Loss of Phytochrome Photoreversibility <i>in Vitro</i>

“…The existence of such a substance, 'Pfr killer,' was confirmed in the extract of pea but not in A vena by Fox (2). Although Shimazaki and Furuya (11) and Fox (3) succeeded in purifying the substance partially, the chemical nature of the substance has remained unknown.…”

mentioning

confidence: 91%

Effects of a Triterpenoid Saponin on Spectral Properties of Undegraded Pea Phytochrome

Konomi

Furuya²,

Yamamoto³

et al. 1982

Plant Physiol.

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Soyasaponin 1, a triterpenoid saponin isolated from etiolated pea (Pisum sativum cv. Alaska) shoots and identified as Pfr killer, was examined for its effects on spectral properties of undegraded pea phytochrome. When soyasaponin I in concentrations of 100 micromolar or lower was added to Pr in the dark, the spectrum of Pr was not significantly affected, whereas in the presence of 120 micromolar or higher concentrations the absorption maximum of Pr shifted from 666 to 658 nanometer with slight decrease of absorbance. After a brief exposure of the mixture to red light, the increase in absorbance at 666 nanometers that occurs in the dark was inhibited at 26 micromolar and higher soyasaponin I concentrations; the maximum effect being reached at about 180 micromolar. The decrease in absorbance at 724 nanometers in the dark after red light irradiation was somewhat inhibited by 60 micromolar and totally prevented by 410 micromolar soyasaponin 1. When P658 was irradiated with red light in the presence of 220 micromolar or higher soyasaponin I concentrations, a bleached form (Pbh) was produced instead of Pfr. Phi showed no dark spectral changes, and the phototransformation of Phi to P658 required a significantly high irradiance of far-red light. When the saponin was added to Pfr in the dark, none of the above-described spectral changes occurred, although the same effects were observed after the mixture was exposed briefly to far-red light followed by red light.In the early days of phytochrome study, Furuya and Hillman (6) found that crude aqueous extracts of etiolated pea tissue contain a substance which almost instantaneously destroys phytochrome photoreversibility in the Pfr but not in the Pr form. The existence of such a substance, 'Pfr killer,' was confirmed in the extract of pea but not in A vena by Fox (2). Although Shimazaki and Furuya (11) Hillman, who played a critical role in the study of photomorphogenesis and also has discovered the Pfr killer effect with M.F. at Brookhaven two decades ago.

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“…In addition, the relation between phytochrome destruction and metal ions (9,11), sulfhydryl reagents (5), chelating agents (14,17), and plant components such as "'killer factor" (5,6) is poorly understood. These experiments were undertaken to clarify the apparent contradiction between the very low levels of phytochrome found in green tissue and the many phytochrome-mediated responses found in green plants. If phytochrome is produced in meristematic cells, as is indicated by the profiles of phytochrome titer in etiolated plants (2) and the correlation between phytochrome synthesis and cell division in tissue cultures (20), then loss of photoreversibility should occur when the meristematic region becomes and extracts of apical and immediately subapical green tissue of light-grown peas.…”

mentioning

confidence: 99%