Spice and medicinal plants grown under water deficiency conditions reveal much higher concentrations of relevant natural products compared with identical plants of the same species cultivated with an ample water supply. For the first time, experimental data related to this well-known phenomenon have been collected and a putative mechanistic concept considering general plant physiological and biochemical aspects is presented. Water shortage induces drought stress-related metabolic responses and, due to stomatal closure, the uptake of CO2 decreases significantly. As a result, the consumption of reduction equivalents (NADPH + H(+)) for CO2 fixation via the Calvin cycle declines considerably, generating a large oxidative stress and an oversupply of reduction equivalents. As a consequence, metabolic processes are shifted towards biosynthetic activities that consume reduction equivalents. Accordingly, the synthesis of reduced compounds, such as isoprenoids, phenols or alkaloids, is enhanced.
In the seeds of Hevea brasiliensis, the cyanogenic monoglucoside linamarin (2-b3-D-glucopyranosyloxy-2-methylpropionitrile) is accumulated in the endosperm. After onset of germination, the cyanogenic diglucoside linustatin (2-[6-f8-D-glucosyl-,f-D-glucopyranosyloxyJ-2-methylpropio- In addition, a linustatin-splitting diglucosidase in Hevea is described. From its activity in different developmental stages and in different tissues it is suggested that this enzyme is involved in the metabolism of cyanogenic glycosides. It is deduced that linustatin is a metabolite in the pathway by which linamarin is metabolized and utilized.
MATERIALS AND METHODSSeed Drainage. The seed drainage technique is described elsewhere (17). Additionally, some of these seed drainage experiments were run in a gastight system in which a stream of moistened air was used to exchange the atmosphere in the experimental system continuously. By bubbling this air through 5 ml of 1 M NaOH any HCN liberated from the seedling during the experiment was trapped for quantitative determinations.HCN Determination. The HCN was estimated with the Merck
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