Chapter 17 Notes
Chapter 17 Notes BIOL 3040
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This 6 page Class Notes was uploaded by Min-Young Kim on Wednesday February 3, 2016. The Class Notes belongs to BIOL 3040 at Clemson University taught by Christina Wells in Spring 2016. Since its upload, it has received 41 views. For similar materials see Biology of Plants in Biology at Clemson University.
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Date Created: 02/03/16
Chapter 17 Notes -‐ Vascular plants: sporophytes more prominent than gametophytes and are free-‐living. o Xylem and phloem solved problem of food and water transport throughout plant body. o Ability to synthesize lignin also helped (adds rigidity allows vascularized sporophytes to reach great heights) o Branch profusely at apical meristems, produce multiple sporangia -‐ Ancient vascular plants gave rise to more specialized plants with highly differentiated plant body o Roots (anchorage and absorption) o Stem and leaves (acquisition of energy, carbon dioxide, and water) o Seeds (structures that provide embryonic sporophyte with nutrients and protect it from rigors of life on land) -‐ Sporophytes of early vascular plants were dichotomously branched axes that lacked roots and leaves o Root system and shoot system (stems and leaves) -‐ Dermal tissue system: outer, protective covering of plant -‐ Vascular tissue system: conductive tissues (xylem and phloem), embedded in ground tissue system -‐ Primary growth: growth that occurs relatively close to the tips of roots and stems; initiated by apical meristems, involved with extension (usually vertical) of the plant body; (primary tissues, primary plant body) -‐ Secondary growth: thickens stem and root. Results from activity of lateral meristems o Vascular cambium: produces secondary vascular tissues (secondary xylem and phloem) o Cork cambium: forms periderm, composed mainly of cork tissue; replaces epidermis as dermal tissue system of plant o Secondary vascular tissues and periderm make up secondary plant body -‐ Tracheary elements: conducting cells of xylem; distinctive lignified wall thickenings -‐ Sieve elements: conducting cells of phloem, soft walls and often collapse after death, don’t fossilize well -‐ Tracheids: only type of water-‐conducting cell in most vascular plants; provide channels for water and minerals, as well as support for stems; rigid lignin in walls -‐ Vessel elements: principal water-‐conducting cell in angiosperms. Evolved independently in several groups of vascular plants (good example of convergent evolution) -‐ Stele: central cylinder in primary plant body made up of primary xylem and phloem, as well as pith (central column of ground tissue) o Protostele: simplest and most ancient; solid cylinder of vascular tissue; phloem either surrounds xylem or interspersed in it (in extinct seedless vascular plants, lycophytes, and most roots) o Siphonostele: in stems of most seedless vascular plants; central pith surrounded by vascular tissue; phloem on outside of xylem or on both sides of it (in ferns, leaf traces marked by leaf gaps, called leaf trace gaps) o Eustele: primary vascular cylinder consists of system of discrete strands around pith (siphonosteles evolved independently from protosteles. None of the seedless vascular plants gave rise to any living seed plants) -‐ Microphylls: relatively small leaves that contain only single strand of vascular tissue; typically associated with stems possessing protosteles and characteristic of lycophytes o Leaf traces not associated with leaf gaps, usually only single vein in each leaf o May have evolved as superficial lateral outgrowths of stem or from sterilization of sporangia in lycophytes ancestors -‐ Megaphylls: larger; associated with stems that have either siphonosteles or eusteles o Leaf traces associated with leaf gaps and leaf trace gaps; blade has complex system of branching veins o Unequal branching resulted in more aggressive branches “overtopping” weaker ones -‐ All vascular plants oogamous and have alternation of heteromorphic generations -‐ Homosporous: early vascular plants produced only one kind of spore as a result of meiosis o Found in most ferns, horsetails, and some lycophytes o Condition from which heterospory evolved o Homosporous plants have potential to produce bisexual gametophytes, but most fern sporophytes are