Plant Tissues Lecture 3 March 7, 2018

Plant Growth and Development Plant Development Growth (an irreversible increase in size) Morphogenesis (a particular shape or form of a plant) Differentiation (cells with identical DNA become different from one another and from meristematic cells) Plant grows through cell division and cell enlargement

Plant Growth and Development Cellular differentiation: Under the control of gene expression and the fate of a plant cell is determined by it final position in the developing organ Differentiation is referred to determination and competence. Determination: Progressive commitment to become differentiated or produce progeny Competency: The ability of a cell to develop in response to a specific signal (light)

Cell Wall Chloroplast Central Vacuole Organelles Plant Organs Plant Tissues Plant Cells Whole Plants Leaves Stems Roots Flowers Vascular System Ground System Dermal System Guard Cells Stomata Epidermis Sclerenchyma Collenchyma Xylem Phloem Parenchyma Cuticle

The Primary Plant Body Primary growth: close to the tips of roots and stems (meristems) Extension of the plant body: vertical growth Forms primary tissues= primary plant body The root system anchors the plant and absorbs water and mineral from the soil The shoot system including stems and leaves provides solar panels to absorbs sunlight to perform photosynthesis Both root and shoot systems are made of different tissue systems.

Check Your Understanding The primary activity of cells of meristematic tissues is ______________________.   A.  support B.  transport of water C.  photosynthesis D.  cell division E.   defense

Check Your Understanding Primary meristems produce tissues that ________________.   A.  increase the width of a plant B.  increase the mass of a plant C.  increase the length of a plant D.  lead to the production of bark E.  produce the cork cambium

Plant Tissues Tissues: structural and functional units Tissue systems: larger units of principal tissues 3 tissue systems Ground (fundamental) tissue system formed from ground meristem Vascular tissue system formed from procambium Dermal tissue system formed from protoderm

two or more types of cells Plant Tissues Ground tissue system: Parenchyma, Collenchyma, Sclerenchyma Vascular tissue system: Xylem and Phloem Dermal tissue system: Epidermis and Periderm Simple Tissues only one type of cell Complex Tissues two or more types of cells

Ground Tissue System: Parenchyma Cells Parenchyma cells: the most numerous cells in the plant body Variable shape and size Living at maturity, capable of cell division, mostly primary cell walls, but some have also secondary walls Involved in regeneration and wound healing

Parenchyma cells Parenchyma tissue: continuous masses in the primary plant body found in the cortex and pith of stems and roots, in leaf mesophyll Rays, parenchyma cells found as: Vertical strands of cells in the primary and secondary vascular tissues and horizontal strands in the secondary vascular tissues Function Photosynthesis, storage and secretion Water movement and food transportation Water-storage tissue in many succulents (Cactaceae)

Ground Tissue System: Collenchyma Cells Collenchyma cells like parenchyma cells are living at maturity Typically elongated With unevenly thickened, nonlignified primary walls Found as continuous cylinders beneath the epidermis in stems and petioles and bordering the veins in eudicot leaves Typical supporting tissue of growing stems, leaves, and floral parts Roots rarely have collenchyma

Ground Tissue System: Sclerenchyma Cells Sclerenchyma cells as continuous masses or small group, individually or among other cells Found in any or all parts of the primary and secondary plant bodies Dead at maturity (due to lack of protoplast) Having thick, often lignified secondary walls Important strengthening and supporting elements in plant parts that no longer are elongated

Sclerenchyma Cells Two types of sclerenchyma: Fiber and sclereids Fibers: long, slender cells as strands or bundles, vary in length (0.8-16 mm in jute and 9-70 mm in flax) Sclereids: variable in shapes and often branched, relatively short cells compared to the most fibers. Found singly or aggregated throughout the ground tissue Seed coats of many seeds, shells of nuts, the stone endocarp) of stone fruits (olives, peaches, cherries) ad gritty texture of pears

Check Your Understanding Groups of cells that have a similar structure or common function are called ______________. A. tissues. B. meristems. C. differentiated cells. D. primary meristems. E. secondary meristems.

Check Your Understanding Which of the following cell types can be used for photosynthesis? A. collenchyma cells B. parenchyma cells C. sieve-tube elements D. sclerenchyma cells E. vessel elements

Vascular Tissue System Stele: vascular tissue of root or stem Xylem: conducts waters and dissolved minerals upwards from roots Tracheids Vessel elements Phloem: transports sugars (from photosynthesis) to roots and other are as of growth Sieve-tube elements Companion cells

Vascular Tissue System: Xylem Xylem: principal water-conducting tissue Involved in transportation of minerals, support and food storage During the primary growth, it is derived from the procambium and in the secondary growth, the xylem is derived from the vascular cambium. Tracheary elements: principal conducting cells of the xylem Tracheids Vessel elements Vessel elements have perforation (area with no primary and secondary walls) Perforation plates at the end walls where the vessel elements joined end- to-end to form long, continuous columns, or tubes called vessel Both are elongated cells with secondary walls, no protoplast at maturity, have pits in their walls

Vascular Tissue System: Xylem Tracheids only type of water- conducting cells in most seedless vascular plants and gymnosperms Angiosperms have both vessel elements and tracheids Vessel elements more efficient than tracheids but less safe due to not filter out the air bubbles

