Plant physiology notes

Upcoming Quiz and Symposium

• Quiz on Thursday will cover water and sugar transport, and plant nutrition; it will be similar in format to exam questions.
• Symposium registration is an assignment due by the end of the week; students must indicate whether they will attend.
• After registration, teams submitting posters will receive an email about abstract submission, which should be done by one representative per team.
• Abstract submission deadlines are common before experiments are complete; vagueness about results is acceptable when necessary.
• Posters are due Week 9, requiring an accelerated effort in the coming days.
• Proposals should be reviewed and approved before starting experiments; only a couple of proposals have been reviewed so far.
• A second exam will be held on finals day, likely Tuesday of finals week, at the usual class time.
• Students not presenting at the symposium will have an alternative evaluation date; badges for scientific presentation will be issued based on performance and may eventually appear on transcripts.

Experimental Design

• The sooner you complete your proposal, the faster you can start experiments.
• Some students are already conducting chemistry-related experiments, which will complement bioassays.
• Using butterflies and caterpillars simultaneously can be difficult due to unpredictable instar availability.
• Collecting butterflies to start a personal colony is recommended.
• Experimental design hinges on timing; synchronize plant readiness with caterpillar availability.
• Organisms are ready on their own schedule; early starters have priority access to caterpillars.

Water Potential

• Definition: Water potential is the potential energy of water, measured at room temperature and atmospheric pressure; zero indicates no movement.

• Factors that Affect:

  • Root Pressure: Pressure potential in roots drives water upwards against gravity.

    • Soil conditions (dry versus wet) and temperature can influence root pressure.

  • Capillary Action: Draws water up cells of xylem.

  • Cohesion-Tension: Force in leaves pulls water from roots through xylem.

• Influence of Temperature:

  • Temperature affects water potential; warmer temperatures increase molecular movement.
  • Transpiration, driven by evaporation at stomata, is significantly impacted by temperature; hot days increase transpiration rates, pulling more water from roots.
  • Water lost through transpiration is replaced by water molecules due to the tension cohesion theory.

• Water Potential Equation

  • $\Psi = \Psi<em>P + \Psi</em>S$
  • $\Psi$ = water potential
  • $\Psi_P$ = pressure potential
  • $\Psi_S$ = solute potential

• Solute Potential:

  • High solute concentrations result in low solute potential, influencing water movement via osmosis.
  • Salty soils, for example, affect solute potential.

• Turgor Pressure:

  • Incoming water causes plant cells to swell, increasing turgor pressure against the cell wall.

• Wilting:

  • Wilting occurs due to loss of turgor pressure when water loss through transpiration isn't replaced.
  • Watering revives plants by restoring turgor pressure.

• Salty Soils:

  • Soils contain high solute concentration which leads to much lower water potential, making water absorption difficult.
  • Plants in salty soils adapt through active transport in the roots.

• Dry Soils:

  • Reduce water potential as water adheres tightly to soil particles.
  • Soil type (clay versus organic matter) affects water potential.

• Overwatering:

  • Overwatering kills plants by depriving roots of oxygen, essential for cellular respiration.
  • It can also leach nutrients from potted plants, reducing soil fertility.

• Water Movement:

  • Water moves from high to low water potential.
  • Factors such as solute potential and pressure potential impact this movement.

• Water Pathways:

  • The apoplastic route, associated with the Casparian strip, filters toxins; other routes do not.

• Adaptations:

  • Plants adapt to water loss through various modifications (CAM plants, C4 plants).

Sugar Concentrations in Plants

• Sugars are needed in actively growing parts of the plant.
• The place where the plant is photosynthesizing will have the highest concentration of sugars.

Source vs. Sink

• Source: Places with the highest concentrations of sugar (e.g., leaves during active photosynthesis).

• Sink: Places where sugar is needed or stored (e.g., roots, fruits, meristems).

• The source and sink in a plant can be changed at different times of the year.

• In the Fall/Winter: concentration is in storage mechanisms with the roots.

• Sink locations are:

  • Roots (especially storage structures like tubers and sugar beets).
  • Meristems (for growth).
  • New leaves.
  • Fruits.
  • Flowers.

Translocation

• Translocation happens via the phloem, and it's the movement from source to sink.
• Sugar can move from plant to plant.
• Source to sink move from local source to local sink

Xylem vs. Phloem

• After a break, class will compare and contrast xylem and phloem, focusing on structure, function, and location differences in water and sugar transport.

• The comparison must address active versus passive transport:

  • Which processes need ATP?
  • Types of structures for sugar uploading.

• Xylem: Dead tubes; one-way system (roots to shoots); passive transport driven by water potential.

• Phloem: Living tissue; bidirectional; active and passive transport.

• Girdling: Cutting off the xylem and phloem of the tree

• Bulk Flow: The movement of sugar along with the gradients.

• Sugar Uploading/Unloading: Active transport moving from low to high sugar concentration areas

• Active and Passive Transport in Water:

  • If there is low water potential, such as in salty soil, the plant may need active transport with specialized proteins in the roots to help water move in.

• Adhesion & Cohesion: These forces are important for the movement of water from the roots to the shoots

Plant Nutrition

• On Thursday, students should prepare for plant nutrition diagnosis activities, focusing on nutrient roles in plant growth and their mobility.

• Nutrient Categories:

  • Mobile vs. Non-mobile.
  • Macronutrients vs. Micronutrients.