PSII-S gene expression, photosynthetic activity and abundance of plastid thioredoxin-related and lipid-associated proteins during chilling stress in Solanum species differing in freezing resistance

We investigated the role of non-photochemical energy quenching (NPQ) in col d acclimation in potato. We first analyzed the expression of the PsbS gene, which encodes a PSII subunit involved in NPQ, during chilling treatment in two potato species, a cold-tolerant Solanum sogarandinum and a cold-sensit ive Solanum tuberosum (cv. Cisa). In in vitro plantlets, a transient transc ript accumulation was observed after 1 h in the light at room temperature i n both species, and this light-induced PsbS transcript accumulation was str ongly amplified at 4 degreesC. Nuclear run-off transcription experiments in dicated that this increase likely originates from a higher transcriptional activity of PsbS gene. In phytotron-grown plants, chilling treatment was sh own also to result in a substantial increase in PsbS mRNA level. However, n o change in protein abundance was noticed in either Solanum species. PSII p hotochemistry and photosynthetic electron transport were severely decreased in S. tuberosum plants at low temperature, while both activities were only slightly affected in S. sogarandinum. NPQ was substantially reduced in bot h species during chilling stress. These results indicate that neither PsbS nor NPQ are involved in acclimation of S. sogarandinum to low temperature. In contrast, the level of two other plastid proteins, one related to thiore doxins, CDSP32, and the other homologous to plastid lipid-associated protei ns, CDSP34 (for chloroplastic drought-induced stress proteins of 32 and 34 kDa, respectively), was higher at low temperature in the cold-tolerant spec ies. This result is discussed in relation to the potential roles of CDSPs i n the protection of photosynthetic structures.