Cecilia Baginsky

Diversity and Evolution of Hydrogenase Systems in Rhizobia

ABSTRACT Uptake hydrogenases allow rhizobia to recycle the hydrogen generated in the nitrogen fixation process within the legume nodule. Hydrogenase (hup) systems in Bradyrhizobium japonicum and Rhizobium leguminosarum bv. viciae show highly conserved sequence and gene organization, but important differences exist in regulation and in the presence of specific genes. We have undertaken the characterization of hup gene clusters from Bradyrhizobium sp. (Lupinus), Bradyrhizobium sp. (Vigna), and Rhizobium tropici and Azorhizobium caulinodans strains with the aim of defining the extent of diversity in hup gene composition and regulation in endosymbiotic bacteria. Genomic DNA hybridizations using hupS, hupE, hupUV, hypB, and hoxA probes showed a diversity of intraspecific hup profiles within Bradyrhizobium sp. (Lupinus) and Bradyrhizobium sp. (Vigna) strains and homogeneous intraspecific patterns within R. tropici and A. caulinodans strains. The analysis also revealed differences regarding the possession of hydrogenase regulatory genes. Phylogenetic analyses using partial sequences of hupS and hupL clustered R. leguminosarum and R. tropici hup sequences together with those from B. japonicum and Bradyrhizobium sp. (Lupinus) strains, suggesting a common origin. In contrast, Bradyrhizobium sp. (Vigna) hup sequences diverged from the rest of rhizobial sequences, which might indicate that those organisms have evolved independently and possibly have acquired the sequences by horizontal transfer from an unidentified source.

Biodiversity of uptake hydrogenase systems from legume endosymbiotic bacteria

Uptake hydrogenases in legume endosymbiotic bacteria recycle hydrogen produced during the nitrogen fixation process in legume nodules. Despite the described beneficial effect on plant productivity, the hydrogen oxidation capability is not widespread in the Rhizobiaceae family. Characterization of hydrogenase gene clusters in strains belonging to Rhizobium, Bradyrhizobium and Azorhizobium reveals a similar overall genetic organization along with important differences in gene regulation. In addition, phylogenetic analysis of hup genes indicates distinct evolutionary origins for hydrogenase genes in Rhizobia.

Symbiotic hydrogenase activity in Bradyrhizobium sp. (Vigna) increases nitrogen content in Vigna unguiculata plants

ABSTRACT Bradyrhizobium sp. (Lupinus) and Bradyrhizobium sp. (Vigna) mutants in which hydrogenase (hup) activity was affected were constructed and analyzed. Vigna unguiculata plants inoculated with the Bradyrhizobium sp. (Vigna) hup mutant showed reduced nitrogenase activity and also a significant decrease in nitrogen content, suggesting a relevant contribution of hydrogenase activity to plant yield.

Gibberellin oxidase activities in Bradyrhizobium japonicum bacteroids

Bradyrhizobium japonicum bacteroids isolated from root nodules of soybean (Glycine max.) plants converted the gibberellin (GA) precursor [(14)C1]GA12 into several products identified by combined gas chromatography-mass spectrometry as [(14)C1]GA24, [(14)C1]GA9, [(14)C1]GA15, GA9 17-nor-16-one and unidentified products. The oxidation of GA12, catalyzed by the GA 20-oxidase, was present in symbiotic bacteroids from plants around flowering, but not in bacteroids from plants at either an early vegetative stage or at late growth stages. Expression of cps and ks genes, involved in ent-kaurene biosynthesis, was also demonstrated in bacteroids from soybean plants around flowering. Earlier precursors of the GA pathway, ent-[(14)C1]kaurenoic acid or [(14)C4]GA12-aldehyde, were efficiently utilized by B. japonicum bacteroids to give labelled GA9 plus intermediates partially oxidized at C-20, as well as GA9 17-nor-16-one and an unidentified product. No 3β or 13-hydroxylated [(14)C]GAs were detected in any of the incubations. Moreover the C19-GAs [(14)C1]GA4 or [(14)C1]GA20 were recovered unconverted upon incubation with the bacteroids which supports the absence of GA 3β-hydroxylase activity in B. japonicum. The bacterial 20-oxidase utilized the 13-hydroxylated substrates [(14)C1]GA53, [(14)C1]GA44 or [(14)C1]GA19, although with less efficiency than [(14)C1]GA12 to give [(14)C1]GA20 as final product, while the 3β-hydroxylated substrate [(14)C1]GA14 was converted to [(14)C1]GA4 to a very small extent. Endogenous GA9 and GA24 were identified by GC-MS in methanolic nodule extracts. These results suggest that B. japonicum bacteroids would synthesize GA9 under the symbiotic conditions present in soybean root nodules.

