Is the gibberellin A4 biosynthesis involved in the removal of dormancy in apple seeds?

Metabolic control of embryonic dormancy in apple seed: seven decades of research

“…The involvement of gibberellins in the cold-mediated removal of dormancy in apple seeds has been demonstrated in a series of experiments where the intensity of incorporation of 2-14 C mevalonate (MVA) into GA 4 was determined at various periods of cold stratification (Sińska and Lewak 1977). The intensity increased sharply between days 10 and 20 of stratification, and then it decreased; accumulation of GA 4 stopped at day 50.…”

Hormones in Seed Dormancy and Germination

“…Sensitivity of isolated embryos to exogenous gibberellin diminishes during stratification, being the highest in dormant embryos. Treatment of the gibberellin-sensitive, GA-synthesisng embryos with AMO-1618, which acts as a gibberellin biosynthesis inhibitor, hinders germination, but treatment of emryos isolated from seeds stratified for 50 days or longer is without effect on germination (Sinska and and Lewak, 1977). It seems that these results univocully confirm the involvement of a hormonal promotor in dormancy removal.…”

“…It seems, thus, that the synthesis of some hormones, observed during germination of the seeds of some species (e. g., Sinska and Lewak, 1977) is not the primary response for the environmental agents; but rather one of the later events in the causal chains that link the stimulus and the end of germination. In this respect one still" unanswered question seems to be most interesting: are the enzymes involved in hormone biosynthesis, degradation and metabolism (reversible formation of conjugates) just activated during seed germination or are they synthesized de novo (stored mRNA) ?…”

“…The phytochrome involvement in stimulation of GA4 biosynthesis has been evidenced by demonstrating that (i) GA4 accumulates during the culture of embryos in the dark only if a short red-light exposure is applied, (ii) the effect of red light is reversed by the subsequent far-red exposure, (iii) incorporation of 2 u C mevalonate into GA4 takes place only during the lightculture. of embryos or in the dark after a red-light exposure and (iv) the treatment of embryos with AMO 1618 (inhibitor of GAs biosynthesis), independently of the light conditions of culture, prevents GA4 accumutation and mevalonate incorportion (Smolenska and Lewak, 1971;Sinska and Lewak, 1977). The GA4 involvement in alkaline lipase activation was shown by proving that (i) the maximum content of GA4 in lightcultured embryos precedes the increase in alkaline lipase activity, (ii) the enzyme activity during the dark-culture of embryos rises in the presence of GA 4 , but is not affected by GA7 treatment, whereas GAa acts with a considerable delay and (iii) the factors that affect the endogenous GA4 level (light conditions of the embryo culture, AMO treatment) similarly affect the activity of alkaline lipase.…”

“…Changes in sensitivity towards some factors affecting germination were also taken into account (Lewak and Bryzek, 1974;Rudnicki, 1969;Sinska and Lewak, 1977). Three phases of after-ripening were also distinguished by demonstrating their different temperature optima .…”