Foliar Supplied Boron Can Be Transported to Roots as a Boron-Sucrose Complex via Phloem in Citrus Trees

• Published in: Frontiers in plant science Vol. 11; p. 250
• Main Authors: Du, Wei, Pan, Zhi-Yong, Hussain, Syed Bilal, Han, Zhong-Xing, Peng, Shu-Ang, Liu, Yong-Zhong
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 10.03.2020
• Subjects: citrus; foliar boron; girdling; phloem transport; Plant Science; shading; sucrose; foliar boron; phloem transport; shading; girdling; sucrose; citrus
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2020.00250

Although foliar boron (B) fertilization is regarded as an efficient way to remedy B deficiency, the mechanisms of foliar B transport from leaves to roots are still unclear. In this study, 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 of B, girdling, and/or shading treatments. Results indicated that B concentration was significantly increased in roots after foliar B treatment. On the other hand, both girdling the scion stem and shading over the plants with a black plastic net significantly reduced the B and B concentration in roots. LC-MS analysis revealed that foliar B-treated plants had higher concentration of sucrose and some sugar alcohols in the phloem sap as compared to foliar water-treated plants. Combining with the analysis in the artificial mixture of B and sucrose, a higher peak intensity of the B-sucrose complex was found in the phloem sap of foliar B-treated plants compared to the control plants. Taken together, it is concluded that foliar B can be long distance transported from leaves to roots via phloem, at least by forming a B-sucrose complex in citrus plants.