Relationship Of Cessation Of Pollen Tube Growth And Mitochondria In Pyrus L.

Alternations of mitochondrial structure and membrane potential are implicated in this process. Changes and distribution of mitochondria are essential for the tremendous enery requirement in high speed growth of pear pollen tubes. However, the exact roles of mitochondria remain unkown in the process of pollen tube death. In present study, pear cultivars’Huanghua’,’Housui’and’Dangshansuli’were selected as plant materials; immunofluorescence label assay, laser confocal scanning microscope, transmission electron microscopy, a new method of isolation mitochondria or gametic nuclei were applied in pear pollen tubes as procedure, mitochondrial roles in the process of pear pollen tube ageing and death were studied in vitro. The main results as follows:1. The changes and functions of mitochondria in the self-incompatible pollen tube were determined. The results showed that oxygen consumption in incompatible pollen tubes was decreased. The respiratory control rate of mitochondria isolated from incompatible pollen tubes was decreased. This indicated that these mitochondria lost their functions. The changes of mitochondrial proteins were examined by2-D SDS-PAGE. Eighteen significant protein spts were selected. Seven protein spots were up-regulated and11protein spots were down-regulated. These proteins could be associated to the changes of mitochondrial function in self-pollen tubes.2. The pollen tubes displayed lower growth rate and drastically decreased viability at>15h post-cultured. Several ageing-related physiological or cellular marker changes, e.g. increased malondialdehyde content and membrane ion leakage and actin cytoskeleton depolymerization, revealed that the gradual cessation of growth of pear pollen tubes was an ageing process. Furthermore, cytoplasmic acidification mainly mediated by vacuolar H+-ATPase inactivity was observed in ageing pollen tubes, and this further resulted in mitochondrial dysfunction (decreases in oxygen consumption and ATP production, mitochondrial membrane potential collapse and mitochondrial structure disruption). Collectively, our findings suggest that the pear pollen development from germination to cessation of elongation is an ageing process, mediated by cytoplasmic acidification and mitochondrial dysfunction. In addition, Valinomycin decreased the membrane potential of mitochondria in pear pollen tubes, which resulted in nuclear degradation. This further suggested that mitochondrial dysfunction could induce nuclear degradation and finally pollen tube death.3. The tip-localized ROS in pear pollen tube is mainly derived from the plasma membrane NADPH oxidase. Our results indicated that NaN3significantly inhibited the oxygen consumption of the pear pollen tubes, but this did not disrupt the tip-localized ROS. This further suggested that mitochondria could not be the main source of the tip-localized ROS. But low temperature (LT) of4℃and DPI, a NADPH oxidase inhibitor, disrupted the tip-localized ROS in pear pollen tubes. The full length gene of PrRBOH was coloned from pear pollen tube. The deduced PrRBOH have the main domain or motif in paint RBOHs. Low temperature decreased the relative express of PrRBOH. This indicated that NADPH oxidase mainly contributed to the tip-localized ROS in pear pollen tubes.4. LT remarkably decreased mitochondrial oxygen consumption and intracellular ATP production. The endocytosis disruption in pear pollen tubes induced by LT may be mediated by mitochondrial metabolic dysfunction. LT stress (4℃) arrested pear pollen tube growth and disrupted tip-localized ROS, as well as depressed mitochondrial respiratory and intracellular ATP production. We also observed that the disruption of endocytosis in pear pollen tubes induced by LT could be mediated by mitochondrial metabolic dysfunction. Our data showed ROS and endocytosis events in the physiological reaction of pear pollen tubes under LT stress.