title: Chloroplast avoidance movement is not functional in plants grown under strong sunlight.
abstract: Chloroplast movement in nine climbing plant species was investigated. It is thought that chloroplasts generally escape from strong light to avoid photodamage but accumulate towards weak light to perform photosynthesis effectively. Unexpectedly, however, the leaves of climbing plants grown under strong sunlight showed very low or no chloroplast photorelocation responses to either weak or strong blue light when detected by red light transmittance through leaves. Direct observations of Cayratia japonica leaves, for example, revealed that the average number of chloroplasts in upper periclinal walls of palisade tissue cells was only 1.2 after weak blue-light irradiation and almost all of the chloroplasts remained at the anticlinal wall, the state of chloroplast avoidance response. The leaves grown under strong light have thin and columnar palisade tissue cells comparing with the leaves grown under low light. Depending on our analyses and our schematic model, the thinner cells in a unit leaf area have a wider total plasma membrane area, such that more chloroplasts can exist on the plasma membrane in the thinner cells than in the thicker cells in a unit leaf-area basis. The same strategy might be used in other plant leaves grown under direct sunlight.
authors.affiliation: Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo, 192-0397, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Higa
authors.affiliation: Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo, 192-0397, Japan.
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Wada
mesh_terms: D048430:Cell Shape / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000528:radiation effects*; D058503:Mesophyll Cells / Q000166:cytology / Q000528:radiation effects; D008856:Microscopy, Fluorescence; D009929:Organ Size; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology / Q000528:radiation effects; D013472:Sunlight; D027844:Vitaceae / Q000254:growth & development* / Q000528:radiation effects*
chemical_list: D002734:Chlorophyll
keywords: chloroplast movement; climbing plants; leaf structure; light; native plants