bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid immunofluorescent determination of cells in the S phase in pea root meristems: An alternative to autoradiography
Authors: Levi Marisa , Sparvoli Elio , Sgorbati Sergio , Chiatante Donato
Published: May 2006

Root meristems of Pisum sativum L. cv. Lincoln were pulsed with bromodeoxyuridine, and after partial DNA denaturation the incorporated precursor was detected with an indirect immunofluorescent method by means of commercial anti‐bromodeoxyuridine monoclonal antibody and fluorescein isothiocyanate‐labeled secondary antibody. The nuclei were counterstained with the DNA‐specific fluorochrome 4′, 6‐diamidino‐2‐phenylindole (DAPI). The labeling indices (percentage of labeled calls) determined on slides prepared with the same nuclear population were very similar and in strict accordance with autoradiographic data. When DAPI fluorescence of the nuclei was measured, the unlabeled nuclei coincided with the G1 and part of the G2 regions, whereas all the labeled nuclei were in the S or G2 region. The method is reliable and, in contrast to autoradiography, data can be collected rapidly and almost immediately after the pulse. Furthermore, labeling index and the distribution of DNA contents can be obtained from the same side.
Interaction between sublethal pollution by sulphur dioxide and drought stress. The effect on photosynthetic capacity
Authors: Cornic G.
Published: May 2006

Five‐year‐oldPicea abiesL. plants were grown in growth cabinets in the presence (3.1 μmol m−3) or absence of SO2. After 5 weeks, the photosynthetic capacity of mature needles produced in the year was the same in both conditions. Trees were then submitted in situ to drought stress by withholding water. The decline of leaf photosynthetic capacity was greatest in the presence of SO2. Chlorophyll decreased only when trees were submitted to dehydration in the presence of SO2; however, this al‐one could not account for the large decline in photosynthetic capacity observed under that condition. Needle water content was the lowest during dehydration in the presence of SO2. It is concluded that the critical factor in the interaction between pollution by SO2and drought stress is the greater dehydration of the tissue found in stressed plants grown in the presence of SO2. The large decline in photosynthetic capacity under such conditions might be due to this greater dehydration.
Tonoplast energization: Two H+ pumps, one membrane
Authors: Rea Philip A. , Sanders Dale
Published: May 2006

The vacuolar membrane (tonoplast) of plant cells contains two functionally and physically distinct phosphohydrolases, which catalyse electrogenic H+ ‐translocation: An ATPase (tp‐ATPase; EC 3.6.1.3) and an inorganic pyrophosphatase (tp‐PPase; 3.6.1.1). Neither enzyme belongs to the F0F1– or E1E2‐categories of primary cation pumps, but instead belong to a third and fourth category of enzyme, respectively. Research priorities for the tp‐ATPase are studies directed at understanding the roles of the 70 and 60 kDa subunits in catalysis and regulation; the involvement of the 16 kDa subunit in transmembrane H+ conduction; and investigations of F0F1‐ like structure/function partitioning. In the longer term, comparisons of sequence homology between the N,N′‐ dicyclohexylcarbodiimide ‐binding (16 kDa) proteins from different sources may enable elucidation of the evolutionary relationship of the tp‐ATPase with other putative third‐category H+– translocases. The tp‐PPase, on the other hand, represents an exciting but largely unexplored biochemical entity, which necessitates a reconsideration of accepted views concerning the involvement of inorganic pyrophosphate (PPi) in transmembrane energy conservation. Just why the tonoplast should be endowed with two H+‐translocases is a problem that can only be approached once consideration is given to the paramount question of H+/PPi stoichiometry. Once the stoichiometry is known, it should be possible to establish the physiological poise of the tp‐PPase, and hence to speculate on its role in the metabolism of plant cells.
Effects of chlorosubstituted indoleacetic acids on root growth, ethylene and ATP formation
Authors: Stenlid Göran , Engvild Kjeld C.
Published: May 2006

7‐Chloroindoleacetic acid and dichloroindoleacetic acids with a Cl in the 7 position showed anti‐auxinic activity and promoted root growth in wheat (Triticum aestivum L. cv. Diamant II). In contrast, 4‐, 5‐ and 6‐chloroindoleatetic acids acted as strong auxins inhibiting the growth of wheat roots. Flax (Linum usitatissimum L. cv. Concurrent) and cucumber (Cucumis sativus L. cv. Favör) roots showed similar, but less clear‐cut responses. 7‐Chloroindoleacetic acid and 4,7‐dichloroindoleacetic acid alleviated root growth inhibition in wheat caused by IAA, monochloroindoleacetic acids and benzyladenine. 2,4‐D, 4‐ and 6‐chloroindoleacetic acids strongly induced ethylene formation in cucumber seedlings; 4,7‐ and 6,7‐dichloroindoleacetic acids did not, except at high concentrations. The more lipid‐soluble dichloroindoleacetic acids were stronger inhibitors of ATP formation in cucumber mitochondria than monochloroindoleacetic acids, while IAA itself had only a very slight effect.
Transformation of photoinactive to photoactive protochlorophyllide in isolated prolamellar bodies of wheat (Triticum aestivum) exposed to low pH and ATP
Authors: Grevby Cecilia , Ryberg Margareta , Sundqvist Christer
Published: May 2006

Isolated prolamellar bodies from the etioplasts of dark‐grown wheat (Triticum aestivumL. cv. Walde, Weibull) contain the enzyme NADPH‐protochlorophyllide oxidoreductase. The organisation of this enzyme in a pigment‐protein complex results in fluorescence emission maxima at 633 and 657 nm. Isolated prolamellar bodies stored in darkness for 24 or 48 h at 4°C (pH 7.2) in the presence of NADPH showed a fluorescence emission ratio 657/633 nm around 4 at −196°C. With acidic conditions this fluorescence ratio increased, with an optimum at pH 5.5. Such an increase was even more pronounced in the presence of ATP and NADPH with ratios up to 8, but was completely blocked when the sulfhydryl inhibitor, dithiobis‐nitrobenzoic acid, was added. As shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis the amount of NADPH‐protochlorophyllide oxidoreductase in the prolamellar bodies did not change during storage for 24 or 48 h.

