Many different lines of evidence have established that ureides in stem exudate originate in nodules and represent the major export products of nitrogen fixation in soybean nodules. Soybean stem exudate can be collected in quantities large enough to permit analysis of individual carbon and nitrogen compounds. The changing spectrum of compounds can be very informative as to the response of the plant to various environmental influences, such as nitrogen nutrition. From the beginning of flowering to the last time when stem exudate could be obtained, ureides were the predominant nitrogenous compounds present. There are numerous precautions which should be taken in gathering and interpreting data on stem exudate composition. Because of multiple sites for storage and assimilation of nitrate, interpretation of exudate composition of nitrate-grown plants is complex and should be undertaken with considerable caution.

Cornish K, Kopicky SL, McNulty SK, Amstutz N, Chanon AM, Walker S, Kleinhenz MD, Miller AR, Streeter JG. 2016. Temporal diversity of Taraxacum kok-saghyz plants reveals high rubber yield phenotypes. Biodiversitas 17: 847-856. Taraxacum koksaghyz is a diploid, out-crossing, rubber-producing species under development as an alternative natural rubber crop. About 17,650 seed were obtained from progeny of 20 wild collected plants. New populations of plants were developed in Ohio from a random subsample of these seed, which were then open pollinated. In November 2011, these seed were direct seeded in outdoor shallow raised beds and in high tunnel deep raised beds. Plants were harvested from the outdoor beds from July 2012 to July 2013 to provide temporal phenotypic data as plants developed and overwintered. The high tunnel beds were harvested July 2013, and provided data on 11 individual accessions, and their progeny, and on the effect of winter bed heating. Plants were highly variable. Rubber concentration in root tissue was not directly correlated with root, shoot or plant size. Across all growing conditions and developmental stage, the highest rubber yields per plant were found in plants with large roots combined with a large rosette, and an above average rubber concentration. These parameters appeared to segregate independently, and rubber concentration was heritable. Interbreeding plants selected for large root, large rosette and then high rubber concentration, should rapidly move Taraxacum kok-saghyz towards domestication and commercialization.

Drought is the most significant limiting factor for plant cultivation. Greenhouse-grown 1-year-old potted M.9EMLA apple trees (Malus domestica Borkh.) (after growing for 6 weeks) were subjected to drought stress by withholding water for an additional six-week period. The photosynthesis, carbohydrates and the nitrogen (N), phosphorus (P) absorb in the upper, middle and lower leaves of the seedlings were determined. The results revealed that drought stress obviously decreased the photosynthesis and carbohydrates contents in the leaves at all sections of shoot compared with the control. Sorbitol and glucose concentrations increased over time and was kept at a higher level during the drought stress period whereas sucrose concentration declined. N content in the leaves kept a flat trend and was higher than that of the control while P concentration decreased compared with the control. These results demonstrated that drought stress prevented N and P absorbtion and decreased RWC of apple leaves, which caused the decline of photosynthesis and transpiration. Thus, the direct phenotype was the slowed growth which was specifically expressed in decreased plant height, number of leaves, average leaf area and stem diameter.

Soluble sugar accumulation was determined in the grape (Vitis spp.) cultivars Frontenac, Couderc 3309, Concord, Cabernet Franc, Traminette and Seyval grown under two temperature regimes. Shoot growth slowed under cold temperature regimes in all cultivars except Concord, which was the least responsive. Among all sugars, raffinose showed distinctive responses associated with the two temperature regimes. Under a non-acclimating temperature regime, raffinose concentrations were low and similar among cultivars, whereas under cold acclimating temperature regimes raffinose accumulation was generally higher, and cold-hardy cultivars accumulated higher concentrations than did cold-sensitive cultivars. Basal leaves and buds accumulated the most raffinose. Cabernet Franc vines exhibited no differences in sugar accumulation at different stages of development. The results suggest that raffinose accumulation might be an early step in the process of cold acclimation that coincides with slowed shoot growth, and may precede the onset of dormancy and freezing tolerance. Leaf raffinose concentration might be useful as a detection tool to distinguish various Vitis genotypes with contrasting freezing tolerance. Key words: Bud, cold acclimation, leaf, raffinose, Vitis

