Rapporti Tra Assunzione D'acqua, Metabolismo e Sintesi di Enzimi Nell'endosperma Di Semi Germinanti di Ricinus Communis

Abstract

Water uptake, activation of metabolism and enzyme synthesis in germinating castor bean seeds. — During the first days of germination water uptake by the castor bean seed endosperm is accompanied by a rapid rise of respiratory activity and of the « in vitro » detectable activity of a number of enzymes. The finding that the increase of enzyme activity is strongly inibited by protein synthesis inhibitors suggests an « ex novo » synthesis of enzymes in the endosperm of the germinating seed. The present investigation on the relationship between water uptake, metabolic activity and enzyme activity level lead to the following conclusions:

I - The increase of enzyme activity is strictly dependent on the availability of water, and on the rate of water uptake. When water uptake is depressed by incubation of the seed in high osmolarity media, enzyme activation is also severely depressed.

This is also observed when the seeds are germinating in contact with an amount of water consistently lower then the one they would taken up, in a given time (24 h), under conditions of unlimeted water availability.

II - The temperature coefficient of water uptake is close to 1.5 during the first 24 h, higher than 2 in the following 3 days. Low temperature almost completely inhibits the increase of enzyme activities in the endosperm.

III - Anaerobiosis inhibits the rate of water uptake by about 50%, in the first 24 h, and almost completely, in the following 3 days. Also the rise of enzyme activities is severely inhibited by lack of oxygen. The effect of protein synthesis inhibitors on water uptake is somewhat smaller, and the one on enzyme activity is somewhat larger than that of anaerobiosis.

These results are interpreted as indicating that during the early period of germination water uptake becomes more and more dependent on the metabolic activities of the endosperm cells, in as much the latter lead to the appearance of osmotically active substances and, possibly, to changes of the cell wall properties.

On the other hand, the level of hydration of the cytoplasm represents a limiting factor for the development of the mechanism involved in enzyme synthesis and metabolic activation.