Main conclusion: Wax coverage on developing Arabidopsis leaf epidermis cells is constant and thus synchronized with cell expansion. Wax composition shifts from fatty acid to alkane dominance, mediated byCER6expression. Epidermal cells bear a wax-sealed cuticle to hinder transpirational water loss. The amount and composition of the cuticular wax mixture may change as organs develop, to optimize the cuticle for specific functions during growth. Here, morphometrics, wax chemical profiling, and gene expression measurements were integrated to study developing Arabidopsis thaliana leaves and, thus, further our understanding of cuticular wax ontogeny. Before 5 days of age, cells at the leaf tip ceased dividing and began to expand, while cells at the leaf base switched from cycling to expansion at day 13, generating a cell age gradient along the leaf. We used this spatial age distribution together with leaves of different ages to determine that, as leaves developed, their wax compositions shifted from C24/C26 to C30/C32 and from fatty acid to alkane constituents. These compositional changes paralleled an increase in the expression of the elongase enzyme CER6 but not of alkane pathway enzymes, suggesting that CER6 transcriptional regulation is responsible for both chemical shifts. Leaves bore constant numbers of trichomes between 5 and 21 days of age and, thus, trichome density was higher on young leaves. During this time span, leaves of the trichome-less gl1 mutant had constant wax coverage, while wild-type leaf coverage was initially high and then decreased, suggesting that high trichome density leads to greater apparent coverage on young leaves. Conversely, wax coverage on pavement cells remained constant over time, indicating that wax accumulation is synchronized with cell expansion throughout leaf development.
Bibliographical noteFunding Information:
The authors thank Mrs. Yan Cao for skillful technical assistance. Seeds of the trichome-less gl1 mutant were obtained from the Arabidopsis Biological Resource Center (ABRC). This work has been supported by the Natural Sciences and Engineering Research Council (Canada), the Canada Foundation for Innovation, the British Columbia Knowledge Development Fund, and the Canada Research Chairs Program.
© 2016, Springer-Verlag Berlin Heidelberg.
- Arabidopsis mutant gl1
- Epidermal cell development
- Fatty acid elongase
- Leaf development
- Very-long-chain fatty acids
- Wax analysis