The total amount of protochlorophyllide measured in acetone extracts did not change significantly during storage for 48 h. The values were similar for storage at pH 7.2 and 5.5, but at lower pH (around 5) the pigment content decreased to a third.

The most plausible explanation for the increase in fluorescence ratio is that low pH and ATP give rise to a change in conformation, which results in transformation of the short wavelength (633 nm) fluorescing protochlorophyllide to the long wavelength (657 nm) fluorescing form.
Nitrogen use efficiency in instantaneous and daily photosynthesis of leaves in the canopy of a Solidago altissima stand
Authors: Hirose Tadaki , Werger Marinus J. A.
Published: May 2006

Photosynthetic capacity was measured on detached leaves sampled in a canopy of Solidago altissima L. Non‐rectangular hyperbola fitted the light response curve of photosynthesis and significant correlations were observed between leaf nitrogen per unit area and four parameters which characterize the light‐response curve. Using regressions of the parameters on leaf nitrogen, a model of leaf photosynthesis was constructed which gave the relationships between leaf nitrogen, photon flux density (PFD) and photosynthesis. Curvilinear relations were obtained between leaf nitrogen and photosynthetic rate on both an instantaneous and a daily basis. Nitrogen use efficiency (NUE, photosynthesis per unit leaf nitrogen) was calculated against leaf nitrogen under varying PFDs. The optimum nitrogen content per unit leaf area that maximizes NUE shifted to higher values with increasing PFD. Field measurements of PFD showed high positive correlations between the distribution of leaf nitrogen in the canopy and relative PFD. The predicted optimum leaf nitrogen content for each level in the canopy, to achieve maximized NUE during a clear day, was close to the actual nitrogen distribution as found through sampling.
Features of the intrageneric Alnus‐Frankia specificity
Authors: Weber Assi , Nurmiaho‐Lassila Eeva‐Liisa , Sundman Veronica
Published: May 2006

Host specificity between local Frankia strains and native alders [Alnus incana (L.) Moench and A. glutinosa (L.) Gaertn.] was evaluated in inoculation experiments. Pure cultures of Frankia, whether originating from A. incana or A. glutinosa, were infective and effective on both host species. These pure cultures were isolated from spore‐negative (Sp−) nodules. From spore‐positive (Sp+) nodules no Frankia isolates were obtained. This strain type resisted all our isolation attempts and therefore crushed nodules had to be used for Sp+ type inoculations.

The Sp+ type Frankia populations differed in their host specificity. Sp+ nodules from A. glutinosa were effective on both alder species, but Sp+ nodules from A. incana induced effective nodules only on the original host; on A. glutinosa only small (1‐3mm) prenodule‐like structures were found. Such A. glutinosa plants died on N‐free medium, thus showing that these nodules were ineffective. In the effective nodules the middle cortex was dominated by infected cells filled with vesicle clusters. In the ineffective nodules only a few cortical cells were infected and sporangia predominated in these cells. Surprisingly enough they also contained vesicle‐like structures as demonstrated in electron micrographs.
Capacity for hexose respiration in symbiotic Frankia from Alnus incana
Authors: Vikman Per‐Åke , Huss‐Danell Kerstin
Published: May 2006

Frankia vesicle clusters were prepared from Alnus incana (L.) Moench root nodules containing a local source of Frankia by an improved homogenization‐filtration procedure. The capacity of the vesicle clusters to metabolize hexoses was investigated by respirometric and enzymological studies. The vesicle clusters could utilize glucose, glucose‐6‐phosphate and 6‐phosphogluconate provided that appropriate cofactors were added to the preparations. The enzymes hexokinase (EC 2.7.1.1), NADP+: glucose‐6‐phosphate dehydrogenase (EC 1.1.1.49) and NAD+;6‐phosphogluconate dehydrogenase (EC 1.1.1.44) were found in cell‐free extracts of the vesicle clusters and kinetic constants for the enzymes were determined. Hexokinase had a lower Km for glucose than for fructose. Extracts from both symbiotic and propionate grown Frankia AvcII also showed activity of these hexose‐degrading enzymes, indicating that their presence is not necessarily dependent on sugars as carbon source. The NAD+‐ dependent 6‐phosphogluconate dehydrogenase was only present in Frankia cells and not in alder root cells, which makes this enzyme a useful Frankia‐specific marker in these symbiotic systems.
Characterization and distribution of invertase activity in developing maize (Zea mays) kernels
Authors: Doehlert Douglas C. , Felker Frederick C.
Published: May 2006

