In vitro pollen functionality of attacin-transgenic “Royal Gala” apple plants and apples transformed with 1-aminocyclopropane-1-carboxylic acid synthase (ACS)-antisense vector

Abstract

To assess pollen functionality of transgenic apple trees, in vitro pollen germination and tube growth were evaluated. Flowers of transgenic “Royal Gala” apple lines containing attacin E gene to confer resistance to fire blight (Erwinia amylovora), or antisense 1-aminocyclopropane-1-carboxylic acid synthase (ACS) construct to improve fruit storage life, were collected, and pollen was harvested. Amongst the 19 transgenic lines, pollen from three lines transformed with an ACS-antisense vector consistently had significantly lower germination rate compared to “Royal Gala”; however, no correlation between ACS level in fruit and pollen germination rate was observed. Western blots showed that the amounts of the lytic protein, attacin, varied in pollen of the four attacin-transgenic lines sampled. There was no significant correlation between attacin level in the pollen and pollen germination rate or pollen tube growth. The addition of boric acid to the germination buffer enhanced germination in attacin-transgenic lines, as well as in lines down-regulated in ethylene synthesis and control “Royal Gala”. This initial study suggests that the majority of transgenic lines tested do not differ from the control “Royal Gala” in pollen germination, and that attacin or down-regulation of ethylene does not influence in vitro pollen functionality.