An exotic Australian <Emphasis Type="Italic">Acacia</Emphasis> fixes more N than a coexisting indigenous <Emphasis Type="Italic">Acacia</Emphasis> in a South African riparian zone

Acacia mearnsii is an introduced Australian acacia in South Africa and has invaded more than 2.5 million ha, primarily establishing in rangeland and riparian areas. Because acacias have the capability to fix N, A. mearnsii invasions may fundamentally change N dynamics in invaded systems. This study compares biological N₂-fixation in the alien invasive A. mearnsii and the native A. caffra growing in a grassland riparian zone in the Komati Gorge Reserve, Mpumalanga, South Africa. A ¹⁵N natural abundance field survey suggested that both mature alien and native acacias fix N under current conditions in the riparian zone. Significantly depleted δ¹⁵N was observed in both acacias relative to reference species, although variation in δ¹⁵N was not correlated with N concentrations. Calculated contributions of N₂-fixation (%Ndfa) suggest that alien acacias fix significantly more of their N than native acacias (~75 ± 5% SE and 53 ± 9% SE, respectively). There was a larger variation in δ¹⁵N and %Ndfa in the native acacia, suggesting relatively high plasticity in its N₂-fixation contributions. This plasticity was interpreted as a facultative N₂-fixation strategy for the native acacia, while the N₂-fixation strategy of the alien acacia remained unclear. Our results emphasize the importance of potentially elevated N inputs through N₂-fixation by invasive legumes in invaded landscapes. Furthermore, they suggest that N₂-fixation by invasive acacias may not respond to fine-scale patchiness in soil N in the same manner as native acacias, making them potential contributors to N excess in Southern Africa.     

<Emphasis Type="Italic">Rhizophagus manihotis</Emphasis> promotes the growth of rhizobia-nodulated <Emphasis Type="Italic">Vigna luteola</Emphasis> L in phosphorus deficient acid montane soils devoid of ground cover vegetation

The failure of Vigna luteola L. to colonize tropical montane regions of Venezuela with acid P-deficient soils that lack vegetation has been mainly attributed to the inability of indigenous arbuscular mycorrhizal fungi (AMFi) to be effective suppliers of P to this host plant. To test this hypothesis, Vigna luteola plants were grown in non sterile soil collected from this habitat. Plants became nodulated by indigenous rhizobia (Nod⁺) and the roots were colonized by AMFi (AMFi⁺). Some plants were inoculated with the arbuscular mycorrhizal fungus Rhizophagus manihotis (AMFg⁺). Other plants were fertilized with 6 mM nitrate and 2 mM P to inhibit nodulation (Nod^-) and AMFi colonization (AMFi^-), respectively and these served as controls. The Nod⁺AMFi⁺ plants displayed the smallest shoot and nodule dry weights upon harvest, the poorest AMF colonization, lowest foliar mineral content (N, P, Mg, Mn, Fe, Zn, and Cu), highest leaf ureide concentrations and lowest soil dehydrogenase, urease and acid phosphatase activities. Greater growth, nodulation, nutrient uptake, photosynthesis, catabolism of ureides in leaves, leaf superoxide dismutase and soil enzymatic activities were found in Nod⁺AMFg⁺ plants. The Nod^-AMFg⁺ plants grew even better attributed to their higher P uptake that was allocated mainly to the photosynthetic apparatus rather than to N₂-fixation. The results showed that V. luteola plants inoculated with R. manihotis and nodulated by indigenous rhizobia are capable successfully of colonizing open montane regions devoid of ground cover vegetation. The Nod⁺AMFg⁺ plants had greater growth, nodulation and root colonization by AMFg resulting in improved nutrient condition, enhanced uptake of nitrate and high catabolism of ureides in leaves than Nod⁺AMFi⁺ plants. However, more research is needed before the inoculation of open montane regions with AMFg can be recommended to land managers since a) the enhanced N₂ fixation rate in Nod⁺AMFg⁺ plants have an extra cost of 1.2 mg P kg⁻¹ leaf dry weight plant⁻¹ which could places an extra burden on the plants grown in the P-deficient soils, and b) the possible impact of AMFg on the microbiology of these former forest soils must be assessed.     

