bluuebunny/crossref_metadata_2025 huggingface dataset:
High growth rate and regeneration capacity of hypocotyl protoplasts in some Brassicaceae
Authors: Glimelius Kristina
Published: April 2006

Protoplasts isolated from 4‐day‐old hypocotyls of various species of Brassica (Brassica napus, B. campestris and B. oleracea) produced callus with high efficiency in media containing casein hydrolysate and high concentrations of the auxin 2,4‐D (4.5 μM). Cell division began after 24 h and 60% of the cells had divided after 48 h. In contrast, protoplasts isolated from stem and mesophyll of plants grown in vitro or in the greenhouse began to divide after a delay of 3–5 days. In these cases 40–50% of the cells had divided after 5 days as compared to 70% for hypocotyl protoplasts. To obtain a high frequency of regeneration, rapidly growing calli were transferred to media having a high cytokinin:auxin ratio as early as possible, usually 3 weeks after protoplast isolation. The average regeneration frequency for calli obtained from mesophyll protoplasts was 50%, while as many as 70% of the calli derived from hypocotyl protoplasts of B. napus regenerated plantlets on a medium containing zeatin (9.1 μM) and IAA (0.6 μM). On the same medium regeneration of Brassica oleracea was obtained. A low percentage of calli (1%) from Brassica campestris formed shoots when cultured on a combination of zeatin (4.6 μM), BA (4.4 μM) and IAA (0.6 μM).
Changes in the properties of cell wall pectin methylesterase along the Vigna radiata hypocotyl
Authors: Goldberg Renée
Published: April 2006

The properties of cell wall pectinesterase (EC 3.1.1.11) from Vigna radiata (L.) Wilczek hypocotyl were investigated with immobilized and solubilized wall enzymes. Along the hypocotyl, the decrease of growth potential coincides with significant changes of the characteristics of the pectinesterase activities. As hypocotyl cells grow older, the proportion of ionically bound enzymes decreases and pH profile, sensitivity to cations and affinity for pectin change. The possible significance of these observations is discussed.
Orientation nouvelle du métabolisme des acides hydroxycinnamiques dans les fruits de tomates blessés (Lycopersicon esculentum)
Authors: Fleuriet Annie , Macheix Jean‐Jacques
Published: April 2006

A change in the metabolism of hydroxycinnamic acids in wounded tomato fruits (Lycopersicon esculentum).

Healing of lesions in tomato fruits (Lycopersicon esculentum Mill. var. cerasiforme) is partly due to lignification of cells bordering the wounded zones. The pericarp of healthy fruits contains a high level of hydroxycinnamic derivatives but never shows lignification. Thus, the reaction of the fruit to wounding seems to be a change in the metabolism, leading to the formation of monomeric units of which lignins are constituted. Hydroxycinnamate:CoA ligase (EC 6.2.1.12; CL) and O‐methyltransferase (EC 2.1.1.6; OMT) appear to play an important role in this change. In wounded fruits CL acts preferentially on p‐coumarate and ferulate as compared to caffeate, and OMT is particularly active with 5‐OH ferulate as substrate. These changes lead to the formation of p‐coumaroyl CoA, feruloyl CoA and sinapate, which are incorporated into lignin. Phenylalanine ammonialyase (EC 4.3.1.5) and glucosyltransferase activities increase greatly after wounding, whereas the activity of hydroxycinnamoyl‐CoA:quinate hydroxycinnamoyl transferase decreases. These data complement those previously reported on peroxidases and suggest that, after the increase of enzyme activities, monomeric units are formed and then polymerized by some peroxidases specific for lignification.
Physiological and biochemical events leading to vitrification of plants cultured in vitro
Authors: Kevers C. , Coumans M. , Coumans‐Gillès M.‐F. , Caspar Th.
Published: April 2006

Water content, peroxidase activity and isoperoxidases, phenylalanine ammonia‐lyase activity and phenolic content were comparatively analyzed in tissues of normal and vitreous plants cultured in vitro. The release of ethylene in flask atmospheres by normal and vitrifying plants was also measured. On the basis of the results, it is hypothesized that vitrification results from a burst of ethylene controlled by the peroxidase‐IAA‐oxidase system. An initiating stress (e.g. excess of cytokinins or of NH4+ ions) would mediate the enhancement of the activity of soluble and membrane‐bound peroxidases through a rapid modification of the phenolic level. The excess of ethylene in the atmosphere of stressed plants would retroinhibit its own biosynthesis and as a consequence decrease the activities of PAL and acidic peroxidases, thus hindering lignification processes. A parallel decrease in cellulose synthesis due to a diverted conversion of sugars to amino acids is expected (from data in the literature). Deficiency of both cellulose and lignin would allow more water uptake due to reduced wall pressure and bring about the hyperhydric malformations.
Growth inhibitors in oat grains. I. Leakage of inhibiting factors from oat grains during imbibition and the effect of these on germination and growth
Authors: Häggquist Maj‐Lis , Pettersson Agneta , Liljenberg Conny
Published: April 2006

During imbibition, oat (Avena sativa L. cv. Sol II) grains leak inhibiting substances originating mostly from the hulls. The inhibitors repress the growth of roots causing morphological changes in roots of Avena seedlings. Neither the activity of microorganisms nor the osmotic potential of the growth medium was responsible for these changes. The major inhibiting substances of the leachate appear to be triterpenoid glycosides.
Starch fermentation via a formate producing pathway in Chlamydomonas reinhardii, Chlorogonium elongatum and Chlorella fusca
Authors: Kreuzberg Karlheinz
Published: April 2006

Starch degradation was investigated during anaerobic dark incubation in the algae Chlamydomonas reinhardii, Chlorogonium elongatum and Chlorella fusca. The pathway of algal formate fermentation was elucidated by determination of the relationship between substrate consumption and product accumulation. The fate of reducing equivalents was also determined. Investigations were done on dependence of pH, fermentation time, cell cycle, and after addition of H2, hypophosphite and inhibitors of protein synthesis.

