The nitrogen content of a plant is only one of the many plant characteristics that are vitally important to herbivores. However, because of its central role in all metabolic processes as well as in cellular structure and genetic coding, nitrogen is a critical element in the growth of all organisms. Supplementary N often elicits enhanced health, growth, reproduction, and survival in many organisms. This suggests that N is a limiting factor. Since N makes up a large portion of the earth's atmosphere (about 78%), the problem is not an absolute but a relative shortage-that is, a scarcity of usable or metaboliza­ ble N during critical growth periods (159, 328). Plants encounter shortages of inorganic nitrogen (nitrate and/or ammonium ions); animals experience shortages of organic nitrogen (specific proteins and/or amino acids). This article reviews and examines the evidence (a) that N is scarce and perhaps a limiting nutrient for many herbivores, and (b) that in response to this selection pressure, many herbivores have evolved specific behavioral, morphological, physiological, and other adaptations to cope with and uti­ lize the ambient N levels of their normal haunts. McNeill & Southwood (201) and White (328) have also reviewed these general questions. There­ fore, this review explores additional evidence and further develops the fundamental arguments. The review is organized into three major divisions. The first focuses on important sources of variation in plant N (seasonal and ontogenetic trends, different tissues and species, etc) because such variation may be the basis

Herbivory in relation to plant nitrogen content

INTRODUCTION. Internal Organization of the Plant Body. Summary of Types of Cells and Tissues. General References. DEVELOPMENT OF THE SEED PLANT. The Embryo. From embryo to the Adult Plant. Apical Meristems and Their Derivatives. Differentiation, Specialization, and Morphogenesis. References. THE CELL. Cytoplasm. Nucleus. Plastids. Mitochondria. Microbodies. Vacuoles. Paramural Bodies. Ribosomes. Dictyosomes. Endoplasmic Reticulum. Lipid Globules. Microtubules. Ergastic Substances. References. CELL WALL. Macromolecular Components and Their Organization in the Wall. Cell Wall Layers. Intercellular Spaces. Pits, Primary Pit--Fields, and Plasmodesmata. Origin of Cell Wall During Cell Division. Growth of Cell Wall. References. PARENCHYMA AND COLLENCHYMA. Parenchyma. Collenchyma. References. SCLERENCHYMA. Sclereids. Fibers. Development of Sclereids and Fibers. References. EPIDERMIS. Composition. Developmental Aspects. Cell Wall. Stomata. Trichomes. References. XYLEM: GENERAL STRUCTURE AND CELL TYPES. Gross Structure of Secondary Xylem. Cell Types in the Secondary Xylem. Primary Xylem. Differentiation of Tracheary Elements. References. XYLEM: VARIATION IN WOOD STRUCTURE. Conifer Wood. Dicotyledon Wood. Some Factors in Development of Secondary Xylem. Identification of Wood. References. VASCULAR CAMBIUM. Organization of Cambium. Developmental Changes in the Initial Layer. Patterns and Causal Relations in Cambial Activity. References. PHLOEM. Cell Types. Primary Phloem. Secondary Phloem. References. PERIDERM. Structure of Periderm and Related Tissues. Development of Periderm. Outer Aspect of Bark in Relation to Structure. Lenticels. References. SECRETORY STRUCTURES. External Secretory Structures. Internal Secretory Structures. References. THE ROOT: PRIMARY STATE OF GROWTH. Types of Roots. Primary Structure. Development. References. THE ROOT: SECONDARY STATE OF GROWTH AND ADVENTITIOUS ROOTS. Common Types of Secondary Growth. Variations in Secondary Growths. Physiologic Aspects of Secondary Growth in Roots. Adventitious Roots. References. THE STEM: PRIMARY STATE OF GROWTH. External Morphology. Primary Structure. Development. References. THE STEM: SECONDARY GROWTH AND STRUCTURAL TYPES. Secondary Growth. Types of Stems. References. THE LEAF: BASIC STRUCTURE AND DEVELOPMENT. Morphology. Histology of Angiosperm Leaf. Development. Abscission. References. THE LEAF: VARIATIONS IN STRUCTURE. Leaf Structure and Environment. Dicotyledon Leaves. Monocotyledon Leaves. Gymnosperm Leaves. References. THE FLOWER: STRUCTURE AND DEVELOPMENT. Concept. Structure. Development. References. THE FLOWER: REPRODUCTIVE CYCLE. Microsporogenesis. Pollen. Male Gametophyte. Megasporogenesis. Female Gametophyte. Fertilization. References. THE FRUIT. Concept and Classification. The Fruit Wall. Fruit Types. Fruit Growths. Fruit Abscission. References. THE SEED. Concept and Morphology. Seed Development. Seed Coat. Nutrient Storage Tissues. References. EMBRYO AND SEEDLING. Mature Embryo. Development of Embryo. Classification of Embryos. Seedling. References. Glossary. Index.

