BIOL 1442 1nd Edition Lecture 3 Outline of Last LectureI: Vascular Tissue SystemII: Ground Tissue SystemIII: Plant CellsIV: MeristemsV: Primary Growth of Roots and Shoots Outline of Current Lecture I: Tissue organization of leavesII: VeinsIII: Vascular cambium and Cork cambiumIV: Growth, morphogenesis, and cell differentiationV: Flower genetics and the ABC hypothesisCurrent Lectureo Tissue Organization of Leaves:-The epidermis in leaves is interrupted by stomata, which allow CO2 and O2 exchange-Stomata: pores that allow or inhibit gas exchange and maintain proper water levels-Between surrounding air and photosynthetic cells -Each stomatal pore is flanked by two guard cells-Guard cells: control opening and closing of stomata-The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis-Mesophyll mainly parenchyma cells specialized for photosynthesis-The mesophyll of eudicots has two layers:-The palisade mesophyll in the upper part of the leaf-Main photosynthesis occurs-The spongy mesophyll in the lower part of the leaf-Gas exchange occurso Veins: -Leaf’s vascular bundles (vascular tissue of stem continuous in leaf)-Allow xylem and phloem to come into close contact with photosynthetic tissue-Bundle-Sheath cell: allows for C4 metabolismThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-C4 metabolism: incorporates carbon dioxide into organic acids which then transitions into the Calvin Cycleo Secondary growth increases the diameter of stems and roots in woody plants:-Occurs in stems and roots of woody plants but rarely in leaves-Plant body consists of the tissues produced by the vascular cambium and cork cambium-Characteristic of gymnosperms and many eudicots, but not monocotso The Vascular Cambium and Secondary Vascular Tissue:-A cylinder of meristematic cells one cell layer thick-It develops from undifferentiated parenchyma cells-Located outside the pith and primary xylem, and inside the cortex and primary phloem-In cross section, the vascular cambium appears as a ring of initials (stem cells)-The Initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside-Secondary xylem accumulates as wood-Early wood, formed in the spring, has thin cell walls to maximize water delivery-Late wood, formed in late summer, has thick-walled cells and contributes more to stem supporto Dendrochronology:-Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age-The better the climate temperature, the better the plant growth-Ring thickness allows scientists to study climate changeso Cork Cambium and the Production of Periderm:-Cork Cambium gives rise to two tissues:-Phelloderm is a thin layer of parenchyma cells that forms to the interior of the cork cambium-Cork cells accumulate to the exterior of the cork cambium-Cork cells deposit a waxy substance called Suberin in their walls, then die-Dead cork tissue functions as a barrier to protect stem or root from water loss, physical damage, and pathogens-Periderm consists of cork cambium, phelloderm, and cork cells it produces-Most periderm is impermeable to water and gases-Bark consists of all the tissues external to the vascular cambium, including secondary phloem and peridermo Growth, morphogenesis, and cell differentiation produce the plant body:-Cells form specialized tissues, organs, and organisms through the process of development-Development: consists of growth, morphogenesis, and cell differentiation-Growth: an irreversible increase in size-Morphogenesis: the development of body form and organization-Cell differentiation: the process by which cells with the same genes become different from each other-Developmental Plasticity: plant’s ability to adapt to altered environmental changes, due to the fact that plants are unable to moveo Growth: Orientation of Cell Expansion:-Plant cells grow rapidly and “cheaply” by intake and storage of water in vacuoles-Plant cells expand primarily along the plant’s main axisCellulose microfibrils in the cell wall restrict the direction of cell elongation -Cell expansion controlled by cellulose microfibrils-Cellulose microfibrils controlled by the orientation of microtubuleso Morphogenesis and Pattern Formation:-Pattern formation is the development of specific structures in specific locations-Two types of hypotheses explain the fate of plant cells-Lineage-based mechanisms: propose that cell fate is determined early in development and passed on to daughter cells-Position-based mechanisms: propose that cell fate is determined by final position-Positron-based mechanisms proven the be more accurate hypothesis-Largely depends on signaling from neighbor cells-Experiments suggest that plant cell fate is established late in development and depends on cell positiono Gene Expression and Control of Cell Differentiation:-Cells of a developing organism synthesize different proteins and diverge in structure and function even though they have a common genome-Cellular differentiation depends on gene expression, but is determined by position-Gene expression: regulation of transcription and translation, resulting in the production of specific proteins-Positional information is communicated through cell interactions-Gene activation or inactivation depends on cell-to-cell communication-For example, Arabidopsis root epidermis forms root hairs or hairless cells depending on the number of cortical cells it is touchingo Genetic Control of Flowering:-Flower formation involves a phase change from vegetative growth to reproductive growth-Transition from vegetative growth to flowering is associated with the switching on of floral meristem identity genes-In a developing flower, the order of each primordium’s emergence determines its fate: sepal, petal, stamen, or carpel-Sepal: outermost organ, protection-Petal: attract pollinators -Stamen: male reproductive organ-Carpal: innermost organ, female reproductive organ-Plant biologists have identified several organ identity genes (plant homeotic genes) that regulate the development of floral pattern-Researchers have identified three classes of floral organ identity genes-The ABC hypothesis of flower formation identifies how floral organ identity genes direct the formation of the four types of floral organs-Group A activated, form