A mixed acid fermentation that produced formate, acetate and ethanol (2:1:1) with only small amounts of H2 and CO2 was shown for the algal strains used. The failure of inhibition with cycloheximide and chloramphenicol indicated the constitutive presence of all fermenting enzymes. Nevertheless, glycerol, D(–)lactate and stoichiometrical amounts of ethanol and CO2 were found additionally at extreme pH (pH 4.6 and 7.9), and after addition of H2 and hypophosphite (7 mM). During long‐term incubation (28 h) fermentation changed from mixed acid to ethanol production. The pathways of algal fermentation did not depend on cell cycle, and fermentation rate corresponded directly to the actual starch content of algal cells. The results gave evidence for synthesis of formate during anaerobic metabolism in algae by a thioclastic cleavage of pyruvate via the enzyme pyruvate formate lyase. This indicated an algal fermentation pathway thought to be present only in procaryotic organisms.
Effect of light during regeneration from leaves of Polytrichum juniperinum
Authors: Gay Lucien
Published: April 2006

The complete regeneration of protonema from leaves of Polytrichum juniperinum Willd. is primarily related to the trophic effect of continuous white light but can be fulfilled with low irradiance (0.6 W −2) or with short photoperiods (6 h per day). Provided the threshold level (3.6 W−2 during 12 h) is applied, white light also acts as an inductive stimulus independent of photosynthesis around the 24th hour of culture. During this stimulation by light, RNA synthesis and then protein synthesis are required but DNA synthesis is not. The effect of light may be related to phytochrome.
Photocontrol of the cotyledonary blade epinasty of Sinapis alba seedlings. Effects of irradiance and quality of light
Authors: Baumgartner Nicole , Fondeville Jean‐Claude
Published: April 2006

The effects of the fluence rate of continuous light (far‐red, fluorescent white, blue and red light) on the increase of epinastic percentage of cotyledons were recorded for six days. The epinastic photoresponse was compared to the cotyledonary enlargement and to the inhibition of the hypocotyl extension of irradiated Sinapis alba L. seedlings. Fluence rate response curves and wavelength response curves showed that the photoepinasty is a typical high irradiance response (as is the inhibition of hypocotyl extension) with two maxima, one in the blue and one in the far‐red. The epinastic photoresponse was not directly related to cotyledonary growth, which was greater in red and far‐red light than in blue light.
Development of flower buds in thin‐layer cultures of floral stalk tissue from tobacco: Role of hormones in different stages
Authors: van den Ende G. , Croes A. F. , Kemp Anke , Barendse G. W. M.
Published: April 2006

The in vitro development of flower buds was studied on tissue explants of epidermis and subepidermal cortex from the flower stalks of Nicotiana tabacum L. cv. Samsun. The number of flower buds formed depended mainly on cytokinin concentration. Auxin acted as a modifier in a complex way. In early development, NAA at 1 μM decreased the number of buds initiated and delayed bud emergence. At a later stage, auxin promoted bud outgrowth at the same concentration. Optimal results were obtained when explants were first incubated at low auxin concentration for 3–5 days and subsequently transferred to an elevated auxin level. Physiological processes that lead to flower bud initiation start very soon after the onset of incubation. This was inferred from experiments whereby explants were first cultured at an inductive cytokinin concentration and then transferred to a non‐inductive hormone level.
Metabolism of indole‐3‐acetic acid and indole‐3‐methanol in wheat leaf segments
Authors: Langenbeck‐Schwich Beatrix , Grainbow Hans J.
Published: April 2006

Indole‐3‐methanol is a product of indole‐3‐acetic acid metabolism in wheat leaves (Triticum compactum Host., cv. Little Club). It leads either to the production of the corresponding aldehyde and carboxylic acid, to the production of a polar glucoside which releases indole‐3‐methanol on β‐glucosidase treatment, or to an unidentified apolar product on mild alkaline hydrolysis in aqueous methanol. With reference to a published pathway of indole‐3‐acetic acid degradation, the results provide evidence for a prominent role of indole‐3‐methanol and also for the occurrence of co‐oxidation processes in wheat leaves involving indole‐3‐acetic acid and phenolic cosubstrates.
The development of Pisum sativum explant systems for studies concerning source‐sink activities
Authors: Achhireddy N. R. , Kirkwood R. C. , van den Berg G.
Published: April 2006

Using excised fruit/shoot systems of pea (Pisum sativum L.), the effect of the 10‐day‐old (post anthesis) fruit (sink) on the translocation of 14C‐sucrose applied to the stipule (source) was investigated. We also examined the influence of various growth regulators on the source‐sink relationships using this system. Indole‐3‐yl‐acetic acid (100 or 200 ppm), gibberellic acid (25‐100 ppm) increased 14C‐sucrose translocation into the growing fruit by about 13% and 22–29%, respectively. 2‐chloroethyl phosphonic acid, 6‐benzyladenine and 2‐methyl‐4‐chlorophenoxyacetic acid also increased 14C‐sucrose translocation into the fruit by about 11–26%, 11–23% and 24–37%, respectively. Elevated fruit 14C‐sucrose levels found in other treatments include, methyl‐2‐chloro‐9‐hydroxyfluorene‐9‐carboxylate (300 or 1000 ppm), 2,3,5‐triiodobenzoic acid (100 and 300 ppm) and butanedioic acid mono‐(2,2‐dimethylhydrazide) (30‐300 ppm) by about 34%, 39–52% and 7–13%, respectively.
Phosphate accumulation in leaves of wheat seedlings measured in leaf cell protoplasts isolated after root or foliar treatment with orthophosphate
Authors: Smyth Douglas A. , Chevalier Peggy
Published: April 2006