Vascular Tissue System: Xylem Tracheids and vessel elements of protoxylem (primary xylem) vary in the thickening of cell walls Form annular/ring-like or helical/spiral thickenings to be able to extend or stretch after cell differentiation Amount of elongation affects the thickening of wall Little elongation : non-extensible rather extensible elements Much elongation: more annular or spiral thickenings

Metaxylem or Secondary Xylem Metaxylem or secondary xylem: primary walls completely covered by secondary walls at the pit membranes and at the perforations of vessel element Pitted elements; rigid and can’t be stretched Tracheary element differentiation: programmed cell death (total elimination of protoplast) Xylem tissue has parenchyma cells to store different substances Xylem parenchyma cells: Vertical strands, but in the secondary xylem found in rays Fibers in xylems living at maturity and serve a dual function of storage and support

Vascular Tissue System: Phloem Phloem: principal food-conducting tissue Transport of sugars, amino acids, lipids, micronutrients, hormones, the floral stimulus (florigen), proteins and RNAs Route for movement of plant viruses Protophloem formed first and meta-phloem differentiates later Principal conducting cells of phloem: the sieve elements Sieves: clusters of pores at sieve area that interconnect the protoplasts of adjacent sieve elements Two types of sieve elements in seed plants: Sieve cells (only type of food-conducting cell in gymnosperms) Sieve-tube elements (only can be found in angiosperms)

Vascular Tissue System: Phloem Sieve cells: The sieve area pores are narrow the sieve areas are uniform in structure on all walls and mostly concentrated on the overlapping ends of the long, slender sieve cell Only type of food-conducting cell in gymnosperms

Vascular Tissue System: Phloem Sieve- tube elements: The sieve areas on some walls have larger pores than those on other walls of the same cell (Sieve plate) Sieve plates located on the end walls Sieve tubes: sieve-tube elements arranged end- on-end in longitudinal series Sieve elements have living protoplasts at maturity Selective breakdown (losing the Golgi apparatus, cytoskeleton, ribosomes)

Vascular Tissue System: Phloem Companion cells: parenchyma cells associated with sieve-tube elements cell Connects through a small pore on the side of the sieve-tube element and branch plasmodesmata on the companion cell side Life-support system of the sieve-tube element by providing proteins, ATP and informational molecules In gymnosperms, albuminous cells are parenchyma cells associated with the sieve cells Fibers and sclereids are also present.

Check Your Understanding Which of the following cell types is dead at maturity?  A. collenchyma cells B. companion cells C. parenchyma cells D. all of these E. none of these

Check Your Understanding Which of the following pairs of cells function together?  A. companion cells and fibers B. companion cells and sieve tube elements C. guard cells and root hairs D. parenchyma cells and sclerenchyma cells E. sieve tube elements and vessel elements

Stele/Pith Central column of ground tissue in stems and roots: Pith or central cylinder (stele) 3 types of stele Protostele Simplest and most ancient type Solid cylinder of vascular tissue; phloem surrounds the xylem or interspersed within it Found in seedless vascular plants such as club mosses, young stems of some other living group It is the type of stele fond in most roots

Stele/Pith 2. Siphonostele in the stems of most species of seedless vascular plants Central pith surrounded by vascular tissues Phloem forms outsides the cylinder of xylem or on both sides of it 3. Eustele primary vascular cylinder Evolved directly from protostele Discrete strands around a pith

Dermal Tissue System Epidermis: the dermal tissue system of leaves, floral parts, fruits, and seeds Provide mechanical protection for the plant body by their compact arrangement Cuticle made of cutin and wax minimizes water loss Site of the light protection involved in circadian leaf movement and photoperiodic induction Epidermal cells diverse both structurally and functionally

Dermal Tissue System Guard cells: regulate opening/closing of the small epidermal pores (stomata) to manage the movement of gases and water into and outside Trichomes: variety of functions Root hairs are trichomes to facilitate the water and mineral absorption from the soil Increase in leaf hairiness because of leaf trichomes lower leaf temperature and rates of water loss by increasing reflection of solar radiation Many air plants absorbs water and minerals through their leaf trichomes Trichomes provide a defense system against insects

Periderm Replaces epidermis in stems and roots undergoing secondary growth Arranged compactly but lenticels loosely arranged to provide air for the internal tissues of roots and stems Protective cork (phellem): nonliving cells with heavily suberized walls at maturity Cork cambium (phellogen) Phelloderm: a living parenchyma-like tissue Cork cambium forms cork tissue on its outer surface and phelloderm on its inner surface

Plant Tissues Arrangement in Plant Organs Within the plant body, the various tissue are distributed in a radial pattern with specific arrangements depending on the plant part or plant taxon or both The vascular tissues are embedded within the ground tissue with the dermal tissue forming the outer covering. The relative distribution of the vascular and ground tissues is the main difference in patterns

Plant Tissues Arrangement in Plant Organs Leaf Vascular systems form vascular bundles (veins) embedded in mesophyll (photosynthetic ground tissue) Stem Pith (the region formed internal to the strands of vascular system) Cortex (the region external to them) Root Vascular tissues form vascular cylinder (stele) surrounded by a cortex

Check Your Understanding In which tissue would you find guard cells and stomata?  A. epidermis B. ground tissue C. periderm D. phloem E. xylem

Check Your Understanding True/False: Vessel elements are the conducting cells of the phloem. True/False: Meristems are localized regions of growth in plants.