Botany Final Exam study Guide

GWU BISC 2305 - Evolutionary Development -> Water & Solute Movement

evolutionary development

• (Evo-Devo) - the study of the evolution of developmental patterns.

• Great strides have been made by studying conserved genes. Much of what we know about developmental gene regulation comes from studying mutations that disrupt normal embryo development

conserved genes

genes with similar DNA sequences in distantly related organisms that regulate key developmental pathways

embryogenesis

• formation of the embryo

• the first two stages of seed development.

• Establishes the body plan of the plant, which consists of two superimposed patterns: apical/basal and radial

apical-basal pattern

pattern that is found along the main axis and establishes polarity.

apical cell

• one of two daughter cells (apical and basal) of fertilized zygote

• gives rise to most of the mature embryo

basal cell

• the other of two cells arising from the original zygote

• gives rise to a stalk-like suspensor that anchors the embryo at the micropyle

radial pattern

concentrically arranged tissue system that consists of three tissue types (the

primary meristems):

• protoderm

• ground meristem

• procambium

protoderm

outer tissue layer in embryo. Precursor to the epidermis

ground meristem

middle tissue layer in embryo. Precursor to the ground tissue.

Surrounds the procambium

procambium

inner tissue layer. Precursor to the vascular tissues

globular stage

• Embryo is spherical and displays apical-basal pattern, but cells are undifferentiated

heart stage

• radial polarity is established.

• Cotyledon(s) begin to develop, in eudicots forming a heart shape.

• Apical and root meristems begin to form

torpedo stage

• embryo is partitioned into: meristems, elongated cotyledon(s), and hypocotyl.

• Suspensor dissolves. Embryo may begin to curve.

plumule

• present in mature embryo

• the embryonic shoot which contains a stem (epicotyl), the apical meristem at the tip,

  and one or more young leaves

hypocotyl

• present in the mature embryo

• the stem below the cotyledon(s) that attaches it (or them) to the radicle

radicle

the embryonic root, which contains the root meristem at the tip

cotyledons

• attached to the seed and radicle via the hypocotyl and to the plumule via the epicotyl.

• In eudicots, two cotyledons. In monocots, one dominant cotyledon (scutellum) that is folded over the plumule

eucot cotyledons

• may be large and fleshy, act as food reserves (like the endosperm) for the developing seed and germinating seedling once the endosperm runs out.

• Or may be thin and membranous, helping the embryo absorb food from the endosperm and taking over photosynthetic functions upon germination

the monocot seed contains:

• Scutellum – single cotyledon - dominant structure in the seed.

  • Acts as a bridge between endosperm and developing embryo by aiding in endosperm digestion and moving digested food to the embryo

• Coleorhiza – protective sheath that covers the radicle

• Coleoptile – protective sheath that covers the plumule

seed coat

• outer protective coat.

• Develops from the integuments of the ovule.

• May be hard and impenetrable or thin and papery. Micropyle is sometimes still visible.

• Also, may display a scar from where the seed was shed from the plant, called a hillum

seed maturation

• at the end of embryogenesis, cell division in the mature embryo stops and the seed enters the final stage of development: maturation.

• Reserves of food (starch, lipids, proteins) have accumulated in the endosperm.

• Seed undergoes desiccation and loses 90+% of its water weight. Seed coat hardens.

quiescent pase

• “resting” phase of a mature seed.

• Once a quiescent seed imbibes water, it will germinate if environmental conditions are met

germination

resumption of embryonic growth. Depends on external and (sometimes) internal factors

external germination factors

 sufficient water, oxygen, temperature, and (sometimes) light

internal germination factors

• after maturation, some seeds will go dormant (primary dormancy) and will not germinate until internal (and external) conditions are met.

• Even if environmental conditions are perfect, dormant seeds will not germinate until their dormancy is broken.

• Dormancy may be imposed by the seed coat, by the embryo itself, or both

coat-imposed dormancy

• seed coat may be too hard to imbibe requisite water, may be too rigid for the expanding radicle to penetrate, may contain inhibitors that suppress growth

embryo-imposed dormancy

• ratio of hormones Gibberellic Acid (GA) and Abscisic acid

  (ABA) can play a part.

• ABA promotes dormancy

• GA promotes germination by synthesizing the enzymes necessary to digest endosperm.

• When GA concentration outweighs ABA concentration in the mature seed, embryo dormancy may be broken.