Evaluation of soil fertility and fertilisation practices for irrigated maize (Zea mays L.) under Mediterranean conditions in Central Chile

The main aim of this study was to carry out an evaluation of soil fertility and fertilisation practices for irrigated maize (Zea mays L.) under Mediterranean conditions in central Chile. Soil samples were collected from 31 maize fields for macro- and micronutrient analysis; additionally a crop management survey was carried out in each field. These data were used to identify the range of critical soil-test concentrations of nutrients and the relationships among these soil fertility parameters; to assess the relationship between maize yields and nutrient status of soils; to evaluate the current fertiliser practices of farmers comparing them with nitrogen (N), phosphorus (P) and potassium (K) fertiliser model calculations; and to analyse whether The results showed that there was a dominance of neutral-alkaline soils with low organic matter and N levels, and high P, cations and micronutrient levels. Regression analysis explained at least 59% of the variation in maize yields, when soil pH and available zinc (Zn) content were identified as the most important variables controlling maize yield. Results suggest that in neutral-alkaline soils cultivated with maize and high inputs of N-P-K, there may be a maize yield response to Zn applications. It was found that most farmers over-fertilised with N (from 60 to 360 kg N ha-1) and P (from10 to 120 kg P2O5 ha-1), converting maize fields in an important non-point source of pollution of water bodies in Central Chile.

Growth and yield of chia (Salvia hispanica L.) in the Mediterranean and desert climates of Chile

5 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 76(1) JANUARY-MARCH 2016 3 ULY-SEPTEMBER Chia (Salvia hispanica L.) is a species with seeds that have high essential fatty acid content, which has encouraged increased crop production worldwide. However, the expansion of chia is limited because it is a photoperiodsensitive plant adapted to areas without cold. The objective of the present study was to determine the effect of different climatic conditions on the growth, grain yield and oil production of chia under irrigation in three geographic areas of Chile: Valle de Azapa (18°30’ S lat) with a coastal desert climate, normal desert climate in Canchones (20°26’ S lat), and Las Cruces (33°30’ S lat) with dry Mediterranean climate with marine influence, and two chia phenotypes: white and dark. Results indicated that desert conditions in the Valle de Azapa (VA) and Canchones (CH) provided better conditions for plant growth; the highest yield (> 2900 kg ha-1) and oil production (> 550 L ha-1). In Las Cruces (LC), at higher latitude, low temperatures present beginning in April coincided with the reproductive stage, affecting yield which was no more than 129 kg ha-1; thus this zone is not recommendable for chia cultivation. This study also determined an 11.8 h day length threshold for the beginning of flowering; when plants are exposed to shorter days flower initiation is more precocious, but when day length is not adequate plants only begin to flower when they have accumulated 600-700 oC d.

CHANGES IN PHYSICAL PROPERTIES OF A TYPIC HAPLOCAMBID BY ANNUAL CROP CULTURE

As an alternative to organic soil amendments used in the Copiapo Valley (northern Chile), this study analyzed the magnitude of changes in physical soil properties associated with different crop rotations on the rows on a grape orchard. The study was performed in the locality of Los Loros, Atacama Region, during the 2006-2008 seasons. In a Typic Haplocambid soil (2-5% slope, coarse loam) with a 6-year old grape plantation, a control and three crop rotations were established, each with four replicates. Soil samples were taken at three depths (0-10; 10-40; 40-60 cm), evaluating bulk density, penetration resistance, aggregate stability, pore size distribution and air and water flux. Crop rotation did not produce statistical differences in soil density compared with the control treatment; nevertheless, soil mechanical strength decreased compared to the control without crops. Aggregate stability increased on the surface horizon when Poaceae and Fabaceae were used separately, but not when they were planted together. Below the surface this effect vanished and no significant differences were observed compared with the control. The leguminous crops promoted a more continuous porous system, with an increase of coarse porosity and a higher air and water flux capability. A longer time period of crop rotation is required to improve the productive potential of grapes.

