共查询到20条相似文献,搜索用时 31 毫秒
1.
Abstract A series of fluence-response curves for the binding of phytochrome to membranes in the absence of divalent cations, as described by Watson & Smith (1982), were constructed to demonstrate that the response obeys the law of reciprocity. Analysis of the binding of P fr (the far-red-absorbing form of phytochrome) showed that two P fr molecules bind to the membrane for each P r (the form with an absorption maximum in the red) photoconverted to P fr in the intrinsic membrane-bound phytochrome pool. Using this stoichiometry we have been able to model the binding curve of Pr and match the binding data. P r binding can be simulated if P r binds only as a consequence of the binding of P fr, i.e. when P fr is part of a P r: P fr dimer. The enrichment of the membranes with P fr as a result of the binding of P fr was also accurately simulated. There is no binding cooperativity. Phytochrome binding is a low-fluence response and the possibility that it has physiological significance as a mediator of phytochrome action is discussed. 相似文献
2.
Summary Under continuous high intensity incandescent light the decay of phytochrome in Amaranthus seedlings deviates from the predicted first order rate characteristic of the P
fr/ P
total ratio maintained. This deviation takes the form of a slower decay than would be predicted and is only observed at high intensities. Experiments are presented to test the hypothesis that this reduced rate of decay is the result of a high level of phytochrome intermediates maintained under high intensity incandescent light. Accumulation of intermediates under these conditions has been demonstrated using a quasi-continuous measuring spectrophotometer. They are weakly absorbing and their concentration increases with light intensity. Although they form P
fr in darkness, it is proposed that they do not decay. The model predicts that in a sample cuvette, where a light intensity gradient exists, there is more probability of a phytochrome molecule being presnet as P
fr at the back of the cuvette: the region of lowest light intensity. Under conditions which favour phytochrome decay, a preferential loss of phytochrome should result at the back of the cuvette and an increasingly higher proportion of the remaining phytochrome will consequently be measured as intermediate as the experiment progresses. The results confirm the hypothesis and in addition, after 60 min incandescent light, demonstrate an accumulation of intermediates which form P
fr with a longer half-life that at the begining of the experiment. Pisum epicotyl hooks show no such intermediate accumulation or preferential decay at the back of the cuvette, which is in agreement with the observed first order phytochrome decay under high intensity incandescent light. A scheme is presented explaining the results on the basis of the decay process.Abbreviations FR
far-red light
- R
red light
-
P
phytochrome
-
P
fr
far-red-absorbing form of P
-
P
r
red-absorbing form of P
321st communication of this Laboratory. 相似文献
3.
The phytochrome system is analyzed in light-grown maize ( Zea mays L.) plants, which were prevented from greening by application of the herbicide SAN 9789. The dark kinetics of phytochrome are not different in the first, second or third leaf. It is concluded that in light-grown maize plants phytochrome levels are regulated by P r formation and P fr and P r destruction, rather than by P frP r dark reversion. P r undergoes destruction after it has been cycled through P fr. The consequences of this P r destruction on the phytochrome system are discussed.Abbreviations SAN 9789
4-chloro-5-(methylamino)-2-(,,-trifluoro-m-tolyl)-3(2H) pyridazinone
- P fr
far-red absorbing form of phytochrome
- P r
red absorbing form of phytochrome
- P tot
P fr+P r 相似文献
4.
In the green alga Mougeotia, the dichroic orientation of the red-absorbing form of phytochrome (P r) is parallel of the cell surface, whereas the far-red-absorbing form (P fr) is oriented normal to it. The time course of the change from parallel to normal was investigated by double-flash irradiation with polarized red and far-red light. The results obtained by two different methods indicate that most of the phytochrome intermediates existing in the first 5 ms after the inducing red flash are still oriented parallel to the cell surface, similar to P r. At increasing intervals between the red and the far-red flashes, more and more phytochrome molecules turn their transition moments to the P fr orientation. This reaction is finished after approximately 30 ms. We conclude that the change in dichroic orientation of the phytochrome molecules in Mougeotia occurs during the last relaxation steps of the intermediates on the way from P r to P fr. It cannot be decided yet, whether the first surface-normal phytochrome species is an intermediate or P fr itself.Abbreviations P r
red-absorbing form of phytochrome
- P fr
far-red-absorbing form of phytochrome
A preliminary report of this work was presented at the European Symposium on Photomorphogenesis, University of Reading, UK (Kraml et al. 1982) 相似文献
5.