• Some seeds must undergo a complex series of enzymatic changes before they will germinate, known as after-ripening

secondary dormancy

• seeds that are no longer dormant, but encounter unfavorable conditions for germination will reenter a dormant state until environmental conditions are met

primary root

• the first structure to emerge from the germinating seed is the radicle, which will develop into the primary root, or tap root.

• As it grows it will form lateral roots, which will give rise to more lateral roots and form a branching root system in many gymnosperms and eudicots.

• In monocots, the primary root is short lived, and the main root system originates from the crown of the plant (adventitious)

epigeal germination

• eudicots

  • the second structure to emerge from the germinating seed is the hypocotyl, which bends to protect the apical meristem and elongates toward the soil surface in the shape of a hook, carrying the cotyledon and plumule above ground.

  • Once all reserves are digested from the cotyledon, they will wither and fall off.

• In monocots,

  • the second structure to emerge from the germinating seed is the tubular single cotyledon (scutellum), which bends and elongates toward the soil surface in the shape of a hook, carrying the seed coat and plumule above ground.

  • The plumule emerges from the interior of the cotyledon (which is rolled up like a tube). Once all reserves are digested from the cotyledon, it will wither and die.

hypogeal germination

• (eudicots)

  • the second structure to emerge from the germinating seed is the epicotyl, which bends to protect the apical meristem and elongates towards the soil surface in the shape of a hook, carrying the plumule above ground.

  • The cotyledon(s) remain below-ground, where they will eventually decompose.

• In monocots

  • the first structure to emerge is the coleorhiza, and the radicle emerges from the center of this sheath.

  • The second structure to emerge is the coleoptile, and the plumule emerges from this sheath.

  • The scutellum and seed coat remain below-ground

Why is Evo-Devo an important field of modern biological study?

What three selective advantages do seeds provide to seed-bearing plants?

1. stored food

2. protective seed coat

3. facilitation of dispersal

What are the primary meristems of the developing seed, and what tissues do they

differentiate into? Where are these tissues located in the mature plant body, and what

functions do they serve?

• protoderm—> outer tissue layer; precursor to the epidermis

• ground meristem—> middle tissue layer; precursor to ground tissue

• procambium—> inner tissue layer; precursor to vascular tissue such as xylem and phloem

How does early seed development differ between monocots and eudicots. Where is the

apical meristem located in each?

How can mutations affect the development of the suspensor and the radial pattern of an

embryo?

• suspensor is important for supplying plant with nutrients and hormones like gibberellins

• mutations causing proliferation of suspensor can disrupt normal embryogenesis and result in twin or triplet embryos

What metabolic changes occur inside a seed as it imbibes water?

• water activates enzymes that promote germination

• cells enlarge and division is initiated

What happens if a non-aquatic seed germinates underwater? Can it develop sucessfully?

Why or why not?

• likely not

• germination requires oxygen non-aquatic seeds don’t have adaptations to facilitate gas exchange

Apical meristems

cells in these regions retain the potential to divide after embryogenesis ends.

Found at the tips of all stems and all roots. Involved in primary growth – the extension of the

plant body. Produce two types of cells:

Initial

undifferentiated cells that maintain the meristem as a continuing source of new cells.

When initials divide, one sister cell remains in the meristem as an initial. The other becomes a

new body cell, or a:

Derivatives

may divide serval times near the meristem before differentiating into specific cell

types in the primary tissues

Shoot apical meristem

generates cells that create the stems, leaves, and flowers

Root apical meristem

generates cells that create the root system

Indeterminate growth structure

a plant’s ability to form new organs and continue to grow

during its entire lifespan

Developmental plasticity

 a plant’s ability to modify its relationship with its environment by

modifying its phenotype

Development

the events that progressively form an organism’s body. Consists of three

overlapping processes:

Growth

an increase in size via a combination of cell enlargement and division

Morphogenesis

 the assumption of a particular shape and form. Via the expansion of tissue, that

then differentiates into smaller units

Differentiation

 the process by which cells with identical genetic constitutions become different

from one another, and from the meristematic cells from which they are derived. Via the

expression of specific genes (which are not expressed in other cell types), which is determined

by a cell’s final position in a developing organ

Tissues

cells form different structural and functional units. Distributed in a radial pattern

throughout the plant body, with specific arrangements that depend on the plant part, plant taxon,

or both

Permanent tissue

are not meristematic. Cells within permanent tissues are mature,

differentiated, and have often lost the ability to divide. They may be small or large, living or

dead, and have thin or thick cell walls

Tissue Systems

permanent tissues of vascular plants are grouped together by function into

three different systems:

