Late Maturation of Large Metaxylem Vessels in Soybean Roots: Significance for Water and Nutrient Supply to the Shoot

Publisher Website
Google Scholar
Abstract
The large, late metaxylem (LMX) in the roots of soybean begins development in the centre of the stele after lignification of the early metaxylem poles. Subsequent maturation of the first appearing LMX elements is gradual. They were never mature in the 8-d-old seedlings examined. In 10 to 15-d-old plants the first LMX matured to open vessels at a mean of 17 cm proximal to the root tip. Additional LMX vessels developed in more proximal regions of the roots and these also matured gradually. Based on calculations from relative vessel diameters, the potential flow of xylem sap in a single central LMX vessel is 50 times that in the total of all the early metaxylem (EMX) vessels of a typical primary root of soybean. There was a marked dependence of relative leaf area on the length of primary root with open LMX vessels. This may result from the predicted increased water and nutrient flow to the shoot, facilitated by the opening of the large vessels. It is suggested that, as in maize, the living LMX elements may function in ion accumulation.