Leaf cell protoplasts were isolated from wheat seedlings (Triticum aestivum L. cv. Urquie) after orthophosphate (Pi) treatment of the plant to determine the capacity for intracellular phosphate accumulation. Seedlings were treated with Pi concentrations near the phytotoxic level to maximize the Pi concentration in the leaf prior to protoplast isolation 1 day later. Both foliar and root treatment of seedlings with Pi increased the phosphate content of leaf protoplasts by approximately 20 μmol (mg chlorophyll)−1 over Pi levels in untreated controls. Phosphate‐loaded protoplasts from treated seedlings had similar photosynthetic rates and starch content but 50% more soluble reducing sugar than protoplasts from untreated seedlings. Protoplast dark respiration decreased after treatments which increased protoplast potassium content. The results suggest that similar amounts of Pi can be accumulated by leaf cells of wheat after foliar or root application of Pi to the seedling without hindering Pi‐sensitive processes such as photosynthesis and starch synthesis.
Nitrate reduction and compartmentation in tomato leaves. I. Nitrate accumulation in leaf sections in aqueous and gaseous medium
Authors: Mills David , Lips Herman S.
Published: April 2006

Nitrate pools in tomato (Lycopersicon esculentum Mill. cv. Azes) leaf sections were estimated. Nitrite accumulation in aqueous medium was found to be an inadequate estimate of nitrate pools in tomato leaves. The main reason for the cessation of nitrite accumulation was not depletion of nitrate in the metabolic pool but rather a rapid decay of nitrate reductase (NR) activity as measured by nitrite accumulation in vivo and in vitro. Nitrate diffuses out of the tissue into the medium at a rate higher than the accumulation of nitrite in the tissue. Nitrate leakage from the tissue accelerates the loss of NR activity. Nitrite accumulation in leaf sections kept in an anaerobic gaseous atmosphere ceased earlier than in aqueous medium, at a time when NR activity was still relatively high. Measuring nitrite accumulation in gaseous atmosphere is preferable since NR is more stable and movements of nitrate between pools more restricted.
Nitrate reduction and compartmentation in tomato leaves. II. Nitrate loss by leaf sections in a gaseous atmosphere and the size of the metabolic nitrate pool
Authors: Mills David , Soares Ines M. M. , Cresswell Cristopher F. , Lips Herman S.
Published: April 2006

Nitrate disappearance in tomato ((ycopersicon esculentum Mill. cv. Azes) leaf sections kept under a stream of gas (nitrogen or air) has been studied, using leaf sections from plants supplied with low (7.5 mM) or high (17.5 mM) nitrate levels in their nutrient solution. Cessation of nitrate loss occurred in leaf sections taken from plants irrigated with low (7.5 mM) nitrate‐containing nutrient solution. Resumption of nitrate disappearance occurred upon addition of exogenous nitrate by vacuum infiltration to leaf sections, suggesting that cessation of nitrate loss was due to exhaustion of the metabolic pool. We estimated that 53% of the total nitrate in leaf sections from low nitrate plants was located in a storage pool, probably the vacuole. The remainder was located in a pool, readily available for reduction (the metabolic pool). This pool is composed of nitrate in the free space as well as in the cytoplasm which was estimated to contain about 20% of the total nitrate.

Either under air or nitrogen, less nitrite was accumulated than nitrate assimilated suggesting that nitrite accumulation was not an adequate parameter for the estimation of nitrate utilization. Anaerobic conditions inhibited nitrite reduction whereas nitrate assimilation was not blocked. Nitrate loss from endogenous pool in leaf sections placed under aerobic conditions is suggested as an adequate method for the estimation of the metabolic pool of nitrate.
The periodic induction of dormancy during the rhythmic growth of Gnetum africanum
Authors: Mialoundama F. , Lauzac M. , Paulet P.
Published: April 2006

The rhythmic growth of Gnetum africanum Welw. has an endogenous origin. Correlations between the apical bud and young leaves located at the top of the epicotyl can explain this kind of growth. Young leaves inhibit the apical bud and a prolonged inhibition leads to bud dormancy. The period of inhibition coincides with the growth of these leaves. When growth stops, dormancy is induced. Moreover a removal of young leaves suppresses inhibition which prevents dormancy induction; here again a continous suppresses inhibition which prevents dormancy induction; here again a continuous growth results. A prolonged exogenous treatment of the apical bud with abscisic acid and auxin shows that these two growth substances can play a part in the induction of dormancy after removal of the young leaves.
Application of electric field fusion in plant tissue culture
Authors: Zachrisson Anders , Bornman Chris H.
Published: April 2006

Manipulation of protoplasts via fusion and organelle transfer is expected to be facilitated by the technique known as electric field fusion. Construction and use are described of three flow‐through fusion chambers that incorporate flat‐sided electrodes in a manner that makes fusion of protoplasts possible througout the chambers’ total volume (4, 49 or 110 μl) under constant electrical, chemical and physical conditions. Brassica napus L. protoplasts subjected to fusogenic conditions, that is, application of voltages that induce reversible membrane breakdown, were capable not only of survival but also of cell wall resynthesis, cell division and subsequent growth and development. Intraspecific (B. napus × B. napus), interspecific. (B. napus × B. campestris L.) and intergeneric (B. napus × Primula acaulis L.) fusion and engulfment events were followed by using on the one hand autofluorescence and fluorescein isothiocynate as respective markers or on the other hand autofluorescence and vacuolar anthocyanin (Primula). Properties and merits of flat‐sided versus cylindrical electrodes are discussed.
Galactose inhibition of auxin‐induced cell elongation in oat coleoptile segments
Authors: Yamamoto Ryoichi , Masuda Yoshio
Published: April 2006

