BIOL 425 Chapter 23

Fibers

Generally long, slender cells that occur in strands or bundles. Bast fibers: hemp, jute and flax- derived from stems of eudicots.

Sieve Tube Elements

Occur only in angiosperms. Sieve areas on some walls have larger pores than those on other walls of the same cell. Arranged in longitudinal series called sieve tubes. Walls are described as primary.

Sieve Cells

Only type of food-conducting cell in gymnosperms. Sieve areas are rather uniform in structure on al walls. Most sieve areas are connected on the overlapping ends of the long, slender sieve cells. No sieve plates present.

Epidermis

Outermost cell layer of the primary plant body- leaves, floral parts, fruits, stems, seeds and roots (secondary growth). Contain guard cells, many types of appendages or trichomes and other specialized cells.

Three tissue systems

1. Ground (fundamental) Tissue System 2. Vascular Tissue System 3. Dermal Tissue System Each consists of one or more distinct tissues.

Competency

Ability of the cell to develop in response to a specific signal, such as light

Growth

An irreversible increase in size, accomplished by a combination of cell division and enlargement. Most plant growth is brought about by cell enlargement.

Morphogenesis

Assuming a specific shape or form. Expansion of tissue, subdivided into smaller units by cell division.

Periderm

Commonly replaces the epidermis in stems and roots that undergo secondary growth. Cells are generally arranged compactly. Consists largely of a protective cork or phellem. Cork cambium- forms cork tissue on its outer surface and phelloderm on its inner surface.

Complex tissues

Composed of more than one cell type (xylem, phloem, epidermis and periderm)

Simple tissues

Composed of only one type of cell (parenchyma, collenchyma, and sclerenchyma)

Vascular Tissue System

Consist of xylem and phloem- conducting tissues

Ground Tissue System

Consists of parenchyma (most common), collenchyma and sclerenchyma.

Vessel Elements

Contain perforations- areas lacking both primary and secondary walls (perforation plate- bearing the perforations, occur on the end walls, vessel elements joined end to end). More efficient conductors of water than the tracheas because water can flow relatively unimpeded from vessel element to vessel element through the perforations. Less safe than tracheids.

Primary Phloem

In plants without secondary growth- constitutes the only conducting phloem in adult parts

Tracheid

Lacks perforations, less specialized type of cell, is the principal water conducting cell in angiosperms. Only type of water-conducting cell found in most seedless vascular plants and gymnosperms.

Collenchyma cells

Living at maturity. Occurs in discrete strands or as continuous cylinders beneath the epidermis in stems and petioles. Also found bordering the veins in eudicot leaves. Typically elongated. Most distinctive feature- unevenly thickened, nonlignified primary walls (soft and pliable). They can continue to develop thick, flexible walls while the organ is still elongating (specially adapted for support of young, growing organs).

Initials

Makes up meristems. After division of one initial, one daughter cell remains the initial, the other a derivative which divides further and differentiates.

Parenchyma cells

Most numerous cells in the plant body, in primary plant body- occur as continuous masses (tissue). Occur as vertical strands of cells in primary and secondary vascular tissues and as horizontal strands called rays in secondary vascular tissues. Capable of cell division, some have secondary walls. Involved in photosynthesis, storage and secretion- dependent on living protoplasts. Also, water movement and food storage.

Transfer cells

Parenchyma cells with wall ingrowths. Greatly increase the surface area of the plasma membrane and facilitate movement of solutes over short distances. Generally correlated with the existence of intensive movement of solutes either inward (uptake) or outward (secretion) across the plasma membrane.

Sieve Plate

Part of the wall bearing sieve areas with larger pores. Generally located on the end walls.

Meristems

Perpetually young tissues, divide and generate the plant body. Located at tips of roots/shoots. Responsible for primary extension. Indeterminate growth. Three primary meristems: protoderm (epidermis), ground meristem (parenchyma, sclerenchyma and collenchyma), and procambium (primary xylem and phloem).

