Preservation of the Tonoplast in Metaphloem Sieve Elements of Embryonic Roots of Zea mays L.

Decortication of embryonic roots of 4- to 5-day-old Zea seedlingsand subsequent chemical fixation permitted comparison of cutand uncut developing sieve elements In a decorticated root wheresieve tubes are not severed, metaphloem sieve elements in latestates of development and some mature sieve elements exhibita highly vacuolate condition When roots are cut or diced inthe course of fixation intact vacuoles are not observed in latestages of sieve-element ontogeny The degree of callose formationat sites of developing sieve-plate pores and in the pores ofmature sieve elements varies greatly with both decorticationand non-decortication treatments Nuclei were not observed insieve elements at the electron microscope level, but they wereseen at the light microscope level in serial sections of sieveelements in the late to mature developmental stages representedAlthough the occurrence and distribution of plastids, mitochondria,endoplasmic reticulum, dictyosomes and nbosomes also vanes insieve elements of decorticated roots, disruption or surgingof sieve-element contents is greater for sieve tubes that aresevered during fixation treatment A discussion is presentedrelating effects of trauma on observed developmental stagesand sieve-element structure Zea mays L, maize, corn, phloem, Sieve elements, tonoplast, ultrastructure