Auxin‐induced cell elongation in oat coleoptile segments was inhibited by galactose; removal of galactose restored growth. Galactose did not appear to affect the following factors which modify cell elongation: auxin uptake, auxin metabolism, osmotic concentration of cell sap, uptake of tritium‐labeled water, auxin‐induced wall loosening as measured by a decrease in the minimum stress‐relaxation time and auxininduced glucan degradation. Galactose markedly prevented incorporation of [14C]‐glucose into cellulosic and non‐cellulosic fractions of the cell wall. It was concluded that galactose inhibited auxin‐induced long‐term elongation of oat coleoptile segments by interfering with cell wall synthesis.
Action spectra for polarotropism and phototropism in protonemata of the fern Adiantum capillus‐veneris
Authors: Kadota Akeo , Koyama Motoko , Wada Masamitsu , Furuya Masaki
Published: April 2006

The action spectrum for polarotropism was determined, using the Okazaki large spectrograph, by brief irradiation with light between 260 nm and 850 nm in single‐celled protonemata of the fern Adiantum capillus‐veneris L., which had been cultured for 6 days in red light and then in the dark for 15 h. The action spectrum had a peak at around 680 nm. This effect was nullified by subsequent irradiaton with far‐red light, and typical red/far‐red reversibility was observed, indicating the involvement of phytochrome. Polarized ultraviolet or blue light had no effect on the direction of apical growth. The action spectrum for phototropism was also determined in the red light region by means of brief microbeam irradiation of a flank of the subapical region of the protonema. This spectrum showed a peak at 662 nm which was consistent with the absorption peak of phytochrome, but not with the peak of the action spectrum for polarotropism.
Temperature control of germination and its possible role in the survival of a non‐dormant population of Avena fatua
Authors: Sawhney Ramma , Hsiao Andrew I. , Quick William A.
Published: April 2006

Germination of freshly harvested seeds of a non‐dormant (ND) line (Stonehouse 319) of wild oats (Avena fatua L.) was inhibited by incubation of the seeds at relatively high temperatures of 25 and 30°C. The germination inhibition in these seeds appeared to be a case of thermo‐inhibition which was the direct effect of hightemperature treatment (HIT), since it did not persist after transferring the seeds to an optimum germination temperature of 20°C. Even a prolonged HTT of 30°C for over 5 weeks did not prevent germination of about 80% of the seeds transferred to 20°C. However, in a significant proportion of the seeds, thermo‐dormancy was induced by 10 days of HTT at 30°C if the seeds were then incubated at sub‐optimal temperatures of 5 to 15°C. This thermo‐dormancy would appear to be ‘restrictive’ in form, since its expression was restricted to very specific conditions. Relatively low inclubation temperaturs of 5 and 10°C markedly slowed germination whether HTT was applied or not. The results suggest that thermo‐inhibition and thermo‐dormancy, induced during seasonal temperature fluctuations, may provide a survival mechanism for seeds of such ND lines as Stonehouse 319.
Leghaemoglobin biosynthesis in a new single cell system from soybean root nodules
Authors: Uheda Eiji , Syöno Kunihiko
Published: April 2006

Single cells were effectively released from 35–45‐day‐old soybean (Glycine max L. cv. Yaefusanari) nodules by treatment with an enzymic solution containing 1 mg/ml maceration enzyme (Pectolyase Y‐23), 0.5M mannitol, 2% (w/v) sucrose and 0.5% (w/v) potassium dextran sulfate. Bacteroid‐containing cells were purified by Percoll density gradient centrifugation. Electron microscopic observation showed that these cells were protoplasts enclosed by a thin wall and with well preserved internal structures including bacteroids. The single cells obtained were stable against centrifugation and vigorous pipetting. The cells retained the ability to synthesize proteins including leghaemoglobin. The ratio of leghaemoglobin components synthesized in the single cells was similar to that of components synthesized in the nodules. The bacteroidal cell fraction was further separated into three fractions by a Percoll density gradient centrifugation. Comparison of the absolute and relative leghaemoglobin content, the activity of glutamine synthetase in the cytoplasm and the activity of 3‐hydroxybutyrate dehydrogenase in the bacteroid suggests that these fractions contained cells in different stages of symbiosis. This new single cell system should provide a useful experimental system for analyzing events in the root nodule.
Chloroplast structure in normal and pigment‐deficient soybeans grown in continuous red or far‐red light
Authors: Eskins Kenneth , Duysen Murray
Published: April 2006

Clark L1, a normal green soybean [Glycine max (L.) Merrill] and Clark y9y9, a backross‐developed isoline exhibiting pigment deficiency, were grown under continuous red (11 W m−2 and far‐red (9 W m−2) light. Chloroplast thylakoids from the unifoliolate leaf (9–10 days old) were isolated and analyzed for pigments, pigment‐protein, membrane polypeptides, electron transport and ultrastructural differences. Chloroplasts of soybean plants grown under far‐red light have decreased chlorophyll a to chlorophyll b ratio, increased light‐harvesting complexes, and grana structure with few stroma‐type thylakoids. Photosystem II/photosystem I ratios (PSII/PSI) are higher in far‐red due to decreased synthesis of PSI reaction center and/or less antenna associated with PSI.
Mode of high temperature injury to wheat during grain development
Authors: Al‐Khatib Kassim , Paulsen Gary M.
Published: April 2006

