Arsenic Toxicity To Metabolism Of Carbon And Nitrogen In Flue-Cured Tobacco And Toxicity-Alleviating Effects Of Iron And Fulvic Acid

Abstract:Arsenic,a high toxic heavy metal,was one of the most serious contaminants in soil and a potential threat to crops growth and human health.Therefore,it was very important to study effects of arsenic toxicity and on metabolism of carbon and nitrogen in flue-cured tobacco and on its yield and quality,and to study toxicity-alleviating effects of iron and folvic acid.In order to prevent or decrease losses of tobacco yield incurring economic losses,and to increase benefits of growers and health of smokers as much as possible,3 experiments were conducted on the farm of Henan Agricultural University,Zhengzhou,China.With Yunyan 85 planted in plastic pots(400 mm in diameter and 340 mm in height)in 2004 and 2005.The first experiment was carried out at eight levels arsenic toxicity:0(CK),5,20,40,60,100,200 and 400 mg·kg^-1[added to sodium arsenate(Na₃AsO₄·12H₂O)]in 2004 and at five levels of 0(CK),5,20,40,and 60 mg·kg^-1in 2005 to determine effects of arsenic toxicity on growth,development,yield,and quality of flue-cured tobacco,and to determine the critical content of arsenic in soil.The second experiment carded out with 50 mg·kg^-1of arsenic toxicity(added to sodium arsenic):with ferrous sulphate of 0, 200,400,600,800 mg·kg^-1in 2005 to study the effects of iron on alleviation of arsenic toxicity. The third experiment was carried out with 50 mg·kg^-1of arsenic toxicity with 0,200,400,600, 800 mg·kg^-1(added to 95%fulvic acid)in 2005,to study the effects of fulvic acid on alleviation of arsenic toxicity in flue-cured tobacco.Effects of arsenic toxicity on metabolism of carbon and nitrogen in flue-cured tobacco and on yield and qualityArsenic toxicity significantly affected on carbon metabolism during the whole growing period.Chlorophyll content,photosynthetic rate and sucrose synthetase(SS,synthetic direction) activity during the growing period as well as activity of sucrose phosphate synthetase(SPS)after budding stage all decreased.But activity of sucrose synthetase(decomposition direction)and content of soluble sugar during the growing period increased.This suggested that assimilation of carbon and synthesis of sucrose in flue-cured tobacco be inhibited,and decomposition of sucrose be accelerated as a result of arsenic toxicity,which was not favorable for carbon transformation. The results also indicated that activity of soluble starch synthetase(SSS)at rosette stage and harvest stage,and accumulation of starch at harvest stage were inhibited,SSS activity at budding stage,activity of adenosine diphosphoglucose pyrophosphorylase(ADPG-PPase)during the growing period,and starch content at rosette stage and budding stage all increased by arsenic toxicity.Therefore,arsenic toxicity caused the disarray of metabolism of accumulated carbon and the decrease of starch content during the last part of the whole growing period.Arsenic toxicity also significantly affected on nitrogen metabolism in flue-cured tobacco.On one hand,activity of nitrate-reductase(NR)during the growing period was reduced:And on the other activity of glutamine synthetase(GS)during the growing period was increased.These indicated that assimilation of NO₃^--N was inhibited but that of NH₄⁺-h+-N was enhanced by arsenic toxicity.The results also showed that activity both of glutamate-pyruvate transaminase(GPT)and asparaginase(ASG)during the growing period,and content of free amino acids after the budding stage were increased,indicating that arsenic toxicity led to exuberance of transformation metabolism in flue-cured tobacco.In the meantime,compared with those in CK,protein content during the early growing stage and nicotine during the growing period decreased,however protein content increased during the middle and last growing stages.Arsenic toxicity inhibited growth and development of flue-cured tobacco.It delayed the growing process,and decreased leaves,leaf area,plant height,and yield.Besides,it decreased economic properties such as output value per plant,average price,and ratio of high level,and chemical quality properties such as increase in total sugar,reduced sugar,total nitrogen,and nicotine.It also decreased content of potassium,calcium,magnesium,and chlorine.Therefore,it resulted in disproportion of sugar-nitrogen,nitrogen-nicotine,sugar-nicotine,and potassiumchlorine. And hence,arsenic induced decrease both in economic and in chemical value.The results also showed that when flue-cured tobacco was planted in soil added to 100 mg·kg^-1of arsenic, flue-cured tobacco was so affected that there was no production value.When soil was added to more than 200 mg·kg^-1of arsenic,flue-cured tobacco could not grow.When soil was added to 16.89 mg·kg^-1of arsenic,yield was decreased by 10%.Arsenic content in leaves increased with arsenic addition in soil.After cutters were burned at 300 temperatures,only 39.58%of accumulated arsenic remained in ash,and the remaining was away with smoke.The arsenic residues in lower leaves,cutters,upper leaves and smoke of cutters was less than those specified in food hygienic standard when the critical content of arsenic in soil was 2.63,6.56,13.91,and 12.90 mg·kg^-1,respectively.The arsenic in soil increased content of arsenic in flue-cured tobacco.And the higher content of arsenic in soil,the higher content of arsenic in the plant.On the contrary,the arsenic in soil decreased the plant's ability to transfer arsenic from root to shoots.The higher there was content of arsenic in soil,the lower there was ability to transfer arsenic of the plant.Arsenic could be distributed in every organs of the plant.Accumulation of arsenic in flue-cured tobacco was frist from roots,to lower leaves,to stalks,to cutters,and then to upper leaves.Residues of arsenic in ash were 39.58%,the remaining(60.42%)were inbreathed by smokers or entered into the air.Effects of iron on metabolism of carbon and nitrogen,yield,and quality of