heterozygous -‐ Fern mechanism for cross-‐fertilization: maturation at different times for antheridia and archegonia. Sperm produced by one gametophyte fertilize eggs of neighboring o Sex expression determined by age of plant of water-‐soluble substances called antheridiogens. Self-‐fertilization does occur -‐ Heterospory: production of two types of spores in two different kinds of sporangia o Found in some lycophytes, few ferns and all seed plants o Microspores and megaspores produced in microsporangia and megasporangia; differentiated based on function and not necessarily size. Microspores à male gametophytes. Megaspores à female gametophytes. o Heterosporous plants – gametophytes form within the spore wall (endosporic). Homosporous plants – gametophytes develop outside spore wall (exosporic development) -‐ Relatively large gametophytes of Homosporous plants are independent of sporophyte for nutrition. Gametophytes of many Heterosporous vascular plants, especially seed plants, are dependent on sporophyte for nutrition -‐ Within vascular plants, evolution of gametophytes is characterized by overall trend toward reduction in size and complexity -‐ In angiosperms and in most gymnosperms, entire microgametophytes (pollen grains) are carried to vicinity of megagametophyte. Transfer of pollen grains is pollination. Germination of pollen grains produces special structures called pollen tubes, through which motile sperm swim to the egg to achieve fertilization -‐ Overall pattern of diversification of plants: 1. Early vascular plants, characterized by relatively small stature and simple presumable primitive morphology (rhyniophytes, zosterophyllophytes, trimerophytes) 425-‐370 mya 2. Monilophytes, lycophytes, and progymnosperms. 375-‐290 mya 3. Seed plants; 380 mya 4. Flowering plants; 135 mya -‐ Rhyniophyta: seedless plants, consisting of dichotomously branching axes with terminal sporangia o Rhynia Gwynne-‐vaughanii. Marsh plant, numerous lateral branches and short branches on which sporangia often borne; single layer of superficial cells (epidermis) surrounded by photosynthetic tissue of cortex; center of axis consisting of xylem and phloem-‐like cells o Aglaphyton major: extensive dichotomously branched rhizome system; protracheophytes (intermediate stage in vascular plants); ells more like hydroids of modern mosses than tracheids o Cooksonia: rhyniophyte inhabited mud flats; oldest known vascular plant; slender leafless aerial stems; long and terminated in globose sporangia; tracheids identified -‐ Zosterophyllophyta: leafless and dichotomously branched; aerial stems covered with cuticle, only upper ones contained stomata; lower branches produced lateral branches forking into two axes; sporangia borne laterally on short stalks; homosporous; centripetal differentiation; ancestors of lycophytes -‐ Trimerophytophyta: evolved from rhyniophytes; diverse evolutionary relationships and ancestral stock of both ferns and progymnosperms; larger and more complex; relatively short period of existence; lacked leaves but had complex branching; more massive vascular strand -‐ Lycopodiophyta: representatives of evolutionary line extending back to Devonian period; basal split separated lycophyte clade (modern lycophyte lineage) and euphyllophyte clade (monilophytes and seed plants); non-‐ woody herbaceous plants; possess Microphylls o Lycopodiaceae (club mosses): sporophytes consist of branching rhizome from which aerial branches and roots arise; both stems and roots protostelic; Microphylls usually spirally arranged; homosporous; sporangia on sporophylls; strobili: cones at ends of branches § Upon germination, spores give rise to bisexual gametophytes that are either green irregularly lobed masses or subterranean non-‐photosynthetic mycorrhizal structures § Gametophytes predominantly cross-‐fertilize; self-‐fertilization rates low § Water required for fertilization. Biflagellated sperm à archegonium àfertilization àzygote àembryo àyoung sporophyte remains attached to gametophyte, but eventually becomes independent o Selaginella (spike mosses): resurrection plant; bears Microphylls and sporophylls arranged in strobili; small scale-‐like outgrowth (ligule) near base of upper surface of each microphyll and sporophyll; stem and root protostelic § Heterosporous: unisexual gametophytes. Each sporophyll bears single sporangium on upper