Phytochrome‐mediated accumulation of free amino acids in radicles of germinating watermelon seeds

Abstract

The total free amino acid pools in radicles of watermelon seeds, investigated during imbibition of water at 25°C, were higher under the most (darkness) than under the least (continuous broad spectrum far‐red light) favourable light regime for germination. When seeds were imbibed in an appropriate osmotic solution of PEG‐6000 (fully suppressing germination), in darkness or under continuous red or far‐red light, the biochemical analyses of the radicles after 1,2,3 and 4 days from the onset of imbibition show that while the total soluble sugar content remains rather constant in all treatments, significant changes are observed in the total free amino acid pools. After the first day, a considerable increase characterizes the “darkness” pool in contrast to a moderate one under red, while the “far‐red” pool remains constant. Ultimately, at 4 days, the three pools are 190,142 and 123% of the 0 day radicle one. The qualitative free amino acid determination of the 4 day darkness and far‐red pools shows a considerably increased percentage contribution of glutamic acid, arginine and citrulline in the “darkness” pool. The free amino acid increase in non‐illuminated radicles may be correlated to germinability; moreover, it is evidently a phytochrome‐mediated, pre‐germinatory event, probably due to the hydrolysis of proteins (known to be rich in glutamic acid and arginine), stored in the radicle. Copyright © 1984, Wiley Blackwell. All rights reserve