PHYTOCHROME-MEDIATED GERMINATION: EFFECTS OF BRIEF HIGH TEMPERATURE TREATMENTS

Abstract— Brief high temperature treatments, applied early in the pregerminative period to radiation-requiring seeds of lettuce, inhibited both dark and radiation-induced germination. The inhibition increased with increasing incubation temperature. There was little difference in the germination percentage whether the inductive irradiation was applied before or after the high temperature treatment. When the high temperature treatment preceded induction, there was an increase in the radiation dosage required for maximum germination. These findings are interpreted in terms of lability of physiologically active phytochrome to higher temperatures.     

THE TEMPERATURE DEPENDENCE OF Pfr ACTION GOVERNS THE UPPER TEMPERATURE LIMIT FOR GERMINATION IN LETTUCE

In most cultivars of lettuce (Lactuca saliva L,), red light acting through the red/far-red reversible phytochrome system promotes full germination within the20–30°C range, but at progressively higher temperatures germination declines sharply. The relationship between this upper ternperature limit for germination and the temperature dependence of phytochrome action was investigated in Grand Rapids lettuce. In fresh seeds the GT₅₀ (temperature giving half maximal germination) was ca 29–30°C. In these seeds, escape from far-red reversibility did not occur at 35°C, a temperature above the GT₅₀, but occurred rapidly at 27°C, a temperature below the upper limit. Increasing periods of dark pretreatment at high temperature (35°C) or increasing concentrations of the germination inhibitor coumarin caused a progressive decline in the GT₅₀, Escape from photoreversibility did not occur at 27°C in seeds in which the GT₅₀ had been reduced to less than 25°C by coumarin or by prolonged high temperature pretreatment. These results indicate that there is a close correlation between the position of the upper temperature limit for germination, and the temperature dependence of phytochrome action. We conclude that factors that alter the upper temperature limit for germination do so by changing the temperature dependence of phytochrome action.     

LIGHT PROMOTION OF SEED GERMINATION IN Datura ferox IS MEDIATED BY A HIGHLY STABLE POOL OF PHYTOCHROME

Abstract— The duration of the far-red light-absorbing form of phytochrome (Pfr) of the photoreceptor pool involved in the control of seed germination was investigated for Datura ferox seeds. These seeds require both Pfr and alternating temperatures (20/30°C) to germinate. After 24 h imbibition (25°C), the seeds received pretreatment-light pulses providing different phytochrome photoequilibria (Pfr/P), followed by a 24 h dark incubation (25°C), and test-light pulses providing different Pfr/P immediately prior to transfer to alternating temperatures. Germination increased with increasing Pfr/P provided by the test-light pulses, but was unaffected by the pretreatment-light pulses. This suggests that phytochrome synthesis, phytochrome degradation and phytochrome-mediated changes in response to phytochrome were negligible. In other experiments, red light-pretreatment pulses were followed by dark incubations (25°C) of different duration before transfer to alternating temperatures. The proportion of Pfr remaining after the 25°C incubation period was estimated by comparing germination rates with those of seeds that received test-light pulses of known calculated Pfr/P immediately prior to the start of the cycles of alternating temperatures. More than 80% of the Pfr established by a Pfr/P= 0.87 light pulse was present and active even after 48 h dark incubation at 25°C. Surprisingly, when a pretreatmentlight pulse providing a Pfr/P= 0.70 was given, the reduction in [Pfr] was significantly faster.
Germination of Datura ferox seeds is under the control of a highly stable (type II like) phytochrome pool. Apparently, this pool follows Pfr dark reversion to the red light-absorbing form, the times to reach half the original Pfr pool being > 96 h or <14 h after light pulses providing Pfr/P= 0.87 or 0.70, respectively.     

PHYTOCHROME IN ETIOPLASTS IN RELATION TO CHLOROPHYLL ACCUMULATION*

Abstract— De-etiolation of maize seedlings reduces their sensitivity for red light potentiation of rapid chlorophyll accumulation in white light. An earlier proposal (Raven and Spruit, 1973) attributes this to migration of the far-red absorbing form of phytochrome (P_fr) to receptors essential for chlorophyll synthesis, thereby increasing the local P_fr/total phytochrome (P_tot)ratio. We have studied etioplasts as possible loci for such P_(r receptors. The level of spectrophotometric phytochrome in purified etioplasts isolated from red preirradiated maize seedlings was higher than that of dark grown plants. The difference was marginally significant, however. We argue that migration of a fraction of cytoplasmic P_fr to the etioplasts, too small to be spectrophotometically demonstrable, could still meet the requirements of the model. Dark destruction of bulk spectrophotometric P_fr following saturating red irradiation of seedlings is not paralleled by a decrease of etioplast phytochrome. the latter remaining essentially constant over long periods. On the other hand, the potentiating effect of red light in intact seedlings is still partially reversible by far red light even after 24 h of darkness when destruction of bulk P_fr is complete. Since this demonstrates persistent presence of P_fr active in potentiation, we propose that at least part of this P_fr is associated with the etioplasts.     