arsenic-toxicated flue-cured tobaccoArsenic toxicity to carbon metabolism in flue-cured tobacco was alleviated by application of ferrous sulphate in soil.The increase both in chlorophyll content and in photosynthetic rate indicated that iron improved assimilation of carbon in arsenic-toxicated flue-cured tobacco during the whole growing period.Iron also increased activity of sucrose synthetase(SS,synthetic direction)and sucrose phosphate synthetase(SPS),and decreased activity of sucrose synthetase (decomposition direction)and soluble sugar content,which not only helped to synthesization of sucrose and transformation to carbon accumulation,but also inhibited exuberance of transformed-carbon metabolism caused by arsenic toxicity.Although soluble starch synthetase (SSS)activity at rosette stage,adenosine diphosphoglucose pyrophosphorylase(ADPG-PPase) activity at budding stage,and accumulation of starch both at rosette and at budding stage were inhibited,which decreased accumulation of carbon,accumulation of carbon was increased in late growing.The increase in nitrate-reductase(NR)activity and the decrease in glutamine synthetase activity(GS)during the whole growing period indicated that iron improved assimilation of NO₃^--N and inhibited assimilation of NH₄⁺-N in flue-cured tobacco toxicated by arsenic.In the meantime,decrease in free amino acids content,glutamate-pyruvate transaminase(GPT)activity after budding stage,and in asparaginase(ASG)activity during the whole growing period showed that iron inhibited exuberance of transformed-nitrogen metabolism as a result of arsenic toxicity. The result also indicated that iron increased nicotine content during the growing period,but protein content only increased by iron during the middle and late stages.Iron increased leaves,leaf area,and plant height in arsenic-toxicated flue-cured tobacco during the growing period,and hence it improved plant growth and development and remarkably increased yield.Iron decreased content of total sugar,reduced sugar,ratios of sugar-nitrogen, sugar-nicotine and nitrogen-nicotine,and thus it resulted in decrease in acidity in smoke and possibility of tar damage to smoker.When iron content was 600 mg·kg^-1or higher in soil,nicotine content was increased in arsenic-toxicated flue-cured tobacco.However,increase both in total nitrogen content and in protein content strengthened stimulation of cigarettes.When iron content was 400 mg·kg^-1or lower in soil,decrease both in total nitrogen content and in protein content improved stimulation and fragrance of cigarette,while nicotine content was decreased.Increase in potassium content was helpful to burning ability of cigarettes,but not to chlorine content. However,iron could either improve or worsen chemical quality of arsenic-toxicated flue-cured tobaccot.Residues of arsenic in soil were increased by iron.Absorption of arsenic by flue-cured tobacco and arsenic contents in plant and in leaves in different plant positions were decreased,and bioaccumulation factor(BCF)and arsenic content both in ash and smoke were also decreased,but translocation factor(TF)in plant and arsenic content in shoots were increased.There was difference of arsenic content in the five organs of the plant.Arsenic accumulation order in flue-cured tobacco leaves was roots＞stems＞lower leaves＞cutters＞upper leaves.In the meantime, because of iron application,absorption of iron by arsenic-toxicatecd flue-cured tobaccowas decreased,but iron content in shoots and translocation factor(TF)were increased.Accumulation order of iron in flue-cured tobacco leaves was roots＞lower leaves＞cutters＞upper leaves＞stems.Effects of fulvic acid on metabolism of carbon and nitrogen,yield and quality in arsenic-toxicated flue-cured tobaccoReasonable content of fulvic acid improved assimilation of carbon in arsenic-toxicated flue-cured tobacco.Although unreasonable content of fulvic acid in soil enhanced arsenic toxicity in carbon transform metabolism,and caused disarray of carbon metabolism during the early growing period,reasonable content of fulvic acid could finally improve transformation and accumulation of carbon during plant growth and development.Different contents of fulvic acid had different effects on nitrogen metabolism in arsenic-toxicated flue-cured tobacco,reasonable content of fulvic acid enhanced arsenic toxicity during the early growing period,but finally improved NO₃^--N assimilation and inhibited NH₄⁺-N assimilation and transformation of nitrogen during the process of growing and development. Fulvic acid increased protein content after budding stage and nicotine content during the whole period,but decreased protein content at rosette stage.Reasonable content of fulvic acid improved the growth and development of arsenic-toxicated flue-cured tobacco,affecting leaves,leaf area,and plant height.Therefore,the yield was significantly improved.There was not an interrelationship between fulvic acid application in soil and chemical compositions and their coordination arsenic-toxicated flue-cured tobacco,but application rate of fulvic acid of 600 mg·kg^-1in soil decreased content of total sugar,reduced sugar, total nitrogen,protein,and ratios of sugar to nitrogen,nitrogen to nicotine,sugar to nicotine,and increased content of nicotine and potassium.Therefore chemical quality of arsenic-toxicated flue-cured tobacco was improved by fulvic acid application at a rate of 600 mg·kg^-1.Resedues of arsenic in soil were increased by reasonable application of fulvic acid,but the absorption of arsenic by flue-cured tobacco and arsenic content in the plant were decreased. Bioaccumulation factor(BCF)and arsenic content in ashes and smoke were also decreased,but translocation factor(TF)of the plant and arsenic content in shoots were increased.There was difference in arsenic contents in the five parts of plant.The accumulation order of arsenic in flue-cured tobacco plant was roots＞lower leaves＞stems＞cutters＞upper leaves.The best treatment of fulvic acid in the experiment was 600 mg·kg^-1.