MRes project: Oonah Lessware

Most plants surfaces are water-repellent; some, like the lotus leaf, famously so. The collar-shaped, micro-textured trap rim of carnivorous Nepenthes pitcher plants is a remarkable exception to this rule. Guided by an intricate ridge pattern, water spreads rapidly on this surface and forms a thin, stable film. This causes insects to slip, like a car tyre aquaplaning on a wet road. While the effects of the rim surface on insect adhesion and locomotion are well documented, virtually nothing is known about how the rim surface is formed. We investigate the development of the pitcher rim and its genetic regulation for the first time.

 

Development of a new Nepenthes pitcher. Pitcher plants are climbers and each new leaf emerges from the previous leaf sheath at the top of the climbing shoot. The leaf blade (LL = leaf length and LW = leaf width) and climbing tendril (TL = tendril length) are first to grow. Only after the new leaf opens, the pitcher bud at the tip of the tendril starts to first elongate, then swell, fill with fluid, and finally break open (PL = pitcher length; PD = pitcher depth; PW = pitcher width).

The epidermis of most leaves is composed of flat or slightly convex pavement cells forming a jigsaw-like pattern. The surface of the pitcher rim is in stark contrast to this: a hierarchical micro-topography of radial ridges and grooves, with the smaller microscopic grooves further sectioned by acute-angled overhanging arches. Using scanning electron microscopy (SEM), we have identified a series of sequential growth processes during rim surface development. We use state-of-the-art transcriptome analyses to identify candidate genes for the regulation of each of these processes, and newly developed transient transformation techniques to verify the function of these candidates. By unravelling the secret behind the formation of wetness-activated slippery plant surfaces, we hope to develop novel approaches to pesticide-free crop protection.

The wetness-activated slippery surface of the pitcher rim is characterised by an intricate micro-pattern of parallel ridges and grooves, on two distinct length scales. The microscopic grooves provide capillarity, causing water to spread rapidly along their length. Overlapping arched ‘steps’ inside the smaller-scale grooves facilitate water transport against gravity, towards the pitcher outside.