bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of proteolytic enzymes in protein degradation during senescence of rice leaves
Authors: Cheng Shu Hua , Kao Ching Huei 
Published: April 2006

The role of proteolytic enzymes in protein degradation of detached and intact leaves of rice seedling (Oryza sativa L. cv. Taiching Native 1) during senescence and of mature leaves during reproductive development was investigated. The amount of soluble protein decreased by about 50% in 2, 4, and 15 days for detached, intact and mature leaves, respectively. Three proteolytic enzyme activities were monitored with pH optima of 4.5 for hemoglobin‐digesting proteinase, 5.5 for carboxypeptidase and 8.0 for aminopeptidase. No azocoll‐digesting proteinase activity could be detected in rice leaves. Dialysis did not alter the activities of any of the three proteolytic enzymes. Acid proteinase activity and aminopeptidase activity were highly unstable during storage of the enzyme extracts at 4°C. Proteolysis was stimulated by inclusion of meroaptoethanal either in the extraction medium or the assay medium.Acid proteinase, carboxypeptidase and aminopeptidase were all present in detached, intact and mature leaves throughout senescence. There seems to be a direct correlation between protein degradation and increases of acid proteinase and carboxypeptidase activity in seedling leaves (detached and intact) during senescence. In senescing (detached and intact) leaves of seedlings the acid proteinase activity developed first, while that of carboxypeptidase developed later. Acid proteinase and carboxypeptidase may play major roles in protein degradation of leaves from seedlings during senscence. During reproductive development, protein degradation was associated with decreases in the activities of acid proteinase, carboxypeptidase and aminopeptidase in mature leaves suggesting that the enzymes were less important for protein degradation in this system. Hence, the role of protelytic enzymes in protein degradation during senescence of rice leaves appears to depend largely on the leaf system used.
Effects of temperature and gibberellin on the activity of endogenous cytokinin‐like substances in leaves of Begonia x cheimantha
Authors: Zieslin Naftaly , Kopperud Cor. , Heide Ola M. , Moe Roar 
Published: April 2006

Changes in activity of endogenous cytokinin‐like substances were examined in intact plants and excised leaves of Begonia x chemantha Everett cv. Prinsesse Astrid (Christimas Begonia) by means of the tobacco callus bioassay. Cytokinin activity in the leaves of intact plants was higher in plants grown at 18°C than in those grown at 21° or 24°C. In excised leaves, an increase in cytokinin activity was observed during the first 4 days following leaf detachment. However, after the seventh day cylokinin activity decreased again. This decrease was more profound in leaves exposed to 24°C than in those exposed to 18°C.Treatment of detached leaves with gibberellic acid (2.8 mM) caused an increase in measurable cytokinin activity. This increase was more profound in the zones of activity which correspond with zeatin glucosides on paper and Sephadex LH‐20 chromatography. Additional zones of activity appeared after Sephadex chromatography. These were of a more slow moving nature with elution volumes corresponding to Nb‐(Δ2‐isopentenyl)adenine and its derivaties. Water‐treated control leaves had higher activity in the regions corresponding to zeatin and zeatin riboside.
Changes in the activity of enzymes involved in purine “salvage” and nucleic acid degradation during the growth of Catharanthus roseus cells in suspension culture
Authors: Hirose Fumiko , Ashihara Hiroshi 
Published: April 2006

Changes during growth in the activity of several enzymes involved in purine “salvage”, adenine phosphoribosyltransferase (EC 2.4.2.7), guanine phosphoribosyl‐transferase (EC 2.4.2.8), hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) and adenosine kinase (EC 2.7.1.20), the enzymes which catalyze the conversion of nucleoside monophosphate to triphosphate, nucleoside monophosphate kinase (EC 2.7.4.4) and nucleoside diphosphate kinase (EC 2.7.4.6), and several degradation enzymes, deoxyribonucleae(s), ribonuclease(s). phosphatase(s), nucleosidase (EC 3.2.2.1), 3′‐nucleotidase (EC 3.1.3.6) and 5′‐nucleotidase (EC 3.1.3.5) were examined in cells of Catharanthus roseus (L.) G. Don cultured in suspension. In addition, the incorporation of [8‐14C] adenine, [8‐14C] adenine, [8‐14C]hypoxanthine. [8‐14C] adenosine and [8‐14C]inosine into nucleotides and nucleic acids was also determined using intact cells.The activities of all purine “salvage” enzymes examined and those of nucleoside monophosphate and diphosphate kinases increased rapidly during the lag phase and decreased during the following cell division and cell expansion phases. The rate of incorporation of adenine, guanine, hypoxanthine, and adenosine into nucleotides and nucleic acids was higher in the lag phase cells than during the following three phases. The highest rate of [8‐14C]inosine incorporation was observed in the stationary phase cells. The activity of all degradation enzymes examined decreased when the stationary phase cells were transferred to a new medium.These results indicated that the increased activity of purine “salvage” enzymes observed in the lag phase cells may contribute to an active purine “salvage” which is required to initiate a subsequent cell division.
Photosynthate partitioning and nodule formation in soybean plants that received red or far‐red light at the end of the photosynthetic period
Authors: Kasperbauer M. J. , Hunt P. G. , Sojka R. E. 
Published: April 2006

