User:David D./sandbox2
LEVELS OF ORGANIZATION IN THE PLANT BODY
organs:
- root: the portion of a plant axis produced by the root apical meristem.
- stem: the portion of a plant axis produced by the shoot apical meristem
- leaf: a lateral appendage of the stem produced by the shoot apical meristem.
PLANT CELLS
organelle: (literally "little organ") a region within a cell where specialized metabolic tasks occur; typically surrounded by a membrane.
- plastids: a group of organelles characterized by a double membrane envelope and a complex of internal membranes. Plastids contain DNA and replicate autonomously.
- proplastids: specialized for dividing to form new plastid, usually found in meristematic cells.
- chloroplast: contains chlorophyll, internal membranes organized as grana, specialized for photosynthesis.
- [[etioplast: a chloroplast that develops in the absence of light.
- chromoplast: contains red, orange, or yellow carotenoid pigments that are water insoluble, impart color to fruits, etc.
- amyloplast: contains large amounts of starch, but no chlorophyll, specialized for storage.
- elaioplast: contains oil droplets, usually found in fruits or seeds.
- vacuole: membrane bound organelle that typically occupies a large volume of the cell cytoplasm. Vacuoles may contain:
- anthocyanins: red, blue or purple pigments that are water soluble.
- tannins: phenolic compounds than complex with protein; function in plant defense.
- calcium oxalate. Types are classified according to shape and include:
- raphide crystals: needle-like, may inhibit herbivory.
- druse crystals: granular.
cell wall: a rigid layer of cellulose and other polysaccharides, proteins and sometime lignin on the outside of the plasma membrane of a plant cell.
- primary cell wall: a cell wall layer deposited while a cell is growing; typically extensible.
- secondary cell wall: innermost layer of a cell wall deposited after cell enlargement has ceased, often lignified.
- Casparian strip: a band of suberin within the anticlinal walls of endodermal and exodermal cells.
- cuticle: a water repellent layer that coats the outer cell walls of the epidermis on aerial parts of plants, composed of cutin with a surface coating of wax.
- mucigel: a slime sheath secreted by roots.
- polysaccharide: a polymer composed of sugars.
- cellulose: the structural (microfibrillar) portion of the plant cell wall. Cellulose is a polymer of glucose.
- hemicellulose: the alkali-soluble portion of the cell wall matrix.
- pectin: the hot-water-soluble portion of the cell wall matrix.
- lignin: an aromatic polymer that rigidifies may secondary cell walls. Ligin is stained red by phloroglucinol solutions.
intercellular connections:
- plasmodesmata): cytoplasmic channels lined with plasma membrane that connect the protoplasts of adjacent cells across the cell wall.
- pit: a region where the secondary cell wall is absent, but the primary cell wall is present.
- simple pit: a pit that is not bordered, may be round or slit-shaped.
- circular-bordered pit: a round pit with a thickened margin.
TISSUES AND CELL TYPES OF THE PLANT BODY
ground tissue system: tissues derived from the ground meristem. All are simple tissues composed of a single type of cell, which is named after the tissue. The tissues of the ground tissue system include:
- parenchyma: tissues composed of cells with thin primary cell wall. Types include:
- chlorenchyma: contains chloroplasts and functions in photosynthesis.
- aerenchyma: contains large intracellular air spaces and functions in gas exchange.
- endodermis: characterized by a suberized Casparian strip; regulates transport of materials into the vascular bundles of most roots and some leaves and stems.
- storage parenchyma: characterized by large accumulations of storage products such as starch, protein, oil, hemicellulose, or water.
- collenchyma: tissues composed of cells with unevenly thickened primary cell walls that strengthen growing organs. Types are classified according to the arrangement of the wall thickenings and include.
- angular collenchyma: cell wall is thickest in the corners.
- lamellar collenchyma: cell wall is thickest on two opposite sides.
- lacunar collenchyma: cell wall is thickest in the corners, intercellular air spaces present.
- sclerenchyma: tissues composed of cells with thick, secondary cell wall that are usually lignified. Types are classified according to cell shape and include:
- fiber: long, straight and thin, often occurring in bundles. Sometimes called "extraxylary fibers" to distinguish them from xylary fibers, which look similar, but have a different evolutionary origin.
- sclereids: variable in shape, but not like fibers. Types are classified according to shape and include:
- brachysclereids: also called stone cells, length and width nearly equal.
