Notetaking - Midterm 2 - Plant Physiology - Slideshows 15-27

15 - Patterns in Plant Development - Chap. 15

Cell Wall Development:

• Cellulose is synthesized in plasma membrane

• Cellulase synthase (rosette pattern) creates microfibril of cellulose

  • Cellulose is formed as a crystalline ribbon composed of many (1,4)-linked beta-D-glucan chains

• Cell wall assembly: Matrix components synthesized in Golgi apparatus and deposited into cell membrane via secretory vessels

  • Synthesis of cellulose microfibrils at plasma membrane surface

  • Synthesis and glycosylation of proteins and wall modifying enzymes at the rough ER

  • Synthesis of all non-cellulosic polysaccharides at Golgi apparatus

• Orientation of cellulose microfibrils informs direction of expansion: cell walls “girdled” by cellulose

• Microtubules, made of tubulin, lay under plasma membrane and signal directionality of cellulose microfibrils

  • When inhibited by oryzalin, the lack of microtubules cause cells to expand in all directions

• Rosette complex is “fed” activated glucose (UDP-glucose) to generate cellulose

Embryogenesis:

• Embryogenesis: transformation of a single-celled zygote into a multicellular embryonic plant

• Three essential features must be established:

  • Radial pattern of tissues

  • Apical-basal axial development pattern (aka. top and bottom)

  • The primary meristems (shoot, root)

• Asymmetric cell division of zygote into small “proembryo” and long trailing “suspensor”

  • The proembryo begins to multiply and differentiate, while the suspensor anchors the embryo to the endosperm and conducts nutrients

  • Forms “heart stage”, then “bunny stage”.

• Meristems are host to undifferentiated stem cells (called initials) which can divide and differentiate.

• Meristematic Regions:

  • Apical meristems: located on tips of shoot and root, responsible for elongation. AKA. primary meristems, as they are responsible for primary growth

    • Size can vary from one cell to multiple

    • Distinct stratified arrangement can be apparent, where the two topmost layers (L1 and L2) are divided anticlinal while the bottom layer (L3) divides in all directions

    • SAMs have some cells with indeterminate identity, and some with determinate identity, that will become particular organs

    • Phytomeres occur in SAMs, but not RAMs

    • Phyllotaxy: arrangement of leaves around stem, determined by the activity of the SAM

      • Leaves can take alternate, opposite, decussate, whorled, spiral formation…

      • Every species has a distinct phyllotaxis, though it may change during development

      • Phyllotaxy affects the amount of light received by each leaf, and evolves due to evolutionary pressures to maximize light absorption.

  • Secondary meristems:

    • Axillary meristems: form later in development, in the axils of leaves

    • Lateral root meristems

    • Vascular cambium: forms both xylem and phloem (fusiform initials), and rays of pith (ray initials)

Roots:

• Primary root: very simple structure, no lateral roots

• Radial patterning:

  • Epidermis

  • Cortex

  • Endodermis

  • Pericycle: site of lateral root initiation

  • Casparian strip

    • “Forces” water and solutes through the cytoplasm of the cells, disallowing it from entering the apoplast

    • This blocks pathogens, forces solutes and nutrients to be acted upon by cells proteins, and prevents salts from directly entering stele of plant

  • Protoxylem

• Simple root tip: one apical cell

• Root cap is only present when the root tip needs protection, i.e. in soil. In aquatic plants, there is often no root cap

• Developmental zones of the root:

  • Root cap (stable, little-to-no change in cell comp.)

  • Meristematic zone (meristematic cells and quiescent center)

  • Elongation zone (where root cells become long and “root like”, where sieve tube elements differentiate)

  • Maturation zone (where root cells are differentiated and slow elongation, eventually having a fixed shape and identity)

Light:

• Development in the dark leads to etiolation

• When light is introduced, greening occurs and hypocotyl expansion is inhibited

• Photoreceptors trigger a transducing mechanism or chain, which converts light signals into developmental response. Involves amplification of signal. Plant must be in a proper developmental state to respond to stimulus.

