AN IN-VITRO ASSAY FOR ASSESSING THE EFFECTS OF GROWTH-FACTORS ON NICOTIANA-ALATA POLLEN TUBES

A new method for assessing the effects of test compounds on Nicotiana alata pollen tubes in culture is described. Pollen tubes grow from a c luster of grains placed beneath a thin layer of gelled medium in which test substances are incorporated and from which evaporation is preven ted by a covering layer of oil. Pollen tubes can grow to 8 mm in lengt h in 24 h, which corresponds to about 25% of the maximum growth rate i n styles. Growth is non-destructively measured. The developmental stag es reached by cultured tubes are similar to those of tubes growing in styles; growth changes from being reserve-dependent to reserve-indepen dent, callose plugs form, and the nucleus of the generative cell divid es. Because culture volumes are small (10-20 mu l per replicate), the effects of known concentrations of microgram quantities of compounds o n the growth of pollen tubes can be tested.