07 PPT NOTES Vascular Plant Growth

Lecture Notes

Basic plant tissues:

• Outer covering (Protoderm)

• Vascular tissue (Procambium, candy corn)

• Everything else (Ground meristem)

3 plant organs, these organs are not determined in their growth and location early on → Indeterminate growth

• Roots:

  • Prop: Help with erosion of the ground to dissipate it’s consequences. Advantageous in flooded areas

  • Storage → storing nutrients

  • Aerial → growing atop another tree to get sunlight

  • Buttress → provide structural support

  • Pneumatophores → lungs of the plant

• Leaves

  • Tendrils → modified leaves for climbing

  • Spines

  • Storage

  • Reproductive

  • Bracts → to attract pollinators

• Stems

  • Rhizomes → underground stems. Help the plant asexually reproduce

  • Bulbs

  • Stolons → overground reproductive stems

  • Tubers → storage stems

Plant growth:

Plant growth vs. Animal Growth

• Plants have indeterminate growth with the location of organs all over the place, animals have determinate growth with a plan of the location of organs.

• Plants have varying regions of maturity throughout the organism, whereas animals have the same level of maturity throughout.

• Plants exhibit apical base-polarity (shoot and root growth), whereas animals grow from the center.

  

  • Plant growth is done by meristems → a localized region of embryonic stem cells.

  • Primary Growth: growth that occurs at the tips of roots and shoots, leading to an increase in length (vertical growth). Driven by the apical meristems (Shoot Apical Meristems - SAM and Root Apical Meristems - RAM).

    • Involves three primary meristems:

      • Protoderm: Differentiates into the epidermis (outer covering).

      • Ground Meristem: Differentiates into cortex and pith, involved in support and storage.

      • Procambium: Differentiates into primary xylem and phloem (transport tissues), and vascular cambium.

    • Results in the formation of new tissues and the establishment of the plant's primary structure (roots, stems, leaves).

    Secondary Growth:

    • Refers to the growth that occurs laterally (thickness growth) in stems and roots.

    • Driven primarily by the lateral meristems, including the vascular cambium and cork cambium.

    • Vascular cambium produces secondary xylem (wood) and secondary phloem, increasing girth.

    • Cork cambium produces cork, contributing to the outer protective layer of the plant (bark).

    • More common in woody plants, allowing for structural support and increased vascular capacity.

    • Typically occurs after the initial growth from the apical meristems has already established the primary structure of the plant.

    Contrast:

    • Location: Primary growth occurs at the tips of stems and roots (apical), while secondary growth occurs in the lateral regions of stems and roots (lateral meristems).

    • Output: Primary growth increases the length of the plant, while secondary growth increases the width of the plant.

    • Timeframe: Primary growth happens first in the life of the plant and continues as long as the plant is growing. Secondary growth usually occurs after primary growth has formed a solid structure.

    

    • Shoot growth is fueled by shoot apical meristems (SAM)

      • SAM has three primary meristems that drive primary growth: Protoderm (Forms initial covering and leaves via anti-clinal division), Ground meristem (differentiates to parenchyma, collenchyma, sclerenchyma, and the cork cambium). Procambium (differentiates into vascular cambium, primary xylum and primary phloem)

      • SAM differentiates into two secondary meristems that drive secondary growth (secondary xylem, secondary phloem, and cork): Vascular cambium maintains embryonic capabilities and drives secondary growth of secondary xylem and phloem. Cork cambium maintains the rigidity of the outer covering after the SAM moves away from that growth by making cork.

    • Root growth is fueled by root apical meristems (RAM)

      • Exibits anti-clinal and peri-clinal division to account for damage to the root cap

      • Root cap is protected by mucous secretion.

How do cells accomplish this growth in the RAM and SAM?

1. Cells must be made: Mitosis

2. Elongation: How does it work?

   

   • Auxin (made in SAM) gets into the cell and stimulates proton pumps to pump H+ into the cell wall space

   • This makes the cell wall region more acidic which activates enzymes called expansins

   • Expansins cut the polyssacharides that form the cell wall to soften it

   • Water can now enter the cell wall due to higher solute concentration

   • The cell wall may now elongate.

3. Maturation: Differentiation into primary and secondary tissues.

Phototrophism: Plants bending towards towards the light due to increased auxin on the shaded side of the plant to trigger elongation towards the light.

Coordinating root and shoot growth:

• Auxin

• Cytokinins

  

How do plants show their age?

• Plants allocate resources for different priorities depending on the season

  • In the spring, the plant is dedicated to growth. The cells will appear bigger.

  • In the summer, the plant is dedicated to sexually maturing (making flowers and fruits). The cells will appear smaller.

  • The switch from big to small cells represents the transition from spring to summer. aka one year of growth.

BUG questions

What are the major plant organs?

