Water is essential for photosynthesis. In this process, plants use the energy from sunlight to split water molecules. 10% is split for its hydrogen other 90% ish is cooling related. Irrespective of temperature the plant is fighting a constant balance between water input and water output. If over 18 hours it ever drops to around 10-15% moisture in the medium (reachable/stored) the plant will initiate water preservation and sacrifice the cooling of less critical parts of the plant first which will always be presented as margin tips curling up, with no cooling the tips denature and enzymes dissolve.
There are obviously degrees and yours is very light and nothing to really worry about. But that's more or less the mechanism at work under the hood.
Gluck.