Effects of boron on aluminum adsorption and desorption of cell wall components of pea root tips

Objectives Comparing the difference of aluminum adsorption and desorption characteristics of cell wall components pea root tips under boron and non-boron conditions to reveal the alleviating mechanism of boron on aluminum stress in plants.

Methods Seeds of pea (Pisum sativum) were hydroponically cultured with Hoagland solution at 0.6 μmol/L B (H₃BO₃) level for 6 days, then the root tips were collected and the different cell wall components were extracted, including chelated pectin (pectin 1), alkaline-soluble pectin (pectin 2), hemicellulose, and cellulose. They were used to study the adsorption and desorption of aluminum under different boron treatments (i.e. no B, 50 μmol/L H₃BO₃, 50 μmol/L 3-NBA).

Results The content of each component in the cell wall of pea root tips was cellulose>hemicellulose>pectin 2>pectin 1. The results revealed that boron may combine with pectin 1, pectin 2, and hemicellulose, thereby affecting their adsorption and desorption capacity for aluminum. Under aluminum toxicity, the pectin in the root cell wall was the major aluminum binding site, especially pectin 2. Further, pectin 2 came from the cell wall with a boron supply adsorbed much more aluminum, but the desorption amount didn’t change significantly. At pH 3.5, compared with 3-nitrophenylboronic acid (3-NBA), boron more effectively affected the adsorption and desorption of aluminum by pectin. Therefore, the immobilization of aluminum in pectin 2 may be one of the important mechanisms for boric acid to alleviate aluminum toxicity.

Conclusions Pectin 2 is the main aluminum binding site in root tip cell wall, and the binding of boron to pectin 2 is an important mechanism of boron alleviating aluminum toxicity.