Physiological Responses Of Two Astragalus Membranacus Seedlings To Sulfur Deficiency

Astragalus is a traditional Chinese medicinal material in China,which has strong pharmacological activity in improving immunity and delaying aging.In this paper,the seedlings of two original plants:Astragalus membranaceus(Fisch.)Bge.(A.membranaceus)and its variant Astragalus membranaceus Bge.Var.mongholicus Hsiao(A.mongholicus).were used as experimental materials.Under the conditions of hydroponics,the changes of growth indexes,photosynthetic fluorescence parameters,antioxidant system activity,nutrient element absorption and secondary metabolism of two kinds of Astragalus seedlings under different levels of sulfur deficiency treatment were studied by using the technology of ionomics and metabolomics synthetically.The response mechanism of Astragalus to sulfur deficiency stress was systematically described,which provided basic theoretical guidance for artificial planting of Astragalus in low sulfur soil area.The main results of this article are as follows:(1)Compared with the supply of Hoagland total nutrient solution,the low-sulfur and non-sulfur supply treatments significantly inhibited the elongation and biomass accumulation of roots and shoots of two kinds of Astragalus seedlings,and caused a series of sulfur deficiency symptoms such as Leaf Chlorosis and yellowing,root browning and so on.In addition,sulfur deficiency also led to a decrease in the chlorophyll content and photosynthetic parameters of the two Astragalus seedlings,and an increase in the degree of cell membrane lipid peroxidation in all parts of the plant.We infered that the decrease in sulfur supply in the nutrient solution caused sulfur malnutrition in Astragalus seedlings,affected plant chlorophyll synthesis,reduced plant photosynthetic capacity,and caused oxidative stress in the whole plant,which ultimately inhibited the growth and development of Astragalus seedlings.Compared with A.membranaceus,A.mongholicus showed stronger tolerance under sulfur deficiency stress.(2)With the aggravation of sulfur deficiency,the contents of soluble sugars and soluble proteins of the two Astragalus significantly increased,and the content of A.mongholicus was higher than that of A.membranaceus,indicating that A.mongholicus cells have strong tolerance to sulfur.The increase of sulfur deficiency significantly reduced the SOD and POD activities in the roots of Astragalus,disrupted the antioxidant system,and resulted in the increase of ROS accumulation in various tissues of Astragalus and led to the increase of ROS accumulation in Astragalus roots,but the changes of stems and leaves were not significant.The activities of CAT and APX were affected in different parts.The balance system of active oxygen in Astragalus was broken and caused serious damage to all parts of Astragalus.(3)With the decrease of sulfur concentration,the absorption of mineral elements had a significant effect on the accumulation of Astragalus seedlings.A large number of elements are mainly accumulated in roots and leaves,and trace elements are mainly accumulated in roots.The accumulation of isoflavone synthesis may be the main role of sulfur tolerance in roots.Under low-sulfur or sulfur-free conditions,the total phenol content in various parts of A.membranaceus plants significantly decreased,while the total phenol content in the roots and leaves of A.mongholicus significantly increased due to sulfur deficiency.At the same time,we also found that sulfur nutrient deficiency induced the accumulation of isoflavones in various parts of Astragalus mongholicus,which effectively alleviated the effect of sulfur deficiency stress on its growth.Stronger patience.(4)The content of compounds in different parts of A.membranaceus was determined by UPLC-MS,and the difference was analyzed by clustering and distribution.In this paper,24 phenolic compounds in different parts of Astragalus were detected.The accumulation of A.mongholicus in roots was increased by sulfur stress,mainly in C6C1 andC6C3C6 compounds;the accumulation of A.membranaceus in stems was higher than that of A.mongholicus,mainly in C6C1 and C6C3C6 compounds;the accumulation of A.membranaceus in leaves was slightly higher than that of A.mongholicus,with no significant difference.The results showed that the root of A.mongholicus showed stronger tolerance than that of A.membranaceus.In summary,in physiological indicators,A.mongholicus has a stronger resistance to sulfur deficiency stress than A.membranaceus;in the active ingredient,A.mongholicus in the root has a stronger resistance to sulfur deficiency stress than A.membranaceus Abilities;A.membranaceus in stems and leaves is more resistant to sulfur deficiency than Mongolian Astragalus.Because A.membranaceus is used as a medicine in the roots of medicinal plants,A.mongholicus was more tolerant than A.membranaceus in response to sulfur deficiency stress in this experiment.In the northeast and northwest regions of Astragalus,Mongolian A.mongholicus is more suitable for producers.