Profiling of StvacINV1 Expression in Relation to Acid Invertase Activity and Sugar Accumulation in Potato Cold-Stored Tubers

Reducing sugars (RS) accumulation in potato (Solanum tuberosum L.) tubers stored at low temperature, a phenomenon known as cold-induced sweetening, is a serious postharvest problem for the potato processing industry. RS accumulation is prevented by suppression of a gene encoding potato vacuolar acid invertase (StvacINV1), which catalyzes irreversible hydrolysis of sucrose into glucose and fructose. Six potato genotypes were selected for dynamic analysis of sugar accumulation and invertase expression pattern in tubers during 1 month of low-temperature storage. The significant increase of sucrose content was found to occur earlier than the remarkable rise of RS content in all the genotypes tested. RS accumulation continued from 15 to 30 days of storage while sucrose content was almost steady in this period. The transcripts of StvacINV1 increased rapidly in tubers exposed to cold treatment and the activity of soluble acid invertase increased accompanied with sugar accumulation. Correlation analysis across eight genotypes revealed that invertase activity was positively correlated with RS content while the correlation between soluble acid invertase activity and the level of StcacINV1 transcripts was weak. Our results suggest that sucrose cleavage is causal for RS accumulation in cold-stored tubers and the acid invertase activity is possibly modulated by post-translational mechanisms.