Border Cells Alleviating Aluminum Toxicity in Soybean Root Tips

Abstract

Root border cell (BC) is a group of cells from the apex of root, which has been considered to play a vital role in protecting root tip from extracellular biotic and abiotic stresses. It is known that the BC may secrete saccharide to chelate Al3+ and alleviate cell damage under aluminum stress. In this paper, we aimed to reveal the effects of root BC on alleviation of aluminum toxicity to root tips with soybean [Glycine max (L.) Merrill] cultivar Zhechun 3 during the development of roots. The BC number, activities of peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) as well as protein content were measured under 0 (CK), 50, 100, 200, and 400 μmol L1 Al3+ stress for 12 and 24 h respectively, with static culture (to maintain border cells adhered to root tips) and shaking culture (to remove border cells from root tips completely). The results showed that the viable border cells accounted for 60%-80% when root length was 5 mm. 50-400 μmol L1 Al3+ treatment for 12 h increased the number of border cells, but inhibition of border cell development by Al3+ turned up after 200, 400 μmol L1 Al3+ treatment for 24 h. When soybean roots were cultivated by shaking to remove border cells from root tips, root elongation was decreased with increasing Al3+ concentrations. However, this kind of inhibition of root growth was alleviated under static culture. At the same time, POD, CAT (under Al stress for 12 h), SOD activities and protein content were higher significantly than those under shaking culture withlower Al3+ concentration (0-100 μmol L1 Al3+ treatment for 12 h and 0, 50 μmol L1 Al3+ treatment for 24 h) stress. And no significant difference in POD, SOD activities and protein content was observed between static culture and shaking culture under higher Al3+ concentration (200, 400 μmol L1 Al3+ treatment for 12 h and 100-400 μmol L1 Al3+ treatment for 24 h) (P0.05). The results suggested that border cells adhered to the root tips can significantly affect root relative elongation rate, POD, CAT, SOD activities and protein content of soybean root tip, and alleviate the toxicity Al3+ to plant root tips through increasing the number of border cells, enhancing the protein content of root tips and maintaining higher POD and SOD activities.