title: Photosynthetic leaf area modulates tiller bud outgrowth in sorghum.
abstract: Shoot branches or tillers develop from axillary buds. The dormancy versus outgrowth fates of buds depends on genetic, environmental and hormonal signals. Defoliation inhibits bud outgrowth indicating the role of leaf-derived metabolic factors such as sucrose in bud outgrowth. In this study, the sensitivity of bud outgrowth to selective defoliation was investigated. At 6 d after planting (6 DAP), the first two leaves of sorghum were fully expanded and the third was partially emerged. Therefore, the leaves were selectively defoliated at 6 DAP and the length of the bud in the first leaf axil was measured at 8 DAP. Bud outgrowth was inhibited by defoliation of only 2 cm from the tip of the second leaf blade. The expression of dormancy and sucrose-starvation marker genes was up-regulated and cell cycle and sucrose-inducible genes was down-regulated during the first 24 h post-defoliation of the second leaf. At 48 h, the expression of these genes was similar to controls as the defoliated plant recovers. Our results demonstrate that small changes in photosynthetic leaf area affect the propensity of tiller buds for outgrowth. Therefore, variation in leaf area and photosynthetic activity should be included when integrating sucrose into models of shoot branching.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, 77843, USA.
authors.forename: Tesfamichael H
authors.initials: TH
authors.lastname: Kebrom
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, 77843, USA.
authors.forename: John E
authors.initials: JE
authors.lastname: Mullet
mesh_terms: D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D010788:Photosynthesis / Q000187:drug effects / Q000235:genetics; D057445:Plant Dormancy / Q000235:genetics; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000187:drug effects / Q000254:growth & development*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D036226:Seedlings / Q000187:drug effects / Q000235:genetics; D045868:Sorghum / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013395:Sucrose / Q000494:pharmacology
chemical_list: D010940:Plant Proteins; D013395:Sucrose
keywords: apical dominance; axillary bud; defoliation; dormancy; shoot branching; sucrose; tillering