bluuebunny/crossref_metadata_2025 huggingface dataset:
A Solanum (+) Potentilla interfamily protoplast regenerant with Solanum characteristics but with a Potentilla plastome fraction
Authors: Wang Guirong , Binding Horst
Published: May 2006

A Potentilla‐specific plastome fraction in a predominantly Solanum‐type regenerant from a protoplast co‐culture was detected by RFLP. Fifty variegated lines from mixed protoplast populations of wildtype Potentilla caulescens and a Solanum hybrid containing albino‐mutant potato plastids were studied. The nuclear genome of all lines was uniparental Solanum, as indicated by morphology, isozyme patterns and chromosome number. Heterofamily plastid DNA was detected in one line by using 6 plastid DNA probes of barley. All of the Solanum restriction fragments were recovered. Additionally, probes of the psbA gene and 16SrDNA revealed Potentllia‐specific signals, and an ndhE+G gene probe detected a nonparental fragment. Only Solanum‐type fragments hybridized with the pshA gene probe in albino sublines. Protoplast‐derived clones were either albinic or variegated. It is proposed that the line represents a cybrid with recombinant Solanum (+) Potentilla plastid DNA transmitted in combination with the entire Solanum plastid DNA.
Salt stress induces a decrease in the oxygen uptake of soybean nodules and in their permeability to oxygen diffusion
Authors: Serraj Rachid , Roy Gérard , Drevon Jean Jacques
Published: May 2006

The effects of short‐term NaCl‐salinity on nodules of soybean (Glycine max L. cv. Kingsoy) were studied on hydroponically‐grown plants. Both acetylene reducing activity (ARA) and nodule respiration (O2 uptake and CO2 evolution) were immediately inhibited, and the stimulation of them by rising the external partial pressure of O2 (pO2) was diminished by the application of 0.1 M NaCl in the nutrient solution. The permeability of the nodule to O2 diffusion, estimated by O2 consumption or CO2 evolution, was significantly lower in the stressed nodules than in the cootrol ones. The respiratory quotient of intact nodules and the ethanol production of excised nodules were increased by low pO2 and by salt stress. These data confirm that in salt‐stressed soybean nodules, O2 availability is reduced and fermentative pathways are stimulated.
Wilt‐induced ABA biosynthesis, gene expression and down‐regulation of rbcS mRNA levels in Arabidopsis thaliana
Authors: Williams J. , Bulman M. P. , Neill S. J.
Published: May 2006

The kinetics of wilt‐induced abscisic acid (ABA) biosynthesis were investigated in shoots of Arabidopsis thaliana (L.) Heynh Landsberg erecta. ABA concentrations were measured using a radioimmunoassay (RIA) based on the monoclonal antibody MAC 252, and the RIA validated by comparison with combined gas chromatography‐mass spectrometry using a [2H3] labelled internal standard. The basal ABA content of Arabidopsis shoots was ca 10 ng g−1 fresh weight; the concentrations had increased ca 4‐fold within 30 min of the initiation of wilting, increased ca 8‐fold after 4 h and 11‐fold after 8 h. This stress‐induced ABA production was dependent on de novo gene expression; pre‐treatment of leaves and shoots with the metabolic inhibitors cordycepin and cycloheximide reduced the rate of subsequent stress‐induced ABA biosynthesis from 12.5 ng g−1 h−1 to 1 ng g−1 h−1 and 0 ng g−1 h−1, respectively. In vitro translation of mRNA isolated from shoots subjected to wilting or ABA treatment followed by one‐dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis revealed only minor changes. The effects of wilting and ABA on the content of total ribulose 1,5‐bisphosphate carboxylase/oxygenase small sub‐unit (rbcS) mRNA were also determined. Both wilting and exogenous ABA resulted in a substantial reduction in the amount of rbcS mRNA, an effect readily reversed by rehydration of wilted shoots. However, the effects of wilting were not mediated solely by newly‐synthesised endogenous ABA, as wilting also reduced rbcS mRNA levels in the ABA‐deficient aba‐1 mutant, which did not produce ABA in response to loss of turgor. The amount of rbcS mRNA was higher in aba‐1 shoots, suggesting that cellular rbcS mRNA levels are normally down‐regulated by ABA. Cold treatment induced ABA production in wild type shoots only, but resulted in an increased rbcS mRNA content of both wild type and aba‐1 shoots.
The lack of control of water loss in micropropagated plants is not related to poor cuticle development
Authors: Santamaria J.M. , Kerstiens Gerhard
Published: May 2006

To assess if cuticular transpiration could contribute significantly to the high rates of water loss often observed in micropropagated plants after transfer to the nursery, it was tested whether adaxial cuticular water permeance (P) of leaves grown in vitro was higher than that of leaves grown ex vitro. For four species of micropropagated plants with hypostous leaves (Delphinium elatum hybrid, Doronicum hybrid, Hosta sieboldiana var. elegans, Rodgersia pinnata), P was determined with two independent techniques which gave similar results. Minimum adaxial overall conductance was measured with the same methods for a Heuchera hybrid which had amphistomatous leaves. Leaves of all species except Heuchera lost 36–65% of their original weight within 25 min after excision. Detached leaves whose abaxial surfaces had been coated lost only 25–38% of their original weight within 5–9 h. Permeances (P) were between 1 × 10−5 m s−1 and 1 × 10−4 m s−1, which was within the range of typical values found with leaves grown ex vitro. From these results and a critical assessment of the literature it is concluded that there is no evidence that P of micropropagated plants was high enough to contribute significantly to the desiccation problem at the transfer stage.
Relationship between banding and photosynthetic activity in Chara corallina as studied by the spatially different induction curves of chlorophyll fluorescence observed by an image analysis system
Authors: Plieth Christoph , Tabrizi Hamed , Hansen Ulf‐Peter
Published: May 2006

Image analysis was applied for studying the kinetics of chlorophyll fluorescence in the alkaline and acid zones of internodal cells of Chara corallina Klein ex Willd., in order to test the hypothesis that in the acid bands an outward proton current yields a conversion of HCO3− ions to CO2, thus facilitating inward diffusion of CO2.

