Experimental procedures
Plant material and growth conditions
Tomato (Lycopersicon esculentum Mill.) plants derived from an F2 population segregating for the fa mutation were used. F2 seeds were firstly provided by the Tomato Genetic Resource Centre (TGRC accession number LA854), Department of Vegetable Crops, University of California, Davis. Seeds were germinated in plastic pots filled with a sphagnum peat/vermiculite substrate mixture (3 : 1) at 25°C, and grown in a greenhouse, 25°C daytime maximum to 10°C night minimum temperature under approximately 14 h natural light. The +/+ and +/fa genotypes in the F2 population were distinguished by progeny analyses of F3 families.
Scanning electron microscopy
For SEM, floral buds were fixed, prepared, visualized and photographed as described by Sommer et al. (1990) .