The relationship between phytochrome-photoequilibrium and Development in light grown Chenopodium album L.

Chenopodium album seedlings were grown in light environments in which supplementary far-red light was mixed with white fluorescent light during various parts of the photoperiod. Both the logarithmic rate constant of stem extension and the leaf dry weight: stem dry weight ratio were linearly related to estimated phytochrome photoequilibrium () in each treatment regime. These data are taken to be indicative of a functional link between phytochrome and development in the green plant. A layer of chlorophyllous tissue only affected the linearity between calculated and the logarithmic stem extension rate at high chlorophyll concentrations, whilst even low concentrations-equivalent to the levels found in stem tissue-caused a significant shift in measured . End-of-day supplementary far-red (FR) light induced between 0–35 per cent of the response elicited by all-day supplementary FR, whilst daytime supplementary FR (with a white fluorescent light end-of-day treatment) induced approximately 90 per cent. The ecological significance of this difference is discussed with respect to shade detection.Paper 7 in the series The function of phytochrome in the natural environment [for paper 6 see McLaren, J.S., Smith, H., Plant, Cell and Environment 1, 61–67, 1978]     

Absence of fluence rate dependency of phytochrome modulation of stem extension in light-grown Sinapis alba L.

In background white light, supplementary far-red (_max 700 nm) is an order of magnitude less effective than supplementary far-red (_max 739 nm) in the stimulation of stem extension in Sinapis alba. The relationship between phytochrome photoequilibrium and extension rate increase for the two supplementary far-red treatments is, however, very similar. This evidence indicates that phytochrome cycling is not involved in the phytochrome control of stem extension in light-grown Sinapis alba and that the response to supplementary far-red light is not fluence rate (irradiance) dependent.Abbreviations Pfr far-red absorbing form of phytochrome - the phytochrome photoequilibrium (Pfr/Ptotal)     

Light quantity and quality interactions in the control of elongation growth in light-grown Chenopodium rubrum L. seedlings

The spectral control of hypocotyl elongation in light-grown Chenopodium rubrum L. seedlings has been studied. The results showed that although the seedlings responded to changes in the quantity of combined red and far-red radiation, they were also very sensitive to changes in the quantity of blue radiation reaching the plant. Altering the proportion of red: far-red radiation in broad waveband white light caused marked differences in hypocotyl extension. Comparison of the responses of green and chlorophyll-free seedlings indicated no qualitative difference in the response to any of the light sources used, although photosynthetically incompetent plants were more sensitive to all wavelengths. Blue light was found to act primarily of a photoreceptor which is different from phytochrome. It is concluded that hypocotyl extension rate in vegetation shade is photoregulated by the quantity of blue light and the proportion of red: far-red radiation. In neutral shade, such as that caused by stones or overlying soil, hypocotyl extension appears to be regulated primarily by the quantity of light in the blue waveband and secondarily by the quantity of light in the red and far-red wavebands.Abbreviations B blue - FR far-red - k ₁, k ₂ rate constants for photoconverison of Pr to Pfr and Pfr to Pr, respective - k ₁/k ₁ +k ₂= phytochrome photoequilibrium - k ₁ +k ₂= phytochrome cycling rate - Pr=R absorbing form of phytochrome - Pfr=FR absorbing form of phytochrome - P_tot Pr+Pfr - PAR photosynthetically active radiation = 400–700 nm - R red - WL white light     

Rapid photomodulation of stem extension in light-grownSinapis alba L.

Treatment of the whole of aSinapis alba plant with supplementary far-red light (FR), in back-ground white light (WL), induces a rapid increase in stem extension rate. This rapid increase is regulated by the light environment of the stem itself. Supplementary FR to the stem increases extension rate after a lag period of 10–15 min. A lag period of 3–4 h follows FR irradiation of the leaf, before an increase in extension rate is detectable. When the stem is given supplementary FR, the change in extension rate which is induced increases with increasing FR fluence rate, and with decreasing phytochrome photoequilibrium. There is no difference between the effects of supplementary FR _max 719 nm and supplementary FR _max 739 nm for these relationships. The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R). These data indicate that the response is controlled by phytochrome photoequilibrium.Abbreviations B blue light - FR far-red light - R red light - WL white light - Pfr far-red absorbing form of phytochrome - Pr red absorbing form of phytochrome - P_tot total phytochrome level (=Pr+Pfr); -Pfr/Ptot, measured - ER difference in stem extension rate, before and after treatment     

Coaction of blue/ultraviolet-A light and light absorbed by phytochrome in controlling growth of pine (Pinus sylestris L.) seedlings

Photomorphogenesis is a conspicuous feature in conifers. In the case of the shade-intolerant Scots pine (Pinus sylvestris L.), control of stem growth by light is well expressed at the seedling stage and can readily be studied. The present data show that hypocotyl growth is controlled by the far-red-absorbing form of phytochrome (Pfr). However, the Scots pine seedling requires blue or ultraviolet (UV-A) light to become fully responsive to Pfr. Blue/UV-A light has no direct effect on hypocotyl growth and its action appears to be limited to establishing the responsiveness of the seedling to Pfr. This type of coaction between phytochrome and blue/UV-A light has been observed previously in a number of angiosperm seedlings. With regard to the high irradiance reaction of phytochrome in long-term far-red light the pine seedling deviates totally from what has been observed in etiolated angiosperms since continuous far-red light has no effect on stem growth.Abbreviations B light of wavelength between 500 and 400 nm - FR standard far-red light - HIR high irradiance reaction of phytochrome - R high-fluence-rate red light (_R = 0.8) - RG9-light long-wavelength far-red light defined by the properties of the Schott RG9 glass filter (_RG₉<0.01) - = Pfr/Ptot wavelength-dependent photoequilibrium of the phytochrome system (far-red-absorbing form of phytochrome/total phytochrome) - UV-A near ultraviolet light of wavelength between 400 and 320 nm - W white light Research supported by a grant from the Deutsche Forschungsgemeinschaft (Schwerpunkt Physiologie der Bäume).     

