Dormancy implications of phosphorus levels in developing caryopses of wild oats (Avena fatua L.)
1997
Quick, W.A. | Xiao, Ai | Hanes, J.A.
The element phosphorus made up 0.5% of the dry weight of dehulled Avena fatua caryopses 7 days after anthesis (DAA), half of it inorganic (Pi). Caryopses detached and pierced 7 DAA germinated in vitro with a rapid drop in Pi levels. By 15-20 DAA caryopsis dry weight had increased three- to fourfold, but phosphorus made up less than 0.04% of the dry weight of this enlarged caryopsis. Caryopses at this stage germinated readily without piercing if incubated in vitro. A further decrease in Pi accompanied by a marked increase in phytate phosphorus began about 15 DAA and continued during later seed maturation. By 20 DAA, when embryos were relatively mature and endosperm cell division had ceased, a decrease in caryopsis water content (as a percentage of dry weight) began, and seed dormancy became apparent. As starch and phytate reserves accumulated, Pi and water levels of the caryopsis diminished. Higher levels of endogenous Pi coincided with the anabolic events of initial seed formation and, to a lesser extent, with anabolic events of seed germination. Decreasing Pi levels coincided with accumulation of nutrient reserves, lowering of water content, and the initiation of dormancy. The data suggest that (1) enzymes associated with the formation and development of the embryo may be activated by the high Pi levels present during initial seed differentiation; (2) embryo quiescence and dormancy are facilitated by the drop of Pi levels which accompanies the accumulation of starch and phytate reserves; and (3) the increase in Pi which accompanies seed afterripening aids in the termination of dormancy and the resumption of germination.
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