Pollination and CPPU Treatment Increase Endogenous IAA and Decrease Endogenous ABA in Muskmelons during Early Development

Abstract

An investigation was conducted to determine how pollination and CPPU treatment influence endogenous IAA and ABA content in netted muskmelon [Cucumis melo L. (Reticulatus Group) `Crest Earl's'], and to clarify their roles in fruit set and development in relation to these endogenous plant hormones. CPPU treatment at anthesis significantly increased the fresh weight of ovaries, whether the flowers were pollinated or not, but from 6 days after anthesis (DAA) the growth rate in the nonpollinated + CPPU treatment tended to be lower than the growth rates in the pollination treatment plots. Ovaries of nonpollinated flowers not treated with CPPU failed to grow and turned brown within 4 DAA. IAA content in the placenta of fruit from pollinated flowers increased rapidly from the day of anthesis to 2 DAA and remained at relatively high levels. IAA content in the placenta of parthenocarpic fruit induced to develop by CPPU treatment was lower than that of fruit from pollinated flowers but the pattern was almost the same as that in fruit of pollinated flowers. Conversely, IAA content in the placenta of fruit from nonpollinated flowers not treated with CPPU decreased sharply after anthesis. IAA content in the mesocarp of CPPU-treated fruit, whether or not the flowers were pollinated, increased significantly from the day of anthesis to 2 DAA, then decreased to almost the same level as that of the pollination-only treatment by 10 DAA, while the IAA content of nonpollinated CPPU-treated fruit declined even further. IAA content in the mesocarp of fruit from nonpollinated flowers not treated with CPPU decreased sharply. ABA contents in both the placenta and mesocarp of muskmelon that would set decreased after anthesis while the ABA content of muskmelon that would not set increased rapidly. Results suggest that pollination and CPPU treatment increased endogenous IAA content and decreased endogenous ABA content to promote the set and growth of fruit during early development. Chemical names used: [1-(2-chloro-4-pyridyl)-3-phenylurea] (CPPU); indole-3-acetic acid (IAA); abscisic acid (ABA).