Anatomy of Seed Plants

Much research has been conducted in an attempt to fit the so-called plant secondary substances into the general framework of plant metabolism. Though some success has been achieved in this area, e.g., chlorogenic acid as a regulator of plant metabolic systems under stress21, most such studies have met with a conspicuous lack of success. Possible metabolic roles for the plant alkaloids as intermediate metabolites have probably received the greatest such attention and it was concluded at an early stage44 that, since a definitive metabolic role could not be assigned to alkaloids, they best be considered as plant waste products. More recent workers in the field of alkaloid biochemistry have concurred with this evaluation44,83 and the “waste product hypothesis” has been expanded, principally by Muller (1969, 1970), to include plant secondary substances in general.

Toward a general theory of plant. antiherbivore chemistry

Production of the phytohormone indole-3-acetic acid (IAA) is widespread among bacteria that inhabit the rhizosphere of plants. Several different IAA biosynthesis pathways are used by these bacteria, with a single bacterial strain sometimes containing more than one pathway. The level of expression of IAA depends on the biosynthesis pathway; the location of the genes involved, either on chromosomal or plasmid DNA, and their regulatory sequences; and the presence of enzymes that can convert active, free IAA into an inactive, conjugated form. The role of bacterial IAA in the stimulation of plant growth and phytopathogenesis is considered.

Bacterial biosynthesis of indole-3-acetic acid

Indole-3-acetic acid (IAA), the main auxin in higher plants, has profound effects on plant growth and development. Both plants and some plant pathogens can produce IAA to modulate plant growth. Although the genes and biochemical reactions for auxin biosynthesis in some plant pathogens are well understood, elucidation of the mechanisms by which plants produce auxin has proven to be difficult. So far, no single complete pathway of de novo auxin biosynthesis in plants has been firmly established. However, recent studies have led to the discoveries of several genes in tryptophan-dependent auxin biosynthesis pathways. Recent findings have also determined that local auxin biosynthesis plays essential roles in many developmental processes including gametogenesis, embryogenesis, seedling growth, vascular patterning, and flower development. In this review, I summarize the recent advances in dissecting auxin biosynthetic pathways and how the understanding of auxin biosynthesis provides a crucial angle for analyzing the mechanisms of plant development.

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Auxin Biosynthesis and Its Role in Plant Development

The regulation of cell-division activity in the vascular cambium and of secondary xylem and phloem development is reviewed for temperate-zone tree species in relation to auxins, gibberellins, abscisic acid, cytokinins, and ethylene. Representatives of the first four of these PGR classes (IAA, GA1, GA4, GA7, GA9, GA20, ABA, Z, ZR, DCA) have been identified conclusively by mass spectrometry in the cambial region in some Pinaceae, but not in any hardwood species. Endogenous ethylene has yet to be definitively characterized in this region in any species. Evidence concerning the source and metabolism of cambial PGRs is scanty and inconclusive for both conifers and hardwoods.

