bluuebunny/crossref_metadata_2025_split huggingface dataset:
A precursor of the reserve‐protein, phaseolin, is transiently associated with the endoplasmic reticulum of developing Phaseolus vulgaris cotyledons
Authors: Bollini Roberto , Van der Wilden Willem , Chrispeels Maarten J. 
Published: April 2006

Developing cotyledons of Phaseolus vulgaris L. were labeled for 30 min with [3H] amino acids, homogenized, and the proteins fractionated on sodium dodecylsulfate (SDS) polyacrylamide gels. Fluorographs of these gels showed that the polypeptides of phaseolin, the major reserve protein of P. vulgaris, were synthesized as precursors which could be distinguished from the polypeptides of mature phaseolin by their slightly lower mobility.When extracts of cotyledons labeled for 45 min with [3H] amino acids were fractionated on isopynic sucrose gradients, radioactive phaseolin banded at the same density (1.14 g cm‐3) as the endoplasmic reticulum (ER)‐marker enzyme NADH‐cytochrome c reductase. Fractionation in the presence of 3 mM MgCl2 indicated that the newly‐synthesized phaseolin was associated with the rough ER. Pulse‐chase experiments showed that phaseolin was transiently associated with the ER, and later accumulated in the protein bodies.Treatment of isolated ER with proteinase K showed that phaseolin polypeptides were degraded only if Triton X‐100 was present, indicating that phaseolin was membrane‐protected, probably enclosed within the vesicles. ER‐associated phaseolin associated to an 18S form at pH 4.5 in the presence of 0.3 M NaCl and 100 mM sodium acetate. The polypeptides of ER‐associated phaseolin had a slightly lower mobility on SDS‐gels than polypeptides of protein body phaseolin. ER‐associated phaseolin had a carbohydrate content of 6.8%, while protein body‐derived phaseolin had a carbohydrate content of 6.2%. When cotyledons were labeled simultaneously with [14C] amino acids and [3H] glucosamine or with [14C] amino acids and [3H] mannose, the [3H]/[14C] ratio of ER‐derived phaseolin was similar to that of protein body derived phaseolin, indicating that the faster mobility on SDS‐gels was not due to the detachment of carbohydrate. Experiments in which the carbohydrate side chains were removed with endoglycosidase H, and the resulting polypeptides subjected to electrophoresis in SDS‐gels showed that the differential mobility of the glycopolypeptides of phaseolin resided in their polypeptide chains.
On the possible site of inhibition of photosynthetic electron transport by ultraviolet‐B (UV‐B) radiation
Authors: Noorudeen A.M. , Kulandaivelu G. 
Published: April 2006

In Amaranthus chloroplasts that are exposed to ultraviolet‐B (UV‐B) radiation, the electron flow from water to dichlorophenol indophenol (DCPIP) was inhibited, but the electron flow from reduced DCPIP to methyl viologen remains unaffected. Diphenylcarbazide was ineffective in restoring the activity of DCPIP Hill reaction in UV‐B irradiated chloroplasts. Electron flow from water to ferricyanide or dichloro‐dimethoxy‐p‐benzoquinone was inhibited to a degree similar to that of the DCPIP Hill reaction.The rate of carotenoid photobleaching in the presence of carbonyl cyanide‐m‐chlorophenylhydrazone, an indicator of the photochemical reaction near the vicinity of reaction centre of photosystem II, was suppressed and paralleled with the inhibition of the DCPIP Hill reaction.In the UV‐B treated chloroplasts, the variable part of the fluorescence transient was diminished. Though the fluorescence yield was lowered by the UV‐B radiation, addition of 3‐(3,4‐dichlorophenyl)‐l, l‐dimethylurea (DCMU) and/or sodium dithionite increased the emission markedly. With the increase in the dosage of UV‐B irradiation, the time required to reach the steady state fluorescence level became longer in the absence of DCMU and shorter in the presence of DCMU. The kinetics of 520 nm absorbance change was markedly unaltered by the UV‐B irradiation but its dark decay was prolonged. It is concluded that UV‐B irradiation inactivates the photosystem II reaction centre.
Physiological studies on pea tendrils. XII. Effects of temperature on contact coiling and uncoiling
Authors: Riehl T. E. , Jaffe M. J. 
Published: April 2006

