Cyanogenic glycosides can be isolated by general procedures used for other glycosides with previous de-activation of the glycosidases present in the plant tissue (Kofod and Eyjolfsson, 1969; Maher and Hughes, 1971).
Removal of cyanogenic glycosides of flaxseed meal: Extract the meal (100 g) with 80% ethanol (1:10, w/v) at 7°C for 1 hour. Dry the ethanol extract and dissolve the residue in 10 ml of methanol followed by the addition of 20 mL chloroform; recover the precipitates by centrifugation. Evaporate the supernatant to dryness using a rotary evaporator. Redissolve the dried residue in 4 mL of 15% (v/v) HPLC grade methanol in water. Filter the solution through a 0.45 ^m nylon filter before continuing with the isolation (Wanasundara et al., 1993).
Sample extraction and processing for analysis of alkaloids is described in Chapter 7, Experiments 1 to 6.
2.5 Cytokinins, Purines and Pyrimidines
Plant purines and pyrimidines can be considered in four groups according to structural and functional characteristics.
(i) Group I: These are purines and pyrimidines that are common to all living organisms and are the basis of nucleic acids (DNA and RNA), certain nucleotides as adenosine triphosphate (ATP) and uridine diphosphate glucose that play important functions in the plant metabolism. These subjects are out of the scope of this book and can be referred to in biochemistry books.
(ii) Group II: These are bases closely related to the nucleic acid bases in structure and characteristics that show unusual structure and are present in plants.
(iii) Group III: These contain methylated purines (theobromine and caffeine are most common).
(iv) Group IV: These are substituted purines in C6-position, known as cytokinins.
Cytokinins are a class of plant hormones, which in cooperation with auxin, play a unique role in the control of developmental processes in plants such as cell division and differentiation, formation and growth of roots and shoots, apical dominance and senescence. Natural cytokinins are 6-N-substituted purine derivatives. Those which occur in plants as free bases are supposed to be the biologically active compounds. Glycosidic conjugates of cytokinins are transport, storage or inactivated forms of cytokinins; while cytokinin riboside phosphates mainly represent the primary products of cytokinin biosynthesis. More than 40 natural cytokinins are present in plant tissues.
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