ATP in Sieve Tube Sap from Willow

Abstract

HYPOTHESES explaining the mechanism of longitudinal sieve tube transport in higher plants can be divided into two groups. First there are the hypotheses, typified by the pressure flow hypothesis of Münch¹, in which energy for the transport process need only be applied at either end of the transport system, the sieve tubes themselves being metabolically inert. On the other hand, hypotheses such as the electro-osmotic mechanism proposed by Spanner², or the transcellular streaming hypothesis of Thaine³, would require a continuous expenditure of energy throughout the whole length of the sieve tubes. Ultra-structural studies on phloem have as yet failed to produce any unanimity as to the metabolic capabilities of sieve elements^4,5.