Importance of non-systemic leaf autophagy for suppression of zinc starvation induced-chlorosis.

Autophagy, which is one of the self-degradation systems, promotes intracellular zinc (Zn) recycling under Zn deficiency (-Zn) in plants. Therefore, autophagy defective plants show severe chlorosis under -Zn. Root is the plant organ which directly exposed to Zn deficient environment, however, in our recent study, -Zn symptom was prominently observed in leaves as chlorosis. Here, we conducted micrografting to determine which organ's autophagic activities are important to suppress the -Zn induced chlorosis. Grafted plants that have autophagic activities only in roots or leaves were grown under -Zn and then compared chlorotic phenotypes among them. As a result, regardless of the autophagic activities in rootstocks, -Zn induced-chlorosis in leaves was occurred only when autophagy in scion was defective. This data indicates that Zn resupplied by autophagic degradation in root cells could not contribute to suppress the chlorosis in leaves. Thus, autophagy in the aerial part is critical for controlling -Zn induced-chlorosis in leaves. Taken together, along with our recently reported data, we conclude that the mechanism of Zn resupply by autophagic degradation is not systemic throughout the plant but rather a local system.