| Abstract: | Abstract On the inhibition of seeds germination and of growth by cell enlargement by the osmotic pressure of the medium. — The mechanism of inhibition by osmotic pressure (O.P.) of the medium on growth and respiration of germinating wheat, castor bean and lettuce sèeds and of etiolated pea internode segments was investigated. The following results were obtained: 1 - External osmotic pressure (up to 0.3 M) of various substances such as mannitol, urea, glucose, NaCl, was shown to inhibit the germination and growth of lettuce, wheat and castor bean seeds. 2 - a) A remarkable decrease of the development of respiration during the first 48 h of germination was demonstrated in embryos of wheat seeds germinated and maintained in mannitol solutions at concentration from 0,2 to 0,3 M. b) A slight but reproducible inhibition of óxygen uptake by O.P. was also observed in embryos isolated from wheat seeds germinated in water for 24 and 34 h and transported respectively in water or into 0,2 M mannitol solutions. This is interpreted as indicating that high external O.P. inhibits both the respiratory metabolism and the development with time of enzyme systems supporting respiration. 3 - Mannitol solutions (0,2–0,3 M) inhibited completely growth by cell enlargement in pea internode sections, while they did not at all affect oxygen uptake and protein synthesis ( 14 C - leucine incorporation). The stimulatory effect of auxin on pea elongation was almost completely suppressed by mannitol, whereas the hormone stimulation of respiration remained unchanged. These data are interpreted as indicating that in tissues, presenting an advanced differentiation, high external O.P. inhibits growth by a direct physico-chemical mechanism; while the inhibitory effect in embrional tissues seems to comprehend, besides this direct effect, a complicated metabolic component, apparently influencing protein synthesis. |
