An analysis of relative elemental growth rate, epidermal cell size and xyloglucan endotransglycosylase activity through the growing zone of ageing maize leaves

Abstract

The effect of development on leaf elongation rate (LER) and the distribution of relative elemental growth rate (REGR), epidermal cell length, and xyloglucan endotransglycosylase (XET) activity through the growing zone of the third leaf of maize was investigated. As the leaf aged and leaf elongation slowed, the length of the growing zone (initially 35 mm) and the maximal REGR (initially 0.09 mm mm-1 h-1) declined. The decline in REGR was not uniform through the growth profile. Leaf ageing saw a maintenance of REGR towards the base of the leaf. Epidermal cell size was not constant at a given position in the growing zone, but was seen to increase as the leaf aged. There was a peak of XET activity close to the base of the growing zone. The peak of XET activity preceded the zone of maximum REGR. XET activity declined as leaves aged and their elongation rate slowed. When leaf elongation was complete a distinct peak of XET activity remained close to the base of the leaf.