Effect Of Exogenous Benzoic Acid On The Growth And Quality Of Andrographis Paniculata(Burm.f.)Nees

In the production of Chinese medicinal materials,continuous cropping obstacle has always been a difficult problem to its output and quality.Andrographis paniculata?burm.f.?nees is one of a medicinal plant of the genus andrographis family,and it is mainly produced in Guangxi and Guangdong.In the cultivation and production of andrographis,there are serious continuous cropping obstacles,which have a serious impact on the output and quality of its medicinal materials.Based on the previous research in the laboratory,this paper have studied the effect of benzoic acid,a high-level allelochemicals in the soil of Andrographis paniculata continuous cropping,effects of benzoic acid on growth and quality of Andrographis paniculata and its mechanismon,so as to provide a basis for revealing the mechanism of obstacles of Andrographis paniculata continuous cropping obstacles.The main results were as follows:1.The effect of exogenous benzoic acid on plant height,leaf area,main root length,total root length,aboveground fresh weight and underground fresh weight of Andrographis paniculata in different growth periods all showed the change of low concentration promotion and high concentration inhibition.When the concentration of benzoic acid was higher than 80?g/mL,the main root length of Andrographis paniculata in seedling period and rapid growth period was significantly inhibited?P<0.05?,when the concentration of benzoic acid was more than120?g/mL,the main root length of Andrographis paniculata at harvest period was significantly inhibited?P<0.05?.When the concentration of benzoic acid was higher than 120?g/mL,the leaf area of seedling stage and rapid growth period were significantly inhibited?P<0.05?.The relative chlorophyll content of Andrographis paniculata at seedling period decreased with the increase of benzoic acid concentration.When the concentration of benzoic acid was more than 80?g/mL,the relative chlorophyll content decreased significantly?P<0.05?,when the concentration of benzoic acid was more than 120?g/mL,the chlorophyll content of Andrographis paniculata decreased significantly?P<0.05?,the relative chlorophyll content of Andrographis paniculata was lower than the control.When the concentration of benzoic acid was higher than40?g/mL,the fresh weight at seedling period showed inhibitory effect?P<0.05?compared with the control.When the concentration of benzoic acid was higher than 120?g/mL,it had a significant inhibitory effect on the fresh weight of the ground in the rapid growth period?P<0.05?.When the concentration of benzoic acid was higher than 80?g/mL,the fresh weight of underground part of Andrographis paniculata in seedling period and rapid growth period was significantly inhibited?P<0.05?.The effect of exogenous benzoic acid on growth index of Andrographis paniculata has concentration effect and growth period effect.2.The effect of benzoic acid on root growth?total surface area,average root diameter,total root volume,root tip number,branch number,cross number?in seedling period and rapid growth period was also shown the effect of low concentration promotion and high concentration inhibition.When the concentration of benzoic acid was higher than80?g/mL,the root growth indexes in seedling stage were significantly inhibited?P<0.05?.When the concentration of benzoic acid was higher than 120?g/mL,the root growth index of rapid growth period was significantly inhibited?P<0.05?.The total surface area of root system in harvest period showed the effection of low concentration promoting and high concentration inhibitory,but the difference was not obvious.The effect of exogenous benzoic acid on root growth index of Andrographis paniculata has concentration effect and growth period effect.3.The total protein contents,CAT enzyme activities and H₂O₂contents in the leaves of Andrographis paniculata increased first and then decreased with the increase of benzoic acid concentration in different growth periods,and there were significant difference when it reached the peak value compared with the control?P<0.05?.With the increase of benzoic acid concentration,PPO activities and root activities of Andrographis paniculata at different growth periods increased first and then decreased.SOD activities of Andrographis paniculata leaves showed first increasing and then decreasing changes with the increase of benzoic acid concentration,and when they reached the peak value were significantly different from those of the control?P<0.05?.The activities of SOD in Andrographis paniculata leaves decreased first and then increased with the increase of benzoic acid concentration.The activities of SOD reached the lowest value when treated with 80?g/mL benzoic acid?P<0.05?.The contents of MDA decreased first and then increased with the increase of benzoic acid concentration in seedling period,and reached the peak value in 160?g/mL benzoic acid treatment,which was significantly higher than the control?P<0.05?,the content of MDA increased with the increase of benzoic acid concentration in rapid growth period,the content of MDA decreased first and then increased with the increase of benzoic acid concentration within a certain concentration range in harvest period.The effect of exogenous benzoic acid on the activity of antioxidant enzymes in Andrographis paniculata has concentration effect and growth period effect.4.The effect of benzoic acid on the content of andrographolide and dehydroandrographolide in different growth stages of Andrographis paniculata has concentration effect and growth stage effect.At seedling period,the content of andrographolide increased with the increase of benzoic acid?P<0.05?,while the content of dehydroandrographolide decreased first and then increased with the increase of benzoic acid?P<0.05?.At rapid growth period,the content of andrographolide increased first and then decreased with the increase of benzoic acid concentration.When the concentration of benzoic acid was 40?g/mL,the content of andrographolide reached the peak value?P<0.05?,while the content of dehydrated andrographolide was lower than that of the control group.At harvest period,benzoic acid had no significant effect on the content of andrographolide and dehydroandrographolide in andrographolide plants.At seedling stage,the content of total lactone increased with the increase of benzoic acid concentration?P<0.05?,the content of total lactone increased first and then decreased in rapid growth period,and the change of total lactone content in harvest period was not obvious.5.The results showed that the activities of SOD,CAT,POD,MDA and H₂O₂ contents in the leaves of Andrographis paniculata treated with120?g/mL benzoic acid+1mmol/L DMTU and 120?g/mL benzoic acid+1?mol/LDPI were significantly lower than those in the leaves treated with 120?g/mL benzoic acid.The content of andrographolide in 120?g/mL benzoic acid+1mmol/L DMTU and 120?g/mL benzoic acid+1?mol/LDPI treatment was higher than that in 120?g/mL benzoic acid treatment treatment,but the effect on the content of dehydrated andrographolide was significantly lower than that in 120?g/mL benzoic acid treatment treatment.H₂O₂,as a signal molecule,may be involved in the regulation of benzoic acid metabolism of antioxidant enzymes and the biosynthesis of andrographolide and dehydroandrographolide.6.The exogenous benzoic acid could up-regulate the expression of GGPS and CAT genes in Andrographis paniculata,down-regulate the expression of ApCPS gene,and have a concentration effect on these genes.Under the treatment of 1mmol/LDMTU+120?g/mLbenzoic acid,the expression of GGPS gene was up regulated by 53.92%,and CAT gene was up regulated by 28.88%,however,there was no significant effect on the expression of ApCPS gene.H₂O₂,as a signal molecule,may be involved in the mechanism of benzoic acid on the expression of CAT and GGPS genes of Andrographis paniculata.