CHAPTER 35 PPT

• Overall Organization of Vascular Plants:

  • Plants have a hierarchical organization consisting of organs, tissues, and cells
• 3 Basic Plant Organs:

  • Roots: absorb water, minerals and other nutrients from the soil, anchor & support plant in the ground
  • Stems: structural support of plant above ground, transport of water & nutrients throughout the plant
  • Leaves: harvesting light & CO2 for photosynthesis
• Root Function:

  • Anchorage in the soil
  • Roots supply the plant with water, mineral nutrients, carbohydrate storage
  • Roots rely on shoot system for carbohydrates
  • Roots also need access to O2
• Root Structures:

  • The primary root gives rise to lateral roots to increase absorption and anchorage
  • Tiny root hairs maximize surface area for absorption
  • In many plants, the primary root develops into a taproot for support and carbohydrate storage
• Fibrous Root Structures:

  • In some plants, the primary root disappears and a fibrous root system forms to retain topsoil and increase survival from grazing animals
• Evolutionary Adaptations of Roots:

  • Prop roots
  • Buttress roots
  • Pneumatophores
  • Adventitious roots develop from unusual sources (stems, leaves) for greater structural support and O2 access in watery environments
• Stem Structure and Function:

  • Internodes
  • Apical buds at shoot tips where growth occurs
  • Axillary buds give rise to lateral branches, thorns or flowers
• Evolutionary Adaptations of Stems:

  • Rhizomes grow just beneath the soil surface and give rise to vertical shoots from axillary buds
  • Stolons function as "runners" along the soil surface giving rise to new plantlets
  • Tubers serve as storage "sinks" for carbohydrates
• Leaf Structure & Function:

  • Petiole
  • Axillary bud
  • Leaflet
  • Compound leaf
  • Simple leaf
  • Veins with branched (dicots) or parallel (monocots) arrangement
• Evolutionary Adaptations of Leaves:

  • Tendrils cling to larger support structures
  • Spines repel herbivores
  • Bulbs store nutrients
  • Reproductive leaves detach and give rise to a new plant (asexual)
• 3 Basic Plant Tissue Types:

  • Dermal tissue: outer, protective covering of the plant
  • Vascular tissue: transports water, nutrients & gives structural support
  • Ground tissue: everything else
• More on Dermal Tissue:

  • Epidermis in nonwoody plants and structures, covered with a waxy cuticle
  • Trichomes in epidermal tissue provide protection from water loss, intense light, and insects
  • In woody plants, epidermis develops into periderm (part of the bark)
• More on Vascular Tissue:

  • Xylem transports water & minerals upward
  • Phloem transports photosynthetic products downward
  • Phloem & xylem organized into vascular bundles or cylinders called steles
• More on Ground Tissue:

  • Pith: ground tissue found internal to the vascular tissue
  • Cortex: ground tissue found between the dermal and vascular tissue
  • Ground tissues include cells involved in storage, transport, structural support, and photosynthesis
• Basic Plant Cell Types:

  • Parenchyma: metabolically active, capable of cell division and further differentiation
  • Collenchyma: provide flexible support without restraining growth
  • Sclerenchyma: provide rigid support due to thick cell walls containing lignin
  • Water-conducting cells of xylem and phloem
• Meristem Tissue:

  • Plants have indeterminate growth throughout life due to meristem tissue with unlimited replicative potential
  • 2 types of meristems: Apical Meristem and Lateral Meristem
• Apical Meristem:

  • Located at the tips of roots and shoots, responsible for growth in length (primary growth)
• Lateral Meristem:

  • Responsible for secondary growth in stems
• Secondary growth in stems is due to 2 types of lateral meristem:

  • Vascular cambium which adds new layers of phloem & xylem
  • Cork cambium which replaces the epidermis with protective periderm
• Primary growth of roots:

  • Root tips have a protective, non-dividing root cap
  • Zone of Cell Division contains apical meristem cells
  • Zones in successive developmental stages:
  • Zone of Elongation pushes root into soil
  • Zone of Differentiation where cells adopt specific fates
• In most eudicot roots, there is a central vascular cylinder (stele) with a “X-shaped” arrangement of xylem as seen in cross section with phloem filling in between the “arms” of the X
• Lateral root growth occurs from the meristematic pericycle, the outermost layer of cells in the vascular cylinder just inside the endodermis, the innermost layer of cortex
• Primary growth of shoot structures occurs from:

  • Apical meristem which lengthens the stem and gives rise to leaf primordia
  • Axial meristem which gives rise to new branches from the main stem
• In most eudicot stems, the vascular tissue consists of bundles of phloem and xylem arranged in a ring around the central pith tissue

  • Xylem is always located inside the phloem adjacent to the pith
• In most monocot stems, the vascular tissue consists of bundles of phloem and xylem scattered throughout the ground tissue
• Leaf structure:

  • Epidermis: outer cell layer on both sides of leaf, secretes waxy cuticle to waterproof the leaf
  • Mesophyll: loosely packed photosynthetic parenchyma cells in palisade or spongy arrangement
  • Vascular Bundles: phloem & xylem surrounded by bundle sheath cells
  • Stomata: openings for gas exchange, transpiration, regulated by guard cells
• Secondary growth of stems & roots:

  • Vascular cambium is a single-celled ring of meristem between primary xylem and phloem, produces new (secondary) xylem toward the inside and new (secondary) phloem toward the outside
  • Cork cambium produces cork cells periderm in place of the original epidermis to produce a protective outer layer
• Growth rings in woody stems reveal past climates:

  • Spring wood differs from summer wood, wider rings indicate warm & wet conditions, narrower rings indicate cold & dry conditions
• Genetic control of flowering:

  • Environmental cues trigger flower development in plants like Arabidopsis
  • Mutants have led to the ABC hypothesis of flower development where inner whorls develop into petals and sepals instead of stamens and a carpel
• Asymmetrical cell division in plants:

  • Asymmetrical cell division precedes the adoption of distinct cell fates
  • Mutants like gnom demonstrate the importance of asymmetric cell division in early plant development
• Arabidopsis - A model plant:

  • Much plant development knowledge comes from studying Arabidopsis thaliana
  • Advantages include small size, fast growth, and small genome size
• Genetic modification of Arabidopsis:

  • Agrobacterium tumefaciens is used to introduce new traits into plants
  • DNA of interest can be cloned into the Ti plasmid region and then introduced into the host plant genome
• More on Vascular Cambium:

  • 2o phloem and xylem cells form adjacent to the vascular cambium cells, pushing earlier layers further away from the vascular cambium
• More on Woody Stems:

  • Older xylem that no longer transports fluid is hardwood
  • Newer, active xylem is sapwood
  • 2o phloem + periderm make up the bark