Rapid degradation of <Emphasis Type="Italic">N</Emphasis>-3-oxo-acylhomoserine lactones by a <Emphasis Type="Italic">Bacillus</Emphasis><Emphasis Type="Italic">cereus</Emphasis> isolate from Malaysian rainforest soil

A bacterial strain, KM1S, was isolated from a Malaysian rainforest soil sample by using a defined enrichment medium that specifically facilitates selection of quorum quenching bacteria. KM1S was clustered closely to Bacillus cereus by 16S ribosomal DNA sequence analysis. It degraded N-3-oxo-hexanoyl homoserine lactone and N-3-oxo-octanoyl homoserine lactone in vitro rapidly at 4.98 and 6.56 μg AHL h⁻¹ per 10⁹ CFU/ml, respectively, as determined by the Rapid Resolution Liquid Chromatography. The aiiA homologue, encoding an autoinducer inactivation enzyme catalyzing the degradation of N-acylhomoserine lactones, of KM1S was amplified and cloned. Sequence analysis indicated the presence of the motif ₁₀₆HXDH-59 amino acids-H₁₆₉-21 amino acids-D₁₉₁ for N-acylhomoserine lactone lactonases.     

Benzyladenine Promotes Flowering in <Emphasis Type="Italic">Doritaenopsis</Emphasis> and <Emphasis Type="Italic">Phalaenopsis</Emphasis> Orchids

Two experiments were performed to determine how application of the cytokinin benzyladenine (BA) influenced flowering in Doritaenopsis and Phalaenopsis orchid clones. In the first experiment, two vegetative orchid clones growing in 15-cm pots were transferred from a 28°C greenhouse that inhibited flowering to a 23°C greenhouse for flower induction (day 0). A foliar spray (0.2 L m⁻²) containing BA at 100, 200, or 400 mg L⁻¹ or 25, 50, or 100 mg L⁻¹ each of BA and gibberellins A₄ + A₇ (BA+GA) was applied on days 0, 7, and 14. Plants treated with BA alone at 200 or 400 mg L⁻¹ had a visible inflorescence 3–9 days earlier and had a mean of 0.7–3.5 more inflorescences and 3–8 more flowers per plant than nontreated plants. The application of BA+GA had no effect on inflorescence number and total flower number at the rates tested. In the second experiment, three orchid clones received a single foliar spray of BA at 200 mg L⁻¹ at six time points relative to time of transfer from 29°C to 23°C (−1, 0, +1, +2, +4, or +6 weeks). A separate group of plants received a BA application at week 0 but was maintained at 29°C. Inflorescence number was greatest in all three orchid clones when plants were treated with BA 1 week after the temperature transfer. Plants that were sprayed with BA and maintained at 29°C did not initiate inflorescences. The promotion of flowering by the application of BA suggests that cytokinins at least partially regulate inflorescence initiation of Doritaenopsis and Phalaenopsis, but its promotion is conditional and BA application cannot completely substitute for an inductive low temperature.     

Chemoorganoheterotrophic Growth of <Emphasis Type="Italic">Nitrosomonas europaea</Emphasis> and <Emphasis Type="Italic">Nitrosomonas eutropha</Emphasis>

The ammonia oxidizers Nitrosomonas europaea and Nitrosomonas eutropha are able to grow chemoorganotrophically under anoxic conditions with pyruvate, lactate, acetate, serine, succinate, α-ketoglutarate, or fructose as substrate and nitrite as terminal electron acceptor. The growth yield of both bacteria is about 3.5 mg protein (mmol pyruvate)⁻¹ and the maximum growth rates of N. europaea and N. eutropha are 0.094 d⁻¹ and 0.175 d⁻¹, respectively. In the presence of pyruvate and CO₂ about 80% of the incorporated carbon derives from pyruvate and about 20% from CO₂. Pyruvate is used as energy and only carbon source in the absence of CO₂ (chemoorganoheterotrophic growth). CO₂ stimulates the chemoorganotrophic growth of both ammonia oxidizers and the expression of ribulose bisphosphate carboxylase/oxygenase is down-regulated at increasing CO₂ concentration. Ammonium, although required as nitrogen source, is inhibitory for the chemoorganotrophic metabolism of N. europaea and N. eutropha. In the presence of ammonium pyruvate consumption and the expression of the genes aceE, ppc, gltA, odhA, and ppsA (energy conservation) as well as nirK, norB, and nsc (denitrification) are reduced.     

