Chemistry and genetics of plant cuticle function as a permeability barrier
Abstract
The plant cuticle is a lipidic heterogeneous polymer layer covering the epidermis of all aerial plant tissues. The research described here examines associations between lipid composition and cuticle permeability. Involvement of the cuticle in Snapdragon floral volatile emission demonstrated methylbenzoate emission followed closely internal methylbenzoate levels, but not petal cuticular wax amount and composition, or cuticle thickness and ultrastructure suggesting petal cuticle provides little diffusive resistance to floral volatiles. Post-harvest water loss rate of various pepper cultivars was found to be associated with cell membrane ion leakage, lipoxygenase activity, and total cuticular wax amount. But total cuticle amount (cutin and cuticular waxes), total cutin monomer amount, cutin monomer composition, and cuticular wax composition did not correlate with post-harvest water loss. To examine interactions between various genes involved in cuticular wax biosynthesis, fourteen double mutants were created from eleven eceriferum mutants. Stem wax analysis of these double mutants revealed little epistasis and complex interactions suggesting significant redundancy in wax metabolism as well as raising the possibility that some CER genes function in more than one step in wax biosynthesis. An Arabidopsis mutant, wax2, exhibited reduced waxes and cuticle membrane, cuticle ultrastructure disruption, reduced fertility, increased epidermal permeability, and reduced stomatal index. The N-terminal portion of the predicted WAX2 protein has homology with sterol desaturases while the C-terminal portion has homology with short-chain dehydrogenases/reductases, providing evidence WAX2 may have a metabolic function in both wax and cuticle membrane synthesis. An Arabidopsis mutant, designated att1, was identified as having increased susceptibility to a virulent Pseudomonas syringae strain. ATT1 encodes the cytochrome P450 monooxygenase CYP86A2 and the att1 mutant exhibits a 70% reduction in cutin monomer amount, altered cuticle ultrastructure and elevated water loss demonstrating CYP86A2 plays a role in cutin biosynthesis. Another Arabidopsis mutant, designated rst1 , exhibited a reduced wax amount on both stems and leaves and a seed abortion phenotype where 70% of seeds are shrunken due to embryo abortion at the heart stage. Seed storage lipids of shrunken seeds are only 34% of wild-type seeds and have altered lipid composition. RST1 encodes a novel protein of unknown function.
Degree
Ph.D.
Advisors
Jenks, Purdue University.
Subject Area
Horticulture|Plant sciences|Botany
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