Photoreversible Conductance Changes Induced by Phytochrome in Model Lipid Membranes

ABSTRACrRed light given to dark-grown etiolated leaves of Hordeum vulgare L. in vio or to cnrde homogenates increases the phytochrome content of the 20,000g pelet on centrifugation. The steroids cholesterol and stgmasterol ihibit this red light-induced phytochrome pelletability. Filipin (a polyene antibiotic, which is known to combine with steroids) inhibits red lghtinduced phytochrome pelletabiElty. Fdipin and steroids at the appropriate concentration appie together prevent the inhibition caused by either when aplied aloe. These results suggest that phytochrome may bind to a steroid component of mranes. The phospholid pbophatidyl choline dipalmitoyl has no effect on red lght-induced phytochrome pelletability.Preliminary evidence demonstrates a direct association of soluble phytochrome in its active form and steroids. The physiological significance of red light-induced pelletability and the primary anism of phytochrome action are discussed in terms of a hypothetical steroid-binding site.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Effects of Filipin and Steroids on Phytochrome Pelletability

Roth‐Bejerano¹,

Kendrick²

1979

“…The postulate that phytochrome works in membranes has also been supported by direct demonstration of phytochrome incorporation into "black lipid" model membranes containing oxidized cholesterol (119). The resistance of such membranes change markedly with alternating R and FR, indicating that conformational changes of the phytochrome alters membrane structure.…”

Section: Tirelymentioning

confidence: 63%

Plant Photobiology in the Last Half-Century

Galston

1974

The absorption of light energy not only nourishes the plant through photosynthetic phosphorylation and concomitant carbon dioxide fixation, but it also determines the nature and the direction of plant growth. This review will summarize the major advances in the physiology of both of the latter processes over the last half-century. Because of severe limitations of space, only a few key concepts can be mentioned, let alone emphasized, and some fields, like algal phototaxis, must be omitted entirely.Although there was certainly provocative earlier work by Klebs and others (100) (49,144). Although a definite conclusion cannot yet be made, the bulk of recent evidence favors the flavin hypothesis. I shall try to summarize this evidence and certain other aspects of the physiology of phototropism as well. Although experimentation in phototropism has been relatively quiescent for about 20 years, recent developments provide encouragement for new insights into this process.Some methodological problems are unique to this kind of biology. Decisions about photoreceptor pigments depend on correlations between action spectra for the process and absorption spectra for the pigment (10,160). Light, to be effective, must first be absorbed, and in energy ranges where photon absorption limits the rate or extent of a process, there should be rough correspondence between regions of the spectrum that are most active in eliciting a process and regions of high light absorption by the pigment. One cannot push these coincidences too far, however, because other pigments can act as light screens, differential refraction of different wavelengths inside the tissue can produce distortion in relative actinic effectiveness, attachment of pigments to different proteins can 1 Dedicated to the memory of Harry A. Borthwick, a wise and compassionate man. Generous support from the National Science Foundation has made possible the author's active involvement in this field for more than 20 years. alter their absorption properties in different ways, resonance transfer of energy between pigments or unequal quantum efficiencies at different wavelengths can alter curves, and dichroic orientation of a pigment in a lamella may produce aberrant or unrepresentative values. Despite these caveats, action spectra remain the major method for inferring the nature of the photoreceptor (130,131).Action spectra are prepared by doing dose-response energy experiments at each of the wavelengths employed. From such data, provided that the reciprocity law holds, one can calculate the energy required to produce a standard effect, e.g. 50% promotion of seed germination. When corrected for the different energy of quanta in the different portions of the spectrum and transformed to reciprocal values, these data tell us the relative effectiveness of quanta in producing the observed physiological effect. A plot of this parameter against wavelength gives the standard action spectrum.Deducing the nature of the photoreceptor pigment is only the first step along the difficult road of ...

“…A conformational change (1) in the structure of phytochrome (Pfr) is known to produce a rapid positive potential in the plasma membrane (2). Phytochrome has been reported to cause a fast change in the permeability of artificial membranes (9). A rise in the positive potential of the membrane would then increase the rate of flow of fluorescein, auxin, and other negatively charged ions in receptor cells.…”

Section: Discussionmentioning

confidence: 99%

Phytochrome-induced Increase of Fluorescein Translocation in Mung Bean Hypocotyls

Tanada¹

1978

Moderate doses of red (660 nanometer) irradiation cause a rapid increase in the translocation of fluorescein in dark-grown mung bean hypocotyl ( Vigna radiata L.) segments. The increase fails to appear following large doses of red (660 nanometers Consequently, by using fluorescein as a probe, it might be possible to obtain information which could lead to a better understanding of the mechanism of the action of light on some physiological processes. In this paper, some data are presented which suggest that red light has a rapid effect on the translocation. The reversal of the red light effect by far red light indicates the participation of phytochrome in the photoprocess. MATERIALS AND METHODSMung beans ( Vigna radiata L., cv. Oklahoma 612) seeds were screened for uniformity in size, spread over cheesecloth supported by a stainless steel wire screen over 5 liters of aerated tap water, and placed in darkness at 25 C. Four days later, seedlings growing upright were selected in dim green light at 25 C. The top 1.5 cm of a seedling was cut off, and the next 5-cm section was excised and used for experimentation. Seedlings and hypocotyl sections were handled gently and without pressure. Ten of the hypocotyl sections were placed apical end downward and vertical in a glass vial (1.4 x 4 cm) containing about I ml of distilled H20. The sections were then irradiated from above with narrow bands of red or far red light for various times. The light source was a 300-w projection lamp. White light from it was first passed through 9 cm of flowing water and then through interference filters (Ditric Optics, Inc.'). Bandwidths were 11.6 nm at 660 nm and 12.9 nm at 730 nm. The irradiance was 65 Aw/cm2 at 660 and 90 IAw/cm2 ' Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable. RESULTSThe effects of increasing length of exposure to red radiation on the translocation of fluorescein in mung bean hypocotyl section are depicted in Figure 1. Each data point is the mean of 150 measurements. After 5 to 40 sec of irradiation, red light significantly increases the movement of fluorescein in the hypocotyl sections. However, increasing the time of exposure beyond 60 sec results in nullification of the red induced increase.The red induced increase in fluorescein translocation is apparently controlled by phytochrome. Supporting data for phytochrome involvement in the photoprocess are presented in Figure 2. There is no increase if a 10-sec red exposure is immediately followed by a 15-sec far red exposure. Reversibility can be shown for at least two cycles. The difference between any final red and any final far red treatment is significantly different. DISCUSSIONRed light has been reported by Huisinga (4) to reduce the transport of fluorescein in mesocotyls of Avena seedlings. In contrast, results of this study show that a rapid increase o...