Effect of temperature on the dose–response curves for auxin-induced elongation growth in maize coleoptile segments

The dose–response curves for IAA-induced growth in maize coleoptile segments were studied as a function of time and temperature. In addition, the kinetics of growth rate responses at some auxin concentrations and temperatures was also compared. It was found that the dose–response curves for IAA-induced elongation growth were, independently of time and temperature, bell-shaped with an optimal concentration at 10⁻⁵ M IAA. The kinetics of IAA-induced growth rate responses depended on IAA concentration and temperature, and could be separated into two phases (biphasic reaction). The first phase (very rapid) was followed by a long lasting one (second phase), which began about 30 min after auxin addition. For coleoptile segments incubated at 30°C, the amplitudes of the first and second phase were significantly higher, when compared with 25°C, at all IAA concentrations studied. However, when coleoptile segments were incubated at 20°C, the elongation growth of coleoptile segments treated with suboptimal IAA concentrations was diminished, mainly as a result of both phases reduction. In conclusion, we propose that the shape of the dose–response curves for IAA-induced growth in maize coleoptile segments is connected with biphasic kinetic of growth rate response.     

Effect of arbuscular mycorrhizal fungi, organic fertilizer and soil sterilization on maize growth ☆

The effects of inoculation with arbuscular mycorrhizal (AM) fungi, organic fertilizer (F) applications, and soil sterilization on maize growth were evaluated in a pot experiment. The experiment was in a completely randomized factorial design (2 × 4 × 2) with six replicates for each treatment. There were two soil treatments (sterilized soil, SS and unsterilized soil, US), four organic fertilizer treatments (0.0, 0.5, 1.0 and 2.0 g kg^-1 soil), and two AM fungi treatments (inoculation with Glomus mosseae, +AM and uninoculated control, －AM). Inoculated plants generally had greater AM colonization, plant height, dry weight and phosphorus (P) uptake than uninoculated controls, and these parameters were significantly increased as the organic fertilizer application increased up to 0.5 g kg^-1 but decreased or had no significant effect compared to the uninoculated plants at the highest fertilizer rate (2.0 g kg^-1). Plant growth, P uptake and AM colonization of root system were significantly higher in sterilized soil compared to the unsterilized control. Our results indicated that the inoculation of AM fungi in field soil with optimal organic fertilizer application greatly improved maize growth and nutrient uptake, and the effect was greater under sterilized soil condition.     

Are source and sink strengths genetically linked in maize plants subjected to water deficit? A QTL study of the responses of leaf growth and of Anthesis-Silking Interval to water deficit

Leaf growth and Anthesis-Silking Interval (ASI) are the main determinants of source and sink strengths of maize via their relations with light interception and yield, respectively. They depend on the abilities of leaves and silks to expand under fluctuating environmental conditions, so the possibility is raised that they may have a partly common genetic determinism. This possibility was tested in a mapping population which segregates for ASI. Maximum leaf elongation rate per unit thermal time (parameter a) and the slopes of its responses to evaporative demand and soil water status (parameters b and c) were measured in greenhouse and growth chamber experiments, in two series of 120 recombinant inbred lines (RILs) studied in 2004 and 2005 with 33 RILs in common both years. ASI was measured in three and five fields under well-watered conditions and water deficit, respectively. For each RIL, the maximum elongation rate per unit thermal time was reproducible over several experiments in well-watered plants. It was accounted for by five QTLs, among which three co-localized with QTLs of ASI of well-watered plants. The alleles conferring high leaf elongation rate conferred a low ASI (high silk elongation rate). The responses of leaf elongation rate to evaporative demand and to predawn leaf water potential were linear, allowing each RIL to be characterized by the slopes of these response curves. These slopes had three QTLs in common with ASI of plants under water deficit. The allele for leaf growth maintenance was, in all cases, that for shorter ASI (maintained silk elongation rate). By contrast, other regions influencing ASI had no influence on leaf growth. These results may have profound consequences for modelling the genotype x environment interaction and for designing drought-tolerant ideotypes.     

Effect of maternal age and growth on placental nutrient transport: potential mechanisms for teenagers' predisposition to small-for-gestational-age birth?

