title: Blue light dose-responses of leaf photosynthesis, morphology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light.
abstract: The blue part of the light spectrum has been associated with leaf characteristics which also develop under high irradiances. In this study blue light dose-response curves were made for the photosynthetic properties and related developmental characteristics of cucumber leaves that were grown at an equal irradiance under seven different combinations of red and blue light provided by light-emitting diodes. Only the leaves developed under red light alone (0% blue) displayed dysfunctional photosynthetic operation, characterized by a suboptimal and heterogeneously distributed dark-adapted F(v)/F(m), a stomatal conductance unresponsive to irradiance, and a relatively low light-limited quantum yield for CO(2) fixation. Only 7% blue light was sufficient to prevent any overt dysfunctional photosynthesis, which can be considered a qualitatively blue light effect. The photosynthetic capacity (A(max)) was twice as high for leaves grown at 7% blue compared with 0% blue, and continued to increase with increasing blue percentage during growth measured up to 50% blue. At 100% blue, A(max) was lower but photosynthetic functioning was normal. The increase in A(max) with blue percentage (0-50%) was associated with an increase in leaf mass per unit leaf area (LMA), nitrogen (N) content per area, chlorophyll (Chl) content per area, and stomatal conductance. Above 15% blue, the parameters A(max), LMA, Chl content, photosynthetic N use efficiency, and the Chl:N ratio had a comparable relationship as reported for leaf responses to irradiance intensity. It is concluded that blue light during growth is qualitatively required for normal photosynthetic functioning and quantitatively mediates leaf responses resembling those to irradiance intensity.
authors.affiliation: Wageningen University, Department of Plant Sciences, Horticultural Supply Chains Group, Wageningen, The Netherlands. sander.hogewoning@gmail.com
authors.forename: Sander W
authors.initials: SW
authors.lastname: Hogewoning
authors.forename: Govert
authors.initials: G
authors.lastname: Trouwborst
authors.forename: Hans
authors.initials: H
authors.lastname: Maljaars
authors.forename: Hendrik
authors.initials: H
authors.lastname: Poorter
authors.forename: Wim
authors.initials: W
authors.lastname: van Ieperen
authors.forename: Jeremy
authors.initials: J
authors.lastname: Harbinson
mesh_terms: D002734:Chlorophyll / Q000032:analysis* / Q000378:metabolism; D018553:Cucumis sativus / Q000737:chemistry* / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects*; D018515:Plant Leaves / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects
chemical_list: D002734:Chlorophyll; D009584:Nitrogen