Variation in Endogenous Concentration of Abscisic Acid, Gibberellic Acid, Zeatin and 3-Indoleacetic Acid during Cold Storage in Bulbs of Lily (Lilium ‘Siberia’)

Dormancy in lily (Lilium sp.) bulbs is broken by a cold period of several weeks. Sprouting percentage, growth and flower quality are reduced when bulbs are partially released from dormancy. To understand the involvement of phytohormones in dormancy release in lily bulbs, the concentration of endogenous abscisic acid (ABA), gibberellic acid (GA3), zeatin (ZT) and 3-indoleacetic acid (IAA) was examined in the primary shoot, outer scale and root of bulbs of Oriental hybrid Lilium ‘Siberia’ during the dormancy release period. Cold treatment (4 °C) enhanced ABA, GA3 and ZT concentration in the primary shoot. GA3, ZT and ABA reached their maximum levels on the 14th, 49th and 63rd days of cold storage, respectively. IAA concentration remained at a constant level in the primary shoot of bulbs at 4 °C up to 21 d. Thereafter, it increased gradually up to the maximum level on the 84th day. In the outer scale of the bulbs, GA3 increased dramatically on the 7th day, then declined till the end of the 4 °C treatment. In the root, GA3 was at a higher level in the bulbs at 4 °C than at 25 °C treatment before 42 d. The ratios of phytohormone that promote plant growth to phytohormone that inhibit plant growth were higher in the outer scale of the bulbs at 4 °C than those at 25 °C treatment before 42 d. The ratios were lower in the primary shoot of the bulbs after 42 d of the 4 °C treatment than those at 25 °C. In conclusion, cold treatment enhanced ABA, GA3 and ZT concentration and effectively regulated IAA concentration to reach the maximum level at the end of dormancy release period in the primary shoot of bulbs under 4 °C treatment. Apparently, changes in ABA and GA3 concentration differ in the primary shoot, outer scale and root of the bulbs of lily. These changes act as multipurpose signals in the control of bulb dormancy release in the different tissues of the bulb and during the different stages of bulb development. Apparently, there is a relationship between ABA and IAA concentration and bulb sprouting. Key Words: bulb, dormancy, Lilium sp., phytohormone