Bertrand Annick, Prévost Danielle, Bigras Francine J, Castonguay Yves
Agriculture and Agri-Food Canada, 2560, Soils and Crops Research and Development Centre, 2560 Hochelaga Boulevard, Quebec, Quebec, G1V 2J3, Canada.
Ann Bot. 2007 Feb;99(2):275-84. doi: 10.1093/aob/mcl254. Epub 2007 Jan 11.
The objective of the study was to assess the impact of elevated CO2 in interaction with rhizobial strains on freezing tolerance and cold-induced molecular changes in alfalfa.
Alfalfa inoculated with two different strains of rhizobium (A2 and NRG34) was grown and cold acclimated (2 weeks at 2 degrees C) under either 400 (ambient) or 800 micromol mol(-1) (elevated) CO2.
Plants acclimated under 400 micromol mol(-1) CO2 were more freezing tolerant than those maintained under 800 micromol mol(-1). Cryoprotective sugars typically linked with the acquisition of freezing tolerance such as sucrose, stachyose and raffinose increased in roots in response to low temperature but did not differ between CO2 treatments. Similarly high CO2 did not alter the expression of many cold-regulated (COR) genes although it significantly increased the level of transcripts encoding a COR gene homologous to glyceraldehyde-3-phosphate-dehydrogenase (GAPDH). A significant effect of rhizobial strain was observed on both freezing tolerance and gene expression. Plants of alfalfa inoculated with strain A2 were more freezing tolerant than those inoculated with strain NRG34. Transcripts of COR genes homologous to a pathogenesis-related protein (PR-10) and to a nuclear-targeted protein were markedly enhanced in roots of alfalfa inoculated with strain A2 as compared with strain NRG34. Transcripts encoding the vegetative storage proteins (VSPs) beta-amylase and chitinase were more abundant in roots of non-acclimated plants inoculated with strain NRG34 than with strain A2.
Taken together, the results suggest that elevated CO2 stimulates plant growth and reduces freezing tolerance. The acquisition of cold tolerance is also influenced by the rhizobial strain, as indicated by lower levels of expression of COR genes and sustained accumulation of VSP-encoding transcripts in alfalfa inoculated with strain NRG34 as compared with strain A2.
本研究的目的是评估升高的二氧化碳与根瘤菌菌株相互作用对苜蓿抗冻性及冷诱导分子变化的影响。
接种两种不同根瘤菌菌株（A2和NRG34）的苜蓿在400（环境浓度）或800 μmol mol⁻¹（升高浓度）二氧化碳条件下生长并进行冷驯化（2℃下2周）。
在400 μmol mol⁻¹二氧化碳条件下驯化的植株比在800 μmol mol⁻¹条件下的植株更耐冻。通常与获得抗冻性相关的低温保护糖，如蔗糖、水苏糖和棉子糖，在根中因低温而增加，但在不同二氧化碳处理之间没有差异。同样，高浓度二氧化碳虽然显著增加了与甘油醛-3-磷酸脱氢酶（GAPDH）同源的一个COR基因的转录本水平，但并未改变许多冷调节（COR）基因的表达。观察到根瘤菌菌株对耐冻性和基因表达均有显著影响。接种A2菌株的苜蓿植株比接种NRG34菌株的更耐冻。与NRG34菌株相比，接种A2菌株的苜蓿根中与病程相关蛋白（PR-10）同源的COR基因和与核靶向蛋白同源的COR基因的转录本显著增强。接种NRG34菌株的未驯化植株根中编码营养贮藏蛋白（VSP）的β-淀粉酶和几丁质酶的转录本比接种A2菌株的更丰富。
综合来看，结果表明升高的二氧化碳刺激植物生长并降低抗冻性。与接种A2菌株的苜蓿相比，接种NRG34菌株的苜蓿中COR基因表达水平较低以及VSP编码转录本持续积累，这表明根瘤菌菌株也会影响耐寒性的获得。
