Aurea Mutant Research Articles

EXTENSION GROWTH AND ANTHOCYANIN RESPONSES OF PHOTOMORPHOGENIC TOMATO MUTANTS TO CHANGES IN THE PHYTOCHROME: PHOTOEQUILIBRIUM DURING THE DAILY PHOTOPERIOD

Abstract—Four genotypes of tomato (Lycopersicon esculentum Mill.) in the genetic background ‘Aha Craig’ were used: an aurea (au) mutant, deficient in the bulk light‐labile phytochrome pool; a high pigment (hp) mutant, showing exaggerated phytochrome responses at the time of de‐etiolation; the au,hp double mutant and the isogenic wild type (WT). A dramatic increase in plant height resulting from an increase in the length of all internodes for each of the genotypes studied was observed upon reduction of the red light: far‐red light photon ratio (R:FR) from 6.90 to 0.13 by addition of FR for the whole photoperiod. A concomitant increase in leaf length was also observed. Since au and au,hp mutants, deficient in the bulk light‐labile phytochrome pool, respond to this reduction in the R:FR these data demonstrate that the phytochrome pool that mediates this response is present and fully functional. Anthocyanin was detectable in the comparably developed young growing leaves of the WT and hp mutant under the high R:FR, but not in the au and au,hp mutants, suggesting that the potential for anthocyanin synthesis is correlated with the presence of the bulk light‐labile phytochrome pool. The kinetics of anthocyanin decrease in the young growing leaves were investigated in the hp mutant and the results suggest a very rapid cessation of flavonoid biosynthesis upon reduction of the R:FR. The functions of different phytochrome types are discussed.

Light-regulated expression of the nitrate-reductase and nitrite-reductase genes in tomato and in the phytochrome-deficient aurea mutant of tomato

The phytochrome-deficient aurea mutant of tomato (Lycopersicon esculentum (L.) Mill) was used to investigate if phytochrome plays a role in the regulation of nitrate-reductase (NR, EC 1.6.6.1) and nitrite-reductase (NiR, EC 1.7.7.1) gene expression. We show that the expression of the tomato NR and NiR genes is stimulated by light and that this light response is mediated by the photoreceptor phytochrome. The red-light response of the NR and NiR genes was reduced in etiolated aurea seedlings when compared to isogenic wild-type cotyledons. The relative levels of NR mRNA and NiR transcripts and their diurnal fluctuations were identical in mature white-light-grown leaves of the wild-type and of the aurea mutant. The transcript levels for cab and RbcS (genes for the chlorophyll-a/b-binding protein of PSII and the small subunit of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, respectively) in aurea leaves grown in white light were indistinguishable from the respective transcript levels in the leaves of the wildtype grown under the same conditions. Despite a severe reduction in the chlorophyll content, the rate of net CO2 uptake by leaves of the aurea mutant was only slightly reduced when compared to the rate of net photosynthesis of wild-type leaves. This difference in the photosynthetic performances of wild-type and aurea mutant plants disappeared during aging of the plants. The increase in zeaxanthin and the concomitant decrease in violaxanthin in leaves of the aurea mutant compared with the same pigment levels in leaves of the wild-type indicate that the activity of the xanthophyll cycle is increased in aurea leaves as a consequence of the reduced CO2-fixation capacity of the mutant leaves.

PHYSIOLOGICAL CHARACTERIZATION OF A HIGH‐PIGMENT MUTANT OF TOMATO

Abstract— A high‐pigment (hp) mutant, which shows exaggerated phytochrome responses and three other genotypes of Lycopersicon esculenrum Mill. cv. Ailsa Craig: the aurea (au) mutant deficient in the bulk light‐labile phytochrome (PI) pool, the au, hp double mutant, and their isogenic wild type, were used in this study. Measurements of phytochrome destruction in red light (R) revealed that the exaggerated responses of the hp mutant are not caused by a higher absolute phytochrome level or a reduced rate of phytochrome destruction. Fluence‐response relationships for anthocyanin synthesis after a blue‐light pretreatment were studied to test if the hp mutant conveys hypersensitivity to the far‐red light (FR)‐absorbing form of phytochrome (Pfr), i.e. the threshold of Pfr required to initiate the response is lower. The response range for the hp mutant and wild type was identical, although the former exhibited a 6‐fold larger response. Moreover, the kinetics of anthocyanin accumulation in continuous R were similar in the wild‐type and hp‐mutant seedlings, despite the latter accumulating 9‐fold more anthocyanin. Since the properties of phytochrome are the same, the hp mutation appears to affect the state of responsiveness amplification, i.e. the same amount of Pfr leads to a higher response in the hp mutant. We therefore propose that the hp mutation is associated with an amplification step in the phytochrome transduction chain. Escape experiments showed that the anthocyanin synthesis after different light pretreatments terminated with a R pulse was still 50% FR reversible after 4–6 h darkness, indicating that the Pfr pool regulating this response must be relatively stable. However, fluence‐rate response relationships for anthocyanin synthesis and hypocotyl growth induced by a 24‐h irradiation with 451, 539, 649, 693, 704 and 729 nm light showed no or a severely reduced response in the au and au, hp mutants, suggesting the importance of PI in these responses. We therefore propose that the capacity for anthocyanin synthesis (state of responsiveness amplification) could be established by PI, while the anthocyanin synthesis is actually photoregulated via a stable Pfr pool. The Hp gene product is proposed to be an inhibitor of the state of responsiveness amplification for responses controlled by this relatively stable Pfr species.

Retention of Phytochrome-Mediated Shade Avoidance Responses in Phytochrome-Deficient Mutants of Arabidopsis, Cucumber and Tomato

Summary Phytochrome-mediated shade avoidance responses have been studied in light-grown wild type and phytochrome-deficient mutant seedlings of Arabidopsis thaliana , tomato and cucumber. Light-grown seedlings of the long-hypocotyl hy -1, hy -2 and hy -6 mutants of A. thaliana retain a qualitatively normal shade avoidance response to growth under a low red: far-red (R:FR) ratio, namely an increase in elongation growth and a acceleration of flowering. This indicates that, despite the fact that etiolated tissues of these mutants are severely deficient in spectrophotometrically-detectable phytochrome, light-grown seedlings of the mutants possess some functional phytochrome. The hy -3 mutant, which is deficient in seed phytochrome, retains a similar, but less dramatic, shade avoidance response. The aurea ( au ) mutant of tomato, in which etiolated tissues are deficient in spectrophotometrically- and immunochemically-detectable phytochrome, also retains a qualitatively normal shade avoidance response to reduced R:FR ratio. This is consistent with the hypothesis that au seedlings are deficient only in a light-labile phytochrome species that normally accumulates in etiolated tissues and is involved in the deetiolation process. Light-grown seedlings of the long-hypocotyl ( lh ) mutant of cucumber, a mutation that appears to lead to a deficiency in a light-stable phytochrome species, retain a small, but significant, phytochrome-mediated increase in elongation growth in response to reduced R:FR ratio.

Different blue-light requirement for the accumulation of transcripts from nuclear genes for thylakoid proteins in Nicotiana tabacum and Lycopersicon esculentum

We have isolated recombinant lambda gt11 phages which carry cDNA clones for the major light-harvesting chlorophyll a/b-binding proteins of photosystem I (LHCPI) and II (LHCPII), subunit II of photosystem I, a chlorophyll a/b-binding protein of photosystem II (CP24), the Rieske iron—sulphur protein of the cytochrome b 6/ f complex, and the 33, 23 and 16 kDa proteins of the water-oxidizing complex of photosystem II from Nicotiana tabacum. The nucleotide sequences of cDNA clones encoding the precursors for LHCPI and the FeS protein are presented. If tobacco or tomato seedlings, or seedlings of a phytochrome-deficient aurea mutant of tomato which lacks more than 95% of the phytochrome of the isogenic wild type, are kept in blue light, the transcript level of each of these genes is higher than in seedlings grown in red light suggesting the involvement of a blue—UVA-light photoreceptor. In the case of LHCPI, a 1 min blue-light pulse applied to red-light-grown seedlings is sufficient to increase the transcript levels to those present in blue-light-grown seedlings, whereas almost no increase is observed for transcripts encoding the FeS and 33 kDa proteins. If dark-grown tomato seedlings receive a single far-red-light pulse, significant stimulation is detected for LHCPI transcripts, whereas transcripts encoding the FeS and 33 kDa proteins are not stimulated. It is concluded that the lower light requirement for the increase in the LHCPI transcript level is not specific for one of the light-dependent signal transduction chains.