Physical properties of a fine textured haplocambid after three years of organic matter amendments management

AbstractIn Copiapo Valley, the 3 th Region of Chile, a three-year study (2007-2009) was conducted to evaluate the effect of organic amendments and cover crops on soil physical properties (Typic Haplocambid) in a table grape ( Vitis vinifera ) orchard. Four treatments were established during three seasons: control without organic amendments (T1), broad bean-corn-rape rotation (T2), goat manure addition (15 t ha -1 ) (T3) and corn-broad bean-barley rotation (T4). Soils measurements, bulk density, pore size distribution, aggregate stability, water repellence and air conductivity were conducted on soil samples collected at three soil depths (0-10, 10-30 and 30-50 cm). Saturated hydraulic conductivity and mechanical strength were also evaluated. On grape plant measurements, root development, pruning weight and harvested grape production were evaluated. Soil bulk density was reduced with goat manure addition in comparison with any other treatment, which resulted in lower mechanical strength in the top soils. None of the treatments had negative effects on water repellency. The crop treatments enhanced the coarse porosity throughout the soil profile, improving the continuity of porous system with their root development and inducing high air conductivity. Other hand, the control soil and manure application showed a pore discontinuity in a pre-existing plow pan. Aggregate stability and saturated hydraulic conductivity were greater in goat manure application, but the treatments which included crop rotation did not show significant differences compared with the control. Because of the short duration of the study, it is assumed that the soil improvements were not detected as expected in grape production yet. Keywords: Compaction, cover crops, aggregate stability, soil porosity

Photosynthetic Responses of Beans to Water Stress in the Field

Under water stress plants decrease their growth rate, first because of a decrease in their assimilatory surface and, second, because the photosynthetic rate is inhibited (Lawlor and Uprety, 1993). CO2 reaches the carboxilation sites through stomata, the same than water lost, therefore as an attempt to save water under drought conditions, the stomatal closure affects photosynthesis by limiting CO2 availability (Mansfield 1990). Also, water stress restricts photosynthesis through “non-stomatal” effects, among which PSII and ATP synthase inhibition in thylakoids are thought to be important (Boyer, 1977; Boyer and Younis, 1983). Non-stomatal effects are believed to occur mainly because CO2 shortages would induce an over-excitation of PSII complexes, which in time, and depending on the capacity for absorbed energy dissipation as heat, would induce inhibition of photosynthesis. This water induced inhibition of PSII activity is light dependent, and therefore recognised as photoinhibition.

Effect of sowing date and water availability on growth of plants of chia (Salvia hispanica L) established in Chile

From 2010 to 2014 two trials were performed to assess the effect of sowing date (SD1, SD2) and irrigation treatments (IT1, IT2) on the growth of chia in central Chile, measuring leaf area (LA) and dry matter (DM) as primary parameters and relative growth rate (RGR), net assimilation rate (NAR), leaf weight ratio (LWR), crop growth rate (CGR) and specific leaf weight (SLW) as secondary parameters. Both LA and DM reached maximum values between 640 and 1150 accumulated degree days (ADD). However, LA and DM were 25% greater for sowing dates than for available water. Flowering date was also not affected by sowing date or water availability; plants flowered at 1140 and 942 ADD in SD1 and SD2 respectively, and at 499 ADD in the water availability trial. Sowing date had a significant effect on RGR 0.15 g g-1 d-1 for SD1 and 0.12 g g-1 d-1 for SD2 at 410 ADD. Greater water availability increased RGR by 60% compared to stressed plants, however NAR was similar between sowing dates with a tendency to greater values in SD2 plants; maximum values were recorded at 514 ADD in IT1 and IT2, with a tendency toward higher values in IT1. Thus, the primary growth variables LA, DM and flowering are genetically determined. However, the derived growth variables RGR, LWR, NAR, CGR and SLW were affected by sowing date and water availability, with significant differences at p≤ 0.05. The results showed that the sowing date and water availability influence significantly the growth parameters. The physiological component (NAR) show a strong influence on the growth rate of the chia (RGR), above the morphological component (SLW and LAR).