Teenagers have an increased risk of delivering small-for-gestational-age (SGA) infants. Young maternal age and continued skeletal growth have been implicated as causal factors. In growing adolescent sheep, impaired placental development and nutrient transfer cause reduced birth weight. In human pregnancies, SGA is associated with reduced placental amino acid transport. Maternal growth has no effect on placental morphology or cell turnover, but growing teenagers have higher birth weight:placental weight ratios than nongrowing teenagers. We hypothesized that placental nutrient transporter activity would be affected by maternal age and/or growth status. Placentas from teenagers and adults were collected. Teenagers were defined as growing or nongrowing based on knee height measurements. System A amino acid transporter activity was quantified as sodium-dependent uptake of [(14)C]methylaminoisobutyric acid into placental fragments. Teenagers had lower placental system A activity than adults (P < 0.05). In adults, placental system A activity was lower in SGA infants than appropriate-for-gestational-age (AGA) infants (P < 0.05). In teenagers, AGA and SGA infants had lower placental system A activity than AGA infants born to adults (P < 0.05). Placental system A activity was higher in growing teenagers than in nongrowing teenagers (P < 0.001). Placental mRNA expression of system A transporter isoforms SLC38A1 and -2 was lower in teenagers than in adults (P < 0.05) but did not differ between growing and nongrowing teenagers. There was no difference in transporter protein expression/localization between cohorts. Teenagers have inherently reduced placental transport, which may underlie their susceptibility to delivering SGA infants. Growing teenagers appear to overcome this susceptibility by stimulating the activity, but not expression, of system A transporters.     

Effect of a ceiling fan ventilation system on finishing young bulls’ health,behaviour and growth performance

This research aimed at assessing the effects of a ceiling fan ventilation system on health, feeding, social behaviour and growth response of finishing young bulls fattened indoors during a mild summer season. A total of 69 Charolais young bulls were housed in six pens without any mechanical ventilation system (Control) and in six pens equipped with ceiling fans. The experimental period lasted 98 days from June until mid-September 2014. Four experimental days were considered in order to assess the effect of the ventilation system under two different microclimatic conditions: 2 alert days at monthly interval with temperature humidity index (THI) between 75 and 78, and 2 normal days with THI⩽74. Health and behaviour of the bulls were evaluated through 8-h observation sessions starting after morning feed delivery. The study was carried out during a rather cool summer with a climate average THI of 68.9 and 4 days with average THI>75. Despite these mild climate conditions, ceiling fans lowered litter moisture and acted as a preventive measure for bulls’ dirtiness (odd ratio=47.9; 95% CI 19.6 to 117.4). The risk of abnormal breathing was increased for Control bulls (odd ratio=40.7; 95% CI 5.4 to 304.2). When exposed to alert THI conditions, respiration rate and panting scores increased and rumination duration dropped in Control bulls compared with bulls provided with a ceiling fan. During observations under alert THI, bulls spent less time eating, more time being inactive and consumed more water compared with normal THI conditions. Bulls’ daily dry matter intake measured during the observation sessions decreased on alert compared with normal THI days (P<0.001) due to a drop of intake during the daylight hours. Ceiling fan treatment had no effect on bulls’ growth performance or water consumption but these results most likely depended on the mild climate conditions. Ceiling fans proved to mitigate some of the negative effects of heat stress on bulls’ behaviour (rumination, lying down and drinking water) and respiration rate, however. The lack of a significant improvement of bulls’ growth response should not discourage beef farmers from using ceiling fans in indoor systems, considering the likely increase in frequency and intensity of heat waves in the planet’s temperate areas induced by global warming.     

