Help! leaves rapidly turning yellow

[Calbears]

Any ideas? I haven't got a clue. My leaves started with a brown mottled appearance now they're turning yellow. This is affecting the newest mature cane as well so I don't think it's natural senescence.

[Leafmite]

I agree that this isn't natural. Has anything happened to the orchid lately? What temperature range/light does this dendrobium get? Are the roots good?

[Calbears]

The roots are healthy. I had it in the garage under a T5HO so it got colder than usual and with more light. I moved it back inside after a lot of the leaves developed the brown patches. The yellowing has happened since.

For what's its worth, none of the other plants in the garage have had this issue so I think I can rule out pests.

I'm not the most experienced orchid grower, but I'm kinda shocked to see my previously vigorous plant decline so fast. The night time lows maybe dipped into the high 40s but nowhere close to freezing.

It's a den bracteosum by the way.

[Calbears]

Mesophyll Cell Collapse?

http://edis.ifas.ufl.edu/m/#publication?id=PP265

[Leafmite]

I just looked up the orchid in IOSPE and it is a hot growing orchid. Has this orchid been okay at other times when temperatures have been lower than ideal? If it has tolerated cooler temps before, then this would not be the problem and we have to try again.

---------- Post added at 10:48 PM ---------- Previous post was at 10:42 PM ----------

Yes, that might be possible.

[silken]

According to OrchidWiz and Baker's culture sheets, this is a warm growing Den with normal nighttime lows of 68F but could tolerate lows of 59F. So 40's may be too cold for it.

[Calbears]

Thanks for the responses. It's been indoors since I aquired it in June 2012. Even though the temps got low, I didn't realize what an effect it would have. I figured it would just slow the growth but live and learn.

[silken]

Hopefully there are some parts that will still be OK if you give it a warmer home. Orchids are pretty tough usually.