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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.

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Effects of various periods of R and FR on hook curvature and emission rate of endogenous ethylene. After grown in the dark, cap-loose mode for 5 days, seedlings were shifted to the cap-tight mode, immediately irradiated with various periods of R or FR, and then grown in the dark for 48 h in total after the shift of mode until ethylene emission rate and hook angle were determined. Irradiation: (A) Rp, 10 s; FRp, 20 s; (B) 60 min each; (C) 90 min each; (D) 24 h each. Non-irradiated controls were similarly cultured for the same period in the dark throughout. (A)–(D) are of different runs of experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1; R60 min and R90 min: RFL, 33.8 μmol m-2 s-1; FR60 min and FR90 min: FRFL, 21.9 μmol m-2 s-1; R24 h: RFL, 49.9 μmol m-2 s-1; FR24 h: FRFL, 23.5 μmol m-2 s-1. Histogram bars: mean ± SE (n = 40–77) for hook angle, and mean ± SD (n = 4–7) for ethylene emission rate. Different letters of A, B, and C on the top of bars for hook angles show statistically significant differences at P < 0.05 within each Figure. All bars for ethylene emission rate have only a, showing no significant difference. cv. Seiko No.17 for (A) and (C); Sekaiichi, (B); Ponte-Rosa, (D).
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Figure 8: Effects of various periods of R and FR on hook curvature and emission rate of endogenous ethylene. After grown in the dark, cap-loose mode for 5 days, seedlings were shifted to the cap-tight mode, immediately irradiated with various periods of R or FR, and then grown in the dark for 48 h in total after the shift of mode until ethylene emission rate and hook angle were determined. Irradiation: (A) Rp, 10 s; FRp, 20 s; (B) 60 min each; (C) 90 min each; (D) 24 h each. Non-irradiated controls were similarly cultured for the same period in the dark throughout. (A)–(D) are of different runs of experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1; R60 min and R90 min: RFL, 33.8 μmol m-2 s-1; FR60 min and FR90 min: FRFL, 21.9 μmol m-2 s-1; R24 h: RFL, 49.9 μmol m-2 s-1; FR24 h: FRFL, 23.5 μmol m-2 s-1. Histogram bars: mean ± SE (n = 40–77) for hook angle, and mean ± SD (n = 4–7) for ethylene emission rate. Different letters of A, B, and C on the top of bars for hook angles show statistically significant differences at P < 0.05 within each Figure. All bars for ethylene emission rate have only a, showing no significant difference. cv. Seiko No.17 for (A) and (C); Sekaiichi, (B); Ponte-Rosa, (D).

Mentions: To determine the ethylene concentrations in culture bottles, gas-sampling was made similarly by concerted motions of two syringes, one of which was filled with ethylene-free air of the same volume as that of the sample air to be taken with the other empty syringe. In this way, sample air of 1 or 2 ml was taken out and injected into a gas chromatograph (GC-14A; Shimadzu Co., Kyoto) equipped with a 100 cm × 0.26 cm active alumina (60–80 mesh) column (Gasukuro Kogyo Inc., Tokyo, Japan) and a flame ionization detector. In some experiments (Figures 7 and 8) ethylene emission rate was calculated with the equation (ethylene concentration × bottle capacity)/(Fresh weight of seedlings × incubation period).


Ethylene Is Not Responsible for Phytochrome-Mediated Apical Hook Exaggeration in Tomato
Effects of various periods of R and FR on hook curvature and emission rate of endogenous ethylene. After grown in the dark, cap-loose mode for 5 days, seedlings were shifted to the cap-tight mode, immediately irradiated with various periods of R or FR, and then grown in the dark for 48 h in total after the shift of mode until ethylene emission rate and hook angle were determined. Irradiation: (A) Rp, 10 s; FRp, 20 s; (B) 60 min each; (C) 90 min each; (D) 24 h each. Non-irradiated controls were similarly cultured for the same period in the dark throughout. (A)–(D) are of different runs of experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1; R60 min and R90 min: RFL, 33.8 μmol m-2 s-1; FR60 min and FR90 min: FRFL, 21.9 μmol m-2 s-1; R24 h: RFL, 49.9 μmol m-2 s-1; FR24 h: FRFL, 23.5 μmol m-2 s-1. Histogram bars: mean ± SE (n = 40–77) for hook angle, and mean ± SD (n = 4–7) for ethylene emission rate. Different letters of A, B, and C on the top of bars for hook angles show statistically significant differences at P < 0.05 within each Figure. All bars for ethylene emission rate have only a, showing no significant difference. cv. Seiko No.17 for (A) and (C); Sekaiichi, (B); Ponte-Rosa, (D).
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Figure 8: Effects of various periods of R and FR on hook curvature and emission rate of endogenous ethylene. After grown in the dark, cap-loose mode for 5 days, seedlings were shifted to the cap-tight mode, immediately irradiated with various periods of R or FR, and then grown in the dark for 48 h in total after the shift of mode until ethylene emission rate and hook angle were determined. Irradiation: (A) Rp, 10 s; FRp, 20 s; (B) 60 min each; (C) 90 min each; (D) 24 h each. Non-irradiated controls were similarly cultured for the same period in the dark throughout. (A)–(D) are of different runs of experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1; R60 min and R90 min: RFL, 33.8 μmol m-2 s-1; FR60 min and FR90 min: FRFL, 21.9 μmol m-2 s-1; R24 h: RFL, 49.9 μmol m-2 s-1; FR24 h: FRFL, 23.5 μmol m-2 s-1. Histogram bars: mean ± SE (n = 40–77) for hook angle, and mean ± SD (n = 4–7) for ethylene emission rate. Different letters of A, B, and C on the top of bars for hook angles show statistically significant differences at P < 0.05 within each Figure. All bars for ethylene emission rate have only a, showing no significant difference. cv. Seiko No.17 for (A) and (C); Sekaiichi, (B); Ponte-Rosa, (D).
Mentions: To determine the ethylene concentrations in culture bottles, gas-sampling was made similarly by concerted motions of two syringes, one of which was filled with ethylene-free air of the same volume as that of the sample air to be taken with the other empty syringe. In this way, sample air of 1 or 2 ml was taken out and injected into a gas chromatograph (GC-14A; Shimadzu Co., Kyoto) equipped with a 100 cm × 0.26 cm active alumina (60–80 mesh) column (Gasukuro Kogyo Inc., Tokyo, Japan) and a flame ionization detector. In some experiments (Figures 7 and 8) ethylene emission rate was calculated with the equation (ethylene concentration × bottle capacity)/(Fresh weight of seedlings × incubation period).

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