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

• 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

1. Cell Division2. Elongation3. 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– 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– 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