Guys,

i am trying to load a plugin directly from item.php code:

<?php echo $this->item->fulltext; ?>

{tab=Title1}content1{tab=Title2}content2{/tabs}

<?php ... ?>

but it is not working ... is it possible to load it somehow directly from within k2 template code?

You can add a module inside your item.php. Make sure that module has Prepare content enabled.