Topic 6 - The histology of plant organs (regarding to nutrition value and digestibility)

Question 1

Histology of the root

Answer 1

Root tip: Initial stem cells → meristematic tissues → permanent tissues

Protection: root cap

Question 2

The root cap

Answer 2

A parenchymal tissue with amyloplasts which sediment to the lower side of the cell

Accumulation of Ca++ → auxin release → gravitropism

Question 3

Mature region of the root cap

Answer 3

Dermal tissue (rhizodermis)
Cortex
Stele

Question 4

Dermal tissue (root cap)

Answer 4

Generally one cell layer

Asymmetrci divisions → root hairs (extensions of dermal cells) → increase absorption surface area

Root hairs live only a few days

Question 5

Cortex

Answer 5

Multiple layers of parenchymal cells (stored nutrients, starch, crystals, latex) or aerenchyma (for water plants)

Transport water and minerals to the vessels

Question 6

Stele

Answer 6

Outer most layer is the pericycle → produce branch roots and secondary dermal tissue

Pith: parenchymal cell layers for storage

Simple xylem and phloem bundels alternate with each other

Question 7

older root

Answer 7

Cellular division in the pericycle → new root cap and root tissues

Generally decreasing digestibility (higher proportion of cell with thickened walls)

Question 8

Pericycle activity

Answer 8

Production of vascular cambium → secondary transport vessels → thickening of the root

Question 9

Tissues of storage roots

Answer 9

Generally lack of mechanical tissues (e.g.: carrot)

Sugar beet → cambia are arranged in concentric circles

More parenchymal cells → better digestibility

Question 10

Histology of the stem

Answer 10

Shoot apex: initial cells (tunica, corpus) → meristems → permanent tissues

No protective cell layer

Question 11

Epidermis (stem)

Answer 11

Generally one cell layer

Similar to the leaf, but less stomata

Cuticle, wax, appendages

Question 12

Cortex (stem)

Answer 12

Monocots - not differentiated into cortex and pith → storage parenchyma

Dicots - below dermal tissue: chlorenchyma, mechanical tissues and less storage parenchyma

For water plants: aerenchyma

Question 13

Stele (stem)

Answer 13

Pith (parenchymal) + vascular bundles with rays

If hollow → pith cavity

Question 14

Secondary growth (stem)

Answer 14

Rare in monocots

Four major types in dicot plants

Secondary growth → higher proportion of lignified cells → decreasing digestibility

Question 15

Differentiation of the dermal tissues (stem)

Answer 15

Epidermis → periderm → rhytidome

Rupture, drop off

Tannins, resin → used as a spice or as medicine

Question 16

Histology of the wood

Answer 16

Soft wood: less fibers, less lignification
Hardwood: more fibers, strong lignification
Heartwood: no water conduction parenchyma cells block the vessels
Sapwood: conduction of water and nutrients

Question 17

Histology of leaves

Answer 17

Determined growth - meristematic activity stops

Question 18

Young leaves

Answer 18

Primordia

Question 19

Dermal tissue (leaves)

Answer 19

Mainly one cell layer

Cuticle, wax, appendages
Hypostomatic (underneath)
Epistomatic (upper surface)
Amphistomatic (both)

Question 20

Nervation (leaves)

Answer 20

Transport, mechanical stability

Closed vascular bundle + bundle sheath

Question 21

Mesophyll (leaves)

Answer 21

Middle leaf

Homogenous

Heterogeneous

Assimilation, gas exchange

Secretory cavities, crystals

Question 22

Kranz (leaves)

Answer 22

Leaf anatomy

In C4 plants: bundles surrounded by two rings of cell with different plastds

Better CO2 fixation

Species are tolerant to drought

Question 23

Tissues of the flower

Answer 23

Sepals, petals, tepals
Stamens, pollen
Pistil
Fruits
Seeds

Question 24

Sepals, petals, tepals

Answer 24

Similar structure to leaves

One layered epidermis with papillae and hairs

Pigments in vacuoles → e.g. carotenoids → nutrient supply

Lack of mechanical tissues

Altogether poor nutritive value

Question 25

Stamens, pollen

Answer 25

Stamens are modified leaves Pollen wall → outer layer consists of sporopollenin Chemically very stable Water-solulbe proteins → allergy

Question 26

Sporopollenin

Answer 26

Biosynthesised of fatty acids, phenolics and carotenoids

Question 27

Pollenkitt

Answer 27

Adhesive material around the pollen

Question 28

Pistil

Answer 28

A modified leaf Stigma Tissue of the ovary → fruit wall Chlorenchyma → storage parenchyma

Question 29

Stigma

Answer 29

An epidermis with cuticle and glandular hairs → sticky surface to catch and trap pollens

Question 30

Fruits

Answer 30

Three regions Exocarp Mesocarp Endocarp Secretory cavities

Question 31

Exocarp

Answer 31

One cell layer covered with cuties, wax, hairs, or it can be lignified

Question 32

Mesocarp

Answer 32

In fleshy fruits it's a multilayered parenchyma storing pigments, and nutrients (fatty acids, CH, proteins) In dried fruits it consists of sclereids Can be fused to endocarp

Question 33

Endocarp

Answer 33

One or multilayered cells Can be fused to mesocarp Hard, stoney endocarp consists of sclereids

Question 34

Taxa (and fruit) specific tissues

Answer 34

Fleshy fruits (e.g. berry): storage parenchyma Dried fruits (e.g. capsule): sclerenchyma For some types (e.g. drupe) the two types are combined

Question 35

Fibers (fruit)

Answer 35

Contraction helps fruits to split open (e.g. pods)

Question 36

Seeds

Answer 36

Seed coat + (perisperm (2n)) + endosperm (3c) + embryo Multilayered storage parenchymal cells

Question 37

Taxon specific cells (seeds)

Answer 37

Seed coat can be covered with cuticle, wax, mucilage

Question 38

Parenchyma + sclereids (seeds)

Answer 38

One layer, multilayered dry or fleshy Pigmented cells with tannins Thick seed coat → digestive problems (shelled seeds)

Question 39

Taxonspecific composition (seed)

Answer 39

Carbohydrates, proteins, fatty acids → seed used in animal nutrition (cereals, pulse crops)

Question 40

Absent endosperm and perisperm

Answer 40

Nutrients stored in the embryo (cotyledons)

Question 41

Thin hemicellulose walls

Answer 41

Good digestibility Metabolised rapidly → release of nutrients