Lecture 7 Flashcards
(17 cards)
How much of a plant’s dry weight does potassium make up?
0.5-2%.
What is potassium used for?
Cellular process: opening stomata, transporting molecules, protein synthesis.
What other effects does potassium have?
Indirect effects on plant disease resistance and building of cell walls.
How is potassium commercially produced?
95% of global potassium production is for fertilisers and 90% of this is supplied as potassium chloride.
The production has huge global impacts.
How does passive transport work?
Non-charged molecules like glucose simply diffuse across the membrane from a high to a low concentration, down an electrochemical gradient.
Charged molecules like potassium ions must also move down an electrochemical gradient but other charged molecules may affect this meaning ions must be taken up by active transport.
How does active transport work?
Potassium ions are taken up against the electrochemical gradient using ATP and transporters.
Even in high concentrations, potassium can be energetically costly to uptake.
Why is sodium an issue?
Sodium competes with potassium for uptake as it is similar in size, both can diffuse passively into cells along an electrochemical gradient.
Sodium is toxic in large quantities.
How do plants overcome this?
Plants have a family of potassium transporters (70+ in Arabidopsis). Sodium-potassium selectivity is important in salt tolerance.
How does potassium reduce plant disease?
Used to make plant defence compounds.
Reduces: fungi by 70%, bacteria by 69%, insects and mites by 63%, viruses by 41%, nematodes by 33%.
What are micronutrients?
Those needed in trace amounts <0.02% of plant mass.
What are some micronutrients functions?
Iron: chlorophyll biosynthesis Molybdenum: produce nitrogenase Nickel: nitrogen metabolism Copper: chlorphyll and cell walls Zinc: enzymes and DNA transcription Manganese: cell wall synthesis and chloroplasts
What is the most common micronutrient defficency?
Boron which is responsible for cell walls, fruiting, flowering and pollen.
What is the function of the xylem?
Uni-directional transport of water + nutrients from root to shoot in lignified tubes. Continuous and structurally important.
What is the function of the phloem?
Bi-directional transport of nutrients and sugar from sources to sinks. Water determines direction and speed of flow.
What is the structure of the phloem?
Continuous tube of living cells of different types. Sieve tube elements are joined by sieve plates. Companion cells line either side of the phloem and aid sugar entry/exit. Phloem parenchyma transport sugar into the phloem by mass flow.
What is the mass flow hypothesis?
Excess sugars are loaded into the companion cells. Then sugar flows into the phloem tube, the high concentration forces water in the phloem which pushes sugars towards sinks. Sugar leaves the phloem at the sink. Transport is rapid (30-150cm per hour).
What is phloem sap composed of?
Sugars, AAs, Amides, organic acids, protein, potassium. Usually no ABA or nitrate.
Can transport mRNA.