The analysis of the responses of chlorophyll fluorescence induced by changes in light intensity from 0.15 W m−2 to 2.0 W m−2 (λ <580 nm) revealed different kinetic behaviour. In the alkaline zones, the amplitude of the variable components of fluorescence was smaller than in the acid zones. Curve fitting by a sum of exponentials showed that the 4 time constants of about 2, 22, 48 and 140 s were not significantly different between the alkaline and acid zones. In contrast the related amplitude factors were smaller in the alkaline zones. by a factor of about 1.6 to 2.0 in old calcified cells and by a factor of about 1.2 in young cells without acrustations.

The interpretation of these results in terms of a better supply of carbon dioxide in the acid zones was supported by investigations on leaves of tobacco. Lowering the CO2 concentration of an artificial atmosphere below 20 ppm resulted in a similar reduction of the variable component of chlorophyll fluorescence as found in the alkaline zones of Chara.
Integration of nuclear‐encoded proteins into pea thylakoids with different pigment contents
Authors: Dahlin Clas , Timko Michael P.
Published: May 2006

The in vitro membrane integration of the light‐harvesting protein of photosystem II (LHCP), the Rieske FeS protein of the cytochrome (Cyt) blf‐complex, and the NADPH:protochlorophyllide oxidoreductase (Pchlide reductase) into pea thylakoids with different pigment composition was studied. Pea plants (Pisum sativum L. cv. Kelvedon Wonder) with different contents of chlorophyll (Chl) and carotenoids were obtained by growing the seedlings in a greenhouse or in weak red light with or without the herbicide Norflurazon, an inhibitor of carotenoid biosynthesis. Chloroplasts from untreated and Norflurazon‐treated plants grown in weak red light contained approximately 29 and 14% of Chl compared to chloroplasts from untreated plants grown in the greenhouse. The corresponding carotenoid contents were 66 and 5%. Following an integration reaction using LHCP precursor protein and chloroplast lysate, thylakoids from untreated and Norflurazon‐treated plants grown in weak red light contained approximately 30 and 5% of protease‐protected LHCP, respectively, compared to thylakoids of untreated plants grown in a greenhouse. In contrast to LHCP, the in vitro assembly of the Pchlide reductase was only sligthly reduced in chloroplast lysates of plants grown in weak red light compared to greenhouse‐grown plants. In chloroplast lysates of Norflurazon‐treated plants, however, the amount of membrane associated, protease‐protected Pchlide reductase was reduced to 32% of the amount in untreated plants grown under the same light conditions. In contrast, the integration of the Rieske FeS protein occurred to almost similar levels irrespective of light conditions and herbicide treatments.

Reconstitution assays where stroma from Norflurazon‐treated plants was added to thylakoids from untreated plants, showed that the herbicide did not affect any stromal component(s) vital for the insertion reaction. Removal of samples during the integration reaction of LHCP showed that no degradation of the protein occurred during the assay. Neither was the assembled protein degraded up to 24 h after the termination of the assay. This indicates that growing plants in weak red light, with or without Norflurazon treatment, mainly affected the primary step in thylakoid assembly of LHCP, i.e. the insertion reaction into the membrane. The results further indicate that proteins normally bound to pigments also require pigments for membrane recognition or integration.
Remobilization of fructans in Phippsia algida during rapid inflorescence development
Authors: Solhaug Knut Asbjørn , Aares Erik
Published: May 2006

Plants of Phippsia algida (Sol.) R. Br. were cultivated in short days (SD; 8 h summer daylight) and in long days (LD; 8 h summer daylight + 16 h low irradiance extension of 5 μmol m−2 s−1) at 9, 15, and 21°C. In this plant, inflorescence primordia are initiated in both LD and SD, but LD are required for heading and inflorescence development (Heide, O.M.; Physiol. Plant. 85: 606–610. 1992). Total dry matter production was slightly increased by LD over SD at 9°C, while it was little affected by daylength at 15 and 21°C. Phippsia algida contained mainly fructans with a low degree of polymerization, largely of the kestose series. After 29 to 42 days (depending on the temperatature) of photoperiodic treatment, fructans constituted 15–20 percent of dry mass of SD‐grown plants compared with only 2–3 percent of dry mass for LD‐grown flowering plants. There was no difference due to photoperiod in levels of mono‐ and disaccharides. Shifting the SD‐grown plants to LD conditions resulted in rapid inflorescence development, accompanied by a parallel rapid decrease in the fructan level, while the level of mono‐ and disaccharides remained constant. The results show that fructans are important as storage carbohydrates in the late snow‐bed species P. algida that normally requires several growing seasons for completing its life cycle. Exhaustion of this storage pool during the extremely fast flower and fruit development constitutes an essential part of the plants adaption to a very short growing season.
Phenolic acids and peroxidase activity in alfalfa (Medicago sativa) embryogenic cultures after ethephon treatment
Authors: Cvikrová Milena , Hrubcová Marie , Vägner Martin , Macháčková Ivana , Eder Josef
Published: May 2006

