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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 supplemented ethylene on hook curvatures exaggerated by Rp or FRp and on the dark control in the presence (A) or absence (B) of AVG. The thick lines superimposed for comparison in the low ethylene concentration area in (B) are excerpts from the corresponding three curves in (A). After grown from seeds on 100 μM AVG solution in the dark, cap-tight mode for 5 days, seedlings were exposed to various concentrations of ethylene, irradiated with an Rp or FRp, and cultured for further 48 h in the dark until the resulting ethylene concentration in the bottles and hook angles were determined. The ethylene concentrations determined were used to plot the relevant hook angles. Supplemented ethylene: , 0.3, 1.0, and 3.0 μL L-1(A); , 0.3, 0.9, and 3.0 μL L-1(B); data points: mean ± SE (n = 20–30). Statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.01 as compared with the hook angle at the left end of each curve; ##P < 0.01, ###P < 0.0005, respectively, as compared with the valley of each curve in (A). Rp: RLED, 193 μmol m-2 s-1 for 20 s in (A) and for 15 s in (B); FRp: FRLED, 465 μmol m-2 s-1for 40 s in (A) and for 30 s in (B). cv. Seiko No.17.
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Figure 6: Effects of supplemented ethylene on hook curvatures exaggerated by Rp or FRp and on the dark control in the presence (A) or absence (B) of AVG. The thick lines superimposed for comparison in the low ethylene concentration area in (B) are excerpts from the corresponding three curves in (A). After grown from seeds on 100 μM AVG solution in the dark, cap-tight mode for 5 days, seedlings were exposed to various concentrations of ethylene, irradiated with an Rp or FRp, and cultured for further 48 h in the dark until the resulting ethylene concentration in the bottles and hook angles were determined. The ethylene concentrations determined were used to plot the relevant hook angles. Supplemented ethylene: , 0.3, 1.0, and 3.0 μL L-1(A); , 0.3, 0.9, and 3.0 μL L-1(B); data points: mean ± SE (n = 20–30). Statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.01 as compared with the hook angle at the left end of each curve; ##P < 0.01, ###P < 0.0005, respectively, as compared with the valley of each curve in (A). Rp: RLED, 193 μmol m-2 s-1 for 20 s in (A) and for 15 s in (B); FRp: FRLED, 465 μmol m-2 s-1for 40 s in (A) and for 30 s in (B). cv. Seiko No.17.

Mentions: Secondly, another ethylene biosynthesis inhibitor AVG was sprayed to seedlings at , 10, 100, and 500 μM. At 100 and 500 μM it enhanced the hook curvatures under the three light conditions to similar extents (data not shown). Next, seedlings were grown from seeds on 100 μM AVG for 5 days, and then supplemented with various concentrations of ethylene and irradiated with Rp or FRp, or not irradiated, followed by culture for 48 h (Figure 6A). Another similar experiment made without AVG gave the results as shown in Figure 6B. In both Figures the left ends of the curves indicate the concentration of only ethylene emitted by seedlings. Comparison of the left ends of corresponding curves between the two Figures indicates that the AVG treatment reduced endogenous ethylene from about 0.2 μL L-1 (also seen in Figure 2A) to about 0.08 μL L-1. For easy comparison of the effect of endogenous ethylene at reduced concentrations, excerpts from the three curves in Figure 6A are overlaid as the thick lines on the corresponding curves in Figure 6B. The excerpts fell, respectively, on the extensions of the corresponding curves obtained in the absence of AVG. Thus it is clear that AVG suppressed ethylene evolution, and, in turn, resulted in the enhancement of the hook curvatures, whether exaggerated or non-exaggerated, at the low concentration range below 1.0 μL L-1, and the enhancement was reversed by supplementing ethylene. These data confirm that ethylene suppresses all of the three kinds of hook curvature at the low concentration range.


