The embryonic axis controls lipid catabolism in cotyledons of apple seeds during germination

Abstract

Activities of alkaline lipase (AlkL, EC 3.1.1.3), isocitrate lyase (ICL, EC 4.1.3.1), glucose 6‐phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and pyruvate kinase (PK, EC 2.7.1.40) were determined in embryos of apple (Malus domestica Borb. cv. Antonówka) during culture in darkness or at 12 h photoperiod; in both cases either in the presence of gibberellin A3 (GA3) or AMO 1618 (inhibitor of GA synthesis). AlkL and ICL were stimulated by light and GA3; light stimulation was reversed by AMO. G6PDH and PK were not affected by culture conditions. Almost all the activity of all enzymes was found in the cotyledons; only PK was distributed between axis and cotyledons. GA‐like activity was found almost exclusively in the embryo axis. Cultured isolated cotyledons lost their sensitivity to light and AMO, but AlkL and ICL were still stimulated by GA3. Translocation of GA from axis to cotyledons during the culture of embryos is postulated.

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

“…It is of some interest that under control conditions (incubation of imbibed seeds at 25°C) which do not result in dormancy elimination, the high initial intensity of glycolysis decreased during the first 10 days, and the activity of PPP did not appear. A similar situation was observed for cultured dormant embryos (Bogatek et al 1989). One can conclude that relatively high production of ATP takes place at the beginning of the first phase of dormancy removal and during the induction of growth (last phase), and that the important intermediates of PPP (i.e., pentoses) are produced mainly during the second, catabolic phase (germination sensu stricto).…”

“…Nonetheless, both enzymes are activated by gibberellin treatment, and the appearance of both activities has been shown to be inhibited by AMO 1618, an inhibitor of gibberellin biosynthesis (Smoleńska and Lewak 1974;. Similar relations (GA and AMO effects) have been demonstrated for isocitrate lyase (ICL), the key enzyme of the glyoxylate cycle (Bogatek et al 1989). These observations, together with data presented earlier, allow the relations shown in Fig.…”

“…Its intensity increased in parallel to the increase of the lipolytic activity in cotyledons during the culture of apple embryos (Bogatek et al 1999). Also changes in the activity of isocitrate lyase, the key enzyme of the glyoxylate cycle, paralleled the changes in the AlkL activity in cotyledons (Bogatek et al 1989;. These data indicate that during dormancy removal and early germination of apple seeds, similar to other oily seeds, at least a fraction of storage cotyledonous lipids is converted into saccharides that play the role of ''secondary reserves'', easily available for catabolic processes; they are used for generation of energy and intermediates when the needs of the germinating seed are the highest (Bewley and Black 1983).…”

“…This has been evidenced by the demonstration of activities of key enzymes of these pathways: pyruvate kinase (PK) and phosphofructokinases (PPi-and ATP-dependent, PPi-PFK and ATP-PFK, respectively) for glycolysis, and glucose-6-phosphate dehydrogenase (G6PDH) for PPP (Bogatek and Lewak 1988;Bogatek et al 1989;Bogatek 1995) and by the determination of the ratios of 14 CO 2 derived from 6-14 C-glucose to 14 CO 2 from 1-14 C-glucose (C 6 /C 1 ratio). Changes in this ratio during seed stratification indicate that glycolysis is the dominant way of sugar catabolism during the first few days of stratification and in embryos stratified for 50 days or longer, whereas PPP dominates between days 10 and 50 (Bogatek andLewak 1978, 1988).…”