title: Continuous UV-B irradiation induces endoreduplication and peroxidase activity in epidermal cells surrounding trichomes on cucumber cotyledons.
abstract: Most trichomes on the surface of cucumber (Cucumis sativus L.) cotyledons consist of three cells. We previously showed that continuous UV-B (290-320 nm) irradiation induces rapid cellular expansion and the accumulation of polyphenolic compounds, possibly stress lignin, in epidermal cells around these trichomes.(1)) To examine the mechanism of the UV-B-induced cellular expansion and to determine which step is stimulated by UV-B irradiation in the lignin synthesis pathway, we investigated relative DNA contents in epidermal cells, including trichomes, and enzyme activity and gene expression in the phenylpropanoid pathway. UV-B irradiation increased the ploidy level over 15 days, specifically in the epidermal cells surrounding trichomes, but not in the other epidermal cells or trichomes. In epidermal cells surrounding trichomes, UV-B irradiation induced peroxidase (POX) activity from days 7 to 15. In cotyledons, UV-B exposure induced CS-POX1 and CS-POX3 gene expression within 2 days, and it also induced two other enzymes in the phenylpropanoid pathway, sinapyl alcohol dehydrogenase and coniferyl alcohol dehydrogenase, from days 9 to 11. Thus, exposure to UV-B induces expansion, endoreduplication, POX activity, and the accumulation of polyphenolic compounds in epidermal cells surrounding the trichomes of cucumber cotyledons. Because polyphenolic compounds such as lignin absorb UV-B, our data indicate a physiological protective mechanism against UV-B irradiation in cucumber.
authors.affiliation: Laboratory of Plant Physiology, Department of Science Education, Faculty of Education, Fukuoka University of Education, Fukuoka 811-4192, Japan. yamasaki@fukuoka-edu.ac.jp
authors.forename: Seiji
authors.initials: S
authors.lastname: Yamasaki
authors.forename: Eri
authors.initials: E
authors.lastname: Shimada
authors.forename: Tomoe
authors.initials: T
authors.lastname: Kuwano
authors.forename: Tae
authors.initials: T
authors.lastname: Kawano
authors.forename: Naoto
authors.initials: N
authors.lastname: Noguchi
mesh_terms: D018548:Cotyledon / Q000737:chemistry / Q000166:cytology / Q000201:enzymology / Q000528:radiation effects*; D018553:Cucumis sativus / Q000528:radiation effects*; D018744:DNA, Plant / Q000032:analysis; D004790:Enzyme Induction / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D008031:Lignin / Q000096:biosynthesis; D009195:Peroxidase / Q000096:biosynthesis* / Q000235:genetics; D019441:Plant Epidermis / Q000737:chemistry / Q000166:cytology / Q000201:enzymology / Q000528:radiation effects*; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics; D018514:Plant Structures / Q000528:radiation effects / Q000648:ultrastructure; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014466:Ultraviolet Rays
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins; D008031:Lignin; D009195:Peroxidase