New method for quantitative determination of water potential of mesophyll cells’ apoplast in substomatal cavity of the leaf

A new method for quantitative determination of water potential of mesophyll cells’ apoplast in substomatal cavity of the leaves of herbaceous (maize, millet, wheat, amaranth, and seepweed) and woody (larch, pine, and birch) plants by means of modern instruments designed to assess photosynthetic(СО2/Н2О) gas exchange is described. The method consists in determination in the light of such a level of humidity above the leaf surface, which would nullify transpiration without a noticeable suppression of photosynthetic assimilation of СО2; this makes it possible to calculate the value of water potential at the interface between aqueous and gaseous phases of mesophyll cells’ apoplast in the substomatal cavity.