Invertase (β‐fructofuranoside fructohydrolase, EC 3.2.1.26) activity in developing maize (Zea mays L. inbred W64A) was separated into soluble and particulate forms. The particulate form was solubilized by treatment with 1 M NaCl or with other salts. However, CaCl2 inhibited invertase activity, and neither detergents nor 0.5 M methyl mannoside were effective in solubilizing the invertase activity. The soluble and particulate invertases were both glycoproteins, both had pH optima of 5.0 and Km values for sucrose of 2.83 and 1.84 mM, respectively. The apparent molecular weight of salt‐solubilized invertase was 40 kDa. Gel filtration of the soluble invertase showed multiple peaks with apparent molecular weights ranging from 750 kDa to over 9 000 kDa. Histochemical staining of cell wall preparations for invertase activity suggested that the particulate invertase is associated with the cell wall. Also, nearly all the invertase activity was localized in the basal endosperm and pedicel tissues, which are sites of sugar transport. No invertase activity was found in the upper endosperm, the embryo or in the placento‐chalazal tissue. In contrast, sucrose synthase (EC 2.4.1.13) activity was found primarily in the embryo and the upper endosperm, which are areas of active biosynthesis of storage compounds.
Phosphorus export from roots to shoots of barley, buckwheat and rape seedlings with different P status
Authors: Schjørring Jan K. , Jensén Paul
Published: May 2006

Seedlings of barley (Hordeum vulgare L. cvs Salka and Zita), buckwheat (Fagopyrum esculentum Moench) and rape (Brassica napus L. ssp. napus cv. Line) were grown in complete nutrient solutions with 8 or 10 different P concentrations in the range of 0–2 mM. Phosphate export from roots to shoots was determined from the amount of 32P (or 33P) absorbed and exported to shoots in 1 h from a nutrient solution containing 0.1 mM radiolabelled phosphate. P export was also determined in the presence of a metabolic uncoupler (DNP, 2.4‐dinitrophenol) and a protein synthesis inhibitor (CH, cycloheximide).

Phosphorus export from roots to shoots reached a maximum at a certain optimum level of phosphorus in shoots and roots, and decreased at both higher and lower P levels. Maxinmm P export was 1.7 ± 0.2 and 4.5 ± 0.5 (mean ±se of the three species) times higher than the P export at the lowest and highest [P]root, respectively. Hill plots as well as plots of the untransformed decreasing P export vs root or shoot P concentrations above the optimum were linear and had high correlation coefficients. The Hill coefficient (nH) based on [P]root, was —7.7 for barley cv. Salka and varied between ‐3.8 and ‐4.5 for the other species. Based on [P]shootot nH was—16.1 for barley cv. Salka, ‐3.7 for barley cv. Zita and ‐6.4 for the two dicotyledonous species. Relative to the amount of P simultaneously absorbed by the root system, the import of P per unit shoot weight decreased linearly over the whole range of shoot P concentrations in the dicotyledonous species. In contrast, the relative import of P per unit shoot weight of the two barley cultivars increased at low levels of [P]shoot and decreased at higher levels. DNP and CH almost eliminated P export from roots to shoots of seedlings with low or high P status. In seedlings with medium P status only 60 to 75% of the P export was affected.
Ribulose‐l,5‐bisphosphate carboxylase and photosystem II activities during chloroplast development in mesophyll and bundle sheath cells of Zea mays
Authors: Caers Marleen , Verbelen Jean‐Pierre , Vendrig Jan C.
Published: May 2006

Photosystem II (PS II) activity and the localization of ribulose‐l,5‐bisphosphate (RuBP) carboxylase (EC 4.1.1.39) were studied in primary leaves of young maize plants (Zea mays L. cv. Fronica) by tetra‐nitro‐blue‐tetrazoliumchloride reduction and immunolocalization, respectively. In tissue of 3‐day‐old plants all chloroplasts were structurally identical. From day 4 they developed into their typical appearance of mesophyll and bundle sheath chloroplasts. First PS II‐activity was present in both types of chloroplasts. From day 4 it disappeared in bundle sheath chloroplasts concomitant with the loss of grana. RuBP carboxylase on the other hand was only present in bundle sheath chloroplasts at all stages of development. Thus, the control of the development of the photosystems and the Calvin cycle enzymes seem to differ.
A portable, microprocessor operated instrument for measuring chlorophyll fluorescence kinetics in stress physiology
Authors: Öquist Gunnar , Wass Roland
Published: May 2006

A portable instrument for measuring chlorophyll fluorescence induction kinetics is described and examples of measurements are given. The instrument is centered around a statistically‐mixed bifurcated optical fiber. One fiber branch guides the actinic light to the sample, whereas the other branch carries the emitted chlorophyll fluorescence to the photodetector. Scattered actinic light is cut out from the detector by a red interference filter. The instrument measures fast as well as slow fluorescence induction kinetics, but is particularly well designed for analyzing fast kinetics. The high time resolution and strong, variable actinic light mean that both Fo (non‐variable fluorescence) and Fm (maximal fluorescence at the P‐peak) are well defined. A built in microprocessor unit with attached memory stores the fluorescence induction curve and calculates key fluorescence parameters such as Fo, Fm, Fv (variable fluorescence equals Fm−Fo), Fv/Fm (the photochemical efficiency of photosystem II) and t1/2 (half rise time from Fo, to Fm). These values are digitally displayed after each recording and they (or the whole induction curve) can be stored in a memory and later retrieved. Because of a flexible setting of the instrument it can be used with high accuracy both for optically thick leaves and for diluted suspensions of algae or chloroplasts. A simple, light weight clamp cuvette for dark adaptation of leaves has been developed. It is equipped with a gate allowing the optical fiber to be inserted without daylight reaching the dark adapted portion of the leaf. The instrument has been developed for rapid monitoring of changes in activities and organization of the photosynthetic apparatus in vivo when plants are exposed to environmental stress both in the field and in the laboratory. Examples of measurements are given for differently treated leaves of Pinus sylvestris, Salix sp., Betula verrucosa, Zea mays, Epilobium angustifo‐lium and for chloroplast thylakoids isolated from Spinacia oleracea.
Growth and internal ion concentrations in seedlings of winter wheat are affected by 1 pM tentoxin
Authors: Erdei László , Klotz Martin G.
Published: May 2006

