Phytochemistry and Plant Physiology - Lecture Notes Flashcards

Structure and Function: Adaptation and Acclimation

• Two key concepts: Adaptation and Acclimation (often conflated in discussions).

• Adaptation vs. Acclimation: definitions and timescales.

Time and Space: The Larger Scientific Context

• The Space-Time Scale: hierarchical levels from molecules to ecosystems; examples of units and scales:

  • Population, individual, ecosystem, community

  • Kilometre, metre; millimetre, micron

  • Time scales: million years, century, year, week, hour, second

• Figure context: Mechanistic understanding of plant stress responses at the molecular level is dependent on evolutionary processes that shape species and their interactions (Osmond et al. 1980; Nilsen & Orcutt 1996).

• Concept: The integration of ecology, biochemistry, and physiology to study plant stress processes.

Plant Hormones and Environmental Interactions (The Larger Context)

• Key hormones and signals shown in diagrams: Auxin, Gibberellin, Cytokinin, Abscisic acid, Ethylene, Jasmonic acid, Salicylic acid, Brassinolide, Strigolactone.

• Environment categories: Abiotic (physical & chemical) and Biotic (living).

• Guard cells and stomata regulate gas exchange (CO2 in, O2 out).

• General note: Hormonal signaling intersects with environmental cues to modulate plant responses.

Environmental Conditions and Plant Ecology

• Observations about plant ecology: variation in plant performance (growth, survival, fitness), abundance, distribution, contributions to ecosystem function.

• Links to traits, physiological variation, genetic variation, plasticity, and evolution.

• Emphasizes the Larger Scientific Context of plant physiology under environmental variation.

Niche Theory and Realized Niche

• Relationship to Niche Theory: Fundamental Niche vs. Facilitation; role of symbionts, pollinators, and dispersers in realized niche.

• Reference: Lambers et al. 2008.

Fundamental vs. Realized Niche – Conceptual Illustration

• Two species (x and y) and resource supply: In the absence of competition, physiological amplitudes define each species' growth range (PAx, PAy).

• With competition, the realized niche narrows to a subset of conditions (EAx, EAy).

• Patterns of distribution can arise from differences in maximum biomass, shape of resource-response curves, or physiological amplitude.

• Conceptual reference: Walter (1973); Lambers et al. 2008.

Adaptation and Acclimation: Definitions and Distinctions

• Page 12–13: Two very important concepts frequently conflated:

  • Adaptation vs. Acclimation.

• Page 13: Adaptation is an adjustment in physiology within a population (or lineage) across generations via natural selection.

  • Heritable variation exists in all populations; individuals with advantageous phenotypes have more offspring.

  • Involves changes in alleles that result in different phenotypes.

• Page 14: Acclimation is a physiological adjustment within an individual during a single lifetime in response to environmental stress; involves changes in gene expression that alter phenotype; some acclimations may be adaptive if they improve fitness.

Time Course of Plant Response to Environmental Stress

• Figure 3 (conceptual): Typical time course from perturbation to response:

  • Immediate response: reduction in physiological activity.

  • Acclimation: compensates for stress; activity returns toward control level.

  • Evolutionary adaptation: over generations, populations adapt; activity increases toward that of unstressed plants.

  • Total in situ activity equals the sum of acclimation and adaptation (homeostatic compensation).

• Time scales: from minutes to generations (Min-Day, Day-Month, Month-Year).

• Abbreviations and terms: Acclimation (short-term), Adaptation (long-term evolutionary change), Homeostatic compensation.

Examples of Acclimation and Adaptation to Specific Conditions

• Acclimation examples:

  • Seasonal variation in temperature and light

  • Submergence by flooding

  • Shade responses

• Adaptation examples:

  • Water limitation via succulence

  • Low phosphorus via cluster roots

  • High salinity via salt glands

  • High temperature via Kranz anatomy in C4 plants

• Notation: variations implemented as physiological strategies across contexts.

Diversity of Plant Life and Evolutionary Perspective

• Estimated diversity: ~3\times 10^5 species.

• Emphasis: Plant physiology should be considered through an evolutionary lens; many physiological traits are adaptations, including adaptive acclimation.