The tyrosine <Emphasis Type="Italic">O</Emphasis>-prenyltransferase SirD catalyzes <Emphasis Type="Italic">O</Emphasis>-, <Emphasis Type="Italic">N</Emphasis>-, and <Emphasis Type="Italic">C</Emphasis>-prenylations

Recently, the prenyltransferase SirD was found to be responsible for the O-prenylation of tyrosine in the biosynthesis of sirodesmin PL in Leptosphaeria maculans. In this study, the behavior of SirD towards phenylalanine/tyrosine and tryptophan derivatives was investigated. Product formation has been observed with 12 of 19 phenylalanine/tyrosine derivatives. It was shown that the alanine structure attached to the benzene ring and an electron donor, e.g., OH or NH₂, at its para-position are essential for the enzyme activity. Modifications were possible both at the side chain and the benzene ring. Enzyme products from seven phenylalanine/tyrosine derivatives were isolated and characterized by MS and NMR analyses including HSQC and HMBC and proven to be O- or N-prenylated derivatives at position C4 of the benzene rings. K _M values of six selected derivatives were found in the range of 0.10–0.68 mM. Catalytic efficiencies (K _cat/K _M ) were determined in the range of 430–1,110 s⁻¹·M⁻¹ with l-tyrosine as the best substrate. In addition, 7 of 14 tested tryptophan analogs were also accepted by SirD and converted to C7-prenylated derivatives, which was confirmed by comparison with products obtained from enzyme assays using a 7-dimethylallyltryptophan synthase 7-DMATS from Aspergillus fumigatus.     

Characterization of osmolyte betaine synthesizing sarcosine dimethylglycine <Emphasis Type="Italic">N</Emphasis>-methyltransferase from <Emphasis Type="Italic">Methanohalophilus portucalensis</Emphasis>

To overcome the extracellular salt stress, Methanohalophilus portucalensis FDF1^T synthesizes the compatible solute betaine through the methylation of glycine, sarcosine, and N,N-dimethylglycine. S-adenosylmethionine (AdoMet) is the methyl donor. The enzyme sarcosine dimethylglycine N-methyltransferase (SDMT) of M. portucalensis, that catalyzes the formation of N,N-dimethylglycine and glycine betaine, has been purified and characterized. SDMT, a monomer of 33 kDa with a pI at 5.03, has a narrow substrate specificity limited to using only sarcosine and dimethylglycine as substrates for the methyl transferase reaction. The K _m values for sarcosine and AdoMet were 2.29 and 0.21 mM, respectively, with a V _max of 0.83 μmol/mg-min (k _cat value of 0.44 s⁻¹). The K _m values for dimethylglycine and AdoMet were 3.76 and 0.59 mM, respectively, with a V _max of 4.88 μmol/mg-min (k _cat of 2.68 s⁻¹). A high concentration of the end product betaine (2.0 M) did not affect the SMT activity, but it slightly inhibited the DMT activity. Both activities were also not affected by potassium or sodium ions in concentrations of 200–1,000 mM. We compared this novel archaeal SDMT enzyme to other similar bacterial transferases as well as to the glycine sarcosine dimethylglycine methyltransferase found also in M. portucalensis.     

Diurnal and seasonal trends in photosynthetic performance of <Emphasis Type="Italic">Dalbergia sissoo</Emphasis> Roxb. and <Emphasis Type="Italic">Hardwickia binata</Emphasis> Roxb. from a semi-arid ecosystem

Diurnal and seasonal trends in net photosynthetic rate (P _N), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum P _N in D. sissoo ranged from 21.40±2.60 μmol m⁻² s⁻¹ in rainy season I to 13.21±2.64 μmol m⁻² s⁻¹ in summer whereas in H. binata it was 20.04±1.20 μmol m⁻² s⁻¹ in summer and 13.64±0.16 μmol m⁻² s⁻¹ in winter. There was a linear relationship between daily maximum P _N and g _s in D. sissoo but there was no strong linear relationship between P _N and g _s in H. binata. In D. sissoo, the reduction in g _s led to a reduction in both P _N and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in g _s causes an increase of P _N and E with a significant moderate WUE.     

Transcription of the extended <Emphasis Type="Italic">hyp</Emphasis>-operon in <Emphasis Type="Italic">Nostoc</Emphasis>sp. strain PCC 7120

Background  

The maturation of hydrogenases into active enzymes is a complex process and e.g. a correctly assembled active site requires the involvement of at least seven proteins, encoded by hypABCDEF and a hydrogenase specific protease, encoded either by hupW or hoxW. The N₂-fixing cyanobacterium Nostoc sp. strain PCC 7120 may contain both an uptake and a bidirectional hydrogenase. The present study addresses the presence and expression of hyp-genes in Nostoc sp. strain PCC 7120.     

