[Localization of dehydrogenases of energy metabolism in the pholoem of Cucurbita pepo L]

Abstract

In the stem phloem of Cucurbita pepo the enzymes GAPDH, ADH, MDH, NADP-IDH, NAD-IDH, G6PDH and SDH were localized histochemically with the aid of tetrazolium salt (NBT). When the stems were deep-frozen the most intense formation of formazan was found in companion cells, less in phloem parenchyma cells, and very little in sieve tubes.The distribution of enzymes in phloem markedly changes when stems were cut 2 minutes before freezing: 2,5 cm behind the sectional area little formazan was found. Companion cells and parenchyma cells had lost nearly all activity. 15 cm behind the sectional area there was again a higher concentration of formazan in the companion cells and parenchyma cells. In this region an even higher activity was detected in sieve tubes. 25-30 cm behind the sectional area the distribution of formazan was nearly the same as in the intact stems.Apparently activities of the enzymes tested primaily occur in the companion cells and parenchyma cells only. After wounding they are translocated into sieve tubes or exudate.