Plant Structure & Growth Plant Biology Chapter 35 Kingdom Plantae Plant Structure & Growth

Plants have evolved two systems: subterranean root system aerial shoot system of stems and leaves. shoots roots

Primary Function of Organs Three organs in plants: Stem Leaves Root Shoot system

Roots Roots anchor the plant in the soil Store food Absorb minerals and water Most absorption of water and minerals in occurs near the root tips.

Proproots

Black Mangrove with Pneumatophore                                                                                                                                                                                                                               TPneumatophores allow water-logged roots to obtain Oxygen which is essential for respiration. Pneumatophores contain lots of Aerenchyma which is abundant in submerged and emergent plant organs. They may also contain Lenticels which are areas in the dermis which permit the entry of air into structures that are covered by Periderm his Pneumatophore has a Periderm (Outer Bark) which protects it from the environment but is impervious to air.  However it produces Lenticels which allow for gas exchange with the environment. Black Mangrove with Pneumatophore

Shoots consist of stems and leaves. Stem: Raises leaves and flowers above ground (safer from herbivores and allow leaves to better photosynthesize). Path by which water, minerals, and food are transported. Leaves: Site of photosynthesis, i.e. food production

Shoots System: stems and leaves Stems May be vegetative (leaf bearing) or reproductive (flower bearing). Node- area of stem where leaf is born Internodes- stem area between nodes Buds: Stem elongation. Embryonic tissue of leaves and stem (not flower bud) Terminal bud-Located at tip of stems or branches. Axillary bud- Gives rise to branches Apical Dominance: Prevention of branch formation by terminal bud

Leaves:Photosynthesis Shoots System: Leaves:Photosynthesis Petiole: Stalk of leaf, joins leaf to node of stem Blade: Flattened, expanded portion of leaf. Site of photosynthesis

Shoot System

Modified shoots: Include stolons, rhizomes, tubers, and bulbs, are often mistaken for roots. Stolons: allow plants to colonize large area and to reproduce asexually Pohuehue

Rhizomes: horizontal stems that grow underground. Tubers: are the swollen ends of rhizomes specialized for food storage. Bulbs: vertical, underground shoots consisting mostly of the swollen bases of leaves that store food. rhizomes tubers bulbs

Classification of Leaves Arrangement on the stem Simple vs. compound Overall leaf shape Leaf margin shape Leaf venation

Leaf Taxonomy

Leaf Arrangement on the Stem Opposite: 2 leaves at a node, on opposite sides of the stem Spiral: 1 leaf per node, with the second leaf being above the first but attached on the opposite side of the stem Whorled: 3 or more leaves at a node

Leaf Modifications Tendrils Spines Storage Petal-like Insectivorous leaves

Leaf Modifications tendrils spines storage petal-like

Plant organs are composed of three tissue systems: Dermal tissue Vascular tissue Ground tissue

Dermal Tissue The dermal tissue, or epidermis, is generally a single layer of tightly packed cells that covers and protects all young parts of the plant. Other specialized characteristics : Root hairs: increased absorption Cuticle: waxy coating, prevents water loss

Plant Cell Structure cell wall chloroplast nucleus central vacuole

Cell Wall Structure secondary cell wall primary cell wall middle lamella

Cell Wall Structure plasmodesmata

Plant Cell Types Xylem Phloem Tracheids Vessel elements Sieve-tube members Companion cell

Vascular Tissue Vascular tissue: runs continuous throughout the plant transports materials between roots and shoots. Xylem transports water and dissolved minerals upward from roots into the shoots. (water the xylem) Phloem transports food from the leaves to the roots and to non-photosynthetic parts of the shoot system. (feed the phloem)

Xylem The water conducting elements of xylem are the tracheids and vessel elements.

Xylem Tracheids Characteristics Functions tapered elongated cells connect to each other through pits secondary cell walls strengthened with lignin dead at functional maturity Functions transport of water plus dissolved minerals support

Xylem Vessel Elements Characteristics Functions shorter and wider than tracheids possess thinner cell walls than tracheids Aligned end-to-end to form long micropipes dead at functional maturity Functions transport of water plus dissolved minerals support

Water conducting cells of the xylem

Phloem Food and minerals move through tubes formed by chains of cells, sieve-tube members. sieve plates companion cell

Phloem Sieve-tube Members Characteristics Functions living cells arranged end-to-end to form food-conducting cells of the phloem lack lignin in their cell walls mature cells lack nuclei and other cellular organelles alive at functional maturity Functions transport products of photosynthesis

