Accumulation of label from radioactive precursors into dry matter by wheat endosperm cultured in vitro

The capacity of in vitro cultured common wheat ( Triticum aestivum L.) endosperms to incorporate starch and protein precursors was investigated. Isolated 2–3 week-old endosperms were cultured up to 2 weeks in a liquid medium containing labelled (¹⁴C)-sucrose and (³H)-glutamine. Cultured endosperms were separated into ethanolsoluble, starch and protein fractions and the incorporation of the label into each of these fractions was assessed at different times after commencement of culture. The same medium was introduced through the peduncle into normally-developing grains, which were then similarly analyzed. Accumulation of both ¹⁴C and ³H in the ethanol-soluble fraction occurred, at a decreasing rate, only during the first 3 days, and then ceased. The accumulated label in the starch fraction, which originated mainly as ¹⁴C sucrose, proceeded at a relatively constant rate for one week and reached only about 1/5 of the expected in vivo starch production. Incorporation of both isotopes into the protein fraction reflected similar utilization of sucrose and glutamine from the medium (molar base), decreasing in rate with time. Culturing beyond one week produced deteriorated endosperms. Compared to cultured endosperms, normally-developing grains incorporated proportionally less precursors into the ethanol-soluble and more into the insoluble fraction. It is suggested that the reduced starch and protein synthesis in cultured grains stems from impaired capacity of the biosynthetic machinery rather than from low availability of precursors.