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Chemical Investigations of the Rhubarb Plant

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Chemical Investigations of the Rhubarb Plant Bulletin 424 May, 1939 WERT BRADFORDVICKERY, GEORGE W. PUCHER.ALFRED J. WAKEMANand CHA~LESS. LEAVENWORTH Bulletin 424 May, 1939 Bulletin 424 May, 1939 CHEMICAL INVESTIGATIONSOF THE RHUBARBPLANT PART I CONTENTS INTRODUCTION........................................................... 7 PREPARATIONOFMATERIAL............................................... 9 GENERALBEHAVIOR OF LEAVES........................................... 11 THE VARIATIONIN EIGHT OF TFIE SAMPLES................................ 12 EXPRESSIONOFDATA.................................................... 13 WATERAND ORGANICSOLIDS .............................................. 14 NITROGENOUSCONSTITUENTS .............................................. 16 Tot.alNitrogen ...................................................... 16 ProtcinNitrogen .................................................... 17 Soluble Ni bragen ..................................................... 24 Nilrate Nitrogen ...........r ........................................ 28 Soluble Amino Nitrogen .............................................. 29 Solublc Peptide Nitrogen .............................................. 30 Ammonia Nitrogen ................................................... 30 AmideNitrogen ..................................................... 32 Amitle Metabolism ................................................... 33 "Extra" Ammonia Nitrogcn ........................................... 38 ORGANICACIDS .......................................................... 39 pHofExt.racts ...................................................... 39 ../' Total Organic Acids .................................................. 40 Oxalic Acid ......................................................... 42 Malic Acid .......................................................... 43 Citric Acid .......................................................... 4% Unknown Acids ..................................................... 44 Distribution of Organic'bcidity ........................................ 45 Relationship Between pH and Acid Composition ......................... 45 PART I1 CONTENTS INTRODUC~~ON........................................................... 59 PREPARATIONOF MATERIAL............................................... 60 WATERAND SOLIDS....................................................... 64 NITROGENOUSCONSTITU~S .............................................. 66 Total Nitrogen ..................................................... 66 Protein Nitrogen ..................................................... 67 Soluble Nitrogen ..................................................... 70 Nitrate Nitrogen .................................................. 73 AminoNitrogen ..................................................... 77 Ammonia Nitrogen ................................................... 78 Amide Nitrogen ..................................................... 81 "Asparagine" Amide Nitrogen ......................................... 84 Amide Metabolism ................................................... 85 ORGANICACIDS .......................................................... 89 Total Organic Acidity ................................................ 89 Oxalic Acid ......................................................... 91 Malic Acid .......................................................... 91 Citric Acid .......................................................... 94 Unknown Acids ..................................................... 94 Metabolism of Malic Acid ............................................ 95 CARBOHYDRATES......................................................... 97 PART I11 CONTENTS INTRODUCTION........................................................... 107 THECOMPOSITION OF RHUBARBLEAVES .................................... 108 1936 DWExperiment ................................................ 109 I 1937 DW Experiment ................................................ 112 1937 DG Experiment ................................................. 114 1937 LW Experiment ................................................. 114 TI~EPROTEINMETABOLISM............................................... 115 THE CARBOHYDRATE-ORGANICACIDMETABOLISM ........................... 120 THE SYNTHESISOF GLUTAMINEIN RHUBARBLEAVES ........................ 126 1936DWExperiment ................................................ 126 1937Experiment .................................................... 130 A GENERALVIEW OF AMIDEMETABOLISM ................................... 132 RESPIRATIONOF RHUBARBLEAVES ......................................... 134 1936 DW Experiment ................................................ 135 1937 DW Experiment ................................................ 140 1937 DGExperiment ................................................. 143 1937LWExperiment ................................................ 145 Discussion ........................................................ 146 THE REGULATIONOF PROTEINMETABOLISM IN LEAVES....................... 149 BIBLIOGRAPHY ....................................................... 155 FOREWORD The experiments with rhubarb leaves described in this Bulletin are presented in three parts. The first two parts give the details of separate experiments carried out with leaves collected in two successive years from the same farm. The two lots differed somewhat widely in initial composition and the behavior during culture in water in darkness was correspondingly different. In the experiments of the second year, the conditions of culture were extended to include culture in darkness in glucose solution and culture in light in water, the set of samples cultured in darkness in water serving as a control. The description of these-experiments is given in considerable detail since work that has occupied a laboratory staff for more than two years cannot be unduly compressed without risk of omitting many points concern- ing which information is essential to an appreciation of the significance of the results. An interpretation of the data in terms of modern views of plant metab- olism has been attempted in Part 111. In developing this interpretation, full advantage has been taken of the clear and stimulating presentation of present-day knowledge of protein metabolism in plants given by Professor Chibnall in his Silliman Lectures at Yale in October, 1938. It is a pleasure to acknowledge the help obtained from many personal discussions of the present data with him and also from the opportunity to study the text of his lectures in advance of publication. HUBERTBRADFORD VICKERY, GEORGE W. PUCHER,ALFRED J. WAKEXIAN and CHARLESS. LEAVENWORTH INTRODUCTION MOST of the published chemical investigations of the rhubarb plant have dealt chiefly with the organic acids present in high proportion in the fleshy petiole, or with the substances in the root responsible for the medici- nal properties which have been held in high esteem from early antiquity. Culpepper and Caldwell (21) in their general review of the subject have pointed out that tl~widespread use of the rhubarb petiole for human food is comparatively recent, tui there is a considerable literature that deals with the food value of this part of the plant (22) ancl also with the alleged toxicity of the leaf blade (9). In their own investigat:ons, Culpepper and Caldwell studied the changes in the general chemical composition of the rhubarb plant that take place during an entire growing season Allsopp (5) in England, on the olher hand, in somewhat similar experiments, has restricted his altention to the behavior of the organic acids. By the use of modern methods of analysis, 1le was able to demonstrate transport of the acids from the rhizome to the leaf during the early stages of growth, and also observed Lhe rapicl increase in the quantity of acids that occurs in the shoot during the season of active photosynthesis. This increase was accompanied by a conti~luoustransport of acids back to the rhizome, and the variations in the actual quantities of the individual acids in a single plant clearly indicated that these substances play an active part in the general metabolism. Our own previous work with the rhubarb plant has also had to do with the nature and distribution of the chief organic acids in the leaf (65, 66). This plant has been grouped by Ruhland and Wetzel (69,70) among Lhe so- called "acid plants" which are characterized by highly acid saps ancl are held to behave differently from more nearly neutral plants with respect to the metabolism of ammonia. According to the views of Prianischnikow (643), ammonia, whetller produced by oxidative deamination of amino acids within the cells, or absorbed from the solution that bathes the roots, is promptly converted into asparagine or glutamine, the ammonium ion con- centration being usually maintained at a very low level. The reaclion prob- ably involves carbohydrates, or metabolites of carbohydrates, as the NOTE: The chemical investigations of rhubarh leaves herein described were carried out as part of a general project under the title "Cell Chemistry", by the Department of 13iochemistry of the Connecticut Agricultural Experiment Station. A portion of the expense was borne hy the Carnegie Institution of Washington. 8 Conneclicul Experiment Station Bulletin 424 source of the carbon compound with which the ammonia combines, al- though this is a matter of debate at the present time. This view of the function of the amides has been shown in this laboratory to agree in general with observations on the tobacco
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