Role of alkaline/neutral invertases in postharvest storage of potato

Potatoes stored at cold temperatures undergo undesirable sweetening due to the cleavage of sucrose into reducing sugars by invertases. Although significant research has focused on vacuolar invertase (StVAC) during cold storage of potatoes, little is known about the role of alkaline/neutral invertases (StNI). We identified eight members in the NI family from the potato genome, and phylogenetic analysis suggested their probable subcellular location as plastid/mitochondria (group alpha) or cytosol (group beta). Using three commercially important potato cultivars with known differences in cold storage responses ('Russet Burbank', 'Bintje', and 'Shepody'), we compared the expression of the eight StNI genes to StVAC and vacuolar invertase inhibitor (StINH2) genes during harvest, and after one and five months of storage at 4 degrees C or 22 degrees C. The activity of neutral invertase (NI), soluble acid invertase activity (SAI), and the levels of reducing sugars were also determined. Tubers of 'Russet Burbank' displayed high transcript abundance of StNI5, high reducing sugar content and more NI activity than SAI activity. This was associated with a high level of StINH2 transcripts and low StVAC transcript levels suggesting the susceptibility of these tubers to cold-induced sweetening could be due to cytoplasmic cleavage of sucrose by NI. In 'Bintje', the induction of StNI5 and StVAC transcripts and NI and SAI activities indicate that sucrose degradation is carried out by both NI and SAI. In 'Shepody', a higher abundance of the StNI4 and StNI6 transcripts indicates different isoforms of NI are required for sucrose degradation. This study reveals significant contribution of NI in the regulation of reducing sugars and the process of cold-induced sweetening. Additional studies are needed to determine the in vivo function of NI in cold-stored potato tubers.

Automated summary

This study identified different isoforms of NI in potato cultivars, indicating their varied roles in sucrose degradation during cold storage. The findings suggest the significant contribution of NI in regulating reducing sugars and cold-induced sweetening in potatoes, highlighting the need for further research to determine the in vivo function of NI in cold-stored potato tubers.