A photoperiod-insensitive barley line contains a light-labile phytochrome B

Barley (Hordeum vulgare L.) is a long-day plant whose flowering is enhanced when the photoperiod is supplemented with far-red light, and this promotion is mediated by phytochrome. A chemically mutagenized dwarf cultivar of barley was selected for early flowering time (barley maturity daylength response [BMDR]-1) and was made isogenic with the cultivar Shabet (BMDR-8) by backcrossing. BMDR-1 was found to contain higher levels of both phytochrome A and phytochrome B in the dark on immunoblots with monoclonal antibodies from oat (Avena sativa L.) that are specific to different members of the phytochrome gene family. Phytochrome A was light labile in both BMDR-1 and BMDR-8, decreasing to very low levels after 4 d of growth in the light. Phytochrome B was light stable in BMDR-8, being equal in both light and darkness. However, phytochrome B became light labile in BMDR-1 and this destabilization of phytochrome B appeared to make BMDR-1 insensitive to photoperiod. In addition, both the mutant and the wild type lacked any significant promotion of flowering in response to a pulse of far-red light given at the end of day, and the end-of-day, far-red inhibition of tillering is normal in both, suggesting that phytochrome B is not involved with these responses in barley.

Infrared light-emitting diode radiation causes gravitropic and morphological effects in dark-grown oat seedlings

Oat (Avena sativa cv Seger) seedlings were irradiated with IR light-emitting diode (LED) radiation passed through a visible-light-blocking filter. Infrared LED irradiated seedlings exhibited differences in growth and gravitropic response when compared to seedlings grown in darkness at the same temperature. Thus, the oat seedlings in this study were able to detect IR LED radiation. These findings call into question the use of IR LED as a safe-light for some photosensitive plant response experiments. These findings also expand the defined range of wavelengths involved in radiation-gravity (light-gravity) interactions to include wavelengths in the IR region of the spectrum.

Protein Differences between Two Isogenic Cultivars of Barley (Hordeum vulgare L.) that Differ in Sensitivity to Photoperiod and Far-Red Light

A photoperiodically sensitive cultivar of barley (Hordeum vulgare L. Shabet) (BMDR-8) and an isogenic, single-gene recessive mutant of this genotype that is insensitive to photoperiod (BMDR-1) were grown under continuous cool white light with or without supplemental far-red fluorescent light. BMDR-1 initiates flowers 6 days after germination, irrespective of light treatment, whereas BMDR-8 remains vegetative for at least a week longer, even in continuous light. When far-red light is added, the delay of flowering in BMDR-8 is overcome and both genotypes initiate floral primordia at the same time. Total phenol extracted proteins of seedlings of both genotypes were resolved by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No protein differences were found between the genotypes when isoelectric focusing gels were run in the first dimension. Two qualitative genotypic differences were found when nonequilibrium pH gradient gel electrophoresis was run in the first dimension. An 85-kilodalton polypeptide (A) and a 26-kilodalton polypeptide (B) were always present in BMDR-8 but never found in BMDR-1. The levels of A appeared to decrease from the BMDR-8 during the first 3 days of far-red treatment but did not disappear completely even after 6 days of growth in the presence of farred. Polypeptide B decreases rapidly in continuous cool white light but is stabilized by far-red. The phytochrome content of BMDR-1 was found to be greater than that for BMDR-8. This increase appears to be caused by the type I (etiolated-tissue abundant) phytochrome pool, even in plants grown in continuous light.

Cryptochrome, Phytochrome, and the Photoregulation of Anthocyanin Production under Blue Light

The principle of equivalent light action predicts that two light treatments (wavelengths ;lambda(1) and lambda(2)) producing the same Pfr/P ratio (phi(lambda1) = phi(lambda2)) and the same rate of phytochrome photoconversion (k(lambda1) = k(lambda2)) are perceived by phytochrome as being the same and should produce the same effect. The results of experiments based on the principle of equivalent light action indicate that cryptochrome is involved in the photoregulation of anthocyanin production elicited by blue light in tomato seedlings. This was also the case for one strain of cabbage seedlings. For another strain of cabbage seedlings, the results suggest that cryptochrome is either not involved or that the state of phytochrome is the principal limiting factor.

