Transport and Compartmentation of 1-Aminocyclopropane-1-Carboxylic Acid and Its Structural Analog, alpha-Aminoisobutyric Acid, in Tomato Pericarp Slices

The uptakes of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor to ethylene, and its structural analog, α-aminoisobutyric acid (αAIB) by tomato pericarp slices were investigated. Both uptakes show a biphasic (saturable-linear) dependence on external concentration of the transported amino acid. At low concentrations, ACC uptake is competitively inhibited by αAIB and vice versa. Both uptakes also are inhibited by other neutral amino acids but not by acidic or basic amino acids. ACC and αAIB uptakes are metabolically dependent and are increased with time of tissue incubation. αAIB efflux patterns from pericarp slices indicated three distinct αAIB compartments having efflux kinetics consistent with those for cell wall, cytoplasm, and vacuole. The bulk of the αAIB taken up by pericarp tissue is sequestered into the vacuole. The ability of pericarp tissue to accumulate αAIB in the vacuole declines with fruit development.     

Translational modification of an 18 kilodalton polypeptide by spermidine in rice cell suspension cultures

When rice (Oryza sativa) cell suspension cultures are grown in the presence of [terminal methylenes-³H]spermidine, label is incorporated in a single polypeptide with a molecular mass of 18 kilodaltons on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Preincubation of cell cultures with polyamine biosynthesis inhibitors difluoromethylarginine and difluoromethylornithine, resulted in increased incorporation of the label into the 18 kilodalton polypeptide. In cells in which protein synthesis was arrested by cycloheximide, no label was detected in the 18 kilodalton polypeptide, suggesting a requirement for de novo protein synthesis.     

Effects of organic amines on α-aminoisobutyric acid uptake into the vacuole and on ethylene production by tomato pericarp slices

Experiments were conducted to test the possibility that organic amines inhibit ethylene production by inhibiting transport of the ethylene precursor, 1-aminocyclopro-pane-1-carboxylic acid (ACC), into the vacuole. α-Aminoisobutyric acid (αAIB) was used as a model substrate to study ACC uptake into the vacuole in relationship to ethylene production in pericarp slices of Lycopersicon esculentum Mill. cv. Liberty treated with and without organic amines and related substances. Organic amines (polyamines and other basic amines) inhibited αAIB uptake into the vacuole. These amines also enhanced ACC accumulation in the tissue and reduced the passive efflux of αAIB from the vacuole. Overall, ethylene production was inhibited. The inhibition of αAIB transport and of ethylene production followed a polyvalent cationic progression in the order polyamines > diamines> basic 1-amino acids. Ca²⁺, but not Mg²⁺, strongly stimulated αAIB uptake into the vacuole and ethylene production. At equal concentrations, Ca²⁺ counteracted the inhibitory effects of polyamines on both αAIB uptake and ethylene production. Competitive and irreversible inhibitors of polyamine biosynthesis stimulated αAIB uptake into the vacuole and ethylene production. The results indicate an apparent relationship between polyamines, ACC uptake into the vacuole and ethylene production.     

Effect of plant hormones on sucrose uptake by sugar beet root tissue discs

Abscisic acid (ABA), auxins, cytokinins, gibberellic acid, alone or in combination were tested for their effects on short-term sucrose uptake in sugar beet (Beta vulgaris cv USH-20) roots. The effect of ABA on active sucrose uptake varied from no effect to the more generally observed 1.4-to 3.0-fold stimulation. A racemic mixture of ABA and its trans isomer were more stimulatory than ABA alone. Pretreating and/or simultaneously treating the tissue with K⁺ or IAA prevented the ABA response while cytokinins and gibberellic acid did not. While the variable sensitivities of beet root to ABA may somehow be related to the auxin and alkali cation status of the tissue, tissue sensitivity to ABA was not correlated with ABA uptake, accumulation, or metabolic patterns. In contrast to ABA, indoleacetic acid (IAA) and other auxins strongly inhibited active sucrose uptake in beet roots. Cytokinins enhanced the auxin-induced inhibition of sucrose uptake but ABA and gibberellic acid did not modify or counteract the auxin effect. Trans-zeatin, benzyladenine, kinetin, and gibberellins had no effect on active sucrose uptake. None of the hormones or hormone mixtures tested had any significant effect on passive sucrose uptake. The effects of IAA and ABA on sucrose uptake were detectable within 1 h suggesting a rather close relationship between the physiological activities of IAA and ABA and the operation of the active transport system.     

