Figure 8.

Dynamics of Oligofructan Biosynthesis and the Proposed Functions during Grain Development.

Prior to the onset of starch accumulation in the endosperm, incoming sucrose is transiently stored as levan-/graminan-type fructans. By releasing the glucose moiety during fructan biosynthesis, the high glucose-to-sucrose ratio is preserved. Fructan biosynthesis thereby might contribute to the mechanisms regulating endosperm differentiation in this developmental phase. The transition phase represents a switch in grain fructan metabolism; short-chain inulin-type fructans are biosynthesized in the NP as the endosperm cavity forms and accumulate in the cavity surrounding tissues. The reactivity of oligofructans with the ^•OH radical has been shown in vitro, emphasizing their capability to act as ROS scavenging agents in cells faced with proceedings leading to ROS formation (e.g., the high transport activities in the ETCs and the contiguous degeneration of NP cells directly facing the endosperm cavity). Accumulation of inulins in cells surrounding the cavity might thereby mitigate ROS-inflicted oxidative damage and in turn maintain the massive import rates into the filial grain parts during the storage phase.