Matching Sentences: [ Sen. 9, subscore: 1.00 ]: The regulatory mechanism of shoot apical meristem ( SAM ) initiation is an important subject in developmental plant biology . We characterized nine recessive mutations derived from four independent loci ( SHL1-SHL4 ) causing the deletion of the SAM . Radicles were produced in these mutant embryos . Concomitant with the loss of SAM , two embryo-specific organs , coleoptile and epiblast , were lost , but the scutellum was formed normally . Therefore , differentiation of radicle and scutellum is regulated independently of SAM , but that of coleoptile and epiblast may depend on SAM . Regeneration experiments using adventitious shoots from the scutellum-derived calli showed that no adventitious shoots were regenerated in any shl mutant . However , small adventitious leaves were observed in both mutant and wild-type calli , but they soon became necrotic and showed no extensive growth . Thus , leaf primordia can initiate in the absence of SAM , but their extensive growth requires the SAM . An in situ hybridization experiment using a rice homeobox gene , OSH1 , as a probe revealed that shl1 and shl2 modified the expression domain of OSH1 , but normal expression of OSH1 was observed in shl3 and shl4 embryos . Accordingly , SHL1 and SHL2 function upstream of OSH1 , and SHL3 and SHL4 downstream or independently of OSH1 . These shl mutants are useful for elucidating the genetic program driving SAM initiation and for unraveling the interrelationships among various organs in grass embryos . [ Sen. 10, subscore: 1.00 ]: The regulatory mechanism of shoot apical meristem ( SAM ) initiation is an important subject in developmental plant biology . We characterized nine recessive mutations derived from four independent loci ( SHL1-SHL4 ) causing the deletion of the SAM . Radicles were produced in these mutant embryos . Concomitant with the loss of SAM , two embryo-specific organs , coleoptile and epiblast , were lost , but the scutellum was formed normally . Therefore , differentiation of radicle and scutellum is regulated independently of SAM , but that of coleoptile and epiblast may depend on SAM . Regeneration experiments using adventitious shoots from the scutellum-derived calli showed that no adventitious shoots were regenerated in any shl mutant . However , small adventitious leaves were observed in both mutant and wild-type calli , but they soon became necrotic and showed no extensive growth . Thus , leaf primordia can initiate in the absence of SAM , but their extensive growth requires the SAM . An in situ hybridization experiment using a rice homeobox gene , OSH1 , as a probe revealed that shl1 and shl2 modified the expression domain of OSH1 , but normal expression of OSH1 was observed in shl3 and shl4 embryos . Accordingly , SHL1 and SHL2 function upstream of OSH1 , and SHL3 and SHL4 downstream or independently of OSH1 . These shl mutants are useful for elucidating the genetic program driving SAM initiation and for unraveling the interrelationships among various organs in grass embryos .
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