Biomedical subjects

C A Atkins

Publications and source records attributed to C A Atkins.

53 records · Page 3Linked to original sources

PubMed1979

Transport of organic solutes in Phloem and xylem of a nodulated legume.

Collections of xylem exudate of root stumps or detached nodules, and of phloem bleeding sap from stems, petioles, and fruits were made from variously aged plants of Lupinus albus L. relying on nodules for their N supply. Sucrose was the major organic solute of phloem, asparagine, glutamine, serine, aspartic acid, valine, lysine, isoleucine, and leucine, the principal N solutes of both xylem and phloem. Xylem sap exhibited higher relative proportions of asparagine, glutamine and aspartic acid than phloem sap, but lower proportions of other amino acids. Phloem sap of petioles was less concentrated in asparagine and glutamine but richer in sucrose than was phloem sap of stem and fruit, suggesting that sucrose was unloaded from phloem and amides added to phloem as translocate passed through stems to sinks of the plant. Evidence was obtained of loading of histidine, lysine, threonine, serine, leucine and valine onto phloem of stems but the amounts involved were small compared with amides. Analyses of petiole phloem sap from different age groups of leaves indicated ontogenetic changes and effects of position on a shoot on relative rates of export of sucrose and N solutes. Diurnal fluctuations were demonstrated in relative rates of loading of sucrose and N solutes onto phloem of leaves. Daily variations in the ability of stem tissue to load N onto phloem streams were of lesser amplitude than, or out of phase with fluctuations in translocation of N from leaves. Data were related to recent information on C and N transport in the species.

Journal Article↗

PubMed1979

Economy of Photosynthate Use in Nitrogen-fixing Legume Nodules: Observations on Two Contrasting Symbioses.

The economy of C use by root nodules was examined in two symbioses, Vigna unguiculata (L.) Walp. (cv. Caloona):Rhizobium CB756 and Lupinus albus L. (cv. Ultra):Rhizobium WU425 over a 2-week period in early vegetative growth. Plants were grown in minus N water culture with cuvettes attached to the nodulated zone of their primary roots for collection of evolved CO(2) and H(2). Increments in total plant N and in C and N of nodules, and C:N weight ratios of xylem and phloem exudates were studied by periodic sampling from the plant populations. Itemized budgets were constructed for the partitioning and utilization of C in the two species. For each milligram N fixed and assimilated by the cowpea association, 1.54 +/- 0.26 (standard error) milligrams C as CO(2) and negligible H(2) were evolved and 3.11 milligrams of translocated C utilized by the nodules. Comparable values for nodules of the lupin association were 3.64 +/- 0.28 milligrams C as CO(2), 0.22 +/- 0.05 milligrams H(2), and 6.58 milligrams C. More efficient use of C by cowpea nodules was due to a lesser requirement of C for synthesis of exported N compounds, a smaller allocation of C to nodule dry matter, and a lower evolution of CO(2). The activity of phosphoenolpyruvate carboxylase in nodule extracts and the rate of (14)CO(2) fixation by detached nodules were greater for the cowpea symbiosis (0.56 +/- 0.06 and 0.22 milligrams C as CO(2) fixed per gram fresh weight per hour, respectively) than for the lupin 0.06 +/- 0.02 and 0.01 milligrams C as CO(2) fixed per gram fresh weight per hour. The significance of the data was discussed in relation to current information on theoretical costs of nitrogenase functioning and associated nodule processes.

Journal Article↗

PubMed1979

Assimilation and Transport of Nitrogen in Nonnodulated (NO(3)-grown) Lupinus albus L.