• Cryptochromes and Phototropins: perceive blue and UV-A wavelengths

• Phytochromes: far red and red wavelengths

16 - Patterns in Plant Development, Growth and Development of Cells - Chap. 15

Aside: Flowers

• Flowers have four whorls of organs

  • Sepals

  • Petals

  • Stamens

    • Anthers, the very most end of stamens, develops pollen

  • Carpels

    • Pollen must be rubbed onto carpel to stimulate fertilization

• When pollen is rubbed onto carpel, pollen tubes form, which travel between cells and interact with the ovary

  • Direct interaction occurs at the micropyle

• These pollen tubes carry two sperm cells, which are deposited into the ovaries via the micropyle “orifice”

• After this, the pollen tube can be removed and fertilization will still occur

Back to Light:

• Photomorphogenesis: development in light

• Skotomorphogenesis: development in dark

• Phytochrome: red absorbance

  • A pigment-protein complex, called a holoprotein (combination of chromophore and apoprotein)

  • Pr form: absorbs red light (approx. 660 nm)

  • Pfr form: absorbs far-red light (approx. 730 nm)

• When Pr absorbs red light, it transforms into Pfr, which is active and produces a response

  • When Pfr absorbs far-red light, it transforms back into Pr, which is inert

17 - Growth and Development of Cells - Chap. 17

- Absorption spectra for Pr and Pfr overlap slightly, resulting in an 85-15 distr. of Pr and Pfr even in red light treatment

• They are competing reactions

• In the dark, phytochrome is synthesized as Pr, meaning it is inert

• This is photoreversible: if you shine red light, then far red light, then darkness on a seed, it will still etiolate because the majority of phytochromes are Pr

• Absorption vs Action spectra:

  • Absorption: the degree to which a particular wavelength is absorbed by a pigment

  • Action: the degree to which a particular wavelength generates a response (e.g. seed germination)

• Phytochrome responses:

  • Seed germination

  • De-etiolation

    • Stem length control

    • Hook opening

    • Leaf and cotyledon expansion

    • Chlorophyll synthesis

    • Chloroplast development

  • Gene expression

  • Membrane potential (leaf movements)

  • Anthocyanin synthesis (red/purple pigment)

  • Photoperiodic floral induction

• Some phytochrome (type phyA or type I) is photo-labile, and can be reverted or destroyed in far red light

  • Other types simply revert (phyB, phyC, phyD, phyE, or simply type II)

• PhyA and phyB are the most important

  • phyB is responsible for stem shortening

• Classes of reponses:

  • Very low fluence response (VLFR)

    • 1-50 nmole/m^2

    • Not photoreversible

    • Dark-growth

  • Low fluence response (LFR)

    • 1-1000 micromoles/m^-2

    • Photoreversible

    • Most classical physiological responses

  • High irradiance response (HIR)

    • 1-1000 micromoles/m^-2, proportional to irradiance

    • Many LFR are also HIR

• Phytochrome senses light quality as well as presence/absence

  • R/FR ratio is a reflection of ratio of wavelengths in ambient light

  • Different ratios can cause different responses

  • Ex. during the autumn, when there is less harsh blue light, carotenoids and anthocyanins are promoted to better absorb the light spectra (changing of leaf colors)

  • Phytochrome can sense end-of-day signals, shading, etc., allowing them to adjust growth rate

• Phytochromes can upregulate or downregulate gene expression at the transcriptional level

  • Upregulate: genes involved in photosynthesis, e.g.

  • Downregulate: phyA itself (negative feedback loop)

  • Acts as a kinase, catalyzes the transfer of a phosphate group from ATP to a molecule

• When in Pfr form, the phytochrome is able to move into the nucleus, where gene regulation can occur

18 - Photomorphogenesis - Chap. 13

• Sunset: high red:far-red light ratio; twilight: about equal red:far red ratio, less light overall

  • Changes dramatically over the course of minutes

  • High red:far-red light = low Pr:Pfr

  • As sunset hits, many Pfr molecules convert to Pr

• When shaded, the high concentration of inert Pr = taller growth to try and access light

• Reflected light is also high in FRL, which encourages plants that receive a lot of reflected light from nearby neighbors to grow taller + gain more upright leaves, outcompeting them

