Light Dosage and Phototropic Responses of Corn and Oat Coleoptiles

Briggs, Winslow R.

doi:10.1104/pp.35.6.951

Cited by 81 publications

(55 citation statements)

References 18 publications

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“…Combinations of intensity and length of exposure use(d to achieve a particular light dosage have rarely been reported. The inmportance of precise knowledge of lighlt exposutre conditions in interpreting dosage-response curves has been emphasized elsewxhere (4 ) an(l xvill be consi(lere(l in detail in the discussioni.…”

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Phototropic Dosage-Response Curves for Oat Coleoptiles

1963

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In 1934, DU Bux aiid Nuernbergk (9) compiled from a nunmber of sources the first extensive phototropic dosage-response curve for oat coleoptiles. The Xvarious features of this curve, first positive curvature, firlst negative curvature, and second and third positive curvatuire, are now wvell knownv. The early (losage-respoIise Only very recently has the profound effect of re(l light oni the phototropic responise been appreciated (1,3,5,7,8). But here too the picture was confused. Some authors reporte(l anl increase in phototropic sensitivity (1,3,5) xvhat. and lhave draxv-n atteintioni to the fact that it is not simplv the total amount of light received by the plant that is imilportanlt. but the imlaninier in xv-hicbl it is a( illlnsstel-ed as x-ell. The present paper has tlhree objectives. The first is to obtain a series of (losage-response curves for phototropic tip curvature xvith several intensities of monoclhromiiatic lighlt and exactly-defilled conditions. The second is to clarify the effect of red light on phototropic sensitivitx un(ler a xvi(le range of definle(l con(litions of phototropic induction. The third is to provi(le the basis for a (letaile(l kinetic analysis ot phototropismii of oat coleoptiles (13). Materials & MethodsOats (,4zncna sativa L., cv. Victory) wvere germiiinate(l folloxving in detail a regimiie described elsewlxere (5). The only light used during handling was fromii 15 xv green fluorescent lights wrapped in one layer of green and txvo layers of amber cellulose acetate (Shades. Inc., San Francisco). The tranismissiOI of this combinationi of filtering mlaterial was determined wvith a Bausch and( Lomb Spectronic 505 recording spectrophotometer. It Mvas found to he greater than 0.1 %{ only in a narroxv region of the spectrum from 5220 to 5630 A. When used during early stages of growth of the seedlings, the light described produced no noticeable phototropic effects.After the coleoptiles had reached a length of 0.5 cnm, only a single lamp as above,v wrappedc witl two layers of each type of cellulose acetate, was used, and then only for a short time. If extreme care was not taken even with this latter illumination, enough irregularity andl curvature occurred to pro(luce large variability 248 www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

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Phototropic Dosage-Response Curves for Oat Coleoptiles

1963

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“…Therefore, photosensing for SPPC can occur along the entire length of the coleoptile and does not predominantly take place in the apex. The BunsenRoscoe reciprocity law is valid for FPPC and FNPC, but does not hold for phototropic reactions of the secondpositive type (Briggs, 1960;Zimmermann and Briggs, 1963;Everett and Thimann, 1968). Despite the great number of physiological studies, we know little about the nature of the photoreceptor and the particular steps within the phototropic signaling pathway.…”

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“…The most extensive studies on phototropic-curvature reactions were done on the coleoptile of etiolated oat (Avena sativa L.) seedlings, a classic object of phototropism research. From the fluenceresponse curves obtained by unilateral irradiation of oat coleoptiles with blue or white light at least three different types of bending reactions have been distinguished with respect to the light-stimulus intensity and duration (Briggs, 1960;Zimmermann and Briggs, 1963;Everett and Thimann, 1968;Meyer, 1969aMeyer, , 1969bIino, 1988a). Pulse irradiations at low fluences result in FPPC, whereas longer irradiation times are needed to induce SPPC.…”

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Exposure of Oat Seedlings to Blue Light Results in Amplified Phosphorylation of the Putative Photoreceptor for Phototropism and in Higher Sensitivity of the Plants to Phototropic Stimulation

