Weeks Of Acclimatization Research Articles

“Living high − training low” altitude training improves sea level performance in male and female élite runners

Acclimatization to moderate high altitude accompanied by training at low altitude (living high–training low) has been shown to improve sea level endurance performance in accomplished, but not élite, runners. Whether élite athletes, who may be closer to the maximal structural and functional adaptive capacity of the respiratory (i.e. oxygen transport from environment to mitochondria) system, may achieve similar performance gains is unclear. To answer this question, we studied 14 élite men and eight élite women before and after 27 days of living at 2500 m while performing high-intensity training at 1250 m. The altitude sojourn began 1 week after the USA Track and Field National Championships, when the athletes were close to their season's fitness peak. Sea level 3000-m time trial performance was significantly improved by 1.1% (95% confidence limits 0.3–1.9%). One-third of the athletes achieved personal best times for the distance after the altitude training camp. The improvement in running performance was accompanied by a 3% improvement in maximal oxygen uptake (72.1 ± 1.5–74.4 ± 1.5 ml kg− 1 min− 1). Circulating erythropoietin levels were near double initial sea level values 20 h after ascent (8.5 ± 0.5–16.2 ± 1.0 IU ml−1). Soluble transferrin receptor levels were significantly elevated on the 19th day at altitude, confirming a stimulation of erythropoiesis (2.1 ± 0.7–2.5 ± 0.6 μ g ml-1). Hb concentration measured at sea level increased 1 g dl−1 over the course of the camp (13.3 ± 0.2–14.3 ± 0.2 g dl−1). We conclude that 4 weeks of acclimatization to moderate altitude, accompanied by high-intensity training at low altitude, improves sea level endurance performance even in élite runners. Both the mechanism and magnitude of the effect appear similar to that observed in less accomplished runners, even for athletes who may have achieved near maximal oxygen transport capacity for humans.

Micropropagation, callus and root culture of Phyllanthus urinaria (Euphorbiaceae)

Efficient micropropagation, callus culture and root culture protocols were developed for the medicinal plant Phyllanthus urinaria(Euphorbiaceae) using single node explants. Maximum multiplication (16–20 shoots per explant) was achieved on Murashige and Skoog media supplemented with 5.0 μM kinetin. Murashige and Skoog and Anderson Rhododendron media promoted significant shoot culture growth in terms of numbers of shoots and nodes produced per explant. Rooting was achieved with 93–100% of the microshoots on Murashige and Skoog medium without growth regulators, although 1.25–5.0 μM α-naphthaleneacetic acid significantly increased the number of roots per explant. Regenerated plants were successfully acclimatized and 91% of plantlets survived under ex vitro conditions. Flowering was observed on micropropagated plants after 3–4 weeks of acclimatization. High frequency callus initiation and growth was achieved when single node explants were inoculated in the horizontal position on Murashige and Skoog medium supplemented with 5.0 μM indole-3-butyric acid. Other auxins such as 2,4-dichlorophenoxyacetic acid and α-naphthaleneacetic acid promoted moderate callus fresh weight increase, when used separately. Root cultures were successfully established on Murashige and Skoog medium containing 1.1 μM α-naphthaleneacetic acid. The optimized micropropagation, callus culture and root culture protocols offer the possibility to use cell/root culture techniques for vegetative propagation and secondary metabolism studies.

The re-establishment of the normal blood lactate response to exercise in humans after prolonged acclimatization to altitude.