Effect of environmental enrichment and herbal compound supplementation on physiological stress indicators (chromogranin A,cortisol and tumour necrosis factor-α) in growing pigs

Stress response induces physiological, behavioural, immunological and biochemical changes that directly affect health and well-being. Provision of environmental enrichment and herbal compounds may reduce stress in current commercial pig husbandry systems. The aim of this study was to evaluate the effect of providing different environmental enrichment materials (EE) and a herbal compound (HC) on physiological indicators of acute and chronic stress in growing pigs (salivary cortisol and chromogranin A (CgA), hair cortisol and tumour necrosis factor-α (TNF-α)). Salivary cortisol and CgA have been reported as biomarkers basically of acute stress, whereas hair cortisol and TNF-α have been more related to chronic stress. For this purpose, eight groups of seven pigs each (14 pigs/treatment, 56 pigs in total) were used: (a) two EE groups, (b) two groups supplemented with HC, (c) two groups provided both with EE and HC and (d) two control groups. Samples of hair, saliva and blood were taken to measure cortisol (in hair and saliva), CgA (in saliva) and TNF-α (in blood) at three different times: before starting the experiment (T0), and after 1 (T1) or 2 months (T2) of providing the materials and herbal compound. No differences were found at T0 in salivary or hair cortisol, CgA or TNF-α, whilst at T2, the control group showed significant increased concentrations of CgA and hair cortisol, when compared with the rest of the treatments (P<0.001). These differences were significant at T1 only for CgA (P<0.001). Furthermore, an overall correlation was reported between hair cortisol and salivary CgA (r=0.48, P<0.001). These results support that providing enrichment material or an herbal compound may reduce stress in growing pigs. Furthermore, the results support that hair cortisol and CgA may be proper non-invasive tools to detect stress, specially associated with factors of chronic exposure.     

The midpoint of sleep on working days: A measure for chronodisruption and its association to individuals’ well-being

There is consistent evidence suggesting a relationship between individuals’ sleep–wake rhythms and well-being. The indiscriminate demands from daily working routines, which do not respect this individual physiological rhythm, might be mediating this phenomenon. The aim of the present study was to evaluate the relationship between the characteristics of sleep routines during working days and psychological well-being. This was a cross-sectional study on 825 individuals from rural communities from southern Brazil. The study protocol included a questionnaire on demographic characteristics, working routines, health complaints, and habits; the Munich Chronotype Questionnaire for sleep–wake rhythm and; the WHO-Five well-being index. Since sex has been shown to affect sleep circadian rhythm and well-being, analysis was performed on men and women separately. In the proposed hierarchical regression models, different factors contributed to well-being according to sex. Among men, sleep–wake and work-related variables did not predict well-being scores. Among women, later midpoints of sleep on working days (B?=??1.243, SE B?=?0.315, β?=??0.220), working more days per week (B?=??1.507, SE B?=?0.494, β?=?0.150), having longer working journeys (B?=??0.293, SE B?=?0.105, β?=??0.166), earlier working journey midpoints (B?=?0.465, SE B?=?0.222, β?=?0.115), and being exposed to less sunlight (B?=?0.140, SE B?=?0.064, β?=?0.103) predicted worse well-being. For the subgroup of women with days free from work, we have found a correlation between later midpoints of sleep during the week with worse well-being (Pearson’s r?=??0.159, p?=?0.045) while the same relationship was not significantly observed with the midpoint of sleep on non-working days (Pearson’s r?=??0.153, p?=?0.054). Considering WHO-Five as categorical, based on proposed clinical cut-offs, among women working 7-d/week, those with worst well-being (WHO-Five?<?13) had the latest midpoint of sleep (F?=?4.514, p?=?0.012). Thus, the midpoint of sleep on working days represents the interaction between individuals’ sleep–wake behavior and working routines. It plays an important role as a stress factor and may be a useful alternative variable related to chronodisruption.     

Effects of the dietary protein content and the feeding level on protein and energy metabolism in Iberian pigs growing from 50 to 100 kg body weight

