The Preservation of Plant Cells, particularly Sieve Tubes, by Vacuum Freeze-drying

Abstract

A vacuum freeze-drying apparatus is described. Cell contents were preserved in small, rapidly frozen pieces of plant tissue dried for four hours at – 30° C. After drying, specimens were either directly embedded with the resin ‘Epikote’ or fixed with 2 per cent osmium tetroxide in benzene and subsequently embedded in ester wax or Epikote resin. Mesophyll cells and border parenchyma cells were preserved in leaf pieces, and cell contents are comparable with the protoplasts of living cells. In soybean leaf, files of parenchyma cells occur between palisade and spongy mesophyll cells, linking fine veins. Hand sections of frozen-dried Epikote-embedded petiole phloem from Primula obconica revealed a mature sieve tube containing strands. Preservation by freeze-drying is taken as conclusive evidence for the existence of transcellular strands in living sieve tubes.