Treatment with ethephon increased the concentration of exogenous ethylene in Medicago sativa L. embryogenic cell suspension cultures (consisting of single cells, small cellular clumps and globular somatic embryos) and induced changes in the metabolism of phenolic substances, activities of peroxidase (EC 1.11.1.7) and caused significant suppression of suspension culture growth. Treatment with the ethylene‐releasing substance, ethephon, resulted in a several‐fold increase in phenylalanine ammonia‐lyase (PAL; EC 4.3.1.5) activity above the basal level and was accompanied by an elevated accumulation of phenolic acids (significant increase of methoxy‐substituted acids). The majority of newly synthesised phenolic acids was incorporated into the fractions of glycosides and esters bound to the cell wall. Phenolic glycosides seemed to serve as a metabolic pool from which the phenolics were utilised during further culture. The increased activity of wall‐bound ionic peroxidase after ethephon application correlated with the pronounced incorporation of ferulic acid in the cell walls. In contrast, the increased level of exogenous ethylene did not influence the growth of culture of more advanced embryos nor did it significantly alter phenylpropanoid metabolism.
Phytochrome evolution: Phytochrome genes in ferns and mosses
Authors: Schneider‐Poetsch Hansjörg A. W. , Marx Stefan , Kolukisaoglu H. Üner , Hanelt Sabine , Braun Birgit
Published: May 2006

We have isolated phytochrome genes from the moss Physcomitrella, the fern Psilotum and PCR‐generated phytochrome sequences from a few other ferns. The phytochrome gene of the moss Physcomitrella turned out not to contain the aberrant C‐terminal third of the phytochrome from the moss Ceratodon, but the transmitter module‐like sequences found in other phytochromes. A series of different phytochrome genes was detected in Psilotum. Differences between the amino acid sequences derived from them ranged from about 5 to more than 22%. Some of these genes are likely pseudogenes. Analysis by phylogenetic tree constructions revealed that higher and lower plant phytochromes evolved with different velocities. Lower plant phytochromes form a separate family characterized by a high degree of similarity. The amino acid differences between phytochrome types detected in a single species of higher plants are about two‐fold higher than the differences between phytochromes of species of lower plants belonging to different divisions (Physcomitrella and Selaginella). Future studies on phytochrome sequences may eventually also throw light on the significance of Psilotum in the evolution of vascular plants.
Polyamine translocation following photoperiodic flowering induction in soybean
Authors: Caffaro Silvia V. , Antognoni Fabiana , Scaramagli Sonia , Bagni Nello
Published: May 2006

Radioactivity translocation after [14C]‐spermidine application over the third trifoliate leaf of soybean plants (Glycine max. [L.] Merr, cv. Williams) was checked during the first 72 h of short day (SD) treatment to study the involvement of polyamines (PAs) in photoperiodic flowering induction. PAs and/or their metabolites were translocated from the supplied leaf to all parts of the plant. Radioactivity reached its highest concentration in the upper portion of the stem, i.e. the apical bud and the youngest leaf. After the beginning of the first inductive night, the detected radioactivity showed two peaks of maximal concentration. The first arose after the first inductive night, coinciding with the proper flowering induction process; the second one arose after the third inductive night, coinciding with the first morphological symptoms of the transition of vegetative meristems to the reproductive condition. Soluble free PAs showed a different balance in the apical bud of SD‐induced plants compared with LD‐non induced control plants. Soluble conjugated PAs were detected as traces. It is suggested that under flowering inductive conditions, PAs play a different role according to the stage of the flowering process. Thus, their translocation from the leaves to the axillary and apical buds might be related, in a first step, to the fact that they were part of the complex mechanism of the flowering signal, and in a second step, to the flower transition of vegetative buds.
Nitrate reductase in cotyledons of cucumber seedlings as affected by nitrate, phytochrome and calcium
Authors: Bergareche Carmen , Ayuso Roberto , Masgrau Carles , Simon Esther
Published: May 2006

Regulation by the active form of phytochrome (PFR) and the effect of Ca2+ was examined with nitrate reductase (NR) in etiolated cucumber (Cucumis sativus cv. Beilpuig). Nitrate reductase activity (NRA) was studied in excised cotyledons of cucumber seedlings grown in distilled water and in darkness for seven days at 24 ± 0.5°C. All experiments were performed in the dark and a dim green safelight was used during analyses. In etiolated cucumber cotyledons NRA was induced by nitrate and a brief irradiation (15 min) with red light (R) resulted in 62% increase in NRA. This effect was nullified when R was followed immediately by a brief (5 min) far‐red light (FR). NRA also showed a semidian (12 h) rhythmicity. Both PFR, and nitrate effects were age dependent. Calcium seemed to be involved since the phytochrome effect was only observed when calcium was supplied in the external solution. The effect of R on NRA depended on the period of calcium nitrate incubation. An external supply of calcium ionophore mimicked the effect of R and, if supplied to R‐irradiated cotyledons, produced a higher NR level than that caused by R alone. This suggested that intracellular free calcium was involved.
Impaired stem‐growth responses to blue‐light irradiance in light‐grown transgenic tobacco seedlings overexpressing Avena phytochrome A
Authors: Casal J.J. , Sánchez R.A.
Published: May 2006

