Seed coat development

Razvoj sjemene lupine najbolje je istražen u vrste A. thaliana. Razvoj sjemene lupine iz vanjskih i unutarnjih ovojnih listova sjemenog zametka počinje nakon oplodnje, a signal za početak dolazi iz endosperma. Proces se temelji na diferencijaciji, te u maloj mjeri na rastu stanica. Vanjski ovojni list se diferencira u epidermalni sloj, dok od unutrašnjeg nastaje endotelij. Stanice epidermalnog sloja sintetiziraju i izlučuju mucilago, a u kasnijim stadijima razvoja stvaraju sekundarne stanične stijenke. Mucilago prekriva površinu zrele sjemenke, a u doticaju s vodom dolazi do imbibicije i mucilago se otpušta, te okruži sjemenku. Tijekom sinteze i izlučivanja mucilaga unutrašnjost vanjskog epidermalnog sloja poprima oblik vulkana, što se odražava i u vanjskom izgledu stanica. U stanicama unutrašnjeg sloja endotelija se sintetiziraju proantocijanidini (PA), koji nakon oksidacije u zreloj sjemenci poprimaju smeđu boju. Vanjska dva sloja unutrašnjeg ovojnog lista u ranijim stadijima razvoja prolaze kroz programiranu smrt stanica. Zbog rasta embrija i endosperma u unutrašnjosti sjemenke, svi slojevi osim vanjskog epidermalnog se potisnu i unište. Razvoj sjemene lupine predstavlja dobar model za proučavanje programirane stanične smrti, te usmjerenog izlučivanja tvari iz biljnih stanica. Ovo područje razvojne biologije biljaka stavlja znanstvenike pred brojne izazove, od određivanja puteva kontrole diferencijacijskih procesa, do otkrivanja funkcija strukturnih gena.Seed coat development is best described for Arabidopsis thaliana. Development of a seed coat from two ovule integuments starts right after fertilization. Signal for this process comes from an endosperm. Changes occuring during seed coat development are based on differentiation and, to a small degree, on cell elongation. Outer integument differentiates into epidermal layer, while the inner becomes endothelium. Cells of the epidermal layer synthesize and secrete mucilage and, at late stages, secondary cell walls. Mucilage covers the surface of a mature seed, thus in contact with water it can imbibe and be released. During mucilage synthesis and secretion the cell interior is volcano-shaped, which is evident on the outside. Cells of the innermost endothelium layer synthesize proanthocyanidins (PA), which oxidize at late stages of development and turn from colourless into brown. Two outer layers of the inner integument go through programmed cell death (PCD) in early stages. Growth of embrio and endosperm causes all layers except the outermost to compress and break. Seed coat development can serve as an excellent model for PCD research, as well as for targeted secretion. This area of plant developmental biology is still challenging, since differentiation control pathways and some structural gene functions still have to be elucidated

Seed coat development

Razvoj sjemene lupine najbolje je istražen u vrste A. thaliana. Razvoj sjemene lupine iz vanjskih i unutarnjih ovojnih listova sjemenog zametka počinje nakon oplodnje, a signal za početak dolazi iz endosperma. Proces se temelji na diferencijaciji, te u maloj mjeri na rastu stanica. Vanjski ovojni list se diferencira u epidermalni sloj, dok od unutrašnjeg nastaje endotelij. Stanice epidermalnog sloja sintetiziraju i izlučuju mucilago, a u kasnijim stadijima razvoja stvaraju sekundarne stanične stijenke. Mucilago prekriva površinu zrele sjemenke, a u doticaju s vodom dolazi do imbibicije i mucilago se otpušta, te okruži sjemenku. Tijekom sinteze i izlučivanja mucilaga unutrašnjost vanjskog epidermalnog sloja poprima oblik vulkana, što se odražava i u vanjskom izgledu stanica. U stanicama unutrašnjeg sloja endotelija se sintetiziraju proantocijanidini (PA), koji nakon oksidacije u zreloj sjemenci poprimaju smeđu boju. Vanjska dva sloja unutrašnjeg ovojnog lista u ranijim stadijima razvoja prolaze kroz programiranu smrt stanica. Zbog rasta embrija i endosperma u unutrašnjosti sjemenke, svi slojevi osim vanjskog epidermalnog se potisnu i unište. Razvoj sjemene lupine predstavlja dobar model za proučavanje programirane stanične smrti, te usmjerenog izlučivanja tvari iz biljnih stanica. Ovo područje razvojne biologije biljaka stavlja znanstvenike pred brojne izazove, od određivanja puteva kontrole diferencijacijskih procesa, do otkrivanja funkcija strukturnih gena.Seed coat development is best described for Arabidopsis thaliana. Development of a seed coat from two ovule integuments starts right after fertilization. Signal for this process comes from an endosperm. Changes occuring during seed coat development are based on differentiation and, to a small degree, on cell elongation. Outer integument differentiates into epidermal layer, while the inner becomes endothelium. Cells of the epidermal layer synthesize and secrete mucilage and, at late stages, secondary cell walls. Mucilage covers the surface of a mature seed, thus in contact with water it can imbibe and be released. During mucilage synthesis and secretion the cell interior is volcano-shaped, which is evident on the outside. Cells of the innermost endothelium layer synthesize proanthocyanidins (PA), which oxidize at late stages of development and turn from colourless into brown. Two outer layers of the inner integument go through programmed cell death (PCD) in early stages. Growth of embrio and endosperm causes all layers except the outermost to compress and break. Seed coat development can serve as an excellent model for PCD research, as well as for targeted secretion. This area of plant developmental biology is still challenging, since differentiation control pathways and some structural gene functions still have to be elucidated

