Master of Arts (MA)
Faculty of Arts and Sciences
To minimize water loss, the aerial parts of vascular land plants are covered with a hydrophobic layer called a cuticle. The cuticle typically consists of two major components: cutin and waxes. In contrast to vascular plants, research reports indicate that some primitive nonvascular plants, such as mosses, lack a cuticle. This study attempts to reconcile contradictory literature reports about the presence of a waxy cuticle on the leaves of the moss Physcomitrella patens.
Histochemical staining was utilized to investigate the presence of a cuticle on Physcomitrella leaves. Experiments employing dyes that stain hydrophobic substances were generally consistent with the presence of a cuticle. Hydrophilic dyes were also used to infer the presence of a cuticle through an absence of staining. Histochemical results were supported by observations made using freeze fracture electron microscopy. Leaves consistently fractured through an extracellular layer having a rippled texture, which resembling cuticles known to occur in vascular plants. Attempts to isolate a cuticle from Physcomitrella leaves by partial digestion with chromic acid or treatment with polysaccharide-degrading enzymes were also successful.
The existence of a cuticle on the leaves of Physcomitrella is further supported by genetic observations. The P. patens genome contains several genes that are homologous genes known to participate in cuticle synthesis in vascular plants. One of these, the homolog of the Solanum lycopersicum CD1 gene (SlCD1), may participate in cutin biosynthesis and was selected for further characterization. Using homologous recombination, knockouts of Physcomitrella samples deficient in the homolog CD1 were generated (PpCD1KO). Unfortunately, knockouts showed no changes in phenotype and may indicate the presence of a cuticle, supported by other genes with similar catalytic functions.
Ricci, Eric John, "Investigating the Leaf Cuticle of the Moss Physcomitrella Patens" (2013). Master's Theses, Dissertations, Graduate Research and Major Papers Overview. 62.
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