Nutritional requirements of the Iberian pig, a slow-growing, obese porcine breed, are not well defined and seem to differ from those of conventional or high-performing pigs. The effects of the dietary protein content and the feeding level on the utilisation of metabolisable energy (ME) and the rates of gain, protein, and fat deposition were studied with 81 Iberian castrates growing from 50 to 100 kg body weight (BW) by using the comparative slaughter technique. The animals were fed 4 diets providing 145, 120, 95, and 70 g ideal crude protein (CP) per kg dry matter (DM), and containing 13.94, 14.29, 14.56, and 14.83 MJ ME per kg DM, respectively. Three levels of feeding were evaluated: 0.60, 0.80, and 0.95 × ad libitum intake. Growth rate increased (linear and quadratic, P < 0.001) as the dietary ideal CP content decreased. It also increased with the feeding level (linear, P < 0.001; quadratic, P < 0.05). Gain:feed and gain:ME intake improved by decreasing the ideal CP content in the diet (linear, P < 0.001 and P < 0.05, respectively; quadratic P < 0.001 for both variables). Increasing the feeding level improved linearly gain:feed and gain:ME intake ( P < 0.001). Protein deposition (PD):ME intake ranged between 1.23 and 1.44 g/MJ, and it showed a tendency to reach the maximum value when the diet providing 95 g ideal CP per kg DM was fed (quadratic, P = 0.078). When this diet was offered at 0.95 × ad libitum, PD reached a maximum value of 71 g/day. This dietary treatment resulted in average values for average daily gain and retained energy (RE) of 854 g/day and 21.4 MJ/day, respectively. The average rate of gain was 19.93 g/MJ increase in ME intake, equivalent to an energy cost of 50.2 kJ ME per g gain, irrespective of the dietary ideal CP content. Also, the overall marginal efficiency of protein deposition (ΔPD:ΔME; g/MJ) was 1.34. Increasing the feeding level led to increases in PD (linear, P <  0.001) and RE (linear, P <  0.001; quadratic, P <  0.01) irrespective of the dietary ideal CP concentrations. Between 50 and 100 kg BW, the chemical composition of 1 kg gain averaged 78, 592, 28.7, and 284 g for CP, fat, ash, and water respectively. The net efficiency of use of ME for growth ( k_g) and the maintenance energy requirements were 0.606 and 396 kJ/kg BW ^0.75 per day, respectively. The results support earlier findings that the genotype has marked effects on protein and energy metabolism of growing pigs and underline important compositional differences of the Iberian pig compared with conventional or modern porcine genotypes.     

Effect of increasing the dietary tryptophan to lysine ratio on plasma levels of tryptophan,kynurenine and urea and on production traits in weaner pigs experimentally infected with an enterotoxigenic strain of Escherichia coli‡

This experiment examined if immune system stimulation of weaner pigs, initiated by inoculation an enterotoxigenic strain of Escherichia coli (ETEC), increased the requirement for dietary tryptophan (Trp), modulated the inflammatory response, altered plasma levels of Trp and its metabolite kynurenine (Kyn) and effected post-weaning diarrhoea. Individually housed pigs (n = 72) weaned at 21 d of age were allocated to one of six treatments (n = 12) according to a two by three factorial arrangement of (1) with or without ETEC infection and (2) three dietary ratios of standardised ileal digestible (SID) Trp to lysine (Lys) (SID Trp:Lys) of 0.16, 0.20 or 0.24, in a completely randomised block design. Pigs had ad libitum access to diets (per kg 14.13 MJ ME, 12.4 g SID Lys, 195 g crude protein) for 3 weeks after weaning. Pigs were infected with ETEC (O149:K98:K88) at 72, 96 and 120 h after weaning and then bled on day 3, 11 and 19. An increased dietary Trp:Lys ratio increased plasma Trp and Kyn (p < 0.001) without effect of infection. On day 3, pigs fed 0.24 SID Trp:Lys had lower levels of plasma urea than at 0.20 Trp:Lys (p = 0.047) and on day 11, plasma urea was lower at 0.20 than at 0.16 SID Trp:Lys (p = 0.007). Infection increased (p = 0.039) the diarrhoea index and deteriorated faecal consistency from day 4–10 (p < 0.05). Treatments did not affect haptoglobin and acid soluble glycoprotein levels or daily gain and feed intake. However, 0.24 SID Trp:Lys improved (p = 0.021) feed efficiency without an effect of infection. In conclusion, in the absence of dietary antibiotic growth promotants, increasing the dietary SID Trp:Lys ratio to 0.24 improved feed conversion ratio after weaning and increased plasma levels of Trp and Kyn regardless of infection with E. coli.     