The effects of blue light (B) on stem extension‐growth were compared in light‐grown seedlings, of tobacco overexpressing Avena phytochrome A and its isogenic wild type (WT). Under natural radiation, lowering the levels of B reaching the whole shoot promoted stem extension growth in WT but not in transgenic seedlings. Under controlled conditions, the seedlings were exposed to white light (WL) or WL minus B, each one provided at two different irradiances. In WT seedlings stem extension growth was promoted by lowering B at both irradiance levels. In transgenic seedlings a reduction of B was promotive only at low irradiance levels. The seedlings were also grown under WL, WL minus B, WL minus red light (R) and far‐red light (FR) or WL minus R, FR and B. In the WT, lowering B promoted stem extension growth irrespective of R+FR levels. In the transgenics, B was effective only at very low levels of R+FR (i.e. at low phytochrome cycling rates). Lowering the Pfr levels at the end of the day promoted extension growth in wild type and transgenic seedlings. Responses to B were not observed in transgenic seedlings having low Pfr levels at the end of the day. The results suggest that the overexpressed phytochrome A acts mainly via irradiance‐dependent reactions. When these reactions are highly expressed, B responses are not observed.
Transition from absolute to quantitative short‐day control in Nicotiana tabacum cv. Maryland Mammoth
Authors: Altamura Maria Maddalena , Tomassi Marisa
Published: May 2006

The response in vitro of thin cell layers, excised from different stem regions of Nicotiana tabacum cv. Maryland Mammoth plants at various developmental stages, was studied under different photoperiodic treatments. The aim was to determine at which stage of plant development, and in which region of the stem, the absolute short‐day requirement, indispensable for the induction of the flowering process in this genotype, becomes quantitative and whether it remains short‐day. The explants were cultured on a medium suitable for flower neoformation, and were exposed for 30 days to the following treatments: continuous darkness, 8 h light/16 h dark per day, 16 h light/8 h dark per day, and continuous light. The first flowers on explants were observed from plants that were still in the vegetative state, but whose apex showed an accelerated production of axillary vegetative buds, as observed histologically. These explants were excised from the first 10 internodes below the first node with a leaf ≥ 5 cm in length (apical site), and produced flowers only under short‐day treatment. When the apical dome initiated the organization of the terminal flower, the apical site explants developed flowers under both short‐day and long‐day treatments. At the same stage, explants from the 15th to the 20th internode below the first leaf ≥ 5 cm in length also formed flowers, but only under short‐day. When the plant showed a complete inflorescence, flowers were also present on explants from the most basal stem internodes and from the inflorescence branches. At this stage, flower neoformation occurred under all treatments; however, under short‐day the number of explants showing flowers not associated with vegetative buds on the same sample greatly exceeded that observed under other treatments, as did the mean number of flowers per explant (except the basal regions). In conclusion, in the post‐inductive phases of the flowering process, the photoperiodic requirement of this genotype is always short‐day. The superficial tissues of the stem require either absolute or quantitative short‐day treatment, depending on their position on the stem and the stage of evolution of the flowering process in the terminal apex.
The effect of electron acceptors on the phytochrome‐controlled germination of Paulownia tomentosa seeds
Authors: Giba Zlatko , Grubišić Dragoljub , Konjević Radomir
Published: May 2006

The effect of substances with different redox potentials in the phytochrome‐controlled germination of Paulmtnia tomentosa seeds was examined. Up to 25% of water‐imbibed seeds germinated upon irradiation with 5 min red light The seeds irradiated with 5 min red light and incubated in substances with redox potentials equal or higher than E′0= 360 mV [potassium nitrate, potassium hexacyanoferrate (III) or potassium hexachloroiridate (IV)] and sodium nitroprusside germinated up to 80%. The optimal concentration was between 1 and 10 mM. Other electron acceptors such as 2.6‐dichlorophenol‐indoplhenol, phenazine methosulfate and methylene blue failed to produce and effect. The germination‐promoting effect was obtained when the substances were supplied to the incubation medium from the onset of imbibition or at the onset of irradiation. Delay of application of these chemicals until after the red light treatment diminished their effectiveness and the effect was lost after 48 h. The escape from far‐red reversibility was evident in the presence of substances which stimulated germination. The results presented support the view that phytochrome‐broken dormancy of Paulownia tomentosa seeds is closely connected with redox changes.
Light/dark regulation of higher plant nitrate reductase related to hysteresis and calcium/magnesium inhibition
Authors: Lillo Cathrine
Published: May 2006

Examination of nitrate reductase (NR, EC 1.6.6.1) activity in crude extracts made from squash leaves before and after a light/dark transition, indicates the existence of two different forms of nitrate reductase; a ‘light form’ with a pH optimum of 7.8 that is not inhibited by calcium or magnesium, and a ‘dark form’ with a pH optimum of 7.6 that is strongly inhibited by calcium or magnesium. The same properties also characterise purified NR. The ‘light and dark forms’ of NR correspond to the two kinetically different forms of purified NR showing (1) linear product formation and (2) delayed product formation, i.e. hysteretic behaviour.
Flowering and morphogenic responses of new Aster hybrids to photoperiod
Authors: Farina E , Guda C. Dalla , Scordo E.
Published: May 2006

