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Callus induction, adventitious shoot and root formation, and somatic embryogenesis were investigated in root, cotyledon and mesocotyl cultures of Bellevalia romana (L.) Rchb. grown on a synthetic nutrient medium containing different plant hormones. The combination of naphtaleneacetic acid plus benzylaminopurine was very effective in causing callus growth and plant regeneration from mesocotyl explants. On the contrary 2,4-dichlorophenoxyacetic acid caused suppression of shoot bud development in the same type of callus. Both cotyledon and root derived calli showed a low growth rate and did not regenerate shoots but only roots. Differentiation of somatic embryos which eventually developed into plantlets was promoted by 2,4-dichlorophenoxyacetic acid in suspension cultures. The results are discussed in relation to studies on nuclear behaviour during different morphogenetic pathways. [ABSTRACT FROM AUTHOR]

Observations are presented on the patterns of DNA synthesis and mitotic activity in medullary parenchyma cells excised from tubers of Helianthus tuberosus in four different periods of dormancy. Dormancy break (activation) was induced by in vitro culture on media added with 2,4-dichlorophenoxyacetic acid. The cell cycle response in vitro to different combinations of growth substances has also been investigated. The results show that remarkable changes in the timing of the first and second cell cycles and their phases occur with the progression of dormancy. With increasing time after tuber harvest, the following behaviours are observed: (i) a lengthening of the first cell cycle, chiefly due to a lengthening of the G phase (G is absent at the beginning of dormancy) and an increase in the time interval between the start of the in vitro culture and the onset of the first mitotic wave; (ii) an increased duration of the S phase; (iii) a remarkable reduction in the cell synchrony. These behaviours, as indicated also by their comparison with the in vitro response of the cell cycle to different hormonal treatments, seem to depend on the physiological status of the tubers at the time of explant. It is concluded that the analysis of the cell cycle is an useful tool for understanding some aspects of such a complex physiological situation as dormancy. [ABSTRACT FROM AUTHOR]