Báo cáo lâm nghiệp: "Comparison of nitrogenase and nitrate reductase activities in two nitrogen-fixing tree species: black alder (Alnus glutinosa) and black locust (Robinia pseudoacacia)"

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Nội dung Text: Báo cáo lâm nghiệp: "Comparison of nitrogenase and nitrate reductase activities in two nitrogen-fixing tree species: black alder (Alnus glutinosa) and black locust (Robinia pseudoacacia)"

Comparison of nitrogenase and nitrate reductase activities in two nitrogen-fixing tree species: black alder (Alnus glutinosa) and black locust (Robinia pseudoacacia) 1 Boutekrabt G. Pizelle S. Benamar F. 1 1 G. 2 Thiéry I Laboratoire de Physiologie Végétale et Forestibre, Facult6 c/es Sciences, BP 239, 54506 Vand&oelig;uvre-Iès-Nancy Cedex, and 2 Physiologie V6g6tale, ENSAIA, 54500 !anda°wre-/e5-/B/ancy. France Introduction desire to progress urst, 1983); hence, our understanding of its physiology. in In an extension of our work on nitrogen nutrition of A. glutinosa (e.g., Pizelle and the symbiotic nitrogen-fixing Among trees Thiéry, 1986), the present paper examines of the temperate zone, black alder (Alnus and nitrate reductase the nitrogenase glutinosa, L. Gaertn.) and black locust ac- tivities, measured in vivo, in R. pseudoa- (Robinia pseudoacacia L.) can be re- cacia and compares them with the data garded as typical actinorhizal (frankial) from A. glutino!;a. and leguminous (rhizobial) woody species, respectively. Important differences be- tween both species concern their biologi- cal, ecological and symbiotic characteris- Materials and IMethods tics, and the greater amount of work recently devoted to A. glutinosa, which likely prevails over R. pseudoacacia on Plant material was harvested in the early afternoon from 1 yr old black alders natu- 3-20 ! the following grounds: ubiquity in Europe, rally growing on sandy alluvium and from black better sylvicultural qualities, absence of locusts planted for about 10 yr on a sandy and spines and suckers, easier collection of stony bank; both sites were located on a sili- the nitrogen-fixing organs, attraction to the ceous substrate in the Moselle valley near recently recognized actinorhizal Nancy. more symbiosis (Tjepkema et al., 1986). Never- Nitrogenase (t’BI2ase) activity was assayed by the C reduction method on excised actino- H 2 theless, R. pseudoacacia is also a tree of rhizal lobes of alder and on excised nodules of interest both for its role as symbiont in black locust. Nitrate reductase (NR) activities nitrogen fixation and for its potential value were assayed on 5 mm sections of small roots as timber and wood fiber source (Moiroud (diameter11 mrr!; 100 mg fresh tissue) and on and Capellano, 1982; Turvey and Smeth- disks of young fully expanded leaves (diameter:
disks). The root samples were autumn than in R. pseudoacacia. During 12 mm; 2 infiltrated in 2.5 ml of 0.1 M NaK phos- vacuum the growing season, N activity of the ase 2 phate buffer, pH 7.5, with or without 0.05 M nodules of R. pseudoacacia reached KN0 After incubation for 1 h at 30°C in the . 3 higher values than that of the actinorhizas dark, 1.5 ml of incubation medium were cleared of A. glutinosa (Fig. 1This difference by addition of 0.3 ml of 1 M Zn acetate and cen- trifugation. In the leaf NR assays, Triton X-100 might be explained by the following char- was added (0.1%, v/v) to the incubation acteristics: most nodules of black locust medium and clearance of Zn acetate was not were less than 1 yr old with a large vol- necessary. The nitrite concentrations of the NR ume of inner tissues invaded by the active incubation media and soil nitrate content were determined as described by Pizelle and Thi6ry bacteroids, whereas the alder actinorhizas (1986). included lobes of various ages (often more than 1 yr old) with the tissues containing the active vesicles of Frankia limited to the subapical cortical region. Results NR activity of the small roots ase 2 N activity In A. glutinosa the enzyme activity started Root NR activity of both species did not earlier in spring and disappeared later in disappear in winter (Fig. 2). The enzyme
and the soil nitrate content of the black locust likely accumulated nitrate, activity relevant site showed higher values in A. since the NR activities measured with and without KN0 in the incubation medium glutinosa than in R. pseudoacacia. In 3 contrast with the alder roots, the roots of were similar. . 1 30 hI .