Effect of high temperature on photosynthesis and transpiration of sweet corn (<Emphasis Type="Italic">Zea mays</Emphasis> L. var. <Emphasis Type="Italic">rugosa</Emphasis>)

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate (P _N) of sweet corn was found for the lowest temperature of 28–34 μmol m⁻² s⁻¹ while the P _N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P _N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h⁻¹ (≈5.0–6.5 mm d⁻¹) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h⁻¹ (≈3.5–5.0 mm d⁻¹) for the low temperature treatment. Cumulative CO₂ fixation of the 40/35 °C treatment was 33.7 g m⁻² d⁻¹ and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO₂) kg⁻¹(H₂O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P _N, and E of Zea: the high temperature which reduced P _N, vapor pressure deficit (VPD) that was directly related to E but did not affect P _N, and quasi stem conductance (QC) that was directly related to P _N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.     

Purification and Properties of an <Emphasis Type="Italic">N</Emphasis>-acetylglucosaminidase from <Emphasis Type="Italic">Streptomyces cerradoensis</Emphasis>

An N-acetylglucosaminidase produced by Streptomyces cerradoensis was partially purified giving, by SDS-PAGE analysis, two main protein bands with Mr of 58.9 and 56.4 kDa. The K_m and V_max values for the enzyme using p-nitrophenyl-β-N-acetylglucosaminide as substrate were of 0.13 mM and 1.95 U mg⁻¹ protein, respectively. The enzyme was optimally activity at pH 5.5 and at 50 °C when assayed over 10 min. Enzyme activity was strongly inhibited by Cu²⁺ and Hg²⁺ at 10 mM, and was specific to substrates containing acetamide groups such as p-nitrophenyl-β-N-acetylglucosaminide and p-nitrophenyl-β-D-N,N′-diacetylchitobiose.     

Serpulids on living Eocene larger foraminifer <Emphasis Type="Italic">Discocyclina</Emphasis>

About 70% of the groundnut (Arachis hypogaea L.) produced in Ghana is from the Guinea savanna. However, low soil nutrients, especially N, together with erratic rainfall distribution have often resulted in poor grain yield. The aim of this study was to evaluate plant growth, N₂-fixing efficiency, N contribution, water-use efficiency and pod yield of 21 elite groundnut genotypes in the Guinea savanna of Ghana, using the ¹⁵N natural abundance technique. The data revealed significant variations in plant growth, symbiotic N contribution, and pod yield among the 21 genotypes tested at each field site. Average N contribution by groundnut genotypes ranged from 48 to 108 kg N ha^?1. Also, mean pod yield ranged from 0.58 to 2.1 t ha^?1. Genotypes ICGV-IS 08837, ICG 6222, ICGV 03315 and NKATIESARI demonstrated superior plant growth, symbiotic N contribution and greater pod yield. In fact, ICGV-IS 08837 yielded almost 2.5 fold more than CHINESE which is the most widely cultivated variety in the region. Genotypes ICGV-IS 08837, ICG 6222, ICGV 03315 and ICGV 99247 are therefore recommended for development into varieties for the Guinea savanna of Ghana. Genotypes ICG (FDRS) 4, ICGV00362 and ICGV99247 exhibited increased water-use efficiency, but were low in N₂ fixation and N contribution, and would therefore be good parental material in breeding programs aimed at enhancing water-use efficiency in high N₂-fixing genotypes.     

Efficient separation and purification of allophycocyanin from <Emphasis Type="Italic">Spirulina</Emphasis> (<Emphasis Type="Italic">Arthrospira</Emphasis>) <Emphasis Type="Italic">platensis</Emphasis>

Allophycocyanin (APC) is a minor component of phycobiliproteins in cyanobacteria and red algae. This paper describes a simple and inexpensive extracting method for isolating APC from Spirulina (Arthrospira) platensis with high efficiency. The crude phycobiliprotein extract was pretreated by ammonium sulfate fractionation. Then, by adding hydroxylapatite into crude phycobiliprotein extract dissolved in 20 mM phosphate buffer (pH 7.0), APC was selectively adsorbed by hydroxylapatite but C-phycocyanin (C-PC) was not. The hydroxylapatite was collected and APC was extracted from the crude phycobiliprotein extract. Then, the enriched APC was washed off from the hydroxylapatite using 100 mM phosphate buffer (pH 7.0). In this simple extracting method it was easy to remove C-PC and isolate APC in large amounts. The absorbance ratio A ₆₅₀/A ₂₈₀ of extracted APC reached 2.0. The recovery yield was 70%, representing 4.61 mg · g⁻¹ wet weight. The extracted APC could be further purified by a simple anion-exchange chromatography with a pH gradient from 5.6 to 4.0. The absorbance ratio A ₆₅₀/A ₂₈₀ of the purified APC reached 5.0, and the overall recovery yield was 43%, representing 2.83 mg · g⁻¹ wet weight. Its purity was confirmed by native polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate-PAGE.     

