Interacting Roles of Gibberellin and Ethylene in Corolla Expansion of Ipomoea Nil (Convolvulaceae)

Abstract

The relatively rapid and extensive corolla expansion in Ipomoea nil (L.) Roth cv. ‘Scarlett O'Hara’ appears to be initiated by a shift in the balance between a growth promoter (gibberellin, GA) and a growth inhibitor (ethylene) two days before anthesis. The effects of applied growth regulators in vitro, were measured as a change in area of segments from whole young corollas 16–17 mm long. Applied gibberellic acid (GA3) strongly promoted growth, while a GA action inhibitor (ancymidol) reduced growth. Inhibitors of GA biosynthesis (AMO‐1618, paclobutrazol, tetcyclasis, and chlorocholine chloride) had little effect, implying that the GAs were not being synthesized within the corolla segments, at least at this stage of corolla growth. Both the level of endogenous GAs and response of the segments to sucrose increased as the corolla size also increased from 15 to 20 mm in length. Applied 1‐aminocyclopropane‐l‐carboxylic acid (ACC), an ethylene precursor, inhibited the response of corollas to applied GA3. Applications of ethylene biosynthesis inhibitors (AVG and cobalt ions) promoted growth of the corolla segments. Rapid ethylene production by corollas 15–17 mm long (48 hr before flower opening) appeared to inhibit the growth that may have been induced by low levels of endogenous GAs. Older corollas (longer than 18 mm) had very low levels of ethylene production and much higher levels of GA‐like substances; these changes apparently allow the corollas to begin to expand in vivo and to strongly respond to sucrose applications alone in vitro. Acid‐induced growth does not seem to be an important component of corolla expansion; applied fusicoccin (a proton efflux promoter) and sodium orthovanadate (a proton efflux inhibitor) had no significant effect on growth of the 16–17 mm long corollas. Buffers (Good's and phosphate) over a wide pH range had no effect on corolla expansion. Taken together, our results indicate that the regulation of corolla expansion depends (at least in part) on compensatory shifts in the levels of two plant growth regulators [PGRs], ethylene and GA.

The Role of Ethylene in Corolla Unfolding in Ipomoea Nil (Convolvulaceae)

“…This growth step appears to be promoted by gibberellins (Murakami, 1973), but tissue sensitivity to gibberellins may be reduced initially by ethylene production and later increased by decreases in ethylene production (Raab and Koning, 1984). The relatively slower growth process accelerates about two days before the corolla rapidly unfolds.…”

Molecular understanding of postharvest flower opening and senescence

“…The gibberellins (GA) class of phytohormones, of which there are several bioactive forms, function as promoters of flower opening in several species, including I. nil , Gerbera hybrida , and L. sinuatum (Steinitz and Cohen 1982 ; Raab and Koning 1987 ; Li et al 2015 ). In G. hybrida , GA 3 promotes the expansion of ray floret petals and an increase in cell size (Li et al 2015 ), while in C. sativus , GA 9 is naturally produced in the ovaries and moves to the sepals and petals, where it is converted into bioactive GA 4 , which has been shown to regulate organ growth (Lange and Lange 2016 ).…”

The Vase Life of Cut Gerbera Flowers is Extended by Combined Treatment with Gibberellin A₃ and Calcium Chloride

“…Treatment with GA 3 delays leaf yellowing in cut Alstroemeria (Hicklenton, 1991), lily (Han, 1995), and Narcissus . Exogenous GA 3 promotes petal growth in rose (Goszczynska et al, 1990;Sabehat and Zieslin, 1995) and morning glory (Raab and Koning, 1987) and flower opening of statice (Steinitz and Cohen, 1982). Treatment with GA 3 extends the vase life of cut carnation (Saks et al, 1992) and rose (Goszczynska et al, 1990).…”