A case study Alkaloids and population changes 41 Introduction

There is no question that plants are very important for animals and humans with respect to photosynthesis733. This importance also applies to the Legume plant family. It is the third largest family of flowering plants, containing three sub-families, more than 650 genera with 18 000 species, including trees, shrubs, herbs, climbers and crops734 735. The legume species are well recognized for their good adaptation systems and their growth in various climates and environments around the world, ranging from the humid tropics to sub-arctic zones736'737'738. This means that legume species have a large degree of plasticity and ecological breadth, due to the fact that the ecological distribution of these species is influenced by individual patterns of response to environments for traits that contribute to fitness739. Moreover, legumes also have the genetic ability to produce secondary compounds7 741. This genetic trait carries an ecological significance740. Many types of secondary compounds in this large family have been found and described741. Quinolizidine alkaloids (QAs) are one group of secondary compounds that can be found in legume plants7'742'743'744'745. The QAs are secondary metabolites synthesized from lysine and contain one or several nitrogen atoms as constituents of heterocycles749. Previous studies on QAs have shown by means of genetic experimentation (breeding by pollen crossing) that QAs have a genetic character. By means of hybridization, it is possible to noticeably decrease the alkaloid level746 747. It has also been shown that alkaloid-poor plants do not, over time, become bitter748. Moreover, QAs are biologically active compounds and are known as anti-nutritive factors for animals, but on the other hand, as protective factors for plants and their metabolisms736. As QAs have a hereditary nature controlled by genes expressed through HMT/HLTase and ECTase, they are evolutionary traits of plants and species.

Alkaloid distribution in plants has to interact with the plants' habitats and herbivores. This is a factor for both population and ecosystem stability, and the adaptation of plants to their habitats736 748. In Nordic ecosystems, the adaptation of plants to the cold and to short growing seasons is characteristic for legumes. In sub-arctic and arctic ecosystems, the adaptation of plants to the cold is a typical survival process. Therefore, the adaptation to very stressed and altered life factors in legume habitats is considered to be a micro-evolutionary process in the long-term evolution of plants. Many studies have described plant adaptation to the environment689'739'750'751'752'753'754. However, little is known about the variations in genetic traits by plants in wild or semi-wild populations to produce alkaloids, especially in legumes. Our knowledge in this field is important because these plants enrich the diversity of natural ecosystems and agro-ecosystems around the world, including sub-arctic ecosystems. They also represent an important protein source in the wild and for human and animal nutrition. In this case study, the frequencies of QAs and their distribution in wild and semi-wild Fabaceae populations for 5-years were tabulated during a 5-year period, using valid techniques. A total of 4000 legume plants growing wild in Finland were analysed and found to exhibit certain trends. As there has been no previous study in this exciting subject, therefore, my analysis gives special attention to establishing a formula for possible micro-evolution coefficients for the Fabaceae species. The interpretation of these coefficients is an important part of this work. The micro-evolution is a trend of process in the self-regulation of plant populations. This part of this book documents how alkaloid frequencies differ among wild-growing, Nordic legumes and how QAs are distributed in relation to evolutionary trends in these legume populations.

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