Ground tissue

 system consisting of the three ground tissues:

Parenchyma

most abundant cell in the plant body. Variable shape and size. Involved in

photosynthesis, storage, and secretion. Commonly occur as continuous masses. Living cells that

retain some ability to divide – responsible for initiating adventitious structures. Totipotent

Collenchyma

often occur in strands, typically elongated. Characteristic uneven, thickened, but

also flexible (non-lignified) cell walls. Often border veins in leaves, though often absent in

monocot leaves and stems. Supporting tissue of developing herbaceous organs

Sclerenchyma

dead cells that lack protoplasts. May form continuous masses or occur in small

groups or as individual cells. May develop in any part of the primary or secondary plant body.

Thick, often lignified secondary cell walls. Important strengthening and supporting elements in

mature organs. Two cell types:

Fibers – long, slender cells that occur in strands or bundles

Sclereids – shorter than fiber cells. Contain a branched central cavity.

Make up seed coats, nut shells, and fruit pits (“stone cells”)

Vascular tissue

 system consisting of the two vascular tissues. Together, they form a continuous

system of vascular tissue extending throughout the plant body

Xylem

conducts water and dissolved nutrients from the root through the shoot. Principal

conducting cells are the tracheary elements which are elongated, have secondary walls, and are

nonliving. Two types:

Tracheids – (see Gymnosperms) less specialized (only tracheary element in seedless vascular

plants and gymnosperms)

Vessel elements – specialized conducting cells in angiosperms. Cell walls contain perforations –

areas lacking primary and secondary walls – perforation plates. Plates develop on cell wall

ends. Vessel elements join end-to-end, forming long, continuous columns called vessels

Phloem

primary food-conducting tissue. Responsible for the transport of sugars, amino acids,

lipids, micronutrients, hormones, messenger/signaling proteins and mRNA. Responsible for long

distance signaling. Also, the route of movement for viruses. Principle conducting element:

Sieve tube elements

living cells. Produce a cluster of pores – sieve tube plates – in cell wall.

Adjacent sieve tube cells are interconnected at the sieve tube plates. Characterized by thepresence of P-protein, which acts to plug sieve tube plates when wounded to prevent the loss of

phloem. Each sieve tube cell forms an association with a:

Companion cell – specialized parenchyma cell that derives from the same mother cell as the

sieve tube element cell to which it is paired. Share physical cytoplasmic connections to their

associated sieve tube element cell. If one dies, so will the other. Deliver substances to the sieve

tube cells like ATP and messenger proteins

Dermal tissue

system that consists of only one tissue type: epidermis (See card)

Epidermis

outer protective covering of the entire primary plant body. Cells are functionally and

structurally diverse and compactly arranged for mechanical protection. Upper (arial) cell walls

are covered in a waxy cuticle to reduce water loss. Contains some specialized cells: stomatal guard cells and trichomes

Stomatal guard cells

regulate small pores called stomata (singular: stoma) to control gas

exchange. Usually concentrated on leaf undersides

Trichomes

outgrowths on the epidermis (hairs) that can reflect solar radiation, lower leaf

temperature, reduce water loss, absorb water and minerals, and protect against herbivores

What internal factors determine the final form of a derivative cell?

• differentiation is location dependent

• different gene expression

Describe the three types of ground tissue - parenchyma, collenchyma, and sclerenchyma. How are they similar and different and what roles do they play in the plant body?

• parenchyma: most abundant in plant body; photosynthesis, storage, and secretion

• collenchyma: often occur in strands typically elongated often absent in monocot stems and leaves

• sclerenchyma: dead cells that lack protoplasts

What element makes angiosperm xylem more specialized than gymnosperm xylem? What does this element look like and how does it function?

