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 experiment al 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 t he linear stage of grain development at 25 + 3 d after anthesis. Based on the results of these studies, an experimental system was devised t o permit the direct monitoring and manipulation of photosynthate trans fer from the endosperm cavity to the storage endosperm. A novel approa ch 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 sol ution was delivered into and flowed longitudinally under gravity throu gh the endosperm cavity to exit at the stigma end. The composition of the experimental solution reflected the principal solute concentration s and osmolality of the in vivo endosperm cavity contents. With the in troduction of the solution into the cavity, it was found that the viab ility of grain tissues was maintained for up to 30 h. During a 24 h pe riod both the rate of sucrose uptake and subsequent incorporation into ethanol-insoluble components were shown to reproduce the rate of star ch biosynthesis and in vivo grain growth. Moreover, the experimental s ystem effectively reproduced the in vivo pathway of photosynthate tran sfer from the endosperm cavity via the modified aleurone cells into th e endosperm. As a result, this system provides a new approach to study photosynthate transfer in the developing wheat grain.