Biomedical subjects

A D Hanson

Publications and source records attributed to A D Hanson.

61 records · Page 4Linked to original sources

PubMed1979

Amino Acids Translocated from Turgid and Water-stressed Barley Leaves : II. Studies with N and C.

Movement of labeled amino acids from leaf blades to sheaths was followed after supplying (13)NH(3) gas, (14)CO(2), or (14)C-amino-acids to attached blades of barley plants.Blades of turgid and wilted plants fed (13)NH(3) (at about 120 to 700 microliters per liter) had incorporated (13)N mainly into free glutamine and glutamate after 30 minutes, and turgid blades had exported 1 to 3% of the assimilated (13)N to the sheaths, mostly as glutamine and glutamate. Wilted blades exported less of the assimilated (13)N than turgid blades even though they exported (14)CO(2) assimilates as actively as turgid blades.When substrate amounts (about 0.28 micromole) of [(14)C]glutamate and [(14)C]proline were applied to turgid and wilted blades, these amino acids entered the phloem and were translocated at velocities similar to those for (14)CO(2) assimilates (about 0.2 centimeter per minute). Wilted blades metabolized tracer amounts of [(14)C]glutamate to glutamine and proline, and exported (14)C in the form of these three amino acids. Approximate calculations of mass transfer rates of glutamate, glutamine, and proline made for wilted blades indicated that glutamine and glutamate together carried 76 micrograms of N per day, whereas proline carried only about 9 micrograms of N per day.

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PubMed1978

Water potential in excised leaf tissue: comparison of a commercial dew point hygrometer and a thermocouple psychrometer on soybean, wheat, and barley.

Leaf water potential (Psi(leaf)) determinations were made on excised leaf samples using a commercial dew point hygrometer (Wescor Inc., Logan, Utah) and a thermocouple psychrometer operated in the isopiestic mode. With soybean leaves (Glycine max L.), there was good agreement between instruments; equilibration times were 2 to 3 hours. With cereals (Triticum aestivum L. and Hordeum vulgare L.), agreement between instruments was poor for moderately wilted leaves when 7-mm-diameter punches were used in the hygrometer and 20-mm slices were used in the psychrometer, because the Psi(leaf) values from the dew point hygrometer were too high. Agreement was improved by replacing the 7-mm punch samples in the hygrometer by 13-mm slices, which had a lower cut edge to volume ratio. Equilibration times for cereals were normally 6 to 8 hours. Spuriously high Psi(leaf) values obtained with 7-mm leaf punches may be associated with the ion release and reabsorption that occur upon tissue excision; such errors evidently depend both on the species and on tissue water status.

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PubMed1978

Betaine Accumulation and [C]Formate Metabolism in Water-stressed Barley Leaves.

Barley (Hordeum vulgare L.) plants at the three-leaf stage were water-stressed by flooding the rooting medium with polyethylene glycol 6000 with an osmotic potential of -19 bars, or by withholding water. While leaf water potential fell and leaf kill progressed, the betaine (trimethylglycine) content of the second leaf blade rose from about 0.4 micromole to about 1.5 micromoles in 4 days. The time course of betaine accumulation resembled that of proline accumulation. Choline levels in unstressed second leaf blades were low (<0.1 micromole per blade) and remained low during water stress. Upon relief of stress, betaine-like proline-remained at a high concentration in drought-killed leaf zones, but betaine did not disappear as rapidly as proline from viable leaf tissue during recovery.When [methyl-(14)C]choline was applied to second leaf blades of intact plants in the growth chamber, water-stressed plants metabolized 5 to 10 times more (14)C label to betaine than control plants during 22 hours. When infiltrated with tracer quantities of [(14)C]formate and incubated for various times in darkness or light, segments cut from water-stressed leaf blades incorporated about 2- to 10-fold more (14)C into betaine than did segments from unstressed leaves. In segments from stressed leaves incubated with [(14)C]formate for about 18 hours in darkness, betaine was always the principal (14)C-labeled soluble metabolite. This (14)C label was located exclusively in the N-methyl groups of betaine, demonstrating that reducing equivalents were available in stressed leaves for the reductive steps of methyl group biosynthesis from formate. Incorporation of (14)C from formate into choline was also increased in stressed leaf tissue, but choline was not a major product formed from [(14)C]formate.These results are consistent with a net de novo synthesis of betaine from 1- and 2-carbon precursors during water stress, and indicate that the betaine so accumulated may be a metabolically inert end product.

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PubMed1976

Relationship between Ethylene Evolution and Senescence in Morning-Glory Flower Tissue.

An excised tissue system consisting of corolla rib segments was developed to study the relationship between senescence and ethylene production in morning-glory flowers (Ipomoea tricolor). Such segments, isolated 1 or 2 days (day -1 or day -2) before flower opening (day 0) passed through the same developmental phases as did the corresponding tissues of the intact organ. When excised on day -1 and incubated overnight, the rib segments turned from purple to blue and changed from a slightly curled to a flat configuration. On day 0, these segments rolled up during the afternoon and turned purple again, as did the ribs of an intact corolla; the rolling up coincided with an increased rate of ethylene production. Premature rolling up and associated ethylene evolution were induced by ethylene or propylene treatment. When segments were excised on day -2 and incubated overnight, there were no changes in color or shape; during day -1, no spontaneous rolling up and little ethylene evolution occurred. Application of ethylene or propylene to these immature segments elicited rolling up but did not stimulate endogenous ethylene production.Overnight treatment of segments cut on day -1 with 10(-6)m benzyladenine markedly retarded spontaneous rolling up and ethylene evolution, although the response to applied ethylene was only slightly slowed. Overnight treatment of segments cut on day -1 with the ethoxy analog of rhizobitoxine (10(-5) to 10(-4)m) resulted in almost complete (>99%) inhibition of both spontaneous and propylene-induced ethylene evolution. Although spontaneous rolling up was delayed, it was not abolished, and ethylene-induced rolling up was almost unaffected.These data indicate that an ethylene-generating system develops as an integral part of the aging process in flower tissue. Ethylene hastens aging of the flower, but may not play an obligatory role in flower senescence.