The influence of row orientation on spectral distribution of light received by growing soybean [Glycine max (L.) Merr. (cv. Coker 338)] plants was measured under field conditions, and light spectrum effects on photosynthate partitioning were studied under controlled environments. Light received by leaves under field conditions differed among those grown in north‐south vs east‐west oriented rows. In morning and late afternoon, the far‐red/ red ratio received by leaves at the surface of the canopy differed about 3‐fold from the east to west sides of north‐south rows, but only 1.3‐fold from the south to north sides of east‐west rows.In controlled environments, brief exposures to red or far‐red light at the end of the photosynthetic period influenced partitioning of photosynthate among leaves, stems and roots. The top/root ratios differed significantly between the red and far‐red treated plants. Red treated plants partitioned less photosynthate to stems and more to roots than did those treated with far‐red. Also, plants with larger root systems developed more nodules. Phytochrome effects on photosynthate partitioning between tops and roots may influence yield of soybean plants grown in soils with low water‐holding capacity.
Turgor‐sensitive sucrose and amino acid transport into developing seeds of Pisum sativum. Effect of a high sucrose or mannitol concentration in experiments with empty ovules
Authors: Wolswinkel Pieter , Ammerlaan Ankie 
Published: April 2006

Sugar and amino acid transport into empty ovules of Pisum sativum L. cv. Marzia was examined. In fruits containing 4–6 developing seeds, the embryo was removed from four ovules. After this surgical treatment, each empty seed coat was filled with a solution (pH 5.5) containing a low (0, 50 or 200 mM), medium (350, 400 or 500 mM) or high (0.7 or 1 M) concentration of sucrose and/or mannitol. In pulse‐labelling experiments with sucrose and α‐aminoisobutyric acid (AIB), transport of sucrose and AIB into an empty ovule filled with a solution containing a high sucrose concentration was the same as transport into an ovule filled with a mannitol solution of similar osmolarity, demonstrating that a high sucrose concentration in the seed coat apoplast affects phloem transport of sucrose and AIB into the seed coat only by the osmotic effect. The osmolarity of a given solution filling the seed coat cavity appeared to be important for phloem transport of sucrose and AIB into empty ovules.In our experiments, 350 mM appeared to be the optimal concentration for sucrose and AIB transport into the cavity within an empty ovule, giving results comparable with transport into intact ovules. A lower osmolarity of the solution induced less transport. Very high sucrose or mannitol concentrations caused a strong inhibition of sucrose and AIB unloading from the seed coat, so that transport into the empty ovules was inhibited. A low (strongly negative) but not too low osmotic potential of the solution in the seed coat apoplast seems necessary to maintain a normal rate of phloem transport into developing seeds. Apparently, the “sink strength” of developing seeds is turgor‐sensitive.
Effects of 2‐iodobenzanilide on potassium uptake, H+ extrusion and K+‐stimulated ATPase of corn roots
Authors: Maggioni A. , Varanini Z. , Macrì F. , Vianello A. 
Published: April 2006