surface. Megasporangia borne by megasporophylls, and microsporangia borne by microsporophylls; both occur in same strobilus § Microgametophytes develop within microspore, lack chlorophyll; microspore wall must rupture for sperm to be free § Megaspore wall ruptures and gametophyte protrudes through rupture to outside (megagametophyte) § Water required for fertilization; occurs after gametophytes shed from strobilus § During development of embryos in both Lycopodiaceae and Selaginella, suspensor formed: serves to thrust developing embryo deep within nutrient-‐rich tissue of female gametophyte; developing sporophyte emerges from gametophyte and becomes independent o Iosetes (quillworts): nearest living relative of ancient tree lycophytes of Carboniferous. Sporophyte has short fleshy underground stem (corm) bearing quill-‐like microphylls on upper surface and roots on lower surface § Heterosporous: megasporangia borne on megasporophylls; microsporangia borne on microsporophylls § Specialized cambium adds secondary tissues to corm; only parenchyma tissue externally, but internal tissue of sieve elements, parenchyma cells, and tracheids § Leaves of plants lack stomata; have thick cuticle; no gas exchange; CAM photosynthesis -‐ Monilophyta: ferns and horsetails; ferns are largest and most diverse group of plants other than angiosperms; third of all tropical ferns grow on trunks or branches as epiphytes; most homosporous o Lygodium: climbing fern; leaves with long twining rachis; tissues primarily at origin; thickness is fibrous root mantle o Eusporangium: parent cells located at surface of tissue from which sporangium produced; inner and outer series of cells; inner layer gives rise to irregularly oriented cells from which spore mother cells ultimately arise § Psilopsida and Marattiopsida: single leaf produced each year from stem: 1) vegetative portion 2) fertile segment • Sporophyte of Psilotum has dichotomously branching aerial portion and underground branching portion of rhizomes and rhizoids; generally aggregated on ends of short lateral branches • Tmesipteris: grows as epiphyte on tree ferns and rocks • Marattiopsida: ancient group resembling ferns § Equisetopsida: single homosporous herbaceous genus; horsetails; internodes ribbed; roots at nodes of rhizomes; carinal canals associated with xylem and phloem; sporangiophores (sporangia-‐bearing branches clustered into strobili); sporangia contract and split along inner surface, releasing numerous spores; elaters (thickened bands) coil when moist and uncoil when dry; green and free-‐living gametophytes (in bisexuals, archegonia develop before antheridia) o Leptosporangia: arise from single superficial initial cell; divides transversely or obliquely; cells either produce large part of sporangial stalk or remain inactive; outer cell gives rise to elaborate stalked sporangium, with a spherical capsule (two-‐layered tapetum); inner mass divides into spore mother cells § Tapetum nourishes cells; material from tapetum deposited around spores; spores exposed to lip cells of sporangium; sporangia stalked, containing annulus; sporangium dries; annulus tears middle of capsule; explosion and snap back; catapult-‐like discharge of spores § Polypodiopsida: homosporous; nearly all ferns; siphonostelic rhizomes produce new sets of leaves each year; fronds are megaphylls, high surface-‐to-‐volume ratio allows effective capture of sunlight; lamina divided into pinnae, attached to rachis; circinate vernation; sporangia commonly occur in clusters called sori; young sori covered by indusia; • Gametophyte develops into prothallus (flat, heart-‐ shaped, numerous rhizoids on lower surface) • Archegonia and antheridia develop on ventral surface of prothallus; timing of maturation of antheridia and archegonia can determine self-‐fertilization or cross-‐ fertilization • Embryo (young sporophyte) receives nutrients through foot; develops; independent plant; gametophyte disintegrates (exceptions) § Salviniales: heterosporous; • Marsilea: leaves resemble four-‐leaf clover; grow in mud or on surface of water; sporocarps: drought-‐resistant bean-‐shaped reproductive structures • Azolla and Salvinia: plants on surface of water; Azolla has bi-‐lobed leaves with pouches of cyanobacteria; Salvinia has undivided leaves “roots” hanging down, bear sporangia
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