Issue dependencies are not visible in the Task List.
By default, only subtask relationships are displayed in the Task List.
You can enable 'Show linked tasks' in the 'Additional Settings' section of the repository properties (Window -> Show View -> Task Repositories) to also show issue links in the Task List. After enabling the setting 'Synchronize All Tasks' from the popup menu of the task repository, the Task Repositories view needs to be selected to update all tasks.
See this issue for further information.