Induction of wound-periderm-like tissue in Kalanchoe pinnata (Lam.) Pers. (Crassulaceae) leaves as a defence response to high UV-B radiation levels.
OBJECTIVE
UV-B radiation can be stressful for plants and cause morphological and biochemical changes. Kalanchoe pinnata is a CAM leaf-succulent species distributed in hot and dry regions, and is rich in flavonoids, which are considered to be protective against UV-B radiation. This study aims to verify if K. pinnata has morphological or anatomical responses as a strategy in response to high UV-B levels.


METHODS
Kalanchoe pinnata plants of the same age were grown under white light (control) or white light plus supplemental UV-B radiation (5 h d(-1)). The plants were treated with the same photoperiod, photosynthetically active radiation, temperature and daily watering system. Fragments of the middle third of the leaf blade and petiole were dehydrated and then embedded in historesin and sectioned in a rotary microtome. Sections were stained with toluidine blue O and mounted in Entellan®. Microchemical analyses by optical microscopy were performed on fresh material with Sudan III, Sudan IV and phloroglucinol, and analysed using fluorescence microscopy.


RESULTS
Supplemental UV-B radiation caused leaf curling and the formation of brown areas on the leaves. These brown areas developed into a protective tissue on the adaxial side of the leaf, but only in directly exposed regions. Anatomically, this protective tissue was similar to a wound-periderm, with outer layer cell walls impregnated with suberin and lignin.


CONCLUSIONS
This is the first report of wound-periderm formation in leaves in response to UV-B radiation. This protective tissue could be important for the survival of the species in desert regions under high UV-B stress conditions.
Plant Anatomy Laboratory, Botanical Department, Biology Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Luana Beatriz dos Santos
LB
Nascimento
Plant Anatomy Laboratory, Botanical Department, Biology Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Nattacha dos Santos
Ndos S
Moreira
Federal Institute of Education, Science and Technology, Campos dos Goytacazes, Brazil and.
Marcos Vinícius
MV
Leal-Costa
Chemistry of Natural Bioactive Products Laboratory, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.
Sônia Soares
SS
Costa
Plant Anatomy Laboratory, Botanical Department, Biology Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil, elianast@gmail.com.
Eliana Schwartz
ES
Tavares
D031962:Kalanchoe / Q000254:growth & development / Q000276:immunology* / Q000528:radiation effects*; D057865:Plant Immunity; D018515:Plant Leaves / Q000254:growth & development / Q000276:immunology / Q000528:radiation effects*; D014466:Ultraviolet Rays
Crassulaceae; Kalanchoe pinnata; UV-B radiation; fluorescence microscopy; leaf anatomy; radiation responses; wound-periderm