Parenchyma cells only containing primary walls

Play an important role in regeneration and wound healing. Initiate adventitious structures. Also given proper conditions for growth and development, they have the ability to become embryonic cells and to develop into an entire plant (totipotent).

Callose

Polysaccharide composed of spirally wound chains of glucose residues that lines/blocks mature sieve elements. Deposited in pores of conducting sieve elements in response to injury during preparation of tissue for microscopy. "Wound callose" also "definitive callose"- senescing sieve elements. Also in the form of platelets that appears beneath the plasma membrane around each plasmodesmata at the sites of developing sieve-plate pores.

Sclerenchyma cells

Strengthen and support plant parts no longer elongating. May form continuous masses or occur in small groups or individually among other cells. Often lack protoplasts at maturity. Principal characteristic- think, lignified, secondary walls. Two types of cells- fibers and sclereids.

Sieve elements

Principal conducting cells of the phloem. Refers to clusters of pores known as sieve areas, through which the protoplasts of adjacent sieve elements are interconnected. Two types of sieve elements- sieve cells and sieve-tube elements. Variable in structure. Have living protoplasts at maturity.

Phloem

Principal food-conducting tissue in vascular plants. Also conducts amino acids, lipids, micronutrients, hormones, the floral stimulus and numerous proteins and RNA's- signaling molecules. Long-distance signaling "super information highway". Also the route for movement of plant viruses. May be primary or secondary in origin.

Xylem

Principal water-conducting tissue. Also involved in conduction of minerals, in support and in food storage. In primary plant body it is derived from procambium. During secondary growth it is derived from the vascular cambium.

Differentiation

Process by which cells with identical genetic constitution become different from one another and from the meristematic cells from which they originated. Process usually begins while the cell is still enlarging. Dependent on gene expression.

Determination

Progressive commitment to a specific course of development that brings about a weakening or loss of capacity to resume growth

P-protein

Protoplasts of sieve-tube elements of angiosperms are characterized by the presence of p-protein. Origin is in the young sieve-tube element in the form of discrete bodies called p-protein bodies. During the late stage of differentiation, these p-protein bodies elongate and disperse and become distributed along the cell walls. (usually accumulates at the sieve plates as slime plugs.

Dermal Tissue System

Represented by the epidermis- outer protective covering and the periderm- in plant parts that undergo a secondary increase in thickness (secondary growth-lateral meristems)

Tracheary programmed cell death

Results in total elimination of the protoplast, cell walls are are retained except at the perforation sites of the vessel elements, there the entire primary wall disappears providing uninterrupted conduits for the transport of water and dissolved substances through the vessels.

Albuminous Cells/Strasburger Cells

Specialized parenchyma cells in gymnosperms. Generally not derived from the same mother cell as their associated sieve cells (perform same roles as companion cells).

Companion Cells

Specialized parenchyma cells. Contain all of the components commonly found in living plant cells, including a nucleus. Closely related to sieve tube elements developmentally, have numerous cytoplasm connections with one another. Play a role in the delivery of substances to sieve-tube elements- including informational molecules, proteins and ATP necessary for maintenance. (life-support system).

Development of a plant

Three overlapping processes- growth, morphogenesis, and differentiation. Occurs in response to instructions contained in the genetic information that an organism inherits from its parents. Dependent on position of cells and tissues and by environmental factors.

Tracheary elements

Tracheids and vessel elements. Principal conducting cells of the xylem. Both are elongated cells that have secondary walls and lack protoplasts at maturity. Both types may have pits in their walls.

Sclereids

Variable in shape and often branched but compared with most fibers the are relatively short cells- may occur singly or in aggregates. Make up the seed coats of many seeds, the shells of nuts and the stone of stone fruits (olive, teachers and cherries). They give pears their gritty texture.

Epidermal cells

compactly arranged, providing considerable mechanical protection to the plant part. Covered with a cuticle (cutin and wax) that minimizes water loss.