CHAPTER 35

PLANT STRUCTURE AND

GROWTH

I. INTRODUCTION TO MODERN PLANT BIOLOGY A. MOLECULAR BIOLOGY IS REVOLUTIONIZING

THE STUDY OF PLANTS

B. PLANT BIOLOGY REFLECTS THE MAJOR THEMES IN THE STUDY OF LIFE

THE CORRELATION BETWEEN STRUCTURE AND FUNCTION AND THE EVOLUTIONARY CONTEXT OF ADAPTATION TO THE ENVIRONMENT ILLUMINATE OUR STUDY OF PLANTS.

II. THE ANGIOSPERM BODY A. PLANT'S ROOT AND SHOOT SYSTEMS

ARE EVOLUTIONARY ADAPTATIONS TO LIVING ON LAND

ROOTS ANCHOR ABSORB AND CONDUCT WATER AND MINERALS, AND STORE FOOD.

THE SHOOT SYSTEM CONSISTS OF STEMS, LEAVES, AND FLOWERS.

LEAVES ARE ATTACHED BY THEIR PETIOLES TO THE NODES OF THE STEM, LEAVES AND FLOWERS WITH INTERNODES OF THE STEM SEPARATING THE NODES.

AXILLARY BUDS, LOCATED IN THE AXILS OF PETIOLES AND STEMS, HAVE THE POTENTIAL TO EXTEND AS VEGETATIVE OR FLORAL BRANCHES.

VASCULAR TISSUES INTEGRATE THE PARTS OF THE PLANT.

WATER AND MINERALS MOVE UP FROM ROOTS IN THE XYLEM.

SUGAR IS TRANSPORTED FROM THE LEAVES OR STORAGE ORGANS IN THE PHLOEM.

THE PLANT BODY IS DIVIDED INTO A ROOT SYSTEM AND A SHOOT SYTEM, CONNECTED BY VASCULAR TISSUE

THAT IS CONTINUOUS THROUGHOUT THE PLANT.

THE ROOT SYSTEM THE SHOOT SYSTEM

– STEMS– LEAVES

A.     STRUCTURAL ADAPTATIONS OF PROTOPLASTS AND WALLS EQUIP PLANT CELLS FOR THEIR

SPECIALIZED FUNCTIONS PARENCHYMA CELLS, RELATIVELY UNSPECIALIZED CELLS

THAT RETAIN THE ABILITY TO DIVIDE, PERFORM MOST OF THE PLANT'S METABOLIC FUNCTIONS OF SYNTHESIS AND STORAGE.

COLLENCHYMA CELLS, WHICH HAVE UNEVENLY THICKENED CELL WALLS, SUPPORT YOUNG, GROWING PARTS OF THE PLANT.

SCLERENCHYMA CELLS, FIBERS AND SCLEREIDS, HAVE THICK, LIGNIFIED WALLS THAT HELP SUPPORT MATURE, NON-GROWING PARTS OF THE PLANT.

TRACHEIDS AND VESSEL ELEMENTS, THE WATER- CONDUCTING CELLS OF XYLEM, HAVE THICK WALLS AND ARE DEAD AT FUNCTIONAL MATURITY.

SIEVE-TUBE MEMBERS ARE THE SUGAR TRANSPORTING CELLS OF PHLOEM. THOUGH ALIVE AT FUNCTIONAL MATURITY, SIEVE-TUBE MEMBERS DEPEND ON THE SERVICES OF NEIGHBORING COMPANION CELLS.

C.     THE CELLS OF A PLANT ARE ORGANIZED INTO DERMAL, VASCULAR, AND GROUND

TISSUE SYSTEMS DERMAL TISSUE (EPIDERMIS),

VASCULAR TISSUE (XYLEM AND PHLOEM), AND GROUND TISSUE (MOSTLY PARENCHYMAL CELLS) ARE CONTINUOUS THROUGHOUT THE PLANT, ALTHOUGH IN THE VARIOUS PLANT ORGANS THEY DIFFER IN ARRANGEMENT AND IN SOME SPECIALIZED FUNCTIONS.

III. PLANT GROWTH A. MERISTEMS GENERATE CELLS

FOR NEW ORGANS THROUGHOUT THE LIFETIME OF A PLANT: AN OVERVIEW OF PLANT GROWTH

APICAL MERISTEMS ELONGATE SHOOTS AND ROOTS THROUGH PRIMARY GROWTH.

LATERAL MERISTEMS ADD GIRTH TO WOODY PLANTS THROUGH SECONDARY GROWTH.

B. PRIMARY GROWTH: APICAL MERISTEMS EXTEND ROOTS AND SHOOTS BY GIVING RISE

TO THE PRIMARY PLANT BODY APICAL MERISTEMS PRODUCE CELLS THAT

CONTINUE TO DIVIDE AS MERISTEMATIC CELLS OF THE PROTODERM, PROCAMBIUM, AND GROUND MERISTEM.

THESE PRIMARY MERISTEMS GIVE RISE TO THE DERMAL, VASCULAR, GROUND TISSUES OF THE PRIMARY PLANT BODY.

IN ROOTS, THE APICAL IS LOCATED NEAR THE TIP, WHERE IT REGENERATES THE ROOT CAP AS PRODUCING THE PRIMARY MERISTEMS.

THE APICAL MERISTEM OF SHOOT IS LOCATED IN THE TERMINAL BUD, WHERE IT GIVES RISE, MODULE BY MODULE, TO A REPETITION OF INTERNODES AND LEAF-BEARING NODES.

MODULAR CONSTRUCTION OF A SHOOT

C. SECONDARY GROWTH: LATERAL MERISTEMS ADD GIRTH BY PRODUCING SECONDARY VASCULAR TISSUE

AND PERIDERM

THE VASCULAR CAMBIUM DEVELOPS FROM PARENCHYMA CELLS INTO A MERISTEMATIC CYLINDER THAT PRODUCES SECONDARY XYLEM AND SECONDARY PHLOEM.

THE CORK CAMBIUM GIVES RISE TO THE SECONDARY PLANT BODY'S PROTECTIVE COVERING, OR PERIDERM, WHICH CONSISTS OF THE CORK CAMBIUM PLUS THE LAYERS OF CORK CELLS IT PRODUCES.

SECONDARY GROWTH OF A STEM

BARK IS PERIDERM PLUS SECONDARY PHLOEM-ALL THE TISSUES EXTERNAL TO THE VASCULAR

CAMBIUM.

A SUMMARY OF PRIMARY AND SECONDARY GROWTH IN A WOODY STEM