The response of nonnodulated white lupin (Lupinus albus L. cv. Ultra) plants to a range of NO(3) levels in the rooting medium was studied by in vitro assays of extracts of plant parts for NO(3) reductase (EC 1.6.6.1) activity, measurements of NO(3)-N in plant organs, and solute analyses of root bleeding (xylem) sap and phloem sap from stems and petioles. Plants were grown for 65 days with 5 millimolar NO(3) followed by 10 days with 1, 5, 15, or 30 millimolar NO(3). NO(3) reductase was substrate-induced in all tissues. Roots contained 76, 68, 62 and 31% of the total NO(3) reductase activity of plants fed with 1, 5, 15, and 30 millimolar NO(3), respectively. Stem, petioles, and leaflets contained virtually all of the NO(3) reductase activity of a shoot, the activity in extracts of fruits amounting to less than 0.3% of the total enzyme recovered from the plant. Xylem sap from NO(3)-grown nonnodulated plants contained the same organic solutes as from nodulated plants grown in the absence of combined N. Asparagine accounted for 50 to 70% and glutamine 10 to 20% of the xylem-borne N. The level of NO(3) in xylem sap amounted to 4, 13, 12, and 17% of the total xylem N at 1, 5, 15, and 30 millimolar NO(3), respectively. Xylem to phloem transfer of N appeared to be quantitatively important in supplying fruits and vegetative apices with reduced N, especially at low levels of applied NO(3). NO(3) failed to transfer in any quantity from xylem to phloem, representing less than 0.3% of the phloem-borne N at all levels of applied NO(3). Shoot organs were ineffective in storing NO(3). Even when NO(3) was supplied in great excess (30 millimolar level) it accounted for only 8% of the total N of stem and petioles, and only 2 and 1% of the N of leaflets and fruits, respectively.

Journal Article↗

PubMed1979

Economy of Carbon and Nitrogen in a Nodulated and Nonnodulated (NO(3)-grown) Legume.

Partitioning and utilization of assimilated C and N were compared in nonnodulated, NO(3)-fed and nodulated, N(2)-fed plants of white lupin (Lupinus albus L.). The NO(3) regime used (5 millimolar NO(3)) promoted closely similar rates of growth and N assimilation as in the symbiotic plants. Over 90% of the N absorbed by the NO(3)-fed plants was judged to be reduced in roots. Empirically based models of C and N flow demonstrated that patterns of incorporation of C and N into dry matter and exchange of C and N among plant parts were essentially similar in the two forms of nutrition. NO(3)-fed and N(2)-fed plants transported similar types and proportions of organic solutes in xylem and phloem. Withdrawal of NO(3) supply from NO(3)-fed plants led to substantial changes in assimilate partitioning, particularly in increased translocation of N from shoot to root. Nodulated plants showed a lower (57%) conversion of C or net photosynthate to dry matter than did NO(3)-fed plants (69%), and their stems were only half as effective as those of NO(3)-fed plants in xylem to phloem transfer of N supplied from the root. Below-ground parts of symbiotic plants consumed a larger share (58%) of the plants' net photosynthate than did NO(3)-fed roots (50%), thus reflecting a higher CO(2) loss per unit of N assimilated (10.2 milligrams C/milligram N) by the nodulated root than by the root of the NO(3)-fed plant (8.1 milligrams C/milligram N). Theoretical considerations indicated that the greater CO(2) output of the nodulated root involved a slightly greater expenditure for N(2) than for NO(3) assimilation, a small extra cost due to growth and maintenance of nodule tissue, and a considerably greater nonassimilatory component of respiration in root tissue of the symbiotic plant than in the root of the NO(3)-fed plant.

Journal Article↗

PubMed1978

Carbon Dioxide Fixation in the Carbon Economy of Developing Seeds of Lupinus albus (L.).