The role of plant growth regulators in forest tree cambial growth

Transgenic tobacco (Nicotiana tabacum) SR1 plants expressing the Agrobacterium tumefaciens nopaline transferred DNA iaaH gene were transformed with a 35S-iaaM construct The transformants displayed several morphological aberrations, such as adventitious root formation on stem and leaves, dwarfism, epinastic leaf growth, increased apical dominance, and an overall retardation in development In addition, xylem lignification was higher than in wild type Free and conjugated indoleacetic acid (IAA) levels were quantified by gas chromatography-multiple ion monitoring-mass spectrometry in leaves and internodes of wild-type plants and two transformed lines with different phenotypes Both transformed lines contained elevated levels of free and conjugated IAA, which was associated with increased transcription of the iaaM gene The line with the highest IAA level also had the most altered pattern of growth and development These IAA-overproducing plants will provide a model system for studies on IAA metabolism, IAA interactions with other phytohormones, and IAA roles in regulating plant growth and development

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Transgenic Tobacco Plants Coexpressing the Agrobacterium tumefaciens iaaM and iaaH Genes Display Altered Growth and Indoleacetic Acid Metabolism.

. . -. activity. In bud-bearing cuttings, cambial activity was associated with bud activity. Debudding decreased cambial growth. Application of a mixture of indole-3-acetic acid (IAA) and lanolin to the apex of debudded cuttings promoted cambial activity in a manner similar to that effected by expanding buds. Clearly, bud-produced auxin is required for cambial activity in balsam fir. Cambial activit increased with increasing preexposure to natural chilling until about December; therea&er additional preexposure did not further increase cambial growth. Extending the natural chilling period with a period of artificial chilling enhanced cambial growth in material collected during the autumn, but not in material collected later. The effect of chilling was manifested whether or not buds were present during the chilling period. Long photoperiod partly compensated for lack of chilling in autumn-collected material. It is concluded that the cambium of balsam fir in central New Brunswick has an autumnal rest period that grades into quiescence by about December. Cambial rest was not broken by applications of IAA, gibberellic acid, or kinetin, or by IAA with either of the others. LITTLE, C. H. A., et J. M. BONGA. 1974. Rest in the cambium of Abies balsatnsn. Can. J. Bot. 52: 1723-1730.

Rest in the cambium of Abies balsamea

The combined gas chromatography – mass spectrometry (GCMS) technique of single-ion current monitoring was used to measure indol-3-ylacetic acid (IAA) and abscisic acid (ABA) levels in diffusible, acidic, and conjugated fractions obtained from the cambial region of Sitka spruce (1) during the annual cycle of cambial activity and dormancy in trees reared under natural and controlled environmental conditions, and (2) after debudding, girdling, defoliating, applying exogenous IAA, droughting, or changing the photoperiod. Seasonal changes occurred in the level of IAA and ABA in each fraction, but not obviously and consistently in conjunction with specific changes in cambial activity and dormancy. Debudding and girdling halted tracheid production, decreased the radial enlargement of the last-formed tracheids, and abruptly reduced the content of IAA and ABA in the diffusible and acidic fractions without affecting the ABA level in the conjugated fraction. Applying exogenous IAA to debudded shoots maintained trach...

Control of cambial activity and dormancy in Picea sitchensis by indol-3-ylacetic and abscisic acids

WAREING et al.1–5 established that the naturally occurring plant growth inhibitor, abscisic acid6, is involved in the control of bud dormancy in the diffuse-porous deciduous tree species Acer pseudoplatanus L., Betula alba L. and Salix viminalis L. Exogenous abscisic acid delays bud-break in non-dormant cuttings and causes cessation of longitudinal growth and formation of resting buds in actively growing seedlings. Our results indicate that abscisic acid also delays budbreak in coniferous and ring porous deciduous species, and simultaneously inhibits transpiration.

C. H. A. Little

Papers

The role of plant growth regulators in forest tree cambial growth

Transgenic Tobacco Plants Coexpressing the Agrobacterium tumefaciens iaaM and iaaH Genes Display Altered Growth and Indoleacetic Acid Metabolism.

Rest in the cambium of Abies balsamea

Control of cambial activity and dormancy in Picea sitchensis by indol-3-ylacetic and abscisic acids

Effect of Abscisic Acid on Budbreak and Transpiration in Woody Species