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

Abstract

In this paper the metabolism of gibberellin and nucleic acid was studied with special reference to the bulbing phenomenon of onion plants.1. Gibberellin-like substances, among which the principal substance was considered to be the gibberellic acid (GA3) from the Rf value, were found in the 80% alcohol extracts obtained from oth the terminal part of buds and the leaf blades of onion plants.Following transfer to long days there was a rapid increase in gibberellin-like substance level to a maximum at about 10th day, being followed by a fall to a value below that of the short day controls.The younger the leaf age, the more the content of gibberellins. This tendency was shown in either plants grown under long or short photoperiod. On 30th day after photoperiod treatment, plants grown under short photoperiod was higher than under long one.2. It was shown that the levels of gibberellinlike substances in the terminal part of buds and in the leaf blades were lower with the increase of daylength on 20th day after various photoperiod treatment.3. When gibberellin was supplied to the plants with the injection method every 5 days, it was shown that the leaves, especially leaf blades, elongated remarkably, resulted in the increase in the ratio of leaf blade length to leaf sheath length under short day, whereas the bulb formation under long day was retarded with the application of higher concentration of gibberellin.4. With the progress of plant growth, the content of RNA and DNA in the terminal part of buds gradually increased under short day, whereas RNA decreased in contrast with the rapid increase in DNA under long day.5. Nucleic acid level was correlated with the increase in daylength, that is, the longer the daylength, the more remarkable the increase in DNA and the decrease in RNA.6. The higher the temperature, the more vigorous the plant growth and the more the increase in RNA and DNA. Consequently the effect of temperature on the bulb formation is different from that of daylength.7. The bulb formation was more promoted in the plants supplied with exogenous kinetin solution than in the plants with water. The higher the concentration of kinetin solution, the more the bulbing was advanced.