Abstract
To allow successful germination and growth of a pollen tube, mature and dehydrated pollen grains (PGs) take up water and have to adjust their turgor pressure according to the water potential of the surrounding stigma surface. The turgor pressure of PGs of lily (Lilium longiflorum) was measured with a modified pressure probe for simultaneous recordings of turgor pressure and membrane potential to investigate the relation between water and electrogenic ion transport in osmoregulation. Upon hyperosmolar shock, the turgor pressure decreased, and the plasma membrane (PM) hyperpolarizes in parallel, whereas depolarization of the PM was observed with hypoosmolar treatment. An acidification and alkalinization of the external medium was monitored after hyper- and hypoosmotic treatments, respectively, and pH changes were blocked by vanadate, indicating a putative role of the PM H(+) ATPase. Indeed, an increase in PM-associated 14-3-3 proteins and an increase in PM H(+) ATPase activity were detected in PGs challenged by hyperosmolar medium. We therefore suggest that in PGs the PM H(+) ATPase via modulation of its activity by 14-3-3 proteins is involved in the regulation of turgor pressure.
Highlights
To allow successful germination and growth of a pollen tube, mature and dehydrated pollen grains (PGs) take up water and have to adjust their turgor pressure according to the water potential of the surrounding stigma surface
PGs do not foresee the water potential of the stigma on which they are going to land; interestingly, in vitrocultivated PGs of the same species are capable of germinating in media containing various concentrations of osmolytes, e.g. lily (Lilium longiflorum) PGs can germinate in 5% to 12% Suc corresponding to 150 and 450 mosmol kg21, respectively, with a more or less constant turgor pressure independent from the medium osmolality (Benkert et al, 1997)
Artificial increases of turgor pressure by the pressure probe immediately stopped growth and further increase resulted in bursting of the tube tip with a burst pressure approximately twice the previous pressure, indicating a fine-regulated balance between turgor pressure and cell wall strength at the tube tip that is necessary for successful growth of pollen tube (PT) (Winship et al, 2010)
Summary
To allow successful germination and growth of a pollen tube, mature and dehydrated pollen grains (PGs) take up water and have to adjust their turgor pressure according to the water potential of the surrounding stigma surface. PGs do not foresee the water potential of the stigma on which they are going to land; interestingly, in vitrocultivated PGs of the same species are capable of germinating in media containing various concentrations of osmolytes, e.g. lily (Lilium longiflorum) PGs can germinate in 5% to 12% Suc corresponding to 150 and 450 mosmol kg, respectively, with a more or less constant turgor pressure independent from the medium osmolality (Benkert et al, 1997). One may assume an osmoregulation mechanism taking place in PGs that (1) somehow senses the osmotic conditions on the stigma surface, (2) allows an influx of water to account for the volume increase in germination and tube growth, and (3) adapts the turgor pressure to grow a PT without bursting. Invasive and noninvasive techniques were used to investigate whether PGs are capable to adjust and regulate their turgor pressure and which transport activities are affected by turgor changes and, are involved in osmoregulation of PGs
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