Response Of Cassava To Low Nitrogen Stress

Cassava(Manihot esculenta Crantz)has outstanding nutrient use efficiency and particular morphological,physiological and biochemical regulation methods,and can grow in infertile soil with almost no yield in other crops.It is these characteristics that make cassava the largest food crop in Africa and a pioneer crop for infertile soil in Tropical regions of China.All of these indicate that cassava may have high nitrogen absorption and utilization efficiency.Nearly 800 million people worldwide use cassava as a staple food,but there are few studies on cassava nitrogen nutrition.It is necessary to understand how cassava can efficiently absorb and utilize nitrogen under low nitrogen conditions,which canprovide theoretical basis for increasing the yield of cassava per unit area and reduce the pollution caused by multiple nitrogen fertilizers.In this paper,a solution culture experiment was carried out to study the change law of thenitrogen content and biomass under low nitrogen stress conditions for the four cassava cultivars as SC124,SC7,SC8 and Ro Yong9.And research the changes of nitrogen and carbon metabolism related indexes under low nitrogen and different nitrogen stresses of Ro Yong9 variety by tissue culture experiments,and their responses to low nitrogen stress also were analyzed.The cassava nitrate transporter gene Me NRT2.5 was cloned.The m RNA expression analysis of the gene with different concentrations of nitrate was studied to investigate the morphological,physiological and molecular tolerance mechanisms of cassava under low nitrogen stress.The main results are as follows:1.Different genotypes of cassava varieties have different tolerance to low nitrogen.Among the four cassava varieties,Under the condition of low nitrogen stress,the change of SC124 was the most obvious,and the content of stem and leaf and root dry matter decreased significantly with the decrease of external nitrogen application rate.It is concluded that SC124 may be a low nitrogen sensitive variety.Under the condition of 0.3m M treatment,the biomass and nitrogen content of Ro Yong9 did not fall but increase,and this special phenomenon has not been reported before.Plants may use more substances to root to improve absorption capacity.It is inferred that Ro Yong9 may be resistant to low-nitrogen species.This variety was further studied as a research object of physiology and molecular mechanism of cassava tolerance to low nitrogen stress.2.The low nitrogen stress test was carried out by low-nitrogen-resistant Ro Yong9tissue culture seedlings.The root biomass,root length and root surface area of low nitrogen stress treatment were higher than CK.There is no such thing as slow growth and turn yellow in cassava,but it grows well and the biomass increases significantly.The soluble protein content increased significantly,and the soluble protein content was the highest in the roots.It is speculated that under the condition of low nitrogen stress,more nitrogen is transferred from the aboveground part to the underground part to synthesize nitrogen-containing compounds to complete more efficient nitrogen transport.Absorb and assimilate to gain more nutrients.Nitrate reductase activity and glutamine synthetase activity also showed no decrease in precipitation under low nitrogen stress conditions.Cassava Ro Yong9 tissue culture seedlings was highly resistant to low nitrogen.The chlorophyll content increased significantly,indicating that low nitrogen treatment did not affect the chlorophyll synthesis of Ro Yong9 tissue culture seedlings.The plants had enough nitrogen to participate in the formation of chlorophyll.The low soluble nitrogen content under low nitrogen stress is also confirmed by the increase of chlorophyll content under low nitrogen stress.Efficient photosynthesis will produce more sugar to synthesize starch,and the change of starch content in the aerial part of stems and leaves also proves that it shows that low nitrogen stress treatment has no effect on plant photosynthesis,but instead promotes effect.3.Treatment of low nitrogen-tolerant variety Ro Yong9 with different nitrogen and low nitrogen stress,it was found that higher ammonium nitrogen inhibited the growth of roots,probably because high concentration of ammonium nitrogen inhibited the absorption of nitrate by plants,The absence of NO₃^–affects the growth and development of the root system,which further affects the plant's absorption of nitrogen.At the same time,high ammonium toxicity(3m M)may also affect the growth and development of cassava hydroponic seedlings.In each treatment of 0.15 m M ammonium nitrogen,it showed good growth,biomass and total nitrogen and nitrate nitrogen content are high.Low levels of ammonium nitrogen promote plant growth.When the ammonium nitrogen is at a low nitrogen level of 0.15m M,the NR activity value is relatively high,especially in the root,and the high ammonium inhibits the absorption of the nitrate,so the NR activity in the root is low.The high concentration of exogenous ammonium nitrogen did not increase the GS activity of cassava Ro Yong9 tissue culture seedlings.The effect of nitrate nitrogen on chlorophyll content seems to be greater than that of ammonium nitrogen.4.The cassava nitrate transporter gene Me NRT2.1,Me NRT2.2 and Me NRT2.5 were cloned.Comparing the expression of Me NRT2.1,Me NRT2.2 and Me NRT2.5,it was found that the two nitrate transporters Me NRT2.1 and Me NRT2.2 were mainly expressed in roots and induced by low concentrations of nitrate.Related to the absorption of nitrate in low nitrogen stress.Me NRT2.5 was mainly expressed in stems and leaves.It was concluded that Me NRT2.5 was mainly related to the redistribution of nitrate nitrogen in low nitrogen stress,which may cause nitrate in stems and leaves.