GREEN, CRAIG D. & ROBERT M. AUGÉ
Tennessee Agricultural Experiment Station, O.H.L.D., University of Tennessee, 2431 Center Drive, Knoxville, TN 37996-4500, U.S.A.
Vesicular-arbuscular mycorrhizal (VAM) colonization can alter stomatal behavior of host leaves during drought, and some evidence suggests this may be related to an altered production or reception of a chemical signal of soil drying. We tested whether intact root systems were required to observe an effect of Glomus intraradices on leaf transpiration (E), or whether some residual VAM influence on leaves could affect E of foliage detached from root systems. We performed E assays on detached leaves of VAM and nonmycorrhizal (NM) plants in the presence of several possible candidates for a chemical signal of soil drying. Colonization interacted significantly with ABA and pH in regulating E of detached leaves of Vigna unguiculata (cowpea) plants. E of VAM and NM cowpea leaves were similar when fed varying concentrations of phosphorus and calcium, alone or in combination with ABA. Varying calcium directly affected E of cowpea and also altered stomatal sensitivity to ABA. VAM colonization altered E of detached Rosa hybrida (rose) leaves but had no effect on E of detached Pelargonium x hortorum (geranium) leaves. The pH of the feeding solution directly affected E in cowpea and geranium. In answer to the question, does mycorrhizal influence on stomatal behavior reside in the leaf (phrased another way, do VAM and NM leaves differ in sensitivity to root-sourced xylem constituents implicated in stomatal control)?, the answer was no for geranium, yes for rose, and only slightly for cowpea.