Expression of nuclear genes as affected by treatments acting on the plastids

In a preceding paper (Oelmüller and Mohr 1986, Planta 167, 106–113) it was shown that in the cotyledons of the mustard (Sinapis alba L.) seedling the integrity of the plastid is a necessary prerequisite for phytochrome-controlled appearance of translatable mRNA for the nuclear-encoded small subunit (SSU) of ribulose-1,5-bisphosphate carboxylase and the light-harvesting chlorophyll a/b-binding protein of photosystem II (LHCP). It was concluded that a signal from the plastid is essential for the expression of nuclear genes involved in plastidogenesis. The present study was undertaken to characterize this postulated signal. Chloramphenicol, an inhibitor of intraplastidic protein synthesis and Norflurazon, an inhibitor of carotenoid synthesis (to bring about photooxidative sensitivity of the plastids) were applied. We obtained the following major results. (i) After a brief period of photooxidative damage a rapid decrease of the above translatable mRNAs was observed. Conclusion: the signal is short-lived and thus required continually. (ii) Once the plastids became damaged by photooxidation, no recovery with regard to nuclear gene expression was observed after a transfer to non-damaging light conditions. Conclusion: even a brief period of damage suffices to prevent production of the signal. (iii) Chloramphenicol inhibited nuclear gene expression (SSU, LHCP) and plastidic development when applied during the early stages of plastidogenesis. Once a certain stage had been reached (between 36–48 h after sowing at 25° C) nuclear gene expression became remarkably insensitive toward inhibition of intraplastidic translation. Conclusion: a certain developmental stage of the plastid must be reached before the signal is released by the plastid. (iv) Under the growth conditions we adopted in our experiments the plastids in the mesophyll cells of mustard cotyledons developed essentially between 36 and 120 (-144) h after sowing. Only during this period could translatable mRNAs for SSU and LHCP be detected. Conclusion: the signal is released by the plastids only during this time span.Abbreviations CAP Chloramphenicol (D-threo) - cFR continuous far-red light - FR far-red light (3.5 W·m^-2) - GPD glyceraldehyde-3-phosphate dehydrogenase - LHCP light-harvesting chlorophyll a/b-binding protein of photosystem II - LSU large subunit of RuBPCase - MDH malate dehydrogenase - NF Norflurazon - NIR nitrite reductase - Pfr physiologically active form of phytochrome - R red light (6.8 W·m^-2) - RG9-light long-wavelength far-red light (10 W·m^-2) - RuBPCase ribulose-1,5-bisphosphate carboxylase - SSU small subunit of RuBPCase - WL_s strong white light (28 W·m^-2) - photoequilibrium of phytochrome at wavelength      

Inhibition and promotion by light of the accumulation of translatable mRNA of the light-harvesting chlorophyll a/b-binding protein of photosystem II

The amount of in-vitro translatable mRNA of the light-harvesting chlorophyll a/b-binding protein (LHCP) of photosystem II strongly increases in darkness (D) after a 5-min red-light pulse while continuous illumination of mustard seedlings with far-red (FR), red or white light leads only to a slight increase in the amount of translatable LHCP-mRNA. No increase can be observed after a long-wavelength FR (RG9-light) pulse. However, a FR pretreatment prior to the RG9-light pulse strongly increase LHCP-mRNA accumulation in subsequent D. This is not observed in the case of the mRNA for the small subunit of ribulose-1.5-bisphosphate carboxylase. The increase of LHCP-mRNA in D after a FR pretreatment can be inhibited by a reillumination of the seedlings with FR. The inhibition of LHCP-mRNA accumulation during continuous illumination with FR and the strong increase in D following a FR illumination was found to be independent of chlorophyll biosynthesis since no correlation between chlorophyll biosynthesis and translatable LHCP-mRNA levels could be detected. Even strong changes in the amount of intermediates of chlorophyll biosynthesis caused by application of levulinic acid or 5-aminolevulinic acid did not affect LHCP-mRNA levels. Therefore, we conclude that the appearance of LHCP-mRNA is inhibited during continuous illumination, even though illumination leads to a storage of a light singal which promotes accumulation of translatable LHCP-mRNA in D.Abbreviations c continuous - Chl chlorophyll - D darkness - FR far-red light (3.5 W·m^-2) - LHCP light-harvesting chlorophyll a/b-binding protein of photosystem II - NF Norfluration - PChl protochlorophyll(ide) - Pfr far-red absorbing form of phytochrome - Ptot total phytochrome - R red light (6.8 W·m^-2) - RG9-light long-wavelength FR (10 W·m^-2) - SSU small subunit of ribulose-1.5-bisphosphate carboxylase - WL white light - () Pfr/Ptot=wavelength-dependent photoequilibrium of the phytochrome system     

