Highcharts highlight single point on line

I am using Highcharts to draw a line graph. When the page loads, the line graph is drawn. Please note, that i got an y-Value for every x-Value starting from 0 till 700 ( 0,1,2,3,...,700). This is how i create the graph:

                chart = new Highcharts.Chart({
                                    chart: {
                                         renderTo: 'container',
                                         animation: false,
                                         type: 'line',
                                         marginTop: null,
                                         marginRight: 55,
                                         marginBottom: 50,
                                         marginLeft: 80,
                                         backgroundColor: backgroundColor,
                                         spacingTop: 10,
                                         spacingRight: 10,
                                         spacingBottom: 15,
                                         spacingLeft: 10,
                                         },
                                   title: {
                                         text: ' Graph',
                                         style: {color: graphLabelColor},
                                         x: -20 //center
                                         },
                                   xAxis: {
                                         title: {
                                         text: 'xAXIS',
                                         style: {
                                            color: axisLabelColor
                                            },
                                         },
                                         min:0,
                                         max: 600,
                                         gridLineColor: gridLineColor,
                                         minorTickInterval: 50,