Metabolic snorkeling — the metabolic interaction between plant organs and tissues with different oxygen availabilities

Plants constantly experience partial hypoxia due to varying external oxygen availability and the existence of hypoxic niches, such as the shoot apical meristem, phloem or root nodules. Waterlogging experiments indicate that hypoxic stress at the root does not only lead to a local metabolic response, such as the accumulation of hypoxia-related metabolites, but also causes metabolic alterations in the normoxic shoot. Moreover, hypoxia-related metabolites are exported from the hypoxic root towards the normoxic shoot, where they can be recycled. Maintaining import of glycolytic substrates from the normoxic shoot into the hypoxic root is suggested to play a crucial role in managing hypoxic stress in waterlogged roots. These findings indicate that locally confined hypoxic stress induces systemic responses. The apparent metabolic interplay between hypoxic and normoxic tissue can facilitate the plant to endure differing oxygen availabilities between tissues and organs without active oxygen circulation. Here, we define this mechanism as 'metabolic snorkeling'. Beyond waterlogging, metabolic snorkeling might also occur between hypoxic niches and the adjacent normoxic tissue. In this review, the role of metabolic snorkeling in waterlogging-endurance and its applicability to hypoxic niches is described and discussed.