Articles
THE EFFECT OF SUBCULTURE INTERVAL ON ORGANOGENESIS IN CALLUS CULTURES OF CITRUS SINENSIS
This passage duration gave maximum yields of single cells when callus was enzymically digested.
Macroscopic pseudobulbils and embryoids again developed if the callus was returned to long passage periods.
Three or four long passages were necessary for the embryogenic capacity to be fully restored.
When subcultured at three-weekly intervals, the callus was soft, white, and comprised microscopic aggregates of thick walled ‘mother cells’ which had undergone a series of internal divisions.
Callus growth during these periods was exponential and it appears that under such a regime the microscopic aggregates continue to proliferate rapidly but do not develop into macroscopic structures.
A regular six-weekly passage resulted in development of many macroscopic pseudobulbils and some normal polarised embryoids.
It appears that the two to three week period of slower growth following the exponential phase was associated with a second phase in the process of organogenesis.
During the second phase fewer new ‘mother cells’ were produced and existing ones tended to become further organised into macroscopic pseudobulbils and embryoids depending on whether or not they had developed polarity.
Occasional zones of parenchyma and senescent cells were observed.
The callus subcultured at nine-weekly intervals resembled that of the six-week passage but with larger zones of parenchyma and senescent cells.
More embryoids with normal polarity were observed.
The application of various treatments causing checks in the rate of callus growth were ineffective at substituting for a long subculture interval.