• PhyB = overexpression causes dwarf, and dark green appearance

  • Underexpression or mutant variants are long and skinny

19 - Photomorphogenesis - Chap. 13

• PhyB in the nucleus:

  • PrB can only enter the nucleus after transformation into PfrB

  • PfrB upregulates genes involved in growth, photosynthesis, etc. by removing prohibitory PIF3 regulators

  • Assists in transcription of MYB, which itself assists in transcription of CAB (chlorophyll a/b-binding protein gene)

Blue light signaling:

• Phytochrome can slightly absorb blue light, but not the primary photoreceptor - BL absorbed by cryptochrome and phototropin

• Blue light inhibits hypocotyl elongation (cryptochrome) and allows for phototropism (phototropin)

• Phototropin (aka NPH1) is a flavoprotein associated with the plasma membrane

• Blue light cases phosphorylation of phototropin, occurring in shoot tips

  • Two different fluence ranges are effective - “two pronged” action spectra

• Phototropin consists of two light-oxygen-voltage (LOV) domains each bound to a flavin mononucleotide, and a kinase domain

  • When exposed to blue light, the kinase domain unfolds, leading to each LOV domain and kinase domain binding to a phosphorus

  • This is reversible when no light is present

• Light causes the hormone auxin to retreat to the shaded side, inducing cell expansion and tilting the shoot towards the light source. This is irreversible.

• Two phototropins: PHOT1 and PHOT2

  • PHOT2 function: chloroplast movement

  • The actions of PHOT1 and PHOT2 are considered additive

  • The presence of low light triggers chloroplast accumulation, while high light triggers avoidance

    • In the dark, chloroplasts pool together

• Blue light is also responsible for stomatal opening and closing

  • When phototropin is activated, CBC kinase stops Cl- export and H+ pumps allow K+ in

  • Cl- and K+ accumulate in vacuole, causing an increase in solutes and expansion due to water potential

  • This expansion creates turgor, which opens the stomata

• PHOT1 and PHOT2 are both partially responsible for stomatal opening, but PHOT1 is mostly responsible for bending and PHOT2 is mostly responsible for chloroplast migration, especially in high intensities

20 - Tropisms and Nastic movements- Chap. 14

• Cryptochromes have two different chromophores to allow blue light absorption (pterin and FAD)

• Cryptochromes evolved from photolyases, involved in blue-light activated DNA repair

  • Both cryptochromes and photolyases are blue-light activated, and present in mammals and insects.

• When activated, cryptochrome dimerizes and is able to enter the nucleus, performing gene regulation in a similar manner to phyA and phyB - this is not photoreversible

• Cryptochrome inhibits hypocotyl elongation and sequesters auxin response factors, limiting growth

  • Similar to phototropin, but cryptochrome does NOT have a kinase - therefore it does not cause phosphorylation, and instead directly affects gene expression by entering the nucleus

UV light:

- UVR8 is the UV light receptor for plants and protects plants from high intensity UV

- UV light causes inactive dimers to monomerize and move to the nucleus, changing gene expression, inhibiting hypocotyl growth, and acclimating the plant to UV-B

• Note: phytochrome and cryptochrome both have to dimerize before they enter the nucleus. UVR8 has to monomerize

Root gravitropism:

• Root gravitropism refers to the directional shift of root to grow downwards with gravity

• Four phases:

  • Perception (1st second)

  • Transduction (first 10 seconds)

  • Transmission (10 sec-10 mins after stimulus)

  • Growth response

• Starch grains located within amyloplasts in the columella, which are inside organelles called statocytes

• Starch is heavy, and sinks to the bottom of the cell, interacting with pressure on the endoplasmic reticulum to elicit a response regarding gravity

• Gravitropism is achieved by increased growth on lower side of cell, and decreased growth on other - “trapezoid” shape

• Experiments show root cap is involved in inhibition of growth

  • When cap is removed, the vertical root grows slightly faster

  • When cap is removed on one half, that half grows faster, causing the root to bend towards the side with the remaining half-cap

  • When the cap is removed on a horizontally growing root, the root no longer responds to gravity and will not grow down

• The change in cell shape is due to auxin, which pools on the side of gravity in response to signals from the statoliths + ER; remember: auxin = longer cell walls!

