Effects Of Fluridone And Tungstate On Some Physiological Indexes In Camptotheca Accuminata Seedlings Under Osmotic Stress

To identify the role of abscisic acid (ABA) in biosynthesis of camptothecin and its effects on osmotic materials' accumulation and antioxidant enzymes in Camptotheca accuminata seedlings under osmotic stress, a low water potential environment for the seedlings was created using 15% polyethylene glycol 6000(PEG6000) in 1/2 Hoagland nutrient solution. Prior to refurbishing the seedlings using exogenous ABA, the biosynthesis of ABA was inhibited by 24-hour pretreatment of the seedlings by ABA inhibitors Tungstate and Fluridone. ABA treatment on the seedlings was as well carried out to investigate the changes of osmotic materials content, antioxidant enzymes activity and camptothecin content.The results indicated, under osmotic stress, that in Camptotheca accuminata seedlings, the soluble sugar content, proline content, MDA content and POD activity increased by 112.0%, 32.80%,34.19% and 61.08%, and the soluble protein content, SOD activity and CAT activity decreased by 36.48%,52.01% and 38.41%, respectively. The ABA content was raised 2.67 times and camptothecin content was 6.61% higher.Under osmotic stress, as result of using exogenous ABA, in Camptotheca accuminata seedlings, the soluble sugar content, proline content, POD activity increased by 72.0%, 22.74% and 77.53%, and the soluble protein content, SOD activity and CAT activity decreased by 28.63%, 42.90% and 31.46%, respectively. The ABA content was raised 3.42 times.Under osmotic stress, as result of pretreatment using Tungstate, in Camptotheca accuminata seedlings, the soluble sugar content, proline content, POD activity increased by 43.4%, 14.64% and 35.43%, and the soluble protein content, SOD activity and CAT activity decreased by 14.03%, 23.77% and 14.64%, respectively. The ABA content was raised 1.68 times.Under osmotic stress, as result of pretreatment using Fluridone, in Camptotheca accuminata seedlings, the soluble sugar content, proline content, POD activity increased by 63.7%, 13.68% and 37.48%, and the soluble protein content, SOD activity and CAT activity decreased by 17.96%, 45.66% and 17.74%, respectively. The ABA content was raised 1.60 times.Under osmotic stress, as result of Tungstate pretreatment combined with refurnishing by exogenous ABA , in Camptotheca accuminata seedlings, the soluble sugar content, proline content, POD activity increased by 119.3%, 20.39% and 55.27%, and the soluble protein content, SOD activity and CAT activity decreased by 23.20%, 41.12% and 24.85%, respectively. The ABA content was raised 2.25 times and camptothecin content was 10.85% higher.Under osmotic stress, as result of Fluridone pretreatment combined with refurnishing by exogenous ABA , in Camptotheca accuminata seedlings, the soluble sugar content, proline content, MDA content and POD activity increased by 90.9%, 22.64%, 23.25% and 59.84%, and the soluble protein content, SOD activity and CAT activity decreased by22.51%, 39.81% and 25.93%, respectively. The ABA content was raised 2.79 times and camptothecin content was 8.55% higher.Moreover, under Tungstate and Fluridone pretreatment, camptothecin content in the seedlings was slightly lower than the check, whereas the content was higher than check under exogenous ABA treatment. However, variance of both the aforementioned treatments didn't reach significant level. No available rules can explain changes of 10-OH camptothecin content under all treatments.Consequently, osmotic stress functions to cause osmotic materials accumulation (with the exception of soluble protein), reduce antioxidant enzymes activity (with the exception of POD), tremendously increase ABA content and camptothecin in the seedlings. Exogenous ABA proved to pose negative effects on osmotic materials accumulation and antioxidant enzymes'activity, however, with no marked effects on camptothecin content. ABA inhibitors in nutrient solution can reduce the content of ABA under osmotic stress, whereas failed to inhibit the biosynthesis of ABA completely. In addition, ABA inhibitors can alleviate the damage caused by osmotic stress, decrease ABA content and meanwhile weaken the variety of antioxidant enzymes and decrease the alkaloids biosynthesis under osmotic stress. Refurbishing the inhibited seedlings by exogenous ABA, can lead to significant incrase of camptothecin content, suggesting that ABA can induce the biosynthesis of camptothecin. Exogenous ABA was able to cause a rapid increase of ABA content in camptotheca accuminata seedlings and to decrease osmotic materials'accumulation, antioxidant enzymes activity and reduce the effects of osmotic stress. But exogenous ABA was ineffective to increase camptothecin content.In conclusion,ABA can regulate osmotic materials accumulation and antioxidant enzymes activity in Camptotheca accuminata seedlings, induce biosynthesis of camptothecin. Nevertheless, the specific threshold range of ABA content that can enhance the biosynthesis of camptothecin and the effects of ABA on critical enzymes for biosynthesis of camptothecin remain a problem.