Exam 2- Secondary Growth/Roots

continuous cylinder

• common in dicots/gymnosperms

• narrow interfasicular regions

discrete bundles

• wide interfasicular region

scattered bundles

• randomly scattered vascular bundles, no discrete pith or cortex

• common in monocots

• tend to be higher in concentration near the epidermis

Open vascular bundle

• bundle sheath is present, but there is a gap, doesn’t form a complete ring around bundle

• mostly eudicots

closed vascular bundle

• is surrounded by a bundle sheath

stomata

• exist in stems

• become lenticels

Leaf gap

• space in developing plant near the axillary bud

• appears as if there is no vasculature, but the vascualture actually moves around the axillary bud

• not broken, just moved

branch traces

• protrude for space for the vasculature to grow as the axillary bud grows/matures

• refers to the veins diverging from the stem

leaf trace

• the vein that enters the leaf on a stem

stem trace

• two exist at each leaf gap

• unite above the leaf gap

Proximal-distal

• distance from stem

adaxial

• upper surface of leaf (usually)

abaxial

• lower surface of leaf (usually)

Alternate phyllotaxy

• 1 leaf is formed at a time

• includes spiral/helical and distichous

spiral/helical

• alternate leaf (1 at a time)

• arranged in a circle around the stem

• arranged 137 degrees apart to avoid 1 leaf shading another

• in a short stem, arrangement is usually called a whorl

• ex- sunflower

• arranged as far away from another as possible, trying to position so all leaves get equal sun access

distichous

• alternate (1 leaf at a time)

• arranged in a circle 180 degrees apart

• opposite sides of stem

opposite leaves

• 2 leaves formed at a time

decussate

• a type of opposite leaf (2 leaves at a time)

• 180 degrees apart from one another, as it makes new pairs, the meristem rotates 90 degrees

whorled leaves

• 3 leaves formed at a time

• 3 or more leaves attached at the the same point

Simple leaves

• 1 unit, 1 margin

• a single leaf, undivided blade

• can have lobes

compound leaves

• nondivided leaflets

• blade consists of multiple leaflets, leaflets have no axillary bud at base

double compound leaves

• each leaflet is divided into smaller “leaves”

Compound leaf types

• palmate

• pinnate

palmate leaves

• compound leaves

• leaflets arise from a common point

pinnate leaves

• leaflets arise from several locations along the axis

Abscission zone

• located at the base of the leaf, composed of smaller cells

• has a protective layer that eventually covers the stem and creates a new covering to cover the wound site/abscission site

• protective layer usually occurs on side closest to stem, sometimes makes a second protective layer on the side that will fall

• after abscission, area is heavily lignified and leaves a scar

Kranz anatomy

• a specific arrangement of leaf cells present in C4 photosynthetic plants

• typical of monocots/grasses, but not all monocots/grasses are c4

• consists of a bundle sheath and a ring of mesophyll cells that surround the bundle sheath

• 1:2:2:1 architecture (bundle sheath, mesophyll, bundle sheath)

C4 photosynthesis

• c4 plants use a different pathway for fixing co2

• they have a higher concentration of co2, so rubisco only/mainly fixes co2 instead of o2 (rubisco can accidentally fix o2 and that is not great)

Bulliform cells

• only form on adaxial size

• typical of monocots, but not all

• large and full of water

• when full of water, turgor pressure causes leaves to lay flat for maximum photosynthesis

• when not enough water is present, the bulliform cells lose turgor pressure and fold the leaf in on itself to prevent the sun frying the leaves

Intercalary meristem

• common in grasses

• meristems found between differentiated tissue

• allow for continued growth of leaves and stems in monocots

• located at the base of the internote, leaf sheath, and blade

stomatal crypts

• sunken in cavities where stomata are housed in some plants

• prevent water loss by trapping hot water vapor

• characteristic of plants in arid environments

• lots of trichomes in the crypt to help trap that water

laticifers

• specialized cells, long and stringlike

• can be 1 long cell or many smaller cells joined together

• present throughout the plant, running from root to shoot

• usually located near the phloem

• produce latex

• can be branched(horizontally connected to other laticifers) or unbranched

• evolved independently in multiple lineages

articulated laticifer

• composed of multiple cells that have been fused together

• their cell walls are either completely intact (non anastomosing) or partially dissolved (anastomosing)

• ex - rubber tree and poppy

non articulated laticifers

• compose of one elongated cell, no separation

• ex - cannabis

Latex

• primarily a defensive mechanism against pathogens/threats

• contain peptidases, osmotins, chitinases, and germin like molecules

lithocyst

• located in the epidermis

• forms a crystal called a cystolith

• function as a light refraction mechanism, a way to direct light into photosynthetic cells

taproot

• dicots

• larger and longer than all other roots

• form first

fibrous roots

• monocots

• many small roots

hypocotyl

• segment of plant between the root and the cotyledons

mucigel

• carb based polymer that is hydrophilic

• gel that protects the root tip from being damaged

• located from below root cap to the zone of differentiation

root cap

• zone that covers the root apical meristem for protection

• cells are shed from the root cap into the mucigel during development

quiescence center

• located in the root apical meristem

• divides slowly to maintain the quiesence center/ram

• once cells are pushed to peripheral zone, they then rapidly divide

casparian strip

• restrict the movement of water through a root

• act as a filter to what can access/enter vasculature

• located in the endodermis

Gravity sensing in the root cap

• occurs in root cap collumella cells

• orientation of amyloplast determines directional growth

• will follow gravity (ex- all amyloplasts fall to the bottom with gravity, causing the root to grow downwards)

root hairs

• single celled protrusions that increase the surface area for water, air, etc.

