Two methods to detect the induction of nondisjunction with a diploid stable strain of A. nidulans are described. The first method gives only qualitative results, while the second method is quantitative and dose-effect curves can be done. Some physiological parameters affecting the induction ofnondisjunction can also be studied, because either quiescent or germinating conidia can be treated with the drug under test.Some agents inducing nondisjunction were also tested for the induction of point mutation and somatic crossing-over with these comparative analysis. Two classes of agents inducing nondisjunction may be detected: the first causes ail possible types of genetic damage either on quiescent or germinating conidia (a representative of this chss is MMS) and acts presumably on the DNA level; the second acts only on germinating conidia and does not produce point mutation or crossing over. A representative of this class is Benomyl which interferes with spindle microtubules. A list of compounds tests is included.

G. 1993. The impact of homologous and heterologous nurse cells on the division capability of sparsely plated cells. -Physiol. Plant. 88; 99-104.The growth-promoting effects of nurse cells of carrot, tomato, potato, maize, hean, carnation and two species of tobacco were studied on carrot, tomato, tobacco and potato cells plated at low densities. In an area immediately helow the nurse cells the plating efficiency was very high and found to be independent of cell density. In an area outside the nurse cells, in some cases, the plating efficiency tended to be much higher in combinations with cells from a heterologous source as compared with those from a homologous source. Moreover, in the same area with some combinations the plating efficiency decreased when cell density was lowered, while with other combinations this phenomenon did not occur. This decrease was independent of the absolute value of plating efficiency. In experiments in which the concentration of conditioning factors was presumably changed, no significant difference in the plating efficiency was noticed. We therefore suggest that different plating efficiencies observed with heterologous nurse cells were not due to a higher level of conditioning factors, hut rather to the production of different types of conditioning factors that are presumably degraded with different efficiency.