Comprehensive analysis of in vitro to ex vitro transition of tissue cultured potato plantlets grown with or without sucrose using metabolic profiling technique

This study elucidated the effect of exogenous sucrose on growth parameters and metabolic changes during the in vitro rooting (InVR) and the ex vitro acclimatization (ExVA) stages of potato (Solanum tuberosum L.). During InVR stage, plantlets were cultured on MS medium with 3 % (S+) or without (S-) sucrose, and were then acclimatized under the same ExVA condition. In InVR stage, S+ increased photosynthetic capacity (A(max)) and dry matter percentage. Yet, no significant differences in the other growth parameters have been observed. During acclimatization, A(max) and respiration were higher in ExVA compared to InVR plants. Most growth parameters were significantly higher in S+ plants. Principal component analysis and hierarchical cluster analysis of 108 metabolites identified by GC-MS clearly demonstrated that in vitro culture had a profound impact on metabolic profile. In vitro S- and S+ plantlets accumulated large quantities of amino acids (specially under S+), photorespiration intermediates, putrescine, tocopherol and organic acids, including oxalic and tartaric acid. However, glycolytic and TCA cycle intermediates were found in lower amount. Under InVR S+ conditions, proline, gamma-aminobutyric acid, sugars and sugar alcohols accumulated in larger amounts. InVR S- plantlets characteristically accumulated large quantity of urea. We suggest that ammonia metabolism was redirected towards urea biosynthesis through urea cycle to sequester nitrogen in condition of low carbon availability. In vitro conditions are causing major disruption in the cellular metabolism, which could produce serious consequences on the capacity of plantlets to adapt to uncontrolled growing conditions and may lead to poor development under these conditions.