Suberin mutation and the Péclet effect
Both E and L v were affected by the
compromised ultrastructure of the bundle sheath cells and increased
apoplastic permeability in Zmasft maize double mutants,
especially at the interface of suberin lamellae and adjoining
polysaccharide cell walls (Mertz et al. In review). Suberin is
considered essential as a functional barrier to unrestricted diffusion
of water across cell walls (Botha et
al. 1982; Schönherr 1982;
Mertz & Brutnell 2014). Consequently,
more permissive water flow in the leaf of the Zmasft double
mutants led to greater water flow out of the xylem as evidenced by
greater E under high light and more water channels in and out of
the xylem under low light, increasing the overall effective mixing
length in the xylem (L v). The likely reason for
mutation-related differences in E under high light andL v under low light is an interaction between
water demand and the lack of water channeling. Under high light Ewas 2-3.3x and 2.6-3.8x greater in wildtype and the double mutant
relative to low light, respectively, so the principal water channels
moved the vast majority of water out of the xylem, leading to similar
measures of L v. In contrast, transpiration demand
was low under low light, so greater apoplastic permeability allowed
water to move through more tortuous channels, increasing the overallL v in the Zmasft mutants. Therefore,
channeling of water outside the xylem through suberin lamellae
influenced the Péclet effect in leaf water by restricting water flow
(lower E ) and reducing water movement across the suberin lamellae
(smaller L v). As has been seen previously,
suberin and suberin lamellae play a role in the plant’s ability to
regulate transpiration (Schreiber 2010;
Vishwanath et al. 2015), but
interestingly these differences are detectable with stable isotopes.
Potentially, through the Péclet effect model
Δ18OLW can be used to detect and study
anatomical differences and their physiological consequences on water
movement in leaves.