Regulatory factors involved in gene expression (subunits of ribulose-1,5-bisphosphate carboxylase) in mustard (Sinapis alba L.) cotyledons

Phytochrome-controlled appearance of ribulose-1,5-bisphosphate carboxylase (RuBP-Case) and its subunits (large subunit LSU, small subunit SSU) was studied in the cotyledons of the mustard (Sinapis alba L.) seedling. The main results were as follows: (i) Control of RuBPCase appearance by phytochrome is a modulation of a process which is turned on by an endogenous factor between 30 and 33 h after sowing (25° C). Only 12 h later the process begins to respond to phytochrome. (ii) The rise in the level of RuBP-Case is the consequence of a strictly coordinated synthesis de novo of the subunits. (iii) While the levels of translatable mRNA for SSU are compatible with the rate of SSU synthesis the relatively high LSU mRNA levels are not reflected in the rates of in-vivo LSU or RuBPCase syntheses. (iv) Gene expression is also abolished in the case of nuclear-encoded SSU if intraplastidic translation and concomitant plastidogenesis is inhibited by chloramphenicol, pointing to a plastidic factor as an indispensable prerequisite for expression of the SSU gene(s). (v) Regarding the control mechanism for SSU gene expression, three factors seem to be involved: an endogenous factor which turns on gene expression, phytochrome which modulates gene expression, and the plastidic factor which is an indispensable prerequisite for the appearance of translatable SSU mRNA.Abbreviations CAP chloramphenicol - cFR continuous farred light - LSU large subunit of RuBPCase - NADP-GPD NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) - Pfr far-red-absorbing form of phytochrome - pSSU precursor of SSU - RuBPCase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) - SSU small subunit of RuBPCase     

Appearance of nitrite reductase in cotyledons of the mustard (Sinapis alba L.) seedling as affected by nitrate,phytochrome and photooxidative damage of plastids

Nitrite reductase (NIR; EC 1.7.7.1) is a central enzyme in nitrate assimilation and is localized in plastids. The present study concerns the regulation of the appearance of NIR in cotyledons of the mustard (Sinapis alba L.) seedling. It was shown that light exerts its positive control over the nitrate-mediated induction of NIR via the farred-absorbing form of phytochrome. Without nitrate the light effect cannot express itself; even though the light signal is accumulated in the cotyledons it remains totally cryptic in the absence of nitrate. Moreover, it was recognised that intact plastids are important in the control of the appearance of NIR. If the plastids are damaged by photooxidation the action of nitrate and phytochrome on NIR appearance is abolished. The appearance of nitrate reductase (NR; EC 1.6.6.1) responds similarly to photooxidative damage even though this enzyme is cytosolic. While the data strongly indicate that some plastidic signal is a prerequisite for the nitrate-induced and phytochrome-modulated appearance of NIR and NR, the possibility could not be ruled out that photooxidative damage affects the accumulation of NIR in the organelle.Abbreviations c continuous - D darkness - FR far-red light - NADP-GPD NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.1.13) - NF Norflurazon - NIR nitrite reductase (EC 1.7.7.1.) - NR nitrate reductase (EC 1.6.6.1) - Pfr phytochrome (far-red light obtained with RG9 glass filter - R red light - RG9-light long wavelenght far-red light obtained with RG9 glass filter - RuBPCase ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) - WL white light - WL_s strong white light (28 W m^-2)     

