Plants

Tissues, Transport & Growth Factors

Angiosperms – flowering plants Angiosperms are divided

into two categories– Monocotyledon

Water lilies, onions, orchids, grasses, wheat, corn

– Dicotyledon Maples, oaks, cacti,

peas, beans, potatoes

A cotyledon is a seed leaf that stores carbohydrates for the seedling

Plant Structure and Function

Meristems– Regions of the plant where

some cells have the ability to divide repeatedly by mitosis.

– Root and shoot tips this area is called apical meristems.

This is referred to as primary growth.

• Lateral meristems are cylindrical regions in roots and stems where growth can occur.

• This is referred to as secondary growth.

• Cell division within the vascular cambium will become xylem and phloem…more on those later.

Plant Tissues3 types

1. Dermal Tissue System– Epidermis - outermost layer, waxy non cellular

layer called the cuticle– Periderm created in secondary growth areas of

the roots and stems. Usually dead cells that facilitate protection of inner cells (ex. bark). When the plant matures

2. Ground Tissue System– Make up all internal non-vascular regions

3. Vascular Tissue System – xylem and phloem…coming soon.

Ground Tissues Parenchyma

– Living ground tissue.– Location of photosynthesis and

storage of nutrients and comprises bulk of plant body (pith).

– Cacti – large amounts of parenchyma to store water

Collenchyma– Living ground tissue.– Thickened cell walls provide

flexibility to the plants and these areas provide support for the plant’s primary growth regions.

– Celery stalks

Ground Tissues Sclerenchyma

– Dead ground tissue.– Supports mature plants

and assists in development of hard shells (nuts and spines).

– Secondary cell wall composed of cellulose and lignin for strength and rigidity.

– Pear

All three types of tissues in cross and longitudinal sections

Transport in Plants Malpighi in the seventeenth century

– Stripped bark and outer layer of tissue off of a tree with a swelling above the stripped area with sweet water

– Observations Water not transported in this outer layer Sweet water was nutrients going down to be stored

– Roots continued to live due to prior stored nutrients

Translocation – movement of materials in a plant from one area to another, at this point, had been discovered.

Welcome to the world of the xylem and phloem.

Transport in Plants Xylem Tissue

Formed when certain plant cells thicken, providing structural support to the plant.

This tissue actually works when it is dead as the strong cylinders left behind are stacked one atop another to form hollow tubes up the plant.

– Tracheids (pits) and vessels (longer, fewer openings)

Xylem cells carry water and minerals from roots up to the stem and leaves.

Phloem Tissue Formed of cells that contain living

tissue. Cell walls are porous allowing

exchange of materials to neighboring cells.

Phloem cells transport organic materials including nutrient and hormones throughout the plant.

LeavesWhy are leaves important?

– What do they do?Blades are located at nodes

along the stem– Stem to blade is called a petiole– Petiole branches into net venation

(dicots), parallel venation (monocots).– Leaves can be single, undivided blades

called simple leaves– Leaves can be divided into two or

more leaflets called compound leaves. (p.502, fig. 2 & 3)

Leaves Stomata

– Where the action happens for a leaf and is controlled by guard cells Mesophyll

– Palisade mesophyll Cells are tightly packed, right under the upper epidermis Primary photosynthetic site

– Spongy mesophyll Between palisade mesophyll and lower epidermis with lots of spacing to allow gasses to quickly diffuse

LeavesAdaptations

– Abiotic Broad leaves trap low light emissions but die in open fields Early spring leaf spread Conifers keep leaves year round so energy is not wasted also

reduce water loss due to thick cuticle

Roots Primary root Secondary

roots (lateral) Two main types of roots Tap

and Fibrous Adventitious roots are out-

of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots.

Root Cap is protective Root hairs increase surface

area

RootsSurrounding the vascular cylinder is the

pericycle (meristematic tissue leading to secondary roots) and then the endodermis (acts as a boundary layer).

Roots

Stems Two main types

– Herbaceous Thin, soft, green, short lived and contain

little or no wood– Woody

More traditional dicot trees In the first year of growth both will

look similar with meristematic growth at lateral ends but vascular tissue within will be different.

Cambium is where new xylem and phloem are being created…as such the oldest xylem is more towards the middle of the stem with the newest growth beside the cambium. Similarly, the oldest phloem is out near the bark and the newest phloem is beside the cambium.

