Báo cáo lâm nghiệp: "Carbon partitioning: fructose 2,6-bisphosphate content as an indicator of specific changes in carbohydrate metabolism in needles from class II spruce trees"

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Nội dung Text: Báo cáo lâm nghiệp: "Carbon partitioning: fructose 2,6-bisphosphate content as an indicator of specific changes in carbohydrate metabolism in needles from class II spruce trees"

Carbon partitioning: fructose 2,6-bisphosphate content as an indicator of specific changes in carbohydrate metabolism in needles from class II spruce trees W. Einig R. Hampp F.R.G. D-7400 Tobingen, Tubingen, Biochemie der Pflanzen, Auf der Morgenstelle 1, Universitit available about metabolic acclimation of Introduction tissues to pollutants. It has thus been our aim to screen for biochemical indications It has been shown that very low doses of of altered patterns of carbon allocation in airborne pollutants (ozone, sulfite) can needles of Norway spruce (Picea abies). significantly change source-sink relation- ships. These shifts in allocation or trans- portation out of leaves can occur prior to reductions in photosynthesis (ozone; Mcl_aughlin and McConathy, 1983) and Materials and Methods can take place within minutes (Minchin and Gould, 1986). In spite of intense research in this area, The materials used for our investigations were needles from spruce trees from 2 locations in there is, however, only little information
well as metatrolite analyses the southern part of the Black Forest (Kalbele- descri- were as as bed elsewhere (Einig and scheuer and Haldenhof, near Freiburg, F.R.G.). Hampp, 1988; Collection and freeze-drying of needle samples Hampp etaL, 1989).
control trees have optimum starch levels Results and Discussion in early summer (Fig. 2a). Independent of needle age, there is a continuous decline Season- and age-dependent variations in towards October. Sucrose, in contrast, is pool sizes much more constant in its seasonal pool sizes (Fig. 2b). There is considerable evidence that the There are, however, specific differences, rate of starch synthesis is controlled by when pool sizes of phosphorylated inter- the rates of sucrose formation and trans- mediates are compared. An intimate cor- port. relation between pool sizes of TP, F6P and F26BP is observed when the average Metabolites involved in the regulation of contents of all needles (1980-1985) are carbon partitioning between starch and plotted versus the sampling date (Fig. 3). sucrose are triose phosphates (TP; dihy- droxyacetone phosphate, glyceraldehyde Under the assumption that the changes 3-phosphate), glyceric acid 3-phosphate in pool sizes observed for F6P and TP (PGA), fructose 6-phosphate (F6P), ortho- also occur in the cytosol of our needle phosphate (P and pyrophosphate (PP ). i ) i mesophyll cells, all these observations Levels of these metabolites control syn- can easily be explained by the scheme thesis and degradation of the most impor- shown in Fig. 1. In June samples, e.g., tant regulator, fructose 2,6-bisphosphate starch, F6P and F26BP are high, while TP (F26BP). This compound affects cytosolic are low; high levels of F6P, possibly indi- sucrose synthesis by inhibiting the fruc- cative of limited sucrose export (rates of tose bisphosphatase (FBPase) reaction synthesis exceed rates of export), activate (gluconeogenesis) and activating a PP- i F26BP synthesis. Increased levels of dependent phosphofructokinase (PFP; ac- F26BP, however, favor glycolysis over glu- tive in both directions, glycolysis and glu- coneogenesis and thus TP are diverted coneogenesis (for a review see Stitt, into starch synthesis. In July, in contrast, 1987; compare also Fig. 1 ). opposite situation emerges with an decreased amounts of F6P and F26BP Sucrose and starch as ’endpoints’ of and high levels of TP. This metabolic this regulatory system show distinct dif- situation should thus be indicative of ferences in their pool sizes. Needles from
tween starch and sucrose will partitioning of carbon into precede any increased visible signs of damage. The determina- (starch decreases) and this situa- sucrose tion of F26BP levels in needles could is obviously continued during summer. tion constitute an early indicator of affected carbon allocation. Class li-specific changes in pool sizes There are also significant differences when the metabolite pools are compared Acknowledgments with respect to needle loss (Table I). The average metabolite contents of NS Help in sample aquisition, preparation for analy- needles from class 0 and class II trees sis and metabolite determination by L. Diener, (1980-1983; based on dry weight) differ B. Egger, R. Keil, J.P. Schnitzler and P. Weid- mann is gratefully acknowledged. This investi- significantly in the levels of starch, TP and gation was financed by grants from the ’Project F26BP, in that class II needles show a Europaisches Forschungszentrum fur Mass- decrease in starch, compared to in- nahmen zur Luftreinhaltung’ (PEF; 84/043/1A, creased amounts of TP and F26BP. In 86/018/1A (R.H.)). contrast, sucrose, glucose, fructose, PGA and F6P only show minor differences. Compared to the observations reported for control needles above, the situation in References class II needles is less straightforward to interpret. Einig W. & Hampp R. (1988) Der fructose 2,6- The most interesting change in concen- bisphosphat gehalt als indikator spezifischer tration is shown by F26BP. The significant- veranderungen im kohlenhydratstoffwechsel ly increased amount of this regulator will geschadigter fichtennadeln. KfK-PEF 35, Kern- forschungszentrum Karlsruhe Ber. 163-171 1 surely inhibit cytosolic FBPase and will thus largely reduce carbon flow towards Keil R. & Fink S. (1989) Hampp R., Einig W., Energy status and carbon partitioning in spruce: sucrose (compare Fig. 1 The elevated specific changes in relation to needle age and level of F6P, if cytosolic, could be respon- degree of needle loss. In: International Sympo- sible for this increase in F26BF sium on Plants and Pollutants in Developed and Developing Countries. (Öztürk M., ed.), Izmir, Turkey, pp. 487-508 McLaughlin S.B. & McConathy R.K. (1983) Conclusion Effects of S0 and 0 on allocation of 14 C- 2 3 labeled photosynthate in Phaseolus vulgaris. Plant Physiol. 73, 630-635 Needles from declining trees exhibit a Minchin P.E.H. & Gould R. (1986) Effects of increase of F26BP. This can be significant S0 on phloem loading. Plant Sci. 43, 179-183 2 taken as evidence for impaired sucrose Stitt M. (1987) Fructose 2,6-bisphosphate and export. As such, a metabolic response plant carbohydrate metabolism. Plant Physiol. towards altered carbon partitioning be- 84, 201-204