Changes in axial hydraulic conductivity along elongating leaf blades in relation to xylem maturation in tall fescue

Abstract

Xylem maturation in elongating leaf blades of tall fescue (Festuca arundinacea) was studied using staining and microcasting. Three distinctive regions were identified in the blade : (1) a basal region, in which elongation was occurring and protoxylem (PX) vessels were functioning throughout ; (2) a maturation region, in which elongation had stopped and narrow (NMX) and large (LMX) metaxylem vessels were beginning to function ; (3) a distal, mature region in which most of the longitudinal water movements occurred in the LMX. The axial hydraulic conductivity (K h ) was measured in leaf sections from all these regions and compared with the theoretical axial hydraulic conductivity (K t ) computed from the diameter of individual inner vessels. K t was proportional to K h throughout the leaf, but K t was about three times K h . The changes in K h and K t along the leaf reflected the different stages of xylem maturation. In the basal 60 mm region, K h was about 0.30p0.07 mmol s −" mm MPa −" . Beyond that region, K h rapidly increased with metaxylem element maturation to a maximum value of 5.0p0.3 mmol s −" mm MPa −" , 105 mm from the leaf base. It then decreased to 3.5p0.2 mmol s −" mm MPa −" near the leaf tip. The basal expanding region was observed to restrict longitudinal water movement. There was a close relationship between the water deposition rate in the elongation zone and the sum of the perimeters of PX vessels. The implications of this longitudinal vasculature on the partitioning of water between growth and transpiration is discussed.

Analysis of anatomical and functional traits of xylem in Humulus lupulus L. stems

“…The values of measured Kh were on average only 14-26% of theoretically predicted Kh values based on Hagen-Poiseuille equation for ideal capillary. Similar results were found also in other studies (Ewers et al 1989, Martre et al 2000. There are three main factors that contribute to this discrepancy.…”

Effects of salinity on xylem structure and water use in growing leaves of sorghum

“…Nonami & Boyer (1993) and Silk and colleagues (Silk & Wagner, 1980 ;Silk, 1994) have discussed the importance of such growth-sustaining water potentials. This interpretation seems consistent with some recent results of Martre et al (2000) who measured both water deposition rate and xylem radius through the growth zone of cultivated fescue leaves. They found that within a particular leaf the growth-associated water deposition rate was directly proportional to the local xylem radius throughout the growth zone.…”

A Hydraulic Model Is Compatible with Rapid Changes in Leaf Elongation under Fluctuating Evaporative Demand and Soil Water Status

“…Indeed, mature tissues are located downstream of the growing zone, with a hydraulic connection that is not perfect because minor veins are still at a protoxylem stage (Martre et al, 2000). In addition, mature tissues have an appreciable capacitance, resulting in the relatively slow recovery of leaf water potential upon rehydration, while the xylem vessels have virtually no capacitance because they are rigid.…”