Báo cáo lâm nghiệp: " Assessment of the contributions of glycolysis and the pentose phosphate pathway to glucose respiration in ectomycorrhizas and non-mycorrhizal roots of spruce (Picea abies L. Karsten)"

Chia sẻ: Nguyễn Minh Thắng | Ngày: | Loại File: PDF | Số trang:4

Thêm vào BST

Báo xấu

55
lượt xem 5
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Assessment of the contributions of glycolysis and the pentose phosphate pathway to glucose respiration in ectomycorrhizas and non-mycorrhizal roots of spruce (Picea abies L. Karsten)...

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Báo cáo lâm nghiệp: " Assessment of the contributions of glycolysis and the pentose phosphate pathway to glucose respiration in ectomycorrhizas and non-mycorrhizal roots of spruce (Picea abies L. Karsten)"

Assessment of the contributions of glycolysis and the pentose phosphate pathway to glucose respiration in ectomycorrhizas and non-mycorrhizal roots of spruce (Picea abies L. Karsten) V. Guillot, F. Martin F. Le Tacon I. Bilger, Laboratoire de Microbiologie Forestiere, Centre de Recherches Forestieres de Nancy, Institut National de la Recherche Agronomique, Champenoux 54280 Seichamps, France roots. The substrate used well as the Introduction as in this pro- pathways potentially involved not known. cess are importance of carbon supply in The The aim of this study was to determine mycorrhizal infection and symbiotic activity the relative contribution of glycolysis and has long been recognized. The supply of the pentose phosphate pathway to glu- carbohydrates by the higher plant to the oxidation in Norway (Picea cose spruce fungus is a very basic trait of mycorrhizal abies) ectomycorrhizas. symbiosis. Mycorrhizal plants assimilate more photosynthates than non-mycorrhi- zal ones, allocate a greater fraction of the assimilated carbon to the root systems Materials and Methods and lose a greater fraction of the assimi- lated carbon to respiratory C0 than do 2 non-mycorrhizal plants (for a review, see Plant material Martin et al., 1987). The establishment of Four year old plants of Picea abies L. Karsten, a carbon sink by the ectomycorrhizal grown on a sandy soil, were sampled from hyphae may be attained by: 1 ) rapid car- a commercial bare-roots nursery (Merten, bohydrate degradation for respiration and Vosges, eastern France). The plants were removed with attached soii, stored at 4°C and for energy and reducing power production transferred to the laboratory. The root systems and 2) conversion of plant carbohydrates were washed with tap water and all soil par- into fungal biomass. The high respiration ticles were removed. The pyramidally branched rate of fungal tissues has been pointed out ectomycorrhizas were pale brown, racemose with a prosenchymatous sheath, a thin mantle by several authors (France and Reid, and an extensive Hartig net reaching to the 1983). Most studies of mycorrhizal respi- endodermis. There abundant extramatric- were ration deal with mitochondrial respiration. mycelia (Hebeloma sp.) interconnected with al Much less is known about the oxidative loosely woven, pale yellow mycelial cords (see metabolism of glucose in mycorrhizal Fig. 1 in Al-Abras et al.. 1988; Dell et al., 1989).
Assuming that the same chitin/protein ratio streptomycin and 0.008% (w/v) aureomycin. Soluble compounds were then extracted ac- in the mycelial cords of Hebeloma sp. occurs cording to A[-Abras et aL (1988) and radio- and the fungal component of the ectomycorrhi- zas, then approximately 50% of the protein in activity determined by counting 100 ul aliquots. Chitin was determined by measuring the the ectomycorrhizas is fungal (Dell et al., 1989). amount of fungal glucosamine resulting from hydrolysis of chitin in mycorrhizal roots and acid mycelial cords using the method of Vignon et Radiorespirometry al. (1986). A radiorespirometry study was performed using ectomycorrhizal subsamples and the non- Statistical analysis mycorrhizal apices of exploratory roots. This was done using a 10 ml continuous !4C02- presented as means of 4 or 6 repli- Data are evolving and -trapping reaction flask. About 50 cates. Variance analysis or mean comparison mg of fresh tissue were incubated in 5 ml of performed on the logarithm of the per- was distilled water containing 10 nmol of [1- C] 14 centages or ratios. glucose or 11 nmol of [6- for 90 min C]glucose 14 at 22°C. Experiments were started by the ad- dition of 0.5 !Ci (10.0 nmol) of suitably labeled Theoretical [!4C]glucose. An airflow of 200 ml-min- was 1 maintained and 14 was collected for 90 min. 2 CO Effluent air was passed directly into a C0 -trap- 2 The approach used is based on the assumption ping scintillation fluid containing an organic that the initial yield of !4C02 from [1- C]glu- 14 amine (Carbomax, Kontron) in 10 ml vials and cose represented glycolysis and the pentose counted using a scintillation counter (Betamatic phosphate pathway, whereas that from [6- I, Kontron). Residual radiolabel in the flask was 14 represented only glycolysis (Ap C]glucose determined by counting aliquots. Antibiotics Rees, 1980). The following set of equations were added to the incubation solution at the enables the contribution of the pentose phos- following concentrations to prevent bacterial phate pathway (PPP) to be calculated. activity: 0.02% (w/v) penicillin, 0.04% (w/v) (1 -specific yield of !4CO2 from [6-!4Cjglucose)
