Plant Hormone Changes in Growing Small Watermelon Fruit

Abstract

To elucidate the phytohormone profiles associated with various stages of growing and ripening of small watermelon fruits, small watermelon fruits were collected 7 to 35 days after flowering (DAF) and divided into rind, pulp, and seeds. Indole-3-acetic acid (IAA), abscisic acid (ABA), trans-zeatin (tZ), isopentenyl adenine (iP), jasmonic acid (JA), methyl jasmonate (MeJA), gibberellin₁ (GA₁), and gibberellin₄ (GA₄) from each tissue were simultaneously quantified by liquid chromatography mass spectrometry (LC-MS). From 7 to 28 DAF, pulp weight increased rapidly due to cellular expansion. The IAA concentration increased up to 21 DAF in seeds, but then decreased up to 35 DAF. Similar changes occurred in the pulp approximately 7 days after the pattern of rising and falling IAA levels in the seeds. The GA concentration was higher in the seeds, and peaked prior to the seed growth peak. The ABA level in the pulp peaked at the time of fruit enlargement (21 DAF). The concentrations of iP, GA₁, and GA₄ tended to decrease with growth in all tissues. The results revealed the changes in endogenous plant hormones involved in the growth of small watermelon fruit.