Ethylene Is Not Responsible for Phytochrome-Mediated Apical Hook Exaggeration in Tomato
Effects of supplemented ethylene on hook curvatures exaggerated by Rp or FRp and on the dark control in the presence (A) or absence (B) of AVG. The thick lines superimposed for comparison in the low ethylene concentration area in (B) are excerpts from the corresponding three curves in (A). After grown from seeds on 100 μM AVG solution in the dark, cap-tight mode for 5 days, seedlings were exposed to various concentrations of ethylene, irradiated with an Rp or FRp, and cultured for further 48 h in the dark until the resulting ethylene concentration in the bottles and hook angles were determined. The ethylene concentrations determined were used to plot the relevant hook angles. Supplemented ethylene: , 0.3, 1.0, and 3.0 μL L-1(A); , 0.3, 0.9, and 3.0 μL L-1(B); data points: mean ± SE (n = 20–30). Statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.01 as compared with the hook angle at the left end of each curve; ##P < 0.01, ###P < 0.0005, respectively, as compared with the valley of each curve in (A). Rp: RLED, 193 μmol m-2 s-1 for 20 s in (A) and for 15 s in (B); FRp: FRLED, 465 μmol m-2 s-1for 40 s in (A) and for 30 s in (B). cv. Seiko No.17.
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Figure 6: Effects of supplemented ethylene on hook curvatures exaggerated by Rp or FRp and on the dark control in the presence (A) or absence (B) of AVG. The thick lines superimposed for comparison in the low ethylene concentration area in (B) are excerpts from the corresponding three curves in (A). After grown from seeds on 100 μM AVG solution in the dark, cap-tight mode for 5 days, seedlings were exposed to various concentrations of ethylene, irradiated with an Rp or FRp, and cultured for further 48 h in the dark until the resulting ethylene concentration in the bottles and hook angles were determined. The ethylene concentrations determined were used to plot the relevant hook angles. Supplemented ethylene: , 0.3, 1.0, and 3.0 μL L-1(A); , 0.3, 0.9, and 3.0 μL L-1(B); data points: mean ± SE (n = 20–30). Statistically significant differences, respectively, at ∗P < 0.05, ∗∗P < 0.01 as compared with the hook angle at the left end of each curve; ##P < 0.01, ###P < 0.0005, respectively, as compared with the valley of each curve in (A). Rp: RLED, 193 μmol m-2 s-1 for 20 s in (A) and for 15 s in (B); FRp: FRLED, 465 μmol m-2 s-1for 40 s in (A) and for 30 s in (B). cv. Seiko No.17.
Mentions: Secondly, another ethylene biosynthesis inhibitor AVG was sprayed to seedlings at , 10, 100, and 500 μM. At 100 and 500 μM it enhanced the hook curvatures under the three light conditions to similar extents (data not shown). Next, seedlings were grown from seeds on 100 μM AVG for 5 days, and then supplemented with various concentrations of ethylene and irradiated with Rp or FRp, or not irradiated, followed by culture for 48 h (Figure 6A). Another similar experiment made without AVG gave the results as shown in Figure 6B. In both Figures the left ends of the curves indicate the concentration of only ethylene emitted by seedlings. Comparison of the left ends of corresponding curves between the two Figures indicates that the AVG treatment reduced endogenous ethylene from about 0.2 μL L-1 (also seen in Figure 2A) to about 0.08 μL L-1. For easy comparison of the effect of endogenous ethylene at reduced concentrations, excerpts from the three curves in Figure 6A are overlaid as the thick lines on the corresponding curves in Figure 6B. The excerpts fell, respectively, on the extensions of the corresponding curves obtained in the absence of AVG. Thus it is clear that AVG suppressed ethylene evolution, and, in turn, resulted in the enhancement of the hook curvatures, whether exaggerated or non-exaggerated, at the low concentration range below 1.0 μL L-1, and the enhancement was reversed by supplementing ethylene. These data confirm that ethylene suppresses all of the three kinds of hook curvature at the low concentration range.

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