Photocontrol of the germination of onoclea spores: v. Analysis of germination processes by means of temperature

Photoinduced Seed Germination of Oenothera biennis L: III. Analysis of the Postinduction Period by Means of Temperature

The postinduction period of Oenothera biennis L. seed germination was examined by temperature treatments. For all experiments, seeds received a standard 24 hour/24 degrees C preinduction period and 12 hour/32 degrees C photoinduction period. Germination is inhibited by postinduction temperatures above 32 degrees C. When seeds are briefly incubated at 44 degrees C and then transferred to 28 degrees C, they germinate at a much lower percentage than 28 degrees C controls. When thermally inhibited seeds are placed in the dark at 28 degrees C for 20 hours, they can be promoted to germinate by a single pulse of red light. Seeds incubated at 12 degrees C or below immediately after photoinduction enter a lag period in which they germinate slowly or not at all for a long time and then resume germination. The length of the lag period is exponentially related to the postinduction temperature. When seeds are incubated at a low temperature and then transferred to a warm temperature, they germinate much more rapidly than seeds not incubated at a low temperature. A model is proposed which is consistent with these and additional results. In the model, a germination promoter is irreversibly formed from a precursor and the synthesis of the precursor is favored at low temperatures and its degradation is favored at high temperatures.

Photoinduced Seed Germination of Oenothera biennis L: II. Analysis of the Photoinduction Period

The photoinduction period of Oenothera biennis L. seed germination was analyzed by varying the photoinduction temperature and by substituting red light pulses for continuous red light. At 24 degrees C, seeds require 36 hours of continuous red light for maximal percent germination. The optimal photoinduction temperature is 32 degrees C, with higher and lower temperatures being strongly inhibitory. A 30 minute exposure to far-red light, given immediately after a red light period of 1 to 36 hours, reduces germination by about 25%. Seeds escape from far-red inhibition with a half-time of 5 to 10 hours, depending on the length of the red exposure that precedes the far-red light. Periodic 15 minute pulses of red light can substitute for continuous red light in stimulating germination. Ted red light pulses, with 6 hours of darkness between successive pulses, cause maximal germination. The response to periodic red light is fully reversible by far-red light. Probit analysis of the periodic light response shows that as the length of the dark periods between successive pulses increases, less incident light is needed to induce germination but the population variance in light sensitivity remains constant. Probit analysis of the temperature response shows that as the photoinduction temperature increases from 16 to 32 degrees C, less incident light is needed to induce germination and the population variance in light sensitivity also increases.

Factors Influencing Spore Germination and Early Gametophyte Development in Anemia mexicana and Anemia phyllitidis

Spores of Anemia mexicana Klotzsch and Anemia phyllitidis (L.) Swartz were tested comparatively to investigate the effects of various treatments on spore germination and early gametophyte development in light and darkness. The optimum pH for induction of spore germination is approximately 6. Both species have a minimum 8 hour light insensitive preinduction phase for spore germination. An additional 8 to 12 hours of light are needed to induce 50% germination in A. phyllitidis while at least 24 hours of light are needed for A. mexicana spores. A. phyllitidis has greater sensitivity to the four gibberellic acids tested (GA(3), GA(4), GA(7), and GA(13)) than A. mexicana for induction of spore germination in darkness. In both species the greatest response was observed with GA(4) and GA(7). GA(13) was clearly the least effective. Gametophytes of each species are 100 times more sensitive to their own antheridiogen than to the antheridiogen of the other species. AMO-1618 (1 millimolar), fenarimol (1 mm), and ancymidol (0.1 mm) had essentially no effect on light-induced germination. The latter two did, however, inhibit gametophyte development.

Phase-sequence of redroot pigweed seed germination responses to ethylene and other stimuli

Phase-sequence studies showed that light, ethylene, and high temperature each enhanced germination of redroot pigweed (Amaranthus retroflexus L.) seeds when given during the first 24 hours of seed imbibition. Responses were maximal during the first 12 hours. After 48 hours all three stimuli given together caused 75% germination but each alone was ineffective. The main influence of water potential on seed germination occurred at about 24 hours, but the influence of CO(2) extended into the second and third days. Germination was reduced by water stress (-4 bars) or CO(2)-free air, but ethylene reversed the reduction even when administered after several days incubation. This suggested that environmental and hormonal factors affected redroot pigweed seeds at two distinct stages in the sequence of germination events.