Dark Reversion of Phytochrome in Sinapis alba L

Phytochrome in Sinapis alba L. (white mustard) seedlings undergoes both decay and reversion after an exposure to red light. This is typical of other crucifers and of dicotyledons in general. In the presence of sodium azide, decay is inhibited, and reversion continues at about the same rate as in buffer alone. The reversion has been demonstrated both in cotyledon plus hypocotyl hook and in hypocotyl hook samples alone and is of the same order of magnitude in both. Contrary conclusions in the literature that there is no reversion in Sinapis are based on indirect measurements and are unjustified.     

The growth of new processes from isolated dorsal and sympathetic cell bodies of rat and rabbit

The ganglia were dissected out from very young and adult rats and rabbits, and the cells liberated by teasing. After two weeks incubation at 37 degrees in 199 medium, 29% to 57% of isolated cells had fine filiform processes. On addition of 10u/ml of Nerve Growth Factor 10% to 23% more had such processes. Heated control cells did not.     

Early Receptor Potential Evidence for the Existence of Two Thermally Stable States in the Barnacle Visual Pigment

The early receptor potential (ERP) in the barnacle photoreceptor is shown by intracellular recording to exhibit a strong dependence on the color of the stimulus and of the preceding adaptation. The adaptation effects appear to be stable for at least 3 h in the dark. Most strikingly, the ERP is positive after red adaptation and mainly negative after blue adaptation. The simplest hypothesis which accounts for these observations is that two thermally stable pigment states with different absorption spectra contribute to the ERP. All ERP responses appear to be consistent with the sums of different ratios of the ERP's of the two pure states. The relative populations of the two states are shown to vary reciprocally, suggesting that the two are states of the same closed pigment cycle. Both states have approximately Dartnall nomogram-shaped absorption spectra, one peaked near 495 nm, and the other near 532 nm.     

Spatial properties of the prolonged depolarizing afterpotential in barnacle photoreceptors. II. Antagonistic interactions

In the preceding article, we investigated the spatial properties of the induction of the prolonged depolarizing afterpotential (PDA) by shifting visual pigment from the rhodopsin (R) to the metarhodopsin (M) state in the barnacle photoreceptor. In this work, we have studied the ranges within the cell of the antagonistic effects on the PDA of M-to-R transfer. When this transfer occurs during a PDA, it depresses the PDA; when it precedes PDA induction, it impedes that induction ("anti-PDA"). These ranges were previously shown (by a statistical technique) to be at least a few tens of nanometers within a half-second (D greater than 10(-13) cm2 s-1). We now demonstrate, with local illumination techniques in which a PDA was induced in one side of the cell and PDA depression or anti-PDA was induced in the other side, that both ranges are much smaller than the cell diameter (approximately 100 microns) within 30 s (D less than 10(-6)). We further show, using a less direct but shorter-range technique involving colored polarized light, that the interaction of the PDA with the anti-PDA is restricted to less than approximately 6 microns (D less than 6 X 10(-9)). This figure is quite low and suggests that the interaction may be confined to the pigment molecules, possibly in a complex of the type suggested in the preceding article.     

Uptake of 14C-α-aminoisobutyric acid by Phaseolus vulgaris

Specific uptake (S.U.) of α-aminoisobutyric acid ([1-¹⁴C]AIB), a non-metabolizable neutral amino acid analog, by dwarf bush bean plants (Phaseolus vulgaris cv Top Crop) demonstrated wide differences in active transport between various plant organs. The kinetic and timed uptake data reported were expressed as S.U. because this corrects for the diffusion of AIB which is part of the total AIB uptake process. Roots accumulated AIB to concentrations up to 18 times and leaf disks to twice those of the incubation medium. Stem tissue showed very little uptake, if any, that could not be accounted for by simple diffusion or water free space. Although initial rate kinetic studies demonstrated the presence of a normal transport system, timed uptake studies revealed greatly decreased transport by etiolated plants, suggesting a relationship between active transport and the lack of photosynthate. The reproducibility of the AIB uptake pattern by mature roots strongly supports the concept that the transport of neutral amino acids is biphasic and suggested one or more carrier systems are inducible by either low intracellular concentrations or repressed by high intracellular concentrations of the amino acid.     

Entrainment of Lemna CO(2) Output Through Phytochrome

The entrainability of Lemna perpusilla CO₂ output by periodic 15 minute red (R) and far red (F) illuminations was tested in low nitrate medium. R every 8 hour, symbolized R/R/R, gives a flat output (no entrainment) as does F/F/F. However, R/—/— (R every 24 hour) entrains rapidly, and F/—/— does so as well, in a similar manner. The effects of R/R/— and F/F/— also resemble each other closely. Entrainment by R/F/F or R/R/F is rapid and indifferent to order of presentation, e.g., R/F/F and F/R/F lead to the same steady state. Typical phytochrome reversals occur, e.g., R,F/F/F holds output flat, while F,R/F/F entrains in the manner of R/F/F. Blue (B) light acts like R in schedules such as B/F/F but like F in schedules such as B/R/R. In all schedules studied, the zeitgeber (primary synchronizer) appears to be the sharpest transition from a low to a high level of far red-absorbing phytochrome that occurs with a 24-hr periodicity. Thus in entrainment, and by inference in photoperiodic timing, the level of far red-absorbing phytochrome at any time may be less significant than the succession of levels of which it is a part, a conclusion that implies the existence of a “scanning” mechanism that compares levels of far red-absorbing phytochrome at various times of day.     

Stable concentrations of phytochrome in pisum under continuous illumination with red light

In vivo spectrophotometry showed that the phytochrome concentration in pea epicotyl hooks decreased at a constant rate for 4 hours when the tissue was exposed to continuous red light. Thereafter the rate slowed progressively so that a steady concentration of phytochrome was approached at hour 7. Returning the plants to darkness resulted in an increase in phytochrome due to the apparent synthesis of P_R. A closely similar pattern of changes was found in the amount of phytochrome extracted from the tissue. The establishment of the stable concentration was inhibited by 2,4-dichlorophenoxyacetic acid and did not occur in segments which had been incubated for longer than 24 hours, but was observed when segment growth was inhibited by mannitol. The results may be explained by an equilibrium between P_FR destruction and apparent P_R synthesis.