Shoot Gravitropism:

• Response to gravity in shoot, called “negative gravitropism” because shoots grow opposing gravity (up, not down)

• Relies on amyloplasts found in the endodermis (between cortex and pericycle/vascular bundles)

• Similar auxin-based response, but this time with an opposite growth response - bottom side has increase in growth, not decrease

21 - Tropisms and Nastic movements - Chap. 14

Nastic Movements:

• Nastic movements do not relate to a vectorial component of the stimulus

• Occur faster than tropisms

• Some are reversible, others are not

• Some involve growth responses, others are turgor driven

• Turgor driven: slower (nyctinastic) or rapid (seismonastic/thigmonastic)

  • Involve a motor organ called a pulvinus

• Nutation: bending movement executed by some plant organs

• Nutational movements in vines = spiraling motion to try and grab onto a support

  • If shoot rubs against support, the spirals will become tighter as the shoot begins wrapping upwards around the support, a touch-based tropic response called thigmotropism

• Nutational movements in Venus Flytraps: stimulus causes plant to “snap closed”

• Nyctinastic movements are associated with plants that take up different positions during night and day

  • Ex. open leaf during the day, closed leaf at night

• Pulvinus allows leaf to undergo reversible positional changes by altering turgor

  • The outer cortex of the pulvinus has thin elastic cell walls that can change shape

  • Extensor cells are opposite flexor cells: extensor cells lose turgor during closing and gain turgor during opening, flexor cells gain turgor during closing and lose turgor during opening

  • Adaxial: upper surface, facing toward stem

  • Abaxial: lower surface, facing away from stem

• Seismonastic movements: occur in response to mechanical stimulation (i.e. shaking or vibration, NOT touch), wounding, and heat

  • Extremely rapid, all-or-none (not proportional to stimulus)

  • Ex. Mimosa pudica rapidly closes in response to vibration

Circadian Rhythms:

• Time-measuring in plants is done with the endogenous (internal) circadian clock

  • Rhythms can persist in the absence of external cues, be reset by external signals, and maintain periodicity independent of temperature

• Free-running rhythms persist for several diurnal cycles under constant conditions (not driven by sunset/sunrise!)

  • Circadian: 24 hr period

  • Lunar: 28 day period

  • Annual: 365 day period

  • Ultradian: <24 hrs

• Some nyctinastic movements controlled by circadian rhythms (open during day, closed at night, or only open for a few hours during the day)

• Luciferase gene from fireflies used to track activity of the clock without disturbing/destroying plants - some are mutants with circadian rhythms slower or faster than 24hrs (ex. ZEITLUPE mutant)

22 - Measuring Time - Chap. 16

• Circadian rhythms allow for anticipation of daily events and buffering of daily changes, and allow for timing of particular occurrences throughout the day

• Phase shifting: altering the phase of a rhythm with a single light pulse:

  • I.e. circadian rhythm is at low, but short burst tricks it into restarting at medium

• Circadian rhythms are “entrained” with light/dark or temperature cycles

• Temperature compensated: period stays similar even at different temperatures

• Principles of Operation:

  • Circadian oscillator: generates a rhythm with a 24 hr period within a cell

  • Entrainment/input pathways: synchronize the oscillator with the external time of day so the clock stays accurate - “retuning”

  • Output pathways: communicate temporal information from the oscillator to other parts of the cell

  • Circadian gating: adjusts sensitivity of entrainment and output pathways, depending on time of day

  • Environmental inputs -> entrainment pathways -> circadian oscillator -> output pathways

• Affected by circadian clock: gene expression, enzyme activity, ion fluxes, cell volume changes, flowering time

  • Chlorophyll synthesis generally peaks just before dawn (anticipating light activity)

  • Starch breakdown peaks around dusk

• It’s been proven through competitive testing that plants with accurate circadian rhythms perform better