Differential regulation of the accumulation of the light-harvesting chlorophyll a/b complex and ribulose bisphosphate carboxylase/oxygenase in greening pea leaves

The photoregulation of chloroplast development in pea leaves has been studied by reference to three polypeptides and their mRNAs. The polypeptides were the large subunit (LSU) and the small subunit (SSU) of ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO), and the light-harvesting chlorophyll a/b protein (LHCP). The polypeptides were assayed by a sensitive radioimmune assay, and the mRNAs were assayed by hybridization to cloned DNA probes. LSU, LSU mRNA, and LHCP mRNA were detectable in etiolated seedlings but LHCP, SSU, and SSU mRNA were at or below the limit of detection. During the first 48 hr of de-etiolation under continuous white light, the mRNAs for LSU, SSU, and LHCP increased in concentration per apical bud by about 40-fold, at least 200-fold, and about 25-fold, respectively, while the total RNA content per apical bud increased only 3.5-fold. In the same period, the LSU, SSU, and LHCP contents per bud increased at least 60-, 100-, and 200-fold, respectively. The LHCP increased steadily in concentration during de-etiolation, whereas the accumulation LSU, SSU, and SSU mRNA showed a 24-hr lag. The accumulation of SSU, SSU mRNA, and LHCP mRNA showed classical red/far-red reversibility, indicating the involvement of phytochrome in the regulatory mechanism. LSU and LSU mRNA were induced equally well by red and far-red light. The LHCP failed to accumulate except under continuous illumination. These results indicate that the accumulation of SSU is controlled largely through the steady-state level of its mRNA, which is in turn almost totally dependent on light as an inducer and on phytochrome as one of the photoreceptors. The accumulation of LSU is largely but not totally determined by the level of its mRNA, which appears to be under strong photoregulation, which has yet to be shown to involve phytochrome. Phytochrome is involved in the regulation of LHCP mRNA levels but substantial levels of the mRNA also occur in the dark. LHCP accumulation is not primarily governed by the levels of LHCP mRNA but by posttranslational stabilization in which chlorophyll synthesis plays a necessary but not sufficient role.     

Differential regulation by phytochrome of the appearance of plastidic and cytoplasmatic isoforms of glutathione reductase in mustard (Sinapis alba L.) cotyledons

An increase of glutathione reductase (GR; EC 1.6.4.2) activity during the transformation of mustard (Sinapis alba L.) cotyledons from storage organs to photosynthetically competent leaves was previously found to be controlled by light acting via phytochrome (Drumm, H., Mohr, H., Z. Naturforsch. 28c 559–563, 1973). Two isoforms of GR could be separated by disc electrophoresis. In the present study we have applied ionexchange chromatography to separate isoforms of GR during the development of the cotyledons. Furthermore, the technique of in situ photooxidation of plastids was used to distinguish between plastidic and cytoplasmatic isoforms. The isoform GR₂ is the plastidic enzyme, as shown by its sensitivity to photooxidative treatment, while GR₁ is a cytoplasmatic protein not affected by photooxidative treatment of plastids. Both isoforms are promoted by phytochrome but with different time courses. The appearance of GR₁ is independent of the integrity of the plastids, as one might expect. However, unexpectedly, the phytochrome-mediated re-appearance of GR₂ after a photooxidative treatment is much less affected by photooxidative destruction of the plastids, i.e. by the lack of a particular plastidic factor, than was to be expected from previous experience with typical plastidic proteins. An interpretation of this finding must await measurements at the level of GR₂ mRNA.Abbreviations c continuous - D darkness - FR far-red light (3.5 W·m^-2) - FPLC fast protein liquid chromatography - GR glutathione reductase (EC 1.6.4.2) - NF Norflurazon - R fed light (6.8 W·m^-2) - = Pfr/Ptot wavelength-dependent photoequilibrium of the phytochrome system     

Rapid variations in the content of the RNA of the small subunit of ribulose-1,5-bisphosphate carboxylase of mature tobacco leaves in response to localized changes in light quantity. Relationships between the activity and quantity of the enzyme

Mature green leaves from tobacco (Nicotiana tabacum L.) plants were submitted to contrasting light conditions; half of each leaf was shaded (changed from 60 to 25 mol photons· m^-2 ·s^-1=LL) and the other half was exposed to higher light (changed from 60 to 360 mol·m^-2· s^-1=HL) for 24 h. The activity and quantity of ribulose-1,5-bisphosphate carboxylase (RuBPCase) were measured during the first 24 h in each leaf region and the variation was compared with that of small subunit (SSU)-and large subunit (LSU)-mRNA contents determined by a hybridot technique. Each leaf half responded separately to the actual light received. The activity of RuBPCase increased progressively in the HL zones and decreased in the LL zones. The RuBPCase-protein content was not significantly modified during the first 24 h but SSU-mRNA content responded very rapidly to the treatment. Within 2 h a significant difference in SSU mRNA appeared between LL and HL zones: at the end of the photoperiod the content in LL zones was approx. 25% of the initial value. The increase in the exposed zone, however, was not significant, indicating that there was a dissymmetry of the response to variation in incident white light. The LSU-mRNA contents from the same leaf extracts were totally unaffected by the light treatment. No day-night variations were noted in either SSU or LSU mRNAs in control plants.Abbreviation HL high-light irradiance - LL lower-ligh irradiance - LSU large subunit of RuBPCase - RuBPCase ribulose-1,5-bisphosphate carboxylase - SSU small subunit of RuBPCase     

Time courses for phytochrome-induced enzyme levels in phenylpropanoid metabolism (phenylalanine ammonia-lyase,naringenin-chalcone synthase) compared with time courses for phytochrome-mediated end-product accumulation (anthocyanin,quercetin)

Time course for changes in the levels of enzymes characteristic of general phenylpropanoid metabolism (phenylalanine ammonia-lyase, PAL; EC 4.3.1.5) and of the flavonoid-glycoside branch pathway (naringenin-chalcone synthase, CHS; EC 2.3.1.74) were measured in the cotyledons of mustard (Sinapis alba L.) seedlings and compared with the rates of accumulation of related end products (anthocyanin and quercetin). Induction of enzyme levels and of end-product accumulation was carried out with red and far-red (FR) light, operating via phytochrome. The data are compatible with the concept that the phytochrome-mediated appearance of enzymes such as PAL and CHS is indeed a prerequisite for the appearance of anthocyanins and flavonols. However, there is no close correlation between enzyme levels and the rates of synthesis of end products which could justify the identification of specific rate-limiting enzymes. Rather, the data indicate that there is a second phytochrome-dependent step, beyond enzyme induction, where the actual rate of flavonoid accumulation is determined. Anthocyanin and quercetin accumulation respond differently to light. However, the relative action of continuous FR, red light pulses and stored phytochrome signal is the same in both cases. This indicates that the mode of operation of phytochrome is the same in both cases. The two syntheses differ only in the degree of responsiveness towards phytochrome. The time course for changes in CHS levels in continuous FR, i.e. under conditions of phytochrome photosteady state, is similar to the time course for PAL levels whereas the time courses in darkness, following transfer from FR to darkness, are totally different. In the case of CHS, a transient rise is observed whereas, with PAL, an instantaneous drop in enzyme level occurs after transfer from FR to darkness. It is concluded that the stored phytochrome signal operates in darkness in the case of CHS but not in the case of PAL.Abbreviations c continuous - CHS naringenin-chalcone synthase (EC 2.3.1.74) - FR far-red light (3.5 W·m^-2) - PAL phenylalanine ammonia-lyase (EC 4.3.1.5) - Pfr phytochrome (far-red absorbing) - Pr phytochrome (red absorbing) - R red light (6.8 W·m^-2) - RG9-light long-wavelength far-red light obtained with RG9 glass filter - [Pfr]/[Ptot], whereby - Ptot total phytochrome (Pr+Pfr)     

Phytochrome-mediated effects of near-ultraviolet radiation in the induction of flowering in etiolated Lemna paucicostata T-101, a short-day plant

Induction of flowering of etiolated Lemna paucicostata Hegelm. T-101, a short-day plant, was inhibited by far-red (FR) or blue light (BL) applied at the beginning of a 72-h inductive dark period which was followed by two short days. In either case the inhibition was reversed by a subsequent exposure of the plants to near-ultraviolet radiation (NUV), with a peak of effectiveness near 380 nm. Inhibition by BL or FR and its reversion by NUV are repeatable, i.e., NUV is acting in these photoresponses like red light although with much lower effectiveness. Thus, it is considered that NUV acts through phytochrome and no specific BL and NUV photoreceptor is involved in photocontrol of floral induction on this plant.Abbreviations BL blue light - FR far-red light - NUV near ultraviolet radiation - P red-absorbing form of phytochrome - P_fr far-red absorbing form of phytochrome - R red light     

Coupling of phytochrome B to the control of hypocotyl growth in Arabidopsis

Etiolated seedlings of the wild-type (WT) and of the phyB-1 mutant of Arabidopsis thaliana (L.) Heynh. were exposed to red-light (R) and far-red light (FR) treatments to characterize the action of phytochrome B on hypocotyl extension growth. A single R or FR pulse had no detectable effects on hypocotyl growth. After 24-h pre-treatment with continuous FR (FRc) a single R, compared to FR pulse inhibited (more than 70%) subsequent hypocotyl growth in the WT but not in the phyB-1 mutant. This effect of FRc was fluence-rate dependent and more efficient than continuous R (Rc) or hourly FR pulses of equal total fluence. Hypocotyl growth inhibition by Rc was larger in WT than phyB-1 seedlings when chlorophyll screening was reduced either by using broadband Rc (maximum emission 610 nm) or by using narrow-band Rc (658 nm) over short periods (24 h) or with seedlings bleached with Norflurazon. Hourly R or R + FR pulses had similar effects in WT and phyB-1 mutant etiolated seedlings. It is concluded that phytochrome B is not the only photoreceptor of Rc and that the action of phytochrome B is enhanced by a FRc high-irradiance reaction. Complementary experiments with the phyA-201 mutant indicate that this promotion of a phytochrome B-mediated response occurs via co-action with phytochrome A.Abbreviations D darkness - FR far-red light - FRc continuous FR - Pfr FR-absorbing form of phytochrome - HIR high-irradiance reaction - Pfr/P proportion of phytochrome as Pfr - phyA phytochrome A - phyB phytochrome B - R red light - Rc continuous R - WT wild-type I thank Professors R.E. Kendrick and M. Koornneef (Wageningen Agricultural University, The Netherlands) and Professor J. Chory (Salk Institute, Calif., USA) for their kind provision of the original WT and phyB-1 and phyA-201 seed, respectively. This work was financially supported by grants PID and PID-BID from CONICET, AG 040 from Universidad de Buenos Aires and A 12830/1-000019 from Fundación Antorchas.     

Osmotic adjustment in Spirulina platensis

Unilateral irradiation of maize (Zea mays L.) seedlings results in a fluence-rate gradient, and hence below saturation, a gradient of the far-red-absorbing form of phytochrome (Pfr). The Pfr-gradients established by blue, red and far-red light were spectrophotometrically measured in the mesocotyl. Based on these Pfr-gradients and the fluence-response curves of phytochrome photoconversion the fluence-rate gradients were calculated. The fluence-rate gradient in the blue (460 nm) was steeper than that in the red (665 nm), which in turn was steeper than that in the far-red light (725 nm). The fluence-rate ratios front to rear were 1:0.06 (460 nm), 1:0.2 (665 nm), and 1:0.33 (725 nm). The assumption that phytochrome-mediated phototropism of maize mesocotyls is caused by local phytochrome-mediated growth inhibition was tested in the following manner. Firstly, the Pfr response curve for growth inhibition was calculated; these calculations were based on measurements of Pfr-gradients and data from red-light-induced phototropism. Secondly, the Pfr response curve for growth inhibition was used as a basis for calculating fluence-response curves for blue-and far-red-light-induced phototropism. Finally, these calculated results were compared with experimental data. It was concluded that the threshold for phytochrome-mediated phototropism of maize mesocotyls reflects the apparent photoconversion cross section of phytochrome whereas the maximal inducable curvature depends on the steepness of the light (Pfr) gradient across the mesocotyl.Abbreviations Pfr far-red-absorbing form of phytochrome - Ptot total phytochrome - Fr far-red light     

Photomorphogenesis in Chenopodium album. Effects of supplementary far-red light on the kinetics of stem extension

The effects of far-red light given against a background of white light on the stem-extension kinetics of three-week-old, light-grown Chenopodium album seedlings were investigated. Under white light alone, the stems (cotyledon-to-apex) extended almost exactly logarithmically with time. Under these conditions the increase in log [stem length in mm] per hour was approx. 3.7·10^-3, equivalent to about 1% per h during both skoto-and photoperiods. Supplementary far-red given throughout each photoperiod massively stimulated extension. The calculated logarithmic extension rate, however, slowly returned to that of the controls, following an initial large increase. This is predicted by a model in which far-red light linearly increases the extension rate of individual internodes which arise at an exponentially increasing rate. The behaviour of the model is also consistent with critical experiments in which far-red was given as a pre-treatment or transiently, as well as with other published data. Far-red stimulation of logarithmic extension rate in successive photoperiods was closely and linearly correlated with calculated phytochrome photoequilibrium. Daily short periods of supplementary far-red were especially potent in accelerating extension; the plants seemed least responsive at the end of the photoperiod.Abbreviations FR supplementary far-red light - I stem length (mm) - LSER logarithmic stem extension rate - Pfr far-red absorbing form of phytochrome - R:FR red:far-red fluence rate ratio - WL white light - _c calculated phytochrome photoequilibrium     

Light-induced changes in the photoresponses of plant stems the loss of a high irradiance response to far-red light

De-etiolation results in phytochrome destruction, greening, and the loss of the far-red high irradiance responses (HIR). Evidence is presented against the hypothesis that the loss of the far-red HIR is a direct consequence of phytochrome destruction. Loss of the far-red HIR for the inhibition of elongation in hypocotyls of Raphanus sativus involves two different, but linked, actions of phytochrome. An induction reaction requires the far-red absorbing form of phytochrome for about 20 min after which accumulation of its product depends only on time. A second reaction requires continuous light or frequent short irradiations and involves cycling of the phytochrome system. This acts on the product of the induction reaction. It is proposed that in green plants an important mode of operation of phytochrome in the light depends on pigment cycling, and that during de-etiolation this system is established under phytochrome control.Abbreviations HIR high irradiance response - R red - FR farred light - P_tot phytochrome, P_r its red absorbing form, P_fr its far-red absorbing form A.M. Jose was the holder of Ministry of Agriculture, Fisheries and Food award AE 6819     

Light and metabolite regulation of the synthesis of ribulose-1,5-bisphosphate carboxylase/oxygenase and the corresponding mRNAs in the unicellular alga Chlorogonium

