226 research outputs found
Acetylcholine in plants: presence, metabolism and mechanism of action
Acetylcholine (ACh) has been detected in representatives of many taxonomic groups
throughout the plant kingdom. The site of its synthesis in plants is probably young
leaves. In some plant species choline acetyltransferase (CHAT) activity has been
found. This enzyme showing properties similar to animal CHAT, probably participates
in ACh synthesis from its precursors, choline and acetyl-Coenzyme A. Acetylcholinesterase
(ACHE) activity has also been found in many plant tissues. This
enzyme decomposes ACh and exhibits properties similar to animal ACHE. The
presence of both ChAT and AChE in plant tissues suggests that ACh undergoes
similar metabolism in plants as it does in animals. Exogenous ACh affects phytochrome-
controlled plant growth and development. Mimicking red light (R), ACh
stimulates adhesion of root tips to a glass surface and influences leaf movement and
membrane permeability to ions. It also affects seed germination and plant growth.
Moreover, ACh can modify some enzyme activity and the course of some metabolic
processes in plants. Acetylcholine in the presence of calcium ions (Ca:+), like R
stimulates swelling of protoplast isolated from etiolated wheat leaves. It is proposed
that the primary mechanism of action of ACh in plant cells is via the regulation of
membrane permeability to protons (H+), potassium ions (K+), sodium ions (Na +)
and Ca :+ .Acetylcholin (ACh) wurde in Vertretern vieler taxonomischer Gruppen des Pflanzreiches
gefunden. Es wird wahrscheinlich inden jungen Bltittern synthetisiert. In
einigen Pflanzen hat man daneben Cholin-Acetyltransferase (ChAT)-Activit~t nachweisen
k6nnen; dieses Enzym ziegt tihnliche Eigenschaften wie tierische ChAT und
ist offenbar an der ACh-Synthese aus sienen Vorstufen Cholin und Acetyl-Coenzym
A beteiligt. Acetylcholineesterase (AChE)-Activit~t wurde ebenfalls in vielen Pflanzengeweben
gefunden; dieses Enzym spaltet ACh und ziegt ~ihnliche Eigenschaften
wie tierische ACHE. Die Anwesenheit yon ChAT und AChE in pflanzlichem Gewebe
ltil3t vermuten, dal3 ACh in Pflanzen einem ~ihnlichen Metabolismus unterliegt wie
im tierischen System.
~,hnlich wie Rotlicht stimuliert ACh die Anheftung von Wurzelspitzen an Glasoberfltichen
und beeinflul3t Blattbewegung und Membranpermeabilit~t far Ionen;
dariiber hinaus beeinflul3t es Samenkeimung und pflanzliches Wachstum. Des weiteren
kann ACh Enzym-Aktivit~ten modifizieren und dadurch den Ablauf einiher
metabolischer Prozesse in Pflanzen. SchlieBlich stimuliert ACh in Gegenwart von
Calcium-Ionen (Ca2§ ~ahnlich wie Rotlicht, das Schwellen von Protoplasten etiolierter
Weizenbl~itter. Es wird vermutet, dal3 die Primiirwirkung von ACh in Pflanzenzellen
durch Regulation der Membranpermeabilit~it far Protonen (H§ Kaliumionen
(K§ Natriumionen (Na § und Ca 2§ erfolgt
Cytochemical and histochemical characterization of cotyledonary bodies from Pharbitis nil seedlings
Cytological
and
histochemical
characterization
of
the
structures
from
which
an
obscure
substance
is
secreted
via
open
stomata
to
the
abaxial
surface
of
Japanese
morning
glory
(Pharbitis
nil
Choisy
cv.
Violet)
cotyledons
has
been
carried
out.
Observation
of
intact
cotyledons
using
the
light
microscope
revealed
randomly
distributed
semi-transparent
structures.
These
structures,
which
were
shown
to
be
the
same
as
those
previously
described
as
giant
oil
cells
are
referred
to
here
as
cotyledonary
bodies.
These
bodies
can
be
eas-
ily
isolated
and
purified
after
enzymatic
digestion
of
the
cotyledons.
