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Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Toprak Anabilim Dalı, 2009. / Kaynakça var.

In the soybean nitrogen fixing symbiosis, suboptimal root zone temperatures (RZTs) inhibit the inception and development of nodules, leading to reduced nitrogen fixation and soybean yield. The purpose of this thesis was to evaluate the effects of selected with potential low temperature tolerant strains, originating from the northern areas of the USA, and mutants made from Bradyrhizobium japonicum USDA 110, on soybean nodulation, nitrogen fixation and yield in a short season area with cool spring conditions. Among the 40 B. japonicum strains evaluated, only USDA 30, USDA 31, 532 C and USDA 110 grew well at 15°C. USDA 30 and USDA 31 grew better than 532 C and USDA 110 at 15°C. Mutants Bj 30050--Bj 30059 could not produce lipo-chito-oligosaccharide (LCO) at measurable levels in the absence of genistein. All mutants produced more LCOs than 532 C and USDA 110 at the same temperature and genistein concentration. Temperature and genistein concentration did not affect LCO production dynamics for the following: mutant Bj 30055, 532 C and USDA 110. Both mutant production and identification of low temperature tolerant strains achieved the general objective of improved soybean nitrogen fixation in a cool climate. Inoculation with low temperature tolerant strains (USDA 30, USDA31), or mutants (Bj 30055 and Bj 30058) improved soybean development (increases in leaf area and shoot nitrogen content), nodulation (increases in nodule number and nodule weight), nitrogen fixation and yield relative to inoculation with B. japonicum strain 532 C, the strain currently included in most Canadian soybean inocula.

Nod factors, lipo-chitooligosaccharides (LCOs), are rhizobial signal molecules important in the establishment of nodule formation, leading to atmospheric dinitrogen fixation in legume-rhizobium symbioses. Recently, LCOs were also found to regulate other plant processes. We demonstrated that, at 10 -6 M, four LCOs produced by Bradyrhizobium japonicum enhanced soybean seed germination. Evaluation of G-protein inhibitors showed that U-73122, a phospholipase C inhibitor, also increased soybean seed germination, similar to the increase by LCO NodBj-V(C18:1 MeFuc), indicating different mechanisms for the plant perception to LCOs for nodule initiation and seed germination. This was confirmed as LCOs were not able to break dormancy of skotodormant lettuce seeds. Soybean early seedling growth was also increased by the application of LCOs. Pulse 14Ca2+ experimentation showed that the increase might also be related to an increase in Ca 2+ uptake by shoots. We confirmed this with both genistein-induced and non-induced B. japonicum 532C; however, strain 168 (a mutant unable to produce LCO) and non-host rhizobia (Rhizobium leguminosarum, Sinorhizobium meliloti), did not increase Ca2+ uptake. Addition of 1.6 g L-1 casein hydrolysate in yeast extract mannitol broth drastically increased bacterial growth and increased volume-basis LCO production, but decreased LCO production per cell. Best conditions for sterilizing and storing LCOs were determined. LCO should be sterilized by using polyestersulfone filter or autoclaving for up to 30 minutes. LCO was degraded faster when stored at room temperatures (23 +/- 2°C) than low temperature (4 +/- 1°C) and can be stored more than one year.

Jasmonic acid (JA) and its methyl ester, methyl jasmonate (MeJA), collectively termed as jasmonates, are naturally occurring in plants and are important signal molecules involved in induced disease resistance and stress responses of plants. Besides their role in-planta, they are also rhizosecreted by root cells. Germinating soybean seeds exude large quantities of jasmonic acid; however there is no knowledge regarding how jasmonates influence cells of the soybean symbiont, Bradyrhizobium japonicum, in the rhizosphere. We studied the role of jasmonates in the soybean-Bradyrhizobium symbiosis. Bradyrhizobium japonicum cultures were induced with jasmonates and the resulting Nod factors were isolated and purified. Our results showed that JA and MeJA strongly induced the production of Nod factors by the tested B. japonicum strains. When added together, genistein and jasmonates resulted in greater LCO production than either one alone. Jasmonic acid is produced from linoleic and linolenic acids via the octadecanoid pathway; we studied the effect of these two fatty acids on B. japonicum nod gene induction. Interestingly both linoleic and linolenic acids induced the nod genes and caused LCO production by B. japonicum cultures. Since jasmonates induced the nod genes and also caused LCO production in B. japonicum, I conducted experiments in the greenhouse and field to determine whether incubation of B. japonicum with JA or MeJA prior to inoculation increases soybean nodulation variables and grain yield. Both genistein and McJA increased nodule number and nodule dry weight per plant. Due to enhanced nitrogen fixation, attributed to increased nodule number and weight, soybean dry matter accumulation and grain yield were increased. These results document the discovery of jasmonates and their precursors as new signal molecules in the Bradyrhizobium - soybean nitrogen fixing symbiosis.

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