Photocontrol of Peanut (Arachis hypogaea L.) Embryo and Ovule Development in Vitro

The purpose of the present study was to determine the nature of the photoreceptor that controls the light-dependent development of the peanut ovule and embryo, and to determine whether this photoreceptor activity is located in the ovular or the embryonic tissue. Peanut ovules were aseptically excised from surface sterilized gynophores (pegs) and cultured in darkness, continuous far red (FR), or given 15 minutes daily irradiations with white (W), red (R), blue (B); FR, R/FR, FR/R light for 21 days. Increases in the volume of ovules cultured in dark, continuous FR, FR, or R/FR were significantly greater than for ovules cultured in W, R, FR/R, or B radiation. Halving the ovule or removing the micropyle did not affect the relative change in ovule volume in response to different light treatments. When the light sources were altered after the first 10 days of culture, the ovules exposed first to darkness or FR radiation began to increase in ovule volume which then ceased after subsequent exposure to W, R, or B radiation. Likewise, if W, R, or B radiation was given during the first 10 days, ovule development was inhibited, and could be stimulated by exposure to darkness or FR light. Growth of embryos, when removed from the influence exerted by ovular tissue, was unaffected by the light. However, when embryos remained attached to the ovular tissue, their growth was stimulated in darkness or by FR light and inhibited by W, R, or B light. The R/FR reversibility indicates that the photoreceptor that regulates ovular growth is phytochrome and that the maternal ovular tissue appears to be the site of photoreception, which may then transmit some developmental signal to the embryo.

Stomatal Limitation to Carbon Gain in Paphiopedilum sp. (Orchidaceae) and Its Reversal by Blue Light

Leaves from Paphiopedilum sp. (Orchidaceae) having achlorophyllous stomata, show reduced levels of stomatal conductance when irradiated with red light, as compared with either the related, chlorophyllous genus Phragmipedium or with their response to blue light. These reduced levels of stomatal conductance, and the failure of isolated Paphiopedilum stomata to open under red irradiation indicates that the small stomatal response measured in the intact leaf under red light is indirect.The overall low levels of stomatal conductance observed in Paphiopedilum leaves under most growing conditions and their capacity to increase stomatal conductance in response to blue light suggested that growth and carbon gain in Paphiopedilum could be enhanced in a blue light-enriched environment. To test that hypothesis, plants of Paphiopedilum acmodontum were grown in controlled growth chambers under daylight fluorescent light, with or without blue light supplementation. Total photosynthetic photon flux density was kept constant in both conditions. Blue light enrichment resulted in significantly higher growth rates-of up to 77%-over a 3 to 4 week growing period, with all evidence indicating that the blue light effect was a stomatal response. Manipulations of stomatal properties aimed at long-term carbon gains could have agronomic applications.

Phase Shift in the Circadian Rhythm of Floral Promotion by Far Red Energy in Hordeum vulgare L

Eight-day-old barley seedlings (Hordeum vulgare L. cv. Wintex) were pretreated with a single 24-hour daylight fluorescent photoperiod that was supplemented with sufficient far-red energy (FR) to produce a relative red (R)/FR ratio of 0.5. These plants undergo floral initiation about a week after they are returned to 12-hour daylight fluorescent photoperiods (R/FR ratio, 5.5), but floral development does not begin for an additional 2 weeks. Addition of FR light to a subsequent 12-hour photoperiod decreases the lag period between initiation and development by 10 days without affecting the rate of development. Extending the photoperiod to 24 hours has the same effect on the lag period, but this treatment also increases the rate of development. FR present during the second half of this 24-hour photoperiod only further increases the rate of development. Thus, the presence of FR during the first half of the photoperiod appears to affect the time of onset of floral development, while its presence during the second half of the photoperiod affects the rate of this development.When a 6-hour pulse of FR was given at various times during a 72- to 96-hour continuous daylight fluorescent period, the response varied rhythmically and was maximal during the second half of each 24-hour cycle. When one 6-hour FR pulse, given at a point of maximal response, is followed by a second 6-hour FR pulse at various times relative to the first, the phase of this rhythm is advanced by about 12 hours. This suggests that FR has two separate but concomitant effects. It causes (a) earlier and/or more rapid flowering and (b) it alters the phase of the endogenous circadian rhythm that regulates the ability of the plant to respond.

