Module 9: Abiotic Stress & Water

What are the main abiotic challenges plants face when adapting to land?

Water acquisition, structural support, reproduction in dry environments, and avoiding desiccation.

What is desiccation?

drying out

Bryophyte

nonvascular plant; examples are mosses and their relatives

How does water move in non-vascular plants?

From cell to cell via diffusion

How does water move against gravity?

Water potential difference across plant and environment

What evolutionary adaptation helps plants prevent desiccation?

The evolution of a cuticle.

What is the role of lignin and vascular systems in plants?

They provide structural support and facilitate water transport.

What is water potential (Ψ) in plants?

The difference in potential energy between pure water and water in a system, influencing water movement.

What are the components of water potential (Ψ)?

Osmotic potential (Ψπ)( from dissolved solutes), pressure potential (ΨP)(turgor), matric potential ( cohesive forces of water to other objects) (Ψm), and gravitational potential (Ψg).

What does a gradient in water potential provide?

The driving force for water to move from soil through the plant into the atmosphere, it also leads to evaporation from soil to the atmosphere

How does water move in plants?

Water moves from areas of higher to lower water potential, typically from less negative to more negative values.

What are mesophytes?

Plants that grow in regions with moderate soil moisture and respond to mild water shortages by closing stomata.

What adaptations do xerophytes have for drought conditions?

They possess adaptations to balance photosynthesis with water conservation.

What are hygrophytes?

Plants that grow in areas almost permanently saturated with water and must deal with hypoxic conditions.

How do plants adapt to drought conditions?

By shading, avoiding sun with long-term seed dormancy ( desert plants), leaf abscission (helps minimize photosynthesis), vegetative dormancy ( some herbaceous plants die during the dry season and only retain underground structure eg: rhizomes and corn)

What is a bulb in plant anatomy?

A short, flattened stem bearing fleshy, food-storage leaves, such as onions.

What is a corm?

A short, swollen underground stem with thin, scaly leaves that protect it and can reproduce asexually.

What is the function of a fleshy rhizome?

It serves as a thick underground horizontal stem for water and food storage, like ginger.

What is a tuber?

An enlarged tip of a rhizome that contains stored foods, such as a potato.

What are some morphological adaptations of xerophytes?

Root hairs, photosynthetic stems, greater root-to-shoot ratio, shallow and extensive roots for brief rains, and deep roots reaching the water table.

Why is succulent tissue helpful for desert plants?

reduced surface to volume ratio, reducing water loss while increasing water storage capacity

What is a xerophyte?

A plant adapted to living in dry conditions

What are physiological adaptations to drought?

In some species, water deficit triggers hormonal changes that lead to the abscission of older leaves so their is water for younger ones, plant can also survive cellular desication by modiciation of cytoplasm and cell membrane

What is osmoregulation?

involves the synthesis of solutes to lower the water potential of cells, preventing loss of turgor

What is CAM photosynthesis?

A specialized form of C4 photosynthesis, which separates CO2 absorption at night from the light-dependent reactions during the day, allows plants to open their stomata at night to minimize water loss. Carbon is stored as malic acid in the vacuole and converted to CO2 during the day.

What adaptations do flood-tolerant species have?

They can maintain water relations through adaptations like aerial root formation and aerenchyma for gas exchange. They also can close stomata and reduce water uptake by closing aquaporins (can also lead to drought conditions if closed too long)

What are cypress knees?

Vertical protuberances of roots that serve the same role as aerial roots ( can help with water intake issues)

What are lenticels?

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

Why are floods a problem for plant species?

Oxygen diffusion in flooded soils is severely diminished because there is more water than air in soils. This causes soils to be more compact and less aeriated, which causes hypoxia and toxic waste products, which add stress.

What is aerenchyma?

Modified spongy parenchyma that allows for gas exchange between shoots and roots in flooded conditions.

What are the three generation mechanisms of Aerenchyma?

Lysigeny ( collapse and death of cells in the cortex), Schisogeny (expansion of intercellular spaces), expansigeny ( cell division and expansion)

What is the role of stomata closure in flood-sensitive species?

It reduces photosynthesis and water uptake, leading to drought-like responses such as leaf abscission.

What is the significance of radial O2 loss (ROL) barriers in plants?

They prevent oxygen diffusion to anoxic soil, retaining oxygen in the root for respiration.

What are some physiological adaptations to drought in plants?

Leaf abscission, osmoregulation, and the ability to survive cellular desiccation.

What is the function of lenticels in plants?

They allow for oxygen intake in aerial roots and lower parts of the stem.

What is the purpose of fermentative bypasses in flood-tolerant plants?

To ameliorate poisoning from toxic byproducts accumulated during flooding.

What is the role of antioxidant enzymes in plants under stress?

They help buffer the accumulation of reactive oxygen species during flooding or drought conditions.