if they get to hot they will curl and burn on the edges but im not sure if this is the cause of yours,they may be getting attacked.
where are they,inside or out.a pic would be good,

Are you watering regularly if they are in containers in a green house they will ned regular watering and feeding with liquid tomato food.

they also curl if they are too cold too. as the nights get warmer the problem will disappear.

Too little nitrogen will cause them to turn yellowish and curled. Too little phosphate causes curly purplish leaves. Sometimes they have both problems--often caused by too cool conditions, rather than lack of nutrients.