Experiment Station Report 26: 729-731 (1912)

On protein formation in ripening seeds, E. Schulze (Hoppe-Seyler's Ztschr. Physiol Chem., 71(1911), No. 1, pp. 31-48).—This is a continuation of work done by the author in connection with E. Winterstein (E. S. H., 24, p. 531) and contains, besides a brief notice of other contributions, a summary of the progress made by him to date, in substance as follows:

Without expecting to arrive at an immediate explanation of the progress of protein synthesis in plants, the investigator aimed at the collection of more observation material upon which possibly to base a theory of such process. In the first communication on this subject attention was called to the fact that for answering the question as to which nitrogen compounds serve chiefly in ripening seed as material for protein synthesis, the conclusions reached by investigations of such seed are in themselves of no great importance. It is reasonably certain that for this rapidly advancing process many nitrogen compounds move rapidly from elsewhere in the plant, while others move slowly or not at all, so that the rest of such compounds which are found in unripe seeds along with the protein may vary widely from the mass of nitrogen compounds which go to these seeds out of other parts of the plant. This mass was investigated, and it is claimed that information was gained not only on the seed hulls as receptacles for reserve materials, but also on leaves and stems as such receptacles in the case of young legumes. It appears that of these, asparagin is present in quantities greater than that of any other nonproteid nitrogen compound. The unripe seeds contain amids in very small amounts only. Seeds of Phaseolus vulgaris tested for asparagin gave negative results. This is in keeping with the view that in the ripening seeds asparagin is employed in protein building. This amid probably finds like employment in the young leaves.

Doubtless in the case of the legumes the mixture of nonproteid nitrogen compounds that travel toward the ripening seeds have a great similarity with that which goes to the young leaves of the rest of the plant. This points to the conclusion that in the ripening seed the protein synthesis goes on much as in the young leaves, but the manner of this process is unknown at present.

In unripe legume seeds there are found along with proteins small quantities of asparagin, monoamino acids, arginin, histidin, etc. This is easily explainable, for it may be accepted that the building of protein out of nitrogenous material from the hulls as well as from leaves and stems requires a certain time, and is complete only with the full ripening of the seeds. If unripe seeds were examined at any stage there would be found along with proteins other nitrogen compounds. By comparing these with the mass of nonproteid nitrogen compounds going to the seeds, it was found that only in unripe seed hulls, not in the unripe seeds, was tryptophan to be found. This is comprehensible on the view that the tryptophan is transferred from the hulls into the ripening seeds, there to be employed in protein synthesis, and in consequence is not present in appreciable quantities.

On the other hand, it was found that the unripe seeds contain some glutamin, while this amid was not yet to be found in the seed hulls nor in the leaves and stems. This may be explainable on the supposition that minute quantities of glutamin, along with asparagin, migrate toward the ripening seeds to the end of protein synthesis, and that being more slowly changed than asparagin the glutamin accumulates there in sufficient quantities to respond to test. That one can in like manner account for the great difference as regards arginin content which shows itself between the unripe seeds and the rest of the plant must be considered questionable. It seems that one must here also think of a synthetic manufacture of arginin in the ripening seeds.

The author claims that the question left open by A. Emmerling as to which particular materials migrate to the ripening seed from the rest of the plant may be partially answered, since in the case of the legumes not only out of the reserve-holding seed hulls but also out of the leaves and stems a number of nonproteid compounds have been isolated. Along with these are doubtless others not yet identified.