The Pathway of Radial Transfer of Photosynthate in Decapitated Stems of Phaseolus vulgaris L.

Abstract

C)Sucrose was found to be the predominant component of the 14C-photosynthates that accumulated in the free space of decapitated stems of P. vulgaris plants. The 14C-photosynthates appeared to occupy the entire free-space volume of the stems at total sugar concentrations in the range of 3-12 mM. The free-space sugar levels were found to rapidly decline once photosynthate transfer to the stems was halted. Moreover, it was found that estimates of the rate of in vitro sucrose uptake by the stems could account fully for the decline in free-space sugar levels. Overall, the evidence indicated that at least part of the radial pathway of photosynthate transfer in bean stems involved the stem apoplast. It is tentatively proposed that, based on cell and tissue distribution of 14C-photosynthates, the apoplastic pathway extends from the membrane boundary of the sieve element/companion-cell complex to all other cells of the stem.