Torres, Jonathan , Wu, Jian , Roux, Stanley .
Pollen tubes release ATP as they grow and their continued growth requires the activity of pollen ectoapyrases that hydrolyze the secreted ATP.
Apyrases (NTPDases) are enzymes that can hydrolyze nucleoside tri- and/or diphosphates, but not nucleoside monophosphates. Arabidopsis pollen strongly expresses three different apyrase proteins, APY1, APY2 and APY6. Two of these, APY1 and APY2, are 87% identical in amino acid sequence and contain signal peptides. Pollen of null apy1apy2 mutants is fully developed and viable but cannot germinate, suggesting that expression of at least one of these apyrases is crucial for tube emergence and growth. Localization studies suggest that a significant fraction of cellular APY1 and APY2 is on the plasma membrane. In this locale they could potentially function as ectoapyrases; i.e., with their active site oriented out into the wall, where they, like animal ectoapyrases, could hydrolyze extracellular ATP. To test this possibility, we first confirmed that pollen tubes release significant levels of ATP into the growth medium as they grow, just as root hairs do (Kim et al. Plant Physiol. 142, 2006). We then tested the effects of treating growing pollen tubes with polyclonal antibodies that bind to APY1 and APY2 and block their enzyme activity. We found that this treatment, but not treatment with preimmune sera, results simultaneously in an inhibition of pollen tube growth and a significant increase in the [ATP] of the medium over that observed in control media. These results were replicated when pollen tubes were treated with any one of three small molecule inhibitors of apyrase activity. They are consistent with the conclusion that a crucial function of APY1 and APY2 is the hydrolysis of the extracellular ATP that is released as the tubes grow and that this function is needed to sustain tube growth. (Supported by NSF IBN0344221 to S. J. R.)
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1 - University of Texas at Austin
Presentation Type: ASPB Minisymposium
Location: Waldorf Room/Hilton
Date: Monday, July 9th, 2007
Time: 8:30 AM