Inhibition of electron transport activities in mitochondria from avocado and pepper fruit by naturally occurring polyamines

The effects of the naturally occurring polyamines, spermine, putrescine, and spermidine were explored on mitochondrial state 3. state 4, and uncoupled respiration activities, ADP/O ratio, respiratory control ratio of pepper ( Capsicum annuum L. cv. Early Cal Wonder) and avocado ( Persea americana Mill. cv. Booth-8 or Simmonds) mitochondria oxidizing either succinate, external NADH, malate, α-ketoglutarate or tetramethyl- p -phenylenediamine. Abnormally high concentrations of spermine and spermidine such as might occur during chilling stress of these chilling-sensitive fruits were detrimental to several oxidase activities, especially to external NADH oxidase. State 3 respiration for NADH oxidase was inhibited more than 70% by 10 m M spermine. The spermine inhibition of uncoupled NADH oxidase was not reversed by the presence of divalent cations including Ca²⁺, Mg²⁺, Mn²⁺, and Sr²⁺ at concentrations up to 10 m M or by 100 m M KCl. The inhibition primarily affected the V_max. Other possible sites of polyamine interactions are discussed.     

Influence of arbuscular mycorrhizae on heavy metal (Zn and Pb) uptake and growth of Lygeum spartum and Anthyllis cytisoides

The hypothesis tested in this paper is that, because the freshest water occurs in the largest soil pores (macropores), plants of low to moderate transpiration rate can survive in salinized soil because they preferentially extract water from macropores. The hypothesis predicts that a plant growing in a macroporous soil should have greater growth under a given salinity treatment than a similar plant growing in a soil with the same mineralogy but without macropores. This hypothesis was tested by growing bell pepper (Capsicum annuum) in the greenhouse in pots filled with either a commercial fritted clay (a highly macroporous soil) or the same clay ground to a finer texture and sieved to remove macropores and produce a microporous soil. The pots sat in pans filled with salt water. Half of the pots were irrigated once a day with fresh water and the other half received no fresh water. Plants growing in the macroporous soil had greater growth for a given salinity treatment than the plants growing in the microporous soil under both the irrigated and non-irrigated conditions. Under the irrigated condition for the highest salinity treatment, the non-reproductive fresh weight per plant, total dry weight per plant and fruit fresh weight per plant was 114 g, 12 g and 50 g, respectively, for the macroporous soil and 47 g, 4.5 g and 5 g, respectively, for the microporous soil. The results of this study provide evidence to suggest that a better understanding of what constitutes a good structure in a saline soil may aid us in our efforts to improve the management of saline soils. We suggest that it may be possible to increase the agricultural production on salinized land by no-tillage agriculture which preserves macroporosity. Possible obstacles could be the tendency of field saline-sodic soils to swell and the unavailability of relatively fresh irrigation water in areas with saline soils.     

A <Emphasis Type="Italic">Colletotrichum gloeosporioides</Emphasis>-induced esterase gene of nonclimacteric pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis>) fruit during ripening plays a role in resistance against fungal infection

Ripe fruits of pepper (Capsicum annuum) are resistant to the anthracnose fungus, Colletotrichum gloeosporioides, whereas unripe-mature fruits are susceptible. A pepper esterase gene (PepEST) that is highly expressed during an incompatible interaction between the ripe fruit of pepper and C. gloeosporioides was previously cloned. Deduced amino acid sequence of PepEST cDNA showed homology to both esterases and lipases, and contained -HGGGF- and -GXSXG- motifs and a catalytic triad. Inhibition of PepEST activity by a specific inhibitor of serine hydrolase demonstrated that a serine residue is critical for the enzyme activity. Expression of PepEST gene was fruit-specific in response to C. gloeosporioides inoculation, and up-regulated by wounding or jasmonic acid treatment during ripening. PepEST mRNA and protein was differentially accumulated in ripe vs. unripe fruit from 24 h after inoculation when C. gloeosporioides isinvading into fruits. Immunochemical examination revealed that PepEST accumulation was localized inepidermal and cortical cell layers in infected ripe fruit, but rarely even in epidermal cells in infected unripe one. Over-expression of PepEST in transgenic Arabidopsis plants caused restriction of Alternaria brassicicola colonization by inhibition of spore production, resulting in enhanced resistance against A.brassicicola. These results suggest that PepEST is involved in the resistance of ripe fruit against C.gloeosporioides infection.^†These authors contributed equally to the work     

