Assimilate Uptake and Water Loss in Maturing Barley Grains

When detached ears of barley were supplied with [U-14C] sucrose for 4 h, 14C was detected in the endosperms of grains from ears harvested 50 ‘days’ after anthesis, i.e. 10–15 ‘days’ after cell wall modifications had taken place in the chalazal region of the caryopsis. In 55-‘day’ ears which had been supplied with [U-14C] sucrose for 20 h no 14C was detected in the upper part of the rachis or in grains with a moisture content of less than about 25%. In the rachis of wheat and barley, the walls of the xylem parenchyma and phloem cells stain strongly with ruthenium red, and in immature rachides this stainability is lost when sections are incubated with pectinase. Near the apex of 55-‘day’ ears the pectinaceous wall material in the vascular bundles is resistant to digestion by pectinase, and pectic substances, which are removed by pectinase, fill the lumina of the xylem elements. These observations are discussed in relation to the dehydration of the maturing grain.