A new lotus effect..?

Many of us have heard of the lotus effect, the ‘very high water repellence (superhydrophobicity) exhibited by the leaves of the lotus flower (Nelumbo nucifera)’. Less well known – until this item was penned anyway – is another phenomenon that has been identified in the lotus by Philip Matthews and Roger Seymour.

As an aquatic plant, a high degree of water-repellancy may well have important survival value (and may even have been predictable..?). However, equally important is the ability to aerate below-water cells for aerobic respiration, especially those organs surrounded by waterlogged, anoxic sediment, such as anchoring rhizomes. Although well-aerated water contains oxygen and a range of other gases important to plant biology, their concentrations therein are much lower than those in the atmosphere. Any mechanism that can enhance supply of life-sustaining gases to an organism in such an environment will bring major benefits to its owner.

Well, and very much in keeping with the dictum ‘seek and ye shall find’, the University of Adelaide (Australia)-based pair did just that and found something rather remarkable. The duo propose an important role for large, leaf-sited stomata in regulating the pressure, direction and rate of flow of atmosphere-derived air within the extensive system of gas canals that connect rhizomes to petioles to leaves at the water’s surface. The active opening and closing of ‘central plate stomata’ (situated in the centre of the leaf above a gas canal junction, and which are much larger and less dense than those on the leaf blade proper) is hypothesised to regulate convective airflow within the lotus plant. Furthermore, not only does this ventilate the rhizome, but it may also direct rhizome-derived (‘benthic’) CO₂ towards photosynthesis in the leaves.

It would appear that the spirit of Stephen Hales (17–18th century English clergyman and botanical experimenter) lives on, albeit down under! And another – additional – role stomata can play has been raised by María Nores et al. [http:dx.doi.org/10.1111/boj.12009]. Examining the pollination biology of the ‘four o’clock plant’, they propose that stomata are involved in nectar secretion whereby ‘nectar is secreted through modified stomata, accumulating between the base of the stamens and the ovary’. Multi-facetted stomata, not just mediating photosynthesis; clearly earning their accolade as ‘the most important orifice on the planet’.