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Ethylene Is Not Responsible for Phytochrome-Mediated Apical Hook Exaggeration in Tomato

View Article: PubMed Central - PubMed

ABSTRACT

The apical hook of tomato seedlings is exaggerated by phytochrome actions, while in other species such as bean, pea and Arabidopsis, the hook is exaggerated by ethylene and opens by phytochrome actions. The present study was aimed to clarify mainly whether ethylene is responsible for the phytochrome-mediated hook exaggeration of tomato seedlings. Dark-grown 5-day-old seedlings were subjected to various ways of ethylene application in the dark as well as under the actions of red (R) or far-red light (FR). The ethylene emitted by seedlings was also quantified relative to hook exaggeration. The results show: Ambient ethylene, up-to about 1.0 μL L-1, suppressed (opened) the hooks formed in the dark as well as the ones exaggerated by R or FR, while at 3.0–10 μL L-1 it enhanced (closed) the hook only slightly as compared with the most-suppressed level at about 1.0 μL L-1. Treatment with 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene biosynthesis, did not enhance the hook, only mimicking the suppressive effects of ambient ethylene. The biosynthesis inhibitor, CoCl2 or aminoethoxyvinylglycine, enhanced hook curvature, and the enhancement was canceled by supplement of ethylene below 1.0 μL L-1. Auxin transport inhibitor, N-1-naphthylphthalamic acid, by contrast, suppressed curvature markedly without altering ethylene emission. The effects of the above-stated treatments did not differentiate qualitatively among the R-, FR-irradiated seedlings and dark control so as to explain phytochrome-mediated hook exaggeration. In addition, ethylene emission by seedlings was affected neither by R nor FR at such fluences as to cause hook exaggeration. In conclusion, (1) ethylene suppresses not only the light-exaggerated hook, but also the dark-formed one; (2) ethylene emission is not affected by R or FR, and also not correlated with the hook exaggerations; thus ethylene is not responsible for the hook exaggeration in tomato; and (3) auxin is essential for the maintenance and development of the hook in tomato as is the case in other species lacking phytochrome-mediated hook exaggeration. A possible mechanism of phytochrome action for hook exaggeration is discussed.

No MeSH data available.


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Effects of ambient ethylene on apical hook curvature of dark-grown seedlings of tomato under Rc, FRc or in the dark. After grown from seeds in the cap-loose mode in the dark for 5 days, seedlings were shifted to the cap-tight mode and exposed to various concentrations of ethylene and continuous R (Rc), FR (FRc) or kept in the dark for 50–56 h until the end of experiment, where final concentrations of ethylene for plotting data in (A) and (B), hook curvature (A) and hypocotyl height (B) were determined, and the representative seedlings were photographed (C). Supplemented ethylene concentrations: , 0.3, 1.0, 3.0, and 10 μL L-1; Rc: RFL, 17 μmol m-2 s-1; FRc: FRFL, 14 μmol m-2 s-1. Data points: mean ± SE (n = 19–51) for hook angle and hypocotyl height. Statistical significance, respectively, at ∗P < 0.01, ∗∗P < 0.005, ∗∗∗P < 0.0001 as compared with the values at the lowest ethylene concentration ( supplemented ethylene) within each light condition. cv. Ponte-Rosa.
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Figure 2: Effects of ambient ethylene on apical hook curvature of dark-grown seedlings of tomato under Rc, FRc or in the dark. After grown from seeds in the cap-loose mode in the dark for 5 days, seedlings were shifted to the cap-tight mode and exposed to various concentrations of ethylene and continuous R (Rc), FR (FRc) or kept in the dark for 50–56 h until the end of experiment, where final concentrations of ethylene for plotting data in (A) and (B), hook curvature (A) and hypocotyl height (B) were determined, and the representative seedlings were photographed (C). Supplemented ethylene concentrations: , 0.3, 1.0, 3.0, and 10 μL L-1; Rc: RFL, 17 μmol m-2 s-1; FRc: FRFL, 14 μmol m-2 s-1. Data points: mean ± SE (n = 19–51) for hook angle and hypocotyl height. Statistical significance, respectively, at ∗P < 0.01, ∗∗P < 0.005, ∗∗∗P < 0.0001 as compared with the values at the lowest ethylene concentration ( supplemented ethylene) within each light condition. cv. Ponte-Rosa.

Mentions: To examine whether ethylene causes the exaggeration of the apical hook instead of light, dark-grown 5-day-old tomato seedlings were exposed to various concentrations of ambient ethylene in culture bottles in the dark. As the standard of hook exaggerations mediated by very low and low fluence responses as well as high irradiance response of phytochrome (Shichijo et al., 2010a), seedlings were, without addition of exogenous ethylene, irradiated with continuous red (Rc) and far-red light (FRc) in place of pulsed light. In parallel, effects of ethylene on hook under such irradiated conditions were also examined (Figure 2A). In the present study, such low concentrations of ethylene as endogenous ethylene also matter, the concentrations in the culture bottles were determined at the end of experiments and used as ambient ethylene concentration to plot the hook response in this Figure and others. In the dark, ethylene suppressed (i.e., opened) hook curvature in the neighborhood of 1.0 μL L-1, and as its concentration increased beyond 1.0 μL L-1, the gas enhanced (i.e., closed) the hook, but even at 10 μL L-1, it could not intensify the curvature to the level of the hooks exaggerated by either Rc or FRc in the absence of supplementary ethylene (left end of the curves). As seen in the photos at 10 μL L-1 (Figure 2C), the toxicity of high concentration ethylene, i.e., the severe growth inhibition of the hypocotyl and the swelling at the part just below the hook, implies that no further enhancement of the hook was possible even by further raising ethylene concentration.


