Secondary Compounds as Protective Agents

INTRODUCTION ........ ...... ...... ....... ... ....... ......... 479 THE NATURE OF SECONDARY COMPOUNDS .. ... ..... 480 Introduction 480 Distribution of Secondary Compounds in Space and Time 481 Function of Secondary Compounds 483 Secondary Compounds as Waste Products 483 Secondary Compounds as Protective Agents 484 SECONDARY COMPOUNDS AND PLANT DISEASES .... ..... ... .. ........ .. 485 Introduction 485 Defenses on the Surface of Plants 485 Defensive Function of the Cell Wall ........ ...... ...... ........ 486 Che1ical Defenses within the Cell .... ...... ...... ........ ........ 486 The Role of Tannins 487 The Role of Phytoalexins 488 SECONDARY COMPOUNDS AND ALLELOPATHY ......... ... ..... ....... ..... ..... ......... 489 Introduction 489 The Complexity of Allelopathy 489 Allelopathic Activity of Secondary Compounds 490 Nonprotein Amino Acids and Allelopathy 490 SECONDARY COMPOUNDS AS INSECT DETERRENTS .. ... .. ... ....... 490 Introduction 490 Insect Chemoreceptors 491 Insect-deterrent Properties of Secondary Compounds 492