Photosynthetic responses to elevated CO2and O3 in field-grown potato(Solanum tuberosum)

Potato plants (Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO₂; ambient and 24 h d⁻¹ seasonal mean concentrations of 550 and 680 μmol mol⁻¹) and two ozone levels (O₃; ambient and an 8 h d⁻¹ seasonal mean of 50 nmol mol⁻¹). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO₂ may alleviate the damaging influence of O₃ by reducing uptake by the leaves. Elevated O₃ had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO₂ also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO₂, and declined with time in the youngest leaves examined, as did assimilation rate (A). A generally increased under elevated CO₂, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO₂ and/or O₃ had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO₂ concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO₂-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol⁻¹ CO₂ were subsequently greater than in the ambient and 680 μmol mol⁻¹ treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO₂, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO₂ were measured under ambient CO₂, but increased when leaves grown under ambient CO₂ were examined under elevated CO₂. The results obtained indicate that, although elevated CO₂ initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence.     

Evaluation of rhizosphere bacterial antagonists for their potential to bioprotect potato (Solanum tuberosum) against bacterial wilt (Ralstonia solanacearum)

Bacterial wilt (Ralstonia solanacearum) is one of the production constraints of potato (Solanum tuberosum). The intent of the study was to evaluate potential of bacterial antagonists to suppress bacterial wilt disease development and evaluate the role of the strains as plant growth-promoting rhizobacteria (PGPR) in potato. One hundred-twenty rhizosphere bacterial isolates were screened against virulent strain of Ralstonia solanacearum PPRC-Rs. After in vitro screening, six antagonistic strains (PFMRI, BS-DFS, PF9, PF20, BC, and BS-wly) with inhibition diameter >11 mm were selected and studied further in the greenhouse, in vivo. During in vivo study, the strains were evaluated for their effect in suppressing disease development in terms of area under disease progress curve (AUDPC) and increasing biomass (plant height and dry weight) of potato. Accordingly, PFMRI, BS-DFS, and PF9, significantly reduced AUDPC by 78.6, 66, and 64.3%, and wilt incidence by 82.7, 66.2, and 65.7%, respectively, compared to the control. During the sole application, the strains significantly (P < 0.0001) increased plant height by 35.6, 45.9, and 45%, and dry matter by 111, 130.4, and 129%, respectively compared to non-bacterized control. In the presence of the pathogen strain PFMRI, BS-DFS, and PF9 increased plant height by 66, 50, and 48.2%, and dry matter by 153.8, 96.8, and 92.5%, respectively compared to the pathogen treated control. Hence, the study shows that PFMRI, BS-DFS, and PF9 strains have potential use in potato bioprotection, as PGPR or in an integrated bacterial wilt management; whose effectiveness under a variety of field conditions should be investigated.     

Sequence variability and gene structure at the self-incompatibility locus of Solanum tuberosum

Summary Allelic complexity is a key feature of self-incompatibility (S) loci in gametophytic plants. We describe in this report the allelic diversity and gene structure of the S locus in Solanum tuberosum revealed by the isolation and characterization of genomic and cDNA clones encoding S-associated major pistil proteins from three alleles (S ₁, S _r1, S ₂). Genomic clones encoding the S₁ and S₂ proteins provide evidence for a simple gene structure: Two exons are separated by a small intron of 113 (S ₁) and 117 by (S ₂). Protein sequences deduced from cDNA clones encoding S₁ and S_r1 proteins show 95% homology. 15 of the 25 residues that differ between these S ₁and S _r1alleles are clustered in a short hypervariable protein segment (amino acid positions 44–68), which corresponds in the genomic clones to DNA sequences flanking the single intron. In contrast, these alleles are only 66% homologous to the S ₂allele, with the residues that differ between the alleles being scattered throughout the sequence. DNA crosshybridization experiments identify a minimum of three classes of potato S alleles: one class contains the alleles S ₁, S _r1and S ₃, the second class S ₂and an allele of the cultivar Roxy, and the third class contains at present only S ₄. It is proposed that these classes reflect the origin of the S alleles from a few ancestral S sequence types.     

Transposition of the maize transposable element Ac in Solanum tuberosum

Summary The maize transposable element Ac has been introduced into potato via the T-DNA (transferred DNA) of Agrobacterium tumefaciens. Ac was inserted within the untranslated leader region of a neomycin phosphotransferase II (NPT-II) gene such that excision restored NPT-II activity. Two approaches to monitor Ac excision were used. (i) Using an Agrobacterium strain harbouring plasmid pGV3850::pKU3, leaf discs were selected on kanamycin (Km) after exposure to Agrobacterium. (ii) Using a strain containing plasmid pGV3850HPT::pKU3, the leaf discs were selected on hygromycin (Hm) and the resulting shoots were checked for NPT-II expression. Thirteen kanamycin resistant shoots transformed with pGV3850::pKU3 were isolated, suggesting that Ac had excised from the NPT-II gene. Out of 43 hygromycin resistant shoots transformed with pGV3850HPT::pKU3, 22 expressed the NPT-II gene, indicating that Ac had undergone excision in approximately 50% of the hygromycin resistant shoots. Southern analysis revealed that all kanamycin resistant plants contained the DNA restriction fragments expected when Ac excises from the NPT-II gene. The presence of Ac at new locations within the genomic DNA of several transformants was also detected.     

Two novel oligosaccharides from Solanum nigrum

Phytochemical analysis of Solanum nigrum has resulted in the isolation of two novel disaccharides. Their structures were determined as ethyl β-d-thevetopyranosyl-(1→4)-β-d-oleandropyranoside (1) and ethyl β-d-thevetopyranosyl-(1→4)-α-d-oleandropyranoside (2), respectively, by chemical and spectroscopic methods.     

