Continuous UV-B Irradiation Induces Endoreduplication and Peroxidase Activity in Epidermal Cells Surrounding Trichomes on Cucumber Cotyledons

• Published in: JOURNAL OF RADIATION RESEARCH Vol. 51; no. 2; pp. 187 - 196
• Main Authors: Yamasaki, Seiji, Shimada, Eri, Kuwano, Tomoe, Kawano, Tae, Noguchi, Naoto
• Format: Journal Article
• Language: English
• Published: England THE JAPAN RADIATION RESEARCH SOCIETY 2010; Oxford University Press
• Subjects: Alcohol dehydrogenase; Cotyledon - chemistry; Cotyledon - cytology; Cotyledon - enzymology; Cotyledon - radiation effects; Cotyledons; Cucumis sativus; Cucumis sativus - radiation effects; Data processing; DNA; DNA, Plant - analysis; Endoreduplication; Enzyme Induction - radiation effects; Enzymes; Gene expression; Gene Expression Regulation, Plant - radiation effects; Lignin; Lignin - biosynthesis; Peroxidase; Peroxidase - biosynthesis; Peroxidase - genetics; phenylpropanoids; Physiological aspects; Plant Epidermis - chemistry; Plant Epidermis - cytology; Plant Epidermis - enzymology; Plant Epidermis - radiation effects; Plant Proteins - biosynthesis; Plant Proteins - genetics; Plant Structures - radiation effects; Plant Structures - ultrastructure; Ploidy; Polyphenols; Reverse Transcriptase Polymerase Chain Reaction; sinapyl alcohol; Trichomes; U.V. radiation; Ultraviolet Rays
• ISSN: 0449-3060; 1349-9157; 1349-9157
• DOI: 10.1269/jrr.09101

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.