The carboxanilide systemic fungicide 2‐iodobenzanilide (2‐IB) after 2 h pretreatment at 0.25 mM inhibited K+ and SO42‐ uptake by excised corn roots (Zea mays L., cv. Dekalb 342) up to ca 70 and 40%, respectively. Proton extrusion from corn roots was also reduced by ca 50% after 1 h contact, and the microsomal K+‐stimulated ATPase activity from corn roots and pea stems (Pisum sativum L., cv. Alaska) inhibited by 50 and 72%, respectively. In contrast, the Mg2+‐ATPase activities of microsomes and mitochondria at pH 6.0 and 8.7, respectively, were unaffected. After 2 h of preincubation with 0.25 mM 2‐IB, O2 consumption by corn roots and pea stems was inhibited by 12 and 18%, respectively. ATP content of corn roots was not altered by 2‐IB treatment. Therefore, energy availability “in vivo” was unaffected and the primary effect on corn roots is suggested to be at the plasmalemma ATPase which forms the proton gradient.With isolated pea stem mitochondria, 0.25 mM 2‐IB inhibited O2 consumption by ca 60% when NADH or malate plus pyruvate were added as substrates; when succinate was used O2 consumption was unaffected. The mode of action on isolated mitochondria was different from that shown for carboxin and also formerly attributed to the whole class of carboxanilide fungicides.
Is indolyl‐3‐acetic acid involved in the wave‐like pattern of auxin efflux from Pinus sylvestris stem segments?
Authors: Wodzicki Tomasz J. , Knegt Erik , Wodzicki Alina B. , Bruinsma Johan 
Published: April 2006

The coleoptile curvature bioassay of agar diffusates from successive cambial‐region sections of Pinus silvestris L. stem tissue reveals the existence of a wave‐like pattern, possibly of auxin translocation. Spectrofluorometric determinations of indolyl‐3‐acetic acid (IAA) in these diffusates gave only a poor correlation. Probably another phytohormone, also an auxin, plays a more important role in the pattern.The amplification in the amplitude of the pattern, brought about by apically applied IAA, cannot be induced by the synthetic auxin, 2,4‐dichlorophenoxyacetic acid.
Comparative electrophoretic studies of polypeptides in leaf, petiole and root mitochondria from spinach
Authors: Sahlström Stefan , Ericson Ingemar 
Published: April 2006

Essentially chlorophyll‐free preparations of mitochondria from different tissues of the same plant can be obtained by a combined three step preparation procedure involving differential centrifugation, partition in aqueous polymeric two‐phase system and centrifugation in a Percoll gradient. The polypeptide patterns of mitochondria from photosynthetic (leaves) and non‐photosynthetic (petioles and roots) tissue from spinach were compared by use of SDS‐electrophoresis.About 35 polypeptides were found in leaf mitochondria with molecular weights from 14 to 103 kdalton. The polypeptide patterns of the membrane fractions and matrix fractions showed great differences. The membrane fractions contained significantly more polypeptide bands than the matrix fractions. The polypeptide patterns of mitochondria from photosynthetic and non‐photosynthetic tissues showed some striking differences. The 15.9, 41.7, 50.7 and 101 kdalton polypeptides were clearly detected in leaf mitochondria but these polypeptides were not found or found in only small amounts in petiole and root mitochondria. The differences were mainly associated with the matrix fractions. Staining with 3,3′,5,5′‐tetramethylbenzidine and hydrogen peroxide for heme containing polypeptides showed that the polypeptides which differ do not contain heme.
Transport and accumulation of indole‐3‐acetic acid in pea cuttings under two levels of irradiance
Authors: Baadsmand Søren , Andersen Arne Skytt 
Published: April 2006

The transport and accumulation of 2‐[14C]‐IAA applied to the apex of cuttings of Pisum sativum L. cv. Alaska was greater in cuttings from stock plants grown under 38 W m−2 than 16 W m−2. Accumulation of 14C in the base of the cuttings from the highest level of irradiance was correspondingly more significant. The level of irradiance to the stock plants greatly affected the rate of accumulation, while the light conditions during IAA transport had a minor effect. The amount of IAA reaching the base of the cuttings increased with increasing concentration of IAA in the treatment solution, but the percentage of applied IAA reaching the base decreased.The relative chromatographic partition of ethanol‐extractable 14C showed that, after 12 h of IAA‐transport, the amount of 2‐[14C]‐IAA was higher in the base of cuttings from 38 W m−2 than in those from 16 W m−2. After a further 12 h of transport the relative amounts of 2‐[14C]‐IAA in the two types of cuttings were reduced to the same lower level.A possible role of an irradiance‐mediated difference in the topographic distribution of IAA in the base of pea cuttings on the subsequent adventitious root formation is discussed.
Anatomical observations on somatic embryogenesis from scutellar tissues of immature zygotic embryos of Triticum aestivum
Authors: Magnusson Ingrid , Bornman Chris H. 
Published: April 2006

