Brassinosteroids Promote Parenchyma Cell and Secondary Xylem Development in Sugar Beet (Beta vulgaris L.) Root

Increasing crop yield has always been an important goal in agriculture. Brassinosteroids (BRs) are growth-promoting steroid hormones with vital roles in many root developmental processes. Sugar beet ( Beta vulgaris L. ) is a root crop with a tertiary root structure. The differentiation of vascular bundles and division of cambial cells increases root diameter. However, little is known about how BRs regulate the transverse growth of beetroot. Therefore, sugar beet with eight leaves was grown in medium containing epibrassinolide or brassinazole, an inhibitor of brassinosteroid biosynthesis. BRs increased the spacing between the cambial rings by increasing the size of parenchyma cells between the rings and ultimately increasing root diameter. BRs also promoted secondary xylem differentiation. These findings indicate that brassinosteroids function in transverse development in beetroot.