Photoregulation of seed germination of wild-type and of an aurea-mutant of tomato

Seed germination of an aurea mutant of tomato (Lycopersicon esculentum Mill.) is promoted by continuous irradiation with red, far-red or long-wavelength far-red (758 nm) light as well as by cyclic irradiations (5 min red or 5 min far-red/25 min darkness). Far-red light applied immediately after each red does not change the germination behaviour. Seed germination of the isogenic wild-type, cv. UC-105, is promoted by continuous and cyclic red light while it is inhibited by continuous and cyclic far-red light and by continious 758 nm irradiation. Far-red irradiation reverses almost completely the promoting effect of red light. The promoting effect (in the aurea mutant) and the inhibitory effect (in the wild-type) of continuous far-red light do not show photon fluence rate dependency above 20 nmol m−2 s−1. It is concluded that phytochrome controls tomato seed germination throgh low energy responses in both the wild type and the au mutant. The promoting effect of continuous and cyclic far-red light in the au mutant can be attributed to a greater sensitivity to Pfr.

The germination characteristics of phytochrome‐deficient aurea mutant tomato seeds

The germination of tomato (Lycopersicon esculentum Mill.) cv. Moneymaker seeds of a phytochrome‐deficient aurea (au) mutant and its isogenic wild types were investigated. In contrast to the wild type whose seeds germinate in darkness, those of the au mutant have a low dark germination level. Continuous far‐red light (FR) inhibits the germination of the wild type, whereas in au‐mutant seed batches exhibiting some dark germination, no inhibition of these dark‐germinating seeds was observed. Germination of the au mutant was promoted by continuous red light (R). Intermittent pulses of R were also effective and phytochrome was implicated as the photoreceptor, since cyclic treatments of 2 min R/2 min FR/26 min darkness led to a significantly lower germination than the control receiving 2 min R/28 min darkness. Germination of the au mutant in darkness increased with the period of post‐harvest storage in paper packers at laboratory temperature. Germination could also be induced in darkness at 25°C by treatment of the imbibed seeds for a period of time at a lower or higher temperature. Germination was also promoted by the presence of nitrate ions in the imbibition medium. In this case simultaneous irradiation with FR failed to inhibit germination of the au mutant, whilst germination of the wild‐type controls was strongly inhibited. In the case of a highly dormant au seed batch where continuous R, low temperature treatment and nitrate ions were partially effective (promotive), full germination could be induced by the combination of continuous R with one of the other factors. The stable pool of phytochrome is predicted to be the pool involved in the promotion of seed germination in darkness as a result of residual Pfr being present in it during dehydration. The au‐mutant seeds are more dormant than wild type seeds and therefore require more of the active FR‐absorbing form of phytochrome (Pfr) to achieve germination. Since the au mutant exhibits a phytochrome‐controlled promotion of germination, it must contain phytochrome and it is speculated that this is stable pool of phytochrome which has been demonstrated to be present in the light‐grown au mutant plants.

Blue light is required for survival of the tomato phytochrome-deficient aurea mutant and the expression of four nuclear genes coding for plastidic proteins

When dark-grown aurea mutant tomato seedlings which lack more than 95% of the phytochrome present in isogenic wild-type seedlings are kept in white or blue light, four nuclear-encoded transcripts coding for plastidic proteins (the light-harvesting chlorophyll a/b-binding protein of photosystem I and II [cab-PSII], plastocyanin and subunit 2 of photosystem I) are present in comparable amounts. These transcript levels in red light are strongly reduced in aurea seedlings when compared with those of wild type. Thus, blue light is required for normal expression of these genes in the mutant, while red light alone is not sufficient. Red light-grown aurea seedlings are very sensitive to blue light, even 10 minutes of blue light every day suffices to cause a measurable increase in cab-PSII transcript level. The action of blue light on the expression of cab-PSII in the mutant is under phytochrome control. After 8 days of blue light, phytochrome is almost as effective in inducing cab-PSII mRNA as in the isogenic wild type, whereas after 8 days of red light, only a small phytochrome response was observed in the mutant. It is concluded that blue light sensitizes the mutant to the residual phytochrome which allows normal gene expression and survival of the mutant under daylight conditions.

Characterization of RuBP Carboxylase/Oxygenase of the N. tabacum Mutant Series "Consolation" with Homologous and Non-Homologous Antisera

Abstract The molar ratio of RuBP carboxylase/oxygenase to the CF1 complex was determined in the wild type N. tabacum var. JWB and in various N. tabacum mutants, which differ with respect to their chloroplast structure and their photosynthetic and photorcspiratory activity. It appears that the ratio RuBP carboxylase oxygenase, CF1 is not constant in the different mutants, and apparently depends on the chloroplast structure and the photosynthetic capacity. In the green phenotypes of N. tabacum var. Consolation, var. NC 95 and var. Xanthi. whose lamellar system consists of a balanced ratio of grana and intcrgrana regions the ratio is 3-4 RuBP car- boxylase/oxygenase molecules per CF1 complex. In chloroplasts of the yellow-green mutant Su/su, and the yellow mutant of N. tabacum var. Consolation, whose lamellar system consists of extended intergrana regions and low stacked grana the RuBP carboxylase oxygcnasc/CF1 ratio is reduced to about one half. The aurea mutant A. tabacum Susu var. aurea and the yel- low-green leaf patches of variegated tabacum var. Xanthi arc characterized by the fact that one molecule RuBP carboxylase oxygenase correlates to two CF1 complexes. Also in the two N. tabacum mutants Su/su and Consolation green, that exhibit a 30% higher photorespiration these molar ratios depend on the chloroplast structure. The determination of the maximal binding of antibodies out of homologous and non-homo- logous antisera onto RuBP carboxylase oxygenase of the N. tabacum mutant Consolation showed, that the enzyme of the green mutant, which exhibits a higher oxygenase activity, has in comparison to the yellow-green and yellow phenotype of this mutant series and also in comparison to the wild type a 30 per cent higher antibody binding capacity. These differences in antibody binding arc shown in both the region of enzyme antibody equivalence and that of antibody excess. With the methods of enzyme-antibody precipitation in agarose gels these differences of enzymes, exhibiting higher or lower oxygenase activities, cannot be detected. The native enzymes and the large subunits of the enzyme of the three Consolation mutants yield in these test reactions with the enzyme of the wild-type fusing precipitation bands. Treatment with the chemical agent hydroxylamine. as well as heat treatment at 50 °C alters the enzyme conformation to such an extent that the antibody binding capacity is increased by 70%. The difference in the higher antibody binding capacity of the enzyme of the green mutant of N. tabacum var. Consolation is maintained also after these chemical modifications.

Altered Phytochrome Regulation of Greening in an aurea Mutant of Tomato

A brief pulse of red light accelerates chlorophyll accumulation upon subsequent transfer of dark-grown tomato (Lycopersicon esculentum) seedlings to continuous white light. Such potentiation of greening was compared in wild type and an aurea mutant W616. This mutant has been the subject of recent studies of phytochrome phototransduction; its dark-grown seedlings are deficient in phytochrome, and light-grown plants have yellow-green leaves. The rate of greening was slower in the mutant, but the extent (relative to the dark control) of potentiation by the red pulse was similar to that in the wild type. In the wild type, the fluence-response curve for potentiation of greening indicates substantial components in the VLF (very low fluence) and LF (low fluence) ranges. Far-red light could only partially reverse the effect of red. In the aurea mutant, only red light in the LF range was effective, and the effect of red was completely reversed by far-red light. When grown in total darkness, aurea seedlings are also deficient in photoconvertible PChl(ide). Upon transfer to white light, the aurea mutant was defective in both the abundance and light regulation of the light-harvesting chlorophyll a/b binding polypeptide(s) [LHC(II)]. The results are consistent with the VLF response in greening being mediated by phytochrome. Furthermore, the data support the hypothesis that light modulates LHC(II) levels through its control of the synthesis of both chlorophyll and its LHC(II) apoproteins. Some, but not all, aspects of the aurea phenotype can be accounted for by the deficiency in photoreception by phytochrome.

Response of light-grown wild-type and aurea-mutant tomato plants to end-of-day far-red light

The effect of end-of-day (EOD) far-red (FR) light treatment on tomato ( Lycopersicon esculentum Mill.) plants of the wild type (WT) and an aurea ( au) mutant (which is deficient in the spectrophotometrically detectable light-labile phytochrome pool in etiolated seedlings) was studied. Both the WT and au mutant exhibit a quantitatively similar EOD-FR response ( i.e. stimulation of elongation growth) indicating that phytochrome is functional in light-grown seedlings of the au mutant. However, no dramatic effects of EOD-FR light on leaf elongation, chlorophyll, carotenoid and soluble protein levels were observed in either the WT or au mutant. The au mutant contained less chlorophyll and more soluble protein per unit fresh weight than the WT. Although practically no anthocyanin could be detected in leaves of the au mutant, the WT showed a tenfold reduction in anthocyanin in response to EOD-FR light. The lower productivity of the au mutant compared with the WT results from its reduced leaf surface area, since its maximum rate of photosynthesis or photosynthetic efficiency appears to be slightly higher than that of the WT. Phytochrome was extracted and partially purified from light-grown plants of the WT and au mutant and was quantified by spectrophotometry. On a fresh weight basis the phytochrome content of au-mutant plants was 66% of that of WT plants. It is proposed that the light-labile phytochrome pool regulates the synthesis of the photosynthetic apparatus in light-grown plants and that the light-stable phytochrome pool functions in the EOD-FR elongation response, the latter pool being present and functional in the au mutant.

Blue-light mediated accumulation of nuclear-encoded transcripts coding for proteins of the thylakoid membrane is absent in the phytochrome-deficient aurea mutant of tomato

Polyclonal antibodies against pea phytochrome detect 2 protein bands (about 116 and 120 kDa) on blots of crude protein extracts and protein of microsomal preparations of dark-grown tomato seedlings. Both protein bands are undetectable in Western blots of the aurea mutant extracts. Neither protein band is detectable after isogenic wild-type seedlings are illuminated with 3 h of red light, either in the crude extract or in the membrane fraction of the irradiated seedlings; this result is consistent with the hypothesis that both bands are phytochrome. When dark-grown wild-type seedlings are illuminated with 3 h of red light or blue light against a red light background, the transcript levels for chlorophyll a/b-binding proteins of photosystem I and II, plastocyanin, and the subunit II of photosystem I increase. In all cases, the same fluence rate of blue light is much more effective than red light alone, a result that indicates the involvement of a blue/UV-A light photoreceptor in addition to the involvement of the far-red-absorbing form of phytochrome, Pfr. The aurea mutant responds neither to red light nor to blue light. Thus, no Pfr-independent induction of the four transcripts by a blue/UV-A light photoreceptor can be measured in the aurea mutant.

High Pigment Mutants of Tomato Exhibit High Sensitivity for Phytochrome Action

Summary Anthocyanin synthesis and hypocotyl growth have been studied in tomato ( Lycopersicon esculentum Mill.) seedlings of high pigment ( hp ) mutants, aurea ( au ) mutants deficient in the labile type of phytochrome, an auhp double mutant and wild types. The phytochrome controlled [red light (RL)/far-red light reversible] anthocyanin synthesis occurring in a 24 h dark period after a 12 h pretreatment with RL or blue light (BL) is similar in the hp mutant, whereas in the case of the wild type, pretreatment with BL is more effective than RL. When grown under continuous broad-band UV-A, BL and RL for 5 d the au and auhp double mutants only accumulate low levels of anthocyanin compared to the wild type and the hp mutant. Under these conditions the hp mutant accumulates the highest levels of anthocyanin, but the relative effectiveness of RL and BL in the hp mutant and the wild type is reversed (BL being more effective than RL in wild type, whereas in the hp mutant RL is more effective than BL). These results suggest that the hp mutation enables maximal anthocyanin synthesis to be achieved without activation of the BL photoreceptor. When grown for 7 d in a regime of 14 h white light/10 h darkness the activation of anthocyanin synthesis is reduced in the au and auhp mutants compared to the wild type and the hp mutant. After the same treatment, the hypocotyls of hp -mutant seedlings of each cultivar are similar in length to those of their corresponding wild types and those of the au and auhp mutants are longer. However, after 5 d continuous low fluence rate (3 μ-tmol m- 2 s- 1 ) UV-A, BL and RL, the hypocotyl growth of the hp mutant is inhibited more than the wild type. The auhp double mutant shows a small but significantly higher anthocyanin accumulation than the au mutant, as well as increased inhibition of hypocotyl growth. It is proposed that the hp mutation increases the sensitivity to the labile phytochrome pool.

PHOTOCONTROL OF ANTHOCYANIN SYNTHESIS IN TOMATO SEEDLINGS: A GENETIC APPROACH*

Abstract—The photocontrol of anthocyanin synthesis in dark‐grown seedlings of tomato (Lycopersicon esculentum Mill.) has been studied in an aurea (au) mutant which is deficient in the labile type of phytochrome, a high pigment (hp) mutant which has the wild‐type level of phytochrome and the double mutant au/hp, as well as the wild type. The hp mutant demonstrates phytochrome control of anthocyanin synthesis in response to a single red light (RL) pulse, whereas there is no measurable response in the wild type and au mutant. After pretreatment with 12 h blue light (BL) the phytochrome regulation of anthocyanin synthesis is 10‐fold higher in the hp mutant than in the wild type, whilst no anthocyanin is detectable in the au mutant, thus suggesting that it is the labile pool of phytochrome which regulates anthocyanin synthesis. The au/hp double mutant exhibits a small (3% of that in the hp mutant) RL/far‐red light (FR)‐reversible regulation of anthocyanin synthesis following a BL pretreatment. It is proposed that the hp mutant is hypersensitive to the FR‐absorbing form of phytochrome (Pfr) and that this (hypersensitivity) establishes response to the low level of Pfl. (below detection limits in phytochrome assays) in the au/hp double mutant.

Photophysiology of a Tomato Mutant Deficient in Labile Phytochrome

Summary Photomorphogenetic responses have been studied in a tomato (Lycopersicon esculentum Mill.) aurea (au) mutant which has yellow-green leaves and elongated hypocotyls when grown in white light. Whereas etiolated tissue of the au mutant contains

Molecular analysis of the phytochrome deficiency in an aurea mutant of tomato

The auw mutant allele of the aurea locus in tomato has previously been shown to cause deficiency for the phytochrome polypeptide (Parks et al. 1987). We have begun to characterize the molecular basis and consequences of this deficiency. Genomic Southern blot analysis indicates that there are at least two and probably more phytochrome polypeptide structural genes in tomato. RNA blot analysis shows that the auw mutant contains normal levels of phytochrome mRNA and in vitro translation of auw poly(A)+ RNA yields a phytochrome apoprotein that is quantitatively and qualitatively indistinguishable on SDS-polyacrylamide gels from that synthesized from wild-type RNA. These results indicate that the phytochrome deficiency in aurea is not the result of lack of expression of phytochrome genes but is more likely due to instability of the phytochrome polypeptide in planta. Possible reasons for such instability are discussed. Analysis of the molecular phenotype of aurea indicates that the phytochrome-mediated increase in the abundance of the mRNA encoding chlorophyll a/b binding protein (cab) is severely restricted in the mutant as compared with wild-type tomato. Thus, the auw strain exhibits defective photoregulation of gene expression consistent with its very reduced level of the phytochrome photoreceptor.

Effect of Hydroxylamine Derivatives on Photorespiration in the Tobacco Aurea Mutant Nicotiana tabacum Su/su

O-(p-nitrophenyl)-hydroxylamine affects the size of the Warburg effect measured in leaves of the tobacco aurea mutant Su/su. If leaves are treated with a 10-5 м aqueous solution of the hydroxylamine derivative the Warburg effect which is usually very high in this mutant, is practically reduced to zero. Thus, if in the control (the untreated leaf) the Warburg effect consists in an enhancement of CO2-fixation from 270 μmol CO2 fixed mg·chlorophyll-1·h-1 under 21% oxygen partial pressure to 530 μmol CO2 fixed · mg Chl-1 · h-1 under 3% oxygen, the treated sample yields the maximal rate of photosynthesis already under 21% oxygen partial pressure. At concentrations around 10-4 м the compound is toxic to the plants and inhibits CO2 fixation substantially. A second hydroxylamine derivative used in this study has an additional methyl group in the ortho position to the -O-NH2 group. This compound is already toxic to the plant at concentrations around 10-5 м at which O-(p-nitrophenyl)-hydroxylamine optimally enhances CO2 fixation at normal oxygen partial pressure. From our studies it appears that O-(p-nitrophenyl)-hy- droxylamine binds to ribulose-1.5-bisphosphate carboxylase inducing a conformational change of the enzyme. This is concluded from the observation that a monospecific antiserum to ribulose-1.5- bisphosphate carboxylase is exhausted at considerably higher enzyme concentrations when the enzyme has been treated with the hydroxylamine derivative prior to the antiserum addition. The observation is interpreted as being due to a conformational change induced by the compound, leaving less antigenic determinants accessible in the enzyme surface, when compared to the untreated control. The inhibition of photosynthetic CO2 fixation at high concentrations of both hydroxylamine derivative studied is due to the inhibition of photosynthetic electron transport on the donor side of photosystem II. a phenomenon which is known already for unsubstituted hydroxylamine from the literature. The inhibition of electron transport on the donor side is deduced from an analysis of fluorescence rise kinetics at room temperature.

The aurea mutant of tomato is deficient in spectrophotometrically and immunochemically detectable phytochrome

The aurea locus mutant (au (w)) of tomato contains less than 5% of the level of phytochrome in wild-type tissue as measured by in vivo difference spectroscopy. Immunoblot analysis using antibodies directed against etiolated-oat phytochrome demonstrates that crude extracts of etiolated mutant tissue are deficient in a major immunodetectable protein (116 kDa) normally present in the parent wild type. Analyses of wild-type tissue extracts strongly indicate that the 116-kDa protein is phytochrome by showing that this protein: a) is degraded more rapidly in vitro after a brief far-red irradiation than after a brief red irradiation (Vierstra RD, Quail PH, Planta 156: 158-165, 1982); b) contains a covalently bound chromophore as detected by Zn-chromophore fluorescence on nitrocellulose blots; and c) has an apparent molecular mass comparable to phytochrome from other species on size exclusion chromatography under non-denaturing conditions. The demonstration that the aurea mutant is deficient in this 116-kDa phytochrome indicates that the lack of spectrally detectable phytochrome in this mutant is the result of a lesion which affects the abundance of the phytochrome molecule as opposed to its spectral integrity.

Comparison of photosynthetic parameters of an aurea mutant (Su/su) of tobacco and the wild-type by the photoacoustic method

Oxygen evolution and energy storage yields in tobacco (Nicotiana tabacum L.) wild-type (cv. John Williams Broadleaf) and a mutant (Su/su) deficient in chlorophyll were compared using the photoacoustic technique. Oxygen-evolution and energy-storage quantum yields in the mutant were higher when measured in red light (640-690 nm) than green or blue light (540 nm and 440 nm, respectively), indicating that carotenoids in this mutant do not transfer energy efficiently to the photochemical reaction centers. It is suggested that carotenoids may play a role in protecting the photosynthetic apparatus against damage by high energy fluxes. In the wild-type, the oxygenevolution yield did not change drastically throughout the visible spectrum. The mutant had a higher quantum yield of oxygen evolution than the wildtype. Similarly maximum rates obtained from saturation curves for the mutant were more than twice higher per leaf area and about five times higher per chlorophyll, as compared to the wild-type.

Effect of the sulfur mutation (Su) on levels of ribulose bisphosphate carboxylase/oxygenase and glutamate synthase activities in tobacco plants

The heterozygous (Su/su) aurea mutant, the wild-type (su/su) and albino (Su/su) varieties of John Williams Broadleaf tobacco ( Nicotiana tabacum L.) were grown as shoot cultures on artificial medium. Leaf extracts of the plants were utilized in determining the specific activities of ribulose 1,5-biphosphate (RuBP) carboxylase/oxygenase (EC 4.1.1.39) and glutamate synthase (EC 1.4.7.1). The specific activity level of RuBP carboxylase/oxygenase was found to be about 75% lower in the albino variety than in heterozygote or wild type plants, which had approximately similar activities. Levels of glutamate synthase activity were similar in all three types. Glutamate was synthesized at similar rates by chloroplasts isolated from all three varieties. It was found that mitochondria present in crude chloroplast preparations could compensate for the absence of α-ketoglutarate (α-KG) omitted from assay mixtures for the estimation of glutamate production by the chloroplastic glutamate synthase system.