Research Article: Hormonal regulation of floret closure of rice (Oryza sativa)

Date Published: June 7, 2018

Publisher: Public Library of Science

Author(s): Youming Huang, Xiaochun Zeng, Heping Cao, Prasanta K. Subudhi.


Plant hormones play important roles in regulating every aspect of growth, development, and metabolism of plants. We are interested in understanding hormonal regulation of floret opening and closure in plants. This is a particularly important problem for hybrid rice because regulation of flowering time is vitally important in hybrid rice seed production. However, little was known about the effects of plant hormones on rice flowering. We have shown that jasmonate and methyl jasmonate play significant roles in promoting rice floret opening. In this study, we investigated the effects of auxins including indole-3-acidic acid (IAA), indole-3-butyric acid (IBA), 1-naphthalene-acetic acid (NAA), 2,4-dichlorophenoxy acetic acid (2,4-D) and 3,6-dichloro-2-methoxybenzoic acid (DIC) and abscisic acid (ABA) on floret closure of four fertile and three sterile varieties of rice. The results from field studies in three growing seasons in 2013–2015 showed that the percentages of closed florets were significantly lower in plants treated with IAA, IBA, 2,4-D, DIC and NAA and that the durations of floret opening were significantly longer in plants treated with the same auxins. The auxins exhibited time- and concentration-dependant effects on floret closure. ABA displayed opposite effects of auxins because it increased the percentages of floret closure and decreased the length of floret opening of rice varieties. The degree of auxin-inhibiting and ABA-promoting effects on floret closure was varied somewhat but not significantly different among the rice varieties. Endogenous IAA levels were the highest in florets collected shortly before opening followed by a sharp decline in florets with maximal angles of opening and a significant jump of IAA levels shortly after floret closure in both fertile and sterile rice plants. ABA levels showed an opposite trend in the same samples. Our results showed that auxins delayed but ABA promoted the closure of rice floret regardless of the varieties.

Partial Text

Plant hormones play important roles in regulating every aspect of growth, development and metabolism of plants. For example, brassinosteroids regulate rice lamina joint inclination due to uneven expansion of the cells in the joint [1]. Gibberellins (GAs) regulate the amount of starch and structural polysaccharides in maize endosperm suspension cells via regulating enzyme activities involved in carbohydrate metabolism [2]. Indole-3-acetic acid (IAA), GAs, cytokinins and abscisic acid (ABA) regulate sex differentiation of the flowers of Chinese Chinquapin (Castanea henryi) [3].

This study revealed that plant hormones ABA and auxins (both endogenous and synthetic compounds) promoted and delayed floret closing of rice, respectively. To our knowledge, this is the first report related to the effects of the five classical plant hormones on rice floret closure. In previous studies, treatment with plant hormone MeJA delayed wheat floret closure for 42–70 min [23]. Salicylic acid (SA), another plant hormone, doubled the percentage of glume-gaping grains of sterile wheat after the floret opening was induced by MeJA [24]. ABA was shown to promote floret opening in Ipomoea nil and IAA was shown to inhibit floret opening in Pharbitis nil [25,26]. We performed similar experiments but we did not observe significant effect of ABA and IAA on floret opening in rice (data not shown). These suggest that the mechanisms of hormonal regulated floret opening in Ipomoea nil and Pharbitis nil are different from those in rice and wheat. The different responses of rice and the other species to the same hormonal regulation might be due to the different structures of florets in these two groups of species, in which rice floret opening is caused by the expansion of basal lodicules whereas the other two species do not have similar floral structure. Alternatively, although we thought unlikely, the different observation in these two plant species was due to much higher concentrations of ABA and auxins used in our studies than those used in the previous study.




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