Diagnosis of water transport in a plant by plant excision method.

Abstract

A plant excision method (PEM) was used for diagnosis and understanding of the characteristics of water transport in napiergrass (Pennisetum purpureum Schumach.) and maize (Zea mays L.). During measurement of the time courses of photosynthetic rate and stomatal conductance in a leaf, a temporary, quick increase in these parameters were frequently observed directly after excising the basal part of the leaf. The response of the parameters after excision of different parts of a plant was used here as an indicator for diagnosing water transport situations through a plant. In napiergrass a large increase was frequently observed when a leaf sheath was excised, but it was not detected on excising the stem part below the node having the leaf sheath. This shows that the water flow from stem, node to leaf in this species was greatly regulated by node, by which excessive transpiration from leaves was possible to be restricted. Using a pressure flow meter, the water transporting characteristics through a node were evaluated on the three divided parts; the hydraulic resistance of adaxial (to the stem apex) and abaxial (to the leaf) directions of node, and an internode in the stem. Of these parts, the water flow resistance was highest in the abaxial direction in node. The measurement results obtained by the PEM and the pressure flow meter on both plant species grown under various environmental conditions showed a good agreement with each other, and demonstrated that the hydraulic resistance through maize stem was significantly lower than that of napiergrass.