Exam 1 - Meristem/Primary Growth

TEM - Transmission Electron Microscopy

• looks at the internal structure of things

• black and white

• higher quality that most types

• utilizes electrons for imaging

SEM - Scanning electron microscopy

• visualizes the exterior of things

• utilizes electrons or imaging

• black and white

Nucleus

• contains chromatin/chromosomes

• location of transcription and rna splicing

• nucleolus - ribosome subunit assembly

• bounded by nuclear envelope containing nuclear pores

Chloroplast

• bound by two membranes (inner and outer)

• internal thylakoid membranes and stroma

• contain their own genome

• biosynthetically very active

• contain chlorophyll

• site of photosynthesis

Chromoplasts

• plastids that contain pigments other than chlorophyll (usualyl carotenoids)

• found in flowers, ripening fruit, aging fall leaves, some roots, etc.

• no internal membrane structure

Leucoplasts

• plastids lacking pigments

• no internal membrane structure

Amyloplasts

• a type of leucoplast

• store starch

Etioplasts

• immature plastids

• contain rudimentary internal membrane structures called prolamellar bodies

Mitochondira

• bound by two membranes

• contain their own genome

• import majority of proteins from cytoplasm

• respiration to produce atp

Peroxisomes

• bound by single membrane

• fatty acid degradation

• photorespiration

• auxin metabolism

• detoxify h202 (hydrogen peroxide)

Vacuoles

• terminal storage compounds

• turgor pressure of cell

• bound by tonoplast membrane

• autophagy of organelles

• may contain calcium oxalate crystals

label these structures

(from top to bottom)

1. mitochondria

2. chloroplast

3. nucleus

4. nuclear envelope

5. nucleolus

6. cell wall

7. starch grain

Endoplasmic reticulum

• lipid synthesis

• synthesis of membrane bound and secreted proteins

• intracellular calcium storage

Golgi apparatus

• synthesize cell wall polysaccharides

• glycosylate proteins (adds a sugar to proteins)

• direct vesicles to intercellular compartments

• huge component of the endomembrane system

• composed o 5-7 discs of sacs

• cis face - faces towards the ER

• trans face- faces away from ER/towards cell wall

Plasma membrane

• lipid bilayer with embedded proteins

• regulate transport of nutrients

• protein domains (transmembrane and lipid linked)

Transmembrane domain

• single or multi passes through the membrane, protein domain spans the entire membrane at least once

lipid linked

• linked to plasma membrane via a lipid

• only linked on one side of plasma membrane

Cytoskeleton

• microtubules and actin filaments (no intermediate filaments in plants)

Microtubules

• polymers of alpha and beta tubulin that come together to form dimers

• have dynamic instability, they shrink and grow

• heavily aid in cell division

• aid in phragmoplast positioning

Actin filaments

• tip growth of pollen and root hairs

• movement of nucleus and other organelles

• vesicle mediated secretion

• cytoplasmic streaming

• only 1 type of monomer

Cell wall functions

• constrains expansion of protoplast

• prevents rupture of plasma membrane by water uptake

• determines shape and size of cell

• defense against pathogens

• structural support and rigidity

Primary cell wall

• cell wall synthesis occurs when cell is formed

• can be loosened to allow cell growth

Middle lamella

• region between two adjacent primary cell walls

• composed of primarily pectins

Cellulose

• major component of cell walls

• organized in microfibrils

• deposition orientation determines cell expansion

Cellulose synthase

• takes udp glucose, removes udp and links glucose to microfibrils

• connected to microtubules below which aid in movement for deposition

Components of cell wall

• cellulose

• pectin

• hemi cellulose

secondary cell wall

• usually 3 layers

• array of cellulose is a different orientation in each layer

• created during differentiation

Plant cell wall waxes

• long carbon and hydrogen chains ontop of the epidermis

• prevent water loss

phragmoplast

• plant specific

• formed during cell division

• composed of microtubules, guide the cell wall components to the center to build the cell wall

• builds from center outwards (cell wall ← phragmoplast → cell wall)

Plasmodesmata

• cytoplasmic connects between adjacent plant cells

• plasma membrane lines the pore

• desmotubule (modified er) spans the pore

• usually occur in clusters

• form in pit fields (thin parts of cell wall)

• primary and secondary types

• lots of things move through them (proteins, rna, etc. viruses can hijack them too)

• can open and close

pit fields

• thinner parts of the cell wall

• the secondary cell wall is usually not built over pits

• plasmodesmata are often formed here (easier to bore through less of the cell wall than just a giant chunk of cell wall lol)

primary plasmodesmata

• plasmodesmata that form when the cell wall is built

secondary plasmodesmata

• plasmodesmata built after cell division

shoot apical meristem

• located at the top of stem, protected by leaves

• organized in central and peripheral zones

• gives rise to the stem, leaves, and reproductive structures (like flowers)

Central zone

• slower dividing

• function to grow and replace meristem

Peripheral zone

• faster dividing

• cells that are pushed out of the central zone

• function to give rise to new organs

Corpus

• consists of an L1, L2, and L3 layer

• all function to make organs

L1

• outermost layer

• referred to as tunica

• formed from anticlinal divisions

• usually form epidermis

• function to make organs

L2

• referred to as tunica

• next closest layer to L1

• function to make organs

• formed from periclinal divisions

L3

• referred to as corpus

• formed from periclinal divisions

• not always present

• usually form internal plant structures

Anticlinal

• L1

• daughter cells are in the same plane

• daughter cells are pushed to the sides

• horizontally

periclinal

• L2 and L3, sometimes L1

• daughter cells pushed down 1 plane

• parallel

• vertical

Phytomere

• made by SAM

• consist of a node, leaf, axillary meristem, and internode

Genes that control shoot apical meristem

• knotted 1

• clavata

• wuschel

• shoot meristemless

Clavata 3/1

• restricts wusch

• without it, meristem becomes very large

Wuschel

• increases growth

• without it, less growth occurs

• usually inhibited by clv1

the two main functions of the meristem

• self renewal

• organogenesis/differentiation

Epidermis

• prevent dehydration

• regulate gas exchange

• absorb water and materials

• excrete toxic molecules

• defense against predators

• define organ boundaries

specialized epidermis

• stomata and trichomes

Stomata

• 2 guard cells that open and close a pore

• interlocking cell walls

• subsidiary cells (right next to the guard cells) will swell with water, water will move osmotically to open and close the guard cells/stomata

