Continuous UV-B irradiation induces morphological changes and the accumulation of polyphenolic compounds on the surface of cucumber cotyledons.
Sharp-headed and globular-headed trichomes are found on the surface of cucumber (Cucumis sativus L.) cotyledons. Most sharp-headed trichomes consist of three cells. Toluidine blue O stains sharp-headed but not globular-headed trichomes. The effect of continuous ultraviolet-B (UV-B; 290-320 nm) irradiation on the surface of cucumber cotyledons was examined with respect to the two trichome types. Continuous UV-B irradiation induced cell division at or under the basal part of sharp-headed trichomes, resulting in an increase in the number of cell layers from three to six. In parallel, the area stained by toluidine blue O expanded to include epidermal cells surrounding sharp-headed trichomes. Regions of alkali-induced fluorescence due to the presence of polyphenolic compounds coincided with areas stained by toluidine blue O. In contrast, continuous UV-B irradiation did not cause morphological changes in globular-headed trichomes. Thus, continuous UV-B irradiation causes the accumulation of polyphenolic compounds in cucumber cotyledons and induces specific morphological changes in or around sharp-headed trichomes. UV-B exposure also increases lignin content in this tissue. Therefore, continuous UV-B irradiation may induce the specific accumulation of polyphenolic compounds, especially stress lignins, in and near sharp-headed trichomes.
Yamasaki
Seiji
S
Laboratory of Plant Physiology, Department of Science Education, Faculty of Education, Fukuoka University of Education, Fukuoka, Japan. yamasaki@fukuoka-edu.ac.jp
Noguchi
Naoto
N
Mimaki
Kotaro
K
D048429:Cell Size / Q000528:radiation effects; D018548:Cotyledon / Q000166:cytology* / Q000378:metabolism* / Q000528:radiation effects; D018553:Cucumis sativus / Q000166:cytology* / Q000378:metabolism* / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005419:Flavonoids / Q000493:pharmacokinetics*; D010636:Phenols / Q000493:pharmacokinetics*; D059808:Polyphenols; D011829:Radiation Dosage; D013499:Surface Properties / Q000528:radiation effects; D014466:Ultraviolet Rays
D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols