bluuebunny/crossref_metadata_2025 huggingface dataset:
The relationship between phosphate status and cyanide‐resistant respiration in bean roots
Authors: Rychter Anna M. , Mikulska Maria
Published: May 2006

Bean (Phaseolus vulgaris L.) seedlings were cultured on complete or phosphate‐deficient nutrient medium. After 14 days of culture on phosphate‐deficient medium the visible symptoms of Pi deficiency were observed only in the shoot, the fresh and dry weights of the roots were slightly higher than in control plants. The decreased Pi content in the roots had little effect on total respiration rate but had an effect on the level of inhibition of respiration by cyanide. The high resistance of respiration to cyanide observed in Pi‐deficient roots was the result of the suppression of cytochrome path activity and an increased participation of the alternative, cyanide‐resistant pathway. The cytochrome pathway activity increased when inorganic phosphate was supplied to Pi‐deficient roots for 1 or 3.5 h. It is speculated that the suppression of cytochrome pathway in Pi‐deficient roots may result from restriction of the phosphorylating capacity or a partial inhibition of cytochrome oxidase activity.
Photomorphogenic responses to UV radiation: Involvement of phytochrome and UV photoreceptors in the control of hypocotyl elongation in Lycopersicon esculentum
Authors: Lercari Bartolomeo , Sodi Francesco , Di Paola Michele Lipucci
Published: May 2006

The photo‐inhibition of Lycopersicon esculentum Mill, hypocotyl growth induced by UV radiation may be mediated by both phytochrome and UV‐absorbing receptors. The inhibition of growth induced by continuous irradiation with high fluence rate UV radiation is similar in the au mutant, which is severely deficient in spectrophoto metrically and immunochemically detectable phytochrome, and in the isogenic wild type. Parallel irradiation with 692 nm light, which is equivalent to UV radiation for the phytochrome system in our experimental conditions, induced at high photon fluence rates a significant increase in hypocotyl growth in the au mutant. The same light treatments inhibited the hypocotyl growth of the wild type. The responses of water‐grown seedlings and chlorophyll‐free seedlings (streptomycin and norflurazon treated seedlings) were compared. Water‐grown and chlorophyll‐free seedlings responded similarly to UV radiation. The presence of chlorophyll correlates with a significant increase in hypocotyl growth of au mutants irradiated with 692 nm light. These results support the conclusion that UV‐induced inhibition of growth in the au mutant is independent of phytochrome.
Growth and development of Brassica genotypes differing in endogenous gibberellin content. I. Leaf and reproductive development
Authors: Zanewich Karen P. , Rood Stewart B. , Williams Paul H.
Published: May 2006

Leaf and reproductive development were compared in 3 rapid cycling Brassica rapa genotypes grown for 4 weeks under greenhouse conditions. The dwarf mutant, rosette (ros), is gibberellin (GA)‐deficient, while the tall mutant, elongated internode (ein), has enhanced endogenous GA levels. Germination was delayed in ros and a selection of a more severe form of ros, named dormant (do), has even more retarded germination and some seeds entirely fail to germinate. Seeds of do and ros respond to exogenous GA, by rapid germination.

The 3 genotypes, ros, normal and ein, displayed similar developmental sequences, although floral bud formation and subsequent floral development and anthesis were delayed in ros. Conversely, anthesis was slightly accelerated in ein. Individual leaf areas were reduced in both ros and ein relative to the normal genotype, but leaf numbers were similar in all 3 genotypes. Differences in leaf morphology (heterophylly) were also observed; the normal genotype and ein plants possessed uniform leaf shapes and relatively smooth leaf margins, although petiole length was increased in ein. The mutant ros had scalloped leaf margins and convoluted leaf blades in addition to shortened petioles. These phenotypes suggest a role for GA in the regulation of germination and reproductive and leaf development in Brassica.
Influx and efflux of K+ in sunflower roots after transfer between solutions with different K+ concentrations
Authors: Pettersson Sune , Kasimir‐Klemedtsson Åsa
Published: May 2006

It was investigated whether K+ efflux, like K+ influx, is affected when roots are transferred between solutions with different K+ concentrations. Sunflower plants (Hehanthus annuus L. cv. Uniflorus) were grown on complete nutrient solutions with 0.1, 1.0, 10 or 25 mM K+. This produced plants with K+ concentrations in the roots varying between 9 and 110 μmol (g fresh weight)–1. At the beginning of the experiments the plants were transferred to an 86Rb‐labelled experimental solution initially containing 0.1 mM K+. At intervals during 6.5 h samples were removed from the solution and analyzed for K+ and radioactivity. Based on the analyses K+ (86Rb) influx, K+ net uptake and K+ efflux could be computed. In‘low K+’roots, K+(86Rb) influx and K+ net uptake agreed, suggesting a very low K+ efflux. This was contrary to‘high K+’roots, where K+ efflux was initially higher than K+(86Rb) influx. After about 4 h, K+ efflux declined to a low value also in these roots. When 2‐4‐dinitrophenol was included in the experimental solution, K+ (86Rb) influx was generally depressed, whereas K+ efflux was high throughout the experiment and directly proportional to the K+ status of the roots. Our hypothesis is that after transfer of‘high K+’roots to a solution with low K+ concentration, the K+ efflux from the vacuoles of root cells transiently increases, until a new electrochemical equilibrium is attained.
A new theory of phototropism – its regulation by a light‐induced gradient of auxin‐inhibiting substances
Authors: Bruinsma Johan , Hasegawa Koji
Published: May 2006

Against the wholly indirect evidence of a lateral gradient of auxin as an explanation of phototropic curvature according to the Cholodny‐Went theory, direct measurement of free. extractable or diffusable indoleacetic acid from phototropically curving hypocotyls and coleoptiles invariably shows an even distribution of auxin. On the contrary, growth inhibitors extracted or diffused from these organs turn out to be accumulated at the irradiated side, as proposed already by A. H. Blaauw (Z. Bot. 7: 465. 1915). the classical experiment by F. W. Went (Rec. Trav. Bot. Neerl. 25:1, 1928) has to be interpreted as evidence for a lateral gradient of substance(s) inhibiting auxin activity Phototropic curvature is thus a matter of differential auxin sensitivity across the unilaterally irradiated organ.
Potassium ion channels in the plasmalemma
Authors: Bentrup Friedrich‐Wilhelm
Published: May 2006

The potassium ion is an indispensible cytosolic component of living cells and a key osmolyte of plant cells, crossing the plasmalemma to drive physiological processes like cell growth and motor cell activity. K+ transport across the plasmalemma may be passive through channels, driven by the electrochemical gradient, K+ equilibrium potential (EK) – membrane potential (Vm), or secondary active by coupling through a carrier to the inward driving force of H+ or Na+. Known K+ channels are permeable to monovalent cations, a permeability order being K+ > Rb+ > NH4+ > Na+≥ Li+ > Cs+. The macroscopic K+ currents across a cell or protoplast surface commonly show rectification, i.e. a Vm‐dependent conductance which in turn, may be controlled by the cytosolic activity of Ca2+, of K+, of H+, or by the K+ driving force. Analysis by the patch clamp technique reveals that plant K+ channels are similar to animal channels in their single channel conductance (4 to 100 pS), but different in that a given channel population slowly activates and may not inactivate at all. Single‐channel kinetics reveal a broad range of open times (ms to s) and closed times (up to 100 s). Further progress in elucidating plant K+ channels will critically depend on molecular cloning, and the availability of channel‐specific (phyto)toxins.
Light effects on in vitro adventitious root formation in axillary shoots of mature Prunus serotina
Authors: Fuernkranz H. A. , Nowak C. A. , Maynard C. A.
Published: May 2006

Light effects on in vitro adventitious root formation in axillary shoots of a 95‐year‐old black cherry (Prunus serotina Ehrh.) were examined using microcuttings derived from cultured vegetative buds. Three studies were performed: 1) complete darkness and 4 levels of continuous white light irradiance were tested at 70, 278, 555 and 833 μmol m−2 s−1; 2) white, red, yellow and blue light were tested to assess the importance of spectral quality; and 3) the effect of blue light at intensities of 7,15, 22 and 30 μmol m−2 s−1 was also studied, Measurements included rooting percentage, total number of roots per shoot, and shoot and root dry weight. There was a strong negative effect of white light intensity upon root formation. Blue light between 15 and 22 μmol m−2: s−1 significantly retarded root formation and completely inhibited it at 36 μmol m−2 s−1. Shoots treated with yellow light exhibited the highest rooting percentage, mean number of roots per shoot, and root dry weight.
Effect of zeatin on the growth and indolyl‐3‐acetic acid and abscisic acid levels in maize roots
Authors: Bourquin M. , Pilet P.‐E.
Published: May 2006

Elongation, indolyl‐3‐acetic acid (IAA) and abscisic acid (ABA) levels, – gas chromatography‐mass spectrometry quantification –, in the elongating zone were analysed for maize (Zea mays L., Cv. LG11) roots immersed in buffer solution with or without zeatin (Z). The effect of Z depends on the initial extension rate of roots. The slower growing roots are more strongly inhibited by Z (10−7−10−5M) and they show a greater increase in IAA and ABA content. When compared to the rapidly growing roots, the larger reactivity of the 'slow’ones cannot be attributed to a higher Z uptake as shown when using [14C]‐Z. It is suggested that Z could regulate root elongation by acting on the IAA and/or ABA level. The comparative action of these two hormones is discussed.
Antitrssanspirant action of abscisic acid and ten synthetic analogs in black spruce
Authors: Blake Terence J. , Tan Weixing , Abrams Suzanne R.
Published: May 2006

A rapid screening procedure was developed to compare the antitranspirant action of abscisic acid (ABA) and ten synthetic analogs under well‐watered and droughted conditions. Compounds were applied to black spruce [Picea mariana (Mill.) B.S.P.] seedlings at 10 μM using an aerated root drench. The plants were grown aeroponically under a continuous mist in a misting chamber and a drought stress was then applied, 7 days after treatment with the growth regulators, by switching off the misting unit for 2 h. The activity of 2‐cis and 2‐trans isomers of 4‐transepoxy–β‐ionylideneacetic acid, their corresponding methyl esters, and 4 acetylenic analogs were compared with ABA and control, untreated seedlings. Stomatal conductance and transpiration rates declined in treated seedlings after 3 h, but returned to pre‐treatment levels 2–7 days after treatment. However, transpiration declined significantly as a result of ABA‐ and analog‐treated seedlings when they were drought stressed 7 days after treatment. Since transpiration declined more than net photosynthesis, water use efficiency increased by up to 75% as a result of ABA analog treatment. The 2‐cis‐isomers of epoxy‐β‐ionylideneacetic acids and acetylenic alcohol analogs reduced transpiration and improved water use efficiency more than ABA and 3 out of the 4 2‐trans isomers.
Effects of abscisic acid and its acetylenic alcohol on dormancy, root development and transpiration in three conifer species
Authors: Blake Terence J. , Bevilacqua E. , Hunt G. A. , Abrams S. R.
Published: May 2006

Abscisic acid (ABA) and a synthetic analog, the 2‐cis acetylenic alcohol, were compared to evaluate their effectiveness in conditioning seedlings of Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco], Engelmann spruce (Picea engelmannii Parry) and lodgepole pine (Pinus contorta Dougl.). Following preconditioning with ABA and the analog, seedlings were water stressed with the osmoticum polyethylene glycol (PEG) 3350. The effects of the growth regulators on transpiration, net photosynthesis, their ratio, called water use efficiency, and cell water relations parameters were then compared in stressed and unstressed plants. The antitranspirant action of these compounds varied depending on the species, the growth regulator, and the level of stress. ABA promoted transpiration in unstressed seedlings for all 3 species seven days after application. The analog was superior to ABA as an antitranspirant in osmotically‐stressed lodgepole pine and Engelmann spruce, but neither compound was effective in Douglas‐fir. For Douglas‐fir and Engelmann spruce, net photosynthesis remained consistently higher in ABA‐treated plants during the two levels of osmotic stress, relative to control and analog treatments. Neither compound had any effect on root development or cell water relations. ABA, and to a lesser extent its analog, hastened terminal bud formation in seedlings exposed to short days and low temperatures.
Differential regulation of phenylalanine ammonia‐lyase genes during anthocyanin synthesis and by transfer effect in carrot cell suspension cultures
Authors: Qzeki Yoshihiro , Matsui Kazuhiko , Sakuta Masa‐aki , Matsuoka Makoto , Ohashi Yuko , Kano‐Murakami Yuriko , Yamamoto Naoki , Tanaka Yoshiyuki
Published: May 2006

Phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5) catalyses the first step in the phenylpropanoid pathway and is induced during differentiation and by various stimuli. In carrot (Daucus carota L. cv. Kurodagasun) suspension culture cells, PAL is slowly induced during anthocyanin synthesis which occurs in a medium lacking 2,4‐dichlo‐rophenoxyacetic acid and is also induced rapidly and transiently by transferring and diluting cells to fresh medium. Analyses of nucleotide sequences derived from PAL cDNAs revealed that the PAL mRNAs induced by transfer were transcribed from different carrot PAL genes than the PAL mRNAs induced during anthocyanin synthesis. Northern blotting using probes derived from 3’non‐coding regions for PAL cDNAs confirmed that different PAL genes were induced during anthocyanin synthesis and after transfer. Induction of different PAL genes occurs in response to differences in the induction trigger.
Calcium and photoperiodic flower induction in Pharbitis nil
Authors: Tretyn Andrzej , Cymerski Mariusz , Czaplewska Joanna , Łukasiewicz Hanna , Pawlak Anna , Kopcewicz Jan
Published: May 2006

The relationship between phytochrome‐mediated induction of flowering, Ca2+ transport and metabolism in Pharbitis nil Chois cv. Violet seedlings has been investigated. Ethyleneglycol‐bis‐(β‐aminoethylether)‐N,N,N′, N′‐tetraacetic acid (EGTA), a specific Ca+ chelator, caused a 30–40% inhibition of flowering in Pharbitis subjected to complete photoperiodic induction. It was most effective when applied during the light period preceding along inductive dark period. The agonist of calcium channels. Bay K‐8644, did not affect flowering, while Nifedipine, Verapamil and La3+ (antagonists of calcium channels) only slightly inhibited this process. A similar small effect has been found when the plants were treated with Li+ (inhibitor of the membrane phospholipids pathway), and with chlorpromazine (a camodulin inhibitor). Except for EGTA, the effect of the other substances did not depend on the timing of their application. The results of the present study suggest that the effect of all the substances applied was not specific, and flowering is not directly dependent on transport and intracellular metabolism of Ca2+.
Physiological changes in asparagus spear tips after harvest
Authors: King Graeme A. , Woollard David C. , Irving Donald E. , Borst Wilhelmina M.
Published: May 2006

To extend our understanding of the physiology of asparagus after harvest, changes in respiration rate, protein and amino acid complement, and ultrastructure of tip sections (0–30 mm) of asparagus spears (Asparagus officinalis L. cv. Limbras 10) were investigated. Spears had been stored for up to 4 days in the dark at 20°C. Respiration rate (carbon dioxide efflux) declined rapidly after harvest before stabilizing at 12 h at ca 50% of the rate at harvest. Protein, amino acid, and ammonium content of tip sections of 180 mm spears (intact tip sections) during storage, and comparable sections; excised from spears at harvest and subsequently stored (excised tip sections), were compared. Total protein content of intact and excised tip sections increased ca 10% 6–12 h after harvest, and then declined to ca 85% of harvest levels at 48 h. Gel electrophoresis in the presence of sodium dodecyl sulphate revealed the net loss of specific proteins at 48 h. Free amino acid content of excised tip sections declined to ca 75% of harvest levels 12 h after harvest, and then increased to 150% of harvest levels by 48 h. Glutamine levels declined rapidly after harvest, and asparagine content increased ca 200% at 24 h. Similar trends in free amino acid content were found in sections of intact tips. Ammonia (ammonium ions) accumulated to ca 0.3% dry weight at 48 h in both intact and excised tip sections. Ultrastructural studies revealed that tonoplast breakdown commenced 48–96 h after harvest. Results are discussed in relation to the sequence of physiological events following harvest and the timing of mechanisms responsible for their initiation.
Cortical cell fluxes of cobalt in roots and transport to the shoots of ryegrass seedlings
Authors: Macklon A. E. S. , Sim A.
Published: May 2006

Total uptake and transport of 58Co as a function of time were measured in seedlings of Lolium perenne L. cv. Premo, using nutrient solutions containing either 0.1 or 1.0 μM Co2+. After an initial shoulder, uptake was linear and about 15% of the Co absorbed was transported to the shoot after 72 h. Log total uptake and transport as a function of log Co concentration (0.01 to 1.0 μM) were also linear. Co uptake and transport markedly increased with increasing pH but were unaffected by water flux. Compartmental analysis of 58Co efflux data was used to estimate unidirectional fluxes and compartment al concentrations of Co in root cortex, cells. At both levels of external Co, influx to the cytoplasm was passive and cytoplasmic concentrations were comparable. In the 0.1 μM treatment, cytoplasm concentration was controlled by an efflux pump; fluxes across the tonoplast were passive and concentration in the vacuole was small. In the 0.1 μM treatment, the concentration of Co in the cytoplasm was regulated by both an efflux pump at the plasmalemma and an influx pump at the tonoplast. Stored Co in the vacuole was largely unavailable for transport. Factors limiting transport, and the significance of Co depletion in nutrient solutions due to uptake, were discussed. We also established that 0.1 μM Co was sufficient to provide adequate levels of ryegrass shoot Co for ruminant diets.
Differential regulation of a fruit‐specific 62 kDa protein in developing parthenocarpic (pat‐2/pat‐2) and seeded tomato fruits
Authors: Barg Rivka , Meir Efrat , Lapushner Dvora , Frankel Rafael , Salts Yehiam
Published: May 2006

The denatured protein profiles of developing tomato (Lycopersicon esculentum Mill.) fruits, from the anthesis stage up to fruits at 30% of their final diameter, were examined in a pai‐2l pat‐2 parthenocarpic line and in its near isogenic non‐partheno‐carpic line. At anthesis no differences were detected between the protein patterns of ovaries developed on parthenocarpic and non‐parthenocarpic plants. In subsequent stages the seeded and seedless fruits differed in the pattern of manifestation of several abundant proteins, none of which seem to be included in seeds The most prominent difference was found in an insoluble protein of 62 kDa; in developing seeded fruits of either the parthenocarpic or the non‐parthenocarpic line, its rate of decline was much faster than in seedless fruits. In seeded fruits larger than 4‐6 mm in diameter it was scarcely detected, whereas in parthenocarpic seedless 8–10 mm fruits it was still abundant. This protein is fruit specific; it is also enhanced in chemically (n‐n‐tolyl phthalamic acid) – induced parthenocarpic fruits of the non‐parthenocarpic line. The prolonged manifestation in the parthenocarpic fruits results from de novo synthesis of this protein. There are indications that it is not a stress‐related protein. This is the first demonstration of an association between the pattern of modulation of a protein and the phenotypic expression of genetically controlled parthenocarpy.
Effects of sulfate and nitrate on K+ uptake and growth of wheat and cucumber
Authors: Zsoldos Ferenc , Haunold Ernst , Herger Peter , Vasfaegyi Ágnes
Published: May 2006

The uptake of K+ ion was studied in the roots of wheat (Triuicum aestivum L. cv. GK Szeged) and cucumber (Cucumis sativus L. cv. Budai csemege) seedlings grown in nutrient solution under nitrogen and sulfate stress conditions. Seedlings pretreated with 1 or 10 mM NaNO3, absorbed more K+ than those treated with 0.1 mM NaNO3. However, the posteffect of NaNO3 was considerably influenced by the Na2SO4, treatment. The results suggest that, at least partly, a feed‐back regulation of K+ uptake may occur. However, due to the high Na+ contents of the roots, a Na+ effect in this process cannot be excluded. The growth and dry matter yields of the roots and shoots were strongly influenced by the SO2−/4 and NO−/3 supply of the plants. Appreciable differences were experienced between wheat and cucumber seedlings. The optimum SO2−/4 concentration of the growth solution for maximal growth varied considerably between the species, and was also different for the roots and the shoots in a given species.
The development of dormancy in bulblets of Lilium speciosum generated in vitro. II. The effect of temperature
Authors: Delvallée Isabelle , Paffen Annie , De Klerk Geert‐Jan
Published: May 2006

Upon harvest, lily (Lilium speciosum Thunb. cv. Rubrum) bulblets generated in vitro under standard conditions (11 weeks at 20°C) were dormant and needed a cold treatment prior to planting. During culture in vitro at 20°C, the bulblets proceeded through three phases: (1) at first they were non–viable and non‐dormant (up to 5 weeks), (2) then viable and non‐dormant (5–9 weeks) and (3) finally viable and dormant (from 9 weeks onwards). At 15°C, the bulblets became viable but did not develop dormancy, even after protracted culture. The results suggest that the development of dormancy depends upon an accumulation of‘heat units’occurring at temperatures higher than 15°0. At 25°C, the succession of the three phases occurred more rapidly than at 20°C and heat units were accumulated more rapidly. During the third period, the chilling requirement increased showing that heat units continued to be accumulated during this period.

Dormancy connotes an arrest of growth. In lily bulblets, however, the number of scales continued to increase after the induction of dormancy at 20 or 25°C. Many of the scales initiated before the onset of dormancy were formed by swelling of a petiole, whereas, after the onset of dormancy, all scales were formed directly from a primordium. We conclude that the development of dormancy corresponds to a switch in the development of the primordium. Thus, after the induction of dormancy the primordium lost the ability to become a leaf and always developed into a scale.
Slow‐phase chlorophyll fluorescence characteristics of the donor plant leaf tissue as a predictive parameter of protoplast survival potential in vitro
Authors: Cassells Alan C. , Hurley Deirdre H.
Published: May 2006

Variation in the steady state (FT) to fluorescence peak (FP) ratio of Nicotiana tabacum L. cv. Xanthi‐nc leaves in relation to their position on the plant were correlated with the survival in vitro of protoplasts isolated. The FT/FP ratio detected variation in the protoplast survival potential in individual plants in a batch and between batches of donor plants. Deliberately waterlogged and droughted plants had increased FT/FP values and decreased protoplast survival potential.

The use of slow‐phase chlorophyll fluorescence characteristics as a predictive parameter of protoplast survival potential is discussed and compared with the use of stress ethylene and stress ethane measurements for the same purpose.
Storage protein accumulation during zygotic and somatic embryo development in Picea abies (Norway spruce)
Authors: Hakman Inger , Stabel Priska , Engström Peter , Eriksson Tage
Published: May 2006

Total protein was extracted from zygotic embryos and from somatic embryos of Picea abies (L.) Karst. (Norway spruce) cultured in vitro at different times during their development. An analysis by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and 2‐dimensional gel electrophoresis of the protein extracts showed that protein composition and the temporal changes in protein abundance were very similar in the two embryo types. Both zygotic and somatic embryos accumulated storage proteins in abundance during their maturation phase of growth; the somatic embryos when cultured on medium containing 90 mM sucrose and 7.6 μM ABA. The major storage proteins are composed of polypeptides with molecular masses of about 22, 28, 33 and 42 kDa and they are identical in both embryo types according to their molecular mass and average isoelectric points. These proteins are also the most abundant proteins in the female gametophytic tissue of the mature seed.
Photosynthetic electron transport in tobacco leaves infected with tobacco mosaic virus
Authors: Van Kooten O. , Meurs C. , Van Loon L. C.
Published: May 2006

Tobacco (Nicotiana tabacum L. cv. Samsun) plants inoculated with different strains of tobacco mosaic virus (TMV) inducing mosaic symptoms of widely varying severity were studied with in vivo chlorophyll fluorescence. This method was used to deduce photosynthetic electron transport efficiency in relation to symptom expression. The quantum yields of photosystem II (PS II) electron transport rate were significantly diminished in virus strains inducing loss of chlorophyll. The reduction in young mosaic‐diseased leaves appeared to be due in part to a reduction in the fraction of open reaction centers, whereas in older leaves exhibiting less pronounced symptoms the reduction was mainly caused by a reduced efficiency of capture of excitation energy of open PS II reaction centers. Upon infection with any of the five virus strains PS II seemed to be irreversibly damaged in the inoculated leaves and the ones directly above, indicative of a possible increased susceptibility to photoinhibition in these leaves (Somersalo and Krause 1989) even when no symptoms were apparent. Symptom expression did not appear to be related to the influence of the virus on PS II activity, because the severest effects occurred in the inoculated leaves, which either remained symptomless or developed slight yellowing only. This study demonstrates the usefulness or modulated chlorophyll fluorescence measurements for the investigation of plant‐virus interactions. It is particularly important when visual symptoms are absent.
Peroxidase‐mediated chlorophyll bleaching in degreening canola (Brassica napus) seeds and its inhibition by sublethal freezing
Authors: Johnson‐Flanagan A. M. , McLachlan G.
Published: May 2006

Peroxidase activity in isolated thylakoids from degreening canola (Brassica napus cv. Westar) seeds was demonstrated. The enzyme catalyzes the degradation of thylakoid‐bound pigments in the presence of H2O2 and 2,4‐dichlorophenol. Peroxidase activity is related to degreening, with periods of rapid degreening associated with high enzyme activity. Both de novo synthesis and substrate availability appear to control enzyme activity. Peroxidase is initially inhibited and then stimulated by sublethal freezing. Therefore, inhibition of peroxidase activity following sublethal freezing may be responsible, in part, for a failure of the seed to degreen.
The role of chlorophyllase in degreening canola (Brassica napus) seeds and its activation by sublethal freezing
Authors: Johnson‐Flanagan A. M. , McLachlan G.
Published: May 2006

Chlorophyllase mediates dephytylation of chlorophylls and pheophytins during seed degreening in canola (Brassica napus cv. Westar). Degreening can be correlated with chlorophyllase activity in vitro, but it is difficult to demonstrate in vivo activity because of low levels of the dephytylated breakdown products during rapid degreening. If, however, degreening is inhibited by sublethal freezing, chlorophyllide and pheophorbide accumulation can be related to the action of chlorophyllase. Changes in the rate of in vitro dephytylation during degreening and the dramatic increase following freezing may indicate enzyme activation and de novo enzyme synthesis. Evidence from Western blots is presented in support of de novo synthesis. It is concluded that failure of the seed to degreen following sublethal freezing does not result from a reduction in chlorophyllase activity.
Role of ethylene in auxin‐induced flower bud formation in tobacco explants
Authors: Smulders M. J. M. , Kemp A. , Barendse G. W. M. , Croes A. F. , Wullems G. J.
Published: May 2006

The effect of ethytene on in vitro flower bud formation in thin‐layer explants from tobacco pendicels (Nicotiana tabacum L. cv. Samsun) was studied Endogenous ethylene production was stimulated by l‐minocyclopropanc‐l‐carhoxylic acid (ACT), and inhibited by aminoethoxyviny lglycine (AVG). resulting in higher and lower ethylene accumulation. respectively. In the presence of an elevated ethylene concentration, the number of flower buds formed after 7 days of culture in explants was increased, compared with the control. Treatment with AVG or with AgNO3 which blocks ethylene action resulted in decreased bud numbers after 7 days of culture. A different effect of ethylene was visible after 14 days of culture, when regeneration was complete. Treatment with AgNO3 led to more bud regeneration, and increasing ethylene concentrations to lower bud numbers. The endogenous production of ethylene was enhanced by high concentrations of 1‐naphthaleneacetic acid (NAA).

The inhibitory effect of applied ethylene was almost 100% in explants cultured at low concentrations of NAA (below 1 μM). but hardly visible at high concentrations (4.5 μM). As a consequence, the optimal NAA concentration shifted to a higher value in the presence of ethylene. These results are interpreted as a reduction in tissue sensitivity to auxin and in regenerative capability by ethylene. The effect of ethylene on auxin action is not exerted at the level of hormone concentration. Neither NAA uptake nor conversion to conjugates was effected by ethylene.
Temperature‐dependent photoinhibition and recovery of photosynthesis in the green alga Chlamydomonas reinhardtii acclimated to 12 and 27°C
Authors: Falk Stefan , Samuelsson Göran , Öquist Gunnar
Published: May 2006

Photoinhibition of photosynthesis and subsequent recovery were studied in cultures of the unicellular green alga Chlamydomonas reinhardtii L. (wt strain 137 c mating type +) acclimated at high (27°C) and low (12°C) temperature, Photoinhibition was assayed by fluorescence kinetics (77K) and oxygen evolution measurements under growth temperature conditions Inhibition of 50% was obtained by exposing cultures acclimated at high temperature to a photosynthetic photon flux density (PPFD) of 1 600 μmol m−2 S−1 at. 27°C. and cultures acclimated at low temperature to a PPFD of 900 μmol m−2 s−1 at 12°C When the photoinhibitory conditions were shifted it was revealed that algae acclimated at low temperature had acquired an increased resistance to photoinhibition at both 12 and 27°C. Furthermore, acclimation at low temperature increased the capacity to recover from 50% photoinhibition at both 12 and 27°C Studies of photoinhibition in the presence of the protein synthesis inhibitor, chloramphenicol, revealed that in response to acclimation at low temperature during growth the algae became more dependent on protein synthesis to avoid photoinhibition. It is suggested that acclimation at low temperature rendered C. reinhardtii an increased resistance to photoinhibition by. increasing the rate of turnover of photodamaged proteins in photosystem II (PS II). However, we cannot exclude the possibility that the increased resistance to photoinhibition of C. reinhardtii acclimated at low temperature also involves modifications of the mechanism of photoinhibition.
Heat treatment of ripening apples: Differential effects on physiology and biochemistry
Authors: Lurie Susan , Klein Joshua D.
Published: May 2006

Apples (Malus domestica Borkh.) were heated for 4 days at 38°C immediately after harvest and then placed at 20°C for 7–10 days. Protein synthesis, ethylene production and fruit softening were reversibly inhibited by the heat treatment. Fruit respiration, membrane permeability and chlorophyll degradation in the fruit peel were enhanced during the treatment. The heat‐treated apples ripened normally but more slowly than untreated apple We hypothesize that heat treatment differentially affects processes which normally increase simultaneously during fruit ripening, by inhibiting those processes which require tie novo protein synthesis and enhancing those that do not.
Study of the violaxanthin cycle using a yellow‐green mutant of wheat
Authors: Antonielli M. , Pucceschi N. , Lupattelli M.
Published: May 2006

Variations in the content of pigments involved in the violaxanthin cycle in Triticumdurum L, cv. Cappelli and its yellow‐green mutant were studied when the plants were transferred from darkness in intense sunlight (1600 μmol m−2s−1) and vice versa. Even though the mutant contains less of all the photosymhetic pigments, its violaxanthin cycle is more active than in the wild‐type, but the mutant needs more time in darkness to return to the level of violaxanthin present before exposure to light In both cases, hut particularly in the mutant, not all the violaxanthin is converted into antheraxanthin and zeaxanthin. The activity of superoxide dismutase (SOD: E., C. 1.15.1.1). an enzyme that contributes to the removal of the active forms of oxygen. was lower in the mutant than in the wild‐type. Since the lower SOD activity corresponds to greater phototransformation of violaxanthin, it is argued that the higher rate of violaxanthin photooxidation contributes additional protection to the photosynthetic apparatus.
Chilling‐induced potassium leakage of cultured citrus cells
Authors: Forney Charles F. , Peterson Sharon J.
Published: May 2006

Callus of ‘Marsh’ grapefruit (Citrus paradisi Macf.) albedo tissue was used to investigate the effect of preconditioning temperature on the rate of chilling ‐ stimulated K+ leakage. Callus grew most rapidly at 30°C and attained a weight of about 1 g after 30 days. The rate of K.+ leakage from nonchilled callus tissue decreased as temperature decreased from 20 to 7.5°C, but no measurable change in rate was observed between 7.5 and 0°C. When calli were held for 40 days at 01 2.5 or 5°C, K+ leakage increased 200%, 60% or 0%) respectively. Holding callus for 5 days at 10 or 15°C prior to chilling for 40 days at 0°C prevented the increase in K+ leakage observed in callus receiving no preconditioning treatment. Preconditioning at 7.5 and 20°C was less effective in reducing chilling ‐ induced leakage. Preconditioning at 10°C for 5, 2 or 1 day reduced chilling – induced leakage after 40 days at 0°C by 50%, 33% and 15%. respectively.
Endogenous cytokinin levels and metabolism of zeatin riboside in genetic tumour tissues and non‐tumourous tissues of tobacco
Authors: Nandi S. K. , de Klerk G. J. M. , Parker C. W. , Palni Nandi L. M. S.
Published: May 2006

The cytokinin content of stem tissues, primary genetic tumours (excised from 2‐month‐old plants) and 3‐week‐old in vitro cultured genetic tumour tissues derived from Nicotiana glauca (Grah.) ×langsdorffii (Weinm.) and N. suaveolens (Lehm.) ×langsdorffii (Weinm.) hybrids and stem tissues derived from 2‐month‐old N. suaveolens and N. langsdorffii plants has been analysed by radioimmunoassay. Stem tissues of tumour‐prone hybrids contain high cytokinin levels (3–3.7 nmol g−1). This increase is caused mainly by increased levels of cytokinin nucleotides, particularly those of zeatin nucleotide (0.5 nmol g−1) in stem tissues of parent plants and 2.4 nmol g−1 in stem tissues of hybrids). All other tissues contain lower cytokinin levels (0.7–1.7 nmol g−1). Cytokinin bases and ribosides are major compounds in cultured tumour tissues while the nucleotides are dominant cytokinins in all freshly excised tissues from parent plants and their hybrids. In a separate study, the metabolic fate of supplied [3Hj‐zeatin riboside. which is inactivated mainly by sidechain cleavage, has been studied. The results collectively suggest that cytokinins may be involved in tumourigenesis.
Oxidation of NADH by plant mitochondria: Kinetics and effects of calcium ions
Authors: Soole Kathleen L. , Dry Ian B. , Wiskich Joseph T.
Published: May 2006

The kinetics of NADH oxidation by the outer membrane electron transport system of intact beetroot (Beta vulgaris L.) mitochondria were investigated. Very different values for Vmax and the Km for NADH were obtained when either antimycin A‐insensitive NADH‐cytochrome c activity (Vmax= 31 ± 2.5 nmol cytochrome c (mg protein)−1 min−1; Km= 3.1 ± 0.8 μM) or antimycin A‐insensitive NADH‐ferricyanide activity (Vmax= 1.7 ± 0.7 μmol ferricyanide (mg protein)−1 min−1; Km= 83 ± 20 μM) were measured. As ferricyanide is believed to accept electrons closer to the NADH binding site than cytochrome c, it was concluded that 83 ± 20 μM NADH represented a more accurate estimate of the binding affinity of the outer membrane dehydrogenase for NADH. The low Km determined with NADH‐cytochrome c activity may be due to a limitation in electron flow through the components of the outer membrane electron transport chain.

The Km for NADH of the externally‐facing inner membrane NADH dehydrogenase of pea leaf (Pisum sativum L. cv. Massey Gem) mitochondria was 26.7 ± 4.3 μM when oxygen was the electron acceptor. At an NADH concentration at which the inner membrane dehydrogenase should predominate, the Ca2+ chelator, ethyleneglycol‐(β‐aminoethylether)‐N,N,‐tetraacetic acid (EGTA), inhibited the oxidation of NADH through to oxygen and to the ubiquinone‐10 analogues, duroquinone and ubiquinone‐1, but had no effect on the antimycin A‐insensitive ferricyanide reduction. It is concluded that the site of action of Ca2+ involves the interaction of the enzyme with ubiquinone and not with NADH.
Changes in the concentration of indole‐3‐acetic acid during the growth of etiolated lupin hypocotyls
Authors: Ortuño A. , Sánchez‐Bravo J. , Moral J. R. , Acosta M. , Sabater F.
Published: May 2006

The longitudinal distribution of unaltered radioactive indole‐3‐acetic acid (IAA), after application of [5‐3H]‐IAA to decapitated etiolated lupin hypocotyls. exhibited a wave‐like pattern similar to that obtained with endogenous IAA. Waves of radioactive IAA were localizated both in the elongation zone and in the non‐growing basal region of the hypocotyl. These IAA waves were transient because of basipetal polar transport and metabolism of IAA.

The level of endogenous IAA in different zones of the hypocotyl varied with age, following a wave‐like pattern. During the elongation period of each zone, IAA was parallel to the bell‐shaped curve of the growth rate. In addition, a role in secondary cell wall deposition is suggested for the other IAA wave that appeared after the cell elongation period, since an electron microscopic morphometric analysis of the cell wall showed that the cell wall thickness increased once the cell elongation ceased.

As the oscillation of endogenous IAA level occured in both space (distribution along the hypocotyl) and time (variation with age), it is suggested that the level of IAA really depended on the growth status of the cells. The response of the cells to the positional information submitted by the auxin waves as regards the growth status of the cell is discussed.
Isozyme profiles associated with the hypersensitive response of Chenopodium foetidum to plum pox virus infection
Authors: Visedo Guillermo , Fernández‐Piqueras José , García Juan A.
Published: May 2006

Isozyme profiles of esterases (E.C. 3.1.1.1), glutamate oxaloacetate transaminase (E.C. 2.6.1.1) and peroxidases (E.C. 1.11.1.7) have been determined in healthy tissues of Chenopodium foetidum as well as their modifications during leaf development. The effect of plum pox virus infection on the isozyme profiles has also been studied. Virus‐induced necrotic lesions displayed a peroxidase (POX) pattern that has not been found in any other tissue of the plant so far analyzed. The pattern was similar to that of old yellow leaves, except that POX‐B, which was detected in the necrotic lesions, has not been detected in any developmental stage of healthy leaves. Changes in the peroxidase profile seem to begin early during infection, even before necrosis is visible. We suggest that senescence is established at necrotic lesions extending from there to the rest of the infected leaf affecting the peroxidase isozyme pattern. However, other changes, which induce POX‐B, must also take place at necrotic lesions. These do not extend to the rest of the infected leaves. Plum pox virus infection has less effect on the glutamate oxaloacetate transaminase and esterase isozyme patterns, inducing an almost normal senescence pattern.
The effect of a calcium‐channel antagonist, nifedipine and agonist, Bay K‐8644, on the phytochrome‐controlled swelling of etiolated wheat protoplasts
Authors: Tretyn Andrzej , Kendrick Richard E. , Bossen Margreet E.
Published: May 2006

The effect of external Ca2+ and Ca2+‐channel modulators on the phytochrome‐controlled swelling of etiolated wheat (Triticum aestivum L. cv. Arminda) mesophyll protoplasts has been studied. The red light (R)‐stimulated swelling of the protoplasts requires Ca2+ in the surrounding medium and maximum response was observed in a medium containing I mM CaCI2. Far‐red light (FR) irradiation of protoplasts in the presence or absence of Ca2+ does not influence the protoplast volume. The Ca2+‐channel antagonist nifedipine prevents R‐induced protoplast swelling at very low concentrations (0.1 μM). The Ca2+ ‐channel agonist Bay K‐8644 stimulates the swelling of protoplasts incubated in darkness or irradiated with FR. Action of nifedipine depends on whether it is applied before or after the R pulse. The results are compatible with the hypothesis that phytochrome controls the activity of dihydropyridine‐sensitive L‐type Ca2+ channels.
Contrasts between Citrus species in response to salinisation: An analysis of photosynthesis and water relations for different rootstock‐scion combinations
Authors: Lloyd Jon , Kriedemann P. E. , Aspinall D.
Published: May 2006

Leaf gas exchange, water relations and ion content were measured on two‐year‐old Valencia orange (Citrus sinensis [L.] Osbeck), Washington Navel orange (C. sinensis) and Marsh grapefruit (C. parodisi Macfad) scions budded to either Trifoliata (Poncirus infoliata [L] Raf) or Cleopatra mandarin (C. reticuLua Blanco) rootstoeks. Trees were watered with dülute nutrient solution containing either 0 or 50 mM NaCl for 77 days. Leaf chloride concentrations (cell sap basis) were higher in all scions budded on “Trifoliata but sodium levels were lower than in equivalent foliage budded on Cleopatra mandarin rootstock. Foliar salt levels also varied according to scion. Leaves of Marsh grapefruit had higher levels of both sodium and chloride than leaves of either Valencia orange or Washington Navel orange on both rootstocks. Accumulation of sodium and chloride in salinised leaves caused a reduction in leaf osmotic potential of 0.2–1.4 MPa. and leaf water potential declined by as much as 0.5 MPa. Turgor pressure in salinised leaves was thus maintained at or above the control level. Osmotic potentials determined by psychrometry compared with pressure‐volume curves were taken to imply that some accumulation of sodium or chloride in the apoplast of salinised leaves may have occurred.

Despite turgor maintenance both co2 assimilation and stomatal conductance were reduced by salinity. Following onset of leaf response to salinisation, gas exchange was impaired to a greater extent in scions budded to Cleopatra mandarin compared to those on Trifoliata. Amongst those scions. leaves of salt‐treated Marsh grapefruit showed greater reductions in gas exchange than Valencia orange or Washington Navel orange budded on either rootstock. Increased sensitivity of 1Marsh grapefruit was correlated with a higher foliar sodium and chloride content in this scion. Scion differences in sensitivity of leaf gas exchange to solute concentration were independent of rootstock and appeared unrelated to leaf prolinebetaine concentrations. This implies an inherent difference between scion species with respect to salt tolerance, rather than variation in their capacity to acquire that type of compatible solute.

In terms of rootstock effects, all scions proved more sensitive to salinity when budded to Cleopatra mandarin compared with Trifoliata. That response was attributed to a disproportionately higher concentration of leaf sodium in scions on Cleopatra mandarin.
Hydrogen peroxide formation in cultured rose cells in response to UV‐C radiation
Authors: Murphy Terence M. , Huerta Alfredo J.
Published: May 2006

Suspension‐cultured rose (Rosa damascena Mill. cv. Gloire de Guilan) cells irradiated with UV‐C (254 nm. 558 J m−2) showed a transient production of H2O2 as measured by chemiluminescence of luminol in the presence of peroxidase (EC 1.1 1.1.7). The peak concentration of H2O2, which occurred at about 60–90 min after irradiation, was 8–9 μM. The time course for the appearance of H2O2 matched that for UV–induced K+ efflux. Treatments that inhibited the UV‐induced efflux of K+, including heat and overnight incubation with cycloheximide and diethylmaleate, also inhibited the appearance of H2O2. The converse was not always true, since catalase (EC 1.11.1.6. and salicylhydroxamic acid, which inhibited luminescence, did not stop K+ efflux. We conclude that H2O2 synthesis depends on K+ efflux. Because H2.O2 in the extracellular space is required for lignin synthesis in many plant tissues, we suggest that the UV–stimulated production of H2O2 is an integral part of a defensive lignin synthesis.
Studies on the maintenance and expression of cloned DNA fragments in the nuclear genome of the green alga Chlamydomonas Reinhardtii
Authors: Day Anil , Debuchy Robert , van Dillewijn Jeanette , Purton Saul , Rochaix Jean‐David
Published: May 2006

Using a biolistic device built here and based on the principle of the device described by Klein et al. (1987). we have reproducibly obtained transformants of Chlamydomonas reinhardtii. The reproducibility of the method has allowed us to examine the maintenance and expression of cloned DNA fragments introduced into C. Reinhardtii.