125 research outputs found
An extracellular transglutaminase is required for apple pollen tube growth
An extracellular form of the calcium-dependent protein-crosslinking enzyme TGase (transglutaminase) was demonstrated to be involved in the apical growth of Malus domestica pollen tube. Apple pollen TGase and its substrates were co-localized within aggregates on the pollen tube surface, as determined by indirect immunofluorescence staining and the in situ cross-linking of fluorescently labelled substrates. TGase-specific inhibitors and an anti-TGase monoclonal antibody blocked pollen tube growth, whereas incorporation of a recombinant fluorescent mammalian TGase substrate (histidine-tagged green fluorescent protein:His6– Xpr–GFP) into the growing tube wall enhanced tube length and germination, consistent with a role of TGase as a modulator of cell wall building and strengthening. The secreted pollen TGase catalysed the cross-linking of both PAs (polyamines) into proteins (released by the pollen tube) and His6-Xpr-GFP into endogenous or exogenously added substrates. A similar distribution of TGase activitywas observed in planta on pollen tubes germinating inside the style, consistent with a possible additional role for TGase in the interaction between the pollen tube and the style during fertilization
Spermine delays leaf senescence in Lactuca sativa and prevents the decay of chloroplast photosystems
Aliphatic polyamines (PAs) are involved in the delay or prevention of plant senescence, but the molecular
mechanism is not clarified. The hypothesis is put forward that one of the mechanisms by which PAs
modulate leaf senescence and chlorophyll stabilisation could be due to their modification of chlorophyllbound
proteins, catalysed by transglutaminase (TGase, R-glutaminylpeptide-amine g-glutamyltransferase;
E.C. 2.3.2.13). The retardation of leaf senescence of Lactuca sativa L. by spermine (Spm) was examined
during induced cell death using leaf discs, or during the normal developmental senescence of leaves.
Over 3 days, in leaf discs, Spm caused a delay of chlorophyll (Chl) decay, an increase of endogenous TGase
activity, and a three-fold increase in chlorophyll content when supplied together with exogenous TGase.
Spm was conjugated, via TGase, mainly to 22e30 kDa proteins. Long-term experiments over 5 days
showed a general decrease in all three parameters with or without Spm. When leaves remained on the
plants, Spm-sprayed leaves showed an increase in free Spm 1 h after spraying, mainly in the young
leaves, whereas over longer periods (15 days) there was an increase in perchloric acid-soluble and
-insoluble Spm metabolites. In senescing leaves, Spm prevented degradation of chlorophyll b and some
proteins, and increased TGase activity, producing more PA-protein conjugates. Spm was translocated to
chloroplasts and bound mainly onto fractions enriched in PSII, but also those enriched in PSI, whose
light-harvesting complexes (LHC) sub-fractions contained TGase. Spm was conjugated by TGase mainly
to LHCII, more markedly in the light. Immunodetection of TGase revealed multiple proteins in young
leaves, possibly representing different TGase isoforms when TGase activity was high, whereas in already
senescent leaves, when its activity decreased, one high-molecular-mass band was found, possibly
because of enzyme polymerisation. Spm thus protected senescing Lactuca leaves from the decay of their
chloroplast photosystem complexes. The senescence-delaying effects of Spm could be mediated by
TGase, as TGase was re-activated to the level in young leaves following Spm treatmen
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