Seed coat development

Razvoj sjemene lupine najbolje je istražen u vrste A. thaliana. Razvoj sjemene lupine iz vanjskih i unutarnjih ovojnih listova sjemenog zametka počinje nakon oplodnje, a signal za početak dolazi iz endosperma. Proces se temelji na diferencijaciji, te u maloj mjeri na rastu stanica. Vanjski ovojni list se diferencira u epidermalni sloj, dok od unutrašnjeg nastaje endotelij. Stanice epidermalnog sloja sintetiziraju i izlučuju mucilago, a u kasnijim stadijima razvoja stvaraju sekundarne stanične stijenke. Mucilago prekriva površinu zrele sjemenke, a u doticaju s vodom dolazi do imbibicije i mucilago se otpušta, te okruži sjemenku. Tijekom sinteze i izlučivanja mucilaga unutrašnjost vanjskog epidermalnog sloja poprima oblik vulkana, što se odražava i u vanjskom izgledu stanica. U stanicama unutrašnjeg sloja endotelija se sintetiziraju proantocijanidini (PA), koji nakon oksidacije u zreloj sjemenci poprimaju smeđu boju. Vanjska dva sloja unutrašnjeg ovojnog lista u ranijim stadijima razvoja prolaze kroz programiranu smrt stanica. Zbog rasta embrija i endosperma u unutrašnjosti sjemenke, svi slojevi osim vanjskog epidermalnog se potisnu i unište. Razvoj sjemene lupine predstavlja dobar model za proučavanje programirane stanične smrti, te usmjerenog izlučivanja tvari iz biljnih stanica. Ovo područje razvojne biologije biljaka stavlja znanstvenike pred brojne izazove, od određivanja puteva kontrole diferencijacijskih procesa, do otkrivanja funkcija strukturnih gena.Seed coat development is best described for Arabidopsis thaliana. Development of a seed coat from two ovule integuments starts right after fertilization. Signal for this process comes from an endosperm. Changes occuring during seed coat development are based on differentiation and, to a small degree, on cell elongation. Outer integument differentiates into epidermal layer, while the inner becomes endothelium. Cells of the epidermal layer synthesize and secrete mucilage and, at late stages, secondary cell walls. Mucilage covers the surface of a mature seed, thus in contact with water it can imbibe and be released. During mucilage synthesis and secretion the cell interior is volcano-shaped, which is evident on the outside. Cells of the innermost endothelium layer synthesize proanthocyanidins (PA), which oxidize at late stages of development and turn from colourless into brown. Two outer layers of the inner integument go through programmed cell death (PCD) in early stages. Growth of embrio and endosperm causes all layers except the outermost to compress and break. Seed coat development can serve as an excellent model for PCD research, as well as for targeted secretion. This area of plant developmental biology is still challenging, since differentiation control pathways and some structural gene functions still have to be elucidated

Understanding functions of a putative galactose oxidase, RUBY, and its homologues in plant cell wall modifications

Cell-to-cell adhesion is essential for establishment of multicellularity. In plants, cell adhesion is mediated through a middle lamella composed primarily of pectic polysaccharides, but the molecular interactions that promote and regulate such adhesion are not fully understood. In Chapter 3, Arabidopsis seed coat mucilage was used as a model system to investigate interactions between cell wall carbohydrates. Using a forward-genetic approach, we have discovered a gene encoding a putative galactose oxidase, RUBY PARTICLES IN MUCILAGE (RUBY), that is required for cell-to-cell adhesion in the seed coat epidermis. Cellular and enzymatic analyses support the hypothesis that RUBY facilitates cross-links in the cell walls via the side-chains of rhamnogalacturonan I (RG-I), a constituent of pectin. These results (Chapter 3) provide genetic evidence for oxidative cross-linking in cell walls and assigns a biological function to the galactose/glyoxal oxidase family of enzymes. To better understand functions of galactose oxidases in plants, Arabidopsis homologues of RUBY, GALACTOSE OXIDASE-LIKE (GOXL) genes, were studied (Chapter 4). The expression patterns of these seven genes suggest that all of the members have functions in specialised tissues. Phylogenetic analyses suggest that the GOXL family likely has two pairs of GOXL paralogues, GOXL1 and GOXL6, and RUBY and GOXL3. Surprisingly, RUBY and GOXL3 are expressed in different tissues, whereas GOXL1 and GOXL6 have similar expression patterns, suggesting genetic redundancy. Functional complementation of ruby mutant and qualitative enzyme assays indicate that GOXL1, GOXL3 and GOXL6 are putative galactose oxidases. Plants with mutations in these genes, apart from RUBY, have no obvious phenotypes. When mutations were introduced in both GOXL1 and GOXL6, a collapsed pollen phenotype appeared, indicating that these genes may be redundant. Pollen collapse occurs at the anthesis, when pollen grains are desiccating, suggesting possible roles in pollen wall folding during controlled pollen dehydration (harmomegathy). Further genetic analysis is required to confirm that these mutations are indeed linked to the pollen phenotype. Taken together, putative Arabidopsis galactose oxidases seem to have specialised roles in tissues that may require mechanical support.Science, Faculty ofBotany, Department ofGraduat