| Stevia rebaudiana,also known as stevia,honey chrysanthemum,sweet grass,sweet tea,etc.,is a natural sugar cash crop,known as the ’new sugar source for human health’.The steviol glycoside sweetness contained in stevia is equivalent to about 300 times that of sucrose,but the calories contained in it are only 1/300 of sucrose,which is conducive to regulating blood sugar,blood pressure,improving energy and brain power.As a sweetener,steviol glycosides have been widely used in food,beverage,and pharmaceutical industries in Japan,the United States,Western Europe and many other countries.The steviol glycosides of Rebaudioside A(RA),Rebaudioside C(RC)and Rebaudioside D(RD)are sweeter,purer,and free of after-bitterness than the previously widely studied stevioside(ST).In this experiment,in order to improve the content of RA,RC,RD and the drought resistance of stevia,the varieties of stevia ’Shoutian No.3’ with a large scale of domestic planting and production were used as materials,and colchicine concentrations of 0.05%,0.10%,0.15%and 0.20%were used to induce the growth point of plant stem tips,and the effects of different concentrations of colchicine on the doubling effect of stevia chromosomes,as well as the morphological indexes,physiological and biochemical indexes,and nutritional content and drought resistance of steviol glycosides.The colchicine induction protocol most suitable for polyploid stevia was screened.It provides new ideas for improving the yield and quality of steviol glycosides and improving the drought resistance of stevia.The main findings are as follows:1.Colchicine treatment induced the doubling of the stevia ’Shoutian No.3’ chromosome,enlarged its stomata and reduced the number of stomatas.The concentration of 0.15%obtained by pre-experiments was the optimal treatment concentration of colchicine,and colchicine treatment could double the stevia ’Shoutian 3’chromosome.The stomata of stevia leaves with doubled chromosomes became larger and the number decreased,and the length and width of stomata could be observed to increase by 9.27%18.52%and 6.32%-8.77%,respectively,in the same field of view,and the number decreased by 2.2.Colchicine treatment promoted the growth and development of Stevia rebaudiana’Shoutian 3’ plants.After treatment with colchicine,the stem diameter of polyploid stevia increased by 4.23%,crown width increased by 10.73%,leaf width increased by 17.09%,and leaf number increased by 11.50%compared to the control group.There was no significant difference in plant height and leaf length.3.Colchicine treatment increased the chlorophyll content in the leaves of stevia ’Morita No.3’ plant.After colchicine treatment,the chlorophyll content in plant leaves of polyploid stevia increased by 7.43%compared with the control group.The doubling of chromosomes enables stevia plants to enhance photosynthesis through the increase of chlorophyll in leaves,providing sufficient material support for the growth and development of stevia.4.Colchicine treatment increased the total flavonoid content,total phenolic content and mineral element content in the leaves of stevia ’Shoutian No.3’ plant.Compared with the control group,the total phenolic content of polyploid stevia increased by 15.72%,the total flavonoid content increased by 8.52%,and the content of mineral elements such as Ca2+,Mg2+increased.Chromosome doubling can increase the total flavonoid content,total phenolic content and mineral element content in the leaves of stevia plants,which can enrich the nutrients contained in stevia and improve its quality.5.Colchicine treatment increased the RA content,ST content,RD content and RA/ST content in the leaves of stevia ’Morita No.3’.Compared with the control group,the RA content in polyploid stevia was increased by 7.11%,ST content by 3.85%,RD content by 4.04%,and RA/ST by 3.10%compared with the control group.Chromosome doubling can increase the content of RA,ST and RD and RA/ST in stevia leaves,thereby improving the quality of steviol glycosides.6.Colchicine treatment improved the drought resistance of stevia ’Morita No.3’.The soil water content was 60%～70%,50%～60%,40%～50%,30%～40%,respectively,with the intensification of drought stress:SOD activity in polyploid stevia leaves showed a trend of first increasing and then decreasing,and was always higher than that of the control group.POD activity showed a trend of first increasing and then decreasing,and was always higher than that of the control group.CAT activity showed a trend of first increasing and then decreasing,and was always higher than that of the control group.The content of MDA always showed an upward trend,and there was no significant difference between the control group under mild drought conditions and significantly lower than that in the control group under moderate drought and severe drought conditions.Soluble protein and proline levels continued to rise and were consistently higher than in the control group. |
