Kreuzwieser Jürgen, Rennenberg Heinz
Albert-Ludwigs-Universität Freiburg, Institute für Forstbotanik und Baumphysiologie, Am Flughafen 17, 79085 Freiburg, Germany.
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New Phytol. 1998 Oct;140(2):319-329. doi: 10.1046/j.1469-8137.1998.00266.x.
Beech nuts (Fagus sylvatica L.) were germinated and grown in soil inoculated with the ectomycorrhizal fungus Laccaria laccata or Paxillus involutus for 18-20 wk. The success of mycorrhizal infection was monitored by measuring the ergosterol contents of the mycorrhizas. Ergosterol levels ranged from 122±23 μg g d. wt (Laccaria mycorrhizas) to 94±36 μg g d. wt (Paxillus mycorrhizas), indicating that ectomycorrhizal symbiosis was established. In root incubation chambers, rates of sulphate uptake and the xylem loading of sulphate of excised mycorrhizas were investigated. Both types of mycorrhizas showed saturation kinetics in external sulphate concentrations from 2·5-1000 μmol l . Linearization of these kinetics revealed two phases with low apparent K (Laccaria mycorrhizas: 15±3 μmol l ; Paxillus mycorrhizas: 13±3 μmol l ) and V (Laccaria mycorrhizas: 19±3 nmol h g f. wt; Paxillus mycorrhizas: 25±4 nmol h g f. wt) at low external sulphate concentrations and significantly higher kinetic constants at higher sulphate supplies. Relative xylem loading, i.e. the portion of sulphate loaded into the xylem that was taken up, remained constant over the entire concentration range investigated (c. 4-7% of the sulphate taken up). If trees were supplied for 72 h with different N and sulphur concentrations, both uptake of sulphate and relative xylem loading were unaffected by sulphur availability, but modulated by N supply. Nitrogen depletion diminished the rates of sulphate uptake in Laccaria and Paxillus mycorrhizas. In response to higher N availability combined with sulphur depletion, sulphate uptake of Laccaria mycorrhizas, but not of Paxillus mycorrhizas, increased. Organic compounds considered to be possible signals for the regulation of sulphate uptake were fed to excised mycorrhizas. l-Cysteine but not l-methionine and glutathione (γ-Glu-Cys-Gly) inhibited sulphate uptake of the two mycorrhizas and xylem loading of sulphate was stimulated rather than inhibited by l-Cys in both types. In Paxillus mycorrhizas glutathione had a similar effect. O-Acetyl-l-serine (OAS), a precursor of l-cysteine, stimulated sulphate uptake, but did not affect xylem loading. Apparently, OAS, generated in N metabolism, and l-cysteine, a product of assimilatory sulphate reduction, act as antagonists, together mediating regulation of sulphate uptake.
将欧洲山毛榉坚果（Fagus sylvatica L.）在接种了外生菌根真菌乳白红菇（Laccaria laccata）或卷缘桩菇（Paxillus involutus）的土壤中发芽并生长18 - 20周。通过测量菌根中的麦角固醇含量来监测菌根感染的成功情况。麦角固醇水平范围从122±23μg g干重（乳白红菇菌根）到94±36μg g干重（卷缘桩菇菌根），表明已建立外生菌根共生关系。在根培养室中，研究了离体菌根的硫酸盐吸收速率和硫酸盐的木质部装载情况。两种类型的菌根在外部硫酸盐浓度为2.5 - 1000μmol l时均表现出饱和动力学。这些动力学的线性化揭示了两个阶段，在低外部硫酸盐浓度下具有低表观K值（乳白红菇菌根：15±3μmol l；卷缘桩菇菌根：13±3μmol l）和V值（乳白红菇菌根：19±3 nmol h g鲜重；卷缘桩菇菌根：25±4 nmol h g鲜重），而在较高硫酸盐供应时动力学常数显著更高。相对木质部装载，即装载到木质部中的硫酸盐占吸收的硫酸盐的比例，在整个研究的浓度范围内保持恒定（约为吸收的硫酸盐的4 - 7%）。如果给树木供应不同氮和硫浓度72小时，硫酸盐吸收和相对木质部装载均不受硫有效性的影响，但受氮供应的调节。氮缺乏降低了乳白红菇和卷缘桩菇菌根的硫酸盐吸收速率。响应于较高的氮有效性与硫缺乏相结合，乳白红菇菌根的硫酸盐吸收增加，但卷缘桩菇菌根的未增加。将被认为可能是调节硫酸盐吸收信号的有机化合物添加到离体菌根中。L - 半胱氨酸而非L - 甲硫氨酸和谷胱甘肽（γ - Glu - Cys - Gly）抑制了两种菌根的硫酸盐吸收，并且在两种类型中L - Cys均刺激而非抑制了硫酸盐的木质部装载。在卷缘桩菇菌根中谷胱甘肽有类似作用。L - 半胱氨酸的前体O - 乙酰 - L - 丝氨酸（OAS）刺激了硫酸盐吸收，但不影响木质部装载。显然，在氮代谢中产生的OAS和同化硫酸盐还原的产物L - 半胱氨酸作为拮抗剂，共同介导硫酸盐吸收的调节。