Somatic embryos were observed as early as six days after subculturing immature embryos of Triticum aestivum L. (cvs Froid‐Centurk and Helge) in vitro on 2,4‐dichloro‐phenoxyacetate‐containing nutrient media. Embryo formation followed three pathways, each involving one of the scutellum's three basic tissue systems: dermal, ground and vascular.(1) Single epithelial layer cells divided tangentially to give pseudothallus‐like structures which, through radial and oblique divisions, assumed polar, proembryoid symmetry.(2) In actively dividing ground tissues, localized asymmetrical division in some cells resulted in proembryoids. When contiguous with each other, the proembryoids could be identified as a proembryonic mass.(3) Oblique divisions in some cells of the scutellum's procambium resulted in daughter cells of unequal size, from the smaller of which the embryoid's root would eventually form.
La glutamate déshydrogénase au cours de la gamétogénèse mâle chez Medicago sativa
Authors: de Vienne Dominique , Savina François , Daussant Jean 
Published: April 2006

Glutamate dehydrogenase during male gametogenesis in Medicago sativa.The multiple forms of the alfalfa (Medicago sativa L.) glutamate dehydrogenase (GDH; EC 1.4.1.2–4) are much more numerous in the pollen than in other organs, and in particular in the floral parts. The appearance of the pollen‐specific GDH pattern during male gametogenesis has been followed using electrophoretic, cytological and immunochemical techniques. After the tetrad stage the uninucleate microspore has no glutamate dehydrogenase activity. This activity appears only in the mitochondria of the binucleate young pollen. At this stage the electrophoretic pattern displays a faint intensity, but is already identical to that of mature pollen. On the other hand, the use of monospecific antibodies has revealed the presence of antigen in the microspore, and in the young pollen there is as much antigen as in the mature pollen. Therefore the synthesis of GDH precedes its activation, which follows the first pollen mitosis.
Comparison of phosphorus mobilization during monocarpic senescence in rice cultivars with sequential and non‐sequential leaf senescence
Authors: Mondal W. A. , Choudhuri M. A. 
Published: April 2006

The senescence pattern of the three uppermost leaves of four rice (Oryza sativa L.) cultivars viz. Ratna, Jaya, Masuri and Kalojira was analysed in terms of decline of chlorophyll and by measuring [32P]‐phosphate retention and export from leaf to grains during the reproductive development. With the advancement of reproductive development, the cultivars Masuri and Kalojira showed a sequential mode of senescence, but the cultivars Ratna and Jaya showed a non‐sequential mode of leaf senescence where the flag leaf senesced earlier than the older second leaf. Foliar spraying with benzyladenine (0.5 mM) significantly delayed, and abscisic acid (0.1 mM) accelerated, leaf senescence. In untreated control plants, the second leaf had the highest export of labelled phosphate among the leaves at the grain formation stage (0–7 days) in Masuri and Kalojira. This was compensated by the flag leaf at the grain development stage (7–14 days), whereas export of [32P]‐phosphate was highest from the flag leaf of Ratna and Jaya at the grain development stage. Compared with the control, benzyladenine treatment caused higher retention of [32P]‐phosphate in the leaves and also export to the grains, but abscisic acid treatment gave lower retention and export of [32P]‐phosphate to the grains.The amount of [32P]‐phosphate export from a mother to a daughter shoot developed in the axil of the second leaf of plants with the panicle removed, was less than that to panicles remaining on control plants of all cultivars. When the panicle had been excised, the greatest export of [32P]‐phosphate took place from the second leaf to the daughter shoot in all cultivars. Excision of the panicle delayed leaf senescence as compared with intact controls and maintained an age‐related leaf senescence pattern in all the four cultivars. The results presented here demonstrate that mobilization of phosphorus from leaf to grains, regardless of cultivar or age and position of the leaf, correlates well with the senescence of that leaf.
Water uptake and storage by rhizosheaths of Oryzopsis hymenoides: a numerical simulation
Authors: Bristow Caryn E. , Campbell G. S. , Wullstein L. H. , Neilson R. 
Published: April 2006

Rhizosheaths (sheaths of sand grains that form around the roots of some grasses) are common in perennial grasses that colonise sandy substrates. It has been hypothesised that rhizosheaths increase water availability by increasing the efficiency of water absorption. Others have suggested that rhizosheaths act as storage reservoirs for water. In either case rhizosheaths undoubtedly play an important role in the water relations of these grasses.In an attempt to evaluate the main function of rhizosheaths, we developed a finite element cylindrical water flow model which enabled us to simulate water uptake by Oryzopsis hymenoides (Roem, and Shult.) Ricker. This model allowed us to estimate total water uptake by root systems with and without rhizosheaths and to compare these values to the extra water stored within the rhizosheath. The results of this study suggest that the presence of rhizosheaths is more important in reducing the total resistance to water flow within the rhizosphere than in enhancing water storage.
Investigations into the possible regulation of negative gravitropic curvature in intact Avena sativa plants and in isolated stem segments by ethylene and gibberellins
Authors: Kaufman Peter , Pharis Richard P. , Reid David M. , Beall Frederick D. 
Published: April 2006

