Effects Of Exogenous Spermidine On Senescence Characteristics And Quality Of Upper Leaves Of Flue-cured Tobacco At Maturity Stage

Tobacco(Nicotiana tabacum L.)is one of the significant economic crops in China agricultural manufacture.The quality of flue-cured tobacco leaves is closely related to the development of the cigarette industry.The upper leaves accounted for 40%of the tobacco plant output.Upper tobacco leaves occupy an important position in tobacco production.In recent years,tobacco leaves in the upper part of Xiangxi tobacco area generally have poor maturity tolerance,leading to premature aging of tobacco leaves and decline in harvest maturity,which seriously restricts the yield and quality of flue-cured tobacco leaves.Exogenous spermidine is a plant growth regulator,which has the functions of regulating growth and development,delaying plant senescence,and improving stress resistance.At present,the research on spermidine in flue-cured tobacco mostly focuses on the effects on the growth and quality of flue-cured tobacco seedlings,and there are few studies on tobacco leaves in the field at maturity.Therefore,this experiment selected the main flue-cured tobacco variety K326 in Xiangxi tobacco area as the material,and sprayed clear water(CK),and four spermidine combinations on the upper tobacco leaves 15 days,30 days,and 45 days after topping as 0.1mmol/L(T1),0.3mmol/L(T2),0.5 mmol/L(T3),1.0 mmol/L(T4).By exploring the effects of different concentrations of spermidine on the senescence characteristics of upper leaves in the mature period and the quality of flue-cured tobacco leaves,the aim is to reveal the regulating effect of spermidine in the senescence process of upper tobacco leaves in the mature period and to screen out the appropriate amount of spermidine application.And methods to provide a theoretical basis for the actual production of flue-cured tobacco in local and similar tobacco areas.The main research conclusions are as follows:(1)Spraying spermidine can increase the leaf area,specific leaf weight and pigment content of the upper tobacco leaves at the maturity stage,and reduce the expression of the key carotenoid lyase gene(CCD1).Spraying different concentrations of spermidine all improved the opening and stretching ability and identity thickness of tobacco leaves.The leaf area and specific leaf weight of the leaves treated with each concentration increased at 30 days after topping.The upper leaf area and specific leaf weight of the T3 treatment increased the most.Significantly,they increased by 25.30%and 18.48%respectively compared with CK.In addition,spraying different concentrations of spermidine can effectively improve the photosynthesis of tobacco leaves during the senescence process of upper tobacco leaves in the mature period.After topping 15,30,and 45 days after topping,T3 treatment had the best effect of increasing the content of chlorophyll(Chl)and carotenoid(Car)of tobacco leaves.Chl and Car increased by 42.71%and 24.38%respectively compared with CK;CCD1 after topping at 30 and 45 days,the relative expression level was significantly lower than that of CK.The expression level of CCD1 decreased most significantly at 30 and 45 days after T3 treatment,which was 16.39%and 7.61%lower than that of CK.(2)Spraying spermidine increased the cell membrane stability index(MSI)and soluble protein(SPRO)content during the senescence of upper leaves at the mature stage,and reduced the accumulation of malondialdehyde(MDA).Different concentrations of spermidine can improve the MSI of the upper tobacco leaves in the mature stage after topping,and improve the film stability of the upper tobacco leaves.The effect of T3 treatment is the most obvious,and MSI is increased by 14.76%on average compared with CK.Different concentrations of spermidine can reduce the accumulation of MDA in the upper leaves to varying degrees,and the T3 treatment has the best reduction effect,and enhances the ability of anti-oxidant damage during the senescence of the upper leaves,which is 14.42%lower than that of CK.Spraying spermidine in the upper tobacco leaves before and mid-term(15,30 days after topping)can increase the content of SPRO in the tobacco leaves and significantly increase the nitrogen metabolism capacity of the tobacco leaves.Among them,the effect of T3 treatment is the most obvious,and SPRO is improved compared with CK.11.38%.In the later stage of senescence(45 days after topping),spraying spermidine can reduce the content of soluble protein,which is beneficial to reduce the impurity and irritating gas of flue-cured tobacco leaves.The reduction effect of SPRO with T3 treatment is the most obvious,which is decreased 13.75%,compared with CK treatment.