Hydrogel Regulation of Xylem Water Flow: An Alternative Hypothesis: Figure 1.

Impact of Electroviscosity on the Hydraulic Conductance of the Bordered Pit Membrane: A Theoretical Investigation

“…5). In a real system, this potential would cause the pore walls to repel each other and therefore increase the overall pore size (van Doorn et al, 2011), an effect not accounted for in our model.…”

“…By assuming that bordered pits form the limiting hydraulic resistance in xylem, such that K=K 0 %K xylem =K 0 xylem , we calculate the maximum decrease in K xylem expected due to electroviscosity. Figure 6 presents our predictions for K=K 0 of BPM pores with G high and G low , alongside theoretical predictions by van Doorn et al (2011) and data from experimental studies. Measurements shown are for angiosperms for studies in which K xylem was measured across a range of I c .…”

“…Previous researchers have mentioned electroviscosity as a possible explanation for the ionic effect Nardini et al, 2011). For instance, van Doorn et al (2011) proposed an analysis of electroviscosity in BPMs. We believe that the analysis of van Doorn et al errs in its treatment of the electrokinetic processes that lead to electroviscosity by assuming the Debye layer is immobile.…”

“…First, in some species, K xylem has been observed to decrease as I c increases (Cochard et al, 2010), a behavior opposite of that predicted. Second, various studies question whether pectin hydrogels actually exist in the BPM, as reviewed by van Doorn et al (2011). Third, uncertainties about the distribution of the gels within the membrane make it difficult to predict how swelling should impact conductance (Lee et al, 2012).…”

“…We selected representative data from each reference (given in caption). We begin by remarking that the model by van Doorn et al (2011) (black dash-dot line) qualitatively captures the drop in K xylem with decreasing I c that was observed in some studies but predicts a larger drop in K=K 0 than observed experimentally for I c , 10 mM. Our model (black solid line for G low and black dashed line for G high ) also captures this decrease of K xylem with decreasing I c across the physiological range, consistent with the results of van Doorn et al Indeed, within this range, the trend reported for L. nobilis (purple triangles; Zwieniecki et al, 2001), Dendranthema 3 grandiflorum Tzvelev (Chrysanthemum) (red squares; van Ieperen et al, 2000), and Quercus robur (green circles, Aasamaa and Sõber, 2010) are compatible in both trend and magnitude with our predictions, given a value of G between G high and G low .…”