- astrosclereids: star shaped, with several projecting arms.
- trichosclereids: hair-like, similar to a fibers, except branched.
- macrosclereids: column shaped, longer than wide.
- osteosclereids: bone shaped, elongated with swollen ends.
- fiber: long, straight and thin, often occurring in bundles. Sometimes called "extraxylary fibers" to distinguish them from xylary fibers, which look similar, but have a different evolutionary origin.
- secretory structures:
dermal tissue system: Tissues derived from the protoderm or cork cambium that cover the surface of the plant body. The dermal tissues are complex (composed of several cell types) and include:
- epidermis: a complex tissue that is usually a single cell layer thick and composed of the following cell types.
- pavement cells: the least specialized cells of the epidermis (i.e. cells that are NOT specialized as guard cells, root hairs, trichomes, etc.). May secrete a cuticle.
- guard cells: cells that surround and control the size of stomatal pores.
- stomata): an opening defined by pairs of guard cells that controls gas exchange and water loss.
- subsidiary cells: cells adjacent to guard cells that are distinct in appearance from ordinary epidermal cells.
- trichomes: cells that project from the surface of the epidermis. Types include:
- unicellular trichome: consists of one cell.
- multicellular trichome: consists of several cells.
- secretory (glandular) trichome: secretes a substance.
- root hair: specialized unicellular trichome found in roots.
- Specialized epidermal cells and structures:
- multiple epidermis: an epidermis that is more than one cell layer thick.
- protoderm.
- hypodermis: a layer or layers of cells beneath the epidermis that is derived from the ground meristem, but distinct in appearance from adjacent ground tissue. May be called an endodermisif it has a Casparian strip.
- velamen: a multistratose epidermis found in aerial roots.
- bulliform cells: enlarged epidermal cells that facilitate leaf rolling in response to water stress.
- lithocysts: literally translated "rock cells", cells containing a granule of calcium carbonate called a cystolith.
- silica cells: cells in the epidermis of grasses that contain silica deposits.
- nectary: a gland that secretes nectar.
- multiple epidermis: an epidermis that is more than one cell layer thick.
vascular tissue system: Tissues derived from the procambium or vascular cambium that transport water and photosynthate. The vascular tissues are complex (composed of several cell types) and include:
- xylem: the water-conducting tissue of plants.
- tracheary element: a conducting cell of the xylem, characterized by an elongated shape and lignified secondary cell wall.
- vessel element: a tracheary element with perforation plates.
- perforation plate: the end wall of a vessel element where the secondary cell wall was not deposited and the primary cell wall has been digested.
- foraminate: contains several round perforations.
- scalariform: contains several elongated perforations such that the remaining cell wall resembles the rungs of a ladder.
- simple: contains a single perforation.
- vessel: a long tube of vessel elements connected by perforation plates
- tracheid: a tracheary element that lacks perforations plates, water flows from between tracheids through pits.
- fiber tracheid: a cell in the xylem that is intermediate between a tracheid and a libriform fiber.
- libriform fiber: a cell in the xylem that is very long and thin and has simple pits, sometimes called "xylary fibers" to distinguish them from extraxylary fibers, which look similar, but have a different evolutionary origin.
- phloem: the photosynthate-conducting tissue of plants.
- sieve element: a conducting cell in the phloem.
- sieve-tube member: a sieve element with perforation plates, characteristic of angiosperms.
- sieve plate: the end wall of a sieve-tube element that is perforated by sieve plate pores.
- sieve plate pore: an enlarged plasmodesma that perforates a sieve plate.
- sieve tube: a long tube of sieve elements (also called sieve tube members) connected by sieve plates.
- sieve cell: a sieve element that lacks perforation plates, characteristic of gymnosperms.
- p-protein: a stringy protein within sieve elements that blocks sieve plate pores when the sieve tube is damaged.
- companion cells: a cell in the phloem that is connected to a sieve-tube member by numerous plasmodesmata.
- albuminous cells: a cell the phloem that is connected to a sieve cell by numerous plasmodesmata.
DEVELOPMENTAL TERMINOLOGY
- leaf primordium: arises at the shoot apical meristem.
- axillary bud primordium: arises in the axil of a leaf primordium.
- lateral root primordium: arises in the pericycle.
Planes of cell division:
- anticlinal: perpendicular to the surface.
- periclinal: parallel to the surface.
