Boron deficiency affects root vessel anatomy and mineral nutrient allocation of Poncirus trifoliata (L.) Raf.

Abstract

Citrus plants are frequently exposed to boron (B) deficiency, which has reduced citrus production worldwide. The effects of boron deficiency on citrus rootstock mineral absorption and allocation, and cell and vessel element anatomy are very important in understanding the nutrient absorbing mechanisms and resolving the boron deficiency problems of citrus production. Poncirus trifoliata seedlings were grown in Hoagland’s solution, which contained 0.25 µM H3BO3 (moderate B) and 0 µM H3BO3 (B deficiency). Seedling growth, root tip cell and vessel anatomy, and nutrient contents were investigated 30 days after treatment. B deficiency significantly inhibited the growth of Poncirus trifoliata seedlings, significantly decreased the mean lateral root length and root number, and significantly increased the root diameter and lateral root primordial (LRP) density. Ultrathin section micrographs showed a thickened root tip cell wall and more attachments on the cell wall in the boron-deficient treatment. The vessel wall of all root orders was markedly thickened and the inner vessel diameter decreased in the boron-deficient treatment. The boron and calcium contents in the leaf, stem and root were significantly decreased, and the phosphorus content decreased significantly in the leaf but not in stem or root in the boron-deficient treatment. The changes in root morphology and vessel element anatomical characteristics completely inhibited mineral nutrient absorption and transportation, resulting in a limited nutrient supply and reduced growth of Poncirus trifoliata in the boron-deficient treatment.