The long‐term effect of tentoxin on K+;, Ca2+ and total phosphorus (P) concentrations in the roots and shoots of 7‐ and 14‐day‐old seedlings of winter wheat (Triticum aestivum L. cv. Martonvásári‐8) was studied. Growth (dry weight) and shoot to root ratios (dry weight and mineral concentrations) were also estimated. One pM tentoxin increased the shoot to root ratio for dry weight after a 14‐day period of application. The concentration of Ca2+ slightly increased in the shoot. In roots, tentoxin caused a 30% higher accumulation of Ca2+ after 7 days, which did not change with treatment during the following 7 days. The accumulation of Ca2+ was enhanced by increasing concentrations of tentoxin. K+ and total P levels increased in roots but decreased in shoots after 7 days. However, they were redistributed between root and shoot during days 8–14 of tentoxin treatment. The effect of tentoxin is explained as a stimulation of ion transport mainly into the vacuoles of the immature metaxylem elements. It is suggested that tentoxin and other microbial products effective at very low concentrations may have a general significance in promoting plant infection or symbiosis via the modification of physiological or biochemical processes.
A chlorate‐hypersensitive, high nitrate/chlorate uptake mutant of Arabidopsis thaliana
Authors: Wang Xuemin , Feldmann Kenneth A. , Scholl Randall L.
Published: May 2006

Seedlings hypersensitive to root‐supplied chlorate were isolated from mutagentreated populations of A. thaliana L. (Heynh.). Characterization of one such mutant is described in the present report. The mutant (designated C1), accumulated greater than normal quantities of nitrate in the leaves and took up nitrate and chlorate rapidly in uptake experiments. The nitrate and chlorate uptake rates of this mutant were substantially higher than for eight other genotypes tested in our laboratory. Nitrate reductase (NR; EC 1.6.6.1) activity, glutamine synthetase (GS; EC 6.3.1.2) activity, and cytochrome c reductase (CCR) activity of NR were slightly elevated in young plants. The altered nitrate uptake rates may represent the primary lesion of this mutant. Its phenotype is substantially different from that of a previously described chlorate hypersensitive mutant (C4) and is not controlled by the same locus.
Characterization and partial purification of multiple electron transport activities in plasma membranes from maize (Zea mays) roots
Authors: Luster Douglas G. , Buckhout Thomas J.
Published: May 2006

The plasma membrane of eukaryotic cells contains endogenous, integral electron transport proteins. In the maize (Zea mays L. cv. Golden Cross Bantam) root plasma membrane, these activities include NAD(P)H‐ferricyanide reductase. NAD(P)H‐duroquinone reductase (1.6.5.1) and NAD(P)H‐ascorbate free‐radical reductase (EC 1.6.5.4). Differences in degree of stimulation upon vesicle rupture with detergent and in specificities for pyridine nucleotides suggest that these activities constitute distinct components in the membranes. Solubilization of reductase activities was examined using Triton X‐100 over a wide range of retergent‐to‐protein ratios. The Triton‐solubilized enzymes were purified using dye‐ligand affinity chromatography on Cibacron blue 3G‐A agarose utilizing biospecific elution with NADH. Resolution of the redox activities was accomplished upon differential elution with 0.1.1.0 and 10 mM NADH. The distinctive characteristics of the enzymes and the differential chromatographic behavior of the respective activities provided evidence for the presence of separate enzymatic redox components in maize root plasma membranes with implications for an electron transfer chain.
Adventitious bud production on explants of Begonia×hiemalis depends on the developmental state of the donor plant
Authors: Simmonds John , Nelson Sherman D.
Published: May 2006

In vitro responses can be influenced by the developmental status of the donor plant tissue. The effects of the donor plant photoperiod and the developmental stage of the plant on organogenesis of petiole explants of Begonia×hiemalis cv. Schwabenland Pink are reported. Long day plants had progressively more branches, total stem length, leaf area, and branch and shoot mass. In short days, flowering was earlier and a greater proportion of dry weight accumulation was allocated to reproductive structures. Similar explant responses were obtained from all developmental stages until flowering was well advanced in short days and then the regenerative capacity diminished. Primary measurements of donor leaves (length, area and weight) at the time of explant removal were not well correlated with adventitious bud production. Loss of regeneration was not determined by tissue or plant age but was associated with the progressive development of flowers. Thus the donor plant photoperiod only indirectly affected bud production. Organogenesis decreased with duration of short days but increased in long days and thus both the duration of the multiplication phase and the intensity of the in vitro response was enhanced by maintaining donor plants in long days.
Nitrate utilization in barley: relations to nitrate supply and light/dark cycles
Authors: Mattsson Marie , Lundborg Tomas , Larsson Carl‐Magnus
Published: May 2006

Uptake and utilization of nitrate were investigated in Hordeum vulgare L. cvs Mette and Golf in the vegetative stage, 2 and 4 weeks after sowing. The plants were subjected to a light/dark cycle of 16/8 h (18/12°C). Results obtained with the two genotypes were essentially similar. In the light, xylem nitrate transport and shoot nitrate reduction approximately equalled the amount of nitrate absorbed by the root. A drastic decline in translocation to the shoot in darkness was entirely attributable to decreased transpiration since no major changes in xylem nitrate concentration were observed. Darkening caused only a slight decrease in nitrate uptake, while root nitrate reduction was enhanced. Nitrate starvation for 2 days did not significantlly affect dry matter increment, but resulted in a drastic drop in previously accumulated nitrate, indicating that the stored nitrate is accessible and can sustain unrestricted growth. Uptake increased upon re‐addition of nitrate and after 8 h it was about twice that of non‐starved plants. During recovery, restoration of root nitrate pools and root nitrate reduction took precedence over shoot nitrate accumulation and reduction. Net nitrate uptake and removal of nitrate from the root to the transpiration stream seem to be decisive for the rate of root nitrate reduction.
Synthesis of nucleic acids and protein in tuber buds of Solanum tuberosum during dormancy and early sprouting
Authors: Macdonald Margaret M. , Osborne Daphne J.
Published: May 2006

Autoradiographic studies have demonstrated the continuous synthesis of protein, RNA and DNA in potato (Solanum tuberosum L. cv. King Edward) tuber buds from the time of tuber harvest throughout dormancy. Breaking of dormancy is associated with a rise in all activities. A first rise occurs just prior to (or coincident with) a general increase in cell volume. A second rise accompanies the elongation and outgrowth of the bud. The continuous metabolic activity during dormancy in the absence of cell growth is discussed.
Modification of foliar solute concentrations by calcium in two species of wheat stressed with sodium chloride and/or potassium chloride
Authors: Weimberg Ralph
Published: May 2006

The effects of saline‐stresses due to different salts on growth and on foliar solute concentrations in seedlings of two species of wheat that differed in salt tolerance. Triticum aestivum L. cv. Probred and Triticum turgidum L. (Durum group) cv. Aldura, were studied. Triticum aestivum is the more salt tolerant species. The salts used were NaCl, KCI, a 1:1 mixture of NaCI and KCI, and these same monovalent cation salts but mixed with CaCI2 at a ratio of 2:1 on a molar basis of monovalent to divalent cation salts. Growth inhibition of both species was a function of media osmotic potentials. There was a small additional inhibition of growth if KCI replaced NaCI as the salinizing salt. CaCI2 had little or no effect on growth inhibition beyond an osmotic effect except at the most severe stress level, i.e. when Ca2+ concentrations may be excessive. The amounts of water‐soluble Ca2+ were about 10 times higher in leaves of plants grown in the presence of CaCI2 than in its absence, but its concentrations even then were approximately 10% or less of those of the monovalent cations. Including CaCI2 in growth media resulted in a reduction in the amount of Na+ in leaves compared to the amounts in plants grown at the same osmotic potential but in the absence of CaCI2. Triticum aestivum was a better Na+‐excluder than T. turgidum. With CaCI2 in media, (Na++ K+) remained relatively constant or increased by small amounts as media osmotic potentials décreased. In the absence of CaCI2+ (Na++ K+) increased by large amounts when media osmotic potentials were at −0.6 and −0.8 MPa. It is concluded that the accumulation system in leaves for monovalent cations was under feed‐back control, and that this control mechanism was inhibited by high media concentrations of Na+ and/or K+. Sucrose was present at a constant amount under all growth conditions. Proline started accumulating when (Na++ K+) exceeded a threshold value of 200 μmol (g fresh weight)−1. Its concentration was 5 to 13% of that portion of (Na++ K+) that exceeded the threshold value.
Enzymic hydrolysis of placental cell wall pectins and cell separation in watermelon (Citrullus lanatus) fruits exposed to ethylene
Authors: Elkashif Mohamed E. , Huber Donald J.
Published: May 2006

Watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai, cv. Charleston Gray] fruits were examined to determine the effect of ethylene on cell wall hydrolases. pectin degradation, and cell wall ultrastructure. Enzymic studies showed that activity of polygalacturonase (EC 3.2.1.15) increased in placental tissue following 1 day of ethylene treatment and was 10 times higher after 6 days of treatment. The increase in polygalacturonase activity was accompanied by the appearance in ethanol powders of low‐molecular‐weight pectic polymers and a decrease in total pectin. The enhanced enzyme activity and decrease in total pectins were observed only in fruits exposed to ethylene. Ultrastructural studies of ethylene‐treated tissue revealed an early disintegration of the middle lamella. The onset of wall separation coincided with the first notable increase in polygalacturonase activity. Cell wall of untreated fruit showed no evidence of structural changes. The results indicate that initiation of enzymic activity and cell wall separation in response to ethylene are not characteristic phenomena of normal ripening and senescence in watermelon fruit.
Interaction of ethylene and CO2
Authors: Sisler Edward C. , Wood Carmen
Published: May 2006

Low levels of carbon dioxide regulate ethylene synthesis and higher levels inhibit ethylene action, but the mechanism for these effects is not known.
Subcellular fractionation of triterpenoid biosynthesis in Euphorbia lathyris latex
Authors: Skrukrud C. L. , Taylor S. E. , Hawkins D. R. , Nemethy E. K. , Calvin M.
Published: May 2006

Latex isolated from laticifer cells of Euphorbia lathyris maintained its ability to synthesize triterpenols (and their esters) from acetate. When the latex was centrifugated at 5 000 g for 15 min. this biosynthetic activity could be subdivided into two separate fractions; the acetate to β‐hydroxymethyl glutaryl‐coenzyme A activity remained in the supernatant, while the β‐hydroxymethyl glutaryl‐coenzyme A to triterpenol activity was pelleted. Further purification of the pellet by isopycnic centrifugation on Percoll gradients yielded at least three particles: latex particles, starch grains, and a single membrane‐bound organelle. Electron micrographs were made of all of these latex particles. The single membrane‐bound organelle was only observed in the region of the density gradient that exhibited the ability to incorporate mevalonic acid into the triterpenoids. In addition, the enzyme β‐hydroxymethyl glutaryl‐coenzyme A reductase (EC 1.1.1.34) was found in the 5000 g pellet, while β‐hydroxymethyl glutaryl‐coenzyme A lyase (EC 4.1.3.4) remained in the supernatant.
Correlation between pigment composition and apoproteins of the light‐harvesting complex II (LHC II) in wheat(Triticum aestivum)
Authors: Dahlin Clas
Published: May 2006

Seedlings of wheat(Triticum aestivumL. cv. Walde, Weibull) grown in continuous weak red light (16 mW m−2) with or without SAN‐9789, contained significantly lower amounts of chlorophylls and carotenoids compared to untreated plants grown in a greenhouse. The Chlalbratios were 3.6 in the greenhouse‐grown plants, 5.1 in untreated and ca 16 in SAN‐treated plants grown in weak red light, respectively. The main difference in polypeptide composition of thylakoids isolated from red light‐grown plants, compared to those grown in the greenhouse, was a lower amount of proteins of the light‐harvesting complex (LHC) II. The amount of apo‐LHC and LHC were correlated to the xanthophyll to β‐carotene ratios in these plants. The absence of grana and the absence of proteins of the light‐harvesting complex 11 in SAN‐treated plants, support the general dogma that these proteins are involved in the formation of grana. Since the amount of apo‐LHC and LHC could be correlated to the presence of carotenoids as well as the chlorophylls, it is concluded that the carotenoids are necessary for the correct assembly and stabilization of the apoproteins of LHC II in the thylakoid membranes.
Static electric fields do not cause coleoptile movements
Authors: Johnsson A. , Eidesmo T. , Hannevik M.
Published: May 2006

A photodiode array method has been used to record automatically minute lateral movements of Avena sativa L. (cv. Seger I) coleoptiles in a static electric field. The electric fields, 600 or 5000 V cm−1 did not cause any significant movement of the coleoptiles, in contrast to reports in the literature. Likewise, in experiments where photographic recordings were made, no significant movements were found.
Gibberellins and photoperiodic control of shoot elongation in Salix
Authors: Junttila Olavi , Jensen Einar
Published: May 2006

Effects of exogenous gibberellins GA53, GA44, GA19, GA20 and GA1 on photoperiodically controlled shoot elongation in seedlings of Salix pentandra L. were studied. Gibberellins GA20 and GA1 induced shoot elongation under short days (SD) and could substitute for a transfer to long day (LD), while gibberellins A53, A44 and A19 were inactive. In seedlings exposed to a prolonged SD‐treatment (30 days) there was a significant positive interaction between a transfer to LD and a treatment with GA20 and GA1 on shoot elongation. In addition, GA19 enhanced the growth promotive effect of LD in these seedlings. The results are compatible with the suggestion that conversion of GA19 to GA20 is blocked under SD. This effect is supposed to be an early process leading to the cessation of shoot elongation under SD. Responsiveness of the seedlings to LD and to a GA‐treatment gradually decreased with an increasing length of exposure to SD.
Identification of potentially embryogenic microspores in Brassica napus
Authors: Pechan P. M. , Keller W. A.
Published: May 2006

Studies were undertaken with Brassica napus L. cv. Topas to identify buds containing microspores predisposed to embryogenesis in vitro and to investigate bud and microspore development in relation to this process. No significant correlation was found between the final embryo number and bud components. There appears to be a developmental window of less than 8 h duration during which microspores are very likely to form embryos: over 70% of the microspores can undergo division and up to 70% of these can form embryos. Embryos were mainly obtained from late uninuucleate to early binucleate microspores: the former contained mainly a G2 or M phase nucleus located at the microspore periphery and the latter a generative nucleus (associated with the intine) and a vegetative nucleus. Observations indicated that only the vegetative nucleus contributed to embryo formation. The first embryogenic division occurred between 8 and 16 h for uninucleate‐ and between 8 and 48 h for binucleate‐derived embryos.
Molecular biology of intracellular protein trafficking
Authors: White Joseph A. , Scandalios John G.
Published: May 2006

The evidence accumulated to date indicates that protein compartmentalization is mediated through specific regions of proteins destined for translocation into subcellular organelles. Proteins targeted to mitochondria, chloroplasts or the endoplasmic reticulum have ‘transit’ sequences contained in amino‐terminal peptide extensions. However, most peroxisomal proteins do not have amino‐terminal extensions. Protein importation into mitochondria has been extensively studied and characterized. This post‐translational process appears to involve receptors on the mitochondrial outer membrane, and is dependent upon the electrochemical gradient across the inner membrane. Translocation to one of the submitochondrial compartments is determined by the type of transit sequence contained in a mitochondrial protein. The majority of imported mitochondrial proteins are proteolytically altered prior to assembly into oligomeric enzyme complexes. Protein importation into peroxisomes is distinctly different from importation into mitochondria. Although both processes are post‐translational, their only other similarity is a requirement for ATP. In this review, we present and compare recent evidence for both mitochondrial and peroxisomal protein importation.
Is ribulose bisphosphate carboxylase present in guard cell chloroplasts
Authors: Vaughn Kevin C. , Vaughan Martin A.
Published: May 2006

Evidence for and against the presence of ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39) in guard cell chloroplasts is presented. Methods to investigate this question, including immunocytochemistry, are compared.
Row orientation effects on FR/R light ratio, growth and development of field‐grown bush bean
Authors: Kaul Karan , Kasperbauer M. J.
Published: May 2006