MERISTEMS
apex: the tip of something, usually a shoot, root or leaf. meristematic region: a general zone in which cell division is frequent. initial cell (=stem cell): a cell that, when it divides, leaves one of the daughter cells in the apical meristem.
- apical initials: initial cells in the root or shoot apical meristem.
- apical cell: the single initial in the apical meristems of most seedless vascular plants.
primary meristem: a meristem that is present in the embryo of a plant; generally responsible for increase in the length of plants
- root apical meristem: a meristem located at the apex of a root.
- root cap: a thimble-shaped mass of cells that covers the root apical meristem.
- open: no distinct boundary separates the root cap from the root proper.
- closed: root cap is distinct from the root proper.
- shoot apical meristem: a meristem located at the apex of a shoot.
- tunica: the outer layer(s) that divide only anticlinally.
- corpus: the inner layers that divide anticlinally or periclinally.
- apical dome: the part of the apical meristem interior to the leaf primordia.
- vascular cambium: a sheet-like meristem that produces secondary xylem and secondary phloem.
- residual procambium: procambium located between mature xylem and phloem.
- fascicular cambium: arises within vascular bundles.
- interfascicular cambium: arises between vascular bundles.
- fusiform initial: an elongated cell in the vascular cambium, produces elements of the axial system.
- ray initial: an isodiametric cell in the vascular cambium, produces elements of the ray system.
- storied cambium: fusiform initials aligned with one another.
- non-storied cambium: fusiform initials not aligned with one another.
- phellogen): a sheet-like meristem that produces cork.
primary meristematic tissue: a group of cells beneath the apical meristem that has become distinct in appearance from neighboring groups of cells, a precursor to one of the tissue systems:
- procambium: develops into the vascular tissue system.
- protoderm: develops into the dermal tissue system.
- ground meristem: develops into the ground tissue system.
THE ORGANIZATION OF ROOTS STEMS AND LEAVES
vascular bundle (vascular strand): a strand of tissue containing primary xylem and primary phloem.
- axial bundle: a major vascular bundle in the shoot or root.
- leaf trace: a vascular bundle that connects a leaf to the axial vascular system.
- leaf gap: in a siphonostele, a break in the vascular cylinder above the point where a leaf trace arises.
- vein: a vascular bundle in a leaf.
- sympodium: an axial bundle and its leaf and branch trace.
Bundle types based on arrangement of xylem and phloem:
- collateral bundle: contains a mass of phloem toward the exterior and a mass of xylem toward the interior
- bicollateral bundle: contains one mass of xylem and two masses of phloem, one toward the interior and one toward the exterior.
stele: the arrangement of vascular bundles in roots and stems.
- protostele: a single central vascular bundle.
- polyarch: a protostele with many arms of xylem, most common in monocots.
- siphonostele: a cylinder of vascular tissue with a central parenchymatous pith.
- dictyostele: a siphonostele with numerous leaf gaps; superficially appears to be composed of vascular bundles.
- eustele: a ring of vascular bundles surround a pith.
- atactostele: a complex three dimensional network of vascular bundles; superficially bundles appear to be scattered.
leaves:
- palisade mesophyll: the region of ground tissue in a leaf where the chlorenchyma cells are elongated and arranged perpendicular to the epidermis, usually in the upper half of the leaf.
- spongy mesophyll: the region of ground tissue in a leaf where parenchyma cells are branched and intercellular air spaces are extensive, usually in the lower half of the leaf.
- bundle sheath: the layer of tightly-packed cells that surround the vascular tissue in leaves.
- bundle sheath extension: a group of cells that connect a vein to the epidermis in a leaf.
- abscission zone: a region of the petiole
- protective layer: the layer of cells that produce suberin to seal the petiole before abscission.
- separation layer: the layer of cells that secrete cell wall degrading enzymes forming a weak point where an abscising leaf can drop off.
- epidermis: the epidermis contains stomata arranged in one of the following ways:
- amphistomatic: stomata in upper and lower epidermis.
- epistomatic: stomata in the upper epidermis only.
- hypostomatic: stomata in the lower epidermis only.
- clustered stomata: stomata occur in groups.
- sunken stomata: stomata located below the surface of the epidermis.
- stomatal crypts: a pit containing several stomata.
roots and stems:
- cortex: ground tissue between the vascular bundle and epidermis.
- pith: ground tissue in the center of a stem.
