Topic 5 - The main tissues (regarding to nutrition value and digestibility) Flashcards
Tissue
Determined as aggregations of morphologically, ontogenetically and functionally similar cells
Simple tissue
Tissue composed of a single cell type (ground tissues)
Complex tissue
Tissue composed of more than one cell type (vascular tissue)
Plant tissue systems
A functional unit of tissues – same functions but in different parts of the body, or in different growth stages
Meristematic Permanet o Dermal tissue o Ground tissue o Vascular tissue
Meristematic cells
Differentiation → primary body (permanent tissues)
Tissues of the primary body → cells become meristematic again dedifferentiation → secondary meristems (e.g.: cutting the stem)
Secondary meristems → redifferentiation → secondary body (vascular tissue, repair wounds)
Meristems
Merizein (in greek) = to divide
Dividing, undifferentiated cells with isodiametric (equal in all directions) or fusiform shape
Thin cell wall, large plasma content and high metabolic activity
Initial cells (stem cells) → meristems → permanent tissues (primary body)
Dedifferentiation of permanent tissues can also produce meristems
Functions of meristems
Elongation and thickening of stem and roots
Production of lateral roots
Thickening of dermal tissues
Dermal tissues
Covers the external part of the plant
Generally one, but often multiple cell layers
Primary and secondary dermal tissues
Functions of dermal tissues
o Protection (against herbivores)
o Adsorption of water/minerals
o Water retention
o Gas exchange
Primary dermal tissue
Epidermis
Rhizodermis
Epidermis
Primary dermal tissue of stem an leaves
Epidermal cells + stomata
Tile-like cells with varied shape, no intercellular space and large vacuoles
For monocot species: cells with corks and silicic acid → roughness
The outer cell wall can be covered with cutine, wax or cork → deceasing digestibility
No chloroplastids
Stomata
Singular: stoma
Gas exchange, transpiration
Even 100-300 stomata/mm2
Subsidiary cell: water and ion reservoirs
Major stomata types
Amaryllis type
o bean shaped guard cells, in cross section they have triangular shape, with subsidiary cells – most common type, mainly in dicots
Grass type
o dumbbell shape guard cells
Epidermal appendages
Papillae
Trichromes
Emergences
Papillae
Protrusions of epidermal cells
Petal cells are rounded and soft, but for grass and sedge plant they are sharp and coarse (silicic acid, lignin) - irritation
Trichromes
Single-celled or multicellular outgrowths irritation, bezoars, rough texture animals reluctant to eat Increase water retention Bristle hairs Clinging hairs Helps dispersal Glandular hairs – toxin excretion
Emergences
Dermal and ground tissues together
Prickles - protection, mechanical damage
Rhizodermis
Root epidermis
- Primary dermal tissue of young roots
- Major difference (in contrast with the epidermis): presence of root hairs and the absence of stomata, cuticle and chlorophylls
- Absorb water and nutrients
- Multiple cell layers are possible
Secondary dermal tissues
Secondary growth increase girth (thickness) → epidermis ruptures
A layer of cork cell produced of the cortex below the epidermis
Later cork layers multiplied (phellem) as a result of cell devision and produce the secondary dermal tissue (=periderm)
Accumulation of secondary metabolites in bark (tannic acid, glycosides)
Tertiary dermal tissue
Dermal tisses produced of the phloem
= rhytidome
Ground tissues
Parenchyma
Secretory tissues
Supporting or mechanical tissues
Parenchyma
The most abundant tissue with slightly differentiated cells
More specialized cells evolved from parenchyma: de- and redifferentiation → secondary tissues
Cells are isodiametric, have only primary wall, large vacuoles and prominent intercellular space
Function of parenchyma
Basic metbaolism
Storage
Aeration
Major types
Chlorenchyma
Storage parenchyma
Water storage parenchyma
Aerenchyma
Chlorenchyma
Assimilatory parenchyma
Chloroplast containing parenchymal cells photosynthetic function
Palisade
Spongy
Storage parenchyma
Large number of leukoplastids - fatty acids, starch, protein —> high nutritive value (food for animals)
