Direct Measurements of Cell Turgor and Hydraulic Conductance in Expanding Tulip Tepals

Abstract

The present study was undertaken to clarify the relationship between tepal growth and the hydraulic properties of expanding tulip (Tulipa gesneriana L.) tepals. The growth rate of outer tepals was measured with an extensiometer while growth of the tepals was altered by feeding sucrose solution or trehalose solution to cut tulip flowers. Feeding sucrose to the flowers increased cell elongation rates of tepals and feeding trehalose to the flowers decreased the cell elongation rates. Simultaneously, turgor of the epidermal cells in the zone of elongation of intact outer tepals was measured with a cell pressure probe. Cell osmotic potentials were measured with the isopiestic psychrometer after extracting cell solution of similarly treated cut flowers. Cell water potential was obtained by summing cell turgor and its osmotic potential. When the hydraulic conductance of intact growing tepal tissues was calculated by dividing the growth-induced water potentials by the relative growth rates at the steady states, it was found that the hydraulic conductance was significantly decreased by trehalose feeding. Therefore, it was thought that changes in the hydraulic conductance were responsible for rapid changes in growth rates in tulip tepals when components in the vase solution were modified in cut tulip flowers.