High temperature stress adversely affects wheat growth in many important production regions, but the mode of injury is unclear. Wheat (Triticum aestivum L. cv. Newton) was grown under controlled conditions to determine the relative magnitude and sequences of responses of source and sink processes to high temperature stress during grain development. Regimes of 25°C day/15°C night, 30°C day/20°C night, and 35°C day/25°C night from 5 days after anthesis to maturity differentially affected source and sink processes. High temperatures accelerated the normal decline in viable leaf blade area and photosynthetic activities per unit leaf area. Electron transport, as measured by Hill reaction activity, declined earlier and faster than other photosynthetic processes at the optimum temperature of 25/15 °C and at elevated temperatures. Changes in RUBP carboxylase activities were similar in direction but smaller in magnitude than changes in photosynthesic rate. Increased protease activity during senscence was markedly accentuated by high temperature stress. Specific protease activity increased 4‐fold at 25/15 °C and 28‐fold at 35/25 °C from 0 to 21 days after initiation of temperature treatments. Grain‐filling rate decreased from the lowest to the highest temperature, but the change was smaller than the decrease in grain‐filling duration at the same temperatures. We concluded that a major effect of high temperature is acceleration of senescence, including cessation of vegetative and reproductive growth, deterioration of photosynthetic activities, and degradation of proteinaceous constituents.
Ammonium uptake in Lemna gibba G 1, related membrane potential changes, and inhibition of anion uptake
Authors: Ullrich Wolfram R. , Larsson Marie , Larsson Carl‐Magnus , Lesch Sigrid , Novacky Anton
Published: April 2006

In N‐starved (−N) fronds of Lemna gibba L. G 1, NH4+ uptake rates were several‐fold those of NO3−‐supplied (+N) fronds. NO3−, uptake in +N‐plants was slow and not inhibited by addition of NH4+. However, in −N‐plants with higher NO3− and still higher NH4+ uptake rates, addition of NH4+ immediately reduced the NO3− uptake rates to about one third until the NH4+ was consumed. The membrane potential (Em) decreased immediately upon addition of NH4+ in all fronds, but whereas depolarisation was moderate and transient in +N‐plants, it was strong, up to 150 mV, in N‐starved plants, where Em remained at the level of the K+ diffusion potential (ED) until NH4+ was removed. In N‐starved plants NH4+ uptake and membrane depolarisation showed the same concentration dependence, except for an apparent linear component for uptake. Phosphate uptake was inhibited by NH4+ similarly to NO3− uptake, but only in P‐ and N‐starved plants, not after mere P starvation. Influx of NO3− and H2PO 4− into the negatively charged cells of Lemna is mediated by anion/H+ cotransport, but NH4+ influx can follow the electrochemical gradient. Its saturating component may reflect a carrier‐mediated NH4+ uniport, the linear component diffusion of NH4+ or NH3. Inhibition of anion/H+ cotransport by high NH4+ influx rates may be due to loss of the proton‐driving force, Δμ̃H+, across the plasmalemma. Reversible inhibition by NH4+ of the H+ extrusion pump may contribute to the finding that Δμ̃H+ cannot be reconstituted in the presence of higher NH4+ concentrations.
The isolation and characterization of abscisic acid‐insensitive mutants of Arabidopsis thaliana
Authors: Koornneef M. , Reuling G. , Karssen C. M.
Published: April 2006

Abscisic acid (ABA) insensitive mutants of Arabidopsis thaliana (L.) Heynh. were isolated by selecting plants which grew well on a medium containing 10 μM ABA. From the progeny of approximately 3500 mutagen‐treated seeds, five mutants of at least three different loci were isolated. Three mutants were characterized, moreover, by a reduced seed dormancy and by symptoms of withering, indicating disturbed water relations and, therefore, resembled phenotypically the ABA‐deficient mutants we described earlier in this species. Two mutants showed in addition only a reduction of seed dormancy. Compared to wild type, all mutants showed similar or increased levels of endogenous ABA in developing seeds and fruits (siliquae). The role of the different genes involved is discussed in relation to the mechanism of ABA action.
Biochemical characterization of nitrate and nitrite reduction in the wild‐type and a nitrate reductase mutant of soybean
Authors: Nelson Richard S. , Streit Luc , Harper James E.
Published: April 2006

Enzyme activities involved in nitrate assimilation were analyzed from crude leaf extracts of wild‐type (cv. Williams) and mutant (nr1) soybean [Glycine max (L.) Merr.] plants lacking constitutive nitrate reductase (NR) activity. The nr1 soybean mutant (formerly LNR‐2), had decreased NADH‐NR, FMNH2‐NR and cytochrome c reductase activities, all of which were associated with the loss of constitutive NR activity. Measurement of FMNH2‐NR activity, by nitrite determination, was accurate since nitrite reductase could not use FMNH2 as a reductant source. Nitrite reductase activity was normal in the nr1 plant type in the presence of reduced methyl viologen. Assuming that constitutive NR is similar in structure to nitrate reductases from other plants, presence of xanthine dehydrogenase activity and loss of cytochrome c reductase activity indicated that the apoprotein and not the molybdenum cofactor had been affected in the constitutive enzyme of the mutant. Constitutive NR from urea‐grown wild‐type plants had 1) greater ability to use FMNH2 as an electron donor, 2) a lower pH optimum, and 3) decreased ability to distinguish between NO3− and HCO3−, compared with inducible NR from NO3−‐grown nr1 plants. The presence in soybean leaves of a nitrate reductase with a pH optimum of 7.5 is contrary to previous reports and indicates that soybean is not an exception among higher plants for this activity.
Effect of nonanoic acid and other short chain fatty acids on exchange properties in embryonic axes of Cicer arietinum during germination
Authors: Babiano M. J. , Aldasoro J. J. , Hernández‐Nistal J. , Rodriguez D. , Matilla A. , Nicolás G.
Published: April 2006

Nonanoic acid, which inhibits germination in several seeds, enhanced ion efflux from embryonic axes of Cicer arietinum L., especially at temperatures above 25°C. Other short chain fatty acids had little effect on germination and ion leakage. Nonanoic acid also decreased uptake of 86Rb+ and 22Na+ and increased efflux of both isotopes from the embryonic axes into the incubation solution. Fusicoccin, which stimulates early germination in C. arietinum, counteracted the effects of nonanoic acid at both 25 and 30°C. These results suggest that nonanoic acid affects the integrity of plasmalemma and other membrane systems. Nonanoic acid thus inhibits cell elongation during early germination by disturbing ion exchange and inhibiting water uptake.
Mannitol transport and suitability as an osmoticum in root cells
Authors: Cram W. J.
Published: April 2006

Fluxes of mannitol across plasmalemma and tonoplast of excised carrot storage root tissue were measured using compartmental analysis of 14C tracer exchange. Mannitol metabolism and the contribution of [14C]‐labelled metabolites to efflux was shown to be small. Similar but less extensive measurements were made on red beet (Beta vulgaris L.), barley (Hordeum vulgare L.) and maize (Zea mays L.) roots. Calculated values of the reflection coefficient for mannitol were close to one, but, despite this, the inflow of mannitol was sufficient to dissipate the mannitol concentration gradient between inside and outside the cells within the time it takes them to adjust vacuolar concentrations. Thus mannitol is not suitable as an osmoticum in osmotic adjustment experiments in these root tissues. Mannitol flows appear to be passive. Permeability to mannitol (about 10−10 m s−1 is greater at the plasmalemma than at the tonoplast in carrot, and this would tend to cause the cytoplasm to swell. The implications for the control of cytoplasmic volume are discussed.
Cholinergic constituents in plants: Characterization and distribution of acetylcholine and choline
Authors: Miura George A. , Shih Tsung‐Ming
Published: April 2006

Acetylcholine in plants was identified by gas chromatography/mass spectrometry. Acetylcholine was found in the following species from 13 families: Betula pendula, Codiaeum variegatum, Ilex opaca, Liquidambar styraciflua, Lonicera japonica, Phaseolus aureus, Phaseolus vulgaris, Pisum sativum, Plantago rugelli, Populus grandidentata, Prunus serotina, Rhus copallina, Smilax hispida, Viburnum dilatatum, and Zea mays. Levels of acetylcholine in leaves ranged from a low of 0.14 ± 0.05 (mean ± SEM) nmol (g fresh weight)−1 in I. opaca to a high of 53 ± 6.6 nmol (g fresh weight)−1 in P. aureus. Acetylcholine was found in all tissues examined regardless of the organ (leaves, stems, or roots) or developmental stage (seedlings, mature plants, or seeds). For P. aureus, continuous light exposure increased acetylcholine levels of leaves, and decreased levels in stem when compared to dark controls. Levels of choline, a precursor of acetylcholine, found in leaves ranged from a low of 84 ± 7.0 nmol (g fresh weight)−1 in L. styraciflua to a high of 3700 ± 200 nmol (g fresh weight)−1 in P. aureus. With these findings, three out of the four components of the cholinergic system have now been identified in plants.
Endogenous auxin levels in terminal stem cuttings of Chrysanthemum morifolium during adventitious rooting
Authors: Weigel Ursula , Horn Wolfgang , Hock Bertold
Published: April 2006

Free and ester‐bound IAA were determined in Chrysanthemum morifolium Ramat cv. ‘Yellow Galaxy’ by means of a solid phase enzyme immunoassay. In shoots, free auxin decreases basipetally whereas ester IAA reaches a maximum in the middle part. After making the cuttings, a strong increase in both free and ester IAA (or total IAA, respectively) is found up to the time when the first adventitious roots become visible. Only prolonged irradiance of stock plants at high light intensities (40 W m−2) delays this increase in the cuttings, concomitantly with a lower number of roots compared to the controls (4.5 W m−2), although root growth as determined by measuring root length or fresh weight is not affected. A distinct relation is found between IAA content of stock plants at the time when cuttings are taken and the number of adventitious roots formed by the cuttings 20 days later.
Leaf phosphorus fractionation and growth responses to phosphorus of the forage legumes Trifolium repens, T. dubium and Lotus pedunculatus
Authors: Hart A. L. , Jessop D.
Published: April 2006

‘Grasslands Huia’ white clover (Trifolium repens L.), ‘Grasslands Maku’ lotus (Lotus pedunculatus Cav.) and suckling clover (T. dubium Sibth) were grown in a controlled environment at various levels of P supply. Dry weights and the concentration of inorganic‐, lipid‐, ester‐ and residual‐P in trifoliate leaves were measured. Lotus grew better than white or suckling clover at low P. White clover and lotus responded steeply to increased P and had similar shoot dry weights at high P. Suckling clover had lower shoot weights than the other species at all P levels. The superior growth of lotus at low levels of p was probably due to better root growth and P uptake. Lotus had higher shoot P concentrations at low levels of P but lower concentrations than the others at high levels. White clover and suckling clover had similar shoot P concentrations at all levels of supply. In white and suckling clover total leaf P concentration rose with P supply. Of the P fractions, inorganic‐and residual‐P showed the largest rises in concentration. The increases in lipid‐ and ester‐P were smaller. Increases in lotus leaf P were small, primarily because of the relatively small rises in inorganic‐ and residual‐P. White clover is a vigorous species but requires high levels of P for best growth. Suckling clover has a relatively small response to improvements in P availability. The behaviour of the various P fractions is similar to that in white clover. Lotus grows well at low P but also shows rapid growth at high P supply. Whether efficiency is defined as the ability to extract P from the environment or to maintain low internal P concentration, lotus makes efficient use of P over the whole range of P supply.
A double enhancement of greening in the cotyledons of cucumber seedlings by excision and red light
Authors: Moran R. , Arzee T. , Porath D.
Published: April 2006