• Roots:

  • Support the plant

  • Absorb water and nutrients from the soil

  • Store food

• Stems:

  • Provide support

  • Store nutrients

  • Transport water and nutrients between roots and leaves

• Leaves:

  • Primary site of photosynthesis

  • Capture sunlight

  • Exchange gases (oxygen and carbon dioxide) with the environment

Why are microphylls of nonvascular plants not considered leaves?

• Microphylls:

  • Small leaves with a single unbranched vein

  • Found in non vascular plants

  • They lack the complex structure and multiple vascular bundles typical of leaves in vascular plants.

  • They don’t have vascular tissue

What are 4 evolutionary adaptations (i.e. different types) of roots, stems, and leaves?

• Evolutionary adaptations of Roots:

  • Storage roots → store nutrients and starch ex: Potatoes

  • Aerial (strangler) roots → help them gather sunlight and compete with other plants for sunlight.

  • Prop roots → prevent erosion by anchoring the plant well

  • Pneumatophores → lungs of plants they help the plant get oxygen

  • Buttress roots → shallow roots that prevent it from falling over

• Evolutionary adaptations of Stems:

  • Rhizomes → Underground stems that store nutrients and can produce new shoots, allowing for vegetative reproduction. Shoots that extend horizontally for absorbing nutrients, structural support.

  • Tubers → The ends of rhizomes that store nutrients

  • Stolons → Extends above the ground and along the surface Ex: Strawberries

  • Bulbs → stores nutrients

• Evolutionary adaptations of Leaves:

  • Tendrils → modified leaves used for climbing to reach more sunlight

  • Spines → Used for protection ex: cacti

  • Storage leaves → Store nutrients as starch Ex: Aloe

  • Reproductive leaves → Individual leaf that can grow into a whole new plant

  • Bracts → Flower-looking, function is to attract pollinators.

What are 3 ways that plant growth differs from animal growth?

• Continuous vs Limited growth → Plants have indeterminate growth (they never stop growing). Animals have determinate growth (they stop growing).

• Apical-Base polarity → Plants grow from apical meristems from the shoot and root in a vertical fashion. Animals grow more unifrmly

• Different levels of maturity from region-to-region → some regions of the plants are older than other, and some are more sexually mature.

If you carved your name into a tree at eye level and returned many years later, what level would the carving be at? Explain.

• Apical-Base Polarity causes growth from the root and the shoot from the tip and base, the middle wouldn’t move.

• The carving would remain at eye level when you return to the tree after many years.

• Trees grow from the top (shoot apical meristem) and do not elevate lower sections.

• As the tree grows taller, only the upper part increases in height.

• The carving's position remains unchanged, retaining its original height.

What are the three main meristems of the SAM? What do each of them differentiate to? Do any of these tissues (after differentiation) then make more tissues of their own? What are these “secondary growth” tissues?

1. Protoderm (outer): Differentiates into the epidermis, which is the outer protective layer of the plant. Divides anticlinally (horizontal growth). Produces outer covering, forms leaves, protects the plant.

2. Ground Meristem: Differentiates into cortex and pith, providing support and storage functions. And Non-vascular tissues:

   • Parenchyma cells: Metabolic functioning cells. Involved in synthesis and storage.

   • Collenchyma cells: Early structural support to young tissues, alive, contain lignin which makes wood hard.

   • Sclerenchyma cells: Structural cells, contain thick, lignified walls.

   • Cork cambium:

3. Procambium: Differentiates into primary vascular tissues (xylem and phloem), which transport water, nutrients, and food.

• After differentiation, the vascular cambium can produce more vascular tissues as they form secondary growth.

• Secondary growth tissues include secondary xylem (wood) and secondary phloem, which contribute to the thickness and strength of the plant.

Describe two mechanisms that protect the RAM when moving through soil.

1. Mucilage Production: The RAM secretes mucilage, a slippery substance that coats the root tip, reducing friction and facilitating easier movement through soil.

2. Root Cap: The RAM is protected by a root cap, a specialized structure that covers and shields the meristematic cells at the tip of the root. The root cap helps to sense gravity and direction of growth while also cushioning the delicate cells against physical damage as the root pushes through the soil. Cells in the root cap divide in two ways as it pushes through the soil.

   • Peri-clinal division → increases thickness by adding layers.

   • Anti-clinal division → increases length by adding width.

Why does the root apical meristem have both anti-clinal division (sideways) and peri-clinal division (vertical) in the first layer of cells, while the shoot apical meristem has only anti-clinal division in the first layer?

The root apical meristem (RAM) employs both anti-clinal division (which is sideways) and peri-clinal division (which is vertical) in its first layer of cells. These divisions protect the root cap because it’s pushing through soil and needs protection.

1. Anti-clinal Division: It increases the number of cells in the layer and expands the root's width to accommodate soil movement.

