Callus Induction Stage Research Articles

Patterns of DNA and chromosome variation during in vitro growth in various genotypes of potato

Patterns of variation in nuclear DNA content and chromosome number were analysed in a temporal sequence, during in vitro growth of calli and cell suspensions in two monohaploids, a dihaploid and a tetraploid of potato ( Solanum tuberosum). The results showed that both polyploidization and aneuploidy occurred during the initial stages of callus induction in all the genotypes. With further growth of callus, the frequency and extent of polyploidy and aneuploidy increased. In addition, the patterns of DNA and chromosome variation in cell suspension cultures revealed continued mitotic activity and transmission of cells with higher ploidy levels and aneuploidy. The results suggest that endoreduplication as well as endomitosis are important mechanisms of polyploidization, and that chromosome lagging and non-disjunction contribute to the production of aneuploidy. The various genotypes cultured under the same in vitro growth conditions differed in genetic instability, as assessed from the rate and degree of polyploidization and aneuploidy. Monohaploids showed more rapid rate of polyploidization than the dihaploid and tetraploid potatoes. It was concluded that the differences in genetic stability were due to different ploidy levels and genetic make-up of the genotypes.

Adenine nucleotide contents in callus‐forming potato tuber discs with different respiratory characteristics

ATP content (per g fresh weight) and energy charge were higher during incubation at 8°C than at 28°C in the early stages of callus induction of potato tuber discs (Solanum luberosum L. cv. Bintje). After a transfer from 28°C to 8°C, ATP content increased while a sharp decline in ATP content was observed after a transfer from 8°C to 28°C. ADP and AMP pools did not increase correspondingly. When the callus discs had entered the logarithmic growth phase, the energy charge was maintained within relatively narrow limits (0.77–0.80) at all culture temperatures.

Complex formation by 2,4-dichlorophenoxyacetic acid with histones during callus induction

During callus induction (dedifferentiation by 2,4-dichlorophenoxyacetic acid (2,4-D)) the relatively basic protein fractions from DEAE cellulose column chromatography decreased, while the more acidic protein fractions increased. There was also an increase in complex formation by 2,4-D. 2,4-D formed particularly notable complexes with lysine-rich histones at an early stage of callus induction. This complex formation by 2,4-D with lysine-rich histones seems to be the cause of the decrease in the lysine-rich portions of histone fractions during callus formation.