Phytochrome-controlled extension growth of Avena sativa L. seedlings

The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of P_fr, the far-red light absorbing form of phytochrome (e.g., by [P_fr]0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by P_fr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to P_fr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by P_fr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of P_fr established at the onset of darkness rather than by the actual P_fr level present during the growth period.Abbreviation P_fr far-red light absorbing form of phytochrome     

Action of light on accumulation of carotenoids and chlorophylls in the milo shoot (Sorghum vulgare Pers.)

We have performed a comprehensive study on the mechanism of regulation of carotenogenesis by light in the shoot of Sorghum vulgare. Our work shows that carotenoid accumulation is simultaneously controlled by phytochrome (P_fr) and by the availability of chlorophyll. Throughout plastidogenesis light dependent chlorophyll and carotenoid accumulation are interdependent processes: Accumulation of chlorophyll in natural light requires the presence of carotenoids; likewise, accumulation of considerable amount of carotenoids depends on the availability of chlorophyll. However, in both cases the efficiency of the biosynthetic pathway, the potential biosynthetic rates (capacities) are determined by phytochrome. A push and pull model of carotenogenesis advanced previously (Frosch and Mohr 1980, Planta 148, 279) to explain carotenogenesis in the mustard (Sinapis alba) seedling also applies to the monocotyledonous milo (Sorghum vulgare) seedling. Therefore, we suggest that the model applies to carotenogenesis in higher plants in general.Abbreviations Chl chlorophyll(s) - PChl protochlorophyll(ide) - HIR High irradiance response (of phytochrome) - P_fr far-red absorbing, physiologically active form of phytochrome - P red absorbing physiologically inactive form of phytochrome - P_tot total phytochrome - i.e. [P_r]+[P_fr] =[P_fr]+[P_tot], wavelength dependent photoequilibrium of the phytochrome system - RL red light - FR far-red light     

Analysis of light-controlled accumulation of carotenoids in mustard (Sinapis alba L.) seedlings

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     

Control by light of hypocotyl growth in de-etiolated mustard seedlings

After sowing, mustard (Sinapis alba L.) seedlings were grown for 48 h in white light (25°C). These fully de-etiolated, green seedlings were used as experimental material between 48 and 72 (84) h after sowing. The question researched was to what extent control by light of hypocotyl elongation is due to phytochrome in these seedlings. It was found that the light effect on hypocotyl growth is very probably exerted through phytochrome only. In particular, we found no indication for the involvement of a specific blue light photoreceptor pigment.Abbreviations HIR high irradiance reaction - P_fr far-red absorbing, physiologically active form of phytochrome - P_r red absorbing, physiologically inactive form of phytochrome - Pot total phytochrome, i.e. [P_r]+[P_fr] - [P_fr]/[P_tot] - red red light - fr far-red light - wl white light - bl blue light - di dichromatic irradiation - l hypocotyl length     

Control by phytochrome of urate oxidase and allantoinase activities during peroxisome development in the cotyledons of mustard (Sinapis alba L.) seedlings

The peroxisomal enzyme, urate oxidase (EC 1.7.3.3), and the next enzyme of the urate pathway, allantoinase (EC 3.5.2.5), demonstrate a lightmediated rise of activity in the cotyledons of mustard (Sinapis alba L.). The capacity of the peroxisomes for urate breakdown, marked by the time course of urate oxidase, develops distinctly later than the two other peroxisome functions (fatty acid breakdown, glyoxysomal function; glycolate breakdown, leaf peroxisomal function). The light effect on urate oxidase and allantoinase is mediated through the phytochrome system in all three seedling organs (cotyledons, hypocotyl, radicle), as revealed by induction/reversion experiments with red/far-red light pulses and continuous irradiation with far-red light (high irradiance reaction of phytochrome). Both enzyme activities can be induced by phytochrome in the seedling cotyledons only during a sensitive period of about 48 h prior to the actual light-mediated rise of activity, making it necessary to assume the existence of a long-lived intermediate (transmitter) in the signal response chain connecting enzyme formation to the phytochrome system. Detailed kinetic investigation, designed to test whether urate oxidase and allantoinase are controlled by phytochrome via the same signal response chain (coordinate induction), revealed large differences between the two enzymes: (i) a different onset of the loss of reversibility of a red light induction by a far-red light pulse (=onset of transmitter formation=coupling point; 48 h/24 h after sowing for urate oxidase/allantoinase); (ii) a different onset of the response (=onset of competence for transmitter= starting point; 72 h/48 h); (iii) full loss of reversibility (=completion of transmitter formation) is reached at different times (independence point, 90 h/52 h). These differences show that phytochrome controls urate oxidase and allantoinase via separate signal response chains. While urate oxidase can be localized in the peroxisomal fraction isolated from crude organelle extracts of the cotyledons by density gradient centrifugation, most of the allantoinase activity found in the peroxisomal fraction did not appear to be an integral part of the peroxisome but originated presumably from adhering membrane fragments.Abbreviations AL allantoinase, EC 3.5.2.5 - CAT catalase, EC 1.11.1.6 - GO glycolate oxidase, EC 1.1.3.1 - ICL isocitrate lyase, EC 4.1.3.1 - UO urate oxidase, EC 1.7.3.3. P_r - P_fr red and far-red absorbing forms of phytochrome On the occasion of his 80th birthday we dedicate this paper to Prof. Dr. phil., Dr. mult. h.c. Kurt Mothes, pioneer in research on metabolism of urates