Secrets of life

Alkaloids are structurally very similar to plant growth hormones. Waller and Nowacki16 have critically considered the possibility that alkaloids have a hormonal influence on plant growth. This old hypothesis is still open for discussion; examples in literature attempt to both prove and disprove it. The contradictory results derive from the diversity of alkaloids, not to mention plant diversity and that of other organisms producing alkaloids. There are alkaloid-rich and alkaloid-poor plants from the same species. One such plant is Washington lupine (Lupinus polyphyllus Lindl.), which is capable of growing under various climatic conditions in both the Northern and the Southern Hemispheres327 348. The freely growing genotypes of this plant contained 1.74-3.15 mg of alkaloids in 100 mg of seeds, whereas one hybrid contained only 0.0004 mg. The alkaloid content in leaves was about 1.6 mg in natural genotypes and 0.05 mg in hybrids. The content in shoots was 1.7 and 0.1 mg, respectively348. The Washington lupine is known also by many other common names such as Blomsterlupin (in Swedish), Dauerlupine (in German), De belle lupine (in French), Komea lupiini (in Finnish), Lubin wieloletni (in Polish) and Mnogoletnii liupin (in Russian). As a wild plant it is originally from North America, where its distribution extends from California to Alaska. This plant was brought to Europe in the 19th century and it distributed rapidly in numerous countries as a decoration and animal fodder in pastures and game animal farming327 348. As a perennial and cross-pollinated species, it has many different geno- and ecotypes with different alkaloid levels. It has been hypothesized that the role of alkaloids in alkaloid-rich and alkaloid-poor geno- and ecotypes differs because their amounts and structure vary. Diversity of alkaloid content in the same species and hybrids is one of the most interesting secrets of life. Chemical diversity generally constitutes an intrinsic property of biosynthesis, which is an inherent property. This diversity-oriented strategy is widespread in biosynthesis. Schwab349, when discussing the diversity of secondary compounds, concludes that the number of metabolites in one species often exceeds the number of genes involved in their biosynthesis, and that increasing compound diversity does not correlate with increasing gene number. It has also been suggested that multifunctional enzymes are ubiquitous in the plant kingdom349. In the case of alkaloids, the diversity in content among plants is connected to the genetic code. The proof of this is evident in hybridization, where it is possible to noticeably decrease the alkaloid level of the Washington lupine. This has been done over the period 1982-1990 in Finland348. The mechanism of determining the alkaloid-rich and alkaloid-poor plants is connected with enzymatic activity and production of alkaloid precursor. In the case of quino-lizidine alkaloids, an alkaloid is plant specific and their occurrence in individual plants is connected to the metabolism of lysine. In expanded vegetation, there is a surplus of lysine which leads to the production of quinolizidine alkaloids through the activity of HMT/HLTase and ECTase350. In individual plants without such alkaloids, the biosynthetic pathway of the alkaloids with HTM/HLTase is blocked351.

The difficulty of studying the effect of alkaloids as growth regulators is similar to the problem of alkaloid content variation in plants. Waller and Nowacki16 clearly took up this issue for methodological discussion. Level of alkaloid richness will affect further addition of alkaloids to a plant. However, environmental growth factors such as light, moisture, temperature, nutrition and the genetic factors such as genotype and photosynthesis capacity of a species influence alkaloid precursors and their derivation to alkaloids. The concentrations of these compounds in plants influence their activity as growth regulators. However, many questions arise in the light of this. Do alkaloid-rich plants grow better and faster then alkaloid-poor plants? What empirical evidence exists that alkaloids also have the effect of growth regulators? Waller and Nowacki16 mentioned that alkaloids are growth regulators. They mentioned differences in regulator activity and also pointed out exceptions. The answer to the first question nearly 30 years later is certainly not exactly the same. Research has advanced during this time as the development of techniques and equipment illustrates. According to my studies and observations carried out in experiments in Finland, the answer is just opposite to the one given by Waller and Nowacki16. The alkaloid-rich plants grow at a higher rate and higher canopy than alkaloid poor plants327 352. However, when ripening period is compared, alkaloid-rich plants ripen more slowly than alkaloid-poor plants. The growing conditions in the Boreal zone of Finland are generally very favourable for perennial lupines and especially for the Washington lupine. The populations of this species have been large and this species has had no factors reducing populations (e.g. herbivory or disease). Rapid growth and higher growth rate per day can be considered a result of regulator activity. Empirical studies support this. Lupinus angustifolius cult. Mirela (alkaloid-rich plant) grows more rapidly than alkaloid-poor species. In chamber experiments the mean photosynthetic uptake of L. angustifolius cult. Mirela (alkaloid-rich) was 12.71mgCO2dm-2h-1, and that of L. polyphyllus Lindl. (alkaloid-poor) was 10.04 mgCO2 dm-2 h-1 353.

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