Boron Transport Process In Response To Inarching Or Foliar Boron Appication And Metabolic Changes In Citrus

Boron?B?deficiency is one of the main problems in citrus orchards.Foliar B supply and inarching rootstock are fundamental techniques remedying B deficiency in citrus.Previous studies proved that the B efficiency and B uptake ability of carrizo citrange?Citrus sinensis×Poncirus trifoliata?was significantly stronger than that of trifoliate orange?Poncirus trifoliata?,either as seedlings or rootstocks.However,the B efficiency effects?complementary,synergistic or antagonistic effects?of inarching trifoliate orange and carrizo citrange is unclear;moreover,whether inarching rootstock can enhance B utilization of citrus plants or not,and effects of B absorption and distribution from different inarching rootstock are still unknown.On the other hand,foliar B application can enhance B concentration in citrus tissues and it solved B deficient problems in citrus production to some degree.Whereas,little information is available on the mechanism of B retranslocation from leaves to other tissues.Therefore,performed with sand cultivation,our research studied effects and mechanisms of B transport and distribution by inarching different rootstocks or foliar B application,and investigated leaf metabolism and metabolite transport process after foliar B supply.From this study,we hope to provide theoretical basis for improving B utilization efficiency of citrus.The results are as follows:1. The effects of B absorption and distribution from different inarching rootstock on Newhall/trifoliate orange plantsIn order to study B utilization after inarching different rootstocks,‘Newhall'navel orange plants grafted on Trifoliate orange?N/T?were inarched with trifoliate orange?N/Tt combination?or carrizo citrange?N/Tc combination?rootstock seedlings.The experimental plants were treated with B-sufficient and B-deficient isotope ¹⁰B solution to investigate dry weight,B concentration,¹⁰B concentration and B distribution by using a two-root system.?1?The B concentration of new leaves and old leaves in N/Tt and N/Tc inarching combinations were all more than 1.25 times as that of N/T grafted plans,indicating that inarching can enhance the B utilization in scion tissues in citrus.?2?Under B-sufficient treatment,the carrizo citrange inarching rootstock distribute more B to new leaves,old leaves and stem than the trifoliate orange inarching rootstock.It suggested that carrizo citrange had higher B deliverability to scion tissues than trifoliate orange as inarching rootstocks,under B sufficient treatment.?3?Under B deficient treatment,B concentration in new leaves of N/Tt plants was significantly higher than that of N/Tc;however,no difference of scion¹⁰B concentration and total B absorption were observed between N/Tt and N/Tc.These results indicated that the scion B deliverability of different inarching plant were similar and inarching carrizo citrange rootstock only improved B concentration in new leaves of grafted plant when compared with inarching trifoliate orange.?4?Either adding¹⁰B to inarching rootstock or original rootstock,¹⁰B can be detected in the other rootstock root of an inarching combination.It indicated that B can be translocated from rootstock to leaves and then re-translocated from scion to rootstock,resulting in B mobility between two rootstocks of an inarching combination.2. B retransloation process and mechanisms of foliar B transportIn order to investigate the retranslocation ability and mechanisms of B in citrus leaves,performed with 1-year-old“Newhall”navel orange grafted on trifoliate orange plants,we analyzed the B concentration in leaves and roots,B-sucrose complex in the phloem sap after foliar application of¹⁰B,girdling,and/or shading treatments.The main results and conclusions in this section are summarized as follows:?1?The B concentration in leaves and¹⁰B concentration in roots were all significantly increased after foliar¹⁰B application.Moreover,the foliar B mobility of B-deficient plants were significantly higher than B-sufficient plants.In addition,both girdling the scion stem and shading over the plants significantly reduced the B and¹⁰B concentration in roots.?2?In the phloem sap of citrus,the concentration of sucrose,tagatose,mannitol,dulicitol,lavandulol,and perseitol were all increased after foliar¹⁰B application and sucrose concentration was more than three times as the other 5 sugar alcohols.Through LC-MS analysis of B complexes,a higher peak intensity of the¹⁰B-sucrose complex was increased in phloem sap by foliar¹⁰B application.Taken together,it is concluded that foliar B can be retranslocated from leaves to roots via phloem,by forming a B-sucrose complex in citrus plants.3. The analysis of metabolite synthesis and transport by foliar B application in citrusTo clarify effects of foliar B application on leaf metabolic process and metabolite transport,Newhall/trifoliate orange plants were used to analyze metabolite difference of leaves and phloem sap by foliar B application.?1?The sucrose concentration was increased in leaves and decreased in phloem sap after foliar B application.Moreover,negative correlation was observed between sucrose concentration in leaves and phloem sap.It indicated that foliar B application improved sucrose outward transport from leaves.?2?Foliar B application resulted in changes of amino acids and sugar alcohols in leaves and phloem sap,and it also affected biosynthesis of amino acids and sugar alcohol metabolism.From the above results,foliar B application may promote growth and development of citrus through affecting synthesis and transport process of amino acids and sugar alcohols in leaves.