• Circadian rhythms reflect biorhythms of predator species (i.e. less defenses when eggs, more defenses when caterpillars)

  • Jasmonate levels peak during the day to deter predators

• Circadian oscillator: autoregulatory negative feedback loop

  • Gene A encodes protein A

  • Protein A activates Gene B

  • Gene B encodes protein B

  • Protein B represses gene A

  • Allows for rhythms of transcriptional abundance

• Current circadian rhythm model is highly complex:

  • At its core: CCA1 and TOC1 code for proteins that repress one another

  • Experimental evidence showing sequential PRR protein action could also suppress CCA1

• Post-Transcriptional Processes:

  • Control of protein stability

  • Phosphorylation

  • Nuclear import

23 - Measuring Time, Flower Development - Chap. 16

Flowering:

• The formation of reproductive structures in angiosperms

• Floral evocation: the events in the apex that commit the SAM to produce flowers instead of leaves

• Steps:

  • Phase change; movement from juvenile to adult (sort of a prerequisite)

  • Induction; plant becomes determined to flower (will continue to flower, even if removed from circumstances that triggered flowering: no going back)

  • Expressed; the apical meristem undergoes morphogenesis (the plant actually makes flowers)

• Some stimuli triggering induction are environmental (e.g. photoperiod) while some are developmental (e.g. plant size, number of leaves)

• Signaling molecules produced in response to stimuli are carried to SAM via phloem vasculature

• Certain signs indicate when a plant is matured, or “determined to flower”

  • Make this decision primarily using photoperiod and changes in temperature

    • Long-day plants (LDP) flower only in long days

      • Flowering occurs when day length is greater than critical

      • Flower in spring

    • Short-day plants (SDP) flower only in short days

      • Flowering occurs when day length is sub-critical

      • Flower in late summer or early autumn

    • Day-neutral plants are unaffected by day length

24 - Flower Development - Chap. 16

• Experimental evidence suggests that flowering in SDP and LDPs are determined by length of unbroken darkness

• LDPs typically only flower in response to short nights, when presented with a long night with a short interruption of light in the middle, they will perceive it as a short night and flower, while SDPs will not

• Plants are more sensitive to the night break when it comes in the middle of the night

• Evidence suggests that the photoreceptors involved in perceiving and signaling night break are phytochromes

• How is changing night length measured?

  • Hourglass (less likely)

    • Daylight is measured by some accumulating product. When enough is accumulated, i.e a day is long enough, flowering is triggered

  • External coincidence (more likely)

    • Daylight measurement relies on a circadian oscillator that controls the activity of a regulatory molecule. Flowering occurs when the daylight overlaps with a phase of the cycle during which the levels of the molecule are above a particular threshold

• Flowering time is a highly regulated event centered on flowering locus T (FT)- later determined to be florigen

  • Photoperiod causes induction of FT in leaves, FT protein moves to the SAM, flowering is initiated

• In SDPs, flowering is controlled by Hd1 genes and Hd3a protein, in a similar manner to FT but with a negative feedback loop

25 - Plant Hormones: Intro, Auxin - Chap. 12

Vernalization:

• The effect of temperature treatments on flowering time - extended periods of cold promotes flowering by changing the responsivity to photoperiod

  • Most common in winter annual cereals (wheat, barley, rye) which are planted in the fall, overwinter as seedlings or young plants, and grow in spring

  • Perceived in shoot apex

• FLC is a key regulator, repressing flowering until it is turned off by low temperatures

• Evidence for florigen being FT protein: when an activated leaf is grafted onto the stalk of an uninduced plant, the plant will flower

• Journey of florigen:

  • Photoperiodic stimulus stabilizes CO (clock genes), which acts as a transcription factor

  • CO transcribes florigen, which leaves companion cell and enters adjacent sieve tube

  • Florigen transported through phloem to terminal bud

  • Florigen combines with FD (flowering locus D), and acts as a transcription factor for AP1 (APETALA1)

  • AP1 is made, and initiates flowering

• Four pathways control flowering (in Arabidopsis)

  • Photoperiod (florigen)(sensed in leaf)

  • Vernalization (FLC) (sensed in meristem)

