Low oxygen storage modulates invertase activity to attenuate cold-induced sweetening and loss of process quality in potato (Solanum tuberosum L.)

Russet Burbank and Innovator are mid- to late-season frozen-processing cultivars with inherently different dormancy periods and susceptibilities to low temperature-induced sweetening (LTS). In contrast to Russet Burbank, which is highly prone to accumulation of reducing sugars (Glc + Fru) when stored below 8-9 degrees C, Innovator tubers exhibit moderate resistance to LTS and retain process quality longer at lower temperatures (4-6 degrees C). However, Innovator's LTS resistance is not robust and often varies across production regions. Here we show that low O-2 storage modulates LTS to reveal metabolic differences intrinsic to these cultivars. Changes in tuber respiration, process quality, reducing sugars, sucrose, starch phosphorylase and invertase activities were compared at 4 and 8 degrees C in 2.5 and 21 kPa O-2 over a 212-d storage period. Tuber respiration declined rapidly as O-2 level decreased from 21 to 2.5 kPa during acclimation at 8 degrees C. Respiration rates then fell further as the temperature was lowered from 8 to 4 degrees C, but this response was greatly muted for tubers at 2.5 versus 21 kPa O-2. Tubers at 21 kPa O-2 completed their cold-induced respiratory acclimation response (RAR) within 7 d compared with 13 d at 2.5 kPa O-2, and the RAR was much greater for tubers at 2.5 kPa O-2. While reducing sugars increased most rapidly in tubers over the first 30 d at 4 degrees C, Innovator tubers had lower invertase activity and sweetened less than Russet Burbank tubers, characterizing its LTS-resistant phenotype. Low O-2 greatly attenuated these initial LTS responses for both cultivars; however, the effect was only temporary in Innovator. LTS resumed in Innovator tubers from 93 to 212 d with reducing sugar levels increasing to equal that of Russet Burbank tubers stored at 4 degrees C and 21 kPa O-2. Activities of alpha-1,4 glucan phosphorylase (SP) were higher in Russet Burbank than Innovator and increased progressively over the storage period regardless of temperature and oxygen concentration. Innovator tubers stored at 2.5 kPa O-2 had higher SP activities from 30 to 153 d at 4 and 8 degrees C compared with tubers stored at 21 kPa O-2, which correlated well with increased sucrose buildup and earlier sprouting. The low O-2-mediated inhibition of LTS was largely a consequence of reduced invertase activities. (C) 2016 Elsevier B.V. All rights reserved.