Boron increases root elongation by reducing aluminum induced disorganized distribution of HG epitopes and alterations in subcellular cell wall structure of trifoliate orange roots

Aluminum toxicity limits the plant growth by inducing inhibition of root elongation. Although several mechanisms have been proposed regarding the phytotoxic effects of aluminum on inhibition of root elongation; the primary causes of aluminum induced root inhibition and its mitigation by boron (B) are still elusive. The present study was carried out to explore the mechanisms of B induced mitigation of aluminum toxicity and to investigate the changes in well wall structure under aluminum toxicity coupled with the techniques of confocal laser microscope, lumogallion and transmission electron microscope. The results revealed that aluminum toxicity severely hampered the root elongation and plant biomass. Moreover, alteration in subcellular structure were observed under aluminum toxicity, however, such negative effects were further exacerbated with B deficiency. Aluminum toxicity indicated disorganized distribution of HG (homogalacturonan) epitopes with higher accumulation of apoplastic aluminum. Nevertheless, B supply improved root elongation, and reduced the aluminum uptake. Taken together, it is concluded that B application can reduce aluminum toxicity and improve root elongation by decreasing Al3+ accumulation to cell wall, alteration in the cell wall structure and reducing the distribution of HG epitopes in the roots of trifoliate (Poncirus trifoliate) orange.