ALDEVAUX

Soltan,
I do not know exactly what your problem is but leaf scorch and tip burn, as shown on your picture, is a physiological problem that can occur on any kind of plant. It can be caused by a number of things, but, more often than not, it is the result of bad cultural condition, not outside influences such as air pollutants, fluoride in the water, transplanting, soil compaction, a nutrient deficiency, chemical injury, unfavorable weather conditions (such as drought), limited room for root growth etc..
But more often, and this could be your problem, there could be excess salts built up from fertilizing in your soil or substrate, or in the water you are using as suggested by revt. This excess salts in the soil can damage root hairs which as a result aren't able to supply enough water to offset the water lost through the leaves in transpiration when it is very hot. This results in drying of leaf tips and scorching on leaf edges. The problem mostly occurs in summer when it is very hot, or in a hot house as in your case, often on newly planted trees.
Generally speaking, you can remedy the problem without ever understanding what caused it. Just make a few common sense improvements in the conditions you grow, fertilise and type of water for your trees.
To remove excess salts from soil or substrate, you should drench it with lots of water and letting the excess water drain readily out of the drain holes continuously for at least 5 to 10 minutes.
To test your soil or water salinity you have to take a sample of your soil or water at a laboratory that does that type of work or use a conductivity meter which is often used by tomato greenhouse growers.