Figure 4.
Xylem vulnerability to embolism determines whether foliar ABA levels are synthesized during drought in A. filix-femina. A, The relationship between foliar ABA level (expressed in terms of dry weight) and leaf water potential (Ψl) in the wild-type (black circles) and Frizelliae (open gray circles) forms of A. filix-femina exposed to soil water deficit. The mean Ψl at which 50% of xylem in the stipe is embolized (P50) is marked by a vertical dashed line for each form. B, Optical stipe vulnerability curves used to determine mean P50 for the wild-type (black lines) and Frizelliae (open gray circles) forms of A. filix-femina. C, Representative montages of embolism events observed in the xylem of the stipe of both forms of A. filix-femina (white scale bars in top left = 1 mm). Color scale bars in the wild-type form indicate the Ψl at which each embolism event occurred. Color scale bars in the Frizelliae form indicate the time after leaf excision, as the vulnerability curve for this form was constructed from a series of individual leaves dried until a certain percentage of embolism was observed, at which point Ψl was measured once; see “Materials and Methods.”