Photoperiod treatments of 13, 14.5, 16 and 17.5 h were used to determine the photoperiodic response of the interspecific Aster hybrids ‘Painted Lady’, ‘Snowflake’ and ‘Blue Butterfly’ belonging to ‘Butterfly’ series, under glasshouse conditions. Rate of flowering was higher under 13‐h photoperiods decreasing up to 16‐h photoperiods. The rate of flowering for 13‐ and 17.5‐h photoperiods was nearly similar but under the longest photoperiod flowering was erratic and sometimes abortion of the apical bud was observed. Pholoperiod affected the morphology of the plant. Increasing photo‐periods up to 16 h induced an increase of internode length of the main axis, of total length of lateral shoots, the number of ray florets. In a 13‐h photoperiod the plants produced a paniculate‐racemose shaped inflorescence while in longer photoperiods the inflorescence was paniculate‐corymbose shaped.
Cotton plant size and fiber developmental responses to FR/R ratio reflected from the soil surface
Authors: Kasperbauer M. J.
Published: May 2006

Cotton (Gossypium hirsutum L.) plants were grown in irrigated field plots over red, green or white soil covers (mulches). The far‐red (FR) to red (R) light ratios were higher in upwardly reflected light over the red and green surfaces than in incoming sunlight. Plants that grew over the white mulches received higher photosynhetic photon flux (PPF), but the reflected FR/R ratio did not differ significantly from that in incoming sunlight. At five weeks after emergence, seedling stern lengths were significantly longer over red and green than over white surfaces. At maturity, plants that had grown over the red and green surfaces had longer stems, larger shoots, more bolls (fruit), more seed cotton, and longer fibers than plants grown over the white surfaces even though those grown over the white surfaces had received more reflected photosynthetic light during growth and development.
Light quality beneath field‐grown maize, soybean and wheat canopies – red:far red variations
Authors: Sattin M. , Zuin M. C. , Sartorato I.
Published: May 2006

Using artificial canopies, several authors have shown that horizontally propagated and overall propagated radiation beneath the canopy differ substantially in spectral distribution in the red (R) and far red (FR) wavelengths. Given the lack of information about light quality under real crop canopies, the R:FR ratio of vertical and horizontal radiation beneath field‐grown maize, soybean and wheat was monitored until leaf area index (LAI) reached 4, 2.5 and 6.9, respectively.

A Li‐Cor 1800 spectroradiometer with a remote cosine receptor fitted with a quartz fibre‐optic light‐guide was used. To isolate radiation coming from a given direction, a black coated tube was fitted to the cosine receptor. The viewing angle was 15°. In open conditions, the values of R:FR from the upper hemisphere were between 1.07 and 1.20. For vertically and horizontally‐propagated light, average values were 1.22 and 0.75 respectively.

Beneath the canopy, both R:FR and photosynthetic photon flux density (PPFD) from the entire upper hemisphere decreased in relation to LAI and crop height. R:FR of the horizontal component were found to be generally much lower than the vertical, which decreased significantly only in the later measurements.

The lowest R:FR values were recorded under wheat and soybean canopies. Even the very low LAIs present at early development stages were enough to cause a sharp decrease of R:FR in the horizontal fluxes. Referring to the entire upper hemisphere, PPFD transmittance and R:FR as a percentage of the external references appeared well correlated.
Photocontrol of in vitro bud regeneration: A comparative study of the interaction between light and IAA in a wild type and an aurea mutant of Lycopersicon esculentum
Authors: Marcenaro S. , Voyiatzi C. , Lercari B.
Published: May 2006

In the presence of 0.2 μM IAA both the wild type and the aurea mutant of Lycopersicon esculentum Mill, showed a low but significant percentage of bud formation in the dark, whereas no bud formation occurred in the dark when 20 μM IAA was present in the medium. In both systems blue light always showed a strong promoting effect on bud regeneration, both as final percentage of regeneration and by shortening the initial lag period, suggesting the action of a specific blue light photoreceptor. Red and far‐red light increased the percentage of bud differentiation in wild type explants, with both the IAA concentrations. In the aurea mutant only red at the lowest IAA concentration had such an effect. The final percentage of bud regeneration under red light was greater or equal to that found under blue light in the wild type as well as in the aurea mutant explants cultured in the presence of the lowest IAA concentration.
Changes in spectral properties of ageing and senescing maize and sunflower leaves
Authors: Masoni Alessandro , Ercoli Laura , Mariotti Marco , Barberi Paolo
Published: May 2006

The objective of this study was to determine the differences between maize (Zea mays L.) and sunflower (Helianthus annuus L.) in the pattern of leaf chlorophyll content and spectral properties occurring with leaf ageing and senescence.

Chlorophyll accumulation and leaf spectral properties were determined in growing and senescing leaves of field‐grown maize and sunflower hybrids. Measurements were taken at intervals of 3–4 days during the rapid stem elongation phase on leaf 11 for maize and leaf 17 for sunflower. Reflectance (R) and transmittance (T) spectra of adaxial surfaces of attached leaves were measured using a LI‐COR 1800 hand‐held spectroradiometer with an external integrating sphere, over the wavelength range from 400 to 100 nm. Absorptance (A) was computed as: A = 100‐(R + T).

