Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: Th...

https://www.jstor.org/stable/pdfplus/2830650.pdf

The dilemma of plants: To grow or defend.

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

Article de synthese sur le role des polyamines durant les phases de croissance et de developpement: division cellulaire embryogenese, rhizogenese, floraison et croissance du tube pollinique. Etude des relations entre polyamines et regulateurs de croissance des plantes

Do polyamines have roles in plant development

Increasing interest in the stress physiology of higher plants has, in the last few years, greatly expanded our knowledge concerning the effects of stresses such as drought, freezing, nutrient deficiencies, disease and insect attack on plant metabolism. This work, however, has concentrated on the influences of stress on the basic processes of growth and development (primary metabolism). Very little attention has been paid to the changes in secondary metabolism that may be occurring. Information on the effects of stress conditions on secondary metabolites has come mainly from research efforts to maximize the yield of active constituents from herb, spice and drug plants and from attempts to reduce the levels of toxins in certain food and forage crops. Advances in our understanding of the functional roles of secondary metabolites in plants, however, and new information about how pest resistance is altered by stress should stimulate additional interest in the responses of secondary metabolites to stress.

Changes in the Levels of Plant Secondary Metabolites Under Water and Nutrient Stress

Vascular plants, which are adapted for life on land, first appeared in the late Silurian period, some 400 million years ago. Since then they have evolved to fill a diverse range of habitats all over the earth. The vascular systems of land plants are composed of specialized conducting tissues, the xylem and the phloem, which provide both a pathway for water and nutrient transport and mechanical support for slender plants. The vascular system is also an important conduit for signal-transducing molecules. Tracheary elements (TEs), which are the distinctive cells of the xylem, are characterized by the formation of a secondary cell wall with annular, spiral, reticulate, or pitted wall thickenings. In the primary xylem, TEs differentiate from procambial cells, whereas in the secondary xylem, they arise from cells produced by the vascular cambium. As they mature, TEs lose their nuclei and cell contents, leaving hollow dead cells that form vessels or tracheids. The final stage of TE differentiation represents a typical example of programmed cell death in higher plants (see Pennell and Lamb, 1997, in this issue). TEs can also be induced to form in vitro from various types of cells, including cells of the phloem parenchyma and the cortex in roots, the pith parenchyma in shoots, the tuber parenchyma, and the mesophyll and epidermis in leaves (Roberts et al., 1988; Fukuda, 1992). In Zinnia elegans cell cultures, single mesophyll cells transdifferentiate directly into TEs without cell division in response to phytohormones (Fukuda and Komamine, 1980). The Zinnia system has proven to be particularly useful for studies of the sequence of events during TE differentiation. This is largely because differentiation occurs at a high frequency in Zinnia cultures and because the process can be followed in single cells (Chasan, 1994; Fukuda, 1994, 1996). Recently, I presented a general overview of xylogenesis (Fukuda, 1996). In this article, I focus on efforts to elucidate the molecular mechanisms underlying the in vitro differentiation of parenchyma cells into TEs.

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Tracheary Element Differentiation

The Regulation of Synthesis of Phenolics in Stationary Phase Cell Cultures of Acer pseudoplatanus L.

Polyamines in Relation to Cell Division and Xylogenesis in Cultured Explants of Helianthus tuberosus: Lack of Evidence for Growth-Regulatory Action

Characteristics of the Inhibition of Induced Tracheary Element Differentiation by 3-Aminobenzamide and Related Compounds

Phillips, R., Press, M. C., Bingham, L. and Grimmer, C. 1988. Polyamines in cultured artichoke expiants: effects are primarily on xylogenesis rather than cell division.—J. exp. Bot. 39: 473-480. The relationship between cell division and xylogenesis and polyamine metabolism was investigated in short-term cultures of Helianthus tuberosus tuber expiants via studies on inhibitors of polyamine biosynthesis, exogenous supply of spermidine and comparisons between proliferating and non proliferating treatments. Difluoromethylarginine (DFMA) and difluoromethylornithine (DFMO) did not substantially affect cell division rates but were inhibitory to xylem differentiation, especially higher concentrations of DFMO, which also stimulated endogenous spermidine accumulation. Exogenously supplied spermidine inhibited xylogenesis much more than cell division at concentra tions of 10 mol m~3 and above after 3 d culture. A possible inverse correlation between spermidine accumulation and cytodifferentiation is discussed. No significant differences in polyamines were found between proliferating cultures and those in which DNA replication and mitosis were blocked by gamma-irradiation, except for the late appearance of putrescine in irradiated cultures, possibly asa senescence response. Key words—Polyamines, DFMA, DFMO, Helianthus tuberosas, cultured expiants, cell division, xylem differentiation. Correspondence to: Department of Botany and Microbiology, University College London, Gower Street, London WC1E 6BT, U.K.

R. Phillips

Papers

The Regulation of Synthesis of Phenolics in Stationary Phase Cell Cultures of Acer pseudoplatanus L.

Polyamines in Relation to Cell Division and Xylogenesis in Cultured Explants of Helianthus tuberosus: Lack of Evidence for Growth-Regulatory Action

Characteristics of the Inhibition of Induced Tracheary Element Differentiation by 3-Aminobenzamide and Related Compounds

Polyamines in Cultured Artichoke Explants: Effects are Primarily on Xylogenesis Rather than Cell Division