Effects of turgor potential on 1-aminocyclopropane-1-carboxylic acid uptake into the vacuolar compartment and ethylene production in tomato pericarp slices

While solute transport and ethylene production by plant tissue are sensitive to the osmotic concentration of the solution bathing the tissue, the influence of tissue water relations and specifically tissue turgor potential on the kinetics of 1-aminocyclopropane-1-carboxylic acid (ACC) uptake into the vacuolar compartment and ethylene production have not been examined. 1-Aminocyclopropane-1-carboxylic acid transport and ethylene production were examined in tomato (Lycopersicon esculentum Mill. cv. Liberty) pericarp slices incubated in solutions having a range of mannitol, polyethylene glycol 3350 and ethylene glycol concentrations known to affect tissue water relations. Tissue osmotic and turgor potentials were derived from osmolality measurements of cell saps recovered by freeze-thawing and corrected for the contribution of the free-space solution. When relatively nonpermeable (mannitol or polyethylene glycol 3350) osmotica were used, both ACC uptake and ethylene production were greatest at a solution osmolality of 230 milliosmolal where tissue turgor potential ranged between 120 and 140 kPa. At higher and lower turgor potentials, the high-affinity saturating component of ACC uptake and ethylene production were inhibited, and ACC efflux from the vacuolar compartment was increased. The inhibition of ACC uptake was evident as a decrease in V_max with no effect on K_m. Turgor potential changes caused by adjusting solution osmolality with mannitol or polyethylene glycol 3350 were accompanied by changes in the osmotic potential and water potential of the tissue. The effects of turgor potential vs the osmotic and water potentials of tomato pericarp slices were differentiated by comparing responses to nonpermeable osmotica and mixtures of nonpermeable and permeable osmotica. Ethylene glycol-mannitol mixtures had effects on the osmotic potential and water potential of the tissue similar to those of nonpermeable osmotica but had less effect on tissue turgor, ACC transport and ethylene production. Incubating tissue in solutions without nonpermeable osmotica osmotically shocked the tissue. Increasing solution osmolality with ethylene glycol in the absence of nonpermeable osmotica increased tissue turgor and ethylene production. The present study indicates that tissue turgor is an important factor affecting the kinetics of ACC uptake into the vacuolar compartment and ethylene production in tomato pericarp slices.     

Genetic diversity in Capsicum baccatum is significantly influenced by its ecogeographical distribution

ABSTRACT: BACKGROUND: The exotic pepper species Capsicum baccatum, also known as the aji or Peruvian hot pepper, is comprised of wild and domesticated botanical forms. The species is a valuable source of new genes useful for improving fruit quality and disease resistance in C. annuum sweet bell and hot chile pepper. However, relatively little research has been conducted to characterize the species, thus limiting its utilization. The structure of genetic diversity in a plant germplasm collection is significantly influenced by its ecogeographical distribution. Together with DNA fingerprints derived from AFLP markers, we evaluated variation in fruit and plant morphology of plants collected across the species native range in South America and evaluated these characters in combination with the unique geography, climate and ecology at different sites where plants originated. RESULTS: The present study mapped the ecogeographic distribution, analyzed the spatial genetic structure, and assessed the relationship between the spatial genetic pattern and the variation of morphological traits in a diverse C. baccatum germplasm collection spanning the species distribution. A combined diversity analysis was carried out on the USDA-ARS C. baccatum germplasm collection using data from GIS, morphological traits and AFLP markers. The results demonstrate that the C. baccatum collection covers wide geographic areas and is adapted to divergent ecological conditions in South America ranging from cool Andean highland to Amazonia rainforest. A high level of morphological diversity was evident in the collection, with fruit weight the leading variable. The fruit weight distribution pattern was compatible to AFLP-based clustering analysis for the collection. A significant spatial structure was observed in the C. baccatum gene pool. Division of the domesticated germplasm into two major regional groups (Western and Eastern) was further supported by the pattern of spatial population structure. CONCLUSIONS: The results reported improve our understanding of the combined effects of geography, ecology and human intervention on organization of the C. baccatum genepool. The results will facilitate utilization of C. baccatum for crop improvement and species conservation by providing a framework for efficient germplasm collection management and guidance for future plant acquisitions.     

