Plant Biology: Tissue Systems and Cellular Composition

Tissue Systems and Cellular Composition

The basic plant cell types, the tissue systems in which they occur, their location within plants, and a brief description of their principal functions are presented in Table 1 .

TABLE 1

Tissue Systems, Tissues, Cell Types, and Their Locations and Functions

Tissue System	Tissues	Cell Types Present	Cell Characteristics	Location in Plant	Function in Plant
Ground tissue system	Parenchyma tissue	Parenchyma	many sided (14 common); thin primary walls, living at maturity	throughout the plant; most common type of cell and tissue	most metabolic processes; storage, wound healing, and regeneration
	Collenchyma tissue	Collenchyma	elongate; primary wall unevenly thickened (thicker in corners); living at maturity	in patches near outside of stems, along veins of leaves; example: “strings” in celery	support of young growing plant (primary plant body); flexible support for soft organs
	Sclerenchyma tissue	Sclereid	cuboidal, with thick secondary wall; either living or dead at maturity	throughout the plant; example: the gritty texture of pears	form hard layers of shells (as in peanuts) and pits of fruit (such as peaches); occur in small groups around wounds
		Fiber	long with lignified thick secondary wall; usually dead at maturity	associated with xylem and phloem; example: “strings” in leaves of grasses	support; storage
Dermal tissue system	Epidermis	Parenchyma, guard cells, trichomes (hairs),	specialized, e.g. open and close stomata; cutinized outer walls; alive at maturity; leaf epidermal cells transparent, without	outer layer of primary plant body, herbaceous plants; broken and lost in secondary body development	protection; usually a single layer of cells; root hairs are out-growth of epidermal cells
	Periderm	Parenchyma, cork cells, sclereids, cork cambium	living cork cambial cells produce heavily suberized cork cells that are dead at maturity	bark of woody plants; first layers beneath the epidermis, later layers deeper; many cork cambia, not a single cylinder like vascular cambium	protection for older stems and roots; replaces epidermis
Vascular tissue system	Xylem	Vessel element	elongate, lignified secondary wall with pits; dead at maturity; end walls with perforations	throughout the plant; elements lined up end to end form a vessel in xylem	conduct water and minerals; secondary walls add strength and support to plant body; principal cell type of angiosperm xylem
		Tracheid	long, tapering with lignified walls; have pits, but no perforations; dead at maturity	in xylem throughout the plant	principal water and mineral conducting element in gymno-sperms and seedless vascular plants; of secondary importance to vessels in angiosperms
		Parenchyma, fibers	thin walled, living parenchyma and elongate, dead fibers are accessory storage site	in xylem throughout the plant	parenchyma: storage, repair; fibers: strength and non-conducting support
	Phloem	Sieve-tube elements	elongated; primary wall only; sieve areas on end walls called a sieve plate; living at maturity but lack a nucleus	in phloem throughout the plant; elements lined up end to end form a sieve tube	conducts dissolved carbohydrates and other foods in ngiosperms
		Companion cells	living with variable, usually elongated shape; primary wall only; connected by plasmodesmata to sieve-tube elements	in phloem throughout the plant; derived from same mother cell as sieve-tube element	apparently sends ATP and signal substances to the enucleate sieve-tube elements thus controlling cellular metabolism of the sieve tube elements in angiosperms
		Sieve cell	elongated and tapering, living at maturity; primary cell wall with sieve areas; lacks a nucleus; cytoplasmn with much tubular endoplasmic reticulum	in phloem throughout the plant	conducts dissolved carbohydrates and other foods in gymnosperms