<Emphasis Type="Italic">Agrobacterium</Emphasis><Emphasis Type="Italic">tumefaciens</Emphasis>-mediated transformation of callus cells of <Emphasis Type="Italic">Crataegus</Emphasis><Emphasis Type="Italic">aronia</Emphasis>

A genetic transformation system has been developed for callus cells of Crataegus aronia using Agrobacterium tumefaciens. Callus culture was established from internodal stem segments incubated on Murashige and Skoog (MS) medium supplemented with 5 mg l⁻¹ Indole-3-butyric acid (IBA) and 0.5 mg l⁻¹ 6-benzyladenine (BA). In order to optimize the callus culture system with respect to callus growth and coloration, different types and concentrations of plant growth regulators were tested. Results indicated that the best average fresh weight of red colored callus was obtained on MS medium supplemented with 2 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.5 mg l⁻¹ kinetin (Kin) (callus maintenance medium). Callus cells were co-cultivated with Agrobacterium harboring the binary plasmid pCAMBIA1302 carrying the mgfp5 and hygromycin phosphotransferase (hptII) genes conferring green fluorescent protein (GFP) activity and hygromycin resistance, respectively. Putative transgenic calli were obtained 4 weeks after incubation of the co-cultivated explants onto maintenance medium supplemented with 50 mg l⁻¹ hygromycin. Molecular analysis confirmed the integration of the transgenes in transformed callus. To our knowledge, this is the first time to report an Agrobacterium-mediated transformation system in Crataegus aronia.     

Leaf characteristics and gas exchange of the mangrove <Emphasis Type="Italic">Laguncularia racemosa</Emphasis> as affected by salinity

Under constant salinity we analysed the leaf characteristics of Laguncularia racemosa (L.) Gaertn. in combination with gas exchange and carbon isotopic composition to estimate leaf water-use efficiency (WUE) and potential nitrogen-use efficiency (NUE). NaCl was not added to the control plants and the others were maintained at salinities of 15 and 30 ‰ (S₀, S₁₅, and S₃₀, respectively). Leaf succulence, sodium (Na), nitrogen (N), and chlorophyll (Chl) contents increased under salinity. Salinity had a negative impact on net photosynthetic rate (P _N) and stomatal conductance (g _s) at high and moderated irradiances. Potential NUE declined significantly (p<0.05) with salinity by 37 and 58 % at S₁₅ and S₃₀, respectively, compared to S₀ plants. Conversely, compared to S₀ plants, P _N/g _s increased under saline conditions by 12 % (S₁₅) and 50 % (S₃₀). Thus, WUE inferred from P _N/g _s was consistent with salinity improved short-term WUE. Long-term leaf WUE was also enhanced by salinity as suggested by significantly increased leaf δ¹³C with salinity. Improved WUE under salinity explains the eco-physiological success of mangrove species under increasing salinity. Conversely, decline in NUE may pose a problem for L. racemosa under hyper-saline environments regardless of N availability.     

Population genetic structure of the endangered and endemic medicinal plant <Emphasis Type="Italic">Commiphora</Emphasis><Emphasis Type="Italic">wightii</Emphasis>

Commiphora wightii is a medicinally important endangered species endemic to the Thar Desert of Rajasthan, India and adjoining areas of Pakistan. The populations of this species are declining sharply because of its extensive use as a natural herb. Random amplified polymorphic DNA analysis was conducted to find the genetic variation among 7 populations of C. wightii. Of the 100 random primers screened, 44 primers yielded 220 loci. Statistical analysis indicated low genetic diversity (H _pop = 0.0958; I = 0.1498; mean polymorphic loci = 14.28%), and high genetic differentiation among the populations (G _ST = 0.3990; AMOVA Φ _ST of 0.3390; Bayesian θ ^(II) = 0.3002). The low genetic diversity may be due to geographic isolation and restricted gene flow (N _m = 0.7533) between the fragmented populations. Unsustainable utilization of the plant has fragmented the population continuum which served the purpose of genetic exchange between populations. Mantel’s test was performed which revealed a highly significant positive correlation between genetic and geographic distance (r ² = 0.614, P = 0.023) among the populations studied. Low variation can also be attributed to poor seed setting and the slow growth pattern of the species, which is also an apomict. In UPGMA dendrogram the Commiphora wightii samples were divided into two major and one minor cluster. These findings can serve as a guide to preserving the genetic resources of this medicinal plant species.     