Spore germination in Dryopteris filix-mas occurs via a cascade of cellular responses, and chlorophyll formation, mitosis or rhizoid elongation are commonly used as parameters to determine spore germination. Detailed investigations of these parameters led to the hypothesis that they are regulated by different, independent phytochrome-mediated responses. This concept could be confirmed, as is described in this paper which demonstrates that perception of light via phytochrome occurs within two different phases separated in time. Presence of the far-red absorbing phytochrome form, P fr, for 36 h, induces chlorophyll formation and the first unequal cell division, by which a rhizoid initial and a protonemal initial are formed (first phytochrome-mediated response). However, rhizoid elongation requires a second period of P fr, presence (second phytochrome-mediated response). There is a clear temporal distinction between the first and the second phytochrome-mediated response with respect to the coupling of P fr to the transduction chain; P fr is unable to induce rhizoid growth until 60 h after the start of the first red irradiation. The effectivity of P fr for inducing the second response shows an optimum at ca 96 h after the beginning of the presence of P fr; thereafter, it declines slowly. The fluence-response relationship and the presence of red/far-red reversibility demonstrate that rhizoid elongation is a low-fluence response mediated by phytochrome and is independent of the first phytochrome response. 相似文献
6.
Phytochrome is a proteinaceous pigment that acts as a photoreceptor for photomorphogenetic responses in plants. It exists
as two stable absorbing forms, P r and P fr, which are interconvertible reversibly by irradiation with red or far-red light. The present review discusses (i) the primary
and higher-order structures of phytochrome that permit the reversible photoreaction; (ii) the molecular properties which change
accompanying the phototransformation; and (iii) the four-leaved shape model which has recently been proposed as a model of
quaternary structure of phytochrome. 相似文献
7.
Germination of spores of Dryopteris fllix-mas has been induced by two pulses of saturating red light, separated by a dark period of about 8 to 24 h. By chosing different wavelengths, different P fr/P tot levels could be established. Thus, by a “null method” the second pulse could be used as a “test pulse”, determining the actual P fr level remaining from the “start pulse”, and thus providing information about an apparent Pf r decay. It cannot be decided yet whether this apparent P fr decay results from dark destruction or dark reversion. The apparent P fr decay depends, as expected, on the temperature, being accelerated with increasing temperatures. Moreover, the later after sowing that the decay is tested, the faster it proceeds; a tentative interpretion is that newly synthesized P r undergoes faster decay after phototransformation than that phytochrome pool present in the resting spores. A third factor that influences the apparent P fr decay is the Pf r/P tot level established by the first pulse (start pulse). The lower this level, the slower the decay kinetics. This could be due to phytochrome biosynthesis partly compensating for P fr destruction, and the relative contribution of this biosynthesis to the total effect increases with lower P fr levels. Spores of D. paleacea yield virtually the same results. Whatever the real basis of the observed P fr decay, i.e. destruction, reversion, or a combination of these reactions with biosynthesis, it can be concluded that modification of this P fr decay by various factors is the basis of the effect of those factors on light-induced germination. 相似文献
8.
Phytochromes are photoreceptors in plants which can exist in two different conformations: the red light‐absorbing form (P r) and the far‐red light‐absorbing form (P fr), depending on the light quality. The P fr form is the physiologically active conformation. To attenuate the P fr signal for phytochrome A (phyA), at least two different mechanisms exist: destruction of the molecule and dark reversion. Destruction is an active process leading to the degradation of P fr. Dark reversion is the light‐independent conversion of physiologically active P fr into inactive P r. Here, we show that dark reversion is not only an intrinsic property of the phytochrome molecule but is modulated by cellular components. Furthermore, we demonstrate that dark reversion of phyA may be observed in Arabidopsis ecotype RLD but not in other Arabidopsis ecotypes. For the first time, we have identified mutants with altered dark reversion and destruction in a set of previously isolated loss of function PHYA alleles (Xu et al. Plant Cell 1995, 7, 1433–1443). Therefore, the dynamics of the phytochrome molecule itself need to be considered during the characterization of signal transduction mutants. 相似文献
9.