Cotyledons excised without the hypocotyl hook from 6‐day‐old etiolated cucumber (Cucumis sativus L. var. Elem) seedlings accumulated a significantly higher amount of chlorophyll than cotyledons excised with hooks or intact cotyledons. It was found that maximum ehancement of greening was achieved after 2 h of dark incubation following excision. Pretreatments with red light effected an additive rise in chlorophyll level in subsequent white light after a dark incubation, suggesting that the effects of excision and phytochrome on greening act independently. Etiolated seedlings were variously dissected before greening and it was found that enhancement occurred only when cotyledons were excised at the level of the hypocotyl hook or above it. Similar results were obtained when the dissected plants were pre‐treated with red light.
Fruit set and cytokinin‐like activity in the xylem sap of sweet cherry (Prunus avium) as affected by rootstock
Authors: Stevens Gordon A. , Westwood Melvin N.
Published: April 2006

Using a trace‐enrichment procedure involving solvent partitioning and high pressure liquid chromatography, followed by bioassay, two cytokinin‐like substances believed to be zeatin and zeation riboside were detected in the xylem sap of sweet cherry (Prunus avium L.). The levels of cytokinin varied between rootstocks with the higher yielding and fruit setting rootstocks producing the highest cytokinin levels. Most of the cytokinin activity occurred in the spring during bloom and early fruit set. A relationship between cytokinin level in the xylem sap and fruit set is proposed.
Effects of nitrogen source, calcium concentration and osmotic stress on protoplasts and protoplast‐derived cell cultures of Pinus Pinaster cotyledons
Authors: David Hélène , Jarlet Edith , David Alain
Published: April 2006

The experiments described emphasize the effects of several factors crucial to the maintenance of cell divisions leading to increased cell numbers in suspension and colony formation from cotyledon protoplasts of Pinus Pinaster Ait. Osmotic potential of the incubation and culture media are critical. Reducing the osmolality from 680 mOsm kg H2O−1 during protoplast isolation to 610 mOsm kg H2O−1 during washing and culture was essential to achieve a high frequency of cell division. Survival of the cells beyond 3 weeks of culture occurs only if the calcium concentration is decreased from 5.6 mM to 1.5 mM. Glutamine as sole source of nitrogen shortens the lag phase of response of the protoplasts and increases their plating efficiency. After 6 weeks of culture, a combination of low osmolality (225 mOsm kg H2O−1) and high level of glutamine (40 mM) is a prerequisite for obtaining actively growing cell suspensions.
Cytokinin‐induced switch in development in excised cotyledons of radiata pine cultured in vitro
Authors: Villalobos Victor M. , Oliver Melvin J. , Yeung Edward C. , Thorpe Trevor A.
Published: April 2006

Cotyledons of Pinus radiata D. Don were cultured under shoot‐forming (plus cytokinin) and elongating (minus cytokinin) conditions. Using. autoradiographic and precursor incorporation techniques, the sites and rate of macromolecular synthesis were examined during the first five days in culture. Active incorporation of 3H‐thymidine, 3 H‐uridine and 3H‐leucine occurred. In shoot‐forming cotyledons the incorporation became preferentially located in the epidermal and sub‐epidermal cell layers in contact with the medium. In elongating cotyledons, in contrast, incorporation was randomly distributed, and the amount of incorporation declined with time. Biochemically, differences in DNA, RNA and total protein synthetic patterns were observed. In elongating cotyledons the rates of RNA and protein synthesis were higher during the first 48 h than in shoot‐forming tissues, after which the synthetic rates were similar. Two peaks of newly formed DNA were observed in both tissues. These findings indicate that the cytokinin‐induced changes in developmental pathways began within 24 h in culture.
14C‐Metabolism in cultured cotyledon explants of radiata pine
Authors: Obata‐Sasamoto Hamako , Villalobos Victor M. , Thorpe Trevor A.
Published: April 2006

Excised cotyledons of radiata pine (Pinus radiata D. Don), cultured under shootforming (plus cytokinin) and elongating (minus cytokinin) conditions, were incubated in 14C‐glucose, 14C‐acetate or 14C‐bicarbonate at different stages of growth and differentiation. 14CO2 was produced when the cotyledons were fed 14C‐glucose and 14C‐acetate (no measurement was made for 14C‐bicarbonate feeding). Label from these precursors was incorporated into ethanol‐soluble and ‐insoluble fractions. The largest percentage of radioactivity was associated with the ethanol‐soluble portion, which was further fractionated into lipids, amino acids, organic acids and sugars. The amount of label and the pattern of labelling associated with each of the above classes of metabolites varied with time in culture and morphogenetic behaviour of the cotyledons. In general, there was a tendency towards a high rate of incorporation of label in elongating cotyledons during the period of rapid elongation. On the other hand, a high rate of incorporation of label in shoot‐forming cotyledons coincided with the period of meristematic tissue formation. The data obtained support the hypothesis that organized development in vitro involves a shift in metabolism, which precedes and is coincident with the initiation of the process.
Effect of rigidity of gel medium on benzyladenine‐induced adventitious bud formation and vitrification in vitro in Picea abies
Authors: Bornman Chris H. , Vogelmann Thomas C.
Published: April 2006

