LIGHT ENVIRONMENT, PHYTOCHROME AND GERMINATION OF DATURA-STRAMONIUM L. SEEDS

The role in germination of the maternal pre-existing far-red absorbing form of phytochrome (Pfr) was studied in seeds harvested at different developmental stages. Datura stramonium seeds acquired marked dormanc y in the later ripening stages, independently of phytochrome phototran sformation. However, the balance between stimulators, such as Pfr, and inhibitors (probably abscissic acid and/or phenolic substances) in th e stage prior to complete dehydration appeared to play a crucial role in the degree of progeny dormancy. Enrichment of the far-red (FR) wave length (simulated canopy light) induced light-dependent dormancy if st age IV progeny were incubated in darkness in suboptimal conditions. In contrast, natural storage of seeds in soil led to a uniform degree of dormancy. An increase in photosensitivity owing to storage in soil ap peared to be linked to simultaneous loss of inhibitors. It should be n oted, however, that this extreme sensitivity to very low Pfr levels (7 24 nm monochromatic light pulse) was acquired only by seeds stored dee p in the soil (typical very low fluence response). It is postulated th at these reactions are induced by an elevated quantity of phytochrome typical of etiolated tissue, in conditions of near-absence of inhibito rs. (C) 1997 Elsevier Science B.V.