Angiosperms III Plant Cell Types

Plant Cell Types Most angiosperm plants are composed of 10 fundamental cell types Many more specialized cell types do occur in some plants These 10 cell types are differentiate from the dividing cells found in meristems and cambia (meristematic cells)

Meristematic cells Found in meristems (root and shoot), the cambial layers, and buds Function is cell division (cell cycle) Small (about 10 m) with a large nucleus (the cells you saw in the squashed root tip in the mitosis lab)

Parenchyma Cells Large (100m) cells Thin cellulose cell walls Usually with a large vacuole Function as storage or “packing” cells Common in the pith and cortical layers, the wood rays, petals, etc… A “generalist” cell type

Chlorenchyma Cells Large parenchyma cells with chloroplasts Found in the leaves and in some stems Major function is photosynthesis

Collenchyma Cells Cells used for temporary support, primarily in herbaceous stems Cells walls have extra cellulose thickenings in the corners (strong but flexible) Often found in bundles as “collenchyma tissue” just under the epidermis Best experienced in celery (or rhubarb) as the “ribs” that get stuck in your teeth

Sclerenchyma Cell Types “Sclerenchyma cells” are four cell types which all share these features in common: all have thick secondary cell walls of LIGNIN (and stain red in prepared slides) all are DEAD at maturity include: fibers, sclereids, tracheids, and vessels elements

Fibers Long, narrow cells with thick walls and a small lumen Used for support in woody tissues (secondary xylem) or for support in vascular bundles and herbaceous stems Not found in conifer wood (thus the wood is “soft”)

Fibers (longitudinal section)

Sclereids Irregular cells with thick walls Function primarily for protection (surfaces often look like jigsaw puzzles) Found in dry fruits (nuts etc.), seed coats, some leaves

Sclereids A special form of a sclereid, the stone cell, gives pears their “gritty” texture

Tracheids Water conducting cells of the xylem in gymnosperms, ferns, and fern allies Cells have closed end walls Found along with vessels in angiosperms May have complex “pits” through which water moves from cell to cell Secondary wall may be deposited in rings or spiral shapes

Vessels Elements Water conducting cells of the xylem in angiosperms; also found in gnetophytes Have open end walls May have spiral or ring-like secondary cell wall patterns

Vessel Elements Are short and squat cells, one on top of another, forming vessel “tubes” for conduction

Sieve Tube Members Tall, thin cells with only primary cellulose cell walls Living cells but lack a nucleus at maturity Similar to sieve cells of gymnosperms

Sieve Tube Members Part of the phloem tissue which conducts sugars and hormones throughout the plant

Sieve Tube Members End walls have a “sieve plate”

Companion Cells Long, thin cells with a nucleus directly adjacent to each sieve tube members Sieve tube member and its companion cell are derived from the same initial Responsible for the loading and unloading of substances from the sieve tube members in the phloem Similar to albuminous cells in gymnosperms

Development of Sieve Tubes and Companion Cells

Summary of Cell Types Meristematic Parenchyma Chlorenchyma Collenchyma Sclereids Tracheids Vessel Elements Sieve Tube Members Companion Cells Meristematic Parenchyma Chlorenchyma Collenchyma Fibers