Water Relations of the Banana. II. Physicochemical Aspects of the Latex and Other Tissue Fluids.

Abstract

The water potential and various physical and chemical aspects of latex and other tissue fluids of banana plants were investigated. Fluids including guttation fluid, phloem sap, nectar and expressed leaf sap, were compared with exuding latex to understand their relationships. The relationships between the refractive index and solute potential of the latex from both glasshouse-grown and plantation-grown plants were compared and found to be significantly different.

Latex was analysed for the major chemical constituents contributing to the solute potential. K⁺, Mg²⁺, Na⁺ and Ca²⁺ and Cl^-, SO^2-₄ and PO^2-₄ were assayed. Of these, K⁺, Mg²⁺, Cl^- and NO^-₃ were the major contributors to the solute potential. During exudation the concentration of the above ions declined. However they only partially explain the measured changes in refractive differences; the cause of this is discussed.

The sources of error in determining the water potential of the banana from the solute potential of the latex are discussed. The use of refractometer as a tool for field determination of banana water potential is also substantiated.