Diversity and variability of plant secondary metabolism: a mechanistic view

Abstract

Based upon a brief historical view, the typical features of plant secondary metabolism and its role in chemical interactions between plants and their environment are discussed. Facts and arguments are presented favouring the hypothesis that secondary metabolism evolved under the selection pressure of a competitive environment. The high 'degree of chemical freedom' of secondary metabolism which, in contrast to primary metabolism, allows structural modifications with almost no restrictions, is stressed as mechanistic basis for the generation of chemical diversity. Biochemical and physiological properties of secondary metabolism are in accordance with such a view. It is suggested that the great chemical diversity and intraspecific variability of secondary metabolism is the result of processes of natural selection which act upon highly variable chemical structures. This view is exemplified by the pyrrolizidine alkaloids, a typical class of secondary compounds.

Plantas medicinais: fatores de influência no conteúdo de metabólitos secundários

“…Sabe-se também que tecidos mais novos geralmente possuem maior taxa biossintética de metabólitos 7 , tais como óleos essenciais 76,77 , lactonas sesquiterpênicas 9 , ácidos fenólicos 78 , alcalóides 73 , flavonóides e estilbenos 71 . De fato, nota-se freqüentemente uma correlação inversa entre alta atividade metabólica e produção de aleloquímicos, isto é, um decréscimo na produção de metabólitos secundários (notadamente derivados fenólicos) em períodos de crescimento tecidual rápido 6,79-82 .…”

“…Os carrascos gregos, por ex., coletavam suas amostras do veneno cicuta (Conium maculatum) pela manhã, quando os níveis de coniina são maiores 1,2 . Variações temporais e espaciais no conteúdo total, bem como as proporções relativas de metabólitos secundários em plantas ocorrem em diferentes níveis (sazonais e diárias; intraplanta, inter-e intraespecífica) e, apesar da existência de um controle genético, a expressão pode sofrer modificações resultantes da interação de processos bioquímicos, fisiológicos, ecológicos e evolutivos [3][4][5][6][7] . De fato, os metabólitos secundários representam uma interface química entre as plantas e o ambiente circundante, portanto, sua síntese é freqüentemente afetada por condições ambientais 8 .…”

Dietary mixing in three generalist herbivores: nutrient complementation or toxin dilution?

“…Although we do not know the stability of nutrients and allelochemicals in our leaf disk preparations, the standardised handling of our plant material assures that whatever changes might have taken place in the leaf disks were equally experienced by all our insect species. Recent evidence also suggests low turnover of stored allelochemicals, including pyrrolizidine alkaloids (Mihaliak et al 1991;Hartmann 1996).…”

Identification and Quantification of Cyclolinopeptides in Five Flaxseed Cultivars

“…Unlike primary metabolites (such as protein, carbohydrate, and lipid) that are indispensable, uniform, and conserved for plant growth and development, secondary metabolites (such as flavonoids, lignans, cyclolinopeptides) are often unique, diverse, and adaptive to their environment. 33 The variance in cyclolinopeptide concentration in different flaxseed cultivars has not been thoroughly studied, except for the study of 5 changes in oil during storage. 13 The levels of 5 in that study showed great variance from 0 to 53 mg/kg among flaxseed cultivars at the beginning of the study.…”