Translocation and Nutrient Minerals in Plants

Study Notes

Movement of assimilates (mainly sucrose) from source to sink tissues through the phloem.
Source tissues (mature leaves) produce sucrose, while sink tissues (roots, young leaves, and fruits) utilize or store it.
Münch pressure flow hypothesis explains the process:
- Sucrose is actively loaded into phloem sieve tubes at the source, creating a low water potential.
- This draws water from adjacent xylem, generating pressure that pushes the sucrose-rich sap towards the sink.
- At the sink, sucrose is unloaded, and water moves back into the xylem.
Allocation refers to the use of fixed carbon within a source or sink organ.
Partitioning refers to the distribution of assimilates among competing sinks.

Plants require essential nutrients for growth, development, and reproduction.
Essential nutrients are those a plant cannot complete its life cycle without, and their function cannot be replaced by another element.
Nutrient categories:
- Macronutrients (needed in larger amounts): carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, sulfur, and magnesium.
- Micronutrients (needed in smaller amounts): iron boron, copper, zinc, manganese, molybdenum, and chlorine.
Nutrient deficiencies can limit plant growth and cause characteristic symptoms.
Deficiency symptoms in older leaves indicate mobile nutrients (like nitrogen, phosphorus, potassium, magnesium), as they are easily translocated within the plant.
Deficiency symptoms in younger leaves indicate immobile nutrients (like calcium, sulfur, iron), as they are not easily mobilized from older tissues.

Growth: irreversible increase in cell number and dry mass.
Differentiation: process where genetically identical cells become specialized in structure and function.
Organization: arrangement and integration of differentiated cells into tissues, organs, and ultimately, the whole plant.
Morphogenesis: encompasses growth, differentiation, and organization to determine the final form and structure of the plant.
Plant growth occurs in specialized regions called meristems, containing undifferentiated cells capable of repeated division.
Apical meristems at the tips of roots and shoots drive primary growth (lengthening).
Lateral meristems (cambium) are responsible for secondary growth (thickening) in woody plants.
Plant hormones (phytohormones) are chemical messengers that regulate growth and development at low concentrations.
Major plant hormone groups:
- Auxins: promote cell elongation, apical dominance, root initiation, and fruit development.
- Cytokinins: stimulate cell division, delay senescence, and promote lateral bud growth.
- Gibberellins: regulate stem elongation, seed germination, and flowering in some plants.
- Abscisic acid: inhibits growth, promotes dormancy, and mediates stress responses.
- Ethylene: influences fruit ripening, senescence, and responses to stress.
Plant growth regulators can be natural or synthetic compounds that mimic plant hormones.

Definition: Process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.
Chemical Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Supporting Terms:
- Autotrophs: Organisms that produce their own food.
- Chloroplast: Organelle where photosynthesis occurs.
- Thylakoid: Membrane structure within chloroplasts, site of light-dependent reactions.
- Stroma: Fluid-filled space surrounding the thylakoids where the Calvin cycle occurs.
- Chlorophyll: Pigment that absorbs sunlight, mainly found in the thylakoid membranes.
- Photon: A particle of light that excites electrons in chlorophyll.
- Photosystem: Clusters of pigments and proteins that capture light energy.
- Calvin Cycle: Also called the light-independent reaction or dark reaction, occurs in the stroma, fixing carbon into glucose.
Phases of Photosynthesis:
- Light-Dependent Reactions:
  - Occur in the thylakoid membranes.
  - Water (H₂O) is split, releasing oxygen (O₂).
  - ATP and NADPH are produced.
  - Z-Scheme: Describes electron flow in light reactions.
- Light-Independent Reactions (Calvin Cycle):
  - Occurs in the stroma.
  - Carbon dioxide (CO₂) is fixed into glucose using ATP and NADPH.
  - The cycle regenerates its starting molecule, allowing for continuous carbon fixation.