The effects of CO(2) concentration and illumination on net gas exchange and the pathway of (14)CO(2) fixation in detached seeds from developing fruits of Lupinus albus (L.) have been studied.Increasing the CO(2) concentration in the surrounding atmosphere (from 0.03 to 3.0% [v/v] in air) decreased CO(2) efflux by detached seeds either exposed to the light flux equivalent to that transmitted by the pod wall (500 to 600 micro-Einsteins per square meter per second) in full sunlight or held in darkness. Above 1% CO(2) detached seeds made a net gain of CO(2) in the light (up to 0.4 milligrams of CO(2) fixed per gram fresh weight per hour) but (14)CO(2) injected into the gas space of intact fruits (containing around 1.5% CO(2) naturally) was fixed mainly by the pod and little by the seeds.Throughout development seeds contained ribulose-1,5-bisphosphate carboxylase activity (EC 4.1.1.39), especially in the embryo (up to 99 micromoles of CO(2) fixed per gram fresh weight per hour) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) in both testa (up to 280 micromoles of CO(2) fixed per gram fresh weight per hour) and embryo (up to 355 micromoles of CO(2) fixed per gram fresh weight per hour).In kinetic experiments the most significant early formed product of (14)CO(2) fixation in both light and dark was malate but in the light phosphoglyceric acid and sugar phosphates were also rapidly labeled. (14)CO(2) fixation in the light was linked to the synthesis of sugars and amino acids but in the dark labeled sugars were not formed.

Journal Article↗

PubMed1978

Allantoin and Allantoic Acid in the Nitrogen Economy of the Cowpea (Vigna unguiculata [L.] Walp.).

The ureides, allantoin and allantoic acid, represented major fractions of the soluble nitrogen pool of nodulated plants of cowpea (Vigna unguiculata [L.] Walp. cv. Caloona) throughout vegetative and reproductive growth. Stem and petioles were the principal sites of ureide accumulation, especially in early fruiting.Labeling studies using (14)CO(2) and (15)N(2) and incubation periods of 25 to 245 minutes indicated that synthesis of allantoin and allantoic acid in root nodules involved currently delivered photosynthate and recently fixed N, and that the ureides were exported from nodule to shoot via the xylem. From 60 to 80% of xylem-borne N consisted of ureides; the remainder was glutamine, asparagine, and amino acids. Allantoin predominated in the soluble N fraction of nodules and fruits, allantoin and allantoic acid were present in approximately equal proportions in xylem exudate, stems, and petioles.Extracts of the plant tissue fraction of nitrogen-fixing cowpea nodules contained glutamate synthase (EC 2.6.1.53) and glutamine synthetase (EC 6.3.1.2), but little activity of glutamate dehydrogenase (EC 1.4.1.3). High levels of uricase (EC 1.7.3.3) and allantoinase (EC 3.5.2.5) were also detected. Allantoinase but little uricase was found in extracts of leaflets, pods, and seeds.Balance sheets were constructed for production, storage, and utilization of ureide N during growth. Virtually all (average 92%) of the ureides exported from roots was metabolized on entering the shoot, the compounds being presumably used as N sources for protein synthesis.

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PubMed1977

Nutrition of a developing legume fruit: functional economy in terms of carbon, nitrogen, water.

The economy of functioning of the developing fruit of white lupin (Lupinus albus L.) is assessed quantitatively in relation to intake and usage of carbon, nitrogen, and water. Of every 100 units of carbon imported from the parent plant, 52 are incorporated into seeds, 37 into nonmobilizable material of the pod, and the remaining 11 lost as CO(2) to the atmosphere. An illuminated fruit can make net gains of CO(2) from the atmosphere during the photoperiods of all but the last 2 weeks of its life, suggesting that it is active in assimilation of CO(2) respired from pods and seeds. This conservation activity is important to carbon economy.Phloem supplies 98% of the fruit's carbon and 89% of its nitrogen. Most of the xylem's contribution enters early in development. Xylem and phloem supply similar sets of amino compounds, amides predominating. Ninety-six per cent of the fruit's nitrogen becomes incorporated into seeds. Sixteen per cent of the seed's nitrogen is mobilized from the senescing pod.The transpiration ratio of the fruit is 22.5 ml per gram dry matter accumulated. Xylem supplies 60% of a fruit's total water requirement and the equivalent of two-thirds of its transpiration loss. Phloem becomes prominent as a water donor once the seeds start to fill.The fruit exhibits a 31% conversion by weight of organic imports into food reserves of seeds. This entails an intake through vascular channels of 1756 mg sucrose and 384 mg amino compounds and an accumulation in seeds of 412 mg protein, 132 mg oil, and 110 mg perchloric acid-soluble carbohydrate.

