Physiological studies on the bulbing and dormancy of onion plant. VIII.

Relations between dormancy and organic constituents of bulbs

Abstract

Changes in metabolic activity of carbohydrates, nitrogen compounds, auxins and gibberellins in bulbs during storage were investigated in relation to the dormancy of onion bulbs.
1. It was found that both carbohydrates and nitrogen compounds from the outer thickened leaf base were decomposed into available forms, translocated to the inner thickened leaf base and accumulated there in succession.
The growth of foliage leaf primordia resumed under the consumption of carbohydrates and synthesis of insoluble nitrogen compounds.
It was also proved by the acceleration of sprouting with favorable temperature and wet treatment.
2. Concentrations of carbohydrates and nitrogen compounds in bulbs did not relate with the size of bulbs, but related with the cultural conditions. Bulbs grown in the shade or without additional application of nitrogen fertilizer were smaller in size and lower in carbohydrate concentration than those grown in the full light intensity or with nitrogen application.
3. Concentrations of carbohydrates in the thickened leaf base were slightly lower in early topprostrated bulbs than in late ones, but little difference in concentration of nitrogen compounds was found at harvest time in both.
4. Auxin content in the terminal part of buds gradually decreased with thickening of bulbs and further continued to decrease after harvest, resulted in the lowest value on Aug. 26. Thereafter it began to increase.
On the contrary, content of inhibiting substances in Rf 0.8-1.0 zone showed the highest value at the time of harvest and then gradually decreased during storage at room temperature, but a few quantities of them was recognized even after sprouting.
5. Larger amount of auxin was found in early sprouted bulbs in phytotron than in unsprouted at room temperature, whereas against our expectation the inhibiting substances did not decrease so much even in sprouted bulbs.
6. Auxin content in the terminal part of bud did not relate with the size of bulbs, but related with the time of top-prostration. These results suggested that auxin content correlates with the stage of bulbs.
7. Gibberellin-like substances were not found in bulbs during rest period, but they appeared in bulbs sampled on Aug. 26 and remarkably increased after sprouting.
8. From the above-mentioned results, it may be concluded that the dormancy of onion bulbs closely correlates with the carbohydrate metabolism of bulbs.