Plant Cells and Tissues

Early embryonic plant tissues consist of 3 primary cell types: Collenchyma Sclerenchyma Parenchyma - various combinations, percentages, of these cells make up the different plant tissues

Primary plant body: - primary growth, first year - forms long axis - roots and shoots - only growth in annuals - made up of 4 primary tissues Meristems Ground Tissues Dermal Tissues Vascular Tissues - found in all 3 plant organs

Meristems: Localized regions of cellular division and growth Only places plants grow At tips of roots and shoots, in rings inside second growth plants

Ground Tissue: Arises from ground meristem Most of primary plant growth Throughout plant and in other tissues Ex. Pith and cortex Functions:Basic metabolism Storage Support Filler

Basic Cells There are three basic cells that make up ground tissue and most other tissues Parenchyma Collenchyma Sclerenchyma

Parenchyma Made by all plant’s meristems Throughout plant body Most abundant and simplest cell type Relatively unspecialized Any cell not recognized as another type Very diverse Gives rise to more specialized cells Functions: storage, basic metabolism

Differentiation, Dedifferentiation, and Redifferentiation Parenchyma cont. Thickened primary cell wall Alive at maturity Isodiametric shape Many variations on shape and form

Collenchyma Elongated cells Unevenly thickened primary cell walls Support some parts (growing tissue) Cell walls lack lignin Can form into strands or cylinders (celery) Alive at maturity

Sclerenchyma Rigid, thick, non-stretchable secondary cell walls Support and strength for non-extending, non- growing regions of plant Found in mature stems and trunks Dead at maturity ! Cell wall “skeleton” of wood! Found in all parts of plants Classified into 2 types:

1) Sclereids - Short, variable shape - Occur singly or in small groups forming internal strands - Throughout plant, some support - Hard layers and surfaces 2) Fibers - Long and slender - Normally in large strands - Single or bundles - Near vascular tissue - Between nodes on stems

Dermal Tissue: Covers plant body Epidermis Functions:Water and nutrient absorption Secretion of cuticle Gas exchange Prevents dehydration Cuticle Fatty layer of material called cutin, waterproof May be covered by layer of epicuticular wax

Epidermal Cells and Stomata Epidermal cells: Flat, tile-like, brick pattern No intercellular spaces Lack chloroplasts – clear Only one cell layer thick Store some water Stomata: 2 guard cells, subsidiary cells and gas exchange

Trichomes: One or more cellular outgrowths of the epidermis One cell thick, many long Functions: Protection, Nutrient absorption (root hairs) Cellular Recognition: Loss of Epidermis: (with secondary growth)

Vascular Tissue: 2 types 1) Xylem 2) Phloem Transport water and dissolved materials A composite tissue, many cell types

Xylem Transports water and nutrients From roots to all parts of plant Primary xylem and secondary xylem Throughout plant Secondary cell walls spiral, spring or hoop shaped Principle material of “wood” Conducting cells in xylem: 2 types

Xylary Elements - Elongated - Dead at maturity - Thick, lignified secondary cell walls - Water transport and support of plant 1. Tracheids - Most primitive, long slender cells - Tapered ends, overlap - Bordered pits on cell wall 2. Vessel Elements - Shorter than wide, fit end to end - Long hollow vessels - Transverse walls dissolved away

Phloem Transport food and organics Throughout plant body Transport both up and down directions Primary and secondary phloem Part of bark Conducting cells in phloem: 2 types

Sieve Elements - Alive at maturity - Cells lack nuclei - Typically live less than a year - Most delicate - Very thin primary cell walls only - Sieve areas and sieve pores - Stacked end to end - 2 types:

1. Sieve Cells - Found in non-flowering plants - Most primitive - Quite long, slender, with overlapping ends - Many sieve pores on ends and sides 2. Sieve Tube Members - Shorter and wider - Found in flowering plants, more advanced - Sieve pores larger and found only on the ends - Lack nuclei but still alive * Companion Cells *