2. Plant Structure, Growth & Development Chapter 35 ______________ Plant Responses Chapter 39

3. Chapter 35

4. Hierarchical Organization in Plants  Three basic plant organs: 1.Roots 2.Stems 3.Leaves

5. Roots  Anchors vascular plant in soil  Absorbs minerals and water  Stores carbohydrates  Root Parts: Taproot – main vertical root of eudicots and gymnosperms, develops from embryonic root Lateral roots – branch from taproot  In monocots, embryonic root dies and small roots emerge from stem – fibrous root system

7. Stems  Raise or separate leaves, exposing them to sunlight  Also raise reproductive structures to facilitate pollen dispersal  Alternating system of: Nodes – point where leaves are attached Internodes – stem segments between nodes  Most of the growth of a young plant is in the apical (terminal) bud  Leaves emerge at the axillary bud

9. Leaves  Main photosynthetic organ in vascular plants  Consist of: Blade – generally flat Petiole – stalk that join blade to stem at node  Monocots – parallel veins  Eudicots – branching veins  Simple vs Compound leaves: Simple- single, undivided blade Compound – blade consists of multiple leaflets Doubly compound – each leaflet is divided into smaller leaves

11. Evolutionary Adaptations of Leaves  Tendrils – “lassoes” something to provide more support for the stem  Spines – protection, do not photosynthesize  Storage leaves – succulents  Reproductive leaves – make plantlets that fall off and take root in soil  Bracts – often mistaken for petals; surround a group of smaller flowers and attract pollinators

12. Tendrils Spines Storage Reproductive Bracts

13. Plant Tissues  Dermal – plant’s outer, protective covering (epidermis and cuticle)  Vascular – carries out long distance transfer of materials between roots and stems (xylem & phloem)  Ground – neither dermal nor vascular; performs specialized functions such as storage, photosynthesis & support

15. Plant Cells  Parenchyma – perform most of the metabolic functions of plant  Collenchyma – flexible, support young parts of plant shoot  Sclerenchyma – rigid support for mature plants, especially trees

17. Plant Cells, cont.  Water conducting cells in Xylem (dead at functional maturity) Tracheids Vessel elements  Sugar-conducting cells in Phloem (alive at functional maturity) Sieve tube elements Sieve plates Companion cells

19. Growth in Plants  Unlike animals, plant growth is not limited to an embryonic and juvenile period  Indeterminate growth – at any time the plant as a whole has embryonic, developing and maturing organs  Leaves, thorns and flowers undergo determinate growth

20. Growth in Plants, cont.  Meristems - specific regions of growth Contain stem cells: perpetually embryonic tissue regenerate new cells  Apical shoot & root meristem o Provide growth in length o primary growth  Lateral meristem o Provide growth in girth o secondary growth

21. Apical meristems shootroot

22. Root structure & growth protecting the meristem

23. Woody stem cork cambium vascular cambium xylem early late phloem bark How old is this tree? 1 2 3

24. Chapter 39

25. Response to Stimuli  At the organismal level, plants and animals respond to environmental stimuli by different means  Animals, being mobile, respond mainly by moving toward positive stimuli and away from negative stimuli  Plants are stationary and generally respond to environmental cues by adjusting their individual patterns of growth and development For this reason, plants of the same species can have much more variation in body form than animals of the same species

26. Tropisms  Tropism – any growth response that results in plant organs curving toward or away from a stimulus Phototropism – growth of a shoot toward (positive) or away (negative) from a light source Photoperiodism – physiological response to a photoperiod (like flowering) Gravitropism – growth of shoots and roots in response to the pull of gravity Thigmotropism – directional growth in response to touch

27. Growth in Plants  Etiolation – morphological adaptations for growing in darkness Pale stems Rapid stem elongation Unexpanded leaves Short, stubby roots Example – young potato plant in the soil

28.  De-etiolation (greening) Stem elongation slows Leaves expand Roots elongate Shoot produces chlorophyll Receptor in cytoplasm called a phytochrome is responsible

29. Plant Hormones  Hormone – signaling molecule that is produced in tiny amounts by one part of an organism’s body and transported to other parts, where it binds to a specific receptor and triggers responses in target cells and tissues (phew!!!!)  Plant hormone = plant growth regulator  One hormone can regulate a diverse array of cellular and developmental processes  Multiple hormones can influence a single process

30. Plant hormones  Auxin  Gibberellins  Abscisic acid  Ethylene  and more…

31. Auxin (IAA)  Effects  controls cell division & differentiation  phototropism growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side  apical dominance

32. Gibberellins  Family of hormones over 100 different gibberellins identified  Effects stem elongation fruit growth seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

33. Abscisic acid (ABA)  Effects  slows growth  seed dormancy high concentrations of abscisic acid germination only after ABA is inactivated or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture

34. Ethylene  Hormone gas released by plant cells  Effects fruit ripening leaf drop o like in Autumn o apoptosis

35. Fruit ripening  Adaptation hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed  Mechanism triggers ripening process o breakdown of cell wall - softening o conversion of starch to sugar - sweetening positive feedback system o ethylene triggers ripening o ripening stimulates more ethylene production

36. Apoptosis in plants  Many events in plants involve apoptosis response to hormones o ethylene o auxin death of annual plant after flowering o senescence differentiation of xylem vessels o loss of cytoplasm shedding of autumn leaves What is the evolutionary advantage of loss of leaves in autumn?