In the growing leaf, chlorophyll content increased until full leaf expansion, while no changes in A and T were recorded. After full leaf expansion was reached, chlorophyll dropped from 514.3 to 328.0 μmol m−2 in maize and from 527.2 to 164.1 μmol m−2 in sunflower. Absorptance in the PAR region declined about 5% in maize and about 11% in sunflower and T increased about 1% in maize and 7% in sunflower. Within the PAR region, variations in A and T were recorded only in the green band (520–600 nm) for maize and in the green and red (630–690 nm) bands for sunflower. There were differences between maize and sunflower in the relative timing of the decrease in chlorophyll content and A in senescing leaves: maize retained chlorophyll longer than sunflower and A declined more slowly in maize as a result of the different length of leaf maturity and senescing stages.
Light environment, growth and morphogenesis in a peach tree canopy
Authors: Baraldi R. , Rossi F. , Facini O. , Fasolo F. , Rotondi A. , Magli M. , Nerozzi F.
Published: May 2006

Morphogenic and growth processes were studied in relation to photosynthetically active radiation (PAR), and red, far red and blue spectral bands monitored at three different heights of a peach canopy during the vegetative season. The PAR intercepted by the bottom of the tree was significantly lower than that at the top, and blue fluence rate changed with height and season in a manner similar to PAR. Phytochrome photoequilibria indicated spatial and temporal differences in the three layers of the canopy: significantly lower values were detected at the bottom in correspondence with the maximum leaf area index. In this layer, a stimulation of internode elongation and a decrease of flower density were detected. Higher shoot growth rates and about double number of lateral shoots were found at the top of the canopy, where a greater number of sun leaves was present. Possible explanations in terms of different growth strategies induced by shade, depletion of blue, and low phytochrome levels at the bottom of the canopy are given.
Spectral quality during pod development affects omega‐6 desaturase activity in soybean seed endoplasmic reticulum
Authors: Holden Marcia J. , Norman Helen A. , Britz Steven J.
Published: May 2006

Polyunsaturated fatty acids (i.e. linoleic acid [18:2], linolenic acid [18:3]) in triacylglycerols (TAG) of soybean seeds increase more during reproductive development under simulated shadelight: i.e., light with reduced blue and/or increased far‐red (Britz and Cavins 1993). Elevation of 18:2 and 18:3 is matched by corresponding reduction of oleic acid (18:1), consistent with observations that total seed oil remains constant. We therefore tested the hypothesis that spectral quality affects the activity of the omega‐6 and/or omega‐3 desaturases involved in TAG biosynthesis. Membranes were isolated from developing soybean cotyledons 24–31 days after flowering. Separate fractions, enriched for chloroplasts and endoplasmic reticulum (ER) respectively, were obtained by sucrose gradient centrifugation and incubated in an in vitro desaturase assay system containing 14C‐18:1–CoA at room temperature. Omega‐6 and omega‐3 desaturase activity was calculated from the rate of formation of 14C‐18:2 and 14C‐18:3. Radioactive 18:2 and 18:3 were recovered only from phosphatidylcholine (PC) in both ER and chloroplast membranes, consistent with membrane‐bound desaturases with specificity towards PC. The specific activity of omega‐6 desaturase was high in ER membranes from seeds matured under light sources that promote a canopy shade response, but was reduced in membranes from seeds matured under lamps (high blue and low far‐red emission) previously shown to reduce the level of 18:2 in seed oil by 50%. Chloroplast membranes possessed both omega‐6 and omega‐3 desaturases. Light appeared to have little or no effect on the activity of chloroplast desaturases.
Inhibition of polyamine synthesis by cyclohexylamine stimulates the ethylene pathway and accelerates the germination of Cicer arietinum seeds
Authors: Gallardo Mercedes , Gallardo Manuel Eduardo , Matilla Angel Jesús , de Rueda Paloma Muñoz , Sánchez‐Calle Isabel María
Published: May 2006

Treatment with cyclohexylamine, an inhibitor of spermidine synthase, accelerated radicle emergence in chick‐pea (Cicer arietinum L. cv. Castellana) seeds. Stimulation in the growth of embryonic axis was correlated with: (a) a rise in putrescine (Put) and cadaverine (Cad); (b) a decrease in spermidine (Spd) and spermine (Spm), and (c) a concomitant acceleration of the transformation from S‐adenosylmethionine (SAM) into ethylene with increases in the levels of l‐aminocyclopropane‐l‐carboxylic acid (ACC), l‐(malonylamino)cyclopropane‐l‐carboxylic acid (mACC) and ethylene and ACC synthase and ethylene‐forming enzyme activities. Cyclohexylamine also stimulated the mitotic index in both apical and subapical zones of the radicle and the apical zone of the plumule. The sectional distribution of the ethylene pathway and polyamine content was studied in embryonic axes of seeds germinated for 65 h. Each axis was divided into 5 sections: radicle meristem, elongation zone, differentiation zone, hypocotyl and plumule. In the presence of cyclohexylamine, ACC synthase and ACC were strongly stimulated in both the differentiation and hypocotyl zones, whereas the mACC was stimulated in all sections of the embryonic axis. With respect to ethylene‐forming enzyme activity and ethylene production, the hypocotyl and the zones of elongation and differentiation were affected most by cyclohexylamine. Cyclohexylamine also induced an accumulation of free Put and Spm in the differentiation, hypocotyl and radicle zones, whereas Put and Spm bound to small substances increased most in the hypocotyl and plumule. The Spd bound to small substances decreased in all sections in the presence of cyclohexylamine. With respect to polyamines bound to macromolecules, cyclohexylamine stimulated only the accumulation of Put since Spd and Spm were strongly inhibited in all sections.
The chaotropic anions thiocyanate and nitrate inhibit the electric current through the tonoplast ATPase of isolated vacuoles from suspension cells of Chenopodium rubrum
Authors: Weiser Thomas , Bentrup Friedrich‐Wilhelm
Published: May 2006