- pericycle: in roots, the layer of cells between vascular tissue and endodermis that gives rise to lateral roots and vascular cambium.
flowers, fruits and seeds:
- Floral organs: all are modified leaves.
- receptacle: the tip of a floral stem, supports the floral organs.
- sepal: outermost and most leaf-like, usually encloses the rest of the flower in the bud.
- petal: interior to sepals, usually conspicuous to attract pollinators.
- stamen: interior to petals, produces the pollen.
- filament: stalk-like portion of the stamen.
- anther: pollen-bearing portion of the stamen.
- pollen sac: one of four cavities in an anther that contain pollen.
- pollen: the male gametophyte, includes two cells:
- tube nucleus: located within the tube cell.
- generative cell: divides to form two sperm.
- tapetum: a layer of nutritive cells that lines the pollen sac.
- pistil: innermost, bears the ovules, may occur singly or in clusters.
- stigma: the portion of the pistil that receives the pollen.
- style: the portion of the pistil through which the pollen tube grows.
- ovary: the portion of the pistil that bears the ovules.
- carpel: a unit of the pistil consisting of a single modified leaf, a simple pistil consists of one carpel and a compound pistil consists of fused carpels.
- locule: a cavity containing ovules, in a compound ovary there is one locule per carpel.
- ovule: an embryo sac with egg surrounded by nucellus and two integuments.
- embryo sac: the eight-celled megagametophyte of flowering plants.
- integuments: the outer protective layer of the ovule.
- micropyle: an opening in the integuments through which a pollen tube enters.
- nucellus: the inner nutritive layer of the ovule.
Classification of flowers by ovary position:
- hypogynous: sepals, petals and stamens attached to the receptacle below the ovary.
- epigynous: sepals, petals and stamens attached to the top of the ovary.
- perigynous: sepals, petals and stamens attached to a hypanthium.
- hypanthium: a cup-shaped extension of the receptacle.
Fruits and seeds:
- seed: a mature ovule, includes:
- embryo: a young plant present in the seed before germination.
- radicle: the root portion of the embryo.
- plumule: the shoot portion of the embryo.
- cotyledon: the first leaves of an embryo, may or may not resemble true leaves.
- coleorhiza: in monocots, a sheath that covers the radicle.
- coleoptile: in monocots, a sheath the covers the plumule.
- seed coat: the outermost layer of a seed, develops from the integuments.
- endosperm: a triploid nutritive tissue that develops in the ovule, may be absorbed by the before the seed matures.
- embryo: a young plant present in the seed before germination.
- fruit: a mature ripened ovary. In practice, most plant parts that contains seeds are fruits.
- funiculus: the stalk that attaches a seed to the inside of a fruit.
ENVIRONMENTAL MODIFICATION
- sun/shade leaves: leaves in the sunnier parts of trees are distinct from more shaded leaves.
- air/water leaves: in aquatic plants, leaves that grow below the water surface are distinct from those formed above the surface.
- heteroblastic leaves: leaves produced during one stage of development are distinct from those formed at another stage, for example leaf from may change when a plant flowers.
ORGAN SPECIALIZATIONS
aerial root: a root that grows in air, common in epiphytes. cataphyll (=bud scale): a leaf modified to protect a dormant bud.
- endomycorrhizae: fungal mycelia are internal.
- ectomycorrhizae: fungal mycelia are external
phyllode: a leaf that consists of an enlarged midrib and lacks blades.
WOOD AND BARK
- axial vessels: vessels of the axial system, may be:
- clustered: several vessel occur in a bundle.
- solitary: vessels separated by other types of cells.
- axial parenchyma: parenchyma cells of the axial system.
ray system: cells elongated radially, develop from ray initials.
- uniseriate rays: rays that are one cell wide.
- multiseriate rays: rays that are more than one cell wide.
- homocellular rays: rays consisting on one type of cell.
- heterocellular rays: rays consisting of more that one type of cells, possibilities include:
- ray parenchyma: parenchyma cells of the ray system, may be:
- procumbent cells: elongated parallel to the ray.
- upright cells: elongated perpendicular to the ray.
- ray tracheids: tracheids of the ray system.
- ray parenchyma: parenchyma cells of the ray system, may be:
- phellem): cells produced by the cork cambium that have suberized cells walls and are dead at maturity.
- lenticel: a region of the periderm where cells are loosely packed, allows gas exchange.