When excised tendrils of pea (Pisum sativum L. cv. Alaska 2B) are mechanically perturbed and allowed to coil at different constant temperatures, the greatest amount of coiling occurs between 27°C and 33°C. Coiling of tendrils continues for about 2 h after mechanical perturbation at which time uncoiling usually begins. The temperature at which the rate of uncoiling is greatest appears to be influenced, at least in part, by the temperature at which the tendrils coiled. For example, when tendrils coil at 20°C their rate of uncoiling at 20°C is less than if they had coiled at 23°C. Estimated activation energies for the uncoiling process are greater than for coiling, with 35 J/mol × s and 97 J/mol × s for uncoiling in the temperature ranges 18°C to 23°C and 10°C to 18°C, respectively. The estimated activation energy for coiling is 5.4 J/mol × s. It is suggested that the process of tendril uncoiling, as well as tendril coiling, might be an active, energy requiring process.When mechanically perturbed tendrils are placed in the cold (5°C) they do not coil. But this interruption of the coiling process with a cold (5°C) treatment, either immediately after mechanical perturbation or after coiling has begun, does not prevent coiling from continuing after tendrils are again given a more suitable temperature. It is concluded that the cessation of coiling during the cold period may be due to a slowdown in metabolism. It is suggested that there may be a factor which is responsible for the motor response and which is retained during the cold treatment.
The prevention of dehydration injury in celery seeds by polyethylene glycol, abscisic acid, dark and high temperature
Authors: Biddington N. L. , Brocklehurst P. A. , Dearman A. S. , Dearman Jane 
Published: April 2006

Celery seeds (Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.Celery seeds incubated for 3 days at 17°C in the light and then air‐dried at 20°C germinated slowly when re‐sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion.
The role of plant hormones and carbohydrates in the growth and survival of coppiced Eucalyptus seedlings
Authors: Taylor J. S. , Blake T. J. , Pharis R. P. 
Published: April 2006

Depending on the species, coppicing (decapitation) may promote vigorous growth (Eucalyptus camaldulensis Dehn), or cause rapid senescence and death (Eucalyptus obliqua L'Herit). In seedlings of the latter species, the presence of a small upwardly directed shoot on the decapitated stump prevents or delays decline. Coppiced seedlings of E. camaldulensis and E. obliqua, with and without a remaining shoot, were analyzed for starch and soluble sugars (with the anthrone method), gibberellin‐like substances (GAs) and cytokinin‐like substances (by bioassay), and ethylene (by gas‐liquid chromatography) before and after decapitation.Levels of soluble sugars declined similarly in both varieties of eucalypts, and starch reserves appeared adequate for sprouting, and did not diminish following decapitation of the susceptible species.Decapitation did not markedly alter the relatively high amounts of GAs in roots and shoots of E. obliqua, the susceptible species, although increased levels of Gas were observed in the stumps of seedlings left with 1 shoot after decapitation. The overall levels of GaS were relatively low in the roots and stems of the resistant E. camaldulensis, but higher in the shoots. Marked qualitative changes in GAs with decapitation were apparent in the shoots of E. camaldulensis. A single major GA peak occurred prior to decapitation but afer decapitation several additional peaks of GA‐like activity appeared.Cytokinin‐like activity was initially low in all tissues, but increased dramatically in stump and shoot tissue following decapitation. Increases ranged from approximately 5‐fold (stump tissue of either species, minus‐shoot treatment) to approximately 40‐fold (shoot tissue of the resistant E. camaldulensis seedlings left with 1 shoot). In both E. camaldulensis and E. obliqua ethylene production increased to a peak 7 days after decapitation provided a shoot had been retained. This ethylene peak precedes a marked upturning of the retained shoot, and was not present in the stumps of totally decapitated seedlings. For totally decapitated seedlings ethylene evolution in E. obliqua (the susceptible species), but not E. camaldulensis (the resistant species), had ceased by 15 days.
Kinetin application to roots and its effect on uptake, translocation and distribution of nitrogen in wheat (Triticum aestivum) grown with a split root system
Authors: Simpson Richard J. , Lambers Hans , Dalling Michael. J. 
Published: April 2006

