How Phytochrome Acts — Perspectives on the Continuing Quest

G Gardner and HL Gorton (1985 Plant Physiol 77: 540) demonstrated that gabaculine (5-amino-1,3-cyclohexadienylcarboxylic acid) inhibits the initial synthesis and resynthesis of spectrophotometrically detectable phytochrome in pea, maize, and oat. We show that the level of immunodetectable phytochrome in pea is unaffected by the presence of gabaculine at a concentration that reduces spectrophotometrically detectable phytochrome up to 10-fold. This result indicates that gabaculine inhibits chromophore synthesis without affecting phytochrome apoprotein synthesis and that chromophore-less phytochrome is stable in the cell.

mentioning

confidence: 99%

Synthesis of Phytochrome Apoprotein and Chromophore Are Not Coupled Obligatorily

Jones¹,

Allen²,

Gardner³

et al. 1986

“…The nuclei were irradiated with 2 min actinic R and/or 2 min FR while they were in the assay buffer, just before substrate addition. The actinic R source produced an irradiance of approximately 15 (Fig. 2).…”

Section: Methodsmentioning

confidence: 99%

“…Wagle (31) found that R stimulates the activity of a Mg2+-dependent ATPase in pea nuclei and that FR reverses this effect. Metabolic responses that are photoreversible by R and FR are considered to be under the control of the photochromic pigment, phytochrome, an important regulator ofphotomorphogenesis and gene expression in plants (15). In another study on the regulation of nuclear ATPases, Matsumoto et al (20) demonstrated that calcium and calmodulin modulate an ATPase activity in the chromatin fraction of pea 'Supported by grants from the National Science Foundation (PCM 8402526) and the National Aeronautics and Space Administration (NSG 7480) (27) and refine ideas on the biochemical steps by which light is able to regulate gene activity in higher plants (30).…”

mentioning

confidence: 99%

Characterization of Nucleoside Triphosphatase Activity in Isolated Pea Nuclei and Its Photoreversible Regulation by Light

Chen¹,

Roux

1986

A nucleoside triphosphatase (NTPase) present in highly purified preparations of pea nuclei was partially characterized. The activity of this enzyme was stimulated by divalent cations (Mg2" = Mn2" > Ca2"), but was not affected by the monovalent cations, Na' and K+. The Mg2"-dependent activity was further stimulated by concentrations of Ca2" in the low micromolar range. It could catalyze the hydrolysis of ATP, GTP, UTP, and CTP, all with a pH optimum of 7.5.

“…The results of Blaauw-Jansen and co-workers (2,17) (2). VanDerWoude (14,23) Figure 1 for 35°C treated seeds. made sensitive (VLFR seeds) while the remaining seeds (LFR seeds) will show a fluence response curve over the same range as seeds maintained at 25C (Fig.…”

mentioning

confidence: 91%

Analysis of the Effect of Light and Temperature on the Fluence Response Curves for Germination of Rumex obtusifolius

Takaki

Heeringa²,

Cone³

et al. 1985

Both red light (10 minutes) and 35°C treatment (60 minutes) stimulate the germination of seeds of Rumex obtusifolius otherwise maintained in darkness at 25°C. Fluence response curves were determined for the effect of red light to stimulate germination of seeds with and without 35°C treatment. The endogenous far-red absorbing form (Pfr) level in the seeds was determined using short saturating fluences of wavelengths of light which maintain different proportions of phytochrome as Pfr at equilibrium. In the seed batches investigated, the endogenous Pfr level was found to be 4% or less of the total phytochrome. High dark germination after 35°C treatment does not result from an increase in sensitivity of the whole population to Pfr. Calculated fluence response curves for germination which best fit the experimental data suggest that seeds germinate in darkness after 35°C treatment because of a nonphytochrome-related process (overriding factor).The involvement of phytochrome in the germination of Rumex obtusifolius has been demonstrated by several authors (7,15,24). At 25°C seeds of R. obtusifolius contain a concentration of Pfr below the threshold necessary to stimulate germination. A single (R3) irradiation induces germination by photoconversion of Pr to Pfr (15). However, alternating low and high temperature can induce germination in darkness (7,22). Isikawa and Fujii (15) (19) observed that light-requiring lettuce seeds respond to high temperature in the same way as R. obtusifolius. They also showed broadband FR can partially reverse the induction of germination brought about by the high temperature treatment and concluded that this was due to the reduction of preexisting Pfr to which the seed population had become sensitive.This paper reports detailed fluence response curves for induction of germination of three seed batches of R. obtusifolius by R with or without a short 35°C treatment and estimates of their preexisting Pfr content. Four hundred seeds were sown on four layers of filter paper (Ederol Nr 15, W. Germany) moistened with 4 ml distilled H20 in a 5-cm plastic Petri dish, and incubated in darkness at 25C. All treatments were given after 24 h from sowing when maximum sensitivity to both light and 35°C treatment is attained (18). In determining fluence response curves all fluences were given in 60 s using a custom built projector with a 250-w quartz iodine lamp in combination with an interference filter, (660 nm), bandwidth at 50% transmission 10 nm (Balzers, B40 type, Liechtenstein) in combination with neutral glass filters (NG., Schott u. Gen., Mainz., W. Germany). Different MATERIALS AND METHODS