Key Plant Functions and Structural Basis

• Core idea: Plant physiology depends on, and is emergent from, plant structure starting at the cell level and scaling to tissues, organs, and whole plant.

• Difference between plant cells and animal cells: structural distinctions.

Plant Cell Structure: Why Plants Are Different

• Cell wall: Rigid wall prevents osmotic lysis but restricts cell migration; plant development relies on cell division and expansion.

• Plasmodesmata: Cytosolic connections between neighboring cells enable symplastic transport without crossing cell walls (apoplast).

• Large vacuole: Provides large water reserve, turgor, and storage; separates functions away from vital processes.

• Plastids: Specialized, semiautonomous organelles with their own genome; replicate independently; ability to differentiate into various forms.

Plastids and Endosymbiosis

• Plastids are derived from ancient endosymbiosis with cyanobacteria; photosynthesis evolved once in cyanobacteria (~2.3 Ga).

• Land plants derive from green algae; primary endosymbiosis event.

• Chloroplasts: Most important plastid; essentially a simplified cyanobacterium with multiple membranes and thylakoids; chloroplast genome is a single circular chromosome ~1.5\times 10^5\text{ bp}.

• Chloroplast genome: single ring-shaped chromosome ~150{,}000\text{ bp}; transcription in both directions; contains ~30-50\text{ RNA genes} and ~100\text{ protein-coding genes} (in land plants; mostly photosynthetic genes).

Chloroplasts and Photosynthesis

• Chloroplasts contain thylakoids that concentrate gradients essential for photosynthesis.

• Plastids share an ancestral origin and can differentiate into other plastid types as needed by the plant.

Plant Development: Totipotency and Meristems

• Plants are modular; there is no conserved germ line.

• Stem cells are distributed throughout the plant, most active in meristems.

• Almost all plant cells retain the ability to dedifferentiate into totipotent stem cells.

Plant Tissues: Dermal, Vascular, and Ground Tissues

• Dermal tissue: Protection, uptake, excretion; includes leaf pavement cells, guard cells, trichomes; root hairs; epidermal cells and trichomes.

• Vascular tissue: Transport; Phloem (sieve cells/tube elements, companion cells); Xylem (tracheids, vessel elements).

• Ground tissue: Everything not dermal or vascular; three main types based on cell walls:

  • Parenchyma: Thin primary walls; retains pluripotency; roles in metabolism, storage, repair, secretion (e.g., pallisade and spongy mesophyll in leaves; cortex/pith in stems/roots; pulp/endosperm/seed storage).

  • Collenchyma: Elongated, irregularly thickened primary walls; provides support; often adjacent to vasculature; flexible in growth; includes specialized structures like laticifers (latex ducts).

  • Sclerenchyma: Thick secondary walls; cells dead at maturity; lignin-rich; provides rigid support; fibers (long, slender) and sclereids (short, very hard).

Leaf Anatomy and Cross-Sections

• Bottom of leaf: Spongy mesophyll, parenchyma, chloroplasts, guard cells, stomata, and vascular tissues (phloem/xylem) arranged in typical cross-section patterns.

• Cross-section features observed in typical leaf diagrams: upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, cuticle, and vascular bundles (xylem/phloem) with supporting tissues such as sclerenchyma and collenchyma.

• Vascular and protective tissue arrangement supports photosynthesis and transpiration processes.

Dicot Leaf Cross Section and Bark/Foliage Anatomy

• Dicot leaf cross-section reveals organization: upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis; cork cambium and secondary tissues present in bark.

• Vascular cambium, secondary phloem, secondary xylem (summer wood and spring wood) shown in cross-section diagrams.

• Structural layers include periderm, cortex, pith, collenchyma, and various vascular elements.

Abiotic Stress, Climate, and Course Orientation

• Rationale for Week 1 focus on abiotic stress: Interactions with the environment drive core plant physiology topics (photosynthesis, respiration, water relations, mineral nutrition, growth, hormones, senescence, phenology, secondary metabolism).

• Reading assignment: The chapter on abiotic stress primes thinking about how sessile plants maintain homeostasis through acclimation-based responses or pre-existing adaptations.

• Note: This introductory framing sets expectations for ongoing stress-related topics throughout the course.