Fruit and Seed dispersal

Transcription

1 Angiosperms: Phylum Anthophyta, the flowering plants 1. Overview of seed plant evolution 2. Traits of flowering plants 3. The angiosperm life cycle 4. Seed (fruit) dispersal (continued) 5. Seed morphology and germination 6. Hormones (Auxin) briefly (we ll come back to this) Fruit and Seed dispersal Fruits protect seeds during development and sometimes aid in their dispersal Fleshy fruits or seeds are adapted to animal dispersal Dry fruits can be adapted to air or water dispersal, animal dispersal, or to release the seeds at maturity Seeds themselves often have their own dispersaladapted morphology, and adaptations for survival and germination Fruit adaptations that enhance seed dispersal: Red berries are animal dispersed, while dandelion fruits are wind-dispersed (right). Some fruits, such as these burrs, hitch a ride on the fur of animals The seeds of many plants have elaiosomes fleshy attachments which attract ants. Ants carry the seeds back to their nests, eat the elaiosome, and often discard the seed. (One example is our native wild ginger, Asarum caudatum) Don t forget: many plants also reproduce asexually. Two examples: the maternity plant (Kalanchoe, left), aspen (Populus) groves (right) 1

2 Seed adaptations for survival and germination Many seeds exhibit dormancy, a temporary condition of low metabolism and no growth or development. Some seeds can survive like this for decades or more. What are the potential benefits of dormancy? Figure Review: Three types of seed structure Dormancy in some seeds is simply broken by favorable environmental conditions, but others only germinate after specific cues What would you expect the cues to be for seeds living in deserts, fire-prone habitats (such as California chaparral), or at high latitudes? How about for seeds borne in berries eaten by mammals? The four steps of seed germination: 1. imbibition of water, 2. enzyme digestion of stored food, 3. embryo begins growth and radicle is pushed through the seed coat, and 4. shoot tip grows toward soil surface. Germination of a barley seed is shown below. Figure Two ways that young shoots break through the soil surface. Figure 38.7 The development of a dicot plant embryo Hormones One bad apple 2

3 A word about Auxin: Auxin is a term used for any chemical substance that promotes the elongation of coleoptiles (though they have multiple functions in monocots and eudicots) The natural Auxin occuring in most plants is IAA - indoleacetic acid Plants exhibit phototropism and gravitropism Phototropism: in response to light (shoots) Gravitropism: in response to gravity (pressure really) roots Thigmotropism: in response to mechanical pressure/touch (vines) How do plants grow toward the light? (phototropism) Auxin causes cell elongation along the dark side of the shoot, causing the shoot to bend towards light It also works in conjunction with other hormones.for example in fruit ripening A word about Auxin: Thigmotropism: pressure/mechanical Auxin is a term used for any chemical substance that promotes the elongation of coleoptiles (though they have multiple functions in monocots and eudicots) The natural Auxin occuring in most plants is IAA - indoleacetic acid 3

4 What auxin does in plants Structure and Growth Promotes shoot elongation Suppresses shoot branching (apical dominance) Inhibits root elongation Promotes root branching Promotes growth of fruit The plant body has a hierarchy of organs, tissues, and cells, like multicellular animals Have organs composed of different tissues, which are in turn composed of cells The basic morphology of vascular plants Reflects their evolutionary history as terrestrial organisms that draw nutrients from two very different environments: below-ground and above-ground Figure 35.2 Morphology of a flowering plant: an overview Three basic organs evolved: roots, stems, and leaves They are organized into a root system and a shoot system Roots A root Is an organ that anchors the vascular plant Absorbs minerals and water Often stores organic nutrients In most plants The absorption of water and minerals occurs near the root tips, where vast numbers of tiny root hairs increase the surface area of the root Roots cont. Gymnosperms and eudicots: taproots with lateral roots Seedless vascular and monocots: fibrous root system: spread out Many plants have modified roots: adventitious roots arise above ground from stems and even leaves 4

5 Many plants have modified roots Stems (shoot system) (a) Prop roots (b) Storage roots (c) Strangling aerial roots Nodes: point of leaf attachment Internodes: segments between nodes Axillary buds can form new shoots or branches Terminal buds can lead to apical dominance (grow up!) (d) Buttress roots (e) Pneumatophores Figure 35.4 Modified shoots: Stolons, strawberry (top left); rhizomes, iris (top right); tubers, potato (bottom left); bulb, onion (bottom right) Leaves Leaf types Main photosynthetic organ - but in many, the stems can dominate too. Blade and petiole (monocots don t have petioles - base of the leaf forms a sheath around leaf. Leaf types: 5

6 Figure 35.5 Simple versus compound leaves Leaf types Figure 35.6 Modified leaves: Tendrils, pea plant (top left); spines, cacti (top right); succulent (bottom left); brightly-colored leaves, poinsettia (bottom right) Figure Leaf anatomy Note: Cuticle = waxy or fatty layer on outer wall of epidermal cells 6

7 The plant body organs: root and shoots Root system and shoot system are designed to draw nutrients from two very different habitats Many are modified to accommodate specific conditions or strategies Leaf types can be confusing (like fruits), but you need to know them Leaf anatomy includes many different kinds of cells: living to dead. Pallisade parenchyma and spongy parenchyma can help determine orientation of leaf and stomata. Some leaf morphologies are adapted for specific conditions: oleanders and water conservation The plant cell tissue systems, tissues, and cells Figure 35.7 The three tissue systems A review of the tissue systems and cells this is really here for you to read and review Pay attention to the new context we ll look at monocots vrs. eudicots Figure 35.7 The three tissue systems Tissue Systems Ground Tissues/cells Parenchyma Collenchyma Sclerenchyma Figure Primary tissues, and their functions, in young stems Sclerenchyma tissue: support of mature plant parts Xylem tissue: water & mineral transport; Phloem tissue: food (sugar) transport (a.k.a. pith ray ) Collenchyma tissue: support of young, growing parts Vascular Xylem Phloem Parenchyma tissue: photosynthesis, storage, and/or secretion Dermal Epidermis Epidermal tissue: protection, control of water loss, and a variety of other functions The three tissue systems 7