The ability to respond to phytochrome (P fr, the far-red light absorbing from of phytochrome) with anthocyanin synthesis appears first in some marginal regions of the abaxial epidermis of the mustard cotyledons and from there spreads gradually over the entire tissue (transient phase). The pertinent pattern is independent of environmental influences such as light quality and nutritional culture conditions. The competence for P fr in the epidermal cells, with regard to the initial action of P fr (concerning anthocyanin synthesis), appears considerably earlier than the ability for actual anthocyanin synthesis. An electron microscopical study of the ultrastructural changes occurring in vacuoles and plastids of the epidermal cells during the transient phase showed that a correlation only exists between the differentiation of central cell vacuoles, originating from the aleurone vacuoles, and the appearance of the ability to accumulate anthocyanin. It is suggested that the formation of a central cell vacuole is a prerequisite for anthocyanin accumulation in the epidermal cells of the mustard seedling cotyledons.Abbreviations P r, P fr
red and far-red absorbing forms of phytochrome
- HS
Hoagland's nutrient solution 相似文献
10.
The nonphotochemical reactions of phytochrome in the coleoptiles of dark-grown corn seedlings were studied at 3 temperatures: 14°, 24°, and 34°. The data obtained show that the destruction of Pfr is the only measurable reaction occurring; reversion of Pfr to Pr was not found. The Q 10's (2.7 and 3.5) and zero order kinetics found for the destruction reaction are consistent with the hypothesis that the reaction is enzyme-mediated. In vivo action spectra for phytochrome transformation in the coleoptiles of darkgrown corn seedlings were obtained which agree qualitatively with those obtained by other workers for phytochrome-mediated physiological responses and in vitro action spectra. In vivo conversion of phytochrome by blue light, as determined from spectrophotometric measurements of phytochrome itself, is reported. Action peaks for Pr were found at 667 mμ and in the blue in the region of 400 mμ, with a broad shoulder from 590 mμ to 640 mμ. Action peaks for Pfr were found at 725 mμ and in the blue in the region of 400 mμ with a minor peak at 670 mμ, and a broad shoulder from 590 mμ to 640 mμ. The ratio of the quantum efficiencies of Pr at 667 mμ and Pfr at 725 mμ (Φr667/Φfr725) was estimated to be 1.0. 相似文献
11.
Difficulties arising from the current dogma that the far-red absorbing form of phytochrome ( Pfr) is the only active form are discussed.A new hypothesis is proposed in which phytochrome is held to be the photoreceptor for both low energy (pulse) and high energy (HIR) responses. There is a common basic mechanism of action involving interaction between phytochrome and a binding site within the cell. The phytochrome involvement in low energy responses exhibits an action spectrum for binding that matches the Pr absorption spectrum and reversibility by far-red irradiation. Upon prolonged irradiation the phytochrome-binding site interaction acquires different characteristics that are reminiscent of those displayed in HIR, e.g. dependence on sustained irradiation for continual binding, dependence of the degree of binding on irradiance and the similarity of the action spectrum with that of HIR action spectra, e.g. that for inhibition of lettuce hypocotyl lengthening.As expected on the basis of the new hypothesis the particulate fraction of phytochrome contains both Pr and Pfr. Arguments are advanced that the presence of Pr in pellets of particulate phytochrome cannot be accounted for by (i) the “induced fit” hypothesis, (ii) the “pigment cycling” hypothesis, and (iii) the “open phytochrome-receptor model”. We conclude that phytochrome molecules, after being sufficiently energized can interact with their intracellular binding sites irrespective of their chromophoric configuration. 相似文献
12.
Abstract. Seedlings of Pharhitis nil show a circadian rhythm in the capacity to flower in response to the timing of a second red light pulse given at various times after a first saturating exposure to red when this is given together with a benzyladeninc spray. There are also changes in the photon irradiance required for half maximum response to the second red pulse. The photochemical properties of phytochrome in the photoperiodically sensitive cotyledons were also shown to change rhythmically. Oscillations in both p r→ P fr and P fr→ P r photoconversion characteristics persisted over at least two circadian cycles with a periodicity of about 12 h. There were, however, no significant oscillations in either P fr peak absorbance or in Δ(Δ A). The changes in sensitivity for the photoconversion of P r→ P fr did not parallel the much larger changes in sensitivity of the flowering response to red light. The amplitude of the P r→ P fr rhythm was at least as great as that for P r→ P fr, but the flowering response to far-red light was not rhythmic, nor was there any large change in sensitivity. The changes in photoconversion properties may reflect a basic biochemical oscillation which affects both photoreceptor properties and sensitivity to photoreceptor input. There was also a marked rhythm in the P fr/P ratio that would be established by a saturating pulse of red light and this too may have affected the flowering response to such a pulse. Far-red light inhibited flowering when given at any time during the inductive night. After 14 h in darkness, P fr could still be measured in the cotyledons and it was concluded that far-red light inhibited flowering by removing P fr As red light also inhibited flowering at this time, there may be two pools of phytochrome with different kinetic properties. 相似文献
13.
Summary The binding of phytochrome to a particulate fraction in extracts from hypocotyl hooks of etiolated Cucurbita pepo L. seedlings has been examined as a function of the light dose and P
fr
level established in vitro. As the steady-state level of P
fr
transiently established in the 500× g supernatant is increased, so the level of P
r
subsequently pelletable at 20 000× g increases up to a saturation level. Increasing both the time and irradiance parameters of the light dose while holding the steady-state P
fr
level constant, results similarly in increasing P
r
pelletability. This agrees with results obtained previously with in-vivo irradiations of maize coleoptiles. Thus, like the in-vivo response, phytochrome binding in vitro appears to be a function of the total number of molecules converted to the P
fr
form during the irradiation period.Abbreviations
P
fr
far-red-absorbing form of phytochrome
-
P
r
red-absorbing form of phytochrome 相似文献
14.
Abstract Mustard seedlings were light treated at 24 h after sowing (25°C) to induce phytochrome-mediated anthocyanin synthesis in cotyledons and hypocotylar hook. All light treatments were performed within the range of the reciprocity law. The in situ photoconversion kinetics of phytochrome (P r→ P fr) were measured under the same light treatment. It was found that between 0.4 and 1.0 relative P fr level the amount of anthocyanin extracted from the organs at 52 h after sowing was linearily correlated with the amount of P fr produced at 24 h in cotyledons and hypocotylar hook. It is concluded that an explanation of the fluence response function for red light mediated anthocyanin synthesis in the mustard seedling does not require the concept of active vs. bulk phytochrome. 相似文献
15.
Summary In dry gourd seeds all the phytochrome is in the P fr form. The increase of phytochrome content from the beginning of hydration involves two phases, A and B, in the embryonic axis as well as in the cotyledons. Cycloheximide does not prevent the appearance of P r during phase A. We assume that P r is gradually released from an inactive complex. On the other hand phase B is inhibited by cycloheximide; this could mean that a de novo synthesis of P r occurs.Some experiments indicate that the phytochrome which is localized in the embryonic axis may be involved only in the germinating process.The phytochrome which is synthesized during phase B disappears when the seeds are irradiated with red light, while the original phytochrome does not.According to our data it seems necessary to lay down a new and precise definition of the germination process. 相似文献
16.
Phytochrome controls the appearance of many enzymes in the mustard ( Sinapis alba L.) cotyledons. The problem has been whether the effect of phytochrome on the appearance of enzymes in this organ is due to a common initial action of P fr, e.g. due to the liberation of a second messenger. We have compared the modulation by light (phytochrome) of the appearance of phenylalanine ammonia lyase (PAL) + and ribulosebisphosphate carboxylase (Carboxylase) +. PAL becomes detectable in the mustard cotyledons at 27 h after sowing while Carboxylase starts to appear only at 42 h after sowing (starting points, 25° C). The starting points cannot be shifted by light. As a major result, in the case of PAL the inductive effect of continuous red light (given from the time of sowing) remains fully reversible by 756 nm-light up to the starting point (27 h after sowing) while with Carboxylase full reversibility in continuous red light is lost at approximately 15 h after sowing. While the induction of Carboxylase is already saturated at a very low level of P fr (e.g. continuous 756 nm-light saturates the response) and does not depend on irradiance (e.g. continuous 675 mW m -2 red light and 67.5 mW m -2 red light lead to the same time course), PAL induction is a graded response over a wide range of P fr doses and depends strongly on the fluence rate (high irradiance response, HIR). It is concluded that PAL induction and Carboxylase induction are not only separated in time but differ in every regard except that both responses are mediated by phytochrome.The present data support the previous conclusion that the specification of the temporal and spatial pattern of development is independent of phytochrome even though the realization of the pattern of development can only occur in the presence of phytochrome (P fr). It seems that there is no feedback from pattern realization to pattern specification.Abbreviations P fr
the far-red absorbing, physiologically active form of phytochrome
- P r
the red absorbing physiologically inactive form of phytochrome
- P total
[P r]+[P fr]
- PAL
phenylalanine ammonia-lyase (EC 4.3.1.5)
- Carboxylase
ribulosebisphosphate carboxylase (EC 4.1.1.39) 相似文献
17.
Fluence rate-response curves were determined for the inhibition of hypocotyl growth in 54 h old dark-grown Sinapis alba L. seedlings by continuous or hourly 5 min red light irradiation (24 h). In both cases a fluence rate-dependence was observed. More than 90% of the continuous light effect could be substituted for by hourly light pulses if the total fluence of the two different light regimes was the same. Measurements of the far red absorbing form of phytochrome ([ P
fr]) and [ P
fr]/[ P tot] (total phytochrome) showed a strong fluence rate-dependence under continuous and pulsed light which partially paralleled the fluence rate-response curves for the inhibition of the hypocotyl growth.Abbreviations R
red
- HIR
high irradiance response
-
P
rfr
phytochrome in its red, far-red absorbing form
- [ P
tot]=[ P
r]+[ P
fr]
= k
1/( k
1+ k
2): photoequilibrium of phytochrome at wavelength , whereby k
1,2 rate constants of P
rP
fr, P
frP
r photoconversion
-
[ P
fr]/[ P
tot] 相似文献
18.
The etiolating, intact mustard ( Sinapis alba L.) seedling exhibits a distinct temporal pattern of ethylene production. Light, operating through phytochrome, increases the rate of ethylene production without changing the pattern. Ethylene production of the isolated plant parts (segments), added together, exceed the production of the intact system even if the wound effect is taken into account. There is no significant light effect on ethylene production of the segments. Phytochrome-mediated anthocyanin synthesis in the cotyledons is inhibited by ethylene. The responsiveness towards ethylene of the anthocyanin producing metabolic chain is decreased by phytochrome. As anthocyanin synthesis is only partly inhibited under saturating ethylene concentrations in the atmosphere around the seedlings (100 l l –1), a twofactor analysis becomes feasible. This analysis leads to the result that phytochrome and ethylene show multiplicative behavior, meaning that phytochrome and ethylene act on the same metabolic sequence (leading to anthocyanin) but independently of each other, and at different sites. Therefore, the hypothesis that ethylene mediates the action of phytochrome in anthocyanin synthesis and photomorphogenesis in general appears to be inapplicable.Abbreviations P fr
far-red absorbing form of phytochrome
- P r
red absorbing form of phytochrome
- P tot
total phytochrome, i.e. [P r]+[P fr] 相似文献
19.
Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5.) induction in cotyledons from 96-h dark-grown Lycopersicon esculentum Mill. was studied in response to continuous light and hourly light pulses (blue, red, far red). The increases of PAL promoted by blue and red pulses are reversed completely by immediately following 758 nm irradiations. The response to continuous red light could be substituted for by hourly 6-min red light pulses. The effect of continuous red treatments is mainly due to a multiple induction effect of phytochrome. In contrast to red light, hourly light pulses with far red and blue, light can only partially substitute for continuous irradiation. The continuous blue response could be due to a combination of a multiple induction response and of a high irradiance response of phytochrome. The continuous far red response, could represent a high irradiance response of phytochrome. Dichromatic irradiations indicate that phytochrome is the photoreceptor controlling the light response (PAL) in tomato seedlings.Abbreviations Norflurazon
NF-4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-tolyl)-3 (2H) pyridazinone
- PAL
phenylalanine ammonia-lyase
-
phytochrome photoequilibrium P fr/P tot
- P fr
far-red absorbing form of phytochrome
- P r
red absorbing form of phytochrome
- P tot
total phytochrome: P r+P fr 相似文献
20.
Carotenoid accumulation in the cotyledons of the mustard seedling ( Sinapis alba L.) is controlled by light. Besides the stimulatory function of phytochrome in carotenogenesis the experiments reveal the significance of chlorophyll accumulation for the accumulation of larger amounts of acrotenoids. A specific blue light effect was not found. The data suggest that light exerts its control over carotenoid biogenesis through two separate mechanisms: A phytochrome regulation of enzyme levels before a postulated pool of free carotenoids, and a regulation by chlorophyll draining the pool by complex-formation.Abbreviations Chl
chlorophyll(s)
- PChl
protochlorophyll(ide)
- HIR
high irradiance reaction (of phytochrome)
- P fr
far-red absorbing, physiologically active form of phytochrome
- P r
red absorbing, physiologically inactive form of phytochrome
- P fof
total phytochrome, i.e. [P r]+[P fr]
-
[P fr]/[P fof], wavelength dependent photoequilibrium of the phytochrome system
- red
red light
- fr
far-red light 相似文献
|