[n.s. vol. 6. no. 156.] (Dec 24, 1897)
THE ENZYMIC FERMENTS IN PLANT PHYSIOLOGY
FRANK ALBERT WAUGH
UNIVERSITY OF VERMONT
FERMENTATION, as a general term, covers many of the most important processes in chemistry. Fermentations are of many particular kinds, each depending more or less distinctly upon some specific ferment agent. This makes it convenient to classify the fermentation processes according to the correlated ferment agents. Thus we have yeast fermentation, bacterial fermentation, enzymic fermentation and the like.
The ferment agents, and, following them, the fermentation processes, may be roughly thrown into three classes: (1) Those belonging to the lower orders of fungi, like yeast. (2) Bacteria, like those present in the 'mother' of vinegar, or in the souring of milk. These two classes are often called organic ferments in distinction from the next. (3) Unorganized, or soluble ferments, or enzyms, like diastase, pepsin and ptyalin. The knowledge of these enzyms is mostly of very recent development, and is still fragmentary and generally unsatisfying. They have been best known as they occur in the animal digestive juices. The students of animal physiology have been used for some years to point out the presence of ptyalin and diastase in saliva, of pepsin and trypsin in the gastric juice, and of pancreatin, trypsin and diastase in the pancreatic secretions. And in a very hazy sort of way it has been known for a considerable time that the same and similar ferments are active in the physiological processes of plants. In very recent years the sharp press of experiment upon all phases of plant economy has brought to light many facts of almost startling interest. We may reasonably hope to collect observations enough within a few years to make generalization practicable; but up to the present we are doing fairly well to get some detached notions of certain of these enzyme, of their nature and action, and their relation to important vegetation processes.
The certain determination, even qualitatively, of all the enzyme present in any given part of a plant can hardly be safely made in any case; but it is known that various enzyme are present in nearly all the living organs. Each plant—especially among the flowering plants—takes up quantities of food materials, which it circulates, digests, stores, unstores, circulates again, assimilates, breaks down and finally, perhaps, excretes. In all the multifarious processes of digestion and redigestion the enzyme may take prominent part. They are almost always found in connection with special food storages, as in buds, tubers, bulbs and seeds.
Before a healthy deciduous woody plant enters upon its period of rest it stores up a considerable quantity of food with which to begin work again in the spring. These storages are largely of starch, and may be demonstrated by the iodine stain under a lens in the woody tissues of stems, especially near buds, or in the roots. The regions of fruit buds in such plants as apple and plum commonly show remarkable storages of this sort. With returning spring, before the roots start or before the leaves are put out to capture and digest food, these stores of starch and other materials are put in motion once more, and from them the new leaves are built or the early blossoms pushed forth. Theoretically and from experiment we are led to believe that these early redigestive processes are dependent on certain enzymic ferments.
In a quite similar manner those plants which propagate their species by means of tubers or bulbs store quantities of food in such organs which later can be reabsorbed and used to start the young plantlet. The recent remarkable results reported by Johanssen before the Agricultural High School of Copenhagen, and so liberally noticed in the public prints of America, were brought about by the application of ether fumes to secure an early liberation of these stores of food in bulbs and dormant woody plants.
Seeds act in the same way. When perfectly ripe and viable seeds are brought into conditions favorable to germination, the relatively large stores of food which they contain are released for the use of the nascent plant. In this case the activity of diastasic ferments is comparatively well known. Perhaps other enzyms are also present and active. The chief commercial source of diastase, in fact, is malt, that is, grain taken at the height of the germination activities. It has been often observed that seeds do not germinate well if planted immediately after ripening; that a period of rest increases the promptness and vigor of germination; and it has been thought probable that this period of rest is useful in allowing the accumulation of the necessary enzymic ferments.
One of the facts of commonest knowledge is that seeds deteriorate in viability when kept for some time. The period at which all the seeds of a sample lose their power of germination varies from two to twenty years or more, but most garden seeds deteriorate rapidly after they are three years of age. It has seemed probable that this reduction in viability is due to the diminution in quantity or loss in quality of the enzyms in the seeds. Some very interesting experiments made in the experiment station of the University of Vermont tend to establish this theory, as well as to offer some applications of practical value. Various old seeds were treated with different enzym solutions and were then placed in suitable apparatus for germination. One lot of tomato seeds, twelve years old, soaked for twenty-four hours before germination, gave the following results:
|Soaked in water,||28||per cent||germinated.|
|Soaked in trypsin,||56||"||"|
|Soaked in Extractum pancreatic,||36||"||"|
|Soaked in Enzymol,||52||"||"|
Another lot of seeds of another variety of tomato, twelve years old, gave these results:
|Soaked in water,||34||per cent.||germinated.|
|Soaked in diastase,||70||"||"|
One of the most remarkable experiments was with another lot of tomato seeds, also twelve years old. The result stood:
|Soaked in water,||12||per cent.||germinated|
|Soaked in pepsin,||80||"||"|
|Soaked in diastase,||85||"||"|
This shows an increase of 567 per cent. and 608 per cent. respectively in the germination through the action of the enzyme artificially supplied. Other seeds of other species and other enzymic preparations gave similar results.
In view of our present knowledge it seems quite fair to hope that, when we understand better the enzyme and their relation to the processes of vegetable physiology, we shall be able to control to our advantage many of the critical steps in plant development.