Please help on (root) - variable

Can I call a function (variable) with a deep nested button?


var sushi:Number = 1;

and then from a deep deep nested button within some movie clips :



button.addEventListener(MouseEvent.CLICK, sushiset);
function sushiset (event:MouseEvent):void{
    (root).sushi = 2;
}

recently I tried changing a movieclip just like this and it works with this code:



MovieClip(root).sushiMC.gotoAndPlay(1);


How will I do it **in variables? **Is it possible to create a globally-used variable?
Thank you.