Using the whole‐vacuolar mode of the patch clamp technique, we studied the effect of the chaotropic anions thiocyanate and nitrate on the electric currents generated by the proton pumping tonoplast ATPase and pyrophosphatase (PPiase), respectively, in vacuoles from suspension cells of Chenopodium rubrum L. Addition of KNO3 (150–250 mM) or KSCN (70–150 mM), and ATP (5 mM, obligatory) irreversibly inhibited the subsequent electric current through the tonoplast ATPase driven by 1 mM ATP, whereas PPiase‐activity by 50 μM PPi remained unaffected. The kinetics of inhibition, indicative of ATPase disintegration by the chaotropic anions, follows a single exponential (τ= 3.44 min). However, apparent ATPase disintegration did not measurably increase the tonoplast conductance. We conclude that, by contrast to organellar F‐ATPases, upon disintegration the transmembrane proteolipid of the V‐ATPase does not act as a proton conductor which, in the presence of chaotropic anions, like chloride or nitrate, would severely perturb solute compartmentation in the plant cell.
Changes in the accumulation of flavonoid and isoflavonoid conjugates associated with plant age and nodulation in alfalfa (Medicago sativa)
Authors: Tiller Sarah A. , Parry Andrew D. , Edwards Robert
Published: May 2006

Medicarpin 3‐O‐glucoside‐6″‐O‐malonate (MGM), formononetin 7‐O‐glucoside‐6″‐O‐malonate (FGM) and two glycosides of coumestrol (CG), one of which was characterised as a malonylated glucoside, have been identified as major isoflavonoid metabolites in the roots of healthy alfalfa (Medicago sativa) plants. Foliage contained a conjugate of the flavonoid apigenin, very low levels of medicarpin and MGM, and depending on the cultivar studied, formononetin and FGM. In the foliage the isoflavonoids were restricted to the stems. Seeds contained conjugates of quercetin, luteolin and 7,4′‐dihydroxyflavone but no isoflavonoid conjugates. When alfalfa plants were grown under controlled conditions, isoflavonoid conjugates were first observed in the roots 24 h after emerging, and continued to accumulate as the plants matured over a 57 day period. Inoculating the plants with a commercial formulation ofRhizobium meliloti(Nodulaid) reduced FGM accumulation in the roots but did not affect MGM or CG content. Under field conditions plants accumulated higher concentrations of the isoflavonoid conjugates in both leaves and roots than plants grown under controlled conditions. Field‐grown plants which were not inoculated with Nodulaid contained higher levels of both MGM and FGM in the roots than nodulated plants. The conjugation of isoflavonoids in alfalfa cell cultures resembled that of the roots in that they accumulated FGM and MGM as major metabolites. However, cultures accumulated a higher proportion of their conjugated isoflavonoids as MGM and formononetin glucoside than did the roots and did not synthesise coumestrol. Comparisons with clover species revealed that FGM and MGM were common metabolites in forage legumes but alfalfa was unusual in having negligible levels of isoflavonoid conjugates in the foliage. Our results clarify the nature and distribution of isoflavonoid conjugates in alfalfa and demonstrate that their accumulation is regulated in response to both plant age and nodulation.
Embryo sac development and endogenous gibberellins in pollinated and unpollinated ovaries of walnut (Juglans regia)
Authors: Tadeo Francisco R. , Talon Manuel , Germain Eric , Dosba Françoise
Published: May 2006

The effects of pollination on both embryo sac development and gibberellin (GA) content in walnut (Juglans regia L.) ovaries were investigated. Microscopic observations on early structural changes in the embryo sac indicated that fertilization occurred shortly after pollination (within 5 days). In unpollinated ovaries, the two polar nuclei also fused during this period, leading to a 2n endosperm which started cellularization (wall formation) about 5 days later. Zygote division in pollinated ovaries started approximately 9 days after fertilization while the endosperm at this stage was still in the free‐nuclear phase. Gas chromatography‐mass spectrometry (GC‐MS) analyses of GAs in pollinated and unpollinated ovaries demonstrated the presence of all members of the 13‐hydroxylation GA pathway (GA53, GA44, GA17, GA19, GA20, GA29, GA1, and GA8). In addition, GA4, GA9, and an unknown monohydroxy‐GA12 were also detected. Endogenous GAs were quantified by selected ion monitoring (SIM) from pollination up to 13 days later. At the end of this period, pollinated ovaries contained high levels of C20 GAs whereas C19 GAs had declined. Gibberellins A44 and A19 increased slightly shortly after fertilization, then decreased, and lastly accumulated. Gibberellin A20 followed the same step‐by‐step trend albeit in an opposite manner. Gibberellin A1 showed a transitory increase immediately after fertilization and decreased gradually subsequently. The pattern of GA change in unpollinated ovaries differed mostly as follows: (1) within 13 days after the time of pollination GA53 and GA44 decreased; (2) GA19 increased continuously; (3) GA20 decreased also continuously following the opposite pattern to GA19; and (4) the brief rise in GA1 was higher (2‐fold) than in pollinated ovaries, although 13 days after the time of pollination its levels were much lower in unpollinated ones. These results suggest that the sequence pollination/fertilization modulates GA1 levels, first reducing them immediately after fertilization, and subsequently, stimulating moderate amounts shortly thereafter at the beginning of embryogenesis. In unpollinated ovaries the lowest GAI levels coincided with ovary growth arrest, the onset of a rapid and heavy abscission (100%), and an accelerated 2n endosperm cellularization. However, repeated exogenous GA3 applications did not suppress the growth arrest and abscission.
Lipid peroxidation and peroxide‐scavenging enzymes associated with accelerated aging of peanut seed
Authors: Sung J. M. , Jeng T. L.
Published: May 2006