Journal Article↗

PubMed1977

Significance of photosynthetic and respiratory exchanges in the carbon economy of the developing pea fruit.

The nutritional economy of the developing fruit of Pisum sativum L. (cv. Greenfeast) was studied in terms of intake of translocate, incorporation of C and N into dry matter, transpiration, and CO(2) exchanges of the fruit with its external and internal atmospheres. The environmental conditions were 12-hr days (22 C, 850 mueinsteins m(-2) sec(-1) at fruit level); 12-hr nights of 15 C.Between 6 and 30 days after anthesis, pod photosynthesis resulted in small gains of CO(2) from the external atmosphere, and assimilated most of the CO(2) respired by the fruit during the day. From then until maturity (40 days) the fruit lost CO(2) during the day. Night losses of CO(2) increased with fruit age.The gas cavity of the fruit contained 0.15 to 1.5% (v/v) CO(2). Lower levels were maintained in the day than at night. CO(2) levels were influenced by fruit age, radiant flux, and temperature. Labeled CO(2) injected into the gas cavity was fixed by the pod but not by seeds in the light, and by neither pod nor seeds in darkness. Dark-to-light or light-to-dark transfer of a fruit promoted rapid changes in CO(2) and O(2) levels of the gas space, consistent with a shift in the assimilation-respiration balance of the pod.The fruit transpired 27.6 cm(3) H(2)O per gram dry matter accumulated. Daytime ventilation was greatest 12 to 15 days after anthesis and declined as pod photosynthesis became increasingly involved in the retrieval of CO(2) respired by pod and seeds. Most, 69% by weight, of the translocate from the parent plant was converted to dry matter of seeds; nearly half, 45%, to useful seed reserves (sugar plus starch-protein-oil, 45:20:1). Illumination resulted in a fruit requiring 16% less translocate than if laying down an equal amount of dry matter in darkness.

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PubMed1977

Photosynthetic Pod Wall of Pea (Pisum sativum L.): Distribution of Carbon Dioxide-fixing Enzymes in Relation to Pod Structure.

The pod wall of pea (Pisum sativum L.) was shown to contain two distinct photosynthetic layers. The outer, comprising chlorenchyma of the mesocarp, captured CO(2) from the outside atmosphere; the inner, a chloroplast-containing epidermis lining the pod gas cavity, was involved in photoassimilation of the CO(2) released from respiring seeds.Structural features of the pod included the thick cuticle and stomata of the outer epidermis, the inward projecting veinlets of the vascular network in the mesocarp, the sparsity of air spaces, the fiber and parenchyma layers of the endocarp, and the abundant chloroplasts, thin cuticle, and rounded outer contours of cells of the inner epidermis.The inner epidermis showed high specific activities of ribulose 1,5-diphosphate (RuDP) carboxylase (EC 4.1.1.39) and phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31), contained up to 20% of the pod's chlorophyll, and was capable of fixing 66% of the CO(2) released during the photoperiod to the pod gas space by the seeds of a fully grown fruit.The in vitro carboxylation capacity of the pod exceeded the estimated gross photosynthesis of the fruit for all but the last few days of development. Chlorophyll content and carboxylation activity declined more markedly in the outer photosynthetic layers than in the inner epidermis.The ratio of activities of RuDP carboxylase to PEP carboxylase in pod extracts varied from 2.4:1 to 12:1 as against 48:1 to 156:1 in extracts of leaves.Structural and physiological properties of the pod were related to its capacity to conserve respired CO(2) and provide photosynthate to developing seeds.