Bush bean (Phaseolus vulgaris L. cv. Tenderette) plants were grown in north‐south (N‐S) and east‐west (E‐W) rows under field conditions to test effects of row orientation on reflected far‐red (FR) light patterns and on shoot size and edible bean productivity. Soil water and nutrients were adequate. Plants in N‐S rows received slightly higher ratios of FR relative to red (R) light, because of heliotropic movement of the leaves. Plants in N‐S rows partitioned more dry matter to shoots and edible green beans than those in E‐W rows. We conclude that row orientation of broadleaf plants can affect the FR/R light ratio and the phytochrome‐mediated regulation of plant development under field conditions.
Polyamine oxidase activity and polyamine content in maize during seed germination
Authors: Torrigiani Patrizia , Scoccianti Valeria , Bagni Nello
Published: May 2006

Polyamine oxidase (PAO, EC 1.5.3.3) activity and polyamine content in the cell wall and soluble fractions obtained from embryos, endosperms and shoots and roots of etiolated or green seedlings of maize (Zea mays L. cv. WF9) during the first 7 days of germination were investigated. Polyamine content was also determined in the trichloroacetic acid‐soluble (free polyamines) and trichloroacetic acid insoluble (bound polyamines) fraction obtained from the same tissues. PAO activity, determined by the radiometric method based on the recovery of the labelled reaction product 1‐pyrroline, was mostly localized in the cell wall fraction. The activity was very low in embryos and endosperms and present in traces in roots. In etiolated shoots PAO activity increased sharply, while in green shoots it was low and increased slowly. No polyamines were found in the cell wall fraction and only putrescine was detected in the soluble fraction, with the exception of the embryo, where spermidine and spermine were also present. In the TCA‐soluble fraction of embryos, putrescine increased during imbibition, while spermidine and spermine decreased; in the endosperm no relevant changes in polyamines occurred. In the same fraction of green and etiolated seedlings, putrescine increased, giving a peak at days 3–5, while spermidine decreased to very low levels. The amount of bound polyamines was 1–4% of the free ones. The pattern of PAO activity seems to be unrelated to endogenous free polyamine content, which is the same in shoots and roots of etiolated and green seedlings. Enzyme activity, very low in ungerminated seeds, increased continuously during the progression of germination, especially in etiolated shoots, indicating a possible involvement in cell wall formation.
In vitro shoot development of Prunus GF 655–2: interaction between light and benzyladenine
Authors: Baraldi R. , Rossi F. , Lercari B.
Published: May 2006

Experiments designed to study the effect of light quality and quantity and their possible interaction with benzyladenine (BA) in the control of in vitro proliferation of Prunus insititia Schneider GF 655–2 microcuttings are reported. The action of BA as a promoting factor of shoot formation was expressed only in the presence of light. The concentration response curves for BA‐induced proliferation were very similar under the different light sources, irrespective of proliferation rate values.

Shoot formation under blue, far‐red and white light was enhanced by the highest photon fluence rates, while the efficiency of red seemed to be independent of this factor. The results suggest the action of a low‐energy response in the red waveband and under the low photon fluence rates of blue and white. The inhibition of shoot elongation induced by BA in the dark as well as under all light treatments indicates that, while the BA‐induced release from the apical dominance is light dependent. BA inhibition of shoot elongation is entirely light independent.
Dose responses of cytokinins
Authors: Nissen Per
Published: May 2006

Analysis of published data for the most widely used bioassays for cytokinins reveals that the dose responses are usually subsensitive, i.e. that S90/S10> 81. The data are. in general, insufficiently detailed and/or precise for the kinetics (cooperative, multiphasic or more complex) of the subsensitive responses to be determined. Genus‐and species‐specific differences in response type were found for callus growth, where the responses are ultrasensitive (S90/S10<81) for tabacco and Phaseolus Iunatus but mostly subsensitive for soybean and P. vulgaris.
Stimulation of Pisum sativum epicotyl elongation by gibberellin and auxin. – Different effects of two hormones on osmoregulation and cell walls
Authors: Miyamoto Kensuke , Kamisaka Seiichiro
Published: May 2006

The possible involvement of auxin in the action of gibberellin in stimulating cell elongation was examined by comparing the effects of gibberellic acid (GA) and IAA on the growth, osmoregulation and cell wall properties of the Alaska pea (Pisum sativum L. cv. Alaska) subhook. Both GA and IAA stimulated cell elongation in the subhook region of derooted cuttings. Cotyledon excision decreased the stimulating effect of GA on the growth of the subhook region, but did not affect that of IAA. As the subhook region elongated, the osmotic potential of the cell sap and the total amount of osmotic solutes increased. Cotyledon excision accelerated the increase in the osmotic potential and suppressed the accumulation of osmotic solutes. In cuttings with cotyledons. GA partly counteracted the increase in the osmotic potential and substantially promoted the accumulation of osmotic solutes. On the other hand, in cuttings without cotyledons. GA did not affect the change in the osmotic potential although it slightly promoted the accumulation of osmotic solutes. IAA accelerated the increase in the osmotic potential, but did not affect the accumulation of osmotic solutes. IAA enhanced the extensibility of the cell wall, while GA did not affect it. These results suggest that at least in the Alaksa pea subhook region. GA does not stimulate cell elongation by affecting the level of auxin.
Thigmomorphogenesis: XXIII. Promotion of foliar senescence by mechanical perturbation of Avena sativa and four other species
Authors: Giridhar G. , Jaffe M. J.
Published: May 2006