Effect of monensin on postpartum interval to first estrus and serum LH response to 0, 1, 2 or 4 mg estradiol-17β at 21 days postpartum

A 2×4 factorial design was used to evaluate the effects of monensin (0 vs 200 mg) and estradiol-17β (E2) dose (0, 1, 2 vs 4 mg) on postpartum interval (PPI) to first estrus and on serum LH release at 21 days postpartum. Forty-eight spring calving Brangus cows were randomly stratified by calving date and sex of calf into two feeding groups within 24 hr of calving. Each group received 2.7 kg/head/day of a milo:cottonseed meal (4:1) mixture containing either 0 or 200 mg monensin. Coastal bermuda grass hay and water were available $\text{ad}$$\text{libitum}$. During the period of E2 treatment and bi-hourly blood sampling, suckling was controlled at 6-hr intervals.Mean cow weight and body condition score within cell changed less than 23 kg and 0.5 points, respectively, from day 1 to day 21 postpartum and were unaffected by treatment (P>0.10). PPI was reduced (P<0.01) and proportion of cows exhibiting estrual behavior by 85 days postpartum was increased (P<0.05) by treatment with 200 mg monensin and unaffected by E2 dose. Monensin fed cows had a longer (P<0.05) interval to LH response (ILH) and to peak LH (ILHP) at the 4 mg E2 dose. Monensin had no effect (P>0.10) on LH variables at 0, 1 or 2 mg E2.     

Interactions of elevated carbon dioxide and temperature with aphid feeding on transgenic oilseed rape: Are Bacillus thuringiensis (Bt) plants more susceptible to nontarget herbivores in future climate?

Climate change factors such as elevated carbon dioxide (CO₂) and temperature typically affect carbon (C) and nitrogen (N) dynamics of crop plants and the performance of insect herbivores. Insect‐resistant transgenic plants invest some nutrients to the production of specific toxic proteins [i.e. endotoxins from Bacillus thuringiensis (Bt)], which could alter the C–N balance of these plants, especially under changed abiotic conditions. Aphids are nonsusceptible to Lepidoptera‐targeted Bt Cry1Ac toxin and they typically show response to abiotic conditions, and here we sought to discover whether they might perform differently on compositionally changed Bt oilseed rape. Bt oilseed rape had increased N content in the leaves coupled with reduced total C compared with its nontransgenic counterpart, but in general the C : N responses of both plant types to elevated CO₂ and temperature were similar. Elevated CO₂ decreased N content and increased C : N ratio of both plant types. Elevated temperature increased C and N contents, total chlorophyll and carotenoid concentrations under ambient CO₂, but decreased these under elevated CO₂. In addition, soluble sugars were increased and starch decreased by elevated temperature under ambient but not under elevated CO₂, whereas photosynthesis was decreased in plants grown under elevated temperature in both CO₂ levels. Myzus persicae, a generalist aphid species, responded directly to elevated temperature with reduced developmental time and decreased adult and progeny weights, whereas the development of the Brassica specialist Brevicoryne brassicae was less affected. Feeding by M. persicae resulted in an increase in the N content of oilseed rape leaves under ambient CO₂, indicating the potential of herbivore feeding itself to cause allocation changes. The aphids performed equally well on both plant types despite the differences between C–N ratios of Bt and non‐Bt oilseed rape, revealing the absence of plant composition‐related effects on these pests under elevated CO₂, elevated temperature or combined elevated CO₂ and temperature conditions.     

The growth of Pichia pastoris Mut+ on methanol–glycerol mixtures fits to interactive dual-limited kinetics: model development and application to optimised fed-batch operation for heterologous protein production

Bioprocess and Biosystems Engineering - The methanol–glycerol co-feeding during the induction stage for heterologous protein production in Pichia pastoris has shown significant productive...     