8 Figure Organization of primary tissues in young stems. Note difference from root: vascular tissue is arranged in bundles, with ground tissue in center. Also note difference in arrangement of bundles between dicot and monocot. Figure Organization of tissue systems and tissues in young roots Epidermis: Dermal system, epidermal tissue Cortex: Ground system, parenchyma tissue Stele: Vascular system, xylem & phloem tissues Figure Organization of primary tissues in young roots. Note the difference between the monocot and the dicot in the arrangement of the xylem & phloem in the stele. Tissue Systems Tissues (& cell types) Ground Vascular Dermal Parenchyma (parenchyma cells, transfer cells) Collenchyma (collenchyma cells) Sclerenchyma (fibers & sclereids) Xylem (tracheids or vessel members, also some parenchyma cells, fibers, & sclereids ) Phloem (sieve cells or sieve-tube members, also specialized parenchyma cells called companion or albuminous cells, some fibers & sclereids) Epidermis (ground cells, guard cells, trichomes, and others, also some fibers & sclereids) Three tissue systems of plants Dermal tissue - outer protective covering Epidermis/periderm analogous to skin Cuticle - waxy coating to preserve water Vascular tissue - transport system Xylem: carries water and nutrients from roots to leaves. Support and food storage too. Phloem: transport organic nutrients (sugar), amino acids, lipids, hormones etc. Ground tissue - everything else. Pith (internal to vascular), Cortex Function in storage, photosynthesis, & support Figure Leaf anatomy Note: Cuticle = waxy or fatty layer on outer wall of epidermal cells 8

9 Primary Tissues are arranged in a ring in eudicot stems, and are scattered in monocot stems The stele, within the root, contains xylem that is more centralized in eudicots and more scattered in monocots You remember all those cell types Plant Growth 1. Meristems and overview of plant growth 2. Apical meristems and primary growth 3. Lateral meristems and secondary growth Remember: A major adaptation of land plants is the meristem a region of perpetual cell division that allows the plant to grow rapidly There are two types of meristems: Apical and lateral. Apical meristems lengthen the plant ( primary growth ). Roots and shoots Lateral meristems thicken the plant with bark and wood ( secondary growth ). Figure Locations of major meristems Figure Illustration of primary and secondary growth: Morphology of a winter twig Plant Growth 1. Meristems and overview of plant growth 2. Apical meristems and primary growth 3. Lateral meristems and secondary growth 9

10 Figure Primary growth of a root. Notice that the apical meristem produces three primary meristems, which produce the three primary tissue systems (dermal, ground, and vascular). Figure Organization of primary tissues in young roots. Note the difference between the monocot and the dicot in the arrangement of the xylem & phloem in the stele. Figure The formation of lateral roots. Lateral roots arise from the pericycle the outermost cell layer of the stele. Figure Primary growth of a root. Notice that the apical meristem produces three primary meristems, which produce the three primary tissue systems (dermal, ground, and vascular). Figure The terminal bud and primary growth of a shoot. Just like in the root, the apical meristem produces three primary meristems, which develop into the three tissue systems. Figure Organization of primary tissues in young stems. Note difference from root: vascular tissue is arranged in bundles, with ground tissue in center. Also note difference in arrangement of bundles between dicot and monocot. 10

11 Plant Growth 1. Meristems and overview of plant growth 2. Apical meristems and primary growth 3. Lateral meristems and secondary growth Remember: Secondary growth happens at the 2 lateral meristems The interior lateral meristem, called the vascular cambium, produces secondary xylem (to the interior) and phloem (to the exterior). The exterior lateral meristem, called the cork cambium, produces cork cells to the exterior. Figure Locations of major meristems Vascular cambium: Figure Secondary growth of a stem (Layer 1) Fusiform initials make cells elongated vertically, form secondary xylem (to inside) and secondary phloem (to the outside) Ray initials make cells elongated horizontally-transfer water and nutrients, store starch Figure Secondary growth of a stem (Layer 2) Cork cambium: meristem for tough thick covering - replaces epidermis. Forms from cortex to fill in gaps as epidermis is stretched and broken by lateral expansion of stem Rays maintain connectivity between secondary xylem and secondary phloem, allow exchange of nutrients and water, store starch and organic nutrients Figure Secondary growth of a stem (Layer 3) Anatomy of a three-year-old stem. How can you tell the stem is 3 years old? 11

12 Secondary growth of a stem. How many years old is it? Notes: Figure Anatomy of a tree trunk Wood = secondary xylem, or everything on the interior side of the vascular cambium Bark = everything exterior of the vascular cambium, including the secondary phloem and the periderm (cork cambium + cork) Oldest xyelm nonfuctional Also remember: Secondary growth happens in roots too. Oldest phloem sloughed off A summary of primary and secondary growth in a woody stem A summary of primary and secondary growth in a woody stem Remember: A major adaptation of land plants is the meristem a region of perpetual cell division that allows the plant to grow rapidly There are two types of meristems: Apical and lateral. Apical meristems lengthen the plant ( primary growth ). Lateral meristems thicken the plant with bark and wood ( secondary growth ). There are two of these Figure Locations of major meristems Oldest xyelm nonfuctional Oldest phloem sloughed off 12

13 Record of events from xylem rings Oldest xyelm nonfuctional Old growth trees can provide disease and fire records Oldest phloem sloughed off Aztecs and plagues 13