The root systems of wheat seedlings (Triticum aestivum L. cv. SUN 9E) were pruned to two seminal roots. One of the roots was supplied with a suboptimal level of NO3, the other was deprived of N. Different levels of kinetin were supplied to the NO3‐deprived roots. Root respiration and the increment of C and N in the roots were measured to determine the C/N ratio of the phloem sap feeding the NO3‐deprived roots. Thus, it was possible to determine retranslocation of N from the shoots to the roots, as affected by the rate of kinetin application. It was calculated that the C/N ratio of phloem sap feeding roots growing without kinetin was ca 61. Kinetin application increased this ratio to ca 75, partly due to decreased translocation of N from the shoots back to the roots. Kinetin application decreased the proportion of N that was retranslocated to the roots after translocation to the shoots. Kinetin increased the rate of NO3 uptake per root and the rate of N incorporation in both roots and shoots by ca 60%, but had no effect on shoot dry matter production. In control plants at most 70% of the N incorporated in the NO3‐fed roots could have been imported from the shoots, whilst kinetin application reduced this value to ca 40%. Thus root growth was not fully dependent on a supply of N via the phloem.It is concluded that cytokinins affect the pattern of N‐translocation in wheat plants by increasing incorporation of N in dry matter of the shoot, thus leaving less for export. Cytokinins did not play a major role in the regulation of shoot growth and the shoot to root ratio of the present plants.
Ontogenetic changes in potassium transport in xylem of tomato
Authors: Widders Irvin , Lorenz Oscar A. 
Published: April 2006

The influence of plant ontogeny on xylem exudate K+ concentrations and K+ transport to the shoot was studied in both nutrient‐solution and field‐grown tomato plants (Lycopersicon esculentum).K+ concentrations in xylem exudate from decapitated plants decreased during tomato plant development from a high of 12 mM to a low of 5 mM. In the nutrient‐solution plants, the most rapid decline occurred during the vegetative growth phase, while in field‐grown plants, the xylem K+ concentrations remained high during an‐thesis and then subsequently declined. The rapid decline in nutrient‐solution plants might be related to a decrease in the absorptive efficiency of the root system. In field‐grown plants, a reduction in the availability of assimilates to the root might account in part for the decrease in xylem exudate K+ concentrations. The volume (ml h−1 plant−1) and the net rates of K+ exudation (mmol h−1 plant−1) decreased dramatically as the fruits approached maturity. Since only a small reduction in xylem exudate K+ concentrations occurred during fruiting, the hydraulic conductivity of the root system decreased as the tomato plants aged. It is proposed that the ontogenetic changes in xylem transport of K+ contribute to a reduction in leaf free space K+ concentration which would explain the decline in tomato leaf K+ concentrations.
The simultaneous use of 14CO2 and 15N2 labelling techniques to study the carbon and nitrogen economy of legumes grown under natural conditions
Authors: Warembourg Fernand R. , Montange Denis , Bardin René 
Published: April 2006

A method based on simultaneous short‐term exposure to 14CO2 and 15N2 is described for studying nitrogen fixation and distribution in legumes relative to carbon assimilation and use. Equipment designed to accomodate experiments under natural conditions with very little disturbance of the N2 fixing association is used. It permits continuous measurement and regulation of variables such as air temperature, humidity and CO2 concentration as well as soil aeration. Measurements of distribution and use of assimilates, respiration of nodulated roots, quantitative N2 fixation and the distribution and fate of fixed N as a function of time lead to a precise estimation of C and N budgets for each labelling period. When experiments are done at several phenological stages they give a new insight into the complex C and N interrelations in legume symbiosis.A series of trials throughout the growth period of Glycine max (L.) Merr. cv. Hodgson demonstrated the sensitivity of the method. The development of the plants from vegetative to reproductive stages was accompanied by a complete change in the distribution patterns of current assimilates and products of nitrogen fixation. Maximum sink strength moved from the leaves to the pods and seeds which ended up receiving 70% of the incoming C and 35% of the fixed N. The fact that up to 85% of fixed N in the plants was in the reproductive organs at maturity can be accounted for by remobilisation from vegetative parts.The respiration of nodulated roots utilized 33% of carbon translocated to below‐ground plant parts before nitrogen fixation started, but as much as 50% during the period of optimal fixation. The advantages and limitations of the isotopic method described are critically discussed as a prelude to future investigations.
Effects of desiccation on the 77°K fluorescence properties of the liverwort Porella navicularis and the isolated lichen green alga Trebouxia pyriformis
Authors: Öquist Gunnar , Fork David C. 
Published: April 2006

