No abstract

Kernels of 4 barley cultivars were germinated at 18°C and samples were removed for analysis at short time intervals for the first 30 h and at longer intervals during the ensuing 90 h. o-Amyiase,(1 ■;!)(! 4)-/J-glucanose and (1 -> 3) 0-glucanase activities were measured in each sample. Analysis of kernel sections stained with Calcofluor showed that hydrolysis of /j-glucan in the crushed cell layer commenced 6-9 h after the initiation of germination. Hydrolysis proceeded from the ventral adge to the dorsal edge of the kernel. Starch granule hydrolysis followed a similar pattern in the endosperm region adjacent to the crushed cell layer, but starch hydrolysis was always preceded by 0-glucan hydrolysis.

No abstract

The anatomy of the husk (lemma and palea) and caryopsis coat (pericarp, seed coat or testa, and nucellar epidermis) of a typical mature wild oat (Avena fatua L.) caryopsis was investigated using both scanning electron microscopy and light microscopy. Both the lemma and palea consist of very thick-walled, lignified cells. In section, the lemma appears almost twice as thick as the palea. The pericarp is comprised of only one or two layers of relatively thin-walled cells and is closely appressed to the underlying seed coat over most of the grain. Both the outer seed-coat cuticle and the inner cuticle are present over almost the entire caryopsis and are continuous with the pigment strand that occurs deep in the crease region of the grain. The only discontinuities in the seed coat are at the basal end of the grain near the embryo. In the dorsal region of the caryopsis, the outer cuticle is approximately 3.5 μm in thickness, whereas the inner cuticle is less than 1 μm in thickness. Where the two pass over the embryo they are much thinner, with the inner cuticle becoming almost indistinguishable in places. The remains of the nucellar epidermis are tightly amalgamated to the seed coat and outer tangential walls of the underlying aleurone cells, which are clearly distinguishable by their large size and characteristic appearance.

Shortly after anthesis, empty endosperm cells adjacent to the embryo were crushed between the developing embryo and endosperm tissues to form the crushed cell layer. Starch granules in cells adjacent to this layer were hydrolysed and the empty cells were added to the crushed layer. In this way, the crushed layer increased in thickness throughout kernel development. a-Amylase 2 was detected in the crushed cell layer region of barley endosperms during the period that starch granule hydrolysis was occurring.