My little apple seedlings (from seed) have gone through a bit too much sun this week, as a string of 90-degree days after being indoor plants has been a shock to them. Their leaves were burnt along the top layers and they're curling quite a bit. Most of them are also significantly more faded from what they were a few short weeks ago. (This is just an example, and what incited the questions below)
At what point will the leaves be "dead"? I mean, at what point will I know that they are useless to the plant? Should I trim them so that the lower leaves can get better light? Will they be able to bounce back from the stress that they've experienced?