There are more similarities between plants and humans than we give credit for. Introducing the concept of incontinence in plants!
Leaves are the key parts of a plant which carry out the important act of water exchange with the environment. This being so, how effectively a plant can use water depends on how the easily water vapour gets from inside the leaf through the cuticle (the covering cell layer on the surface of a leaf) to the outside.
Greg Jordan and Tim Brodribb of the School of Plant Science, University of Tasmania have been studying the physiology of plant leaves for some time now and in 2007 published a paper in the scientific journal Functional Plant Biology on an interesting finding that the leaves of Agastachys odorata (Frangrant Candlebush or White Waratah) actually become incontinent with age.
Agastachys odorata is an endemic plant of the Protea family (Proteaceae) and occurs commonly in the high rainfall western Tasmania. The leaves of A. odorata exhibit distinctive annual growth increments, making different aged leaves easy to tell apart. The leaves are also very long-lived, with evidence of some leaves remaining on plants for up to 21 years. This makes A. odorata a fabulous choice for studying plant water relations with regards to leaf age.
Greg and Tim wanted to test the hypothesis that water vapour leaks across plant cuticles more readily as plant leaves age. In A. odorata they found that the older leaves were less effective in controlling water loss and hence used water less effectively than younger leaves. The increasing permeability of the leaf cuticle is implicated as the cause for this but it is also likely that the ability to control stomata opening also decreases with age, much akin to poor urinary sphincter muscle control in sufferers of incontinence. Greg and Tim concluded that the decreasing ability to use water efficiently could be due to natural leaf damage that occurs throughout the life of the leaf.
When the leaves of A. odorata becomes too old, it is simply shed. After all, the plant has no lack of leaves to serve it’s physiological functions. If only humans had the luxury of replaceable urinary sphincter muscles.