a, Nectar droplets can be observed in the lateral nectary of wild-type B. rapa flowers. No nectar was secreted from the nectaries of the Brsweet9-1, Brsweet9-2 and Brsweet9-3 homozygous mutant lines. Less nectar was secreted from the nectaries of the Brsweet9-1, Brsweet9-2 and Brsweet9-3 heterozygous mutant lines. b, Altered expression in Brsweet9-2 and Brsweet9-3. These were both splice site mutants. Brsweet9-1 is a premature stop mutant, and its mRNA level appears normal. c, N. attenuata gynoecium and nectary of wild-type and Nasweet9 flowers in five developmental stages. Nectaries of Nasweet9 lines are indistinguishable from those of wild-type (WT) plants at different developmental stages. d, Southern blotting of the SWEET gene in wild-type and two independent T2 Nasweet9 lines. Single copy insertion of the transgene was confirmed by Southern blotting analysis. Genomic DNA was isolated from wild-type and two Nasweet9 lines and digested with two restriction enzymes (EcoRV, XbaI) before gel electrophoresis. e, Relative expression level of NaSWEET9 in wild-type and Nasweet9 nectaries in three different developmental stages (± s.e.m., n = 3). The expression of NaSWEET9 increased during nectary development. The expression of NaSWEET9 in RNAi knockdown lines of Nasweet9 nectaries is reduced relative to wild-type plants in three developmental stages.