Results and Discussion phate pathway and/or mannitol cycle (Martin et al., 1985). an incubation period of 90 min in The Using radiorespirometric method was labeled glucose, the C6/C1 ratios, R, and applied to non-mycorrhizal exploratory R (Table I), were found to range from roots and young mycorrhizas. Both non- 2 0.10 to 0.13 for mycorrhizal roots and 0.30 mycorrhizal roots and ectomycorrhizas to 0.43 for non-mycorrhizal ones. The low showed virtual simultaneous emission of C6/C1 ratios of the mycorrhizal roots sug- !4C02 from [1- and [6-!4C]glucose 4C]- 1 gests a high activity of the pentose phos- with similar patterns (data not shown). phate pathway. The level of C0 released 2 These data indicated the operation of from [6-!4CJgl!ucose was always compara- more than one oxidative pathway. The tively lower. In non-mycorrhizal explorato- rapid and predominant release of 14 2 CO ry roots, 38% of the carbohydrate oxida- from [1-1 coupled with low C]glucose 4 tion was via the pentose phosphate emission from [6-!4C]glucose, in both pathway and 62% was via glycolysis. On samples, implied both a minor role of the the other hand, 50% of the glucose me- tricarboxylic acid cycle and relatively low tabolism from mycorrhizal roots was cata- recycling of labeled glucose through the lyzed by the pentose phosphate pathway, non-oxidative part of the pentose phos-
changes in the respective demonstrating that the carbohydrate oxi- or enzymes amounts during ectomycorrhi- dative pathways are drastically altered in polypeptide formation must await further analysis. response to fungal colonization of the root. za To determine the distribution of the two catabolic pathways, mycorrhizal roots were further separated into extramatrical hyphae, symbiotic root tissues (mantle, References Hartig net hyphae plus root cortex) and stele. The contribution of the pentose Bilger I., Martin F., Le Tacon F. & Al-Abras K., phosphate pathway was different in the (1988) Morphological and physio- Lapeyrie F. various mycorrhizal tissues, being higher logical changes in ectomycorrhizas of spruce in symbiotic tissues (49.2%) and extrama- [Picea excelsa (Lam.) Link] associated with trical hyphae (46.5%) (Table II). The ageing. New Phytot 110, 535-540 contribution of the pentose phosphate Ap Rees T. (1980) Assessment of the contribu- pathway in the stele of mycorrhizal roots tions of metabolic pathways to plant respiration. In: The Biochemisfry of Plants, A Comprehen- was identical to that of whole non-mycor- sive Treatise. VoL 2 Metabolism and Respira- rhizal roots and accounted for 40%. tion. (Stumpf P.K. & Conn E.E., eds.), Academic These differences between mycorrhizas Press, London, pp. 1-27 and non-mycorrhizal roots and between Dell B., Botton B., Martin F. & Le Tacon F. fungal and host tissues suggest that the (1989) Glutamate dehydrogenases in ectomy- contribution of the pentose phosphate corrhizas of spruce [Picea excelsa (Lam.) Link] and beech (Fagus sylvatica L.). New Phytol. pathway to respiration is higher in the fun- 111, 683-692 gal component than in the plant tissues. France R.C. & Reid C.P.P. (1983) Interactions The fact that the pentose phosphate path- of nitrogen and carbon in the physiology of higher in root tis- activity was even way ectomycorrhizae. Can. J. Bot. 61, 964-984 sues colonized by the fungal cells (mantle Kottke I. & Oberwinkler F. (1986) The cellular and Hartig net) than in extramatrical structure of the Hartig net: coenocytic and hyphae suggests that the contribution of Nord. J. Bot. 7, transfer cell-like organization. this oxidative pathway is stimulated when 85-95 the root is associated with a symbiotic fun- Martin F., Canet D. & Marchal J.P. (1985) !3C gus. This increase in the pentose phos- nuclear magnetic resonance study of mannitol phate pathway activity may be related to cycle and trehalose synthesis during glucose the higher metabolic activity of the Hartig utilization by the ectomycorrhizal ascomycete Cenococcum graniforme. Plant Physiol. 77, net revealed by ultrastructural studies of 499-502 the host-fungus interface (many mito- Martin F., Ramstedt M. & S6derhA[l K. (1987) chondria and ribosomes, extensive devel- Carbon and nitrogen metabolism in ectomycor- opment of the endoplasmic reticulum, lack rhizal fungi and ectomycorrhizas. Biochimie 69, of large vacuoles) (Kottke and Oberwink- 569-581 ler, 1986). Vignon C., Plassard C., Mousain D. & Salsac L. Whether there is an increase in the ac- (1986) Assay of fungal chitin and estimation of mycorrhizal infection. PhysioL V6g. 24, 201-207 tivity of the pentose phosphate pathway