A Research On The Mechanism In Regulating Root Development Of Nicotiana Tabacum Under Phosphorus-Iron Interaction

Phosphorus and iron are two essential nutrients for plant growth and development.As root system is a main part of the plant for absorbing nutrients,the sound development of roots can increase the plant’s absorption of phosphorus and iron.Apart from the external environmental factors such as regulation of soil nutrients,the morphogenesis of plant roots is also influenced by hormones.The synthesis and polar transport of auxin play an important role in the morphogenesis of the root system.In order to investigate the effects of auxin on the growth and development of tobacco roots under phosphorus and iron interactions(in the absence of phosphorus,iron,and phosphorus),the DR5::GUS transgenic tobacco was used as the test material in this study.Several groups were set for comparison including one group with normal treatment(CK,MS medium),one with phosphorus deficiency(-P,-P,MS medium with 5% P),one with iron deficiency(-Fe,MS medium with 5% Fe),and one with both iron and phosphorus deficiency treatment(-P-Fe,MS medium with 5% P and 5% Fe).The research mainly aims at studying the root morphology of the tobacco seedlings under different treatments,the above-ground biomass,phosphorus and iron content in tobacco seedlings,auxin distribution in tobacco,the expression of the genes related to auxin transport protein,as well as the effects brought by the addition of exogenous IAA and NPA on the growth and development of tobacco roots under various treatments.The main results were as follows:(1)The MS solid medium were used to study the phenotype and aboveground biomass,lateral root growth and elongation,and phosphorus and iron content of tobacco plants under various treatment,i.e.,normal treatment(CK),phosphorus deficiency treatment(-P),iron deficiency treatment(-Fe),and phosphorus and iron deficiency treatment(-P-Fe).The results show that: phosphorus deficiency can effectively alleviate the inhibition on tobacco root caused by iron deficiency,and phosphorus deficiency can increase the effectiveness of the iron in the root system,which clearly clarified the antagonistic effect between phosphorus and iron in the tobacco seedlings.(2)DR5::GUS transgenic tobacco seedlings as material,GUS staining method was used to mark the distribution of auxin in tobacco seedlings,and the concentrations of auxin were tested in the underground part and above-ground part of tobacco seedlings.The results further confirmed that the lack of phosphorus could relieve the growth inhibition induced by iron deficiency.The polar transport of auxin from the shoots to the roots is mainly accomplished through the PIN family proteins.To investigate the causes of auxin changes in the roots of tobacco seedlings under phosphorus-iron deficiency,q RT-PCR techniques were used to analyze the expression of Nt PINs family genes in the root of tobacco seedlings under the four types of treatment.The results showed that phosphorus-iron deficiency treatment may affect the polar transport of auxin by changing the expression level of the PIN family gene in the root of tobacco seedlings.(3)In order to further clarify the importance of auxin in regulating the growth and development of tobacco roots under the interaction of phosphorus and iron,we respectively added,based on the four(CK,-P,-Fe,-P-Fe)types of treatments,the auxin IAA and auxin transport inhibitor NPA for 7 days to study the effects of the addition of exogenous auxin on root development.The results showed that: IAA significantly promoted the growth and development of tobacco seedling roots,while NPA inhibited the growth of roots.The tobacoo seeding treated with iron deficiency(-Fe)could reach normal growth or even better when added exogenous auxin IAA.The increase of NPA after CK treatment showed a similar phenotype to iron deficiency stress,which further indicates that auxin plays an important role in the growth and development of tobacco seedling roots under phosphorus-iron deficiency stress.(4)Sugar is not only an important structural component and energy substance for plant growth and development,but also an important signaling molecule and osmotic adjustment substance in plants.In order to further explore the regulating relationship of sucrose and auxin for the growth and development of tobacco seedling roots under phosphorus and iron stress.we investigated the sucrose content,sucrase activity and neutral invertase activity in tobacco seedlings.The results showed that the regulation pattern of sucrose is similar to the reaction of auxin to phosphorus deficiency and iron deficiency.These results indicate that sucrose plays a key role in regulating root growth and development under conditions of phosphorus deficiency and iron deficiency,and that it may be used as a signaling factor that participates in the growth of plant roots by regulating auxin,which requires further investigation.