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PubMed1975

Effect of preconditioning unconditioned stimulus experience on learned taste aversions.

One taste-aversion study using male Long-Evans rats in which ethanol was the unconditioned stimulus (UCS) and six studies in which lithium chloride (LiCl) was the UCS demonstrate that (a) exposure to the UCS prior to conditioning retards subsequent acquisition of learned taste aversions; (b) a single preconditioning UCS exposure is sufficient to attenuate conditioning; (c) the preconditioning UCS exposure must occur within a limited period prior to conditioning to attenuate learning; (d) repeated conditioning trials will override the effect of prior exposure to the UCS; (e) tolerance to the UCS is not a necessary condition for the attenuation effect to occur; (f) pairing the preconditioning UCS with a novel flavor other than the CS does not remove the preexposure effect, although it may reduce its magnitude; and (g) the degree of disruption is a positive function of preconditioning UCS dosage and an inverse function of conditioning UCS dosage.

Animals↗

PubMed1975

Asparagine metabolism-key to the nitrogen nutrition of developing legume seeds.

Asparagine accounted for 50 to 70% of the nitrogen carried in translocatory channels serving fruit and seed of white lupin (Lupinus albus L.). Rates of supply of the amide always greatly exceeded its incorporation as such into protein. An asparaginase (l-asparagine amido hydrolase EC 3.5.1.1) was demonstrated in crude extracts of seeds. In vitro activity was up to 5 mumoles of aspartate formed per hour per gram fresh weight at the apparent Km(Asn) value of 10 mM, and this more than accounted for the estimated rates of asparagine utilization in vivo. Asparaginase activity per seed increased 10-fold in the period 5 to 7 weeks after anthesis, coinciding with early stages of storage protein synthesis in the cotyledons.Double labeled ((14)C (U), (15)N (amide)) asparagine was fed to fruiting shoots through the transpiration steram. Fruit phloem sap analysis indicated that virtually all of the label was translocated to seeds in the form of asparagine. In young seeds (15)N from asparagine breakdown was traced to the ammonia, glutamine, and alanine of endospermic fluid, the (14)C appearing mainly in nonamino compounds. In the cotyledon-filling stage the C and N of asparagine was contributed to a variety of amino acid residues of protein.

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PubMed1972

Plant Carbonic Anhydrases: I. Distribution of Types among Species.

On the basis of polyacrylamide gradient gel electrophoresis of leaf extracts from 24 species of higher plants, two main forms of carbonic anhydrase (EC 4.2.1.1) were recognized; the "dicotyledon" type and the "monocotyledon" type. More than one band of enzyme was found on gels from most species, suggesting the possibility of carbonic anhydrase isoenzymes in higher plants.

Journal Article↗

PubMed1972

Plant Carbonic Anhydrases: II. Preparation and Some Properties of Monocotyledon and Dicotyledon Enzyme Types.

Carbonic anhydrase (EC.4.2.1.1) was purified from leaves of the dicotyledon Pisum sativum L. (56-fold) and from leaves of the monocotyledon Tradescantia albiflora Kunth. (24-fold). The molecular weight of the Pisum enzyme was estimated to be 188,000 +/- 8,000 with subunit sizes of 28,000 +/- 3,000 and 56,600 +/- 3,500. It contained 1 mole zinc per 32,500 +/- 2,000 g protein. The molecular weight of the Tradescantia enzyme was estimated to be 42,000 +/- 2,000 with a subunit size of 27,500 +/- 2,200. It contained 1 mole zinc per 34,000 +/- 2,000 g protein. The two enzyme preparations were different in specific activity, stability in solution, and sensitivity to sulfonamides and inorganic anions. Gel electrophoresis separated each purified preparation into two active enzyme bands.

Journal Article↗

PubMed1971