Jan 29, 1973 - monochromator system modified for 1500-w incandescent sources after Withrow (16) and utilizing Baird Atomic and. Bausch and Lomb blocked ...
Plant Physiol. (1973) 51, 1082-1083
Light-induced Ethylene Production in Sorghum Received for publication January 29, 1973
L. E. CRAKER, F. B. ABELES,' AND W. SHROPSHIRE, JR.Suburban Experiment Station, University of Massachusetts, Waltham, Massachlusetts 02154 ABSTRACT
Ethylene production was induced in sections of dark-grown Sorghum vulgare L. seedlings by treatment with light in the blue and far red regions of the light spectrum. The action spectrum closely resembled the previously reported spectra for high irradiance response; thus, light-induced ethylene production is probably a high irradiance response with phytochrome as the initial photoreceptor.
Ethylene production in plant tissue may be regulated by light. Two modes of regulation are frequently encountered. In one, ethylene production is decreased by light exposure and is associated with low irradiance, short induction time, and the fully reversible phytochrome system. In the second, ethylene production is increased after light exposure and appears not to be mediated through the low irradiance, reversible phytochrome receptor. Ethylene production measured by Goeschl et al. (7) in etiolated pea seedlings decreased after exposure to red light. Far red irradiation immediately following the red light treatment reversed the effect of red light and gave ethylene production identical with that produced by far red alone. Red light has also been shown to reduce the rate of ethylene production in bean hooks (12) and rice coleoptiles (10). An increase in the rate of ethylene production following light exposure has been observed in lettuce seeds (2), cranberries (4), sorghum seedlings (5), rose tissue cultures (14), and oat seedlings (15). In each case, light approximately doubled the rate of ethylene production. However, the particular wavelengths of light that are active in inducing ethylene production by plant tissue are unknown. Earlier work (2) has shown that light-induced ethylene production in lettuce seeds was not caused by red or far red light. The purpose of these experiments was to determine the effectiveness of selected wavelengths of light for inducing ethylene production in plant tissue. MATERIALS AND METHODS Tissue sections from 4-day-old seedlings of Sorghum vulgare L. cv. E55 and E57 were used. The seedlings were grown in the dark on agar in 125-ml Erlenmeyer flasks at 28 + 1 C as previously described (5). For light treatments and subsequent
'Permanent address: Physical Science Division, USAMRIID Ft. Detrick, Frederick, Md. 21701. 2 Permanent address: Smithsonian Radiation Biology Laboratory, Rockville, Md. 20852.
measurements of ethylene production, 10-mm sections were cut just proximal to the first node from the seedling tissue under a green safelight (fluorescent lamp with acrylic and cellophane filters) (3) that produced no detectable effect on ethylene production even after extended, continuous exposure. After cutting, the sections were left on moist paper for 4 hr for dissipation of wound ethylene. The sections of tissue were then mixed, and a random selection of 10 sections for each sample was sealed with a rubber vaccine cap in a 20-ml vaccine bottle containing 2 ml of sterile 1.5% agar along one side. Irradiation treatments were done in an interference filter monochromator system modified for 1 500-w incandescent sources after Withrow (16) and utilizing Baird Atomic and Bausch and Lomb blocked interference filters with maximum half band width of ± 15 nm. The action spectrum was done in two sections (345-450 nm and 450-765 nm). The irradiance (,uw cm-2) was adjusted to approximately equal quanta for each wavelength within each of the wave bands, except for the 345 nm treatment, where only a low irradiance was available. The bottles containing tissue sections were laid on their side for exposure of the tissue sections to the light for 24 hr. Temperature during treatment was maintained at 25 ± 1 C. Controls in the dark and controls exposed to light from cool white fluorescent lamps (250 ft-c) were run with each set of irradiation treatments. After the irradiation treatments, the bottles containing tissue sections were returned to the dark until ethylene concentrations in the bottles were measured with a gas chromatograph (approximately 1 hr). All available samples for each treatment period were divided among the wavelengths available for that treatment period. Each wavelength, except 345 nm and 710 nm, was used in a minimum of three different treatment periods. Both E55 and E57 cultivars were used in the spectral region of 450 to 765 nm, and only E57 cultivar was used in the spectral region of 345 to 450 nm. There were no statistical differences in the ethylene production of E55 and E57 cultivars and they were averaged together. The irradiance and the number of samples at each wavelength are indicated in Table I. An action spectrum was calculated by dividing the response (ethylene production at each test wavelength minus ethylene production in dark control) by the irradiance. Since there was a difference in sensitivity between the two sets of data (Table I), the data in set II were correlated to the data in set I by adjusting for equal sensitivity at 450 nm. The data were then corrected to equal quanta at 400 nm, and all values normalized to an arbitrary value of 1 at 450 nm for plotting in Figure 1.