In the unicellular green alga Chlorogonium elongatum, the synthesis of the plastid enzyme ribulose bisphosphate carboxylase/oxygenase (RuBPCase) and its mRNAs is under the control of light and acetate. Acetate is the sole metabolizable organic carbon source for this organism. Light greatly promotes the synthesis of RuBPCase and the increase in the concentration of the mRNAs of both subunits of the enzyme while acetate has a strong inhibitory effect on this process. There is a good agreement between RuBPCase synthesis and the amount of translateable RuBPCase mRNA present in cells which are cultured under different conditions (autotrophic, heterotrophic, mixotrophic). During the transition period after transfer of the cells from heterotrophic to autotrophic growth conditions the amounts of the large and small subunits of the enzyme increase well coordinated. In contrast to the protein subunits the two subunit-mRNAs accumulate with different kinetics.Abbreviations LSU large subunit of RuBPCase - poly(A)^- RNA - poly(A)⁺RNA non-, poly-adenylated RNA - RuBPCase ribulose-1,5-bisphosphate carboxylase/oxygenase EC 4.1.1.39 - SSU small subunit of RuBPCase     

High-irradiance responses induced by far-red light in grass seedlings of the wild type or overexpressing phytochrome A

The occurrence of phytochrome-mediated highirradiance responses (HIR), previously characterised largely in dicotyledonous plants, was investigated in Triticum aestivum L., Zea mays L., Lolium multiflorum Lam. and in both wild-type Oryza sativa L. and in transgenic plants overexpressing oat phytochrome A under the control of a 35S promoter. Coleoptile growth was promoted (maize, ryegrass) or inhibited (wild-type rice) by continuous far-red light (FRc). However, at equal fluences, hourly pulses of far-red light (FRp) were equally effective, indicating that the growth responses to FRc were not true HIR. In contrast, in maize and rice, FRc increased anthocyanin content in the coleoptile in a fluence-rate dependent manner. This response was a true HIR as FRp had reduced effects. In maize, anthocyanin levels were significantly higher under FRc than under continuous red light. In rice, overexpression of phytochrome A increased the inhibition of coleoptile growth and the levels of anthocyanin under FRc but not under FRp or under continuous red light. The effect of FRc was fluence-rate dependent. In light-grown rice, overexpression of phytochrome A reduced leaf-sheath length, impaired the response to supplementary far-red light, but did not affect the response to canopy shade-light. In grasses, typical HIR, i.e. fluence-rate dependent responses showing reciprocity failure, can be induced by FRc. Under FRc, overexpressed phytochrome A operates through this action mode in transgenic rice.Abbreviations FR far-red light - FRc continuous far-red light - FRp pulses of far-red light - HIR high-irradiance responses - LFR low-fluence responses - OPHYA transgenic rice overexpressing oat phytochrome A - Pfr far-red light-absorbing form of phytochrome - phyA phytochrome A - R red light - Rc continuous red light - VLFR very low-fluence responses - WT wildtype We thank Marcelo J. Yanovsky for his help with the photographs and Professor Rodolfo A. Sanchez for providing a reprint of the paper by P.J.A.L. de Lint. This work was supported by grants from UBA (AG041) and Fundacion Antorchas (A-13218/1-15) to J.J.C.     

Differential expression of the genes for ribulose-1,5-bisphosphate carboxylase and light-harvesting chlorophyll a/b protein in the developing barley leaf

The expression of genes in particular for light-harvesting chlorophyll a/b protein (LHCP) and ribulose-1,5-bisphosphate carboxylase (RuBPCase) has been studied in the developing barley leaf. This has been done by analysis of the occurrence of both proteins within the different regions (1 to 6, beginning from the base) of the primary 7-day-old leaf. It has been found that LHCP already appears in the base of the leaf, whereas RuBPCase is primarily expressed in the apical expanding part of the leaf. The distribution of the mRNAs for both proteins within this gradient is in accordance with that of the proteins themselves, indicating that gene expression is not regulated at the level of translation in both cases. The poly(A) mRNA for LHCP occurs mainly in the basic sections 2 and 3, whereas that for RuBPCase is found throughout the leaf but primarily in the apical sections of the leaf.Abbreviations LHCP light-harvesting chlorophyll a/b protein - RuBPCase ribulose-1,5-bisphosphate carboxylase - TCA trichloroacetic acid