Water uptake and distribution in non-dormant and dormant wild oat (Avena fatua L.) caryopses

The influence of seed coat modification and light quality on water uptake and distribution in caryopses of dormant and non-dormant lines of wild oat (Avena fatua L.) was determined using NMR microimaging. Non-dormant seeds absorbed water more rapidly than dormant seeds during imbibition on distilled water. This effect was detected first in the embryo-scutellar region (8 h) and later in the proximal endosperm (12 h). Cutting the testa and pericarp close to the embryo or scarification with KOH promoted rapid embryo/scutellum hydration and germination. Cutting at the middle part of the caryopsis did not enhance embryo hydration nor did it greatly improve germination. The sensitivity of water distribution to the phytochrome germination effect was examined. Significant differences in imbibitional water uptake by embryos-scutellum tissue were detected by 18 h following red-light (germination promoter) compared with far-red (germination inhibitor) treatment. The results indicated that both the rate and the sequence of embryo/scutellum hydration were important in initiating germination in dormant seeds. A refinement of the model that describes water imbibition in wild oat seeds during the early stages of germination is discussed.