Structure and expression of a hybrid proline-rich protein gene in the solanaceous species,Solanum brevidens, Solanum tuberosum, andLycopersicum esculentum

The full-length cDNA of a previously identified Solanum brevidens gene was isolated and characterised. DNA sequence analysis revealed an open reading frame that encodes a hybrid proline-rich cell wall protein of 407 amino acids. The putative protein was designated SbrPRP. The SbrPRP harbours three parts, an N-terminal signal peptide followed by a repetitive proline-rich domain and a cysteine-rich C-terminus resembling non-specific lipid-transfer proteins. The repetitive proline-rich domain contains two repeated motifs, PPHVKPPSTPK and PTPPIVSPP extended with TPKYP and TPKPPS motifs, respectively, at their N- or C-terminal. The SbrPRP gene of the non-tuberising Solanum species, Solanum brevidens, possesses highly homologous counterparts in the tuberising species, Solanum tuberosum (StPRP) and in the related species, Lycopersicum esculentum (TFM7). All three genes are present in single- or low copy number in the corresponding genome. Organ-specific expression of the genes, however, is different in the three solanaceous species.     

The foliar micromorphology of Solanum pseudocapsicum

Foliar micromorphology of Solanum pseudocapsicum was investigated by electron microscopical examination. The leaves are characterized by anisocytic stomata which are more abundant on the abaxial surfaces. The leaves have short multicellular glandular trichomes sparsely distributed over the entire leaf surfaces. Crystal deposits were also observed on the surfaces above the stomata. Energy dispersive X-ray spectroscopy-SEM showed that Al, K, Na and Si were the major constituents of the crystals analyzed. The presence of glandular trichomes in this plant could be the source of poisonous compounds that are characteristic of this species.     

Glucose Inhibits ACC Oxidase Activity and Ethylene Biosynthesis in Ripening Tomato Fruit

Experiments were carried out to evaluate the effect of glucose on ripening and ethylene biosynthesis in tomato fruit (Lycopersicon esculentum Mill.). Fruit at the light-red stage were vacuum infiltrated with glucose solutions post-harvest and changes in 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC, ACC oxidase, and ethylene production monitored over time. ACC oxidase activity was also measured in pericarp discs from the same fruits that were treated either with glucose, fructose, mannose, or galactose. While control fruit displayed a typical peak of ethylene production, fruit treated with glucose did not. Glucose appeared to exert its effect on ethylene biosynthesis by suppressing ACC oxidase activity. Fructose, mannose, and galactose did not inhibit ACC oxidase activity in tomato pericarp discs. Glucose treatment inhibited ripening-associated colour development in whole fruit. The extent of inhibition of colour development was dependent upon the concentration of glucose. These results indicate that glucose may play an important role in ethylene-associated regulation of fruit ripening.     

Characterization of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing <Emphasis Type="Italic">Methylobacterium oryzae</Emphasis> and interactions with auxins and ACC regulation of ethylene in canola (<Emphasis Type="Italic">Brassica campestris</Emphasis>)

The possible interaction of the plant hormones auxin and ethylene and the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase containing bacteria on ethylene production in canola (Brassica campestris) in the presence of inhibitory concentrations of growth regulators were investigated. The effects of auxin (indole-3-acetic acid and 2,4-dichlorophenoxy acetic acid), auxin transport inhibitor 2-(p-chlorophenoxy)-2-methylpropionic acid, ethylene precursor 1-aminocyclopropane-1-carboxylate and ethylene synthesis inhibitor l-α-(2-aminoethoxyvinyl)glycine hydrochloride on root elongation were concentration dependent. Exogenous addition of growth regulators influences the enzyme activities of ethylene production and we have presented here evidences that support the hypothesis that inhibitory effects of auxin on root elongation are independent of ethylene. Additionally, we have proved that inoculation of ACC deaminase containing Methylobacterium oryzae sequester ACC exuded from roots and hydrolyze them lowering the concentration of ACC in root exudates. However, the inhibitory actions of exogenous additions of auxins could not be ameliorated by bacterial inoculation that reduces ethylene concentration in canola seedlings.     

Inheritance of Fusarium wilt resistance introgressed from Solanum aethiopicum Gilo and Aculeatum groups into cultivated eggplant (S. melongena) and development of associated PCR-based markers

The two eggplant relatives Solanum aethiopicum gr. Gilo and Solanum aethiopicum gr. Aculeatum (=Solanum integrifolium) carry resistance to the fungal wilt disease caused by Fusarium oxysporum f. sp. melongenae, a worldwide soil-borne disease of eggplant. To introgress the resistance trait into cultivated eggplant, the tetraploid somatic hybrids S. melongena + S. aethiopicum and S. melongena + S. integrifolium were used. An inheritance study of the resistance was performed on advanced anther culture-derived androgenetic backcross progenies from the two somatic hybrids. The segregation fitted a 3 resistant (R): 1 susceptible (S) ratio in the selfed populations and a 1R:1S ratio in the backcross progenies for the trait derived from S. aethiopicum and S. integrifolium. These ratios are consistent with a single gene, which we designated as Rfo-sa1, controlling the resistance to Fusarium oxysporum f. sp. melongenae. The allelic relationship between the resistance genes from S. aethiopicum and S. integrifolium indicate that these two genes are alleles of the same locus. Bulked Segregant Analysis (BSA) was performed with RAPD markers on the BC₃/BC₅ resistant advanced backcross progenies, and three RAPD markers associated with the resistance trait were identified. Cleaved Amplified Polymorphic Sequences (CAPSs) were subsequently obtained on the basis of the amplicon sequences. The evaluation of the efficiency of these markers in predicting the resistant phenotype in segregating progenies revealed that they represent useful tools for indirect selection of Fusarium resistance in eggplant.