  • Autonomous (i.e. number of leaves, size of plant, sensed in meristem)

  • Gibberellins (regulated by phytochrome and other triggers, meristem)

• When these pathways hit a certain point, promotion of meristem identity genes causes the meristem to be IDed as flowering, and formation of flower organs can begin

Formation of Flowers:

• Started with the sepals and traveling inwards (sepals -> petals -> stamen -> carpels) in whorls

• ABC Model:

  • Three classes of genes, in combination, define the formation of four organs

    • A alone = sepals

    • A + B = petals

    • A + C = stamen

    • C alone = carpel

    • A and C cannot coexist, and B cannot be by itself

• A is known as apetala2, B is known as apetala3/pistillata, and C is known as agamous

• If one or more of these gene classes is missing, we will see homeotic transformation, like 4 whorls of just sepals, or a carpel-stamen-stamen-carpel design

  • Examples: No A, Carpel-stamen-stamen-carpel

    • No B: sepal-sepal-carpel-carpel

    • No C: sepal-petal-petal-sepal

    • No B or C: sepal-sepal-sepal-sepal

• C, or agamous, is also required for determinacy, so if there is no C, the flower may continue to create new whorls (“flower-within-a-flower”) - the fourth whorl is replaced by a new flower

  • Humans will breed flowers with agamous down-regulation to get more beautiful, petal-filled flowers

• Absence of all three genes (A+B+C) results in the reversion of floral organs to leaves.

26 - Plant Hormones: Auxin - Chap. 12, 14

Plant hormones:

• Hormones are generally small

• Classified into six classes: auxins, gibberellins, cytokinins, ethylene, abscisic acid, brassinosteroids

• Effective even in small quantities

• Hormones in plants are typically:

  • Growth stimulators: cell division; cell elongation; organ initiation; differentiation

    • Auxins, gibberellins, cytokinins, brassinosteroids

  • Growth inhibitors, or stimulator antagonists: involved in senescence; abscission; flower fading; fruit ripening

    • Abscisic acid (ABA), ethylene

• Auxin: indole ring with various side chains

  • Primarily found in plants as indole-3-acetic acid (IAA)

  • Essential features: at neutral pH, intensely polar with charges separated by about 0.55nm

• Cytokinin: derived from adenine

• Abscisic acid: resembles terminal protein of some carotenoids

• Gibberellic acid: terpenoid

• Ethylene: a gas

• Brassinosteroid: plant steroid

• Auxin (IAA) directly correlated with phototropism, can persist in gelatin (most important on side facing away from light, that’s the side that grows)

• Auxin controlled via…

  • biosynthesis (tryptophan dependent or independent)

    • Tryptophan dependent: IAA forms from transformations in tryptophan molecules

    • Tryptophan independent: IAA forms from reactions occurring to chorismate

  • Biodegradation

    • Primarily through oxidation and decarboxylation

  • Conjugation

    • Free IAA is active, but most IAA is covalently bound

    • Conjugated auxins are metabolized to free auxin and the bound/free auxin ratio is a mechanism of regulation

  • Compartmentation

    • Free IAA can be found in chloroplasts & cytosol

    • Conjugated can be found in cytosol

  • Transport

    • Auxin is the only hormone known to be transported in a polar manner

    • Methods:

      • Nonpolar via phloem (passive, with gravity, fast)

      • Polar, from root tip short distances back up the root (basipetally) (slower, requires energy)

        • Via auxin transport proteins

    • Chemiosmotic model:

      • In apoplast, IAA is protonated, resulting in IAAH, being lipophilic and crossing membranes easily into cytosol

      • IAAH diffuses into cytosol, disassociate to IAA-, which accumulates in cytosol because it is less able to cross membrane

      • Polar transport due to auxin efflux and influx transporters at basal end of cells (at basal end of cells, transporters force out IAA-, which will move to the apex end of the following cell to be protonated and enter)

      • Not sure why but this allows it to move from apex to base at a rate of 1 cm/hr

27 - Plant Hormones: Auxin - Chap. 14, 15

• Auxin influx carrier (AUX1) codes for a protein that is localized at apex of protophloem cells

