Effect of light on photosynthetic capacity during cold acclimation in a cold‐sensitive and a cold‐tolerant potato species

The effect of low temperature acclimation at various light levels on the photosynthetic capacity of Solanum species was examined. Two species, Solanum tuberosum L. cv. Red Pontiac and Solanum acaule Bitt., which differ significantly in degree of frost‐tolerance and in their ability to acclimate to low temperature stress, were compared. Acclimation conditions included 5/2°C (day/night) temperatures, and either moderate (400 · mol · m−2· s−1) or low (40 · mol · m−2· s−1) photosynthetic photon flux densities. Several parameters of photosynthesis were measured in tissue pieces during acclimation treatments including chlorophyll content, chlorophyll a/b ratios and carbon dioxide‐saturated photosynthetic oxygen evolution during light‐limited and light‐saturated assays. Most measured photosynthetic parameters of low temperature‐grown plants of both species showed greater declines under the moderate light than the low light conditions. Chlorophyll a/b ratios were unchanged after low temperature exposures in both light level treatments. At low temperatures, the cold‐sensitive S. tuberosum demonstrated a greater inhibition of photosynthetic capacity in light‐ and carbon dioxide‐saturated assays than S. acaule at all light levels. In addition to a pronounced inhibition at the higher light level, S. tuberosum demonstrated a very strong inhibition of photosynthetic capacity at very low light levels. Our results suggest a correlation between ability to maintain essential metabolic processes during low temperature stress in the presence of moderate light levels and the ability to increase cold tolerance.