Chapter 10 – Transport in Plants

Transport in plants  Water and mineral nutrients must be absorbed by the roots and transported throughout the plant  Sugars must be transported from site of production, throughout the plant, and stored

Cellular transport mechanisms

Osmotic potential, solutes, and water movement

Water potential influences water movement  Water potential (Ψ) of a cell: Ψ cell = Ψ Ρ + Ψ Ο Ρ = pressure potential Ο = osmotic (solute) potential

Ψ p - Pressure potential (turgor) Low Ψ p High Ψ p

Ψ Ο – Osmotic (Solute) potential  Pure water Ψ Ο = 0  All solutions, Ψ Ο < 0  As solute concentration increases, Ψ cell …

Water movement in plants  Movement from high Ψ cell to low Ψ cell  Occurs in the xylem  Involves adhesion, cohesion, and pressure

Adhesion and cohesion

Water transport

Tension-cohesion theory explains xylem transport  Water is drawn up the plant by transpiration of water from stomata

A water potential gradient creates tension

low ψ Transpiration creates tension higher ψ cohesion higher ψ lower ψ higher ψ lower ψ higher ψ highest ψ lower ψ

Water transport animation

Transpiration & water transport

Importance of stomata  Regulate transpiration rate –Controls rate of water uptake  Water required for photosynthesis  Water required to maintain turgor pressure  Influences nutrient uptake  Regulate gas exchange –CO 2 required for photosynthesis

Turgid guard cells open stomata

Guard cells & osmotic potential

Transpiration & photosynthesis

Ψ and transpiration rate  In terms of ψ, can you explain how transpiration rate is influenced by: –Atmospheric humidity? –Wind? –Air temperature? –Light intensity?

Which of the following explains why water moves into the root from the soil? 1. The water potential of the root is lower than the water potential of the soil 2. The roots exist in a hypertonic environment 3. The pressure potential of the soil forces water into the root 4. Water is actively transported into the root 5. The soil has a higher solute concentration than the roots, causing water to diffuse into the roots

Stomata close when 1. Photosynthesis lowers CO 2 concentrations in the leaves 2. Potassium ions are pumped into guard cells 3. Abscisic acid levels increase 4. Guard cells become turgid 5. All of these occur

A guard cell with a high internal concentration of K + 1. Is in a hypertonic condition 2. Has a low water potential relative to outside of the cell 3. Has a higher water potential than outside the cell 4. Both 1 and 2 5. Both 2 and 3

Water transport

Sugar transport

Source to sink sugar transport

Pressure-flow hypothesis explains sugar transport

Phloem loading

Sugar transport can be explained by water potential

Transport in plants  Water and mineral nutrients are absorbed by the roots and transported throughout the plant by tension-cohesion  Sugars are transported from site of production (source), throughout the plant, and stored (sinks) by pressure-flow

Mineral nutrition & uptake

Soils and plant nutrition  14 essential mineral nutrients –N,P,K,S,Ca,Mg,Fe,Cl,Mn,B,Zn,Cu,Mo,Ni  3 essential non-mineral nutrients –C,H,O –What makes these nutrients essential?

Magnesium and photosynthesis

Nitrogen and amino acids

Nitrogen, phosphorus & DNA

Potassium and cell function

Macronutrients vs. micronutrients

Fertilizers  Fertilizer analysis (N-P-K)  Analysis varies depending on growth objectives

How can essential elements be determined?

Hydroponics

Recreational hydroponics  Home hydroponics systems Home hydroponics systems

A soil profile  Soil composition –Sand, silt, clay –Humus –Microorganisms –Animals

Mineral nutrients exist as ions

Cation exchange allows mineral ions to be absorbed by roots

Cation exchange and H +

Mineral nutrient transport

How does cation exchange affect soil pH?  Raising soil pH with lime Ca(OH) 2 + 2H +  Ca H 2 O

Soil pH and mineral nutrition Different types of plants have different soil pH requirements (ex. truffles, filbert trees, and alkaline soils)

Which of the following statements concerning plant nutrition is/are true? 1. Macronutrients are large elements and micronutrients are small elements 2. Macronutrients are essential to plant growth and micronutrients are not essential 3. Macronutrients are absorbed from the atmosphere and micronutrients are absorbed from the soil 4. All of these are true 5. None of these are true

Cation exchange 1. Occurs when plants release O 2 and absorb CO 2 through their stomata 2. Involves plants releasing Ca 2+ into the soil in order to absorb H + ions 3. Involves the release of H + ions from roots to displace mineral nutrient ions from soil particles 4. Allows plant roots to absorb C, H, and O through their roots by converting these atoms to cations