A NOVEL EXPERIMENTAL SYSTEM FOR STUDIES OF PHOTOSYNTHATE TRANSFER IN THE DEVELOPING WHEAT-GRAIN

The aim of this study was to develop a valid and convenient experimental system for exploring photosynthate transfer in the developing wheat grain. Structural characteristics relating to photosynthate transfer and the composition of the endosperm cavity sap were examined during the linear stage of grain development at 25 + 3 d after anthesis. Based on the results of these studies, an experimental system was devised to permit the direct monitoring and manipulation of photosynthate transfer from the endosperm cavity to the storage endosperm. A novel approach was used whereby insertions were made into the endosperm cavity by a needle at the embryo end and a piece of microcapillary tubing at the stigma end of the detached grain. By this means, the experimental solution was delivered into and flowed longitudinally under gravity through the endosperm cavity to exit at the stigma end. The composition of the experimental solution reflected the principal solute concentrations and osmolality of the in vivo endosperm cavity contents. With the introduction of the solution into the cavity, it was found that the viability of grain tissues was maintained for up to 30 h. During a 24 h period both the rate of sucrose uptake and subsequent incorporation into ethanol-insoluble components were shown to reproduce the rate of starch biosynthesis and in vivo grain growth. Moreover, the experimental system effectively reproduced the in vivo pathway of photosynthate transfer from the endosperm cavity via the modified aleurone cells into the endosperm. As a result, this system provides a new approach to study photosynthate transfer in the developing wheat grain.