1. One to five weeks of chronic exposure to hypoxia has been shown to reduce peak blood lactate concentration compared to acute exposure to hypoxia during exercise, the high altitude 'lactate paradox'. However, we hypothesize that a sufficiently long exposure to hypoxia would result in a blood lactate and net lactate release from the active leg to an extent similar to that observed in acute hypoxia, independent of work intensity. 2. Six Danish lowlanders (25-26 years) were studied during graded incremental bicycle exercise under four conditions: at sea level breathing either ambient air (0 m normoxia) or a low-oxygen gas mixture (10 % O(2) in N(2), 0 m acute hypoxia) and after 9 weeks of acclimatization to 5260 m breathing either ambient air (5260 m chronic hypoxia) or a normoxic gas mixture (47 % O(2) in N(2), 5260 m acute normoxia). In addition, one-leg knee-extensor exercise was performed during 5260 m chronic hypoxia and 5260 m acute normoxia. 3. During incremental bicycle exercise, the arterial lactate concentrations were similar at sub-maximal work at 0 m acute hypoxia and 5260 m chronic hypoxia but higher compared to both 0 m normoxia and 5260 m acute normoxia. However, peak lactate concentration was similar under all conditions (10.0 +/- 1.3, 10.7 +/- 2.0, 10.9 +/- 2.3 and 11.0 +/- 1.0 mmol l(-1)) at 0 m normoxia, 0 m acute hypoxia, 5260 m chronic hypoxia and 5260 m acute normoxia, respectively. Despite a similar lactate concentration at sub-maximal and maximal workload, the net lactate release from the leg was lower during 0 m acute hypoxia (peak 8.4 +/- 1.6 mmol min(-1)) than at 5260 m chronic hypoxia (peak 12.8 +/- 2.2 mmol min(-1)). The same was observed for 0 m normoxia (peak 8.9 +/- 2.0 mmol min(-1)) compared to 5260 m acute normoxia (peak 12.6 +/- 3.6 mmol min(-1)). Exercise after acclimatization with a small muscle mass (one-leg knee-extensor) elicited similar lactate concentrations (peak 4.4 +/- 0.2 vs. 3.9 +/- 0.3 mmol l(-1)) and net lactate release (peak 16.4 +/- 1.8 vs. 14.3 mmol l(-1)) from the active leg at 5260 m chronic hypoxia and 5260 m acute normoxia. 4. In conclusion, in lowlanders acclimatized for 9 weeks to an altitude of 5260 m, the arterial lactate concentration was similar at 0 m acute hypoxia and 5260 m chronic hypoxia. The net lactate release from the active leg was higher at 5260 m chronic hypoxia compared to 0 m acute hypoxia, implying an enhanced lactate utilization with prolonged acclimatization to altitude. The present study clearly shows the absence of a lactate paradox in lowlanders sufficiently acclimatized to altitude.

In vitro culture of Phyllanthus stipulatus (Euphorbiaceae)

An efficient micropropagation protocol was developed for the medicinal plant Phyllanthus stipulatus (Euphorbiaceae) using nodal segments for axillary shoot proliferation. Maximum multiplication rates (8-9 shoots per explant) was achieved on MS media supplemented with either 2.5-5.0 mM IBA. The best basal media for axillary shoot proliferation when 0.62 mM BA was supplemented were MS, MS/2 and AR (4-5 shoots per explant). Rooting was achieved with 100% of the microshoots on MS medium without growth regulators. Regenerated plants were successfully acclimatized and about 88% of plantlets survived under ex vitro conditions. Flowering was observed in 81% of the ex vitro grown plantlets after 12 weeks of acclimatization. High frequency callus initiation and growth was achieved when nodal segment explants were inoculated either in the vertical position, in the light on MS medium supplemented with 5.0 mM NAA or horizontally oriented, in the dark on MS supplemented with 5.0 mM NAA or 1.25-5.0 mM BA or 2iP. Root cultures were successfully established on MS medium containing 1.1 mM NAA. The optimized micropropagation, callus and root culture protocols offer the possibility to use cell/organ culture techniques for vegetative propagation and secondary metabolism studies.

Peak heart rates at extreme altitudes.

