Physiological Responses And Metabonomics Of Sorghum Seedlings To Alkali Stress

Two sorghum inbred lines,alkali resistant line?SX44B?and alkali sensitive line?262B?,were selected as experimental materials in this study.The effects of 75 mmol·L^-1 mixed alkali solution?NaHCO₃:Na₂CO₃=9:1,pH=8.9?on sorghum seedlings were assessed by measuring the physiological responses and changes of metabolites.The results are as follows:1.The normal growth of sorghum seedlings was inhibited by alkali stress,and the length of aboveground part and root,fresh weight and dry weight of sorghum were reduced.The decreased range of SX44B was lower than 262B,indicating that SX44B had a good tolerance to alkali stress.2.Alkali stress increased the relative conductivity and MDA content of sorghum.The active oxygen was accumulated less in SX44B,which alleviated peroxidation of membrane lipid.After alkali stress,the activities of SOD,POD,CAT and APX in SX44B were higher than those in 262B.SX44B had a stronger ability of scavenging active oxygen,which reduced the damage of active oxygen to membrane lipid.Therefore,SX44B showed a better alkali resistance.3.Under alkali stress,the contents of proline,soluble sugar and soluble protein in sorghum seedlings increased,but the root activity decreased.More accumulated osmoregulation substances and higher root activity were found in SX44B to resist the damage caused by alkali stress.4.Alkali stress increased Na⁺content in sorghum seedlings.The Na⁺content in roots was higher than that in leaves.A large amount of Na⁺was stored in the root,which led to less stress by Na⁺in the aboveground part.The Na⁺content in roots of SX44B was significantly higher than that of 262B,and that in leaves of SX44B was significantly lower than that of262B.Under alkali stress,the content of K⁺and K⁺/Na⁺decreased in sorghum seedlings.SX44B maintained high K⁺absorption capacity,showing stronger selective absorption capacity.5.Under alkali stress,the chlorophyll content of sorghum was decreased and the chloroplast structure was destroyed.The potential activity of photosystem II and the conversion efficiency of light energy were inhibited,which resulted in the decreased photosynthetic rate.Non stomatal restriction was the main reason affecting the photosynthesis of sorghum.SX44B kepthigher chlorophyll content and better chloroplast structure.Excessive light energy was consumed in the form of heat dissipation in SX44B,which protected the photosynthetic structureand prevented the decline of net photosynthetic rate.6.Under alkali stress,compared with 262B,SX44B resisted osmotic stress,protected cell membrane structure and regulated ion balance by accumulating more amino acids,organic acids,phenolic acids,sugars and alcohols,such as aspartic acid,inositol,sucrose,succinic acid,salicylic acid and so on.Meanwhile,SX44B produced more energy to resist alkaline stress by strengthening TCA cycle.