2. Peri-clinal Division: It adds new layers of cells vertically, facilitating the extension of the root downward into the soil.

In contrast, the shoot apical meristem (SAM) has only anti-clinal division in its first layer. This is due to the need for the shoot to maintain its organized structure while growing taller, requiring width expansion without vertical cell layering in the initial layer. This allows it form other structures such as leaves and flowers.

After plant cells experience Auxin, they begin to pump H+ atoms in to their cell wall. What does this lead to? How does water pressure play a role? (need to learn water potential in plants before you can answer this)

After plant cells experience Auxin (hormone) released from the SAM, they initiate the pumping of H+ ions into their cell walls. This process leads to several important effects:

1. Cell Wall Loosening: The uptake of H+ ions in the cell wall, this causes a decrease in pH, activating expansins to cut the polysaccharides forming the cell wall, which weakens the rigidity of the cell wall, this allows water to enter the cell wall, making it easier for the cells to expand.

2. Increased Osmotic Pressure allows for water to enter the cell wall: The accumulation of H+ ions in the cell wall creates a gradient that allows for the influx of water into the cell, boosting its turgor pressure. The turgor pressure allows the cells to expand and elongate.

Role of Water Pressure:

• Water pressure is crucial as it helps maintain the cell's shape and firmness after expansion has occurred. The ability of plants to generate turgor pressure plays a vital role in their growth and structural integrity.

What is phototropism?

• Phototropism is the growth of plant organs in response to the direction of light.

• Plants bend towards light sources to maximize photosynthesis.

• This movement is mainly regulated by the hormone auxin.

• Auxin redistributes on the shaded side of the plant, promoting cell elongation.

• The result is that the plant bends towards the light.

• Growth towards the light (positive phototrophism)

• Growth away from the light (negative phototropism)

• Auxin will always be more prevalent in regions that are hit with less light because it needs to elongate towards the sun.

What is apical dominance? What hormone is responsible for it? How can apical dominance produce fractals?

• Apical dominance is the phenomenon where the main central stem of the plant grows more strongly than the side stems due to a higher Auxin concentration, suppressing the elongation of other branches.

• This growth pattern ensures that the plant focuses its resources on vertical growth to compete effectively for light.

• The hormone responsible for apical dominance is auxin, which is produced at the shoot apex.

• By inhibiting the growth of lateral buds, auxin promotes apical dominance.

• Apical dominance can lead to fractal-like branching patterns in plants, as the controlled growth of lateral branches results in repeating structures that mimic fractal geometry.

Why does cutting off the top of a tree cause it to become more shruby?

• Cutting off the top of a tree removes the apical dominance, which allows lateral branches to grow more vigorously.

• The removal of the shoot apex leads to decreased auxin production, which normally inhibits the growth of side shoots.

• With reduced auxin levels, side stems can grow and develop, resulting in a bushier appearance.

• This change allows the plant to utilize its resources for lateral growth instead of vertical growth.

Why is it beneficial to prune some shoots when repotting or transplanting a plant?

Pruning some shoots when repotting or transplanting a plant is beneficial because:

• It encourages the plant to redirect its energy towards establishing a healthy root system in the new environment.

• Pruning can stimulate new growth, leading to a bushier and more robust plant after re-establishment.

Draw a cross section of wood and identify all major tissues and meristems.

Cross Section of Wood

• Major Tissues:

  • Xylem: Responsible for water and nutrient transport from roots to leaves.

  • Phloem: Transports food (sugars) produced by photosynthesis from leaves to other plant parts.

  • Cortex: Provides support and storage, located between the epidermis and the vascular tissues.

  • Pith: Central part of the stem, involved in storing nutrients and water.

• Meristems:

  • Vascular Cambium: A layer of meristematic tissue between the xylem and phloem; responsible for secondary growth, producing new xylem and phloem cells.

  • Cork Cambium: Produces the outer protective layer of the plant (bark) and is responsible for secondary growth in tissues outside the vascular cambium.

What types of cells is bark made out of? What makes cork impermeable to water?

Bark is primarily made out of secondary tissue that includes the following types of cells:

1. Cork Cells: These are dead cells that form the outer protective layer. They are packed closely together to form a barrier.

2. Cork Cambium: A layer of meristematic cells that produces cork cells and contributes to the thickness of the bark.

3. Phloem: Living cells that transport nutrients from the leaves to other parts of the plant. The phloem is located just beneath the bark layer.

Cork is impermeable to water due to the presence of a waxy substance called suberin, which coats the cell walls of cork cells. This waxy layer prevents water loss and protects the plant from pathogens and environmental damage.

What is the difference between heartwood and sapwood?