We have measured maximal heart rate during a graded maximal bicycle exercise test to exhaustion in five healthy climbers before and during an expedition to Mt. Everest. Maximal heart rates at sea level were 186 (177-204) beats/min(-1) at sea level and 170 (169-182) beats/min(-1) with acute hypoxia. After 1, 4 and 6 weeks of acclimatization to 5400 m, maximal heart rates were 155 (135-182), 158 (144-182), and 155 (140-183) beats/min(-1), respectively. Heart rates of two of the climbers were measured during their attempt to reach the summit of Mt. Everest without the use of supplemental oxygen. The peak heart rates at 8,750 m for the two climbers were 142 and 144 beats/min(-1), which were similar to their maximal heart rates during exhaustive bicycle exercise at 5,400 m, the values being 144 and 148 beats/min(-1), respectively. The peak heart rates at 8,750 m are in agreement with other field studies, but considerably higher than values reported from hypobaric chamber studies.

Leukocyte-endothelial interactions in environmental hypoxia.

Hypoxia induced by reducing inspired PO2 (PIO2) to 70 Torr, promotes a rapid microvascular response characterized by increased leukocyte rolling and adherence to the venular endothelium, leukocyte emigration to the perivascular space and increased vascular permeability. This appears to be a generalized response since it is observed in venules of the mesentery, cremaster muscle and pial microcirculations. After three weeks of acclimatization to hypoxia (barometric pressure 380 Torr, PIO2 70 Torr), the initial microvascular response resolves and exposure to even lower PIO2 (50 Torr) fails to elicit a microvascular response. The initial response is accompanied by a reversible increase in the generation of reactive oxygen species (ROS) and is blocked by antioxidants and by interventions that increase the tissue levels of nitric oxide (NO). In contrast to ischemia/reperfusion, ROS levels increase during hypoxia and return towards pre-hypoxic values after return to normoxia. Acclimatization involves upregulation of inducible NO synthase (iNOS): inhibition of iNOS using two different antagonists results in increased leukocyte-endothelial interactions and increased ROS generation. The results suggest that hypoxia initially leads to an alteration of the ROS/NO balance which is eventually restored during the acclimatization process. This phenomenon may have relevance to the microcirculatory alterations associated with hypoxic exposure, including acute mountain sickness and high altitude pulmonary and cerebral edema.

Efeito da aplicação de baixa temperatura em plantas de macieira sobre o crescimento durante a aclimatização

Este trabalho objetivou avaliar o efeito da aplicação de baixa temperatura (4±1ºC) sobre o crescimento das brotações micropropagadas de um porta-enxerto de macieira (Malus prunifolia Borkh.), cv.Marubakaido, durante o processo de aclimatização. Durante as duas primeiras semanas de aclimatização, as plântulas foram transferidas para uma câmara de crescimento, e submetidas à temperatura de 4±1ºC por 0, 240, 480, 720, 960, 1.200 e 1.440 horas, sob fotoperíodo de 16 horas e radiação de 5µEm-2s-1. Em seguida, foram conduzidas para casa de vegetação e avaliadas por um período de 90 dias. Ao final do experimento, avaliou-se, ainda, o comprimento dos entrenós, o número de gemas e o peso da matéria seca da parte aérea e das raízes das plantas. A porcentagem de sobrevivência também foi avaliada após um mês de permanência das plantas em casa de vegetação. Houve aumento na altura das plantas e no comprimento dos entrenós, proporcional ao tempo de sua permanência sob baixa temperatura. O frio provocou decréscimo no peso seco das raízes, porém não afetou a sobrevivência das plantas, o número de gemas e o peso da matéria seca da parte aérea.

The 'lactate paradox', evidence for a transient change in the course of acclimatization to severe hypoxia in lowlanders.