Biocontrol of Listeria monocytogenes on Fresh-Cut Produce by Treatment with Lytic Bacteriophages and a Bacteriocin

The fresh-cut produce industry has been the fastest-growing portion of the food retail market during the past 10 years, providing consumers with convenient and nutritious food. However, fresh-cut fruits and vegetables raise food safety concerns, because exposed tissue may be colonized more easily by pathogenic bacteria than intact produce. This is due to the higher availability of nutrients on cut surfaces and the greater potential for contamination because of the increased amount of handling. We found that applied Listeria monocytogenes populations survived and increased only slightly on fresh-cut Red Delicious apples stored at 10°C but increased significantly on fresh-cut honeydew melons stored at 10°C over 7 days. In addition, we examined the effect of lytic, L. monocytogenes-specific phages via two phage application methods, spraying and pipetting, on L. monocytogenes populations in artificially contaminated fresh-cut melons and apples. The phage mixture reduced L. monocytogenes populations by 2.0 to 4.6 log units over the control on honeydew melons. On apples, the reduction was below 0.4 log units. In combination with nisin (a bacteriocin), the phage mixture reduced L. monocytogenes populations by up to 5.7 log units on honeydew melon slices and by up to 2.3 log units on apple slices compared to the control. Nisin alone reduced L. monocytogenes populations by up to 3.2 log units on honeydew melon slices and by up to 2.0 log units on apple slices compared to the control. The phage titer was stable on melon slices, but declined rapidly on apple slices. The spray application of the phage and phage plus nisin reduced the bacterial numbers at least as much as the pipette application. The effectiveness of the phage treatment also depended on the initial concentration of L. monocytogenes.     

Selective effects of victorin on growth and the auxin response in Avena

Victorin, the pathotoxin from the host-specific pathogen, Helminthosporium victoriae, promotes the growth of coleoptile segments when given at concentrations that are high but which still show selective effects on susceptible and resistant tissue. The latent period in the growth response of both susceptible and resistant tissue is about 3.6 minutes compared to 11.0 minutes in the response of these tissues to auxin. The victorinpromoted rate of elongation of 8-millimeter segments is about 0.2 millimeter per hour in susceptible tissue and about 0.1 millimeter per hour in resistant tissue compared to about 0.4 millimeter per hour in response to auxin. At low concentrations, the toxin has no growth-promoting effect in either susceptible or resistant coleoptile segments. Over a wide range of concentrations, victorin inhibits the growth response of susceptible tissue to auxin completely while having no effect on the response of resistant tissue to auxin.     

Electrical potentials in stomatal complexes

Guard cells of several species, but predominantly Commelina communis, were impaled by micropipette electrodes and potential differences measured that occurred between cell compartments and the flowing bathing medium. The wall developed a Donnan potential that was between −60 and −70 millivolt in 30 millimolar KCl at pH 7. The density of the fixed charges ranged from 0.3 to 0.5 molar; its dependence on pH was almost identical with the titration curve of authentic polygalacturonic acid. The vacuolar potential of guard cells of Commelina communis L., Zea mays L., Nicotiana glauca Graham, Allium cepa L., and Vicia faba L. was between −40 and −50 millivolt in 30 millimolar KCl when stomata were open and about −30 millivolt when stomata were closed. The vacuolar potential of guard cells of C. communis was almost linearly related to stomatal aperture and responded to changes in the ionic strength in the bathing medium in a Nernstian manner. No specificity for any alkali ion (except Li⁺), ammonium, or choline appeared. Lithium caused hyperpolarization. Calcium in concentrations between 1 and 100 millimolar in the medium led to stomatal closure, also caused hyperpolarization, and triggered transient oscillations in the intracellular potential. Gradients in the electrical potential existed across stomatal complexes with open pores. When stomata closed, these gradients almost disappeared or slightly reverted; all epidermal cells were then at potentials near −30 millivolt in 30 millimolar KCl.     

Inhibition of growth by ancymidol and tetcyclacis in the gibberellin-deficientdwarf-5 mutant ofZea mays L. and its prevention by exogenous gibberellin

Leaf sheath length and shoot dry matter of the gibberellin-deficientdwarf-5 mutant ofZea mays L. were further reduced by micromolar concentrations of two putative gibberellin biosynthesis inhibitors, ancymidol [-cyclopropyl--(p-methoxyphenyl)-5-pyrimidine methyl alcohol] and tetcyclacis [5-(4-chlorophenyl)-3,4,5,9,10-pentaazatetracyclo-5,4,1,0^2,6,0^8,11-dodeca-3,9-diene]. Growth retardant action was prevented by the subsequent application of gibberellin (GA₄₊₇). Plants treated with both gibberellin and growth retardants were identical in all outward respects to those treated with gibberellin alone. Although thedwarf-5 mutant is blocked in the synthesis ofent-kaurene and does not contain detectable quantities of gibberellin, the above results are consistent with the interpretation that biologically active levels of endogenous gibberellin are present in the dwarf which can be decreased by biosynthesis inhibitors.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the United States Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.