9 Springer-Verlag 1982
Endomitosis and the effect of gibberellic acid in different Pisum sativum L. cultivars A. Callebaut*, P. Van Oostveldt and R. Van Parijs Laboratorium Biochemie, Fakulteit Landbouwwetenschappen - RUG, Coupure Links 653, B-9000 Gent, Belgium
Abstract. The evolution of the total amount of
DNA in epicotyls and of the amount of DNA per cell nucleus in epicotyl cortex cells during germination was followed in two closely related pea varieties, Pisum sativum cv. Finale and Pisum sativum cv. Rondo. Under etiolating conditions, growth of the cv. Rondo occurs only by cell elongation which is preceded by endomitotic DNA synthesis, while in the cv. Finale growth is the result of cell elongation accompanied by endomitotic DNA synthesis and cell division. The maximum C-level attained in both cultivars under etiolating conditions is 8 C (C = haploid amount of DNA in a gamete cell). Both the maximum C-level reached and the percentage of cells reaching this C-level seem to be under strict genetic control. In both cultivars, light inhibits the endomitotic DNA replication. Neither gibberellic acid (GA3), nor AMO 1618 alter the maximum C-level or the percentage distribution of the C-classes. Both growth regulators are effective, although in an opposite way, only in tissues where cell division occurs or where endomitotic DNA synthesis is blocked, as in lightgrown pea epicotyls. Key words" AMO 1618 - Cell elongation Endomitosis- Gibberellin and endomitosis Mitosis Pisum (endomitosis and GA).
Recent studies on cell elongation in developing pea shoots (Mohamed and Bopp 1980; Nougar6de and Rembur 1980) confirm our earlier statements concerning the existence of a correlation between cell * P r e s e n t a d d r e s s : Instituut voor Scheikundig Onderzoek, Ministerie van Landbouw, Museumlaan 5, B-1980 Tervuren, Belgium
elongation and endopolyploidy (Van Oostveldt and Van Parijs 1975; Boeken and Van Oostveldt 1977; Callebaut et al. 1977; Van Oostveldt et al. 1978). However, there is still some disagreement about the degree of endopolyploidy in the different cultivars of Pisum sativum L. A variation in the degree of endoreduplication can be explained as resulting from genetic differences or from different experimental conditions. In earlier experiments we studied the dwarf pea cultivar Rondo, which until 1970 was the most important variety among the blue peas in the Netherlands, measured as a proportion of the cultivated area (Sneep et al. 1979). Today, Rondo has been almost completely replaced by the new cultivar Finale. The cv. Finale was selected from a cross between Dik Trom X Cebeco 62207, while Dik Trom itself originated from the hybridization of Pauli X (Rondo X Profusion). Finale was introduced because it had improved resistance to infection and an improved yield, especially under unfavourable soil conditions. Even in laboratory experiments, seeds of the Finale variety germinated more homogeneously and were more resistant to infection than seeds of Rondo. In order to evaluate the influence of genetic and experimental factors on the processes of cell division and endomitosis, the varieties Rondo and Finale were compared. The amounts of DNA, RNA, dry matter, and protein per epicotyl were determined at different stages of development, when grown under continuous white light or under conditions of rigourous darkness. The effect of gibberellic acid (GA3) and AMO 1618 (a synthetic inhibitor of gibberellin biosynthesis) was studied. In earlier experiments, the effect of etiolation and GA3-application on the growth of Rondo epicotyls was examined. From these experiments the authors concluded that the stimula0032-0935/82/0156/0553/$01.40
A. Callebaut et al. : Endomitosis and GA3 in Pisum
tion of epicotyl growth by etiolating conditions and by GA 3 (under light conditions) occur by different mechanisms: Etiolation was accompanied by endoreduplication, whereas the application of GA 3 induced cell division (Boeken and Van Oostveldt 1977; Callebaut et al. 1977).
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Materials and methods