Allelochemicals Biologica... - Name

ALLEOPATHIC ORGANISMS AND
MOLECULES
membrane disruption in root tips and plasmolized cells in the peripheral zone of
beans and bottle gourd roots treated with the aqueous leachate of S. deppei suggesting
that the allelopathics of this plant alter some membrane processes.
4-phenyl coumarins isolated from Exostema caribaeum and Hintonia latiflora
(Rubiaceae) and some semisynthetic derivatives acted as uncouplers in spinach
chloroplasts. The glycoside 5-Ο-β-D-glucopyranosyl-7-methoxy-3’,4’-dihidroxy-4phenylcoumarin,
5,7,3’,4’-tetrahydroxy-4-phenyl-coumarin, and 7-methoxy-5,3’,4’trihydroxy-4-phenylcoumarin
inhibited ATP synthesis and proton uptake. On the other
hand, basal and phosphorylating electron transport were enhanced by these compounds.
The light-activated Mg 2+ -ATPase was slighted stimulated by the last two coumarins.
In addition, at alkaline pH compound 5,7,3’,4’-tetrahydroxy-4-phenyl-coumarin
stimulated the basal electron flow from water to methylviologen, but at the pH range
from 6 to 7.5 the coumarin did not have any enhancing effect. This last compound,
which possesses four free phenolic hydroxyl groups, was the most active uncoupler
agent. Probably, the phenolate anions may be the active form responsible for the
uncoupling behavior of 4-phenylcoumarins (Calera et al., 1996).
Low molecular weight phenolic compounds were identified in two soils with
different vegetative cover, Fagus sylvatica and Pinus laricio, and were tested at different
concentrations on seed germination of Pinus laricio, and on respiratory and oxidative
pentose phosphate pathway enzymes involved in the first steps of seed germination.
There are marked differences in the phenolic acid composition of the two investigated
soils. All the phenolic compounds bioassayed inhibited seed germination and those
extracted from Pinus laricio soil were particularly inhibitory. Inhibition of germination
of seeds is strongly correlated to the inhibition of the activities of enzymes of glycolysis
and the oxidative pentose phosphate pathway (Muscolo et al., 2001).
Seven-day-old seedlings of cucumber (Cucumis sativus cv. Wisconsin) were treated
with 0.1 mM solutions of cinnamic acid (ferulic and p-coumaric acids) and benzoic
acid (hydroxybenzoic and vanillic acids) derivatives as stressors. The content of free
and glucosylated soluble phenols and the activity of phenylalanine ammonia-lyase
(E.C.4.3.1.5), phenol-beta-glucosyltransferase (E.C.2.4.1.35.), and beta-glucosidase
(E.C.3.2.1.21.) in seedling roots as well as their length and fresh weight were examined.
Changes in glucosylated phenolic content and phenol-beta-glucosyltranspherase
activity were observed under the influence of all phenolics applied. Treatment with
ferulic and p-coumaric acids stimulated the increase of phenylalanine ammonia-lyase
and beta-glucosidase activity and slightly inhibited cucumber root growth (Politycka,
1998).
Environmental stresses (biotic and abiotic), including allelochemicals have been
shown to induce the synthesis of new proteins in plants. These proteins might have
evolutionary value for survival under adverse environmental situations. Romero-
Romero et al. (2002) tested the effect of the mixture of toxic allelochemicals from the
aqueous leachates from Sicyos deppei, Acacia sedillense, Sebastiania adenophora,
and Lantana camara on the radicle growth and cytoplasmic protein synthesis patterns
of Zea mays (maize), Phaseolus vulgaris (bean), Cucurbita pepo (squash), and
Lycopersicon esculentum (tomato). In general, high, medium and low molecular weight
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