(3)Spraying spermidine can increase the content of auxin(IAA)and cytokinin(CTK)in the upper tobacco leaves at the mature stage,and reduce the content of abscisic acid(ABA)and aminocyclopropane carboxylic acid(ACC).The content of IAA and CTK in the upper leaf senescence process increased first and then decreased.Foliar spraying spermidine significantly increased the content of IAA and CTK in each treatment,and the effect of T3 treatment was the most significant.After topping 15.On 30 and 45 days,IAA and CTK increased by 42.04%and 52.31%respectively compared with CK.The ABA content increased rapidly with the increase of upper leaf senescence,and then decreased slowly.At 15,30,and 45 days after topping,the ABA content of tobacco leaves with different treatments was significantly lower than that of CK.The ABA content in the leaves treated with T3 decreased most significantly than that of CK,and it was 19.13%lower than that of CK.The content of aminocyclopropane carboxylic acid(ACC)increased with the phases of senescence,and the content of the leaves showed a prompt increase first and then slowly increased.At 15,30 and 45 days after topping,the ACC content of the leaves under the spraying treatment of spermidine was all Significantly lower than CK,T3 treatment has the most obvious reduction effect of ACC content,which is 16.46%lower than CK treatment.(4)Foliar spraying spermidine can reduce the expression of senescence-related genes in the upper tobacco leaves at the mature stage.15,30 and 45 days after topping,spraying,different concentrations of spermidine on the leaves can reduce the expression of senescence marker gene(NtCP1),delay the senescence of upper tobacco leaves,and improve the maturity tolerance.The expression of NtCPl is treated with T3 The decline was the most significant,which was 12.82%lower than that of CK.Foliar spraying spermidine can reduce the expression of ACC synthetase gene(ACS1),and the ethylene synthesis in the upper leaves that promotes senescence in the upper leaves at the mature stage decreases.The expression of ACS1 decreased most significantly when treated with T3,which was reduced by 10.25%compared with CK.Correlation analysis showed that the physiological indicators of the upper tobacco leaf senescence have a high correlation with NtCP1,MDA,ACC,ACS1 and NtCP1 have a very significant positive correlation(P<0.01),and ABA and NtCP1 have a significant positive correlation.(P<0.05).Chl,Car,MSI,SPRO,CCD1 and NtCP1 all have a very significant negative correlation(P<0.01),and IAA,CTK and NtCP1 have a significant negative correlation(P<0.05).In addition,the principal component analysis showed that the T3 treatment had the best physiological effect on the upper leaf senescence in the mature stage.(5)Spraying spermidine can improve the yield and quality in tobacco production.Foliar spraying spermidine increased the sugar content of the upper tobacco leaves after curing,while the nicotine content decreased.Foliar spraying with spermidine increased the specific value of carbohydrates content and the ratio between nitrogen and alkali in the upper leaves after curing.T3 treatment had the most significant effect of improving the ratio of two sugars,which was 19.23%higher than that of CK.The ratio of nitrogen to alkali treated with T2 was the closest to the suitable range of 1.00,which was an increase of 18.57%compared with CK.At the same time,spermidine improves the sensory quality and economic properties of flue-cured tobacco leaves,makes the amount of aroma more abundant,reduces impurities,and is conducive to the manifestation of the characteristics of aroma style.The T3 treatment score is 79.30,the highest score;spermidine can improve For the grade structure,output and economic benefits of flue-cured tobacco,T3 treatment has the most significant improvement effect.The proportion,output and output value of high-quality tobacco have increased by 13.75%,10.76%,and 14.01%compared with CK.This research analyzed the effects of spermidine on leaf growth,cell membrane damage indicators,nitrogen metabolism and endogenous hormones during the senescence of upper tobacco leaves at mature stage,and the relationship between the above physiological indicators and the expression of senescence-related genes,combined with the upper tobacco leaves after curing The yield and quality of Spermidine:Spermidine can delay the senescence of upper tobacco leaves,improve the maturity tolerance of upper leaves,and increase the yield and quality of upper leaves after roasting.The concentration of spermidine is 0.5mmol/L(T3).