ANTAGONISTIC EFFECTS OF RED AND FAR-RED LIGHTS ON THE STABILITY OF PHOTOSYSTEM II IN PEA LEAVES EXPOSED TO HEAT

Abstract— The presence of light during exposure of intact pea leaves to high temperature (40°C) protects Photosystem II (PSII) against inactivation, as indicated by the preservation of the maximal variable 685 nm chlorophyll fluorescence and the photosynthetic oxygen evolution. This photoprotection was observed (i) to be saturated at low fluence rates ( ca 10 W m^-2) and (ii) to be strongly dependent on the spectral characteristics of the light. It was specifically induced by red light (630–670 nm) whereas other wavelengths were much less protective. A strong antagonism between red and far-red lights was also observed, with PSII stabilization by red light being partially cancelled by additional far-red light.     

PHYTOCHROME INTERMEDIATES IN VIVO-I. EFFECTS OF TEMPERATURE, LIGHT INTENSITY, WAVELENGTH AND OXYGEN ON INTERMEDIATE ACCUMULATION

Abstract— Accumulation of weakly absorbing phytochrome intermediates has been demonstrated in Pisum epicotyl tissue under conditions of pigment cycling using a quasi-continuous measuring spectrophotometer. An action spectrum shows 690–700 nm to be the most efficient wavelength range in this process. Difference spectra for the decay of intermediates maintained by 690 nm light show that, if the experiment is done at 0°C, only P_fr is formed. At – 11°C, intermediates decaying to P_r can also be observed. At – 20°C, P_r is produced as well as a pigment with peak absorption at 710nm. Kinetic analysis of intermediate decay at – 11°C reveals that at least two intermediates are maintained by 690 nm light. The level of intermediate maintained by incandescent light at 0°C was 25% higher in air than in nitrogen.     

SIGNIFICANCE OF FLUENCE-RESPONSE DATA IN PHYTOCHROME-INITIATED SEED GERMINATION

Abstract. A model was developed to describe changes in fluence-response kinetics in terms of total phytochrome level (P_tot), level of the factor X interacting with active phytochrome (P_fr), P_frX equilibrium constant, seed sensitivity to P_fr-X interaction, and variation in phytochrome sensitivity within the seed population. Under conditions of stable X levels and stable population variation, the model predicted that a change in any of the other components will result in a parallel fluence-response curve on a probit-logarithmic plot. The linearity of the subsaturation plot is dependent on the ratio of P_tot to X concentrations. The model showed that changes in threshold response fluences can result from many causes other than changes in total phytochrome [P_tot>]. Changes in response-saturating fluences when maximal germination is less than 100% are predicted to be due to limiting levels of X. Changes in slope of fluence-response curves can be explained by changes in seed population variation by this model. Rumex crispus L. fluence-response data for germination is best explained by this model in terms of neither changes in P_tot nor X levels altering kinetics.     

PHYTOCHROME MEDIATION OF UREDOSPORE GERMINATION IN THE FUNGUS PUCCINIA GRAMINIS

Abstract—Applying criteria used for higher plants, phytochrome mediation of uredospore germination in the stem-rust fungus, Puccinia graminis f. sp. tritici (Eriks & Henn) Guyot is established. A 1 min red irradiation at 660 nm promotes uredospore germination and this potentiation of promotion is photoreversible by a 1 min far-red irradiation at 730 nm.     

PHYTOCHROME ACTION AT HIGH PHOTON FLUENCE RATES: RAPID EXTENSION RATE RESPONSES OF LIGHT-GROWN MUSTARD TO VARIATIONS INFLUENCE RATE and RED: FAR-RED RATIO*

