Figure 1.

The Hd Mutant Exhibits Polarity Reversals.

(A) Photograph of wild-type barley (Bowman, 2-row) inflorescence, illustrating the arrangement of florets (Fl) along the rachis (Ra). Clusters of three spikelets are initiated in a distichous pattern along the rachis (only the central spikelet produces a mature floret). Each floret has an outer protective organ, the lemma, with a distal awn (Aw). Bars = 1 cm.

(B) to (D) Floral diagrams of the wild type.

(B) Adaxial wild-type morphology. The lemma and palea are visible and hairs on the lemma point distally (hair orientation, red arrows).

(C) Longitudinal cross section through a wild-type spikelet. The floret has a dorsal lemma and ventral palea.

(D) Transverse cross section illustrating the organ whorls in the wild-type floret.

(E) The Hd inflorescence phenotype resembles the wild type, although the lemma develops ectopic flowers (EF) instead of an awn. Bars = 1 cm.

(F) to (H) Floral diagrams of Hd.

(F) One or more flowers can form on the Hd lemma’s adaxial surface. Analyses of hair and organ orientations (Harlan, 1931; Bonnett, 1938; Stebbins and Yagil, 1966; Müller et al., 1995; Williams-Carrier et al., 1997) have shown that the first ectopic flower (1) is inverted, pointing toward the lemma base, whereas the second ectopic flower (2) points toward the lemma tip. The Hd lemma develops wing-like (Wi) margin outgrowths below the first ectopic flower.

(G) Longitudinal cross section through an Hd spikelet.

(H) Floral diagram of each Hd flower, showing that each ectopic flower retains the same whorled arrangement of organs. Each ectopic flower is thought to use the existing lemma as its own (dashed black line). Pr-Di, proximal-distal axis; Do-Ve, dorsal-ventral axis.