Management of <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> with integration of non-conventional chemicals,vermicompost and <Emphasis Type="Italic">Pseudomonas syringae</Emphasis>

Two non-conventional chemicals, ZnSO₄ (10⁻⁴ mM) and oxalic acid (4 mM) were tested (alone as well as in combination with seeds bacterized with Pseudomonas syringae strain PUR46 and vermicompost substitution in the potting soil), for their ability to suppress collar rot of chickpea (Cicer arietinum) caused by Sclerotium rolfsii under greenhouse conditions. ZnSO₄ and oxalic acid were applied as pre-inoculation foliar spray on chickpea and subsequently challenged with S. rolfsii. Both the chemicals provided significant protection to chickpea compared to control (100% plant mortality) when used alone as well as in combination with PUR46 and vermicompost. However, ZnSO₄ was more effective than oxalic acid against S. rolfsii. Amongst the treatments tried, plant mortality was least when ZnSO₄ was used in combination with seed bacterization with PUR46 and 25% vermicompost substitution. The findings indicate the utility of integration of the above factors in managing collar rot efficiently.     

Foliar nutrition of <Emphasis Type="Italic">in vitro</Emphasis>-cultured <Emphasis Type="Italic">Prosopis chilensis</Emphasis> (Molina) Stuntz shoots

Summary Foliar nutrition has been conceived as a possible means of overcoming the recalcitrance of Prosopis chilensis (Molina) Stuntz explants to standard in vitro culture. The foliar uptake of cations (K from 20 gl⁻¹ KNO₃ and Ca from 50 gl⁻¹ CaCl₂), anions (NO₃ from 50 gl⁻¹ KNO₃ and PO₄ from 50 gl⁻¹ NaH₂PO₄), and glucose from a 100 mg l⁻¹ solution studied. All of the nutrients examined were absorbed. The efficacy of foliar nutrition in prolonging the vigor of micropropagated P. chilensis shoot tips was compared with nutrients supplied as a liquid to the base of the stem (liquid) or as an agar-solidified medium (agar). A foliar-feeding apparatus was constructed that employed pressurization of the medium reservoir to drive the medium into the culture vessel with a passive return by a siphoning effect. The medium used was Murashige and Skoog with 30 gl⁻¹ sucrose, 0.1 mgl⁻¹ benzylaminopurine, and 1 mgl⁻¹ indole-3-butyric acid. Over a 9-wk test period it was found that explants cultured by foliar nutrition performed significantly better than those grown on agar for shoot length, nodal production, and leaf retention; and better than liquid MS for node production. There was no significant difference among the three treatments in percentage survival, percentage rooting, or the mean number of roots.     

Ecological Occurrence of <Emphasis Type="Italic">Gluconacetobacter diazotrophicus</Emphasis> and Nitrogen-fixing <Emphasis Type="Italic">Acetobacteraceae</Emphasis> Members: Their Possible Role in Plant Growth Promotion

Gluconacetobacter diazotrophicus has a long-standing history of bacterial-plant interrelationship as a symbiotic endophyte capable of fixing atmospheric nitrogen. In low nitrogen fertilized sugarcane fields it plays a significant role and its occurrence was realised in most of the sugarcane growing countries. In this mini review, the association of G. diazotrophicus with sugarcane, other crop plants and with various hosts is discussed. The factors affecting survival in the rhizosphere and the putative soil mode of transmission are emphasized. In addition, other N₂-fixing Acetobacteraceae members, including Gluconacetobacter azotocaptans, Gluconacetobacter johannae and Swaminathania salitolerans, occurring in coffee, corn and rice plants are also covered. Lastly, the plant-growth-promoting traits identified in this group of bacteria, including N₂ fixation, phytohormone synthesis, P and Zn solubilization and biocontrol, are analysed.