Abiotic challenges: water and food

how does water move against gravity

water potential differences across plant and environment

Water potential

difference in potential energy between pure water and water in a system

osmotic potential

from dissolved solutes-major component in cells

pressure potential

from hydrostatic and pneumatic pressures-turgor

matric potential

cohesive forces of water to other objects

gravitational potential

gravity

water moves from ____ water potential

higher, lower

-less negative to more negative

___ provides driving force for water to move from soil through plant to atmosphere

gradient in water potential, can also lead to evaporation from soil to atmosphere

mesophytes

grow in regions with moderate soil moisture

• Affected by short, mild water shortages

• Respond by closing stomata

xerophytes

grow in regions with frequent, extended droughts

• Possess adaptations to balance photosynthesis with water conservation

hygrophytes

grow in areas almost permanently saturated with water

• Must deal with hypoxic conditions!

shading

plants some parts to shade other parts from sunlight (e.g. ribs in cacti) to reduce photosynthesis and evaporation

avoidance strategy

long-term seed dormancy can help plants avoid extensive droughts (e.g. desert superbloom)

leaf abscission

during dry season: 20000Helps plants minimize photosynthesis(e.g. kapok tree)

vegetative dormancy

some herbaceous plants die back during dry season, and only retain belowground structures (e.g. rhizomes, corm)

bulb

short, flattened stem bearing fleshy, food-storage leaves (e.g. onions)

corm

short, swollen underground stem with thin, scally leaves protecting it (cormlets - asexual reproduction)

fleshy rhizome

thick underground horizontal stem,serves as water and food storage (e.g. ginger)

tuber

enlarged tip of a rhizome containing stored foods(e.g. potato)

morphological adaptations

roots structure,modified leaves, etc

anatomical adaptations

photosynthetic stems, epidermal hairs, etc

physiological adaptations

osmoregulation,CAM photosynthesis, etc

roots

xerophytes have a greater root-to-shoot ratio than mesophytes (i.e. they invest more in roots).

• Shallow and extensive to take advantage of brief rains (e.g. cancti)

• Deep roots reaching water table (phreatophytes)

succulent tissues in leaves or stems

reduced surface-to-volume ratio: reducing water loss while increasing water storage capacity.

photosynthetic stems

can be only photosynthetic organ (e.g. cacti) or secondary for drought (e.g. paloverde)

leaf abscission

in some species, water deficit triggers hormonal changes that lead abscission of older leaves, preserving water for younger ones

osmoregulation

involves the synthesis of solutes(e.g. proline) to lower the water potential of cells; preventing loos of turgor

• Used by some halophytes ("salt" plants)

resurrection plants

plants survive cellular desiccation;via the coordinated modification of the cytoplasm and cell membrane

CAM photosynthesis

Crassulacean Acid Metabolism (CAM):

• A specialized form of C4 photosynthesis

• Temporarily separates the absorption of CO2(nighttime) from the light-dependent reactions and Calvin cycle (daytime).

• Plants open stomata at night (minimizing water loss); carbon is stored as Malic acid in the vacuole and then converted to CO2 during the day

waterlogging

only the root system is under anaerobic conditions

flooding partial submergence

all roots immersed in water while just portion of shoot covered by water

flooding complete submergence

all plant is under the water level, water depth and turbidity important

physiological responses

-Closure of stomata and reduced photosynthesis

• Reduction of water uptake - closure of aquaporins

• Can lead to drought-like responses, such as leaf abscission In contrast, flood tolerant species can maintain water relations thanks to several adaptations

aerial root formation

several species form adventitious roots that remain above water and can transfer oxygen to submerged roots

cypress knees

vertical protuberances of roots that serve the same role as aerial roots

aerenchyma

modified spongy parenchyma that allows for gas exchange between shoots and roots

-Aerenchyma forms in the root cortex to allow diffusion of oxygen from the shoot

lenticles

form in aerial roots and lower parts of the stem to allow for oxygen intake

3 generating mechanisms of aerenchyma

• Lysigeny: collapse and death of cells in the cortex

• Schisogeny: expansion of intercellular spaces

• Expansigeny: cell division and expansion

Radial O2 loss (ROL) barrier

prevents diffusion of oxygen to anoxic soil, retaining O2 in the root

fermentative bypasses

ameliorate poisoning via accumulation of toxic byproducts

activation of antioxidant enzymes

helps buffer accumulation of reactive oxygen species