PYRIDINE-NUCLEOTIDE LEVELS AND ACTIVITIES OF DEHYDROGENASES IN CAMBIAL DERIVATIVES OF ROBINIA-PSEUDOACACIA L

Despite the importance of the vascular cambial differentiation, little is known about its regulation. In order to address this problem we at tempted to biochemically characterize differentiating xylem and phloem elements during the early stages of development. By applying techniqu es of quantitative histochemistry we show that the total pool size of pyridine nucleotides is similar in the phloem (PD) and xylem (XD) orie nted derivatives of the cambial zone of trees of Robinia pseudoacacia L. Within the PD zone, the amount of NAD + NADH exceeded that of NADP + NADPH [around 600 versus 200 pmol (mg dry weight)(-1)], possibly ind icative of a preponderance of catabolic pathways (ratio of NADH:NAD ab out 1). In contrast, the NADP(H) system dominated in the XD zone. This coincided with a high activity of NAD kinase. In addition, the extrac table activities of the key enzymes of the oxidative pentose phosphate pathway, glucose-6-phosphate dehydrogenase and 6-phosphogluconate deh ydrogenase, were greatly increased. At a ratio of NADPH:NADP of approx imately 1, this could be indicative of increased rates of reductive bi osyntheses, and could thus well be involved in early steps of the form ation of phenols and lignin monomers. Taken together, this first appro ach clearly shows that phloem-oriented and xylem-oriented cambial desc endents exhibit distinct differences in their biochemical patterns eve n in early stages of differentiation.