RESULTS AND DISCUSSION
Light-induced ethylene production in sorghum tissue irradiated with different wavelengths of light is given in Table I. Under the treatment conditions, maximum ethylene production was at the wavelength of 372 nm. Low regions of activity in the
1082
Plant Physiol. Vol.
LIGHT-INDUCED ETHYLENE PRODUCTION
51, 1973
Table I. Ethylenie Productionz from Excised Sorghum Sections at Selected Wavelenigths of Light Set II (450-765 nm)
Set I (345-450 nm)
Wave-
Irradiance
Samples
Ethylene production
nml
'LW cCM2
As.
nl/lg-hr 7.0 -- 0.6i 10.7 -- 1.3: 10.8 ±- 1.6 9.1 i 0.8 8.6 ± 1.2 9.3 - 1.5! 9.4 1 1.0 10.7 - 1.41 12.6 - 1.3k 7.1 - 1.4i
length
345 372
381 386 389 400 416 450 Light Dark
0.008 0.045 0.044 0.045 0.048 0.041 0.040 0.034 0.586 0
7 17 14 14 14 18 14 9 8 8
Ethylene Samplesi amPlesproduction
length
Wave-
Irradiance -
t1t
'W# cmX
Nio.
0.173 0.154 0.141 0.130 0.120 0.110 0.110 0.109 0.102 0.586 0
12 13 14 12 11 10 3 9 11 11 11
450 506 550 602 650 700 710 730 765 Light Dark
nllg-hr 4.8 i 0.6 4.3 i 0.3 3.6 4- 0.2 3.8 it 0.4 3.5 it 0.2 3.4 -- 0.5 4.4 4t 0.8 3.6 4t 0.3 4.2 - 0.2 5.8 - 0.5 3.5 4t 0.4
z
1083
regions. Recent work (5) has shown that ethylene treatment promoted anthocyanin synthesis in sorghum tissue if the ethylene was present as the tissue was placed in the light, but that ethylene inhibited anthocyanin synthesis if it was present later in the anthocyanin synthesis processes. Thus, plant tissue could control its anthocyanin content through light control of ethylene production; one photoreaction (HIR) initially increases ethylene production and promotes anthocyanin formation, whereas the second photoreaction (red light) decreases ethylene production and allows anthocyanin formation to continue. Other workers have suggested that light control of ethylene production through the phytochrome system can intervene as a regulator of phytochrome control of plumular expansion (7), elongation of coleoptiles (13), hook opening (12), and formation of carotene (11). In all of these cases, there is a decrease of ethylene production by plant tissue under red light. The results of these experiments demonstrate that lightinduced ethylene production in sorghum sections occurs in both the blue and far red region of the light spectrum. The fact that the shape of the action spectrum matches the HIR action spectrum (9) lends support to the conclusion that ethylene production in sorghum tissue is another example of a HIR, which is probably operating through phytochrome (8) as the initial photoreceptor. Acknowledgments-The authors thank A. B. Maunder of DeKalb AgResearch, Inc., Lubbock, Texas for the sorghum seed used in this study.
z 46
LITERATURE CITED
-
1.