Using
different
staining
procedures
we
have
confirmed
that
each
cotyledonary
body
originates
from
an
individual
mesophyll
cell
dur-
ing
embryo
development.
Purified
bodies
consist
of
(i)
a
thick
shell-
like
envelope;
(ii)
a
transparent,
hydrophilic
zone;
(iii)
a
hydropho-
bic
core.
Hydrophobic
contents
of
the
bodies
were
readily
extracted
with
methanol
and
shown
to
contain
fatty
acids
and
phenolic
com-
pounds
using
the
gas
chromatography/mass
spectrometry
(GC/MS)
technique.
Methanolic
extracts
of
cotyledonary
bodies
showed
high
fluorescence
with
two
excitation
and
emission
maxima.
Using
a
flu-
orescence
microscope
we
have
shown
that
the
bodies
isolated
from
seedlings
grown
in
continuous
light,
conditions
non-inductive
for
flowering,
and
those
grown
under
conditions
inductive
for
flowering
(a
single
16
h,
long
dark
period)
have
different
fluorescence
emis-
sion
spectra.
Different
levels
of
free
Ca
2+
inside
cotyledonary
bodies
isolated
from
light-grown
and
single
dark-period
treated
P.
nil
seed-
lings
were
found
using
the
fluorescent
calcium
indicator
dye
Fluo-3
under
a
confocal
scanning
laser
microscope.
On
the
basis
of
these
observations
we
speculate
that
cotyledonary
bodies
could
be
in-
volved
in
floral
induction
The Mechanism of Calcium Action on Flower Induction in Pharbitis nil
Calcium ions, calcium ionophores A23187 and ionomycin, as well as caffeine, stimulated the flowering of Pharbitis nil when applied just before and 2 h after starting a subinductive, 14-h long dark period. Effectiveness of all the mentioned compounds decreased over successive hours and when used from 6 h after the onset of the dark period they had no effect or inhibited flowering. Intracellular calcium modulators, ryanodine and thapsigargicin, which are active in animal cells had no effect on flowering. These results suggest that an increase in free Ca2 + before and during the first 2 h of the dark period increases the flowering responses, whereas after the 6th hour it decreases it. We postulate that the targets for calcium action are stomata, which are open before the dark period and remain closed during the first 4 - 5 h of the dark period. The significance of stomata in flower induction was confirmed in experiments with abscisic acid (ABA), a plant hormone which regulates stomatal movements. Treating the cotyledons of plants with ABA at the 8th and 10th hour of the dark period, resulted in plants with about 50 % less flower buds than the control, however, this phytohormone had no effect on flowering when used before the subinductive dark period
Transplantation in children
Kidney transplantation in very young children, less than 2 years of age, has usually failed, mainly because of difficulties maintaining these patients on hemodialysis long enough to permit retransplantation after loss of the original graft. Liver replacement in the very young child has been associated with a higher frequency of vascular and biliary obstruction than in the older child, due to the small size of these structures. Such accidents have contributed to unsatisfactory results with biliary atresia. Transplantation of kidney or liver into older children has been more successful than transplantation of these organs into adults. Related or cadaveric kidney transplantation in the child has been followed by at least a 60 per cent patient survival for 6 to 13 years and a very acceptable quality of life. Liver replacement for diseases other than biliary atresia has been followed by a 56 per cent 1 year survival rate, and two children have survived for more than 5 years
Core handling and processing for the WAIS Divide ice-core project
On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed
Core handling and processing for the WAIS Divide ice-core project
On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed
Photomorphogenic mutants of tomato
Photomorphogenesis of tomato is being studied with the aid of mutants which are either modified in their photore-
ceptor composition or in their signal transduction chain(s)
. Several mutants affecting the phytochrome family of
photoreceptors, some of which appear deficient for specific genes encoding phytochrome apoproteins have been
isolated
. In addition, other mutants, including transgenic lines overexpressing phytochrome A, exhibit exaggerated
photomorphogenesis during de-etiolation
. Anthocyanin biosynthesis and plastid development are being used
as
model systems for the dissection of the complex interactions among photomorphogenic photoreceptors and to
elucidate the nature of their transduction chains
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