The liverwort Porella navicularis and the isolated lichen green alga Trebouxia pyriformis were desiccated in darkness and light. Low temperature (77°K) fluorescence emission spectra were deconvoluted into band components by RESOL. The reasons for the desiccation‐induced decreases of fluorescence yield, particularly of the PSII emission bands, were analyzed by following fluorescence kinetics of PSI and PSII during PSII trap closure at 77°K, and by the determination of two point relative action spectra for PSI and PSII emissions upon excitation of chlorophyll a or b preferentially.It was concluded that the pronounced loss of FII in Porella was largely accomplished by a strong decrease in the rate constant for fluorescence (kFII), whereas the energy transfer from PSII to PSI, (kT(II→I)), was unaffected or slightly decreased. Desiccation of Porella also decreased α, the fraction of absorbed light distributed initially to PSI. Unlike Porella, Trebouxia responded to desiccation by only a small decrease in fluorescence. The drop in FII was probably due to a 10–20% increase in kT(II→I); kFII was unaffected. No significant changes in α were observed in Trebouxia. A general lowering of the fluorescence yields of both species was probably also mediated by some PSII reaction center quenching of Fv in the dry samples. The results of two point relative action spectra confirmed the above findings and it was assumed that the more pronounced effects of light drying compared to that of dark drying, were mediated by changes in similar parameters. The difference in desiccation responses between Porella and Porphyra (Öquist and Fork 1982) are discussed and assumed to be related to the different habitats of these two species, deep shade vs exposed sun, respectively.
Seasonal and physiological aspects of the isolation of tobacco protoplasts
Authors: Cassells Alan C. , Cocker Frances M. 
Published: April 2006

The viability of tobacco (N. tabacum– L. cv. Xanthi‐nc) protoplasts isolated during the winter months is affected by membrane calcium, total calcium, plant age and supplementary lighting. Feeding calcium nitrate and calcium chloride helps to increase protoplast stability. Feeding is important because it increases membrane calcium, but it also has other beneficial effects which may be connected with increased nitrate and chloride (anion) uptake and cation/anion interaction. Whatever optimal feeding regime is chosen, it must be used in conjunction with the correct harvesting practice, which depends on whether or not supplementary light is given. Plants grown without supplementary light are best harvested between 8–9 weeks. If supplementary light is given, older plants (with and without supplementary calcium feeding) of approx. ten weeks are better for protoplast isolation. Plants grown under supplementary light have low leaf shape index (LSI) values (i.e. wider leaves) compared to plants in low light.Spring and summer calcium feeding treatments had no significant effect on increasing total or membrane calcium. Likewise, there was no significant correlation between total/membrane calcium and percentage protoplast viability from days 0–5; and protoplasts isolated from plants grown in shade and fed with calcium salts, were no more stable than protoplasts from control plants. Irrespective of the feed treatments given, spring and summer plants older than about fifty days and grown under shaded and normal light conditions, produced poor protoplasts despite the fact that there was more calcium present in the membranes compared to protoplasts of younger plants. This decrease in percentage protoplast viability appears to be associated with changes in leaf shape. As plants age from 49–63 days, the leaf shape index (LSI) values increase (i.e. leaves are becoming narrower) and % protoplast viability decreases.
In vitro rooting of cloned shoots in Pinus pinaster
Authors: Rancillac M. , Faye M. , David A. 
Published: April 2006

