Originally Posted by Nicolas Naranja

I just read over this:

The laminae of banana leaves fold in response to environmental stimuli.

This movement does not reflect wilting of the leaf because if the leaf is excised and inverted, the laminae do not flop apart.

These leaf movements are due to differential turgor of cells within the pulvinar bands caused by water movement accompanying ion movements (Satter, 1979; W. Robertson, unpublished data).

The folding of banana leaves typically follows a diurnal rhythm with the leaves more horizontal during the night, and early morning, becoming more vertical during periods of bright sunlight, and returning to more horizontal positions in late afternoon.

These changes in turgor within the cells of the pulvinar bands are similar to changes in stomatal aperture that is controlled by the turgor of guard cells.

In addition, the laminae of banana leaves fold in response to soil drought (Milburn et al., 1990; Thomas and Turner, 1998; Turner and Thomas, 1998) suggesting leaf folding may reflect leaf water status, albeit somewhat unreliably.

However, Lu et al. (2002) did not find any link between leaf folding and soil water deficit.

Lu et al. (2002) measured water use of banana plants using a sap flow system calibrated against gravimetrically determined water loss.

This system measured water use by insertion of heat sensing probes into the central cylinder of the banana corm that conducts water from the root system to the shoot.

It is a widely used technique to measure water use of trees, and has the advantage over other systems that measure whole plant water use in that the water sensing unit (typically heat based) is localized thus causing less damage to the plant being measured and hence greater reliability of data.

Alternate systems can overheat and greatly damage or kill banana plants thus rendering measurements useless (D.S. Thomas, unpublished data).