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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.


Related in: MedlinePlus

Effects of ethylene precursor ACC on apical hooks formed in the dark and exaggerated by Rp or FRp (A) and on hypocotyl height (B). Five day-old dark grown seedlings were sprayed with 1-ml/bottle ACC solutions of the indicated concentrations or plane water, and 24 h later they were given 20-s Rp or 40-s FRp or no pulse, and then stood in the dark for further 48 h until the results were determined. The culture bottles were kept in the cap-loose mode throughout the experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1. Histogram bars: mean ± SE (n = 10–29); statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.005, ∗∗∗P < 0.0005 as compared with the  ACC control within each light condition. cv. Sekaiichi.
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Figure 3: Effects of ethylene precursor ACC on apical hooks formed in the dark and exaggerated by Rp or FRp (A) and on hypocotyl height (B). Five day-old dark grown seedlings were sprayed with 1-ml/bottle ACC solutions of the indicated concentrations or plane water, and 24 h later they were given 20-s Rp or 40-s FRp or no pulse, and then stood in the dark for further 48 h until the results were determined. The culture bottles were kept in the cap-loose mode throughout the experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1. Histogram bars: mean ± SE (n = 10–29); statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.005, ∗∗∗P < 0.0005 as compared with the ACC control within each light condition. cv. Sekaiichi.

Mentions: Endogenous ethylene may give some different effect by evolving differently among the target tissues of seedlings; for example, between the concave and convex sides of the hook. To examine this possibility, seedlings were sprayed with various concentrations of ACC, the immediate biosynthetic precursor of ethylene, and kept in the dark for 72 h. To minimize the accumulation of emitted ethylene, the bottles were kept in the cap-loose mode. As the standard for comparison of the expected effects of ACC, Rp or FRp was given to induce hook exaggeration not only in the absence of ACC, but also in the presence (Figure 3A). The hook angles presented themselves comparatively small due to the pulse of light here compared with those of Rc and FRc in Figure 2A. All the three sorts of hook curvatures including the one kept in the dark throughout were similarly suppressed by ACC concentration-dependently, and excluded the above-stated assumption that endogenously evolving ethylene may cause hook exaggeration instead of light. The effects of the ACC on hypocotyl height (Figure 3B) did not differentiate the treatments Dark, Rp and FRp, supporting that ethylene evolved from ACC equally regardless of the light pulse given and operated normally in this test system.


Ethylene Is Not Responsible for Phytochrome-Mediated Apical Hook Exaggeration in Tomato
Effects of ethylene precursor ACC on apical hooks formed in the dark and exaggerated by Rp or FRp (A) and on hypocotyl height (B). Five day-old dark grown seedlings were sprayed with 1-ml/bottle ACC solutions of the indicated concentrations or plane water, and 24 h later they were given 20-s Rp or 40-s FRp or no pulse, and then stood in the dark for further 48 h until the results were determined. The culture bottles were kept in the cap-loose mode throughout the experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1. Histogram bars: mean ± SE (n = 10–29); statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.005, ∗∗∗P < 0.0005 as compared with the  ACC control within each light condition. cv. Sekaiichi.
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Related In: Results  -  Collection

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Show All Figures
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Figure 3: Effects of ethylene precursor ACC on apical hooks formed in the dark and exaggerated by Rp or FRp (A) and on hypocotyl height (B). Five day-old dark grown seedlings were sprayed with 1-ml/bottle ACC solutions of the indicated concentrations or plane water, and 24 h later they were given 20-s Rp or 40-s FRp or no pulse, and then stood in the dark for further 48 h until the results were determined. The culture bottles were kept in the cap-loose mode throughout the experiment. Rp: RLED, 193 μmol m-2 s-1; FRp: FRLED, 465 μmol m-2 s-1. Histogram bars: mean ± SE (n = 10–29); statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.005, ∗∗∗P < 0.0005 as compared with the ACC control within each light condition. cv. Sekaiichi.
Mentions: Endogenous ethylene may give some different effect by evolving differently among the target tissues of seedlings; for example, between the concave and convex sides of the hook. To examine this possibility, seedlings were sprayed with various concentrations of ACC, the immediate biosynthetic precursor of ethylene, and kept in the dark for 72 h. To minimize the accumulation of emitted ethylene, the bottles were kept in the cap-loose mode. As the standard for comparison of the expected effects of ACC, Rp or FRp was given to induce hook exaggeration not only in the absence of ACC, but also in the presence (Figure 3A). The hook angles presented themselves comparatively small due to the pulse of light here compared with those of Rc and FRc in Figure 2A. All the three sorts of hook curvatures including the one kept in the dark throughout were similarly suppressed by ACC concentration-dependently, and excluded the above-stated assumption that endogenously evolving ethylene may cause hook exaggeration instead of light. The effects of the ACC on hypocotyl height (Figure 3B) did not differentiate the treatments Dark, Rp and FRp, supporting that ethylene evolved from ACC equally regardless of the light pulse given and operated normally in this test system.

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