Fig. 1.

The int-m mutants produce a multifloreted TS and spikelets with extra florets. (A–F) Developing shoot apices of the wild-type Bowman and the NIL mutant BW430 (int-m.1a*BC5). No differences are found between Bowman and int-m at the VM stage (A). Sterile leaf ridges (LRs) without subtended spikelet ridges (SPRs, aka TMMs in barley) emerge at the DR stage (B) in int-m, marking the initiation of a TSM. The paired sterile bracts (i.e., glumes; green shaded) subtending a TS become prominent at the TM-SM (C), floret meristem (FM) (D), StP (E), and awn primordium (AP) (F) stages. (G) A multifloreted TS (i.e., multiple pairs of lemmas and paleae per spikelet) in int-m shows that the plane of TS glumes is perpendicular to that of central spikelets (CS) glumes (depicted in Inset). (D–F and H) RSMs are desuppressed in int-m, which may lead to the formation of additional florets in some CSs (circled in H). (I) The int-m mutants produce fewer and a defined number of spikelets. Analysis of covariance is used to compare the predicted regression lines of rachis nodes vs. days after emergence (DAE) of Bowman, int-m.1a, and int-m.85 (n = 340). No significant difference (P = 0.6813) is found between int-m.1a and int-m.85 mutants, while the number of rachis nodes in Bowman is significantly higher than that of each int-m mutant (P < 0.0001). Tukey test finds nonsignificant differences in the number of rachis nodes (adjusted P values for multiple comparisons p-adj > 0.14) between successive time points over development in int-m mutants. (J) The int-m.1a mutants form a determinate IM and an indeterminate SM. These int-m morphologies resemble a determinate IM and multifloreted spikelets in wheat. Floral organs are overlaid with pseudocolors: green glumes, yellow stamens, pink pistils, and blue lemmas. Pink asterisks mark lemma-like sterile bracts forming elongated awns within the TS.