Study On The Responses Of Seedlings Among Different Recombinant Inbred Lines Of Maize Under Low Nitrogen Stress And Its Relationship With Sucrose Allocation

Nitrogen is one of the macronutrients and a key factor for limiting the production formation of crops.Over last several decades,the quality of crops and environment were affected associated with excessive application of nitrogen fertilizers in soils and inefficient nitrogen use efficiency(NUE)in crops.Hence,comprehensively understanding the mechanism of nitrogen use,which is helpful for breeding new genetic resources and crop varieties,thus essential for achieving sustainable agricultural development.In present study,PH6WC and PH4CV,the parents of hybrid Xianyu335 which has been a main breed in modern maize production,and 16 recombinant inbred lines which were selected from above two inbred lines,and analysis the biomass accumulation,photosynthetic characteristics and sucrose partitioning of their seedlings under normal and deficient nitrogen conditions,in order to provide materials for the selection of new maize varieties with high nitrogen use efficiency.In summary,we obtained the following results:1.Analyzing the responses of seedlings of PH6WC,PH4CV and 16 recombinant inbred lines selected from them under normal and deficient nitrogen conditions for 14 days,the results demonstrate that only the average diameter of roots of PH6WC similarly between the two nitrogen levels,and all other traits decrease significantly under low nitrogen stress compared with the control.For example,the length of primary roots shows minimal reduction by 6%,and the shoot biomass appears the maximal reduction by76%,as well as other traits reduced by 34%-70%.While the shoot biomass,average diameter of roots,total root length,surface area of roots,chlorophyll content in the second leaf,and net photosynthetic rate of genotype PH4CV are significantly decreased under low nitrogen stress compared with normal nitrogen condition,thus revealing that PH4CV has higher nitrogen use efficiency than PH6WC.Among the 16 recombinant inbred lines,XY19 shows to have a most nitrogen use efficiency based on the root dry weight,root length,root surface area,root volume and lateral root numbers are greatly increased under low nitrogen stress.Moreover,the comprehensive performances of XY105 under two nitrogen levels are the closest to the parent PH6WC,while the XY4 and PH4CV were the most similar.These results indicate that the responses of different maize genotypes to nitrogen are not consistent,even if the different traits of the same genotypes are different.2.PH4CV and a offspring XY4 are selected as object of study,treated at two nitrogen levels for different times,the results show that the growth rates of roots and shoots of XY4 the growth rates of roots and shoots of XY4 are faster than PH4CV,as well as the root system of which is more developed.Under low nitrogen condition,the chlorophyll contents in the first and second leaves of XY4 decrease more quickly at the early stage,while chlorophyll content in the first leaf of PH4CV is higher than XY4 at different developmental stages,and the SPAD values in the second leaf is similar between them when nitrogen is supplied sufficiently.The results indicate that XY4 response to nitrogen faster than PH4CV,that transferring nitrogen from old to new leaves at the early stage under low nitrogen stress,thus ensuring the growth and development of the new leaves.Referring to the sucrose contents,XY4 and PH4C V transported more sucrose to the roots from above leaves under low nitrogen stress compared with normal nitrogen condition,and XY4 deliver more sucrose to the roots under low nitrogen stress than PH4CV.Theses reaults suggest that increasing of sucrose content in roots is positive to the rapid growth of roots and the absorption of more nitrogen resources.