Water Relations of the Banana. I. Predicting the Water Relations of the Field-Grown Banana Using the Exuding Latex

Abstract

The free exudation of latex from wounded banana plants renders conventional methods for studying water potential impracticable or suspect. Accordingly, several methods have been devised to provide supportive semi-quantitative data on water relations including measurements of leaf angle, tissue turgor and pseudostem girth throughout many diurnal cycles.

Latex exudation itself has been exploited in a new technique for investigating the internal water relations of the banana. The laticifers behave like giant unbranched cells embedded deeply within the tissues of the plant. On wounding, the milky sap escapes at a rate which decreased exponentially. We argue that, as a consequence of pressure-release, the latex is diluted by water influx until equilibrium is reached with the rest of the plant. Hence at equilibrium, the osmotic potential of this diluted latex equals the water potential of the tissues; thus the final osmotic potential can be used to monitor water potential changes of banana tissues. In this study, the water potential of well-watered plants was found to cycle diurnally within the remarkably narrow range of 0 to -0.35 MPa (0 to -3.5 bar). Turgor pressures of intact laticifers were computed from our data, which also exhibit the diurnal fluctuations predictable from our supportive data and reports for other species.