G. Auderset

Glucose-6-phosphate dehydrogenase as an early marker of floral induction in shoot apices of spinacia oleracea var. nobel

Abstract Quantitative cytochemical studies on apices from 4-week-old plants of Spinacia oleracea show that there is an increased glucose-6-phosphate dehydrogenase (G-6-PD) activity in shoot apices from plants transferred from short days (8 h white light) to continuous illumination for 15–24 h. A doubling of the rate of activity occurs in some apices at 15 h and in all apices by 17 h, the higher rate being maintained during the longer periods of illumination up to 24 h. The activity is not significantly affected if the plants are returned to the dark for a further 8 h. This indicates a permanently increased activity of the pentose phosphate pathway and is the earliest reported change in the shoot apex during floral induction. The pathway may be involved in supplying intermediates required for biosynthesis of e.g. membrane components.

Highly Purified Tonoplast Fractions by Preparative Free-Flow Electrophoresis

For the preparation of tonoplasts, the different approaches followed include isolation from homogenates by density gradient fractionation or from vacuoles prepared from protoplasts by osmotic lysis (Wagner, 1983). For our studies, we have used preparative free-flow electrophoresis, a procedure whereby highly purified fractions of both plasma membrane and of tonoplast are obtained from the same homogenate (Sandelius et al., 1986; Auderset et al., in press). In this technique, based on the methodology of Hannig and coworkers (Hannig and Heidrich, 1977), a mixture of components to be separated is introduced into a separation buffer moving perpendicular to the flux lines of an electric field (Fig. 1). Membranes bearing different electrical charge densities will migrate different distances across the separation chamber and thus may be resolved.

The relationship between the activities of the pentose phosphate pathway and glycolysis during early stages of floral induction in spinach.

SummaryA quantitative cytochemical study was made of fructokinase, glucokinase, and fructokinase (both PFK-ATP and PFK-PP+F-2:6-P) activities in shoot apices of 4-week old Spinacia oleracea. The rates of activity of these enzymes in the central zone of the shoot apex of plants kept on a short day regime were compared with those from plants transferred from a range of timing up to 24 h to a continuous light regime when floral induction occurred. A mechanism is suggested explaining how no measurable change in activities of the enzymes assayed could still account for the availability of adequate levels G-6-P as substrate for pentose pathway activity which is almost doubled early on in cells of the central zone of shoot apices induced to flower.

Plasma Membrane and Tonoplast Fractions Isolated from Spinach Leaves by Preparative Free Flow Electrophoresis: Effect of Photoinduction

A change in membrane structure as a result of photoinduction of the flowering response in plants was predicted from physiological studies (Penel and Greppin, 1974; Lenk et al., 1981; Karege et al., 1982). With the availability of purified fractions of plasma membrane and tonoplast from green leaves (Auderset et al., in press), a study was initiated to examine these membranes for structural and compositional changes associated with photoinduction. Spinach (Spinach oleracea) was investigated as an example of a species induced to flower by continuous light (so-called long-day plant) and Japanese morning glory (Pharbitis nil) as an example of a plant photoinduced by a long night (so-called short-day plant).