Ethylene Is Not Responsible for Phytochrome-Mediated Apical Hook Exaggeration in Tomato
Effects of ambient ethylene on apical hook curvature of dark-grown seedlings of tomato under Rc, FRc or in the dark. After grown from seeds in the cap-loose mode in the dark for 5 days, seedlings were shifted to the cap-tight mode and exposed to various concentrations of ethylene and continuous R (Rc), FR (FRc) or kept in the dark for 50–56 h until the end of experiment, where final concentrations of ethylene for plotting data in (A) and (B), hook curvature (A) and hypocotyl height (B) were determined, and the representative seedlings were photographed (C). Supplemented ethylene concentrations: , 0.3, 1.0, 3.0, and 10 μL L-1; Rc: RFL, 17 μmol m-2 s-1; FRc: FRFL, 14 μmol m-2 s-1. Data points: mean ± SE (n = 19–51) for hook angle and hypocotyl height. Statistical significance, respectively, at ∗P < 0.01, ∗∗P < 0.005, ∗∗∗P < 0.0001 as compared with the values at the lowest ethylene concentration ( supplemented ethylene) within each light condition. cv. Ponte-Rosa.
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Figure 2: Effects of ambient ethylene on apical hook curvature of dark-grown seedlings of tomato under Rc, FRc or in the dark. After grown from seeds in the cap-loose mode in the dark for 5 days, seedlings were shifted to the cap-tight mode and exposed to various concentrations of ethylene and continuous R (Rc), FR (FRc) or kept in the dark for 50–56 h until the end of experiment, where final concentrations of ethylene for plotting data in (A) and (B), hook curvature (A) and hypocotyl height (B) were determined, and the representative seedlings were photographed (C). Supplemented ethylene concentrations: , 0.3, 1.0, 3.0, and 10 μL L-1; Rc: RFL, 17 μmol m-2 s-1; FRc: FRFL, 14 μmol m-2 s-1. Data points: mean ± SE (n = 19–51) for hook angle and hypocotyl height. Statistical significance, respectively, at ∗P < 0.01, ∗∗P < 0.005, ∗∗∗P < 0.0001 as compared with the values at the lowest ethylene concentration ( supplemented ethylene) within each light condition. cv. Ponte-Rosa.
Mentions: To examine whether ethylene causes the exaggeration of the apical hook instead of light, dark-grown 5-day-old tomato seedlings were exposed to various concentrations of ambient ethylene in culture bottles in the dark. As the standard of hook exaggerations mediated by very low and low fluence responses as well as high irradiance response of phytochrome (Shichijo et al., 2010a), seedlings were, without addition of exogenous ethylene, irradiated with continuous red (Rc) and far-red light (FRc) in place of pulsed light. In parallel, effects of ethylene on hook under such irradiated conditions were also examined (Figure 2A). In the present study, such low concentrations of ethylene as endogenous ethylene also matter, the concentrations in the culture bottles were determined at the end of experiments and used as ambient ethylene concentration to plot the hook response in this Figure and others. In the dark, ethylene suppressed (i.e., opened) hook curvature in the neighborhood of 1.0 μL L-1, and as its concentration increased beyond 1.0 μL L-1, the gas enhanced (i.e., closed) the hook, but even at 10 μL L-1, it could not intensify the curvature to the level of the hooks exaggerated by either Rc or FRc in the absence of supplementary ethylene (left end of the curves). As seen in the photos at 10 μL L-1 (Figure 2C), the toxicity of high concentration ethylene, i.e., the severe growth inhibition of the hypocotyl and the swelling at the part just below the hook, implies that no further enhancement of the hook was possible even by further raising ethylene concentration.

View Article: PubMed Central - PubMed

ABSTRACT

The apical hook of tomato seedlings is exaggerated by phytochrome actions, while in other species such as bean, pea and Arabidopsis, the hook is exaggerated by ethylene and opens by phytochrome actions. The present study was aimed to clarify mainly whether ethylene is responsible for the phytochrome-mediated hook exaggeration of tomato seedlings. Dark-grown 5-day-old seedlings were subjected to various ways of ethylene application in the dark as well as under the actions of red (R) or far-red light (FR). The ethylene emitted by seedlings was also quantified relative to hook exaggeration. The results show: Ambient ethylene, up-to about 1.0 &mu;L L-1, suppressed (opened) the hooks formed in the dark as well as the ones exaggerated by R or FR, while at 3.0&ndash;10 &mu;L L-1 it enhanced (closed) the hook only slightly as compared with the most-suppressed level at about 1.0 &mu;L L-1. Treatment with 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene biosynthesis, did not enhance the hook, only mimicking the suppressive effects of ambient ethylene. The biosynthesis inhibitor, CoCl2 or aminoethoxyvinylglycine, enhanced hook curvature, and the enhancement was canceled by supplement of ethylene below 1.0 &mu;L L-1. Auxin transport inhibitor, N-1-naphthylphthalamic acid, by contrast, suppressed curvature markedly without altering ethylene emission. The effects of the above-stated treatments did not differentiate qualitatively among the R-, FR-irradiated seedlings and dark control so as to explain phytochrome-mediated hook exaggeration. In addition, ethylene emission by seedlings was affected neither by R nor FR at such fluences as to cause hook exaggeration. In conclusion, (1) ethylene suppresses not only the light-exaggerated hook, but also the dark-formed one; (2) ethylene emission is not affected by R or FR, and also not correlated with the hook exaggerations; thus ethylene is not responsible for the hook exaggeration in tomato; and (3) auxin is essential for the maintenance and development of the hook in tomato as is the case in other species lacking phytochrome-mediated hook exaggeration. A possible mechanism of phytochrome action for hook exaggeration is discussed.

No MeSH data available.


Related in: MedlinePlus