• grow int eh zone of differentiation

• form from trichoblasts - originate from epidermis

atrichoblasts

• non root hair forming cells

lateral roots

• originate from the pericycle

• side roots, smaller than the taproot in eudicots

adventitious roots

• roots derived from non root tissue

• usually from a node, which is called a nodal root

• ex- maize brace roots

maize brace roots

• adventitious root

• produced from the stem nodes sequentially throughout development

• form the major framework of the mature root system

• critical to sustain water and nutrient uptake as the plant matures

• under drought conditions, have to grow into and through the surface soil, which can become very dry

rhizobia

• nitrogen fixing symbiont in legumes

• find the plant by producing a nod signal

• the plant makes flavinoids

• Rhizobium recognize the flavinoids

• infect plant via roothairs

frankia

• nitrogen fixing symbiont in non legumes

nitrogen fixing symbionts (rhizobia/frankia)

• take nitrogen in the atmosphere and convert it into a bioavailable form that the plant can use

leghemoglobin

• bacterial nitrogenase enzyme complex

• sensitive to oxygen

• presence of leghemogloblin in root nodules provides low oxygen environment suitable for nitrogenase activity

indeterminate nodule

• no known end

• branched

determinate nodule

• known end

mycorrhizal fungi

• genera of fungi that form symbiotic relationships with plants

• dramatically expand access to moisture and nutrients from the soil

• in return, the plant feeds the fungi with sugars and organic substances

ectomycorrhizae

• go around plant cells, forming a hartig net between cells

• never enter plant cells

• common in temeprate trees

arbuscular mycorrhizae

• enter in the plant

• goes through the cell wall and forces plant to form a membrane around the haustorium

• never technically enters the cell, only the cell wall

• non woody plants

fasicular

• formed from differentiated procambium

• separates the primary xylem and phloem

interfasicular

• between fasicles (bundles)

• formed from the pith

fusiform initial

• longer, vertically oriented

• produce the axial system of secondary vascular tissues

ray initial

• smaller, square/circle shaped

• form the radial system of secondary vascular tissue

• composed of parenchyma cells that conduct food substance from the secondary phloem to the secondary xylem and water from the secondary xylem to the secondary phloem

• can also store starch, lipid, proteins, and tannins

• extend horizontally through the secondary xylem and phloem

dilated phloem ray

• wedge shaped phloem that grows to fill empty space

• due to the shape of the stem/root being a circle, the outside part is larger than the inner part, leading to more space or gaps that needed to be filled

heartwood

• non conducting portion of xylem

• older in age

• closer to pith

• secondary compound storage

• darker in color

Resin ducts

• found in some gymnosperms

• intercellular spaces lined with thin walled parenchyma cells

• the parenchyma cells secrete resin into the space where it serves as a defense against pathogens

Sapwood

• functional xylem, more recently formed

• has less sap, resin, etc.

• usually lighter in color

• conductive

Tight knots

• living, no dead zone

• branch is integrated into wood

loose knot

• dead zone that forms around the branch

Knots

• result of branches that were buried in the growing stem

• can be tight (living) or loose (dead)

Uniserate

• one column of ray initials

multiserrate

• multiple columns of rays

Ring porous

• large variation in xylem size

• earliest forming vessels are larger

• later formed vessels are smaller

diffuse

• less variation in xylem size

hardwood

• angiosperms/deciduous

softwood

• gymnosperms/confiers

tension wood

• tilted hardwood stem is pulled upright again by tension wood

• forms in the newly developed growth rings - asymmetrical stem cross section

• new growth occurs above to pull the wood back into place

compression wood

• grows below the pith to push the wood up into place

• softwoods

cystolith

• crystal like structure in the lithocyst

• acts like a disco ball, refracting light further into the mesophyll

Paper about xylem velocity

Main focus: looks at sieve tube relation to flow regulation, higher conductivity is not associated with higher velocity and that the temporal development of the callouses show that small sieve plates can be plugged in minutes but larger pores need additional support to be plugged

Method: SEM and NMR flow imaging (magnetic resonance imaging) to measure flow rate

Phloem Size

Main focus: after 90 microns in diameter, the cell wall size for the parenchyma phloem transfer cell is increased, depends plant to plant and environment. Why more plants don’t have thicker phloem: carbon resource

Arabidopsis phloem parenchyma transfer cells paper

Main focus: More towards the apex of the leaf and smaller veins had more ingrowths, classified ingrowths into 5 classes based on ingrowth amount, more correlation with sieve

Trichomes in arid perennial species

Main point: glandular trichome secretions protect against herbivory, non glandular broken down to make gelatinous substance that coats developing organs for protection and preventing degradation

Methods: SEM, TEM, light microscopy, histochemical tests

lavender paper

Main point: peltate trichomes produce most compounds, capitate trichomes were on petals, more glandular trichomes on bottom of leaves

submerged vs aerial leaf paper

main point: both leaves differ developmentally and morphologically

arsenic and amf paper

main point: different levels of arsenic and different mycorrhizae species, G. clarum was the best at taking up arsenic, does not hyperaccumulate, amf takes up arsenic instead of phosphate, causing cell wall collapse and lipid formations. As arsenic levels increased, more severe collapsing and more lipid formations occured

methods: TEM, light microscopy, SEM