Effect of the slow (K) or rapid (k+) feathering gene on body and feather growth and fatness according to ambient temperature in a Leghorn × brown egg type cross

Chicks of both sexes issued from the cross of heterozygous K/k⁺ cocks for the slow-feathering sex linked K allele with k⁺ (rapid feathering) hens, were compared from the age of 4 to 10 weeks at two ambient temperatures. In individual cages, 30 male chicks of each genotype (K/k⁺ and k⁺/k⁺) were raised at 21°C, and 60 others, distributed in the same way, were raised at 31°C. 71 K/W females and 69 k⁺/W females were raised in a floor pen at 31°C till 10 weeks of age. In the males, the body weight, feed consumption and feed efficiency at different ages were influenced only by temperature (lower growth rate and feed intake at 31°C); no significant effects of the genotype at locus K nor genotype × temperature interaction were observed. In females, all at 31°C, the genotype (K/W or k⁺/W) had no significant effect on growth rate. Plumage weight and weight of abdominal fat (absolute or related to body weight) were measured on half of the males of each group in individual cages, at 10 weeks of age. Moreover, on 36 males and 48 females of the two genotypes, in a group battery at 31°C, the absolute and relative weight of plumage were measured on a sample every two weeks between 4 and 10 weeks. In the first case, no significant effect of genotype appeared. In the second case, an interaction between age and genotype was suggested from plumage weight: its growth, especially in male chicks, appears to be temporarily and unexpectedly faster from 4 to 6 weeks of age for the K/k⁺ and K/W genotypes.     

Efficacy of β-mannanase supplementation to corn–soya bean meal-based diets on growth performance,nutrient digestibility,blood urea nitrogen,faecal coliform and lactic acid bacteria and faecal noxious gas emission in growing pigs

A study was conducted to determine the efficacy of β-mannanase supplementation to a diet based on corn and soya bean meal (SBM) on growth performance, nutrient digestibility, blood urea nitrogen (BUN), faecal coliforms and lactic acid bacteria, and noxious gas emission in growing pigs. A total of 140 pigs [(Landrace × Yorkshire) × Duroc; average body weight 25 ± 3 kg] were randomly allotted to a 2 × 2 factorial arrangement with dietary treatments consisting of hulled or dehulled SBM without or with supplementation of 400 U β-mannanase/kg. During the 6 weeks of experimental feeding, β-mannanase supplementation had no effect on body weight gain, feed intake and gain:feed (G:F) ratio. Compared with dehulled SBM, feeding hulled SBM caused an increased feed intake of pigs in the entire trial (p = 0.05). The G:F ratio was improved in pigs receiving dehulled SBM (p < 0.05). Dietary treatments did not influence the total tract digestibility of dry matter, nitrogen and gross energy. Enzyme supplementation reduced (p < 0.05) the population of faecal coliforms and tended to reduce the NH₃ concentration after 24 h of fermentation in a closed box containing faecal slurry. Feeding hulled SBM tended to reduce NH₃ emission on days 3 and 5 of fermentation. In conclusion, mannanase supplementation had no influence on growth performance and nutrient digestibility but showed a positive effect on reducing coliform population and tended to reduce NH₃ emission. Dehulled SBM increased G:F ratio and hulled SBM tended to reduce NH₃ emission.     

Plant characterization of genetically modified maize hybrids MON-89Ø34-3 × MON-88Ø17-3, MON-89Ø34-3 × MON-ØØ6Ø3-6, and MON-ØØ6Ø3-6: alternatives for maize production in Mexico

Environmental risk assessment (ERA) of genetically modified (GM) crops is a process to evaluate whether the biotechnology trait(s) in a GM crop may result in increased pest potential or harm to the environment. In this analysis, two GM insect-resistant (IR) herbicide-tolerant maize hybrids (MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6) and one herbicide-tolerant GM hybrid (MON-ØØ6Ø3-6) were compared with conventional maize hybrids of similar genetic backgrounds. Two sets of studies, Experimental Phase and Pilot Phase, were conducted across five ecological regions (ecoregions) in Mexico during 2009–2013, and data were subject to meta-analysis. Results from the Experimental Phase studies, which were used for ERA, indicated that the three GM hybrids were not different from conventional maize for early stand count, days-to-silking, days-to-anthesis, root lodging, stalk lodging, or final stand count. Statistically significant differences were observed for seedling vigor, ear height, plant height, grain moisture, and grain yield, particularly in the IR hybrids; however, none of these phenotypic differences are expected to contribute to a biological or ecological change that would result in an increased pest potential or ecological risk when cultivating these GM hybrids. Overall, results from the Experimental Phase studies are consistent with those from other world regions, confirming that there are no additional risks compared to conventional maize. Results from Pilot Phase studies indicated that, compared to conventional maize hybrids, no differences were detected for the agronomic and phenotypic characteristics measured on the three GM maize hybrids, with the exception of grain moisture and grain yield in the IR hybrids. Since MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6 confer resistance to target insect pests, they are an alternative for farmers in Mexico to protect the crop from insect damage. Additionally, the herbicide tolerance conferred by all three GM hybrids enables more cost-effective weed management.     