Heartwood vs. Sapwood

• Heartwood: The innermost, dead, oldest part of the wood that is no longer actively transporting nutrients and water. It serves mainly as a support structure and may contain resins and tannins, making it more resistant to decay. Heartwood is typically darker in color due to the accumulation of these substances over time.

• Sapwood: The outer living layer of the wood that actively participates in the conduction of water and nutrients from the roots to the leaves. It is usually lighter in color and surrounds the heartwood, and it can be seen when you cut across the trunk of a tree.

What are the rings within the trunk of the tree (tree rings)? How are they formed/what do they show?

Tree rings, also known as growth rings, are the concentric circles found within the cross-section of a tree trunk. Each ring represents one year of growth. The formation of these rings is influenced by seasonal growth patterns:

1. Spring Growth: During the spring, trees typically grow more rapidly due to favorable conditions (more water and nutrients). The wood produced during this time is lighter in color and has larger cells, creating a wide growth ring.

2. Summer Growth: Growth slows down due to reduced water availability and lower temperatures. The wood produced then is denser and darker in color with smaller cells, resulting in a narrower growth ring.

These rings can provide important information about the tree's age, the environmental conditions during each year of its life, and even historical climate data. A count of the number of rings can reveal the tree's age, while variations in ring width can indicate years of plenty or drought.

I am a cell on the outer bark, also known as the cork. Am I primary or secondary growth? Explain how I got here starting from the shoot apical meristem using a flow chart (Shoot apical meristem → ? → ? → ? etc). Include as many intermediate steps as you can

1. Shoot Apical Meristem (SAM)↓

2. Primary Meristem (Gives rise to the preliminary tissues)

   • Protoderm → Epidermis (primary covering)

   • Ground Meristem → Cortex (primary tissue)

   • Procambium → Primary Xylem and Phloem (transport tissues)↓

3. Secondary Growth Initiation

   • Vascular cambium develops between the primary xylem and phloem

   • Cork cambium (phellogen) forms from the pericycle or outer layer of the vascular cambium↓

4. Formation of Cork Cells (Phellem)

   • Cork cambium produces cork cells which differentiate to form the outer bark

   • Cork cells become dead and provide protective functions

SAM → Ground Meristem → Cork cambium → Cork

Jeopardy questions:

• What is the primary endosymbiotic event? → Heterotropic cells engulfed a prokaryote (cyanobacteria)

• Does the fertility factor move first or last? → First, because it is what allows it to pass on genetic info (stimulates formation of the sex pilus)

• Why should we go by the derived traits of plants when recognizing organisms as plants instead of just saying “oh it’s green and photosynthetic, its a plant!” → Convergent evolution. Algae is green and photosynthetic as well but is not considered a plant.

• What is alternation of generations → alternation between haploid to diploid organisms.

• Relate conjugation to cultural evolution → they are both horizontal transmission of advantageous traits. Conjugation is horizontal gene transfer from one bacteria to another. Cultural evolution is the sharing of skills from friend to friend.

• T/F Bacteria is immortal. Explain → True. Reproduction is clonal, meaning that the genetic information never “dies off,” the DNA never goes away. The bacteria itself can die, not the DNA

• If its not a bacteria/archaea what is it?→ Eukarya

• How does bacteria reproduce clonal and still have genetic variation? → horizontal gene transfer, recombination, and mutations

• What is phototaxis? → Movement towards light (positive = towards, negative = away from).

• Where do the plants grow from? → apical meristems → the tips of the shoots and roots, they grow in polar opposite directions.

• Explain gram-negative bacteria → thinner peptidoglycan wall, causes infections because they are antibiotic resistant, stains pink.

• Explain bacterial transformation → taking DNA from the environment

• What is the structure of bacteria → flagella, no membrane bound organelles, circular DNA, ribosomes, plasma membrane, cell wall, small.

• What is the multicellular spore generation? → Gametophyte

• Is flagella homologous or analogous? → analogous

• Conjugation → horizontal gene transfer via the sex pilus

• What does the procambium differentiate to → primary xylem and phloem, and vascular cambium.

• What are the primary and secondary meristems of the RAM and SAM

  • Primary: Protoderm, Procambium, ground meristem

  • Secondary: Cork cambium, Vascular cambium

Which dispersal phase is most favourable for plants? Why? → Seeds

Why is the gametophyte stage dominant in non-vascular plants? → allows for amplification of gametes which the non-vascular plants needs for a better chance of fertilization.

Why is the sporophyte stage dominant to vascular plants? → Gives importance to variation which the flowering plants focus on as they have pollinators to transport gametes.

Practice quiz qs

• Double fertilization occurs when the egg is fertilized, the other combines with the central cell nuclei

• Cork is secondary growth

• Leaves, vascular cambium are primary growth

• If roots are eaten → less cytokinins will be produced by the roots

• What are process occurs in sporangia during meiosis? → meiosis

• Tendrils allows plants to grow upwards