Physiology in seed germination of Amaranthus hypochondriacus known both as ornamental and summer vegetable crops was studied in relation to the effect of either ethephon(ethylenegenerating agent), red light alone or combination of ethephon plus red light on light-inhibited germination of these seeds comparing with those normally germinating in the dark. The experimental results from the present studies are briefed as in the following compendia;
1. Although the seed germination did not take place in 24 hours when done at 25℃ in the light, and the light inhibition was greater as light intensity increased. 5,000lux of the light caused what is called photodormancy which indicated a strong suppressive action of light in the seed germination.
2. In the consideration of 24-hour period of the seed germination, at least 15-hour dark period was necessary for the starting, 6-hour dark period still inhibited the germination, while 3-hour dark period brought about a photodormancy of the seed. Considering the 24-hour period for the seed germination time, later dark treatment showed greater rate of the germination than the earlier, indicating the fact that the light suppression takes place in a later stage of the 24-hour period.
3. Ethephon treatment at relatively higher concentration level resulted in greater seed germination in the light where otherwise no germination occurs. The ethephon, however, inhibited elongation of hypocotyls more so with the higher level. The ethylene was supposed to increase respiration activity of the seed, yet inhibited the cell elongation.
4. Dark and ethephon plus red light treatment as related to temperature caused faster and much increased percent of germination, suggesting that higher temperature favors increasing respiration level. Lighting caused seeds to be dormant, and a high temperature at 30℃ resulted in rather delayed germination. Although the treatment of either red light or ethephon alone made seeds to germinate faster and more when the higher temperature was provided. Combined treatment between ethephon and red light demonstrated greater level of germination than treated with either ethephon in the light or red light alone. The combined treatment showed almost similar rate of germination to the dark.
5. Fresh and dry weight of seeds showed almost no apparent change in 6 hours after imbibition, whereas seeds in the dark and either ethephon in the light, red light alone, or the combination exhibited obvious increase in water uptake which in turn caused an increase in fresh weight of seeds, although the dry weight was reduced perhaps due to the consumption of stored food materials during the respiration process.
6. Even if three different stages of the seed germination were noticed, water uptake throughout the stages kept relatively steady in the light, whereas it showed an abrupt increase when the germination allowed in the dark. This light inhibition, in the photodormant state, was reversed by the introduction of ethephon. Other than the light, red light also exhibited the similar effect of promoting germination of seeds nearly to what the dark did.
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