  • Columella, lateral root cap, and stele tissues

  • Location of AUX1 determined through antibody testing, where rabbit (example) antibodies are trained to recognize AUX1 as an antigen, and another, fluorescent antibody is trained to recognize rabbit antibodies as antigens, resulting in fluorescence of AUX1 locale. This is called immunolocalization

• Auxin efflux carrier (PIN family) codes for transmembrane efflux carriers (mutants for PIN1 grow uncontrollably because auxin cannot be removed)

  • PIN1 directs vertical auxin movement from shoot-root, and is responsible for recirculation at the SAM

  • PIN3 redirects auxin laterally back into vascular tissue

  • Creates directional flow

• Auxin generally restricted to vascular tissue via PIN3 and ABCB19

• Physiological effects of auxin:

  • Cell elongation (via increasing extensibility of wall)

  • phototropism

  • Gravitropism

  • Apical dominance

  • Lateral root formation

  • Fruit development

  • Vascular differentiation

• Cell elongation occurs through acid growth hypothesis

  • Auxin increases rate of protein extrusion into cell wall

  • Low pH activates apoplast-localized growth hydrolases called expansins

  • Expansins loosen H-bonds between polysaccharides in cell wall, allowing for growth

  • This, in turn, allows for more water to enter cell, inducing even more cell growth

• Lateral and adventitious roots:

  • Horizontal root growth, induced by auxin

  • Originate from pericycle of primary root

  • DR5:GUS reporter indicates that auxin levels are high during lateral growth

Dictionary

Dictionary

Quick reference

• Phloem: part of the vascular bundle, transports sugars, proteins, and organic compounds produced via. photosynthesis up and down. Allows for two-way travel

• Xylem: part of vascular bundle, transports water and water-soluble nutrients from roots to leaves in only one direction. Composed of dead cells.

• Cortex: Tissue layer between epidermis and vascular tissue

  • Parenchyma: soft tissue making up the cortex and pith of stems. In leaves, contains cells for photosynthesis. Also stores starches, proteins, water, and oils.

• Pericycle: layer of cells surrounding the vascular tissue, providing support and structure, site of lateral root initiation

• Apoplast: extracellular space between plant cell membranes

  • Apoplastic pathway: water traveling through cell walls

  • Symplastic pathway: water traveling through cytoplasm

• Stele: central core of stem and root, consisting of vascular tissue and associated supporting tissue

15 - Patterns in Plant Development - Chap. 15

• Cellulose: polysaccharide composed of long fibers of hydrogen, carbon, and oxygen - allows for structural integrity in cell walls

• Microtubules: lay underneath plasma membrane and dictate the orientation of cellulose microfibrils

• Embryogenesis: transformation of a single-celled zygote into a multicellular embryonic plant

• Cotyledon: aka “seed leaves”, leaf-like structure that is part of a plant's embryo and is often the first leaf to appear when a seed germinate, not real leaves

  • Monocot: one seed leaf (i.e. grass)

  • Dicot: two seed leaves (i.e. trees)

• Hypocotyl: area between cotyledon and root

• Plant meristems: similar to human stem cells. Zones of actively dividing cells, and sole occurrence of cell division.

• Apical meristems: located on tips of shoot and root, responsible for elongation. AKA. primary meristems, as they are responsible for primary growth

• Anticlinal division: division to the left or right, perpendicular to the surface

• Periclinal division: division up or down, towards or away from the surface

• Tunica: layers 1 and 2 of a shoot apical meristem, where cell division occurs apically

• Corpus: layers below the tunica, where cell division occurs in all directions

• Phytomere: repetitive developmental unit that a shoot is constructed from, generated from repeating SAM activity

  • Usually consisting of bud, internode, node, leaf

    • Node: connection between leaf and stem

    • Internode: elongated stem portion between nodes

• Phyllotaxy: arrangement of leaves around stem, determined by the activity of the SAM

• Axillary meristems: form later in development, in the axils of leaves

  • Axil: position along shoots where leaves develop (aka base of node)