Phloem Companion Cells Characteristics Functions living cells adjacent to sieve-tube members connected to sieve-tube members via plasmodesmata Functions support sieve-tube members may assist in sugar loading into sieve-tube members

Food conducting cells of the phloem

Ground Tissue Ground tissue fills the interior of the plant. It contains three basic cell types: Parenchyma cells Collenchyma cells Sclerenchyma cells Dermal tissue Ground tissue Vascular tissue Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Parenchyma Characteristics Functions least specialized cell type only thin primary cell wall is present possess large central vacuole generally alive at functional maturity Functions make up most of the ground tissues of the plant storage photosynthesis can help repair and replace damaged organs by proliferation and specialization into other cells

Parenchyma

Collenchyma Characteristics Functions possess thicker primary cell walls the that of parenchyma no secondary cell wall present generally alive at functional maturity Functions provide support without restraining growth

Collenchyma

Sclerenchyma Characteristics Functions have secondary cell walls strengthened by lignin often are dead at functional maturity two forms: fibers and sclereids Functions rigid cells providing support and strength to tissues

Two other sclerenchyma cells, fibers and sclereids, are specialized entirely in support. Fibers are long, slender and tapered, and usually occur in groups. Those from hemp fibers are used for making rope and those from flax for weaving into linen. Sclereids, shorter than fibers and irregular in shape, impart the hardness to nutshells and seed coats and the gritty texture to pear fruits.

Fiber Cells

Sclereids

Plant Growth & Development Growth is the irreversible increase in mass that results from cell division and cell expansion. Development is the sum of all the changes that progressively elaborate an organism’s body.

Meristems generate cells for new organs throughout the lifetime of a plant: an overview of plant growth Most plants demonstrate indeterminate growth, growing as long as the plant lives. In contrast, most animals and certain plant organs, such as flowers and leaves, undergo determinate growth, ceasing to grow after they reach a certain size. Indeterminate growth does not mean immortality.

Germination  flowering  seed production death Plant Lifecycle: Germination  flowering  seed production death Annual- in a single year or less. Many wildflowers and important food crops, such as cereals and legumes, are annuals. Biennial- spans two years. Often, there is an intervening cold period between the vegetative growth season and the flowering season. Perennials- Plants that live many years, Includes trees, shrubs, and some grasses. These often die not from old age, but from an infection or some environmental trauma.

Meristems– embryonic tissue. These cells divide to generate additional cells. Initials- generative cells that remain in the meristem. Derivatives- Those that are displaced from the meristem,and continue to divide for some time until the cells they produce begin to specialize within developing tissues.

The pattern of plant growth depends on the location of meristems. Fig. 35.12 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Locations of Meristematic Tissues Apical meristems: located at the tips of roots and in the buds of shoots, supply cells for the plant to grow in length. Primary growth initial root and shoot growth produced by apical meristem elongation occurs restricted to youngest parts of the plant, i.e, tips of roots & shoots

Locations of Meristematic Tissues Lateral meristems: allow the plant to increase in girth Secondary growth: thickening of roots and shoots. Produced by lateral meristems Develop in slightly older regions of roots and shoots Examples: vascular and cork cambium.

Meristems

Types of Primary Meristems Protoderm: forms dermal tissue system Procambium: forms vascular tissue system Ground Meristem: forms ground tissue system

Primary Growth in Roots Root Cap: covers root tip & protects the meristem as the root pushes through the abrasive soil during primary growth. The cap also secretes a lubricating slime. Growth in length is concentrated near the root’s tip, where three zones of cells at successive stages of primary growth are located. zone of cell division zone of elongation zone of maturation Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Primary Growth of the Root

The zone of cell division includes the apical meristem and its derivatives, primary meristems. Near the middle is the quiescent center, cells that divide more slowly than other meristematic cells. These cells are relatively resistant to damage from radiation and toxic chemicals. They may act as a reserve that can restore the meristem if it becomes damaged.

Fig. 35.14 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The zone of cell division blends into the zone of elongation where cells elongate, sometimes to more than ten times their original length. It is this elongation of cells that is mainly responsible for pushing the root tip, including the meristem, ahead. The meristem sustains growth by continuously adding cells to the youngest end of the zone of elongation. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

In the zone of maturation, cells begin to specialize in structure and function. In this root region, the three tissue systems produced by primary growth complete their differentiation, their cells becoming functionally mature. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Three primary meristems give rise to the three primary tissues of roots. The epidermis develops from the dermal tissues. The ground tissue produces the endodermis and cortex. The vascular tissue produces the stele, the pericycle, pith, xylem, and phloem. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The protoderm, the outermost primary meristem, produces the single cell layer of the epidermis. Water and minerals absorbed by the plant must enter through the epidermis. Root hairs enhance absorption by greatly increasing the surface area. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The procambium gives rise to the stele, which in roots is a central cylinder of vascular tissue where both xylem and phloem develop. Stele Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

