Light Stress Following a Frost Episode Influences the Frost Tolerance of a Wild Potato Species

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Abstract
The effect of light stress following various levels of freezing stress on photosynthetic and respiratory functions in leaf tissue of Solanum acaule (Bitt.) was investigated under laboratory conditions. Terminal leaflets from plants grown at 18/16C (light/dark) and 400 μmol·s−1·m−2 photosynthetically active radiation (PAR) were slowly frozen in the dark to various minimum temperatures and then thawed on ice, also in the dark. Immediately after thawing, paired leaf disks were cut from a single terminal leaflet. Disks were then held at 1.0C for 3 hr, with one disk exposed to 800 μmol·s−1·m−2 PAR and the other disk of the pair was held in the dark. Our experimental approach allowed comparative studies on tissue from the same leaflet. Light during the post-thaw period, as compared to darkness, resulted in greater inhibition of photosynthetic processes, but had little effect on respiration. Our results demonstrate a) the importance of considering a light stress component during the assesment of relative frost tolerance in photosynthetic tissue and b) that chloroplast functions are much more sensitive than mitochondrial functions to a post-thaw light stress.

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