The Mechanism Of Physiological And Molecular Response To Iron-deficiency In Pyrus Betulaefolia

Iron is one of the important elements needed for the growth and development of plant,which participates in many important physiological processes such as electron transport of photosynthesis and respiration,chlorophyll synthesis,nodule formation and nitrogen fixation of plant.Pyrus betulaefolia is widely distributed in northern China because of its well-developed root system,cold and drought-resistance and salt tolerance.Study on iron deficiency stress in its physiological and molecular responses have been rarely reported.Therefore,research on iron deficiency effects on growth and development of Pyrus betulaefolia iron stress mechanism,to solve the production of pear iron nutrient deficiency problems are of great significance.In this study,all the treatments were conducted by seedlings of Pyrus betulaefolia with solution culture method and treatments were set as follows:FeO(0 ?mol/L Fe),Fe10(10 ?mol/L Fe),Fe40(40 ?mol/L Fe),Fe80(80 ?mol/L)to study the changes ofcontent of photosynthetic indexes,photosynthetic products and mineral elements content.The main results were as follows:(1)With the decrease of iron concentration,the dry matter accumulation and root/shoot ratio were significantly decreased.(2)The SPAD value,net photosynthetic rate,transpiration rate,stomatal conductance and intercellular carbon dioxide concentration of leaves were decreased by the effect of insufficient iron supply.Meanwhile,the content of sorbitol and sucrose in leaves were decreased with decrease of iron supply and increase of the time.(3)The difference supplication of iron concentration also affected the uptake and transportation of other mineral elements.The content of P,K,Mg in leaves and roots and Mn in roots were increased with the increase of iron,while the content of Ca,Zn and Cu were decreased.We studied the changes of physiological and biochemical indexes and related gene expression of iron absorption and transportation in Pyrus betulaefolia seedings under Fe-sufficient treatment(40 ?mol/L Fe),Fe-deficiency treatment(0 ?mol/L Fe)and split-root treatment(1/2 for 40 ?mol/L Fe,1/2 for 0 ?mol/L Fe).The results showed that:(I)Iron-deficiency treatment could promote the occurrence and elongation of lateral roots and root hairs.The total root length and root tip number of Fe-deficiency and split-root treatments were significantly higher than Fe-sufficient treatment,while the root diameter was significantly lower than of Fe-sufficient treatment.There was no significant difference in root surface area and root volume.(2)Rhizosphere pH was increased with the treatment time,while the increasing trend of Fe-deficiency and split-root treatments were slower than that of Fe-sufficient treatment.(3)The Fe3+ activity reductase in Fe-sufficient treatment wasn't changed with time but of Fe-deficiency treatment and split-root treatment were increased and then decreased with the time.(4)The root apoplast pH were decreased under the Fe-deficiency treatment and the content of apoplastic iron were decreased significantly from 0-4 d in the Fe-deficiency treatment.(5)The content of malic acid and citric acid in roots of Fe-deficiency treatment were significantly increased and were always higher than that of Fe-sufficient treatment.(6)The expression of iron uptake and transportation-related genes were significantly increased in the Fe-deficiency treatment.The IRTI,FR02 and HA7 in roots were significantly up-regulated from 2 d in Fe-deficiency treatment,whose expression level increased with the treatment time and then decreased.The Fe2+ transporter NRAMP1 was significantly up-regulated in the mid stage of Fe-deficiency treatment(6 d).The NRAMP3 gene was expressed in roots and leaves,and their expression were increased first and then decreased with the treatment time.FRD3 was expressed only in the root,and the expression level of FRD3 increased with the Fe-deficiency treatment time.The citric acid synthase gene CS1 and CS2 were expressed both in roots and leaves,and the expression level of FRD3 reached the peak at 6 days in iron deficiency treatment.The expression of Nasinamide synthase gene NASI was expressed in leaves and roots.NAS2 was only expressed in roots,and the expression level was higher in Fe-deficiency treatment.YSL3 gene was only expressed in leaves,and was significantly up-regulated at 8 days in Fe-deficiency treatment.Iron-regulated transporter 1 gene(IRT1)has been proved to be involved in plant iron absorption as the main transporter when plants are under iron deficiency stress.In this study,for cloning the IRT1 gene sequence and investigating its expression characteristics of Pyrus betulaefolia,the full length cDNA of iron-regulated transporter gene named PbIRT1 was cloned with reverse transcription PCR(RT-PCR)and RACE.RT-PCR and qRT-PCR analysis of PbIRT1 showed that it expressed mainly in the roots.It could be speculated that the PbIRT1 gene could be induced by iron deficiency stress and was involved in the process of iron uptake and transport.In summary,iron-deficiency will affect the growth and development of the upper part of Pyrus betulaefolia,but it will also change the iron related gene up-regulated expression to mediate the physiological stress response to adapt to the iron deficiency environment.Therefore,this study can contribute to further investigation for the physiological and molecular response to iron-deficiency mechanism of Pyrus betulaefolia.