• Vascular cambium: forms both xylem and phloem (fusiform initials), and rays of pith (ray initials)

  • Fusiform initials: elongated initial cells

  • Ray initials: smaller, forms rays of pith

• Quiescent center: collection of proto-differentiated cells surrounding meristematic cells that determines identity of adjacent cells

• Etiolation: result of dark development. Bleached, yellow appearance (no chlorophyll), unexpanded cotyledons, and tall appearance

16 - Patterns in Plant Development, Growth and Development of Cells - Chap. 15

• Sepals: small leaf-like structures on the outside of the flower

• Petals: decorative and colorful leaf-like structures surrounding reproductive organs

• Stamens: consist of a long filament and an anther, which develops pollen

• Carpels: the site for fertilization, connects to ovaries

• Photomorphogenesis: development in light

• Skotomorphogenesis: development in dark

• Chromatophore: blue-green pigment cell that absorbs particular wavelengths of color

• Apoprotein: protein that is involved in structural changes during the photoreversible phototransformation of phytochrome

17 - Growth and Development of Cells - Chap. 17

• Seed germination: the process by which a seed grows into a seedling and eventually a plant

• Membrane potential: the difference in electric potential between the interior and the exterior of a biological cell

• Fluence: amount of light (mole/m^-2), time independent

  • Irradiance: fluence rate (mole/m^-2/s)

• Kinase: an enzyme that catalyzes the transfer of a phosphate group from ATP to a molecule

18 - Photomorphogenesis - Chap. 13

• Phototropism: directional growth in response to light (controlled by phototropin)

19 - Photomorphogenesis - Chap. 13

• Stomata: microscopic pores in the epidermis of leaves responsible for gas and moisture exchange, opening during the day and closing at night

20 - Tropisms and Nastic movements - Chap. 14

• Amyloplast: double-enveloped plastid in plant cells that stores, produces, and breaks down starch

• Statocytes: gravity sensing cells that contain amyloplasts

• Columella: the central portion of the root cap

21 - Tropisms and Nastic movements - Chap. 14

• Nastic: non-directional plant responses, i.e. response to temperature, wounding, mechanical shocks, touch, heat

• Nutation: bending movement executed by some plant organs

• Pulvinus: bulbous structure at the juncture between the petiole and the stem. It has large specialized thin-walled cells which alter the position of the leaf by undergoing reversible changes in turgor.

• Adaxial: upper surface, facing toward stem

• Abaxial: lower surface, facing away from stem

• Seismonastic movements: occur in response to mechanical stimulation, wounding, and heat

• Thigmonastic movements: occur in response to touch

22 - Measuring Time - Chap. 16

• Circadian oscillator: generates a rhythm with a 24 hr period within a cell

• Entrainment pathways: synchronize the oscillator with the external time of day so the clock stays accurate - “retuning”

• Output pathways: communicate temporal information from the oscillator to other parts of the cell

• Circadian gating: adjusts sensitivity of entrainment and output pathways, depending on time of day

• Jasmonate: molecule that stimulates herbivorous defense mechanisms, i.e. production of toxins

• Floral evocation: the events in the apex that commit the SAM to produce flowers instead of leaves

• Apex: very tip of leaf

23 - Measuring Time, Flower Development - Chap. 16

24 - Flower Development - Chap. 16

25 - Plant Hormones: Intro, Auxin - Chap. 12

• Florigen: protein that promotes flowering, generated in the leaf apex and moving to the meristem through the phloem

• Gibberellins (GA): promotive hormone that allows for flowering in SDP

• Homeotic transformation: expression of the right organ in the wrong place

• Cadastral function: acting to limit the range of action of certain genes

26 - Plant Hormones: Auxin - Chap. 12, 14

• Hormones: chemical messengers that mediate intercellular communication

• Receptors: specific proteins within cells that hormones interact with to create active hormone-receptor complexes

• Basipetal transportation: from apex of leaf or root to base of shoot

• Acropetal transportation: towards root tip

27 - Plant Hormones: Auxin - Chap. 14, 15

• Expansins: growth-specific hydrolases that are localized to the apoplast and are activated by low pH