Mechanical perturbation (MP, gentle tubbing) promoted the senescence of detached oat (Avena sativa L. cv. Victory) leaf segments in the dark. The promotion of senescence increased with increase in the number of rubbings and could be seen after 24 h of dark incubation; the maximum effect was reached on day 3. The effect (% of control) of MP on the loss of protein was greater than the effect on chlorophyll (Chl) loss on day 1. However, on day 3 the effect of MP on the loss of Chl became greater than the effect on the loss of protein. Ethephon and 1‐aminocyclopropane‐1‐carboxylic acid (ACC) marginally promoted the loss of Chl by both control and rubbed oat leaf segments, and the effect was additive with MP. Chloramphenicol (CAP), spermine, aminoethoxyvinylglycine (AVG) and Ca2+ marginally delayed the loss of Chl and protein in both control and rubbed segments. Kinetin greatly retarded the senescence of all segments. Even in the presence of these substances, the amounts of Chl and protein in the rubbed segments were always less than in their respective controls, thus retaining the effect of the MP. However, abscisic acid (ABA) and cycloheximide (CHI) caused the rubbed oat leaf segments to retain more Chl and protein than their respective control segments. The effect of CHI was actually enhanced by MP. Rubbing promoted the senescence of attached leaves of oats (Avena sativa L. cv. Victory), maize (Zea mays L. cv. Early Belle) and pumpkin (Cucurbita pepo L. cv. Jack‐o‐lantern) cotyledons in the dark. Rubbing promoted the senescence of oat leaf segments even in light, although to a lesser extent compared to the effect in the dark. The senescence of leaves of pumpkin and cocklebur (Xanthium strumarium Wallr. var. Pennsylvanicum) in situ was also enhanced by MP.
Relationship between transpiration and water potential in grafted scions of Picea
Authors: Beeson R. C. , Proebsting W. M.
Published: May 2006

Total water and osmotic potential, turgor pressure and transpiration rate were measured on scions of Picea pungens (Englemann) during union development. In controlled environments, declines in water potential were correlated with lower transpiration rates to about −2.0 MPa. Water potentials below −2.0 MPa resulted in graft failure and were associated with sharply increased transpiration rates. Bulk turgor pressures remained high in the needles during this period of declining water potential and increasing transpiration. Transpiration rates of successful and unsuccessful greenhouse grafts were not significantly different during union development. Transpiration rates of these grafts were highest around dawn, then declined throughout the day only to increase again after sunset. High bulk needle turgor values (1.3 MPa), maintained by osmotic adjustment, may prevent stomatal closure of Picea scions at water potentials below −2.0 MPa.
Storage of ‘Gloster 69’ apples in the preclimacteric state for up to 200 days after harvest
Authors: Knee Michael , Tsantili Eleni
Published: May 2006

‘Gloster 69’ apples are unusual because they do not accumulate ethylene during storage at 2 kPa O2 at 1.5–3.5°C with continuous ethylene removal. Their ethylene physiology and the extent of various ripening processes in storage were investigated. Ethylene production and l‐aminocyclopropane‐l‐carboxylic acid (ACC) remained low for up to 200 days, and both increased on transfer of fruit to 15°C. The increase in ACC could be stimulated by ethylene treatment of apples after storage. In spite of this evidence that fruit remained preclimacteric, some softening and production of soluble pectin and volatile esters occurred at 3.5°C. These processes were suppressed at 1.5°C, but chlorophyll, starch, malate and sucrose losses and increases in glucose and fructose occurred at both temperatures.
Changes during low‐oxygen storage in the effects of ethylene on induction of ethylene synthesis and stimulation of respiration of ‘Gloster 69’ apples
Authors: Knee Michael , Tsantili Eleni
Published: May 2006

The ability of ethylene to stimulate respiration and advance the onset of rapid ethylene production was investigated at different times during storage of ‘Gloster 69’ apples in 2 kPa O2 at 1.5–3.5°C. Ethylene stimulated respiration in apples at 15°C immediately after harvest; maximal rates were recorded at 10–1000 μl I−1 but attainment of these rates was delayed after low O2 storage until day 3 of treatment at 15°C. The onset of rapid ethylene production at 15°C occurred later in non‐ethylene‐treated apples after storage than after harvest. Ethylene production was induced in some apples during ethylene treatment for 3 or 6 days; in others it was induced about 20 days after treatment, but a proportion of the fruit showed no induction in the 45‐day duration of experiments. An ethylene treatment at 10 μl I−1 led to a near maximal increase in the frequency of induction of ethylene production at all times. After storage apples were mainly induced during treatment or not induced, whereas after harvest induction after treatment was more frequent. The presence of 2000 μl l−1 norbornadiene during ethylene treatment inhibited the stimulation of respiration and the induction of ethylene production; this inhibition was only partly reversed by ethylene at 1000 μl l−1 the experiments suggest that receptors for ethylene were present at all stages but that response capacity changed during storage.
Interaction among sediment anaerobiosis, nitrogen uptake and photosynthesis ofSpartina alterniflora
Authors: Pezeshki S. R. , DeLaune R. D. , Lindau C. W.
Published: May 2006

Spartina alternifloraLois. plants were grown under controlled sediment‐pH‐redox conditions. Uptake of added15NH4‐nitrogen and subsequent photosynthetic activity under different redox conditions in the plant root rhizosphere were measured. Data for total plant nitrogen and15N concentration indicated that nitrogen allocation was not altered by anaerobic conditions of the sediment. However, average net photosynthesis was reduced by up to 35% for plants under anaerobiosis. The results indicate that anaerobiosis in the root rhizosphere, rather than limiting nitrogen uptake, influences photosynthesis and growth ofS. alternifloraunder anaerobic conditions.