Kinetics and time dependence of the effect of far red light on the photoperiodic induction of flowering in wintex barley

Flowering in the long day plant Hordeum vulgare L. var. Wintex barley was enhanced by the addition of far red light to the main light portion of the photoperiod. Far red energy was provided to produce quantum flux ratios (660/730 nm) and phytochrome photoequilibria (Pfr/total phytochrome) equivalent to those reported both beneath a leaf canopy and outside a canopy at twilight. The photoperiodic requirement for long days can be completely eliminated by the addition of far red light. However, both the effect of extending the photoperiod without far red and the addition of far red to 12-hour photoperiods were suboptimal. Maximal stimulation was achieved only when far red was added to continuous light. The duration of the period of maximal apex elongation rate, as well as the reduction of the time required for floral initiation, were saturated by three inductive cycles. When far red energy was provided intermittently during 3 days of continuous light, the ability to respond varied in a circadian manner. This enhancement of flowering by far red appears to be mediated by the "high irradiance response" of phytochrome.

Effects of the herbicide san 9789 on photomorphogenic responses

The herbicide, 4-chloro-5-(methylamino)-2-(alpha,alpha,alpha-trifluoro-m-tolyl)- 3(2H)-pyridazinone (San 9789), an inhibitor that prevents both carotenoid and chlorophyll accumulation and normal chloroplast development in white light, does not affect the physiological effectiveness of phytochrome in dark-and light-grown plants. Red/far red reversibility of growth inhibition, stimulation of anthocyanin synthesis, and stimulation of phenylalanine ammonia-lyase synthesis are not significantly different in plants grown with and without San 9789. Despite the complete absence of photosynthesis, flowering could be induced in the long day plant Hordeum vulgare L. when sucrose was provided to the leaves. Since the nonphotochemical reactions of phytochrome also are not affected by the herbicide, San 9789 may be used as a tool to study the phytochrome system spectrophotometrically in plants grown for relatively long periods under high intensity white light.

Spectrophotometric phytochrome measurements in light-grown Avena sativa L

Phytochrome was studied spectrophotometrically in Avena sativa L. seedlings that had been grown for 6 d in continous white fluorescent light from lamps. Greening was prevented through the use of the herbicide San 9789. When placed in the light, phytochrome (Ptot) decreased with first order kinetics (τ1/2 ≈ 2 h) but reached a stable low level (≈2.5% of the dark level) after 36 h. This concentration of phytochrome remained constant in the light and during the initial hours of a subsequent dark period, but increased significantly after a prolonged dark period. Evidence suggests that the constant pool of phytochrome in the light is achieved through an equilibrium between synthesis of the red absorbing (Pr) and destruction of the far-red absorbing form (Pfr) of phytochrome. It is concluded that the phytochrome system in light-grown oat seedlings is qualitatively the same as that known from etiolated monocotyledonous seedlings, but different than that described for cauliflower florets.

Endogenous oscillations in pathways of energy transduction as related to circadian rhythmicity and photoperiodic control

Evidence is presented for endogenous rhythmicity in energy transducing sequences of cellular metabolism which result in a circadian rhythm in adenylate "energy charge" and redox state (NADPH/NADP). From phase dependent photocontrol of enzymatic activity and pyridine nucleotide pool-size levels it is concluded that light - via photoreceptor(s) of photoperiodic control - modulates energy flow under conditions where overall energy transduction displays a circadian rhythm. The results are discussed in relation to temporal organization of development in general.

Endogenous rhythmicity and energy transduction : IV. Rhythmic control of enzymes involved in the tricarboxylic-acid cycle and the oxidative pentose-phosphate pathway in Chenopodium rubrum L

1. All enzymes tested: malate dehydrogenase (MDH), glutamate dehydrogenase (GDH), glucose-6-phosphate dehydrogenase (G-6-PDH), and 6-phosphogluconate dehydrogenase (6-P-GDH)_behaved rhythmically during a period of continuous white light interrupted by darkness. All showed approximately the same frequency of 12-15 h. 2. The enzymes of the tricarboxylic-acid cycle (MDH and GDH) are in phase with each other but are out of phase with those of the oxidative pentose-phosphate pathway (G-6-PDH and 6-P-GDH) which are in turn in phase with each other. 3. GDH appears to be activated by the addition of Hoagland's solution which leads to an overt rhythm 24 h prior to darkness. The rhythms of MDH, G-6-PDH and 6-P-GDH cannot be demonstrated prior to the onset of darkness due to an inhibition of the MDH and pentose-phosphate cycle enzymes by light. 4. The control of the frequency and phase of these rhythms are discussed in relation to a positive correlation of the rhythms in enzyme activity presented here and the rhythms of the pyridine nucleotides presented elsewhere.