In vitro plantlet regeneration will be a sueful tool in reforestation only when rooting problems are overcome. Our study was therefore focused on Pinus pinaster rooting conditions.Methods were used which permit multiple axillary (instead of adventitious) bud production in order to obtain genetically identical explants and hence to procure more homogeneous resutls. The hormonal treatment efficiency was then tested on several clones for rooting. Different substrates were compared. A mixture of peat and perlite (1/3, v/v) permitted rooting and the further development of the root system if humidity was properly controlled. The use of an agar medium avoided this difficulty; it supported root induction but resulted in limited growth.For hormonal treatment, explants, submitted to a 12‐day‐period with NAA (10−6M) and then subcultured in an auxin‐free medium, gave rooting percentages ranging from 80 to 100%. In terms of rooting quality (intensity, growth rate and branching ability), a 15‐to 19‐day‐period of auxin treatment was more effective.Application of this optimal treatment to several clones revealed slight differences within clones and between clones (80 to 100% of rooting according to the clone). Regenerated plantlets were able to undergo an autotrophic growth after transplantation under greenhouse conditions.
Evaluation of parameters affecting the yield, viability and cell division of Pinus pinaster protoplasts
Authors: David H. , David A. , Mateille T. 
Published: April 2006

Various factors affecting the yield and viability of Pinus pinaster Ait. cotyledon protoplasts and the mitotic activity of or regenerated cells are described. A study of the effect of sterilization procedures of the plant material showed that whereas the organs collected from disinfested seedlings allow for good yield and viability of isolated protoplasts, germination under non‐sterile conditions favours a greater germinating capacity and stronger mitotic activity. Numerous clusters of from 10 to 15 cells were formed after 20 days of culture when a 5% aqueous solution of calcium hypochlorite was used as a sterilizing agent.The effects of an additional purification of the enzymes showed that although yield and viability of the protoplasts are only slightly improved, the more highly purified enzymes on the other hand enhanced the mitotic activity markedly. Between the two total enzyme concentrations used (0.2 and 0.4%, and in which the relative ratio of each element was unchanged), only the lowest level supplied a debris‐free protoplast suspension; mitotic activity occurred only in that case.Comparison of the populations of cotyledon protoplasts collected from seedlings at two different growth stages (not fully‐developed or fully‐expanded cotyledons) did not reveal any appreciable difference in their size distribution. Neither was the extent of cellular viability affected by the degree of cell differentiation at the time of collecting. On the other hand, the yield of protoplasts and the mitotic activity of the regenerated cells were greater when partially‐developed organs were used. Moreover a pretreatment of the elongating cotyledons with a mineral (half‐strength MS macronutrients and full‐strength micronutrients) and hormonal (15 μM BAP, 0.5 μM NAA) solution improved cell division frequency.
Resistance and capacity in the thallus of Marchantia polymorpha
Authors: Paszewski A. , Bulanda W. , Dziubiñska H. , Trębacz K. 
Published: April 2006

Calculations of the resistance r and capacity c of cell membrances and the resistancer 1 of cell interiors of a community of cells in Marchantia polymorpha L. thalli are presented. These parameters of a multicellular system were determined by the adaptation of methods employed for the calculation of the resistance and capacity of single cells. The obtained results indicate that such a procedure is justified. A generally accepted resistance‐capacity model of the cell was used as a basis for the determination of r, c, and r1 (representing membrane resistance, membrane capacity, and resistance of cell interior, respectively). The calculations were based on measurements of impedance and phase shift within the frequency range of 5 Hz‐1000 Hz. Stainless steel plates were employed as the measuring electrodes; polarization resistance and capacity were determined by separate measurements. The calculations confirmed the assumption that the parameters r, c, and r1 were constant within the investigated frequency range.The calculations of resistance and capacity for 25 plants were constant within the investigated frequency range. The calculations of resistance and capacity for 25 plants were carried out by four different methods and they yielded results of the order of : r = 0.45 kΩ± 0.15 kΩ, r1= 1.0 kΩ± 0.45 kΩ, c = 11 μF ± 3.5 μF. Circular diagrams of impedance also confirmed the validity of the accepted model within the frequency range of 25–300 Hz.