Cloning and functional characterization of the high-affinity K<Superscript>+</Superscript> transporter HAK1 of pepper

High-affinity K⁺ uptake in plants plays a crucial role in K⁺ nutrition and different systems have been postulated to contribute to the high-affinity K⁺ uptake. The results presented here with pepper (Capsicum annum) demonstrate that a HAK1-type transporter greatly contributes to the high-affinity K⁺ uptake observed in roots. Pepper plants starved of K⁺ for 3 d showed high-affinity K⁺ uptake (K _m of 6 M K⁺) that was very sensitive to NH and their roots expressed a high-affinity K⁺ transporter, CaHAK1, which clusters in group I of the KT/HAK/KUP family of transporters. When expressed in yeast (Saccharomyces cerevisiae), CaHAK1 mediated high-affinity K⁺ and Rb⁺ uptake with K _m values of 3.3 and 1.9 M, respectively. Rb⁺ uptake was competitively inhibited by micromolar concentrations of NH and Cs⁺, and by millimolar concentrations of Na⁺.     

Unilateral incompatibility in Capsicum (Solanaceae): occurrence and taxonomic distribution

BACKGROUND AND AIMS: Unilateral incompatibility (UI) occurs when pollinations between species are successful in one direction but not in the other. Self-incompatible (SI) species frequently show UI with genetically related, self-compatible (SC) species, as pollen of SI species is compatible on the SC pistil, but not vice versa. Many examples of unilateral incompatibility, and all those which have been studied most intensively, are found in the Solanaceae, particularly Lycopersicon, Solanum, Nicotiana and Petunia. The genus Capsicum is evolutionarily somewhat distant from Lycopersicon and Solanum and even further removed from Nicotiana and Petunia. Unilateral incompatibility has also been reported in Capsicum; however, this is the first comprehensive study of crosses between all readily available species in the genus. METHODS: All readily available (wild and domesticated) species in the genus are used as plant material, including the three genera from the Capsicum pubescens complex plus eight other species. Pollinations were made on pot-grown plants in a glasshouse. The number of pistils pollinated per cross varied (from five to 40 pistils per plant), depending on the numbers of flowers available. Pistils were collected 24 h after pollination and fixed for 3-24 h. After staining, pistils were mounted in a drop of stain, squashed gently under a cover slip and examined microscopically under ultra-violet light for pollen tube growth. KEY RESULTS: Unilateral incompatibility is confirmed in the C. pubescens complex. Its direction conforms to that predominant in the Solanaceae and other families, i.e. pistils of self-incompatible species, or self-compatible taxa closely related to self-incompatible species, inhibit pollen tubes of self-compatible species. CONCLUSIONS: Unilateral incompatibility in Capsicum does not seem to have arisen to prevent introgression of self-compatibility into self-incompatible taxa, but as a by-product of divergence of the C. pubescens complex from the remainder of the genus.     

The pvr1 locus in Capsicum encodes a translation initiation factor eIF4E that interacts with Tobacco etch virus VPg

Mutations in the eIF4E homolog encoded at the pvr1 locus in Capsicum result in broad-spectrum potyvirus resistance attributed to the pvr1 resistance allele, a gene widely deployed in agriculture for more than 50 years. We show that two other resistance genes, previously known to be eIF4E with narrower resistance spectra, pvr2(1) and pvr2(2), are alleles at the pvr1 locus. Based on these data and current nomenclature guidelines, we have re-designated these alleles, pvr1(1) and pvr1(2), respectively. Point mutations in pvr1, pvr1(1), and pvr1(2) grouped to similar regions of eIF4E and were predicted by protein homology models to cause conformational shifts in the encoded proteins. The avirulence determinant in this potyvirus system has previously been identified as VPg, therefore yeast two-hybrid and GST pull-down assays were carried out with proteins encoded by the pvr1 alleles and VPg from two different strains of Tobacco etch virus (TEV) that differentially infected Capsicum lines carrying these genes. While the protein encoded by the susceptible allele pvr1+ interacted strongly, proteins translated from all three resistance alleles (pvr1, pvr1(1), and pvr1(2)) failed to bind VPg from either strain of TEV. This failure to bind correlated with resistance or reduced susceptibility, suggesting that interruption of the interaction between VPg and this eIF4E paralog may be necessary, but is not sufficient for potyvirus resistance in vivo. Among the three resistance alleles, only the pvr1 gene product failed to bind m7-GTP cap-analog columns, suggesting that disrupted cap binding is not required for potyvirus resistance.