Studies on the bulb formation in onion plants. III

Effects of plant growth regulators on the swelling of sheaths

Abstract

This work was conducted to see the effects the plant growth regulators on the bulbing and to clarify the relationship between these chemicals and the bulbing using young onion plants, mainly var. Kaizuka-Wase.
1. The six growth regulators, such as IAA, NAA, 2, 4-D, kinetin, TIBA, and MH were foliar supplied under short-day condition.
The only MH in excess of 500ppm exerted swelling of basal sheaths, which resulted in increase of parenchyma cellsize, although other five chemicals were found to have no effect on the swelling at any concentration.
Moreover, the higher the concentration of MH, the more the sheath swelled, MH-induced swelling was followed by increase in sugar content in leafsheaths and blades, both their leaves and their roots ceased to develop soon after treatment of MH, then increased the ratio of top weight to root weight.
Above mentioned phenomema which induced by MH were similar to those induced by long days, and effects of MH were expressed as a substitution for long-day effect under non-inductive condition.
From these results, it assumed that MH-iuduced swelling mainly will be caused by inhibition of meristematic activity in the bud, and secondly by accumulation of sugar in the sheaths.
2. However, it was possible to induce bulb formation by exposing the plants for several days to the long-day condition, when onion plants were exposed to long day and sprayed with 2, 4-D in excess of 20ppm, the bulb formation was inhibited. Moreover, the higher the concentration of 2, 4-D supplied, the less the sheaths swelled, followed by increase of length of leaf-sheath.
And also inhibition of bulb-formation resulted in decrease of size of parenchyma cell.
Onion plants being exposed to long days (24hr per day) for 5, 7 and 9, were treated with 2, 4-D of 200ppm, and followed by short days.
However, the bulb-formation were inhibited, the longer the exposure to long day, the more the sheaths swelled.
But, in the case of shorter exposure, the onion plants did not form the bulb.