Practical plant biochemistry

Abstract

This chapter should be re-read after the remaining chapters have been studied.All plants are made up of a complex organized mixture of chemical substances, both organic and inorganic. As a preliminary to the study of plant chemistry, the student should realize that the chemical compounds which make up the living plant may be approximately grouped into the six following classes. Thus, in later chapters, when reference is made to any plant product, it will be understood, broadly speaking, to which class it belongs, and what relationship it bears to other chemical compounds.The main classes may be enumerated as follows :(1) Carbohydrates. The simplest members of this class are the sugars, which are aldehydes and ketones of polyhydric alcohols of the methane series of hydrocarbons. The more complex carbohydrates, such as starch, cellulose, dextrins, gums and mucilages, are condensation products of the simpler sugars. The sugars are found in solution in the cell-sap of living cells throughout the plant. Cellulose, in the form of cell-walls, constitutes an important part of the structure of the plant, and starch is one of the most widely distributed solid "reserve materials."(2) Vegetable acids. This term is usually applied to acids and hydroxyacids derived from the lower members of the methane, olefine and acetylene series of hydrocarbons. Such acids as formic, acetic, valeric and caproic are not readily detected in the plant. Nevertheless, it is more than likely that they play an important part in metabolism, for their amino derivatives, glycine, valine, etc. (see section 5) form constituents of practically all proteins. The dibasic and hydroxy-acids, e.g. oxalic, succinic, glutaric, malic, etc., are probably products of oxidation of the sugars in respiration. Aspartic (amino-succinic) and glutaminic (amino-glutaric) acids are also constituents of proteins.(3) Fats. Chemically these are glycerides, that is glycerol esters, of acids derived from the higher members of the methane and olefine series of hydrocarbons, and they usually contain a large number of carbon atoms. The fats occur as very fine globules deposited in the cells, especially in the tissues of seeds where they form reserve materials, though they also occur in other parts of plants.The lecithins, which are compounds of fats with phosphoric acid, are probably present in all living cells and have an important metabolic significance.The above substances belong to the aliphatic series of organic compounds, that is to the series in which the carbon atoms are united in chains.(4) Aromatic compounds. These are characterized by having the carbon atoms united in a ring as in benzene. They may contain more than one carbon ring, and, moreover, aliphatic groupings may be attached to the carbon ring as side-chains. The number of aromatic substances is very great, and every plant contains representatives of the class. Some members are widely distributed ; others, as far as we know, are restricted in their distribution, and may be peculiar to an order, a genus or even ...

The composition of the cell-wall at the apical meristem of stem and root

“…Details as to chemical behaviour, microchemical reactions, etc., will be found in such monographs as Tollens (26) or in text-books such as Onslow (16) and Haas and Hill (10). Mangin (13) has shown that pectic substances are present in the meristem wall.…”

UREASE DISTRIBUTION IN SOJA MAX

“…Concerning the synthesis of urea by urease it has been postulated by ONSLOW (21), EULER (7), and others, that urea might be formed by the action of urease on ammonium carbamate. It has been realized, however, that when urea is brought into contact with urease an almost complete conversion of urea to ammonia results.…”

Composition and Growth Initiation of Dormant Bartlett Pear Shoots as Influenced by Temperature

“…Commercial emulsin seemed open to the same objection stated for "Difco" invertase, namely, that when added to uncleared solutions, precipitation resulted. A very active emulsin was prepared from sweet almonds, using the method described by ONSLOW (28). This preparation was not, however, free from invertase, and for this reason it was used in conjunction with invertase scales in order to be certain that complete inversion of the sucrose was effected as well as hydrolysis of the arbutin.…”