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The velamen protects photosynthetic orchid roots against UV-B damage, and a large dated phylogeny implies multiple gains and losses of this function during the Cenozoic.
- Source :
-
The New phytologist [New Phytol] 2015 Feb; Vol. 205 (3), pp. 1330-1341. Date of Electronic Publication: 2014 Oct 23. - Publication Year :
- 2015
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Abstract
- UV-B radiation damage in leaves is prevented by epidermal UV-screening compounds that can be modulated throughout ontogeny. In epiphytic orchids, roots need to be protected against UV-B because they photosynthesize, sometimes even replacing the leaves. How orchid roots, which are covered by a dead tissue called velamen, avoid UV-B radiation is currently unknown. We tested for a UV-B protective function of the velamen using gene expression analyses, mass spectrometry, histochemistry, and chlorophyll fluorescence in Phalaenopsis × hybrida roots. We also investigated its evolution using comparative phylogenetic methods. Our data show that two paralogues of the chalcone synthase (CHS) gene family are UV-B-induced in orchid root tips, triggering the accumulation of two UV-B-absorbing flavonoids and resulting in effective protection of the photosynthetic root cortex. Phylogenetic and dating analyses imply that the two CHS lineages duplicated c. 100 million yr before the rise of epiphytic orchids. These findings indicate an additional role for the epiphytic orchid velamen previously thought to function solely in absorbing water and nutrients. This new function, which fundamentally differs from the mechanism of UV-B avoidance in leaves, arose following an ancient duplication of CHS, and has probably contributed to the family's expansion into the canopy during the Cenozoic.<br /> (© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.)
- Subjects :
- Acyltransferases genetics
Acyltransferases metabolism
Apigenin metabolism
Crosses, Genetic
Flavonoids metabolism
Gene Duplication
Gene Expression Regulation, Plant radiation effects
Glucosides metabolism
Orchidaceae genetics
Stress, Physiological radiation effects
Time Factors
Orchidaceae physiology
Orchidaceae radiation effects
Photosynthesis
Phylogeny
Plant Roots anatomy & histology
Plant Roots radiation effects
Ultraviolet Rays
Subjects
Details
- Language :
- English
- ISSN :
- 1469-8137
- Volume :
- 205
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- The New phytologist
- Publication Type :
- Academic Journal
- Accession number :
- 25345817
- Full Text :
- https://doi.org/10.1111/nph.13106