Ammonium-excreting Azospirillum sp. become intracellularly established in maize (Zea mays) para-nodules

Maize seedlings develop nodule-like tumour knots (para-nodules) along primary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Inoculated NH ₄ ⁺ -excreting Azospirillum brasilense cells were shown to colonize these tumours, mostly intracellularly, promoting a high level of N₂ fixation when microaerophilic conditions were imposed. The nitrogenase activity inside the para-nodules was less sensitive to free O₂ than in non-para-nodulating roots. Both light and electron microscopy showed a dense bacterial population inside intact tumour cells, with the major part of the cell infection along a central tumour tissue. The bacteria colonized the cytoplasm with a close attachment to inner cell membranes. In an auxin-free growth medium, young 2,4-D-induced para-nodules grew further to become mature differentiated root organs in which introduced bacteria survived with a stable population. These results provide evidence that gramineous plants are potentially able to create a symbiosis with diazotrophic bacteria in which the NH ₄ ⁺ -excreting symbiont will colonize para-nodule tissue intracellularly, thus becoming well protected.     

Endophytic establishment of Azorhizobium caulinodans through auxin-induced root tumors of rice (Oryza sativa L.)

Rice seedlings developed nodule-like tumors (para-nodules) along primary and secondary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Histologically, these tumors appeared as cancerous out-grown lateral-root primordes and were thus comparable with stem nodules of the legume Sesbania rostrata. Azorhizobium caulinodans (a diazotroph known as a specific endophyte of Sesbania rostrata) was introduced and became established inside rice para-nodules and in root tissues around tumor bases. The infection with A. caulinodans followed a typical crack-entry invasion at places where paranodule tumors had emerged through the root cortex and epidermis. The bacteria settled with high cell densities in intercellular spaces of the induced tumors and between root cortical cells. Infection of plant cells took place both in the epidermis and in cortical tissue. Intracellularly established A. caulinodans was found inside the cytoplasm, surrounded by membrane-like structures. N₂ fixation by tumor-inhabiting Azorhizobium sp. was increased at low O₂ tensions (1.5–3 kPa) compared with an untreated control. Only a little activity remained at O₂ tensions of 5 kPa and above. The present results confirm that root-tumor induction offers a suitable method of establishing diazotrophs endophytically in the roots of gramineous crops.     

4种植物生长激素对大果沙棘温室扦插成活率的影响

对沙棘品种(中俄杂交,中国无刺,向阳,楚伊,浑金)嫩枝扦插枝条用4种植物生长刺激素(吲哚丁酸,吲哚乙酸,α-奈乙酸,生根剂)配置成一定浓度溶液浸泡沙棘插条,筛选提高成活率的最佳试剂。试验结果表明:供试的4种刺激素中吲哚丁酸和生根剂处理的大果沙棘插条成活率较好,而供试的大果沙棘品种中浑金﹑向阳成活率较高较易扦插成活。     

N2-fixation by ammonium-excreting Azospirillum brasilense in auxine-induced root tumours of wheat (Triticum aestivum L.)

Summary Wheat seedlings, treated with the auxine 2,4-dichlor-phenoxy acetic acid (2,4-D) during germination developed only a residual root system. Root elongation was extremely restricted and root tips were deformed to thick club-shaped tumours. When 2,4-D was added in a later stage of plant growth the plants developed additional nodule-like knots along primary roots. Root and shoot dry-matter production was slightly repressed in all 2,4-D treatments and N translocation from roots to shoots was repressed as well. When transferred to an auxine-free growth medium, the 2,4-D-affected roots were not capable of complete recovery. In plants inoculated gnotobiotically with Azospirillum brasilense, either with the wild type or with the NH ₄ ⁺ -excreting mutant strain C3, a 2,4-D addition increased rhizosphere acetylene-reduction activity at pO₂ 1.5 kPa. The O₂ sensitivity of root-associated nitrogenase activity tended to be reduced. The number of root-colonizing bacteria, at approximately 10⁸ colony-forming units (cfu) per g dry root, was similar in the 2,4-D treatments and untreated controls. Plant treatment with high concentrations of the chemical isomer 3,5-dichlor-phenoxy acetic acid (3,5-D) did not have comparable effects, either on plant development or on rhizosphere-associated nitrogenase activity. Root-tumour tissue inhabited by A. brasilense showed purple staining when subjected to a tetrazolium chloride solution, which may indicate intensive local nitrogenase activity in this tissue. Exposed to an ¹⁵N₂-enriched atmosphere, plants treated with 2,4-D and with A. brasilense incorporated significantly higher amounts of ¹⁵N than untreated controls. In all cases the highest values of ¹⁵N enrichment were found following inoculation with the NH ₄ ⁺ -excreting mutant strain C3. Present address: F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, Willem de Croylan 42, B-3001 Heverlee, Belgium     

植物生长素在农业中的应用

介绍了植物生长素的作用机理、生理作用以及在农业中的应用。     

4种植物生长激素对大果沙棘温室扦插成活率的影响

对沙棘品种（中俄杂交,中国无刺,向阳,楚伊,浑金）嫩枝扦插枝条用4种植物生长刺激素（吲哚丁酸,吲哚乙酸,α-奈乙酸,生根剂）配置成一定浓度溶液浸泡沙棘插条,筛选提高成活率的最佳试剂。试验结果表明：供试的4种刺激素中吲哚丁酸和生根剂处理的大果沙棘插条成活率较好,而供试的大果沙棘品种中浑金﹑向阳成活率较高较易扦插成活。