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Transcript
The shoot: Primary structure and development Repeated modules (phytomeres) Shoot meristem ü leaves ü Internodes ü Flowers The vegetative shoot apical meristem of most flowering plants has a tunica-corpus organzation The vegetative shoot apical meristem of most flowering plants has a tunica-corpus organzation Anticlinal divisions: perpendicular to the surface of the tissue. Periclinal divisions: parallel to the surface of the tissue Elongation of the stem in monocots is restricted to the base of the internode Internodal elongation can occur simultaneously over several internodes Removing part of a meristem = regeneration of a complete meristem. Removing completely the meristem = incipient meristem (at the base of the leaf) to develop. Thus growing meristems inhibit the growth of nearby ones. Phyllotaxy (from Greek phyllo-, leaf; -taxis, motion/orientation). The pattern of leaves on a plant is controlled by the plant hormone auxin. Helical Helical with elongated internodes (alternatedistichous) (e) opposite Opposite (oppositedecussate) Whorled (verticillate). margin midrib vein Sessile leaves do not possess a petiole. Trichomes: "growth of hair” Development of the flower The development of the flower or inflorescence ends the meristimatic activity of the vegetative shoot apex. Reproductive apex Annuals Perennials A typical flower consists of four whorls of organs 1) Sepals 2) petals 3) stamens 4) carpels A flower bud of the outcrossing variety of Clarkia xantiana ssp. xantiana. § petals (red) § large anthers (blue § small anthers (purple § style/stigma (yellow) At this stage the bud is only 1 mm in diameter. Scanning electron micrograph. John Runions. Homeotic mutations and genes A,B,C normal apetala 2 (ap2) pistillata (pi) agamous (ag) SEPALLATA OR LEAFY Sepal (se) class A activity, petal class A and class B activity, stamen (st) B and class C activity and carpel (ca) C activity. Class E activity is required for the specification of each organ type Mesophytes are terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment. • Usually have broad, flat and green leaves. • Epidermis is single layered usually with obvious stomata and large cortex. Xerophytes Limited water • reduced permeability of the epidermal layer, stomata and cuticle • adaptations of the root system to acquire water from deep underground sources or directly from humid atmospheres • swollen stems, leaves or root tissues Bromelia Hydrophytes Aquatic plants • Thin cuticle • Increased number of stomata that are open most of time, they are on either side of leaves • guard cells are generally inactive • A less rigid structure • Commonly flat leaves • Air sacs for flotation. • Smaller roots • Feathery roots • Specialized roots able to take in oxygen. Stem and leaf modifications tendril: specialized stem, leaf or petiole with a threadlike shape Pea tendril modified leaf Virginia creeper modified stem Cladophylls: branches or portions of a stem that resemble leaves and replace them as the main photosynthetic organs of the plant 1. Ocotillo with spines (modified leaves) 2. Citrus with thorns (modified branches or stems) 3. Rose with prickles (extensions of the cortex and epidermis Attendance From your book, page 579, questions 3, 7 and 9