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article on barren terrain​

Answer 1

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The sparse inflorescence1 (spi1), Barren inflorescence1 (Bif1), barren inflorescence2 (bif2), and barren stalk1 (ba1) mutants produce fewer branches and spikelets in the inflorescence due to defects in auxin biosynthesis, transport, or response. We report that spi1, bif1, and ba1, but not bif2, also function in promoting cell elongation in the inflorescence.

AUXIN is essential for lateral organ and axillary meristem initiation in plants (Barazesh and McSteen 2008b; Delker et al. 2008). The maize (Zea mays) mutants, sparse inflorescence1 (spi1), Barren inflorescence1 (Bif1), barren inflorescence2 (bif2), and barren stalk1 (ba1) produce fewer branches and spikelets in the inflorescence due to defects in axillary meristem initiation (McSteen and Hake 2001; Ritter et al. 2002; Barazesh and McSteen 2008a; Gallavotti et al. 2008). spi1 functions in localized auxin biosynthesis, while bif1 and bif2 regulate auxin transport (McSteen et al. 2007; Barazesh and McSteen 2008a; Gallavotti et al. 2008). spi1; bif2 and Bif1; bif2 double mutants have a synergistic interaction producing dwarf plants with fewer leaves, indicating that spi1, bif1, and bif2 also function in leaf initiation during vegetative development (Barazesh and McSteen 2008a; Gallavotti et al. 2008). Synergistic interactions between mutants affecting auxin biosynthesis and auxin transport have also been reported in Arabidopsis (Arabidopsis thaliana) (Cheng et al. 2007a,b).

Investigation of tassel-length reduction in spi1 mutants: An interesting aspect of the spi1 phenotype is that the length of the tassel (male inflorescence) is reduced compared to a normal tassel (Figure 1, A and F). Previous analysis revealed that spikelets grow over the tip of the tassel (arrowhead in Figure 1C) (Gallavotti et al. 2008). Development of spikelets over the tip of the tassel could consume the apical inflorescence meristem, which would inhibit growth of the tassel. To test whether the production of spikelets over the tip causes the short inflorescence phenotype, we utilized spi1; bif2 double mutants, which produce tassels with no spikelets (Figure 1A) (Gallavotti et al. 2008). SEM analysis verified that spi1; bif2 mutants fail to initiate spikelet pair meristems (SPMs) (Figure 1, B–E). However, there was no significant difference in the tassel length of spi1; bif2 double mutants compared to spi1 single mutants (Figure 1F, P = 0.366), showing that the growth of spikelets over the tip of the inflorescence does not the cause the reduction in tassel length in spi1 mutants.