Botany - Week 2

Growth

Irreversible increase in body size → adds new cells by tissues by cell division

Primary growth

Seen in non-woody parts of plants

Secondary growth

Forms woody stems and roots

What drives primary growth?

Cell division at primary (apical) meristems and subsequent cell expansion

What does the dermal tissue function as?

Epidermis

What does the ground tissue function as?

Filling for the plant body

What do the primary xylem and primary phloem do?

Transport

Secondary growth

Lateral meristems in wooody plants increase girth

Lateral meristem

Secondary meristems fthat form later during plant growth

Is development reversible or irreversible?

Irreversible change in form and function of cells

What do the transitions between growth stages depend on?

Hormones produced within plant and in response to environmental factors

What are some internal signals for plant growth and development?

Hormones and other growth regulators

What are some external signals for plant growth and development?

Stress factors, light level, day length, nutrients, pathogens, herbivory

Abiotic factors for plants

Light, humidity, temperature, wind, gases, gravity, soil,…

Biotic factors for plants

Herbivory, pathogens, toxins, soil microbes

How do plants respond to environmental factors?

External signals → hormones, growth regulators/gene expression, physiological adjustments → plant growth, development, behavior

How do plant hormones behave?

Act locally or at distant locations

Unspecific action

Required concentration varies

Growth promoting hormones

Auxin, cytokinin, gibberallic acid (GA), brassinosteroids

Growth inhibitory hormones

Abscisic acid (ABA) and ethylene

Defense hormones

Salicylic acid and jasmonic acid

Where is auxin usually found?

Young shoots and root tips

What does auxin do?

Involved in nearly all aspects of plant growth/development:

→ Cell division, cell expansion, development, stress response

What does cytokinin do?

Promotes cell division, inhibits lateral roots, and promotes axillary shoots

What two hormones do plants depend on for later growth development (plant architecture)?

Auxin and cytokinin

What does gibberellin (GA) do?

Promotes cell elongation (with auxin) and flowering

Stimulates seed germination

Breaks seed and bud dormancy

What is the process that breads seed dormancy?

Seed gets soaked → burst of GA production → mobilize nutrients in endosperm

What does abscisic acid do?

Helps regulate bud dormancy (balance with cytokinin)

How do short days lead to dormant buds?

Short days allow ABA synthesis which then leads to dormant buds

How does cold weather lead to dormant buds?

Cold weather prevents activity in root tips → no cytokinin synthesis → dormant buds

What do ABA and GA levels look like in a mature seed?

Low ABA, low GA

What do ABA and GA levels look like in a germinating seed?

Low ABA level, high GA level

Vivipary

Seeds germinate inside fruit due to lack of ABA

Which hormone is known as the stress hormone?

Abscisic acid

How do plants close their stomata under drought conditions?

Drought → ABA levels rise → stomata close

How does warm weather break bud dormancy?

Warm weather → active root tips → cytokinin synthesis → active buds

How do long days break bud dormancy?

Long days → GA synthesis → active buds

Ethylene

Gaseous hormone for ripening and senescence

What allows an abscission layer to form?

Auxin level drops, ethylene levels rise, ABA levels rise

Which organelle takes up most of the space in living cells?

Vacuole

Parenchyma

Thin-walled, spherical cells alive at maturity, often with visible intercellular spaces

What plastids can be found in parenchyma cells?

Chromoplasts, chloroplasts, amyloplasts

Sclerenchyma

Cells with heavily thickend and harded walls that are dead at maturity

*Sclereids and fibers

Collenchyma

Elongated cells with walls of irregular thickness that are alive at maturity

What is the function of collenchyma cells?

Structural support → often come in bundles

Where can intercalary meristems be found?

Nodes of many monocots

Describe the process of plasmolysis

1) Water leaves cell

2) Vacuole can no longer exert turgor pressure

3) Plasma membrane splits away from cell wall

Where are apical meristems found?

Growing tips of stems, branches, and roots; axillary buds and tips of each branch shoot/root

Where are lateral meristems found?

Points in plant body other than tips

What kind of growth are apical meristems responsible for?

Increased length

What kind of growth are lateral meristems responsible for?

Increase in diameter

Do monocots have lateral meristems?

No

Where are intercalary meristems found?

Nodes whre leaf bases join stem in many monocots

What do cells in the zone of cell division look like?

Small, cuboidal, with thin cell walls, dense cytoplasm, many small vacuoles, and nucleus that takes up most of cell

What do cells look like in the zone of elongation?

Slightly elongated with thicker cell wall; smaller vacuoles start fusing into one large vacuole; nucleus smaller

What do cells look like in the zone of differentiation?

More structured, start taking of forms of function for mature plant body