Allelochemicals Biologica... - Name

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ANA LUISA ANAYA
cytoplasmic proteins were affected by the different aqueous leachates. Crop plant
responses were diverse, but in general, an increase in protein synthesis was observed
in the treated-roots. Maize was the least affected, but both the radicle growth and also
the protein pattern of tomato were severely inhibited by all allelopathic plants. The
changes observed on protein expression may indicate a biochemical alteration at the
cellular level of the tested crop plants.
Roshchina (2001) discussed the molecular-cellular basis of pollen allelopathy,
related to possible chemosensory mechanisms. The phenomenon consists of a series
of events, viz., a) excretion of signalling and regulatory substances from donor cell
(pollens, pistil stigma); b) recognition of specific signal-stimulus from plant excretions
by acceptor cell (pollen or pistil stigma); c) transmission of chemical information
within the acceptor cell (pollen); and d) development of characteristic response in
acceptor cell. The processes occur in growth, development and normal fertilization.
In the first stage of interactions, allelochemicals are excreted, which act as chemical
signals, growth regulators and modulators of cellular metabolism, etc. The
allelochemicals, acting on fertilization may be, nitrogen-containing substances
(acetylcholine, histamine, serotonin, dopamine, noradrenaline), phenols [(flavonoids:
quercetin, kaempferol, rutin), aromatic acids (benzoic, gallic, vanillic)], terpenoids
(monoterpenes: citral, linalool, cymol), sesquiterpene lactones: azulene and proazulenes
(desacetylinulicine, inulicine, ledol, artemisinine, grosshemine, gaillardine and
austricine), and polyacetylenes (capilline) found in flower excretions. These compounds
were tested in vitro and in vivo on pollen germination of Hippeastrum hybridum.
Nitrogenous compounds stimulate the growth of pollen tube, whereas, their antagonists
blocked normal fertilization and thus fruits or seeds did not form. Terpenoids act on
pollen germination and their stimulatory and inhibitory effects (block fruit formation)
depend on their concentration. These effects of terpenoids on pollen germination are
through chemosignalling and possible steps are: a) spreading of information in pollen
secretions e.g. in olfactory slime; b) binding with special sensors or receptors in
plasmalemma; and c) transfer of stimulus within the pollen cell to nucleus, where
spermia appear and a pollen tube starts to grow. Moving from donor cell,
allelochemicals penetrate the wall of acceptor cell either a) directly (without any
changes in protoplasmic membrane); or b) after conversions [interaction with foreign
substance of low or high-molecular weight (enzymes and protectory proteins) secreted
from donor cells. or compounds of acceptor cell]. Often the second case includes free
radical processes. The transmission of information within cell is third stage which
includes participation of secondary messengers (cyclic AMP and GMP, inositol
triphosphate, Ca ions) and some related enzymatic systems. The final transmission
occurs in membranes of cellular organelles, which respond to information received
through changes in enzymatic activity and metabolism. At cellular level, in pollen
and pistil it may be active excretion, changes in the autofluorescence and membrane
permeability, regulation of alternative pathways in respiration and photosynthesis
and switching on free radical processes.
The phenyl propanoid pathway (PPP) can be stimulated as demonstrated by
Randhir et al. (2004) in mung bean sprouts through the pentose phosphate and