ABSTRACT The growth and persistence of rhizobia and bradyrhizobia in soils are negatively impacted by drought conditions. In this study, we used genome-wide transcriptional analyses to obtain a comprehensive understanding of the response of Bradyrhizobium japonicum to drought. Desiccation of cells resulted in the differential expression of 15 to 20% of the 8,480 B. japonicum open reading frames, with considerable differentiation between early (after 4 h) and late (after 24 and 72 h) expressed genes. While 225 genes were universally up-regulated at all three incubation times in response to desiccation, an additional 43 and 403 up-regulated genes were common to the 4/24- and 24/72-h incubation times, respectively. Desiccating conditions resulted in the significant induction (>2.0-fold) of the trehalose-6-phosphate synthetase ( otsA ), trehalose-6-phosphate phosphatase ( otsB ), and trehalose synthase ( treS ) genes, which encode two of the three trehalose synthesis pathways found in B. japonicum . Gene induction was correlated with an elevated intracellular concentration of trehalose and increased activity of trehalose-6-phosphate synthetase, collectively supporting the hypothesis that this disaccharide plays a prominent and important role in promoting desiccation tolerance in B. japonicum . Microarray data also indicated that σ 54 - and σ 24 -associated transcriptional regulators and genes encoding isocitrate lyase, oxidative stress responses, the synthesis and transport of exopolysaccharides, heat shock response proteins, enzymes for the modification and repair of nucleic acids, and the synthesis of pili and flagella are also involved in the response of B. japonicum to desiccation. Polyethylene glycol-generated osmotic stress induced significantly fewer genes than those transcriptionally activated by desiccation. However, 67 genes were commonly induced under both conditions. Taken together, these results suggest that B. japonicum directly responds to desiccation by adapting to changes imparted by reduced water activity, such as the synthesis of trehalose and polysaccharides and, secondarily, by the induction of a wide variety of proteins involved in protection of the cell membrane, repair of DNA damage, stability and integrity of proteins, and oxidative stress responses.

Although cyclitols are a major portion of carbohydrates in plants, surprisingly little is known about their metabolism. In the halophytic iceplant (Mesembryanthemum crystallinum), ononitol is produced through the action of inositol methyl transferase (IMT), which transfers the methyl group from S-adenosyl-l-methionine to myo-inositol. Through an epimerase reaction, ononitol is then converted to pinitol. In an attempt to modify and study cyclitol production in a pinitol-producing glycophytic plant, an imt gene from M. crystallinum was introduced into soybean (Glycine max (L.) Merr. cv. ‘Jack’) embryogenic tissue using particle bombardment. Southern and northern hybridization analyses showed that all of the transgenic clones contained a low copy number of the introduced plasmid DNA and imt mRNA was present. In transgenic embryogenic soybean tissues, ononitol levels were increased 10–80-fold compared to non-transgenic tissues. Pinitol was first produced late in somatic embryo development in both transgenic and non-transformed tissues, indicating that the epimerase responsible for the conversion of ononitol to pinitol was developmentally regulated. The increase in ononitol levels in transgenic developing embryos led to 2–6-fold higher pinitol levels in transgenic embryos compared to non-transformed tissues. In leaves from mature plants, however, pinitol levels were not significantly different bewteen imt-containing and non-transformed tissues.

Anthocyanins (Antho) are the source of red color in plants and the intensity of redness is an important quality parameter in red leaf lettuce. Despite the importance of Antho in leaf lettuce, little information is available regarding the effects of major production-related factors, such as planting date, on their levels. To address this issue, field studies were conducted in 2002 and 2003 in which Antho levels were measured in nine lettuce varieties planted in early and late summer (ES and LS, respectively) using a RCB design. Leaf tissue was sampled 30 d after transplanting. Data for three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', `Impuls') are reported here. The planting date × variety interaction was significant; however, Antho concentrations were higher following planting in LS than ES, regardless of variety. Planting date effects were more pronounced in 2002, when differences in average daily temperature between ES and LS plantings tended to be larger. Regardless of planting date and year, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations between human visual and two types of instrumented assessments of color are being tested in samples from the same study.

In addition to their physiological and metabolic roles, anthocyanin (Antho) levels in lettuce contribute to visual and nutritional value-based assessments of crop quality. Although 7 genes are now thought to help regulate Antho synthesis, deposition and/or degradation in lettuce, the genetic and abiotic controls of Antho levels remain less well characterized in lettuce than other plants. Previous greenhouse studies demonstrated that Antho levels in diverse lettuce varieties are a function of temperature and lighting regimen. Here, three strongly related Lolla Rossa-type varieties (`Lotto', `Valeria', and `Impuls') varying in the number of genes controlling intensity of anthocyanins were subjected to differential temperature conditions in growth chambers to better discern the independent and interactive effects of temperature (T) and variety (V) on Antho levels. Fifteen day-old seedlings were placed into one of three chambers maintained at 20 °C day/night (D/N), 30 °C/20 °C D/N or 30 °C D/N. Antho levels were measured in leaf tissue collected 30 d after transplanting. The entire experiment was replicated twice. Although significant, the T x V interaction resulted from differences in the magnitude, not direction, of the change in Antho concentrations among varieties with changes in T. This suggests that T was a main driver of Antho levels in this study. Regardless of V, Antho concentrations were highest, moderate and lowest after growth at 20 °C D/N, 30 °C/20 °C D/N and 30 °C D/N, respectively. Likewise, regardless of T, Antho levels followed the pattern `Impuls' (three genes) > `Valeria' (two genes) > `Lotto' (one gene). Correlations among instrumented and human eye-based evaluations of color are also being tested in samples from both studies.

Fe chelators produced by compost microorganisms in C enrichment culture can efficiently improve Fe nutrition of soybean and oat under slightly alkaline conditions. Little information is available, however, concerning the identity of these chelators. A study was conducted to identify the Fe chelators and the microorganisms responsible for their production and to evaluate the mechanism of Fe uptake by soybean of these Fe chelates. One Fe chelator predominated in the culture solution and, after purification using chromatography, it was identified by nuclear magnetic resonance and mass spectrometry as the siderophore, aerobactin. A strain of Citrobacter diversus, which produced a high concentration of aerobactin, was isolated and purified from the culture. Bathophenanthrolinedisulfonic acid (BPDS), an Fe2+ trap, did not decrease soybean uptake of Fe of which more than 90% was in the form of an Fe-aerobactin complex. Reduction of Fe as Fe-aerobactin by soybean roots was not detected. Iron uptake was, however, significantly (P similar to 0.05) inhibited by NaN3, a respiratory inhibitor. These results suggest that the Fe may have been taken up by soybean as an Fe-aerobactin complex through an active transport mechanism.

Conventional methods of soluble carbohydrate determination in soybean (Glycine max [L.] Merr. seeds involve time consuming and labour intensive extraction using organic solvents. In this study, a conventional plant tissue soluble carbohydrate extraction method using 75% ethanol was compared with a simultaneous extraction-derivatization in a pyridine-based reagent (pure pyridine and stox) for recovery of sugars and cyclitols in developing soybean seed axes. The comparison was performed in lyophilized or oven-dried tissue to determine the effect of oven drying on soluble carbohydrate recovery. The degree of polymerization and/or position in the oligosaccharide biosynthesis pathway was important in the response of sugars and cyclitols to both extraction methods. Pyridine was superior to ethanol extraction for reducing sugars, sucrose and free cyclitols. Ethanol was superior to pyridine extraction for sucrosyl oligosaccharides and galactosyl cyclitols. Pyridine is a more rapid, less costly, and convenient method for extraction of low molecular weight soluble carbohydrates in soybean seeds. For soluble carbohydrate quantification, this study suggests that the size of the soluble carbohydrate may determine whether pyridine or ethanol extraction is used. The better recovery of galactosyl cyclitols in oven-dried than lyophilized tissue has important implications for their determination in studies where heat drying or roasting is mandatory.

Iron availability to plants is often limited when soil pH is 7 or higher. In C rich, but Fe limiting environments, microorganisms may produce organic chelators that complex Fe and increase its availability to plants. Seedlings of soybean (Glycine max L.) and oat (Avena sativa L.) plants, with Fe-efficient or inefficient uptake mechanisms, were grown in an Fe free nutrient solution at pH 7.5. Experiments (using a complete factorial design) were conducted in which these seedlings were transferred to a fresh nutrient solution and treated with Fe sources (FeCl3, FeEDDHA, and Fe complexed with chelators produced by compost microorganisms (CCMs) after their enrichment in an Fe free, glucose medium), Fe concentrations (0 and 6.7 μM) and antibiotic (0 and 100 mg streptomycin L-1). Dry weight of soybean plants and Fe uptake were significantly (P ≤ 0.05) higher when Fe was supplied as 59FeCCM than as59 FeCl3 and similar to when Fe was supplied as59 FeEDDHA. Dry weight of the Fe-inefficient Tam 0-312 oat cultivar was also significantly higher when Fe was supplied as FeCCM. Fe uptake by oat, when supplied as 59FeCCM, was twice that for59 FeEDDHA and 59FeCl3. Chlorophyll concentration in plants supplied with FeCCM and FeEDDHA was significantly greater (P ≤ 0.05) than in minus Fe control plants and in FeCl3 supplied plants. Activities of catalase and peroxidase, measured as indicators of Fe nutrition in soybean and oats, were generally increased when Fe was supplied with FeCCM as compared to the other Fe sources. The experimental conditions in which the CCMs were produced are similar to those in soil after amendment with manures or other readily available organic materials. These CCMs can bind with Fe, even under slightly alkaline conditions, and effectively improve Fe nutrition of soybean and oat.

The accumulation of massive quantities of PHB in bacteroids of many rhizobia has been known for many decades. Based on a small sample of genera and species, it appears that the fast-growing rhizobia do not accumulate PHB whereas the slow-growing rhizobia do (see reviews by McDermott et al., 1989; Streeter, 1995). A role for the polymer, which can amount to 50% of bacteroid dry weight in Bradyrhizobium japonicum (Wong & Evans, 1971), has never been established. Recent genetic evidence suggests that PHB metabolism does not play a major role in Rhizobium meliloti; however, the possibility of some role in slow-growing rhizobia remains an open and potentially important question.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Documentation of the problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 13 Distribution of B,~~cly~~l i i~oDi~~rri groups in the United States . . . . . . . . . . . . . . . . . . . . . . . . . 5 13 Effects of bacterial and plant genotype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 14 Soil properties and levels of indigenous bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 15 Other factors in the field environment that may affect survival and (or) infection . . . . . . . . . . . . . . 5 15 Approaches to controlling infection in the field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 16 Use of high inoculant doses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 16 Use of bacteriocidal agents in conjunction with resistant strains . . . . . . . . . . . . . . . . . . . . . . . 5 16 Inoculant formulation or placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 16 Modification or selection of host genotype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 16 Modification or selection of bacterial genotype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 17 Potential problems confronting researchers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 17 Genetic diversity of rhizobial soil residents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 17 Prediction of field dominance by studies of "competitiveness" . . . . . . . . . . . . . . . . . . . . . . . . 5 17 Antibiotic-resistant ibolates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 18 Sampling of field populations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 18 Summary and prospects for the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 18 Key worcls: competitiveness, nitrogen fixation, rhizobial ecology, Blncl~rliizobi~~rri.

A hypothesis is presented that the availability of water for export of nitrogenous products from legume nodules is a major factor limiting the efficiency of symbiotic nitrogen fixation. Water for export of solutes in the xylem probably depends largely on the import of water and reduced carbon in the phloeum, and one function of respiration may be to dispose of reduced carbon in order to increase the supply of water. A second hypothesis presented is that control of gas diffusion in soybean nodules is largely restricted to the cortex nearby the vascular bundles, thus making possible the linkage of solute balances in xylem and phloem with resistance to diffusion. These concepts are used in a re‐examination of literature on manipulations of nodules and nodulated plants such as lowering of light levels, water stress, defoliation, stem girdling, and alteration of oxygen supply. The concept of translocation as a major factor limiting efficiency of symbiotic fixation is consistent with the failure of superior rhizobial isolates to improve N input significantly, and this limitation could also prevent exploitation of superior bacterial symbionts in the future

Treatment ofRhizobium leguminosarum bvphaseoli bacteroids with 25 mM citrate buffer, pH 4.0, prior to treatment with 50 mM Tris, pH 8.0, containing 1 mM EDTA, 20% (wt/vol) sucrose, and 1 mg lysozyme/mL increased by two- to three-fold the release of the periplasmic marker enzymes phosphodiesterase and pyrophosphatase. Release of malate dehydrogenase, a cytoplasmic marker, was largely unaffected by the citrate pretreatment. The pretreatment was shown to be a pH effect, with a narrow optimum pH range. Above pH 4.0 the enhancement of release of periplasmic enzymes decreased sharply to almost no effect at pH ≥ 5.5, and below pH 4.0 release of malate dehydrogenase increased sharply. The effectiveness of pretreatment with low pH did not appear to be owing to increased entry of lysozyme into the periplasmic space, and an effect of low pH on the suceptibility of the peptidoglycan layer to hydrolysis is suggested.