• gymnosperms lack vessel elements

• it’s a perforated cell wall on either end of the cell that joins end-to-end with the other cells

Root

 the first structure to emerge from a germinating seed. Provides anchorage, storage,

and conductive and absorptive functions to the plant. Growth is a continual process that

only stops under adverse conditions and follows a path of least resistance, concentrating

in nutrient-dense areas. The young root consists of 3 regions of growth, with a gradual

transition between regions:

Region of cell division

the area of actively dividing cells (the apical meristem)

Region of elongation

cells elongate, resulting in an increase in length of the root

Region of maturation

ells differentiate and mature. Root forms root hairs,

tubular epidermal outgrowths that increase surface area

Internal structure consists of three concentric rings of tissue types, the Epidermis, Cortex,

and Vascular Cylinder

Epidermis

pecialized absorbing tissue in young roots due to highly permeable cell

wall

Cortex

 represents the ground tissue system. Occupies the largest area within the Plastids are present, but they serve to store starch and are not usually

photosynthetic. Contains many air spaces (aerenchyma) for gas exchange.

Contains two distinct strips of tissue, the endodermis and the exodermis:

Endodermis

innermost cortical layer, tightly packed and lacks air spaces.

Characteristic presence of Casparian strips in cell walls. Helps to direct the

flow of water into the vascular cylinder

Casparian strip

band-like portion of the cell wall reinforced with

suberin and lignin, hydrophobic

Exodermis

outermost cortical layer, similar in structure to the endodermis Casparian strips embedded in cell walls. Reduces water loss and acts physical barrier against microbial attack

Vascular cylinder

contains the primary vascular tissues (xylem and phloem) and a non-

vascular tissue, the pericycle

Pericycle

 completely surrounds the vascular cylinder. Also originates from procambium. Lateral roots arise in the pericycle. During secondary growth, gives rise to vascular and cork cambium

Xylem

solid core that occupies the center of roots. Ridgelike extensions

project into the pericycle. Number and shape of ridges is species dependent

Phloem

strands nestled between the xylem ridges

Root exudates

an array of substances secreted by the root into the rhizosphere

Rhizosphere

 the soil directly surrounding living plant roots and that is influenced by root

activity (0.5-4mm border around each root)

Primary root (taproot)

develops from the embryonic radicle and grows straight down,

giving rise to lateral roots as it matures

Taproot system

a root system formed from a strongly developed primary root

Fiberous system

a root system found in monocots and some herbaceous eudicots where

the primary root is short-lived and the system develops from roots that arise from the stem

(adventitious roots), which then produce lateral roots. No one root is more prominent

than the others

Fine roots (feeder roots)

the roots actively engaged in the uptake of water and minerals.

Occur in the upper ~15cm of soil

Mycorrhizal fungi

soil fungi that form symbiotic relationships with plants by colonizing

fine roots. Fungi provide the plant with a wider network of access to water and nutrients,

while harvesting photosynthetic compounds from the plant in return

Root to Shoot ratio

 a functional balance of mass maintained by the plant wherein the

amount of tissue in the root system is consistent with the amount in the shoot system

Root cap

tip of each root is covered with a thimble-like cap made of parenchymal cells

which protects the apical meristem

Mucilage

 a highly saturated polysaccharide gel secreted by the periphery cells of the root

cap. Lubricates and hydrates the root

Border cells 

periphery cells that are released and separate from plant tissue. Can remain

alive in the rhizosphere for weeks and exude messenger proteins to repulse or attract

microbial life or prevent desiccation. Border cells and their exudates account for 98% of

Carbon sequestered in soil

Root apical meristem 

New root tissue develops at the tip of every root as the apical

meristem adds new derivatives. Divided into two regions:

promeristem and quiescent center

Promeristem

 area of least differentiation. Composed of initials and their

immediate derivatives

Quiescent center

inactive middle area of the meristem. Can repopulate

meristematic tissue if it is damaged

Arial root 

roots produced from above-ground structures, often serve support functions

Air root (pneumatophore)

roots developed out of soil (or water) for the purpose of

necessary gas exchange in soils with low oxygen content. Grow upwards, against gravity

Velamen

a specialized epidermal coating produced by the air roots of epiphytes to

aid in absorption of water vapor

Storage roots 

specialized, fleshy roots that function as storage organs. Contain storage

parenchyma which store water, sugars, and other carbohydrates

What are two defense mechanisms roots use to protect against microbial attack?

• the cortex in the epidermis acts as a physical barrier to defense from microbial attack

• exudates attract beneficial microbes and repel bad ones

Shoot

the aboveground portion of the plant, consisting of stems, nodes and internodes,

and leaves