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PubMed1976

Methionine metabolism and ethylene biosynthesis in senescent flower tissue of morning-glory.

In immature rib segments prepared from morning-glory (Ipomoea tricolor) flower buds, the major soluble metabolite formed from tracer amounts of l-methionine-U-(14)C was S-methylmethionine (SMM). In segments of senescing ribs, (14)C was progressively lost from SMM and appeared in free methionine. Immature segments contained about 4 nmoles of free methionine and about 16 nmoles of SMM per 30 segments. As the segments senesced, the methionine content increased about 10-fold while the SMM content remained unchanged; during this time about 0.8 nmole of ethylene was produced per 30 segments. Tracer experiments with l-methionine-U-(14)C, l-methionine-methyl-(3)H, and l-homocysteine thiolactone-(35)S indicated that SMM was capable of acting as a methyl donor, and that in senescent segments the methyl group was utilized for methionine production with homocysteine serving as methyl acceptor. Of the 2 molecules of methionine produced in this reaction, 1 was re-methylated to SMM, and the other contributed to the observed rise in the content of free methionine.Internal pools of methionine and SMM were prelabeled (but not significantly expanded) by overnight incubation on 10 mum l-methionine-U-(14)C. The specific radioactivity of the ethylene subsequently evolved during the senescence of the segments closely paralleled the specific radioactivity of carbon atoms 3 plus 4 of free methionine extracted from the tissue, demonstrating that methionine was the major precursor of ethylene in this system. The specific radioactivity of carbon atoms 3 plus 4 of extracted SMM was about twice that of the free methionine.Based on these results, a scheme for methionine biosynthesis in senescent rib tissue is presented. The operation of this pathway in the control of ethylene production is discussed.

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PubMed1976

Biosynthesis of wound ethylene in morning-glory flower tissue.

Production of wound ethylene was investigated in rib segments excised from flower buds of morning-glory (Ipomoea tricolor). Segments of the ribs were cut from buds 2 days before flower opening, floated overnight on 5 mm KCl solution, and transferred to agar the following morning. These immature segments evolved only a small quantity of ethylene during incubation on agar, with most of the production occurring in the morning. When such segments were wounded mechanically early in the afternoon, the rate of ethylene production rose more than 10-fold within 1 hour and returned to a low rate after about 3 hours.Production of ethylene by both untreated and wounded rib segments was inhibited more than 95% by overnight pretreatment with the ethoxy analog of rhizobitoxine (3 x 10(-5) and 10(-4)m). After overnight exposure of segments to 9 muml-methionine-U-(14)C, the specific radioactivity of the ethylene evolved by untreated and wounded tissue was determined and compared to the specific radioactivities of carbon atoms 3 plus 4 of methionine and S-methylmethionine (SMM) extracted from the segments. The specific radioactivity of methionine was about one-half that of SMM; neither value was significantly affected by wounding. The specific radioactivity of ethylene evolved by untreated tissue was close to that of SMM. In wounded tissue the specific radioactivity of the ethylene evolved was lower, but still above that of methionine. These results are consistent with the interpretations that wound ethylene is synthesized from carbon atoms 3 plus 4 of either SMM or methionine. On the basis of earlier experiments with senescing rib segments, it is suggested that methionine serves as the precursor of the wound ethylene.

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PubMed1975

Ethylene-enhanced Ion and Sucrose Efflux in Morning Glory Flower Tissue.

Rib tissue segments excised from open flowers or buds of Ipomoea tricolor Cav. and floated on aqueous media responded to ethylene treatment by rolling up after 2 to 3 hours; a simple method for quantitating the rolling up is presented. The rolling up response was temperature- and oxygen-dependent and was critically affected by the pH of the medium. The ethylene concentration giving a half-maximal response was 0.1 mul/l; continuous ethylene treatment was not required for the response as a 1-hour ethylene exposure enhanced rolling up.Rib segments rolling up during ethylene treatment unrolled when transferred to 0.5 m sucrose, indicating that rolling up was due to asymmetric turgor changes in the segments. Compartmental analysis of (36)Cl(-) efflux from rib segments showed a fast and a slow phase; the slow phase, with a half-time of about 6 hours, is tentatively identified as efflux from the vacuolar compartment. During ethylene treatment, the rate of (36)Cl(-) efflux in the slow phase rose markedly as the rolling up response developed. A similar result was obtained with the efflux of (86)Rb(+). The release of (14)C-metabolites, labeled either by a period of (14)CO(2) fixation in darkness or by exposure to (14)C-(U)-glucose, also increased during ethylene-induced rolling up.These results suggest that ethylene causes an increase in membrane permeability in certain cells of the rib tissue.

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