Abstract— Extension growth rate of light-grown mustard (Sinapis alba L.) seedlings was monitored continuously using a sensitive linear displacement transducer system. When high fluence rates (ca 2 mmol m^?2 s^_1) of mixed red and far-red light were presented to the growing internodes from fibre optic probes, fluctuations in extension rate occurred during the first 30 min. High red: far-red ratios (R: FR) caused growth deceleration, whilst low R: FR caused transitory growth acceleration. These changes in extension rate were not exactly as predicted from the proportions of Pr (the red-absorbing form of phytochrome) and Pfr (the far-red absorbing form of phytochrome) calculated to be established by the light sources. Nevertheless, the data demonstrate that phytochrome is able to control extension growth at fiuence rates approaching those of summer sunlight, thereby providing the capacity to sense the presence of neighbouring vegetation before shading seriously compromises photosynthesis. Varying fiuence rate over two orders of magnitude whilst maintaining R: FR constant evoked transient fluctuations in extension rate. At high R: FR, a 100-fold step down in fiuence rate led, after a lag of ca 10 min, to a transient (i.e. 20 min) deceleration of extension that was followed by a marked transient (i.e. 20 min) acceleration. After a 100-fold step up in fiuence rate, a transient (i.e. 20 min) acceleration only was observed, beginning after a lag of ca 10 min. When R: FR was low, neither a step-down nor a step-up in fluence rate resulted in appreciable fluctuations in extension rate. The data are discussed in relation to the possible role played by the accumulation of photoconversion intermediates using a simple computer model for simulating active phytochrome concentrations at high fluence rates. The possibility that the mechanism for the photoperception of light quality by phytochrome may be capable of rapid adaptation to fluence rate fluctuations is proposed.     

FLUENCE RATE COMPENSATION OF THE PERCEPTION OF RED: FAR-RED RATIO BY PHYTOCHROME IN LIGHT-GROWN SEEDLINGS*

Abstract— The hypothesis that phytochrome functions as a sensor of vegetational shade through the perception of the red: far-red photon fluence rate ratio requires that the mechanism of perception be compensated for wavelength-independent fluctuations in fluence rate (Smith, 1982). This paper seeks to establish the lower limit of fluence-rate compensation and to assess whether or not compensation is effective at the total fluence rates typical of herbaceous canopies. Using specially-designed cabinets, Sinapis alba L. (white mustard) seedlings were grown from germination under a range of total photosynthetically-active radiation (PAR = 400 to 700 nm) values and a range of red: far-red ratios. The data indicate that fluence-rate compensation is effective above a PAR value of ca. 60 μ.mol m² s'. Pretreating seedlings at high red: far-red ratio and a PAR level of 300 (μmol m₂S_-1for increasing periods of time led to an extension of fluence rate compensation to lower fluence rates. The results are discussed in relation to the photosynthetic competence of the seedlings grown under these conditions.     

RED-LIGHT-INDUCED GERMINATION OF LETTUCE SEEDS: RELATIONSHIP BETWEEN ESCAPE FROM REVERSIBILITY AND FLUENCE*

Abstract— Dormant seeds of Lactuca saliva L. (cv. ‘May Queen’) germinate after a brief light treatment. The seeds escape from photoreversibility by far-red irradiation after a lag time. The duration of the lag decreases with increasing levels of the far-red absorbing form of phytochrome (P_fr). During the lag time the percentage of seeds germinating after the reversing far-red irradiation is slowly rising. This is not due to an escape reaction proper, but to an increase of sensitivity to P_fr.     

PHYTOCHROME AND EFFECTS OF SHADING ON GROWTH OF WOODLAND PLANTS

qrowth of Circaea lutetiaim plants was studied in various locations in or near a mixed deciduous woodland. Morphological changes resulting from increased shading included increases in leaf area ratio, specific leaf area and specific water content. Parallel measurements with a spectroradi-ometer confirmed that shading involved a reduction in both light fluence rate and light quality (e.g. red/far-red ratio). Phytochrome P_fr/P status was also studied by spectrophotometric measurements on Avena seedling test material and by biological (Lactuca seed germination) assay. Attempts were made to demonstrate phytochrome controlled changes in plant morphology under controlled environment, using both end-of-day far-red treatment and far-red enrichment of the main light period. Effects of natural shading were most clearly simulated by varying light fluence rate while maintaining a constant but high red/far-red ratio     

INDEPENDENT EFFECTS OF PHYTOCHROME AND NITRATE ON NITRATE REDUCTASE AND NITRITE REDUCTASE ACTIVITIES IN MAIZE

Abstract— Involvement of phytochrome in the regulation of nitrate reductase (NR) and nitrite reductase (NIR) activities in excised, etiolated leaves of Zea mays (L.) variety 'Ganga-5' is demonstrated using low energy and high irradiance responses of phytochrome action. Photoreversibility by far-red light of red light stimulated increases in NR and NIR activities was lost by 2 h. Red light given to the leaves, when induction by NO^-₃, was saturated, further increased both enzyme activities. Even if red light was given 4–8 h before NO^-₃, it still increased both NR and NIR activities.     