Accelerated aging is known to reduce seed viability and vigor in many crop species. The phenomenon is due in part to aging‐induced lipid peroxidation, which has the potential to damage membranes of the seed tissues. This study was undertaken to evaluate the effect of accelerated aging on germinability and several physiological characteristics related to peroxidation in the seed of two peanut cultivars. Accelerated aging was achieved by incubating seed at 45°C and 79% relative humidity in a closed chamber for 3, 6, or 9 days. The results indicate that accelerated aging inhibited seed germination and seedling growth. Enhanced lipid peroxidation and increased peroxide accumulation were observed in the axis and cotyledons of aged seed. Accelerated aging also inhibited the activity of superoxide dismutase, peroxidase, ascorbate peroxidase, and lipoxygenase. Seed axes appeared to be more susceptible to aging than cotyledons. The changes in germination and physiological activities, expressed as a function of aging duration, were similar in the two cultivars, despite differences in their seed weight.
Carbohydrate starvation is a major determinant of the loss of greening capacity in cotyledons of dark‐grown sugar beet seedlings
Authors: Elamrani Abdelhak , Gaudillère Jean‐Pierre , Raymond Philippe
Published: May 2006

The transition of cotyledons from heterottophy to autotrophy is a critical step of seedling establishment. We have studied the greening capacity of sugar beet (Beta vulgaris L. cv. Véga) cotyledons in relation to carbohydrate and energy metabolism during dark growth. During early growth, sugar beet cotyledons behaved mainly as a lipid‐mobilizing and gluconeogenic tissue providing substrates to the seedling. Reserve mobilization was followed by a maximum of the adenine nucleotide pool on day 6 in strict correlation with the maximum of greening capacity. This was immediately followed by the onset of a typical situation of carbohydrate starvation characterized by substrate limitation of respiration, a decrease in the adenine nucleotide pool and, as shown by the respiratory quotient and the loss of proteins, a probable utilization of cellular proteins and lipids to sustain respiration. The conversion from etioplast to chloroplast, as determined by the rate of chlorophyll synthesis, was less and less efficient as carbohydrate starvation continued, finally leading to incomplete and heterogeneous greening on day 12. The relationship of the loss of greening capacity with carbohydrate starvation is discussed.
Sodium partitioning within the shoot of soybean
Authors: Durand Monique , Lacan Dominique
Published: May 2006

Uptake and partitioning of Na+ and Cl− in plants of soybean (Glycine max L. Merr. cv. Hodgson) exposed to moderate NaCl concentrations were studied over an 8‐day period. Plants showed marked retention of Na+ in the stems and low transport to laminae of young leaves. The xylem sap ascending the main axis was progressively depleted in Na+. The oldest leaf greatly contributed to Na+ depletion of the sap flowing to younger leaves. These results in combination with estimates of phloem recirculation indicated that Na+ accumulation in the young leaf was prevented both by depletion of Na+ from the xylem stream, and by a high recirculation of Na+ via the phloem. However, this protection of young leaves was effective only for very mild salinity treatment.
Effect of decreased irradiance on N and C metabolism in leaves and roots of maize
Authors: Merlo Lucia , Ferretti Massimo , Passera Calvino , Ghisi Rossella
Published: May 2006

The effects of decreased irradiance on fresh and dry weight, root respiration, levels of carbohydrates and N‐compounds, and extractable activities of enzymes involved in C and N metabolism were evaluated in maize (Zea mays L. cv. Plauto) seedlings during the 7 days following transfer from 450 to 200 μmol m−2 s−1 PAR. The fresh weight of roots and stems, the initiation of new leaves, root respiration rate, and the accumulation of dry matter, soluble sugars, starch, malate and amino acids in both leaves and roots were strongly reduced at low irradiance. In contrast, the level of nitrate was increased in leaves and only marginally affected in roots. Leaf phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity started to decrease after 24–34 h, whereas ribulose‐1,5‐bisphosphate carboxylase (EC 4.1.1.39) activity and chlorophyll content were unaffected or only slightly reduced. In both leaves and roots, the adjustment of N metabolism to low irradiance occurred through a relatively rapid (30% after 10 h) and large (60% after 3 days) decrease of nitrate reductase (NR; EC 1.6.6.1) activity, followed by slower and smaller changes in the activity of nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2) and NAD‐dependent glutamate dehydrogenase (EC 1.4.1.2). We suggest that the preferential decrease of NR activity relative to other N‐assimilating enzymes may be important for preventing the accumulation of toxic N‐compounds like ammonia in both leaf and root tissues.
Three carboxypeptidases occurring in the starchy endosperm of germinating barley grain have different sites of synthesis
Authors: Ranki Harri , Mendez‐Lozano Jesus , Sopanen Tuomas
Published: May 2006

Northern hybridizations were used to study the site of synthesis of three carboxypeptidases (Cpases I‐III) which occur in the starchy endosperm of germinating barley grain (Hordeum vulgare L.). Further evidence was obtained by studying secretion of these enzymes from scutella or aleurone layers separated from germinating grains. Messenger RNA for Cpase II was detected only in developing grain, and the bulk of the mRNA was localized in the starchy endosperm. This suggests that Cpase II is synthesized at the site of its accumulation, the starchy endosperm. In contrast, Cpase I is expressed during germination and the predominant site of synthesis is the scutellum, from which it is secreted into the starchy endosperm. Cpase III is also synthesized during germination, but the bulk of it is synthesized in and secreted from the aleurone layer. Thus, the three carboxypeptidases, all of which seem to play a role in hydrolysis of the reserve proteins in the starchy endosperm during germination, have different sites of synthesis.