Salomon¹,

Zacherl²,

Luff³

et al. 1997

Plant Physiology

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Dark recovery of blue light-induced i n vitro phosphorylation in oat (Avena safiva L.) seedlings after in vivo preirradiation with blue light revealed different recovery kinetics for the coleoptile base and tip. Although, in both cases, maximum in vitro phosphorylation was observed 90 min after i n vivo blue light treatment, the phosphorylation levels for the entire base were about 3-fold higher than those found in nonpreirradiated plants. l h e tip response only slightly exceeded that of the dark controls. l h e fluence applied during preirradiation determined the extent of the increase in phosphorylation. Consequently, unilateral irradiation and subsequent dark incubation resulted in a more pronounced increase in phosphorylation in the irradiated than in the shaded side of the coleoptile base. Furthermore, blue light-irradiation conditions, known to induce neither first-nor second-positive curvature in nonpreirradiated plants, stimulated both asymmetric distribution of protein phosphorylation and second-positive phototropic curvature in the coleoptile base when administered to blue light-pretreated plants. Based on these data, we conclude that photosensitivity of the coleoptile base increases upon exposure to blue light i n a time-and fluence-dependent manner, providing an excellent explanation of the invalidity of the Bunsen-Roscoe reciprocity law for secondpositive phototropism.Phototropism has been studied in a variety of dicotyledoneous and monocotyledoneous plants over the last century (for reviews, see Firn and Digby, 1980;Briggs and Baskin, 1988;Iino, 1990; Firn, 1994). The most extensive studies on phototropic-curvature reactions were done on the coleoptile of etiolated oat (Avena sativa L.) seedlings, a classic object of phototropism research. From the fluenceresponse curves obtained by unilateral irradiation of oat coleoptiles with blue or white light at least three different types of bending reactions have been distinguished with respect to the light-stimulus intensity and duration (Briggs,

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“…1,2,7,12). Because the amplitude of phototropic curvature to blue light can be increased by a preirradiation with red light, it was reasonable to measure the effect of such a preirradiation on the time threshold for second positive curvature.…”

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Time threshold for second positive phototropism is decreased by a preirradiation with red light.

A-K

Konjević

Apel³

et al. 1992

Plant Physiol.

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A second positive phototropic response is exhibited by a plant after the time of irradiation has exceeded a time threshold. The time threshold of dark-grown seedlings is about 15 minutes for Arabidopsis thaliana. This threshold is decreased to about 4 minutes by a 669-nanometer preirradiation. Tobacco (Nicotiana tabacum) seedlings show a similar response. The time threshold of darkgrown seedlings is about 60 minutes for tobacco, and is decreased to about 15 minutes after a preirradiation with either 450-or 669-nanometer light. The existence of a time threshold for second positive phototropism and the dependence of this threshold on the irradiation history of the seedling contribute to the complexity of the fluence response relationship for phototropism.Understanding the mechanism for phototropism has been hindered by the complexity of the fluence response relationship for this response by seedlings. Phototropic curvature increases with increasing fluence in an ascending arm above a threshold fluence, reaches a maximum, and then decreases in a descending arm. This relatively symmetrical curve is known as first positive phototropism. At even higher fluences, curvature increases again with increasing fluence in what is known as second positive phototropism. Reciprocity is valid for first positive phototropism but not for second positive phototropism (3,8).The suggestion by Zimmerman and Briggs (12,13) that first and second positive phototropism result from separate systems has been interpreted to mean that the two phototropic responses are controlled by different photoreceptor pigments. However, Janoudi and Poff (5) suggested that the apparent lack of valid reciprocity for second positive phototropism is, at least in part, a consequence of an irradiation time requirement for that response. When that time requirement is met in Arabidopsis thaliana, fluence response relationships for second positive phototropism show a fluence threshold that is the same as the fluence threshold for first positive phototropism. Based on this common fluence threshold for first and second positive phototropism, they noted that it is not necessary to postulate a difference in the

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Light Dosage and Phototropic Responses of Corn and Oat Coleoptiles

Cited by 81 publications

References 18 publications

Phototropic Dosage-Response Curves for Oat Coleoptiles

Phototropic Dosage-Response Curves for Oat Coleoptiles

Exposure of Oat Seedlings to Blue Light Results in Amplified Phosphorylation of the Putative Photoreceptor for Phototropism and in Higher Sensitivity of the Plants to Phototropic Stimulation

Time threshold for second positive phototropism is decreased by a preirradiation with red light.

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