity at ambient CO2, while only significantly enhanced SOD activity at elevated CO2. (3) Elevated CO2 significantly decreased YLES per mg/head of brachypterous-BPH females while only significantly decreased YLES per mg/head as brachypterous-BPH males fed Bt rice. And there were significant differences in YLES width or length between females and males. Elevated CO2 can markedly affect the symbiosis relationship between YLES and BPH through the bottom-up forcing on BPH physiological metabolism.3. The physiological and ecological responses in plant growth and nitrogen metabolism for transgenic Bt rice (KMD) and nontransgenic cotton (XSD) to elevated CO2 (750μl/L vs 375μl/L) and nitrogen fertilization levels (5,20,40 mg N/L) were studied during the squaring peek in the closed-dynamic CO2 chambers. The results indicated that:(1) With the increase of CO2 increased,a significant increase in content of the free-amino-acids,and reduce of N, a significant reduction in Soluble -protein (2) By the seedling stage,the protein, nitrate content and glutamine synthetase activity are Significantly effceeted by CO2. (3) Under MN-level, free-amino-acids has the lowest content, but glutamine synthetase has the highest activity, sensitive to the change of CO2. GS is only significantly effected by CO2 undeer MN-level, and activity increased under the high high CO2. (4) Under MN-level, SOD has the highest activity, GS has the highest activity,free-amino-acids has the lowest content, activity of POD and SOD have no increase under the stress of CO2. 4. The physiological and ecological responses in plant growth and nitrogen metabolism for transgenic Bt rice (cv. KMD) and non-transgenic rice (cv. XSD) to elevated CO2 (750μl/L vs.375μl/L) were studied during the 60 days and 120 days of rice plants in open-top chambers. The results indicated that, (1) elevated CO2 will cause a series of responses, water content,soluble protein,chlorophyll a and c content would be reduced. chlorophyll b would be increased at the beginning and then decreased. The change of glutamine synthetase activity in the early was not significant, in the latter part there would be a significant reduction. (2) Different rice varieties would markedly affect the soluble protein content and glutamine synthetase activity while only little effect on chlorophyll and free amino acid content. (3) With the growth time of rice, the content of chlorophyll a, chlorophyll b, chlorophyll a+b, soluble protein content, glutamine synthetase activity would increased, on the other hand, free amino acid content would reduce with time, the value of chlorophyll a/b descreased in ambient CO2 and increased in elevated CO2.