Embryonic dormancy is defined as a set of blocks imposed upon a process(es) cardinal for growth. In apple seeds, all these blocks are removed as a result of cold treatment (stratification), but some of them are also affected by light and/or hormonal treatments. This review summarizes published data related to the modes of action of above factors on the changes in the levels of endogenous hormones and some other plant growth regulators (e.g., hydrogen cyanide), and on certain enzymes involved in mobilization of seed reserves and catabolism of their hydrolysis products. Phytochrome and activities of acid lipase and a protease have been indicated as receptors of light and low temperature, respectively. Several chains of events initiated by these two environmental factors and leading to dormancy removal are proposed, and the sites of their control by hormones and HCN are indicated. These chains are postulated to contribute to the elimination of particular blocks that hinder germination and therefore to be involved in the mechanisms of dormancy breakage.

The effects of (−)jasmonic acid (JA) on germination of embryos isolated from dormant seeds of apple (Malus domestica Borb. cv. Antonówka) cultured in darkness or at 12‐h photoperiod were studied, as well as its effects on the activity of alkaline lipase (AlkL, EC 3.1.1.3) in these embryos. The maximum sensitivity of germination to JA occurred on days 3 and 4 of embryo culture. Both germination and enzyme activity were stimulated by JA, its effect being additive to that of light. Inhibitors of lipoxygenase inhibited embryo germination and AlkL activity, both effects being partially reversed by JA treatment. We suggest that (1) JA is implicated in an endogenous complex controlling apple seed germination, and that (2) it acts independently of the mechanism triggered by light.

The ratio of glycolysis to the pentose phosphate pathway (PPP, C6/C1 ratio), and the activities of glucose 6‐phosphate dehydrogenase (EC 1.1.1.49) and pyruvate kinase (PK, EC 2.7,1.40) were determined in apple seeds (Malus domestica Borb, cv. Antonówka) submitted to cold and warm stratifications. Our results indicated that the elimination of embryonal dormancy in apple seeds was connected with a change from domination of PPP to domination of glycolysis in sugar catabolism during cold stratification. Cyanide pretreatment affected the C6/C1 ratio and the activities of the enzymes under study in such a manner that the maxima of PPP and glycolysis appeared earlier during stratification. We suggest a regulatory role of cyanide in removal of dormancy.

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