The metabolic response to exercise at high altitude is different from that at sea level, depending on the altitude, the rate of ascent and duration of acclimatization. One apparent metabolic difference that was described in the 1930s is the phenomenon referred to as the 'lactate paradox'. Acute exposure to hypoxia results in higher blood lactate accumulation at submaximal workloads compared with sea level, but peak blood lactate remain the same. Following continued exposure to hypoxia or altitude, blood lactate accumulation at submaximal work and peak blood lactate levels are paradoxically reduced compared with those at sea level. It has recently been shown, however, that, if the exposure to altitude is sufficiently long, blood lactate responses return to those seen at sea level or during acute hypoxia. Thus, to evaluate the 'lactate paradox' phenomenon in relation to time spent at altitude, five Danish lowland climbers were studied at sea level, during acute exposure to hypoxia (10% O2 in N2) and 1, 4 and 6 weeks after arrival in the basecamp of Mt Everest (approximately 5400 m, Nepal). Basecamp was reached after 10 days of gradual ascent from 2800 m. Peak blood lactate levels were similar at sea level (11.0 +/- 0.7 mmol L-1) and during acute hypoxia (9.9 +/- 0.3 mmol L-1), but fell significantly after 1 week of acclimatization to 5400 m (5.6 +/- 0.5 mmol L-1) as predicted by the 'lactate paradox'. After 4 weeks of acclimatization, peak lactate accumulation (7.8 +/- 1.0 mmol L-1) was still lower compared with acute hypoxia but higher than that seen after 1 week of acclimatization. After 6 weeks of acclimatization, 2 days after return to basecamp after reaching the summit or south summit of Mt Everest, peak lactate levels (10.4 +/- 1.1 mmol L-1) were similar to those seen during acute hypoxia. Therefore, these results suggest that the 'lactate paradox' is a transient metabolic phenomenon that is reversed during a prolonged period of exposure to severe hypoxia of more than 6 weeks.

Growth, Stomatal Conductance, Photosynthetic Rate, Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Phosphoenolpyruvate Carboxylase Activities during Rooting and Acclimatisation of Rosa Hybrida Plantlets

The rooting of shoots of micropropagated Rosa hybrida cv. Madame Delbard was conducted on MS medium with 30 kg m−3 sucrose or on hydroponic medium (containing less mineral salts), under higher photosynthetic photon flux density (PPFD) (100 in comparison with 45 µmol m−2 s−1) and flushed by ambient air [AC, 340 µmol(CO2) mol−1] or by CO2-enriched air (EC, 2 500 µmol mol−1) and lower relative humidity (80–90 % vs. 96–99 %). This cultivation led to plantlets with longer roots and adventitious root formation. Net photosynthetic rate and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activities, RuBPCO/phosphoenolpyruvate carboxylase activities ratio, and starch accumulation increased under these conditions. After 14 d, plantlets had functional stomata and could be acclimated on open benches without gradual decrease in relative humidity. The percentage of survival was higher when the rooting took place in EC than in AC. However, the advantage acquired during rooting phase by plantlets cultured in liquid medium was not maintained after 4 weeks of acclimatisation.

In vitro culture of Phyllanthus caroliniensis (Euphorbiaceae).

An efficient micropropagation protocol was developed for the medicinal plant Phyllanthus caroliniensis (Euphorbiaceae) using nodal segments for axillary shoot proliferation. Maximum multiplication (21–23 shoots per explant) was achieved on MS or AR media supplemented with either 5.0 μM BA, 1.25–5.0 μM kinetin or 2.5–5.0 μM 2iP. Rooting was achieved with 80–100% of the microshoots on MS medium without growth regulators, although 1.25 μM NAA and 1.25–5.0 μM IAA promoted significant increases in the number of roots per explant. Regenerated plants were successfully acclimatized and about 88% of plantlets survived under ex vitro conditions. Flowering was observed on in vitro grown plantlets and after 3–4 weeks of acclimatization. High frequency callus initiation and growth was achieved when nodal segment explants were inoculated in the vertical position on MS medium supplemented with 5.0 μM 2,4-D. Root cultures were successfully established on MS medium containing 1.1 μM NAA. The optimized micropropagation, callus and root culture protocols offer the possibility to use cell/root culture techniques for vegetative propagation and secondary metabolism studies.

