Comparative analysis of end wall resistivity in xylem conduits

Abstract

The hydraulic resistivity ( R , pressure gradient/flow rate) through end walls of xylem conduits was estimated in seven species of diverse anatomy and affinity including a vesselbearing fern, a tracheid-bearing gymnosperm, and angiosperms with versus without vessels. Conduit lengths were measured with a silicone injection method which was easier and more accurate than the usual paint injection. The R declined linearly with the removal of end walls as stems were shortened from 10 to 0.3 cm. This relationship gave the minimum R with no end walls present, or the lumen resistivity ( R L ). This was indistinguishable from the HagenPoiseuille value. The maximum R with all end walls present gave R C , the resistivity of end wall and lumen in series. Average end-wall resistivity ( R W ) was the difference R C ----R L and the 'wall fraction' was R W / R C . Wall fraction was approximately constant, averaging 0.54 ± ± ± ± 0.07. This suggests that end wall and lumen resistivities are nearly colimiting in vascular plants. Average conduit length was proportional to the diameter squared across species ( r 2 = 0.94). Together with a constant wall fraction, this was consistent with the end wall resistance ( r w , pressure difference/flow rate) being inversely proportional to conduit length. Lower r w in longer conduits is consistent with their having more end wall pits than shorter conduits.

The role of leaf hydraulic conductance dynamics on the timing of leaf senescence

“…Neither petiole vessel size distributions nor PLC were associated with changes in K rachis across leaf age categories, but PLC values reflected considerable amounts of embolism at both leaf developmental stages. Alternatively, vascular bundle radial hydraulic conductance, instead of conduit diameter, could have determined rachis hydraulics, as in ferns , but it remains to be tested if pit membrane permeability in angiosperm leaves is as great a contributor to leaf xylem resistance as it is in stems (Sperry et al 2005). Our results contrast with those regarding Populus tremula Michx., in which midrib conduit size, but not cross-sectional area, was the driver in K leaf changes during leaf ontogeny (Aasamaa et al 2005).…”

Decline of Leaf Hydraulic Conductance with Dehydration: Relationship to Leaf Size and Venation Architecture

“…Such work will also need to consider other aspects of the structure of the vein system (e.g. vessel widths and lengths and the degree that conduits span across vein orders), as these factors have been found to have great importance in stem vulnerability (Sperry, 2003;Sperry et al, 2005) and vary greatly across species (Sack and Frole, 2006). These traits may contribute to the correlation of vulnerability with low major vein density, because the major veins have especially long and wide vessels that span multiple orders.…”

Polysaccharide Compositions of Intervessel Pit Membranes Contribute to Pierce’s Disease Resistance of Grapevines

“…Given the importance of PM function in processes other than limitation of pathogen spread, e.g. providing check points that limit vessel embolisms (Sperry et al, 1991(Sperry et al, , 2005Choat et al, 2003) and providing pathways for water to move around damaged vessels (Zwieniecki et al, 2001;Tyree and Zimmermann, 2002;Sun et al, 2006Sun et al, , 2008 our adaptation of the use of mAbs to characterize PM polysaccharide compositions may prove useful in explaining other aspects of xylem system function.…”