Pollen tube growth is a rapid process restricted to the only tip region. Many factors cooperate to allow this apical growth, creating an intricate signalling network. The continuous rebuilding of the cell wall and apical migration of the cytoplasm sustained by cytoskeleton re-organisation are the most important driving forces needed for growth (1), but many other factors are involved in this process, among which polyamines (PAs), that are essential during pollen tube emergence (2) and ROS, that support the apical growth, at physiological concentration (3). We investigated the effect of the natural PA Spermine (Spm) and BD23, a synthetic aromatic derivative of Spm on the apical growth of Pyrus communis pollen tube and observed that both Spm inhibited the growth from 10 M onwards. Thanks to a FITC-labelled Spm we were able to observe, that PAs enter through the pollen tube tip, then diffuse in the sub-apical region. The same region underwent drastic morphological changes, showing loss of polarity and enlarged tip when Spm and BD23 were supplied at 100 M or higher. The effects of PAs were related, at least in part to their ability to act as ROS scavengers of both O2 and H2O2 in the apical zone, probably altering the Ca2+ signalling network or disrupting the balance between ROS species that affect cell-wall relaxation or stiffening. Interestingly, the actin cytoskeleton was not affected by the treatment with 100 M of both the PAs and, instead, seemed to follow the swelling of the apex. Intriguing the cell wall was enriched in both callose and cellulose exactly in the region where the swelling of the tip begins, probably to contrast the excess of ductility of the cell wall after treatment with PAs 100 M. The viability of pollen was slightly affected by 100 M treatment, and the degradation of nuclear DNA, as shown by DAPI labelling of pollen tube, was completely inhibited when pollen had been pre-treated with the caspase-3 inhibitor I peptide, Ac-DEVD-CHO (DEVD). Different was the scenario when the PAs were supplemented at 500 M, concentration that is far away from the physiological concentration. In this case, the effects on the pollen were more drastic, with a rapid drop of cell viability, actin depolimerisation, stimulation of DNA-laddering after 30 minutes incubation and the complete degradation of both vegetative and generative nuclei; these degradative effects were only in part inhibited by the pre-treatment with DEVD. Thus the present data may open new research avenues to understand how the diameter of the pollen tube is regulated and which role PAs could play in the puzzling process of apical growth.

Aloisi, I., Faleri, C., Cai, G., Del Duca, S. (2014). COULD SPERMINE PLAY A ROLE DURING THE APICAL GROWTH OF POLLEN TUBE?.

COULD SPERMINE PLAY A ROLE DURING THE APICAL GROWTH OF POLLEN TUBE?

FALERI, CLAUDIA;CAI, GIAMPIERO;
2014-01-01

Abstract

Pollen tube growth is a rapid process restricted to the only tip region. Many factors cooperate to allow this apical growth, creating an intricate signalling network. The continuous rebuilding of the cell wall and apical migration of the cytoplasm sustained by cytoskeleton re-organisation are the most important driving forces needed for growth (1), but many other factors are involved in this process, among which polyamines (PAs), that are essential during pollen tube emergence (2) and ROS, that support the apical growth, at physiological concentration (3). We investigated the effect of the natural PA Spermine (Spm) and BD23, a synthetic aromatic derivative of Spm on the apical growth of Pyrus communis pollen tube and observed that both Spm inhibited the growth from 10 M onwards. Thanks to a FITC-labelled Spm we were able to observe, that PAs enter through the pollen tube tip, then diffuse in the sub-apical region. The same region underwent drastic morphological changes, showing loss of polarity and enlarged tip when Spm and BD23 were supplied at 100 M or higher. The effects of PAs were related, at least in part to their ability to act as ROS scavengers of both O2 and H2O2 in the apical zone, probably altering the Ca2+ signalling network or disrupting the balance between ROS species that affect cell-wall relaxation or stiffening. Interestingly, the actin cytoskeleton was not affected by the treatment with 100 M of both the PAs and, instead, seemed to follow the swelling of the apex. Intriguing the cell wall was enriched in both callose and cellulose exactly in the region where the swelling of the tip begins, probably to contrast the excess of ductility of the cell wall after treatment with PAs 100 M. The viability of pollen was slightly affected by 100 M treatment, and the degradation of nuclear DNA, as shown by DAPI labelling of pollen tube, was completely inhibited when pollen had been pre-treated with the caspase-3 inhibitor I peptide, Ac-DEVD-CHO (DEVD). Different was the scenario when the PAs were supplemented at 500 M, concentration that is far away from the physiological concentration. In this case, the effects on the pollen were more drastic, with a rapid drop of cell viability, actin depolimerisation, stimulation of DNA-laddering after 30 minutes incubation and the complete degradation of both vegetative and generative nuclei; these degradative effects were only in part inhibited by the pre-treatment with DEVD. Thus the present data may open new research avenues to understand how the diameter of the pollen tube is regulated and which role PAs could play in the puzzling process of apical growth.
Aloisi, I., Faleri, C., Cai, G., Del Duca, S. (2014). COULD SPERMINE PLAY A ROLE DURING THE APICAL GROWTH OF POLLEN TUBE?.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11365/47172
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