The ground tissue between the protoderm and procambium gives rise to the ground tissue system. These are mostly parenchyma cells between the stele and epidermis. They store food and are active in the uptake of minerals that enter the root with the soil solution. The innermost layer of the cortex, the endodermis, is a cylinder one cell thick that forms a boundary between the cortex and stele. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Dicot Monocot Fig. 35.15

Monocot Root Anatomy epidermis cortex endodermis cortex pericycle stele pith phloem xylem pith

Dicot Root Anatomy cortex endodermis pericycle epidermis cortex stele xylem phloem

Each growing season, primary growth produces young extensions of roots and shoots, while secondary growth thickens and strengthens the older part of the plant.

Organization of Primary Tissues in Young Stems Fig. 35.18

Primary Growth of the Shoot

Monocot Stem Anatomy phloem epidermis vascular bundles ground tissue xylem

Dicot Stem Anatomy epidermis phloem cortex vascular bundle pith cambium xylem

The meristematic bands make a continuous cylinder of dividing cells surrounding the primary xylem and pith of the stem. Fig. 35.21 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

This ring of vascular cambium consists of regions of ray initials and fusiform initials. Ray initials (xylem rays and phloem rays) that transfer water and nutrients laterally Fusiform initials form 2o xylem to the inside of the vascular cambium and 2o phloem to the outside. Fig. 35.21 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

As secondary growth continues over the years, layer upon layer of secondary xylem accumulates, producing the tissue we call wood. Wood consists mainly of tracheids, vessel elements (in angiosperms), and fibers. These cells, dead at functional maturity, have thick, lignified walls that give wood its hardness and strength.

Secondary Growth of a Stem

Production of Secondary Xylem and Phloem The accumulation of this tissue over the years accounts for most of the increase in diameter of a woody plant. Secondary xylem forms to the interior and secondary phloem to the exterior of the vascular cambium. C=cambium cell X=2o xylem P=2o phloem D=derivative

Anatomy of a Tree Trunk After several years of secondary growth, several zones are visible in a stem.

Primary and Secondary Growth in a Woody Stem

The Leaf The leaf epidermis is composed of cells tightly locked together like pieces of a puzzle. It is the first line of defense against physical damage and pathogenic organisms The waxy cuticle prevents desiccation.

Leaf Anatomy

Typical Dicot Leaf X-Section Cuticle Epidermis Palisade Parenchyma Vascular bundles Guard Cells Spongy Parenchyma Stoma

Typical Monocot Leaf X-Section Bundle sheath cell Midvein Vein Epidermis Phloem Xylem Bulliform Cells Stoma

Guard cells with chloroplasts Leaf Stomata: Allow Gas Exchange Guard cells with chloroplasts Stomata in Zebrina leaf epidermis Stoma Subsidiary cells

Mesophyll- the ground tissue of the leaf, located between the upper and lower epidermis. mainly of parenchyma cells equipped with chloroplasts and specialized for photosynthesis. CO2 and O2 circulate through the air spaces The air spaces are particularly large near stomata, where gas exchange with the outside air occurs.

The vascular tissue of a leaf is continuous with the xylem and phloem of the stem. Leaf traces, branches of vascular bundles in the stem, pass through petioles and into leaves. Within a leaf, veins subdivide repeatedly and branch throughout the mesophyll. xylem brings water and minerals phloem carries sugars the vascular infrastructure reinforces the shape of the leaf.

Molecular Biology and Plants Plants have tremendous developmental plasticity. Environmental factors can influence growth and development, and reproductive output A broad range of morphologies can result from the same genotype as the plant undergoes three developmental processes: growth, morphogenesis, and differentiation. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Molecular biology is revolutionizing the study of plants Much plant research has focused on Arabidopsis thaliana, a small weed in the mustard family. Ideal research subject: Cultivates quickly Requires little lab space Generation time 6 weeks Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

first plant genome sequenced, taking six years to complete. Arabidopsis first plant genome sequenced, taking six years to complete. Arabidopsis has a total of about 26,000 genes, with fewer than 15,000 different types of genes. The functions of only about 45% of the Arabidopsis genes are unknown. Fig. 35.25 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Now plant biologists work to identify the functions of every gene and track every chemical pathway to establish a blueprint for how plants are built. One key task is to identify which cells are manufacturing which gene products and at what stages in the plant’s life. Potential to develop a designer plant from a computer model. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings