Plant structure, growth, & development ~ 35

1. Plants have a hierarchical organization consisting of organs, tissues, and cells 3 basic organs Roots, stems, leaves Shoot System Stems Raises or separates leaves to expose to sunlight Leaves Main photosynthetic organ Root System Anchors a vascular plant in the soil Absorbs minerals & H2O Stores carbohydrates

Dermal, Vascular, and Ground tissues = Tissue System Tissue system connects all of the plants organs Dermal Tissue System Epidermis, cuticle, periderm Outer protective covering Vascular Tissue System Xylem, phloem, stele Long distance transport of materials btwn root & shoot systems Ground Tissue System Pith, cortex Specialized cells for storage, photosynthesis and support

Differentiated Cell Types

Differentiated Plant Cells Parenchyma Cells Typical plant cell w/ lg central vac Metabolic functions, synthesizing, & storing organic products Collenchyma cells Flexible Support & strength w/o restraining growth (young parts of plant shoot), grouped in strands

Water Conducting cells of xylem Sclerenchyma Cells Support & hardness Much more rigid than Collenchyma lignin in cell walls Water Conducting cells of xylem Support; harden as die at maturity Hardening of tracheids & vessel elements tubes to transport water; migrate btwn cells thru pits Sugar Conducting cells of Phloem Transport sugars throughout; alive at maturity Chains of cells = sieve-tube elements & sieve plates facilitate flow of sugars throughout plant

2. Meristems generate cells for primary & secondary growth Intermediate Growth Growth occurs throughout life of plant Meristems Apical Primary Growth Roots to extend in soil Shoots expose to sunlight Tips of roots, buds & shoots Lateral Secondary Growth Growth in thickness Vascular cambium, Cork cambium Determinate Growth Leaves, thorns, flowers stop growing after reach certain size

3. Primary Growth Lengthens Roots & Shoots Primary growth of roots Growth occurs behind root cap in three overlapping zones Cell Division Elongation Differentiation/Maturation

Primary growth of shoots Apical meristem Dome shaped mass of dividing cells at the shoot tip Shoot elongation due to lengthening of cells below shoot tip Leaf primordia Development of leaves Tissue Organization of Stems

Tissue Organization of Leaves Epidermis Upper & lower Pores = stomata Gas exchange Prevent loss of water Guard cells regulate opening/closing of stomata Mesophyll Ground tissue (middle tissue) Layers of parenchyma cells Vascular Tissue Xylem & phloem reinforcing shape of leaf = Vein Bundle sheath cells protect Vein

4. Secondary Growth Increases the Diameter of Stems and Roots in Woody Plants Secondary growth (thickness produced from lateral meristems) occurs in stems and roots of woody plants, rarely in leaves Tissues produced by vascular cambium & cork cambium V.Cambium  adds secondary xylem (= wood) and phloem Inc vascular flow and support for shoots C.Cambium  tough, thick covering of wax protect the stem from water loss, insects, bacteria, fungi

Growth rings Gymnosperms Angiosperms Temperate regions Layers of sec. xylem accum Tracheids, vessels, fibers Walls of sec xylem heavily lignified= hardness & strength of wood Gymnosperms Tracheids only Angiosperms Tracheids & vessel elements Temperate regions Early wood (spring; lrg cells) & late wood (summer; sml cells) V.Cambium inactive in winter Forms seasonal rings

5. Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body Growth – inc in size by cell division Morphogenesis = creation of plant shape Tissue, organ, organism its shape & position of cell types Development of specific patterns = Pattern Formation Cell fate Lineage-based determined early in development Position-based  cell’s final position in an emerging organ determines what kind of cell it will become Differentiation = cells with same genes become different from one another Gene expression; Hox genes in animals = MADS-box in plants for transcription factors

Organ identity genes Meristem identity genes Organ identity genes Vegetative growth  flowering (floral meristems) Organ identity genes Regulate development of floral pattern ABC Hypothesis 3 classes of genes direct the formation of 4 types of floral organs via gene activation for expression A  sepals & petals B  petals & stamens C  stamens & carpels