Inhibitor studies of leaf lamina hydraulic conductance in trembling aspen (Populus tremuloides Michx.) leaves

Abstract

The present study investigated leaf water transport properties in trembling aspen (Populus tremuloides) leaves. Leaf lamina hydraulic conductance (Klam) and stomatal conductance (gs) were drastically suppressed by NaF (a general metabolic inhibitor). In leaves treated with 0.2 mM HgCl2 (an aquaporin blocker), Klam declined by 22% when the leaves were sampled in June but the decline was not significant when the leaves were sampled in August. The leaves sampled in June that transpired 30 mM β-mercaptoethanol following mercury application showed similar Klam as those in control leaves transpiring distilled water. When leaves were pressure-infiltrated with 0.1 mM HgCl2, Klam significantly declined by 25%. Atrazine (a photosystem II inhibitor) drastically reduced leaf net CO2 uptake by the leaves from seedlings and mature trees but did not have any effect on Klam regardless of the irradiance at the leaf level during the Klam measurements. When PTS3 (trisodium 3-hydroxy-5,8,10- pyrenetrisulphonate) apoplastic tracer was pressure-infiltrated inside the leaves, its concentration in the leaf exudates did not change from ambient light to high irradiance treatment and declined in the presence of HgCl2 in the treatment solution. Trembling aspen Klam appears to be linked to leaf metabolism and is uncoupled from the short-term variations in photosynthesis. Aquaporin-mediated water transport does not appear to constitute the dominant pathway for the pressure-driven water flow in the leaves of trembling aspen trees.