Figure 2. Embryo lethality of the spp-1 and spp-2 mutations.

(A) Appearance of aborted seeds within mature siliques of heterozygous spp-1 and spp-2 plants. Aborted seeds indicative of embryo lethality (see black arrows) are smaller in size than normal seeds, and have a darker, shrivelled appearance. (B) Frequencies of normal and aborted seeds within ripe siliques of spp-1 and spp-2 heterozygotes. The data shown are means (±SD) derived from analyses of six different siliques per genotype, each one from a different plant. Values shown refer to fertilized seeds only. (C) Reciprocal crossing analysis. Transmission of the spp-1 and spp-2 mutations through the male and female gametes was assessed by crossing heterozygotes of both mutants to wild type, in both directions, multiple times (28–50 crosses using 3–4 different plants were conducted per direction, per allele). Inheritance of the spp mutations in the F₁ progeny was assessed by determining antibiotic resistance of the F₁ plants (kanamycin for spp-1; phosphinothricin for spp-2). Transmission efficiencies were calculated for each plant as described previously [31], and then these values were used to derive the means shown (±SD).