The integral peroxisomal membrane proteins PEX10, PEX2, and PEX12 contain a zinc RING finger close to the C terminus. Loss of function of these peroxins causes embryo lethality at the heart stage in Arabidopsis. Preventing the coordination of Zn(2+) ions by amino acid substitutions in PEX10, PEX2, and PEX12 and overexpressing the resulting conditional sublethal mutations in WT uncovered additional functions of PEX10. Plants overexpressing DeltaZn-mutant PEX10 display deformed peroxisomal shapes causing diminished contact with chloroplasts and possibly with mitochondria. These changes correlated with impaired metabolite transfer and, at high CO(2), recoverable defective photorespiration plus dwarfish phenotype. The N-terminal PEX10 domain is critical for peroxisome biogenesis and plant development. A point mutation in the highly conserved TLGEEY motif results in vermiform peroxisome shape without impairing organelle contact. Addition of an N-terminal T7 tag to WT PEX0 resulted in partially recoverable reduced growth and defective inflorescences persisting under high CO(2). In contrast, plants overexpressing PEX2-DeltaZn-T7 grow like WT in normal atmosphere, contain normal-shaped peroxisomes, but display impaired peroxisomal matrix protein import. PEX12-DeltaZn-T7 mutants exhibit unimpaired import of matrix protein and normal-shaped peroxisomes when grown in normal atmosphere. During seed germination, glyoxysomes form a reticulum around the lipid bodies for mobilization of storage oil. The formation of this glyoxysomal reticulum seemed to be impaired in PEX10-DeltaZn but not in PEX2-DeltaZn-T7 or PEX12-DeltaZn-T7 plants. Both cytosolic PEX10 domains seem essential for peroxisome structure but differ in metabolic function, suggesting a role for this plant peroxin in addition to the import of matrix protein via ubiquitination of PEX5.