4-Chlorophenoxyacetic Acid as a Regulator of Ontogenesis in Parthenocarpic Fruits of Tomato
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4-Chlorophenoxyacetic Acid as a Regulator of Ontogenesis in Parthenocarpic Fruits of Tomato V. V. Karyagina, *, O. N. Prudnikovaa, and V. Yu. Rakitina a
Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Moscow, 127276 Russia *e-mail: [email protected] Received November 20, 2019; revised December 5, 2019; accepted December 5, 2019
Abstract—The effect of synthetic auxin 4-chlorophenoxyacetic acid (4-CPA) on the ontogenesis of fruits was studied in tomato. Pollination of flowers of Solanum lycopersicum L., cv. Slivovidnyi, brought about the production in the ovaries of auxin indole-3-acetic acid (IAA) governing fruit development. The treatment of castrated flowers with 4-CPA also induced IAA synthesis in the ovaries, which caused the formation of parthenocarpic fruits that reached complete ripeness 6 days earlier, and their biomass was 17% greater than in seedbearing fruits. The content of abscisic acid, evolution of ethylene, and the rate of respiration were greater in parthenocarpic fruits than in seed-bearing fruits during almost the whole period of development, but these parameters changed identically in both types of treatment. Removal from the growing fruits of emerging seeds (the main sources of auxin) caused a complete termination of fruit growth that recommenced to the normal level upon replacement of ovules with a source of exogenous auxin: IAA or 4-CPA. The obtained data not only suggest that synthetic auxin participates in the initiation of parthenocarpic fruit growth via stimulation of synthesis of endogenous IAA but also show a possibility of IAA-independent regulation of fruit development in all the stages up to ripening. Keywords: Solanum lycopersicum, ABA, IAA, ontogenesis, parthenocarpy, fruit, 4-CPA, ethylene DOI: 10.1134/S102144372004007X
INTRODUCTION Phytohormones regulate fruit development in all the stages of ontogenesis, with IAA playing a key role in this process [1, 2]. Pollination of flowers and subsequent fertilization bring about a rise in IAA content in the ovary, which is a signal of the onset of fruit growth and development. Adverse factors (high and low temperatures, too high or low humidity, insufficient illuminance, etc.) impair the process of fertilization; as a result, induction of IAA synthesis does not occur, which causes cessation of fruit development and loss of yield. One of the methods mitigating conditions adverse to fruit setting is treatment of flowers with synthetic auxins, specifically, with chloride-substituted phenoxyacetic acids, for instance, with 4-chlorophenoxyacetic (4-CPA) acid. Parthenocarpic fruits produced after such a treatment are notable for an accelerated development and ripening as compared with seed-bearing fruits [3, 4]. The mechanism of synthetic auxins' action on growth and development of fruit is still unknown. At least three modes of action of synthetic auxins on fructification are possible: (1) stimulation of synthesis of endogenous auxin (IAA), (2) compensation for the Abbreviations: 4-CPA—4-chlorophenoxyacetic aci
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