© 1992 Oxford University Press
RESEARCH-ARTICLE |
Phytochrome–induced Germination, Endosperm Softening and Embryo Growth Potential in Datura ferox Seeds: Sensitivity to Low Water Potential and Time to Escape to FR Reversal
IFEVA, Depto de Ecologia,Facultad de Agronomia U.B.A Avda San Martin 4453, 1417 Buenos, Argentna
1To whom correspondence should be addressed.
In Datura ferox seeds, the far-red absorbing form of phytochrome (Pfr) induces endosperm softening, larger embryo growthpotential, and germination. We investigated the effect of exposing the seeds to a range of water potentials in the presence of Pfron its induction of these responses. In addition, the escape time to far-red-light (FR) reversal of the three responses wasdetermined.
Low water potential inhibited Pfr action on endosperm softening and germination in a similar way. In both cases, a 50% reduction in the response to a saturating red-light (R) irradiation was observed at a water potential of c. —0·5 MPa and therewas very good correlation between the percentage number of seeds with softened endosperm at 45 h after R and germination at 72 h after R (R2=0·95). In contrast, the effect of decreasing the external water potential on Pfr induction of a larger embryogrowth potential was more complex. Moderate decreases in water potential (—0·3 to —0·5 MPa) enhanced Pfr action and thegrowth potential of the embryos was larger (20—25%) than the water controls; water potentials below —0·7 MPa inhibited the Pfr stimulus.
The escape time to FR reversal of the R effect was shorter for the increase in embryo growth potential than for endospermsoftening. Twenty-four h after R, the embryo response had escaped in more than 80% of the population whereas endospermsoftening and germination were susceptible to FR inhibition in 100% of the seeds.
These results indicate that in D. ferox seeds the increase in embryo growth potential is not sufficient for germination and thatendosperm softening is a necessary condition.
Key words: Germination, dormancy, phytochrome, endosperm softening, water potential
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