Reproduction Flowers

– Angiosperms are flowering plants

– Main goal is pollination with indirect connection to protect and distribute seeds.

Seed Growth and Development– Seed has an embryo, nutrients

for embryo and protective covering

If the plant is a monocot, one seed leaf (cotyledon) develops, if it is a dicot, two seed leaves develop

Plant Propagation Layering is a means of plant propagation

in which a portion of an aerial stem grows roots while still attached to the parent plant and then detaches as an independent plant– Raspberries, gooseberries, rubber plant

Grafting is a technique whereby tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together.– In most cases, one plant is selected for

its roots and this is called the stock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion.

Plant Propagation Plant cutting, also known as

striking or cloning, is a technique for vegetatively (asexually) propagating plants in which a piece of the source plant containing at least one stem cell is placed in a suitable medium such as moist soil or potting mix. The cutting produces new roots, stems, or both, and thus becomes a new plant independent of the parent.– Geraniums, begonia, violets, horse radish

Transport in PlantsRoot Pressure

– Plant roots build up pressure that forces water upward1. Water is actively pumped into

xylem tissues2. Minerals and ions actively

pumped into roots and water follows– Either way water in the xylem

builds pressure and forces water up

– This process is effective in short plants but if our tree is 100m tall this can equate to 1000 kPa!

Transport in PlantsCapillary Action

– Relies on adhesive properties of water

– If you touch a capillary tube to the surface of water the water will rise up the tube because the polarity of the capillary walls attracts water molecules, which cling to the side of the tube.

– The more narrow the tube, the higher the water will climb

– Very narrow vessels will facilitate a height of 60 to 90 m

Transport in PlantsCohesion-tension or

transpiration pull– Each molecule of water vapour

evaporates from a stomata in the leaf to the air, and another molecule is right behind the first

– Transpiration is the key (which means water loss) however it has been found that water will move even if transpiration is not occurring

– Widely accepted however how does water move up a tree in the spring?

– Mineral Transport – considered different but not separate from transport of water

Believed to be taken in through active transport and then incorporated with water.

Transport in Plants Transport in phloem is still not fully understood:

– Phloem cells must be living for transport to occur– Material can move through the phloem in more then one

direction at the same time Radioactive carbon and phosphorous in geraniums

– Phloem may transport large amounts of material rapidly within a plant

Pumpkin can gain 5.5kg (12 pounds) in less than a month– Oxygen deficiencies and low temperatures inhibit but do not

stop phloem transport– Characteristics of movement of a particular substance may

vary from one plant to another Carbohydrates enter cotton bolls during the day, but tend to enter date

fruits at night.

Transport in Plants Mass-flow theory – phloem

– Relies on combination of osmosis and pressure dynamics to explain movement of materials

Sucrose is manufactured in leaves and it travels to other parts of the plant for storage (starch) or used by the plant (plant tissues)

Transportation in Plants– This theory is widely accepted however pressures involved in

mass flow should lead to higher internal pressure within the phloem then what is actually observed.

– Another problem is that it is not clear that mass flow can account for the speed or distance over which transport in phloem occurs.

– Also simultaneous bi-directional transport and low oxygen and low temperature meaning slow transport are not explained.

However, these are addressed by saying that the living tissue of the phloem itself plays a role in movement of organic materials possibly by utilizing cytoplasmic streaming

External Plant Growth Factors Light Requirements

– Photoperiodism – amount of light that a plant requires to grow.

Soil Nutrients– Macronutrients

Obtained primarily from carbon dioxide and water (95%) C, H, O, N, K, P, Ca, Mg, S

– Micronutrients Fe, Cl, B, Mn, Zn, Cu, Mb, Ni

Nitrogen– Plants that make a lot of proteins need a lot of N– Organic matter ammonium nitrate ions (NO3

-) which is then used by the plant

– Atmospheric nitrogen ammonium nitrate ions which is then used by the plant

Symbiotic Relationships and root nodules

Internal Plant Growth Factors Auxins

– Can stimulate plant growth, usually cell elongation.– Influence plants dropping fruits and leaves.

Gibberellins– Act like auxins– Bolting cause the stem to elongate just prior to the plant flowering

Cytokinins– Stimulate cell division

Ethylene– Fruit ripening– Released prior to rise in cellular respiration that corresponds to the mass

conversion of starch to sugars. Abscisic Acid

– Inhibitor which acts by promoting closure of the stomata.