Phytohormonal regulation of transpiration and stomatal conductance among canopy layers of a mature Sugar Maple (Acer saccharum) stand.
Reeves, Ian *,1, Emery, RJ Neil1, 1 Trent University, Peterborough, Ontario, Canada
ABSTRACT- Despite vastly different microclimates and functional roles that exist among mature hardwood tree canopy layers, there has been little or no study of corresponding hormonal physiology. Recently cytokinins (CK) have been associated with the regulation of stomata in several species of plants. This study addresses the potential role of CKs in regulating leaf water loss in mature trees. A high-wire canopy walkway was constructed at the James McLean Oliver Ecology Centre (JMOEC) in order to study a stand of 80 year old sugar maples (Acer saccharum). Leaf samples were collected from the upper and lower canopies of ten trees during August 2003. CKs of those leaves were identified and quantified using (LC −(+) ESI-MS/MS). The outer region of the upper canopy had the highest CK levels. All leaves contained higher levels of ribosides (active forms) than nucleotides or free base forms of CK. The upper canopy had higher transpiration (E) and stomatal conductance (gs) coinciding with higher photosynthetically active radiation (PAR), ultra-violet B radiation (UV-B) and leaf temperature. Total CK and riboside concentrations had significant positive linear relationships with E. These results were supported by experimental application of low concentrations of the synthetic CK, Benzyl aminopurine, which reduced E and gs. Similarly, exogenous application of a range of ABA concentrations reduced E and gs. Current results suggest that CKs tend to accumulate in canopy leaves in response to harsh microclimate conditions and play a role in controlling water loss. This study has been continued through 2004 to further investigate the roles of CKs and ABA in leaf water relations and potential interaction of the two phytohormones. Specifically the focus is on elucidating the interaction between CKs and ABA in the regulation of E and gs. This will help clarify the apparent redundant function of these two phythormones within a forest canopy.
Key words: acer sacharrum, phytohormone, forest canopy, stomatal conductance
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