Water storage parenchyma
Tissues of succulent plants living in arid habitaits
Cells have thin wall, large vacuoles, and water is absorbed in the form of mucilage
Aerenchyma
Parenchyma of water plants and species living in moist habitats
Enlarged intercellular cavities
Importance for the oxygen supply and gas exchange
Low nutrient value
Secretory tissues
Intra- and extracellular secretion
Endogeneous and exogenous secretion
Thin walled cells with numerous nuclei, and many organelles
Excretion of secondary metabolites → favours pollinators, or a defence mechanism
Intracellular secretion
Metabolites are secreted into vacuoles or cell wall
Extracellular secretion
A group of cells secrete metabolites into the intercellular space
Endogeneous secretion
Secretory cavities
Secretory ducts
- For protection and to seal wounds (prevent insect and disease entry)
- Resin ducts
- Gum ducts
- Latex vessels (laticifers)
Exogeneous secretion
Secretion to epidermal surface through glands
Hydathodes
- Secretes water through pores (open water stoma)
Salt glands
Nectar glands (nectaries) - Sugar-rich liquid with amino acids for pollinators
Supporting or mechanical tissues
Providing mechanical strength to the growing organs
Differentiates usually from parenchyma cells with cell wall thickening
Types of supporting or mechanical tissues
Collenchyma
Sclerenchyma
Collenchyma
Colla (in latin) = glue
Characteristic supporting tissue of your dicot plants
Cells are elongated and contain living cytoplasm
High tearing resistance → provides flexibility
Cells are considerably but unevenly thickened
Sclerenchyma
Scleros (in greek) = hard
Composed of dead cell with evenly thickened cell wall
Lignin is deposited into the walls → low digestibility
Main cell types of sclerenchyma
Sclerenchyma fibers
Sclereids
Sclerenchyma fibers
Extended cells often with tapering ends
Small cell lumen and thick wall
the longest plant cells
Economic value
Sclereids
Occur scattered or in clusters
Non-elongated, isodiametric cells
Sclereids are variable in shape
The vascular tissue system
Mosses - single transport cells (no thickening or lignification)
Vascular plant = vascular tissue
Complex tissue - conducting, parenchymal and sclerenchymal cells
Xylem
Wood
Conducts water and mineral from the root to the leaves
Composed primarily of dead cells
components in the xylem
Tracheids
Vessels
Wood parenchyma
Fibers
Tracheids
Elongate dead cells with tapering ends
Typical in ferns and gymnosperms
Specific cell wall thickenings
Vessels (xylem)
Consists of vessel elements
The wall is considerably thickened and lignified
Mainly in angiosperms
Vessel elements are short and broad → 10-20 cm size tubers or up to 2 m (oaks), or 5-10 (creepers)
Wood parenchyma
The sole living cells of the xylem with a rectangular shape
Role: storage and secretion
Fibers
Elongate cells with thick, lignified walls
Phloem
Bark
Conducting sugars, composed primarily of living cells
Component of Phloem
Sieve cells Sieve tubes Companion cells Fibers Phloem parenchyma
Sieve cells
similar to Tracheids, narrow, elongated, angular cells
Connects to each other with piths
Typical in ferns and gymnosperms
Sieve tubes
Consists of short and broad sieve-tube elements
Mainly in angiosperms
Longevity: 1-3 years
Sieve plate
Interface between two sieve tube elements
Companion cells
(albuminous cells)
Carry out all the metabolic functions of the sieve-tube elements
Regulate transport and metabolic processes
Fibers
Elongate cells with thick, lignified walls (industrial fibers)
Phloem parenchyma
Mainly food storage
Vascular bundles
Simple Compound Concentric Collateral Bundle-sheath
Simple vascular bundles
Xylem and phloem elements constitute separate bundles
Compound vascular bundles
Bundles are composed of both xylem and phloem elements
Concentric vascular bundles
Xylem and phloem elements form concentric rings in gross section
Collateral vascular bundles
Bundles containing xylem and phloem adjoining each other side by side
Bundle-sheath
Parenchymal or sclerenchymal ring around the vascular bundles
Temporary storage for nutrients, protection of bundles