Discussion and Conclusion At the A. glutinosa site, higher values of soil nitrate content and of enzyme activity were measured during the growing sea- Though the age of the trees and the na- son, but no significant correlation (r= = ture or nitrate content of the soil differed 0.25; n = 21 ) was found between these respective sites ofeach spe- between the parameters. cies, the present data reveal char- some acteristics of the in vivo ase and NR 2 N activities in field-grown A. glutinosa and activity of the leaves NR R. pseudoacacia. N activity of the actinorhizas of A. ase 2 Previous experiments showed that the leaf glutinosa lasted longer but reached lower NR activity of field-grown A. glutinosa was values than that of the nodules of R. high after bud opening in the spring, then the growing season. pseudoacacia during decreased during the growing season, These differences are probably related to before disappearing at the leaf fall; the the length of the period of active photo- presence of this NR activity was found to synthesis and to the anatomical structure be independent of the supply of nitrate to of the nitrogen-fixing organs in each spe- the leaves via the xylem sap (Pizelle and cies. Since N activity is measured per ase 2 Thi6ry, 1977 ). ;986 mg dry weight of actinorhiza or nodule, further data, such as the mass of symbio- From the present data (Table I), it tic organs per tree, would be necessary to appears that field-grown R. pseudoacacia compare the nitrogen-fixing potential of also had a notable leaf NR activity; the the trees of both species. values were lower in spring than in sum- The presence of a root NR activity in mer, unlike the pattern observed in A. glu- winter indicates the persistence of the tinosa. It is presently unknown whether enzyme and reducing power in the roots the variations of the leaf enzyme activity out of the growing season. Since nitrate were controlled by the nitrate supply under was found in the soil, even in winter, it field conditions. However, assays using might suffice to maintain a nitrate-indu- young nodulated black locusts grown on cible NR activity in the roots throughout nutrient solution without nitrate showed an the year. The presence of non-reduced increase of their leaf NR activity from nitrate in the roots of R. pseudoacacia, in 0.78 ± 0.16 to 3.23 ± 1.15 nmol N02 !mg-! 1 DW-h- (means of 4 samples ± SE) after 3 spite of a low nitrate content in the soil, indicates a limited root NR activity in this days of 4 mM NaNO supply. 3
In A. glutinosa, the negligible species. References accumulation of nitrate in the roots and the absence of a close correlation bet- Moiroud A. & Capellano A. (1982) Le robinier, ween root NR activity and soil nitrate Robinia pseudoacacia L., une espbce fixatrice content suggest that the roots have an NR d’azote int6ressante ? Ann. Sci. For. 39, 407- capacity able to reduce higher amounts of 418 nitrate than those available in the soil. Pizelle G. & Thiéry G. (1977) Variations saison- The seasonal profile of the leaf NR ac- nieres des activites nitrogenase et nitrate reductase chez I’aune glutineux (Alnus glutino- tivity of A. glutinosa appears to be inde- sa L. Gaertn.). Pl Veg. 15, 333-342 ysiol. 1 pendent of the nitrate supply; it decreases from the early leaf expansion to the Pizelle G. & Thièry G. (1986) Reduction of ni- trate in the perennial tissues of aerial parts of approach of the leaf fall. In R. pseudoa- Alnus glutinosa. Phys;b/. Plant. 68, 347-352 cacia the leaf NR activity shows a different profile with values lower in spring and Tjepkema J.D., Schwintzer C.R. & Benson D.R. (1986) Physiology of actinorhizal nodules. higher in summer. Given the results ob- Annu. Reu. Plant Physiol. 37, 209-232 tained from young laboratory-grown plants Turvey N.D. & Smethurst P.J. (1983) Nitrogen as well as the presence of a limited ni- fixing plants in forest plantation. In: Biological trate-reducing capacity of the roots, it can Nitrogen Fixation in Forest Ecosystems: Foun- be proposed that the leaves of R. pseu- dations and Applications. (Gordon J.C. & doacacia have an NR activity commensu- Wheeler C.T., eds.), Martinus Nijhoff, The rate with their supply of nitrate. Hague, pp. 233-260