• opening and closing can occur quickly

Grass/monocot stomatas

• have asymmetric cell division

• the smaller cell (guard mother cell) becomes the guard cell when it divides symmetrically

• appear like a road/track under a microscope, oriented very straightly/orderly

Dicot stomatas

• not uniform

• t least 1 cell separates one stomata from another stomata

• asymmetric cell division with the primary meristemoid

Trichomes

• grow outwards above the cell surface/leaf

• many types

• can be glandular

• have many functions (ex- additional shade/sun protection, defense against predators, triggering the closing of a mouth on a venus fly trap)

Ground meristem

• parenchyma

• collenchyma

• sclerenchyma

Parenchyma

• uniform cell wall thickness (usually thin)

• living at maturity

• capable of cell division, but usually dont divide

• function in photosynthesis, storage, secretion, and wound regeneration

Chlorenchyna

• chlorophyll containing parenchyma

Mesophyll ground tissue

• both parenchyma

• consists of pallisade and spongy mesophyll

Palisade cells

• parenchyma

• specialized for light capture

• rectangular/long cells

Spongy mesophyll

• parenchyma

• irregular in shape, more blob like

• distant gaps from neighboring cells

• located in the middle of the leaf (underneath palisade cells)

Parenchyma stem tissue

• the pith and cortex are both parenchyma

• found in the stem

• pith = area inside the ring of vascular tissue

• cortex = area outside the ring of vascular tissue

Parenchyma root tissue

• the cortex in roots is parenchyma

• no pith is present

Collenchyma

• uneven cell wall thickness

• living at maturity

• often found in leaves and supporting stem

• non lignified cell walls

• function in supportive tissues

• tend to form in continuous strands beneath the epidermis of leaves and petioles

brightfield microscopy

• light is transmitted from below

Sclerenchyma

• thickened, hard secondary cell walls

• usually lignified

• often dead at maturity

• has two types, sclerids and veins

• function as strengthening and supporting tissue

Sclerids

• smaller

• aid in supporting surrounding tissue

• smaller clusters of cells

fibrids

• larger than sclerids

• run in the long axis paralel to the vein

Protoderm

• gives rise to epidermis

Procambium

• gives rise to vascular tissues

• primary xylem and primary phloem

Xylem

• conducts transportation of water, dissolved nutrients

• lignified and dead at maturity

• can have fibers/parenchyma for support

• usually located on the top side of the vein

Midrib

• a vein that runs down the middle of the leaf that is very rigid

• has a large amount of sclerenchyma

Evapotranspiration

• the process of water leaving the leaves through the stomata drives the xylem to pull water up the stem of the plant

Tracheary elements

• a component of the xylem

• tracheids

• vessels

• lignified, involved in water movement

Tracheids

• much smaller than vessels

• no perforation in end walls

• end wall is not modified, it is capped at the end

Vessels

• usually much larger than tracheids

• perforation in the end walls

• end wall is gone/dissolved, or it has grates/vents

Pits

• holes/tubes between xylem cells

Pit membrane

• the space where water can cross via pits

Annular rings

• present in protoxylem

• no complete casing of lignin leaves an empty space when the cells are stretched as the tissue grows rapidly

Protoxylem

• first formed xylem

  • is stretched as the tissue of the plant rapidly grows, leading to annular rings

meta xylem

• formed later

• has no annular rings

• aids in conducting water

• has lignin

Vessel element cell apoptosis

• primary cell wall swells as perforation plate

• localized synthesis of secondary cell walls

• dna and tonoplast degenerate

Phloem

• principal photosynthate conducting tissue

• also conducts amino acids, lipids, hormones, protein, rna, and sometimes viruses

• living at maturity

• composed of sieve elements and companion cells

Sieve elements

• collection of sieve tubes

  • still living, has reduced cellular contents

companion cells

• cells adjacent to sieve elements

• support sieve elements by making and providing materials the sieve element cannot make due to its reduced cellular contents

• have a smaller vacuole

• densely packed

• high amount of mitochondria to help support sieve element

why are cucurbits phloem’s studied?

• they have two phloem

sieve/sieve plate

• at the ends of the sieve element

• has small holes similar to a strainer/sieve/net

• promotes flow

callose

• glucan polymer

• regulates pore size of sieves (modified plasmodesmata)

• high concentrations = pores close

Sieve Element differentiation

• nucleus goes through mitosis, asymmetric cell divison

• callose deposited around plasmodesmata to mark sieve pore sites

• future sieve tube goes through some of apoptosis, but doesnt fully go through apoptosis and die, many organelles denegerate

• pores are developed

• callose is degraded

protoplast

the entire cell excluding the cell wall

transitory starch

• temporary starch reserves formed during the day during photosynthesis in the thylakoid

• broken down at night

prolamellar body

• located inside of the etioplast

• differentiates to become whatever type of plastid it becomes

co translational

• in some scenarios, dna is translated and transcribed at the same time