D. Rodríguez

During the first 12 h of germination of Cicer arietinum L. (cv. Castellans) seeds, K + is first lost into the surrounding medium and is later reabsorbed. Thiourea accelerates this reabsorption. Since there is an increase in the mobilization of K + in response to thiourea, a greater accumulation of malate due to the carboxylation of phosphoenolpyruvic acid takes place as compared with that occurring in water. The subapical zone of the radicle accumulates the greatest amounts of water, K + and malate. The variation in the “in vitro” activity of phosphoenolpyruvate carboxylase does not explain the difference in malate in response to the different treatments, consequently there must be chemical changes in the cytoplasm which favour this carboxylation “in vivo”. These results show that thiourea accelerates the mobilization of K + and stimulates the dark fixation of CO 2 in embryonic axes of Cicer arietinum.

Thiourea, hydroxyurea, phenylthiourea, methylurea, methylthiourea, thiosemicarbazide and 2,2‐dithiodipyridine affected the germination of Cicer arietinum L. cv. Castellana (chick‐pea) seeds. Microscopic observations of the subapical zone of the radicle showed that thiourea induced an increase in cell volume and length when compared with control seeds germinated at 25° or 30°C in water. These results emphasize the importance of the processes controlling solute and water uptake during early germination of chick‐pea seeds. In contrast to this stimulation of volume increase, the thiourea‐treated seedlings were unable to synthesize chlorophyll when exposed to light. This toxic effect was reduced when thiourea was administered only during the first few hours of germination. Thiourea also caused an increase in the uptake of 3 H‐thymidine and 14 C‐leucine but it decreased their incorporation into DNA and protein, respectively. These results suggest a stimulation of plasmalemma exchange activities, but toxic or inhibitory effects on other metabolic processes necessary for normal development of seedlings.

Nonanoic acid, which inhibits germination in several seeds, enhanced ion efflux from embryonic axes of Cicer arietinum L., especially at temperatures above 25°C. Other short chain fatty acids had little effect on germination and ion leakage. Nonanoic acid also decreased uptake of 86 Rb + and 22 Na + and increased efflux of both isotopes from the embryonic axes into the incubation solution. Fusicoccin, which stimulates early germination in C. arietinum , counteracted the effects of nonanoic acid at both 25 and 30°C. These results suggest that nonanoic acid affects the integrity of plasmalemma and other membrane systems. Nonanoic acid thus inhibits cell elongation during early germination by disturbing ion exchange and inhibiting water uptake.