Using Avena sativa L. cv. Victory oat seedlings and excised p‐1 stem segments (including the p‐1 and p‐2 internodes) the effect of exogenously supplied ethylene and the removal of ethylene on internodal extension and gravitropic bending was assessed. Similarly, the ability of the excised system to respond to gravistimulation was assessed in the presence of inhibitors of ethylene action (AgNO3) and ethylene synthesis (3,5‐diiodo‐4‐hydroxybenzoic acid and benzyl isothiocyanate; BITC). The production of ethylene from both intact and excised systems was also measured from 0 to 48 h after gravistimulation, relative to vertical controls.Although gravitropic curvature is initiated, and indeed enters the most rapid phase of upward bending during the first 6 h, there is no difference in ethylene production between vertical and geostimulated plants during this period. The ethylene production of gravistimulated plants rises sharply to a maximum at 24 h, then decreases steeply to almost the control level by 48 h, at which time the rate of upward curvature is diminishing. Neither the addition nor removal of ethylene, nor the addition of inhibitors affecting ethylene‐action (AgNO3) or synthesis (DIHB) influence gravitropic bending or internodal extension in excised segments. Although the ethylene synthesis inhibitor BITC showed down the rate of upward bending, this effect could not be reversed by addition of ethylene. We conclude that the burst in ethylene production that develops in leaf‐sheath bases (pulvini) after they have started to curve upwards is not primary to the induction of curvature. We further suggest that ethylene has no major effect or role in the induction of upward bending after gravistimulation.The metabolism of high specific activity gibberellin A1 ([3H]‐GA1) in the excised system was assessed during 1, 2 and 4 h of gravistimulation. Changes in endogenous GAs and GA metabolism have been shown previously to be correlated (at the later stages) with gravistimulated bending in intact Avena shoots. The excised segments ‘leaked’ free [3H]‐GAs and [3H]‐GA glucosyl conjugate‐like substances into the bathing medium, and this was a confounding factor. Nevertheless, gravistimulated stem segments, and especially the bottom half of the segment, were significantly less leaky then vertical segments. Thus, just 1 h after gravistimulation, bottom segment halves retained 22% more precursor [3H]‐GA1, 36% more free [3H]‐GA‐like metabolites, and 48% more [3H]‐GA glucosyl conjugate‐like metabolites than vertical segments. In contrast, the 1 h gravistimulated top halves retained slightly less (1–4%) precursor [3H]‐GA and free [3H]‐GA metabolites, but 21% more [3H]‐GA glucosyl conjugate‐like radioactivity than vertical segments.
Nitrate and nitrite reduction by alfalfa root nodules: Accumulation of nitrite in Rhizobium melioti bacteroids and senescence of nodules
Authors: Becana M. , Aparicio‐Tejo P. M. , Sánchez‐Díaz M. 
Published: April 2006

Addition of NO−3 rapidly induced senescence of root nodules in alfalfa (Medicago sativa L. cv. Aragon). Loss of nodule dry matter began at the lowest NO−3 concentration (10 mM) but degradation of bacteroid proteins was only detected when nodules were supplied with NO−3 concentrations above 20 mM.Bacteroids from Rhizobium meliloti contained high specific activities of nitrate reductase (NR) and nitrite reductase (NiR). Both enzymes were presumably substrate‐induced although substantial enzyme activities were present in the absence of NO−3 Typical specific activities for soluble NR and NiR of bacteroids under NO−3 free conditions were 1.2 and 1.4 μmol (mg protein)−1h−1, respectively. In the presence of NO−3, the specific activity of NR was considerably greater than that of NiR, thus causing NO−2 accumulation in bacteroids. Nitrite levels in the bacteroids were linearly correlated with specific activities of NR and NiR, indicating that NO−2 is formed by bacteroid NR and that this NO−2 in turn, induces bacteroid NiR. Accumulation of NO−2 within bacteroids also indicates that NO−2 inhibits nodule activity after feeding plants with NO−3