The structure and function of maize scutellum during early stages of germination

• Autores: Hedia Tnani
• Directores de la Tesis: Carlos M. Vicient Sánchez (dir. tes.), Albert Ferrer Prats (dir. tes.), Ignacio López-Ribera (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2012
• Idioma: inglés
• Tribunal Calificador de la Tesis: Pere Puigdomenech Rosell (presid.), Teresa Altabella Artigas (secret.), M. Pilar Vallés Brau (voc.)
• Materias:
  • Ciencias de la vida
    • Biología vegetal (botánica)
      • Genética vegetal
• Enlaces
  • Tesis en acceso abierto en:  TDX  Dipòsit Digital de la UB 
• Resumen

  • The embryo in grasses, at grain maturity, comprises the embryonic axis and the scutellum. The scutellum is supposed to be the single cotyledon in the monocotyledoneus embryos and is attached to the embryo axis in the scutelar node. The embryo has the highest concentration of lipid and lipid soluble vitamins in cereal grains. The embryo in grasses, at grain maturity, comprises the embryonic axis and the scutellum. The scutellum is supposed to be the single cotyledon in the monocotyledoneus embryos and is attached to the embryo axis in the scutelar node. The embryo has the highest concentration of lipid and lipid soluble vitamins in cereal grains. The embryonic axis originates the root, leaves and stem of the new plant. In the mature seed, the embryo axis is formed by the primary root, protected by the coleorhiza, and the stem tip with five or six short internodes and leaf primordia which, as a whole, form the plumule that is surrounded by the coleoptile. The name scutellum (small shield, in latin) derives from its shield-like shape and it liesbetween the embryonic axis and endosperm. Dissected scutellum constitutes 11% or the kernel mass, and about 90% of the embryo. During germination, scutellar epithelial cells suffer an elongation that increases the contact surface between the endosperm and the scutellum and facilitates the transport of the nutrients from the endosperm to the embryo. Scutellar cell elongation is inhibited by ABA and salicylic acid, basic and acid pH and high concentrations of sorbitol. Exogenous gibberellins stimulate elongation, but a reduction in gibberellin synthesis or perception does not inhibit it. Elongation is inhibited by sucrose, but not glucose. Transcription and translation inhibitors reduce scutellar cell elongation, indicating that transcription and translation are necessary for the elongation process. Scutellar epithelium cells play specific roles during germination different to parenchymal cells. So, we expect some differences in the gene expression pattern of this tissue. That’s why we construct a cDNA library using RNA extracted from scutellar epithelial cells 1 day after imbibition and selected them using array hybridization comparing the mRNA accumulated in epithelial cells with the mRNA accumulated in the other scutellar tissues. We identified 30 genes up-regulated in the epithelium. A high proportion of these genes are involved in metabolic processes, the production of energy or in the transport of peptides into the embryo. The roles of 43% of these genes remains undetermined, 27% of them are involved in metabolic processes, 13% in protein synthesis or processing and 7% in cell structure. One of the identified genes from the macroarrays is a peptide transporter: ZmPTR1. It encodes a non-characterized maize peptide transporter protein which has 587 amino acids with a calculated molecular mass of 64.52 kDa. This maize transporter is predominantly expressed in the scutellar epithelium during germination. ZmPTR1 is also expressed to a less extent in the radicle and the hypocotyl. ZmPTR1 is located in the tonoplast and has high sequence similarity with tonoplast di- and tripeptide transporters AtPTR2, AtPTR4 and AtPTR6 from Arabidopsis thaliana. ZmPTR1 is able to transport at least Ala-Ala dipeptide across the membrane and could have a role in the intracellular transport of di- and tripeptides. Seed germination is a complex process that requires cell division, expansion and differentiation. It involves the activation of many metabolic pathways and signal transduction processes, which require a great quantity of energy and stored materials which are provided by seed reserves (oil, storage proteins and starch) and the synthesis and/or activation of many proteins. Plant seeds store triacylglycerols (TAGs) into oil bodies (OBs), specialized organelles which serve as an energy reserve during germination and post-germinative growth. Protein composition analysis of oil bodies from maize embryos during germination identified, in addition to the previously characterized OB-associated proteins, other proteins of diverse function: an embryonic protein DC-8, a globulin 2, 4 proteins with enzymatic activity (protein disulfide isomerase, xylose isomerase, strictosidine synthase and precursor and ATP synthase beta chain), a protein similar to karyopherin- beta-3 (Kap) and a stress induced membrane pore protein involved in membrane transport. Quantitative subproteomic analysis of germinating related changes in the oil bodies of maize scutellum between dry seeds and 2 dai seeds allowed the identification of new proteins interacting with oil bodies in dry seeds or in germinating seeds. In dry seeds: oleosins, cupins, disulfide isomerases, a nucleoside phosphate kinase, a class IV heat shock protein, an embryonic protein DC-8, a 60S acidic ribosomal protein P0 and a rubber elongation factor protein. In germinating seeds: oleosins, mitochondrial protein Tim17, prohibitin-2 and a manganese superoxide dismutase (Mn-SOD).