Observations on the effects of different degrees of rigidity of both an agar (Tayio) and a non‐agar (Gelrite) gel on the uptake of radiolabelled N6‐benzyladenine (14C‐BA) were also extended to mode of application and positioning of the explant. Regression analysis showed a highly significant inverse correlation between 14C‐BA accumulation and degree of gel stiffness. Significantly greater numbers of adventitious buds per explant were induced at low to medium levels of rigidity (2.5–10 g Tayio 1−1, 1–5 g Gelrite 1−1); this advantage was almost completely nullified at the lower levels (2.5 and 5.0 g Tayio 1−1, 1 and 1.5 g Gelrite 1−1) as a result of the high incidence of vitrification. In addition to turgor distension, vitrified buds displayed cellular damage. Explants with their cotyledons flattened onto the agar surface accumulated less 14C‐BA after 96 h than upright explants, but produced greater numbers of adventitious buds, pseudobuds and phylloids. It was suggested that BA was taken up only by “target” cells, presumably the differentiating subsidiary cells of those stomatal complexes in surface contact with the medium. Pulse treatments of relatively short durations (2 h) with optimal concentrations of BA (ca 125 μM), followed by subculturing on hormone‐free media gelled with 10 g agar 1−1, produced a satisfactory balance between yield and competence of adventitiously‐induced buds.
Uptake of benzyladenine in explants of Picea abies and Pinus sylvestris
Authors: Vogelmann Thomas C. , Bornman Chris H. , Nissen Per
Published: April 2006

Primary explants ofPicea abies (L.) Karst. and Pinus sylvestris L. were incubated for various periods in solutions containing different concentrations of [14C]‐benzyladenine. Time course analysis showed that uptake was linear for the initial 60 min; after this time linear uptake continued but at a much reduced rate. The amount of benzyladenine taken up by the explants saturated at a concentration about one third of that of the medium, Concentration dependence experiments showed that BA uptake was directly proportional to the external concentration. These results and those from experiments in which uptake was examined at different temperatures are consistent with a passive mode of BA uptake. The results are discussed with respect to in vitro micropropagation.
Phase change in loblolly pine:Shoot development as a function of age
Authors: Greenwood Michael S.
Published: April 2006

The growth behavior of grafted scions from 1‐, 4‐, 8‐ and 12‐year‐old ortets representing five half‐sib loblolly pine families was observed over a two‐year period (three for strobilus production) following grafting. Significant, persistent decreases in total number of cycles produced, height and diameter increment, number of branches produced, foliar surface area and total scion biomass were observed with increasing age. Needle length, diameter, and ability to form male and female strobili increased with increasing scion age. The persistence of these differences is not a function of size since the scions were the same length at grafting. The significance of these results to the establishment of breeding orchards, early genetic evaluation, and the nature of phase change is discussed.
Structural and cytochemical characterization of three specialized peroxisome types in soybean
Authors: Vaughn Kevin C.
Published: April 2006

Structural and cytochemical comparisons were made between three peroxisome types in soybean [Glycine max (L.) Merr. cv. Centennial]. Leaf peroxisomes were densely granular organelles with an amorphous nucleoid and were generally located in close proximity to the chloroplasts. Catalase (EC 1.11.1.6) and glycolate oxidase (EC 1.1.3.1) were localized in these peroxisomes although glycolate oxidase was absent from the nucleoid region. Glyoxysomes, present in the etiolated cotyledons, were coarsely granular organelles that were generally in close proximity to lipid bodies. Malate synthase (EC 4.1.3.2), catalase, and glycolate oxidase were present throughout the matrix. Although peroxisomes were found in both infected and uninfected nodule tissue, uninfected interstitial cell peroxisomes were the most developed. These organelles contained a core surrounded by a less electron‐opaque periphery that frequently was in close association with (but distinct from) a network of smooth endoplasmic reticulum. Of the enzymes studied, only catalase and urate oxidase (EC 1.7.3.3) were detected in the nodule peroxisomes. Neither enzyme was detected in the peripheral area of the peroxisome. These data indicate that peroxisomes in the three tissue types have organelle associations, internal structures, enzyme constitutions and packaging that reflect their metabolic differences.
Relationship of steroidal structure to ethylene production by etiolated mung bean segments
Authors: Arteca Richard N. , Bachman Jeannette M. , Yopp John H. , Mandava N. Bhushan
Published: April 2006

Several brassinosteroid (BR) analogues, cholesterol and aldosterone were evaluated for their effectiveness alone and in combination with indole‐3‐acetic acid (IAA) in stimulating ethylene production by etiolated mung bean (Vigna radiata L. Rwilcz cv. Berken) hypocotyl segments. Changing the conformation of the two hydroxyl groups on C‐22 and C‐23 positions from α to β did not greatly reduce the efficiency of these compounds to stimulate ethylene production alone or in combination with IAA. There was little difference in activity observed when the conformation of the methyl group in the C‐24 position was changed from α to β. However, when hydroxyls were deleted from the side chain in the C‐22 and C‐23 positions, the compound was rendered inactive alone or in combination with IAA. The compound was also inactivated by removing the 7‐oxa function on the B‐ring and by substituting an ethyl group for the methyl group in the C‐24 position. Both aldosterone and cholesterol were ineffective in promoting ethylene production. This study shows that very stringent structural features are required for a steroid to have BR‐like activity and to act synergistically with auxin in the promotion of ethylene synthesis.