WAVELENGTH (nm
)
FIG. 1. Action spectrum for induction of ethylene production by Sorghum vulgare L.
spectrum for ethylene production were from 550 to 650 nm, from 730 to 765 nm, and at 345 nm. The calculated action spectrum indicating relative quantrum effectiveness for ethylene production is given in Figure 1. This action spectrum closely resembles that designated by Hartman (9) for the HIR3 for hypocotyl growth inhibition in Lactuca sativa seedlings. This study did not determine whether the light-induced ethylene production from sorghum sections was enzymatic or nonenzymatic. Previous work (17) has demonstrated that in in vitro systems light in the presence of flavin mononucleotide can cause ethylene formation from methionine nonenzymatically. However, in plant tissue, ethylene appears to be produced only through enzyme controlled pathways (1). Our observed increase in ethylene production by sorghum tissue through an HIR response and the previously reported decreases in ethylene production under low irradiance red and far red light control agree with physiological observations for ethylene control of light-induced anthocyanin synthesis by sorghum seedlings. Downs and Siegelman (6) demonstrated that for anthocyanin formation in milo seedlings, two photoreactions in sequence were necessary, one requiring high energy and absorbing in the blue region (HIR) and the second one requiring low energy and absorbing in the red and far red 'Abbreviation: HIR: high irradiance response.
ABELES, A. L. AND F. B. ABELES. 1972. Biochemical pathway of stress-induced
ethylene. Plant Physiol. 50: 496-498. 2. ABELES. F. B. AND J. LoNsKI. 1969. Stimulation of lettuce seed germination by ethylene. Plant Physiol. 44: 277-280. 3. CORRELL, D. L., J. L. EDWARDS, W. H. KLEIN, AND W. SHROPSHIRE, JR. 1968. Phytochrome in etiolated annual rye. III. Isolation of photoreversible phytochrome. Biochim. Biophys. Acta 168: 36-45. 4. CRAKER, L. E. 1971. Postharvest color promotion in cranberry with ethylene. Hortscience 6: 137-139. 5. CRAKEER, L. E., L. A. STANDLEY, AND M. J. STARBUCK. 1971. Ethylene control of anthocyanin synthesis in sorghum. Plant Physiol. 48: 349-352. 6. DowN-s. R. J. A-ND H. W. SIEGELMAN-. 1963. Photocontrol of anthocyanin synthesis in milo seedlings. Plant Physiol. 38: 25-30. 7. GOESCHL, J. D., H. K. PRArr, AND B. A. BONNER. 1967. An effect of light on the production of ethylene and the growth of the plumular portion of etiolated pea seedlings. Plant Physiol. 42: 1077-1080. 8. HARTMANN, K. M. 1966. A general hyopthesis to interpret "High Energy Phenomena" of photomorphogenesis on the basis of phytochrome. Photochem. Photobiol. 5: 349-366. 9. HALRTMAN.N, K. M. 1967. Wirkungsspektrum der Photomorphogenes unter Hochenergiebedingungen und seine Interpretation auf der Basis des Phytochroms: Hypocotylwachstumshemmung bei Lactuca sativa L. Z. Naturforsch. 226: 1172-1175. 10. IMASEKI, H., C. J. PJON, AND M. FURUYA. 1971. Phytochrome action in Orzya sativa L. IV. Red and far red reversible effect on the production of ethylene in excised coleoptiles. Plant Physiol. 48: 241-244. 11. KAN-G, B. G. AND S. P. BURG. 1972. Involvement of ethylene in phytochromemediated carotenoid synthesis. Plant Physiol. 49: 631-633. 12. KANG, B. G. A-ND P. M. RAY. 1969. Role of growth regulators in the bean hypocotyl hook opening response. Planta 87: 193-205. 13. Kr, H. S., H. SUGE, L. RAPPAPORT, AND H. K. PRATT. 1969. Stimulation of rice coleoptile growth by ethylene. Planta 90: 333-339. 14. LARUE, T. A. G. AND 0. L. GAMBORG. 1971. Ethylene production by plant cell cultures. Plant Physiol. 48: 394498. 15. MEHERIUK, M. AND M. SPENCER. 1964. Ethylene production during germination of oat seedling and Pesnicillium digitatum spores. Can. J. Bot. 42: 337340. 16. WITHROW, R. B. 1957. An interference-filter monochromator system for the irradiation of biological material. Plant Physiol. 32: 355-360. 17. YANG, S. F., H. S. KU, AND H. K. PRATT. 1967. Photochemical production of ethylene from methionine and its analogues in the presence of flavin mononucleotide. J. Biol. Chem. 242: 5274-5820.
