lecture 10: plant growth -- shoots

Question 1

Casparian strip / suberin

Answer 1

a layer of waxy material called suberin that blocks all passage

• Minimizes leakage of accumulated solutes out of the vasculature
• part of travel through the apoplast

Question 2

primordia

Answer 2

an organ, structure, or tissue in the earliest stage of development.

Question 3

Phyllotaxy

Answer 3

• the non-random order and arrangement of primordia initiation
• Each successive leaf emerges ~ 137.5˚ from the site of the previous one
• One hypothesis is that phyllotaxy averts self-shading, also maximizing leaf coverage of ground area + shading shorter competitors

Question 4

basic leaf types: simple / compound

Answer 4

simple leaf:
- Has a single, undivided blade
- Some are deeply lbed

compound leaf:
- The blade consists of multiple leaflets
- A leaflet has no axillary bud (embryonic shoot) at its base
- In some plants, each leaflet is further divided into smaller leaflets

Question 5

stem diversity (rhizomes, stolons, stem tubers)

Answer 5

rhizomes:
- underground stems that can put up new shoots

stolons (“runners”):
- stems that extend along the soil surface and establish new plantlets with leafs and roots at nodes
- persist even if stolon cut or original plant dies

stem tubers:
- enlarged ends of rhizomes or stolons that store food

Question 6

spines, thorns, and prickles

Answer 6

*all modifications of stems

spines = modified leaf tissue (dead, fibrous
thorns = modified stem tissue, woody
prickles = modified epidermal extensions of the stem (corky projections from plant’s skin) - no vascular tissue, merely sharp projections and pop off easily (like roses)

Question 7

secondary growth

Answer 7

• drives the thickening of plant stems (or roots)
• mostly occurs only in eudicots and conifers
• involves lateral meristems (self-renewing tissues that form cylindircal bands) once that part of the stem has finished elongating (primary growth)

Question 8

vascular cambium, cork cambium

Answer 8

• part of secondary growth

vascular cambium (VC): lateral meristematic tissue that runs between xylem and phloem
- adds more of those tissues, widening the shoot while also increasing vascular flow and support

cork camium: lateral meristematic tissue that develops from parenchyma within the cortex
- produces a tough, thick, waxy covering called cork that protects stem from water loss and from invasions by pathogens and insects