Many plants (e.g. roses, palms) can be protected from frost during the winter if shielded with an appropriate coat that can be bought in garden shops. Do plants produce any heat that can be kept inside with these "clothes"?
Cellular respiration in plants is slightly different than in other eukaryotes because the electron transport chain contains an additional enzyme called Alternative Oxidase (AOX). AOX takes some electrons out of the pathway prematurely - basically the energy is used to generate heat instead of ATP.
The exact purpose of AOX in plants is still unclear. Plants will make more AOX in response to cold, wounding, and oxidative stress. We know of at least one plant (skunk cabbage) that exploits this pathway to generate enough heat to melt snow. This link gives a pretty good overview.
(AOX is dear to my heart, since my first 3 years working in a laboratory were spent studying this gene <3)
Plants will be respiring continuously, which is an exothermic process. Therefore the plants will be producing a small amount of heat. The protection from frost may be more a result of the vastly smaller convection current of the coat compared to the atmosphere rather than by reducing any conduction away of heat produced by the plant, however.
Keeping the plant out of the wind by 'dressing it' will reduce the rate of transpiration when the stomata are open. I would very tentatively suggest that, as water has a very high specific heat capacity, having a greater volume of water within the plant would help to retain any heat that was produced by respiration. However this is entirely speculation on my part.
Some plants have mitochondrial pathways that produce heat. That's why skunk cabbage can be seen poking outing of the snow in late winter/early spring. Here's a review: http://onlinelibrary.wiley.com/doi/10.1111/j.1744-7909.2010.01004.x/pdf
Yes, respiration is exothermic and plants (like all living things) respire.
I think the effect of covering the plant has to more to do with reducing sensible heat loss , e.g. direct transfer of heat from plant to air) rather than latent heat loss (through evaporation).
The cover is effectively reducing the mixing of the air near the plant (and closer to the temperature of the surface of the earth) with the free atmosphere (closer to the temperature reported by the weatherman)