Plant Anatomy Study Notes

Overview of Plant Anatomy

  • Basic review of plant anatomy relevant for upcoming lab sessions.

  • Importance of understanding plant anatomy for tests, especially focusing on abortion queries regarding:

    • Gymnosperms

    • Angiosperms

    • Angiosperm evolution

    • Plant speciation

    • Economic botany

Pollination Mechanisms

  • Discussion on plant reproductive strategies, particularly outcrossing and self-pollination.

  • Importance of pollinators in spreading plant genes.

Self-Pollination in Flowering Plants

  • Many flowering plants can self-pollinate; e.g., Mimulus guttatus (Monkey Flower).

  • Native to California and hybridization occurs with Mimulus nasutus.

  • Mimulus nasutus features:

    • Both open flowers and closed (claistogamous) flowers that do not open.

    • Advantages of closed flowers: assure reproductive success in absence of pollinators.

Benefits of Self-Pollination

  • Reliable seed production: Ensures reproduction where pollinators are scarce.

  • Increases the chance of seed set even without external pollination.

Costs of Self-Pollination

  • Lower genetic diversity: Leads to reduced heterozygosity.

    • Heterozygosity refers to variations in alleles (genetic diversity).

    • Homozygosity indicates identical alleles.

  • Increased homozygosity results in:

    • Lower fitness of offspring.

  • Biological fitness does not solely refer to survival:

    • It emphasizes reproductive success and adaptability.

    • Greater vulnerability to diseases and pests due to lack of genetic variability.

Strategies to Prevent Self-Pollination

Methods and adaptations to limit self-pollination to enhance genetic diversity.

Monoecious Plants

  • Plants possess separate sex flowers on the same individual.

  • Example: Begonia

    • Has male (stamen) and female (stigma) flowers.

    • Male flowers often produced first, reducing opportunities for self-fertilization.

  • Example: Cucumber

    • Female flowers possess inferior ovaries and separate anthers on male plants.

Dioecious Plants

  • Separate male and female plants.

  • Example:

    • Male flowering plants receive more visits from pollinators than females but do not produce nectar.

  • Example: Wormbia

    • Males have larger flowers to attract pollinators, increasing chances of cross-pollination but with risks of failure to fertilize if pollinators miss them.

Temporal and Spatial Separation

  • Mechanisms to reduce self-pollination linked to timing and spatial distribution of reproductive structures.

Protogyny and Protandry

  • Protandry: Stigmas are closed while anthers shed pollen.

  • Protogyny: Stigmas open before anthers shed pollen.

  • These mechanisms lower the chances of self-fertilization by staggering reproductive phases.

Heterostyly

  • Refers to the presence of two flower forms (differing styles) on one plant.

  • Promotes outcrossing through pollinator movement from one flower type to another.

Self-Incompatibility Mechanisms

  • Mechanisms that prevent self-fertilization.

Sporophytic Self-Incompatibility (SSI)

  • The genome of the plant (S-alleles) determines rejection of own pollen.

  • Example: S1/S3 receiving and S1/S2 donating does not fertilize due to S-alleles being recognized in both plant genomes.

Gametophytic Self-Incompatibility (GSI)

  • Based on the alleles of pollen grains rather than the plant’s overall genome.

  • With certain combinations (e.g., S1/S2), pollen may not germinate if corresponding alleles match.

Plant Structural Systems

  • Root System: Anchors plants and absorbs water/nutrients.

    • Important functions include

    • Stability and nutrient translocation.

    • Interactions with soil-fungi (e.g., mycorrhizae and nitrogen-fixing bacteria).

Types of Roots

  • Taproots (e.g. Carrot): Storage roots.

  • Fibrous roots (e.g. Grasses): Major anchoring and absorption role.

  • Adventitious: Arrangements like aerial roots (e.g. Bonsai).

  • Pneumatophores: Aerial roots for oxygen in waterlogged areas (e.g. Mangroves).

  • Tuberous Roots (e.g. Sweet Potato): For nutrient storage.

Shoot System Functions

  • Main functions include:

    • Photosynthesis (primarily in leaves)

    • Gas exchange

    • Reproduction (flowers/cones)

    • Transporting nutrients and water.

Stem Diversities

  • Different types include:

    • Runners/Stolons (Strawberries): Asexual reproduction.

    • Rhizomes: Underground stems for propagation.

    • Tubers (e.g., Potatoes): Storage for carbohydrates during dormancy.

    • Corms: Thickened stem for starch storage.

Leaf Structure and Function

  • Leaf function involves:

    • Gas exchange and photosynthesis.

  • Structure includes:

    • Cuticle (waxy layer): Protects against dehydration.

    • Mesophyll layers: Site for photosynthesis, including palisade and spongy parenchyma.

    • Stomata regulation through guard cells.

Leaf Diversity and Modifications

  • Simple and compound leaves.

  • Modifications for specific functions (e.g., tendrils for climbing, succulents with spines, carnivorous plants).

Plant Development Mechanisms

  • Plant development includes:

    • Growth: Elongation of roots and stems (

    • Primary growth: lengthening

    • Secondary growth: thickening).

    • Morphogenesis: Changing of forms.

    • Differentiation: Specializing cells into tissue types.

  • Apical meristems: Active cell division areas at tips (root and stem).

    • Can transition to form three primary meristems:

    • Epidermal, Ground, Vascular tissues.

Cell and Gene Expression in Growth

  • Differential gene expression controls cell specialization and development into various tissues.

Questions and Review

  • Questions about strategies, examples of self-pollination prevention methods, functions of various root structures, and leaf configurations related to plant survival and reproduction.