Structural Evidence for Plastid Inclusions as a Possible ‘Sealing’ Mechanism in the Phloem of Monocotyledons

Abstract

Sieve elements in monocotyledons possess unique plastids. Structural evidence indicates that when mature sieve-tube members are mechanically perturbed the plastids release proteinaceous, quasi – crystalline inclusions. The inclusions become lodged in sieve-plate pores and appear to seal portions of phloem sieve tubes.