Effect of some electron donors and acceptors on redox capacity and simultaneous net H+/K+ fluxes by aeroponic sunflower seedling roots: Evidence for a CN−-resistant redox chain accessible to nonpermeative redox compounds

Summary Excised roots from aeroponic axenically 48 h dark-grown sunflower (Helianthus annuus L.) seedlings showed redox activities, being able to oxidize/reduce all the exogenously added electron donors/acceptors, that affected the H⁺/K⁺ net fluxes simultaneously measured in the medium. Trials were performed with in vivo and CN^–-poisoned roots; these showed null⁺/K⁺ net flux activity but still oxidized/reduced all the e^– donors/acceptors tested except NADH. NADH enhanced the rate of H⁺ efflux by in vivo roots, otherwise not changing any of the normal flux kinetic characteristics, suggesting that NADH donates e^– and H⁺ to the exocellular NADH oxidoreductase activity of a CN^–-sensitive redox chain in the plasmalemma of the root cells. K⁺ influx was not affected, probably because the NADH concentration was not very high. The e^– donor HFC(hexacyanoferrate)(II) activated the H⁺ efflux in a very different way: maximum H⁺ efflux rate was maintained, but both the maximum rate plateau and the optimal pH range were extended, and hence the total H⁺ efflux was significantly enhanced. At the same time, the K⁺ influx was doubled. The different H⁺-efflux kinetics, together with the small but significant HCF(II) oxidation by CN^–-poisoned roots, were taken as evidence that, besides the CN^–-sensitive redox chain, an alternative CN^–-resistant redox chain in the plasmalemma was involved in HCF(II) oxidation. The effect of the oxidized form HCF(III) on H⁺ and K⁺ fluxes was the opposite to that described for HCF(II), but the other H⁺ efflux kinetic characteristics were similar (the maximum rate plateau was extended so that total H⁺ efflux equaled that of the controls). It is proposed that HCF(III) accepts e^– only from the alternative CN^–-resistant redox chain. We could not measure the effect of HCI(hexachloroiridate)(IV) on H+ efflux, as the pH electrodes alone quickly reduced the compound. HCI(IV) promoted a rapid transitory K⁺ efflux, followed by recovery of K⁺ influx. The HCI(IV) reduction by in vivo or CN^–-poisoned roots was extremely rapid, following similar kinetics. Thus, only the CN^–-resistant redox chain was involved in both cases. The redox chain inhibitor cis-platinum(II) annulled ion fluxes in the presence of both NADH and HCF(III), and later even inverted them (a small H⁺ influx down the gradient would induce K⁺ efflux). Cis-platinum(II) did not affect HCF(III) reduction by in vivo roots, and only slightly depressed that by CN^–-poisoned roots. Overall, the effects of the exogenously added e^– donors/acceptors tested were consistent with the existence of a CN^–-resistant redox chain in the plasmalemma of the root cells which would donate/accept e^– even when the H⁺ and K⁺ fluxes were annulled by CN^– or even inverted by cis-platinum(II) treatments. Thus, in the plasmalemma of in vivo roots this chain would compete for electrons with the normal CN^–-sensitive one, as in plant mitochondria. The effects on the K⁺ flux were consistent with the current hypothesis that this contributes to counteracting the changes in membrane potential caused by redox activities and the H⁺ flux induced by the different redox compounds tested.Abbreviations cis-Pt(II) cis-platinum(II) diammine dichloride - HCF(II) hexacyanoferrate(II) (or ferrocyanide) potassium salt - HCF(III) hexacyanoferrate(III) (or ferricyanide) potassium salt - HCI(IV) hexachloroiridate(IV) - PMOR plasmalemma oxidoreductase complex