ULTRAVIOLET RESONANCE RAMAN SPECTRA OF PHYTOCHROME: A COMPARISON OF THE ENVIRONMENTS OF TRYPTOPHAN SIDE CHAINS BETWEEN RED LIGHT-ABSORBING AND FAR-RED LIGHT-ABSORBING FORMS

Ultraviolet resonance Raman spectra of phytochrome in the red light-absorbing form (Pr) and the far-red light-absorbing form (Pfr) are reported. The spectra excited at 240-nm provide structural information about the protein part of phytochrome. The protein contains only a very small amount of β-sheet structure and most of the tyrosine side chains are located in hydrophobic environments. Indole rings of tryptophan (Trp) interact with neighboring groups in the Pr form and these interactions become weaker with the conversion from Pr to Pfr. Some Trp side chains of Pfr are surrounded by aliphatic groups but such is not the case in Pr. These changes in the environment occur at the same time as changes in orientation of Trp side chains. Our observations suggest that interactions between Trp residues and the tetrapyrrolic chromophore occur in the Pr form and that the strength of these interactions diminishes in the Pfr form.     

PROBIT ANALYSIS OF LOW AND VERY-LOW FLUENCE-RESPONSES OF PHYTOCHROME-CONTROLLED Kalanchoe blossfeldiana SEED GERMINATION*

Abstract— Kalanchoë blossfeldiana seeds are light-requiring for seed germination. On water or KNO₃ solution and irradiated with several daily red (R) irradiations, the seeds show a low-fluence (LF) response which is far-red (FR) reversible. Incubated on gibberellic acid (GA₃) the seeds show a very-low-fluence (VLF) response which can be saturated with red as well as with far red light. As germination is a quantal response, the sub-optimal segments of the dose-response curves are analysed by means of probit analysis in order to calculate the seed population parameters. There is a linear relation between the probit of the germination response and the logarithm of the fluence. Moreover, the slope for the VLF as well as for the LF response is the same. The VLF requires about 8 × 10⁴ times less fluence than the LF. VLF saturation with FR requires about 200 times more fluence than with R. Although, GA₃ and KNO₃ modulate VLF and LF, respectively, there is no direct influence on the phytochrome-phototransformations. Once P_fr is formed (in VLF or LF, or preserved in dry seeds) germination is proportional to the GA_S concentration (for VLF and dark germination) or proportional to the KNO, concentration (for LF). The non-photochemical events leading to germination seem to be triggered by a similar action mechanism for both GA, and KNO₃.     

ENERGY TRANSFER IN TRITON X-405 MICELLES: THE EFFECTS OF TEMPERATURE AND BRIJ 35

–Energy transfer from the phenyl groups of micellar Triton X-405 (TX-405) to solubilized pyrene molecules has been measured at a range of temperatures and in the presence of different polyoxyethylene 23 lauryl ether (Brij 35) concentrations. Increases in temperature lead to elimination of water from the outer, wet, micelle layer and an inward movement of associated pyrene. The addition of Brij also leads to a reduction in polarity of the microenvironment of pyrene. However, sensitization is observed even at high Brij concentrations. The donor/acceptor separation caused by the introduction of Brij proceeds slowly, continuing for several minutes after its addition to micellar TX-405.     

THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT—III. MEASUREMENT AND CALCULATION OF PHYTOCHROME PHOTOEQUILIBRIA

Abstract— Phytochrome photoequilibria have been measured in dark-grown Phaseolus uulgaris L . and Cucurbita pepo I . hypocotyl hooks which had been exposed to various natural and artificial radiation sources. Mean phytochrome photoequilibria ( φ ) varied from 0.20 within a wheat canopy to 0.54 above, although lower values were occasionally observed in densely shaded areas. Greater variation in phyto chrome photoequilibria and lower levels of P_fr were recorded within a sugar beet canopy. The range of photoequilibria was φ= 0.04 in dense shade to φ= 0.54 above the canopy. Photoequilibrium was achieved within 5 s in mid-day sunlight and approximately 30 s in dense canopy shade.
A close correlation was found between φ and the ratio of the quantum flux in the red and far-red wavelength bands (ζ) in broad spectrum (400–800 nm) radiation. This relationship allows direct prediction of φ from a knowledge of ζ. Phytochrome showed greatest sensitivity to spectral changes in the range ζ= zero to ζ= 1.0, which is the range found in the natural environment.
The observations provide support for the hypothesis that phytochrome is involved in the detection of shading by plants.     

水处理用强型离子交换树脂抵抗反复渗透压冲击能力测定方法的研究

本研究提出的强渗磨圆球率测定方法，将GB／T12958－1990中已有的树脂强度测定方法（渗磨圆经）中的渗透压冲击由一个周期增加为五个周期，以便更加实地反映凝结水处理树脂在实际使用中在强度方面的差别。对国内主要树脂厂家生长的凝结水处理用强酸，强碱各9种样品的测定结果表明，78％的强酸树脂和56％的强碱树脂的强渗磨圆球率可达到或大于90％的指标，大型型树脂的强渗磨圆球率一般高于凝胶型均粒树脂。该测定方法已作为电力行业标准－《火电厂水处理用离子交换树脂选用导则》的“标准的附录”。