Dormancy of the seeds of leaf mustards. II

Abstract

In the previous paper, the authors reported that the mature seeds of leaf mustards except Negarashi had a kind of dormancy which was gradually broken in 2 or 3 months in dry storage after harvesting, or could be easily broken by the low temperature (0-5°C) treatment extending only three days even when the dormancy was deepest.
Besides the low temperature treatment, several other methods or reagents effective in breaking dormancy were investigated, and the following results were obtained.
1) The seed coats were observed to be permeable to water, and the radicles started their growth immediately when the swollen seed coats were removed carefully. The germination was also made possible by injuring seed coats, but was slower and less uniform.
2) Katsuona seeds at the middle stage of dormancy germinated well when washed by the running water for 6 hours or more, but could not germinate when merely soaked in water for 20 hours or more.
3) Germination of dormant seeds was not obtained by increasing concentration of oxygen, or of both oxygen and carbon dioxide simultaneously.
4) Thiourea, which is known to break dormancy of lettuce seeds and potato tubers, was also effective in leaf mustard seeds, and its effective cocentration in our method was 0.5 to 1% at the middle stage of dormancy.
Urea was almost as effective as thiourea and its effective concentration was wider, that is, 0.01 to 1%, but 0.1% was less effective than the higher and lower concentrations.
5) The effect of thiocyanates was not decisive, while some amino compounds, such as alanine and arginine were as effective as urea in 0.02 to 0.5% concentrations, and ammonia was also effective in 0.005 to 0.5% concentrations.
Nitrates and ammonium salts had no decisive effect.
The possibility that amino compounds were effective through ammonia produced in their hydrolysis was seemed to be scarce.
6) The mechanism of the dormancy was discussed. There seemed to be much possiblity that there is any inhibiting substance in the seed coats, though it cannot be known whether it affects physical properties of seed coats or affects embryo directly. The physical properties of the seed coats are difficult to measure and their direct participation in the mechanism of dormancy cannot be denied by our simple experiments.