Intro to Crop Science

  • Types of roots:

    • Fibrous roots: Many small roots. Ex. grasses

    • Tap roots: One larger root with smaller roots coming off of it. Ex. Carrots

Node- part of attachment to Leaf

Bud- underdeveloped and elongated stem

Terminal bud- tip of stem

Internode- part of the stem between nodes

Lenticels- cells on epidermis

Modified stems- dont always grow upright or vertically

Crowns- compressed stem

Stolons- stem that grows horizontally above ground

Spurs- found on branches of woody plats on stems whose growth has been severely restricted

Rhizomes- underground horizontally growing stems

Corms- underground structures that are compressed and thickened stems

Bulbs- compresses stem; promanant part of the structure is the stem but modified leaves

Tubers- underground stems that are highly enlarged

Vascular bundles- run the length of a plant’s stem, from root to top of plant, moves water, nutrients, sugar, hormones. Strength and support, connects all parts of the plant

Definition of Photosynthesis:

The process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose.

Photosynthetic Pigments

  • Chlorophyll a:

    • The primary photosynthetic pigment in plants.

    • Absorbs mainly blue (around 430 nm) and red (around 662 nm) light.

  • Chlorophyll b and Carotenoids: Additional pigments that aid in capturing light and reflect other wavelengths (green reflects chlorophyll).

Leaf Structure and Photosynthesis Location

  • Chloroplasts: Organelles where photosynthesis occurs.

    • Parts of a Chloroplast:

    • Thylakoid: Membranous sacs where light reactions occur; contains pigments.

    • Granum: A stack of thylakoids.

    • Stroma: The fluid-filled space surrounding thylakoids where the Calvin cycle occurs.

  • Gas Exchange: Occurs in the stomata, regulating the intake of CO2 and release of O2.

Mesophyll Cells

  • Contains many chloroplasts, responsible for photosynthesis within the leaf.

Photosynthesis Stages

A. Overview of the Two Main Stages

  1. Light Reactions: Occur in the thylakoid membranes, require light and water; produce ATP, NADPH, and O2 as byproducts.

  2. Calvin Cycle (Carbon Reactions): Occurs in the stroma; uses ATP, NADPH, and CO2 to produce glucose.

B. Details of the Light Reactions

  • Process:

    • Photosystem II: Absorbs light, ejects electrons, splits water to replace the lost electrons.

    • Electron Transport Chain: Ejected electrons move through, creating a proton gradient; H+ ions are pumped into the thylakoid space, leading to ATP generation through ATP synthase.

    • Photosystem I: Light energizes electrons to reduce NADP+ to NADPH, facilitating the production of energy carriers.

    • Byproduct: Oxygen (O2) is released when water is split.

C. Calvin Cycle Details

  • Uses ATP and NADPH from the light reactions to convert CO2 into sugar through a series of reactions, ultimately resulting in glucose production.

Different Carbon Fixation Pathways

  • C3 Plants: Normal photosynthesis pathway, directly fix CO2.

  • C4 Plants: Adapted to dry conditions, fixes CO2 into a four-carbon compound before the Calvin cycle.

  • CAM Plants: Collect CO2 at night and run the Calvin cycle during the day, minimizing water loss.

Appendix: Terminologies

  • Chloroplast: Organelle responsible for photosynthesis in plant cells.

  • Stroma: The fluid center of chloroplasts, where the Calvin cycle occurs.

  • Thylakoid: Membrane-bound structures within chloroplasts where light-dependent reactions take place.

  • ATP (Adenosine Triphosphate): Energy currency of the cell, produced during photosynthesis.

  • NADPH: Electron carrier that provides reducing power for the Calvin cycle.

Transpiration

  • Is the loss of water from plants in the form of water vapor

  • This evaporative process is dependent on energy

  • 97-95% of water taken up is lost in transpiration

  • Heat of Vaporization: 539 cal $g^-1

Importance

  1. Keeps cells hydrated

  2. Maintains favorable turgor pressure for the transport of nutrients absorbed by the roots from the soil

  3. Cools the plant

    • Heat load is dissipated in the process due to the high heat of vaporization of water

    • If transpiration is extremely high → dehydration and desiccation → death

Types

  • Classified based on the avenue of exit water vapor

  • Cuticular Transpiration - Loss of water through the epidermis covered by a cuticle

  • Lenticular Transpiration - pores in the outer layer of woody plant stem

  • Stomatal Transpiration - Through the stomata

    • Guttation — Water released by plants in liquid form. Water droplets are secreted through the hydathodes due to very high root pressure.

    • Hydathodes — usually located along the margin of the leaves

Stages

  1. Evaporation - water from cell structures (phase change of water)

  2. Diffusion - water vapor from leaf intracellular spaces to the atmosphere\

   

  1. Is the movement of substances from a region of higher concentration to a region of lower concentration.

Soil-Plant-Air Continuum of Water

  • Movement of water from the Soil to the Root Xylem

    • Water and nutrients are absorbed by root hairs due to difference in water potential

    • Water is then transported radially towards the xylem

Extracellular (Apoplastic Route) - Water moves through non-living parts, e.g. capillary spaces of the cell walls and intercellular spaces

Intracellular Route

  1. Symplastic Pathway - plasmodesmata

  2. Transmembrane or Transcellular Pathway - vacuolar membrane and plasma membranes

  • Movement from Root Xylem to Leaf Xylem

    • Transpiration-cohesion-adhesion-theory

     1. Water vapor leaves the air spaces of the plant via the stomates 2. This water is replaced by evaporation of the thin layer of water that clings to the mesophyll cells 3. Tension (pulling) on the water in the xylem gently pulls the water toward the direction of water loss 4. The cohesion of water is strong enough to transmit this pulling force all the way down to the roots 5. Adhesion of water to the cell wall also aids in resisting gravity

  • Movement from Leaf Xylem to Air

    • Influenced by Rh and VPD

    • Towards lower water potential

Factors Affecting Transpiration

  • Leaf number: more leaves, more transpiration

  • Number, size, position of stomata: more and large, more transpiration, under leaf, less transpiration

  • Cuticle: waxy cuticle, less evaporation from leaf surface

  • Light: more gas exchange as stomata are open

  • Temperature: high temperature, more evaporation, more diffusion

  • Humidity: high humidity, less transpiration

  • Wind: more wind, more transpiration

  • Water availability: less water in soil, less transpiration (e.g. in winter, plants lose leaves)

Perfect Flowers- Possess both stamens (male organs) and carpels/pistils (female organs) within the same bloom. this gives them the ability to self pollinate

Types of Perfect flowers- roses, lilies, peas, beans