Water stress and photoinhibition in acclimatization ofRosa hybrida plantlets

MicropropagatedRosa hybrida plantlets were simultaneously rooted and acclimatized under 100 and 200 μmol m−2 s−1 light for 2 wk. At the end of the first week of acclimatization, the plantlets were transferred onto a low water potential medium (from −0.06 MPa to −0.3 MPa). Dry weight was decreased by increased hight and low water potential. Photoinhibition of photosynthesis, expressed as a decrease in Fv/Fm ratio and ΦPSII and an increase in 1 −qp, occurred in plants grown under 200 μmol m−2 s−1. When high light (200 μmol m−2 s−1) and water stress were applied simultaneously, their effects on chlorophyll fluorescence parameters depended on stress duration; after 1 d of water stress, photoinhibition was more pronounced; after 7 d of stress, Fv/Fm ratio and ΦPSII were higher than after 1 d of stress; photoinhibition was reduced. This suggests that after a 1-d stress, the effect of water stress alone included a superimposed effect of photoinhibition to which the water-stressed plants were sensitized; after 7 d, plantlets had adapted to water stress. The photoprotective effects under high light might result in energy dissipative mechanisms linked to photochemical and nonphotochemical quenching other than CO2 fixation.

Cold Acclimatization of Tropical Men during Short and Long Term Sojourn to Polar Environment

This study was undertaken to assess the status of cold acclimatization (CA) resulting from short- and long-term exposure of tropical men to severely cold environment of the Arctic and the Antarctic regions. Five Groups (seven each) of male subjects participated in this study. Cold-induced vasodilatation (CIVD) response was elicited during immersion of the right hand in cold water at 4 degree centigrade for 30 min at both the polar regions to evaluate peripheral CA. The 'standard cold test' at 10 degree centigrade for 2 hr was administered at the Arctic region on tropical and arctic residents and the data were compared with those for tropical men monitored at Delhi to ascertain the level of general CA. Group A (control) was studied at Delhi (29 degreeN, 77 degreeE) while Groups B and C were sailed to Antarctica (70 degreeS,11.5 degreeE). Their CIVD responses were monitored during thirteenth month and seventh to eighth week of stay, respective1y .There was no deliberate cold exposure, except during their 'occupation demand' outdoor duties. However, outdoor exposure for Group C was more. Group D was airlifted to the Arctic (70 degreeN, 38 degreeE) and studied during the seventh week of acclimatization. The subjects had regular deliberate cold exposure. For comparison, Group E of arctic residents was studied at the Arctic Group B did not show any adaptive modification to cold even after an year of sojourn in antarctic environment compared to Group A; while Group C subject, despite their short stay showed better CIVD response. Group D subjects recorded significant improvement in the response of general cold exposure as well as peripheral vascular response to local cold stress; their responses were comparable to those of the arctic residents (Group E). It is evident that human CA is impossible just by living in the coldest region of the globe even for prolonged periods. Deliberate regular exposure to atmospheric cold is the mandatory factor in developing human CA, the degree of which is related to the intensity of cold exposure.

Acclimatization and Growth of Dwarf Pampas Grass in Response to Fertilizer Application Following In Vitro Culture

Abstract Dwarf pampas grass (Cortaderia selloana Schult. ‘Pumila’) plantlets produced in vitro were subjected to one of seven fertilization treatments during acclimatization to greenhouse conditions. Though all plantlets survived acclimatization, level of fertilizer significantly affected growth rate. Increase in fresh weight, leaf number and tillering during the first 6 weeks of acclimatization was greater when Osmocote micro-fertilizer at 2 kg/m3 (oz/ft3) was incorporated into the growing mix (Pro-Gro 200 with starter nutrients) as compared to 4 kg/m3 (oz/ft3) of Osmocote or addition of liquid fertilizer. The slowest growth was obtained from plants growing without Osmocote or liquid fertilizer. Once adapted to the greenhouse, plants fertilized with 400 mg/1 (ppm) N from 17N-4P-11K (17-9-13) soluble fertilizer twice per week had the most rapid growth.

DEVELOPMENT OF CARBOXYLATION CAPACITY IN TISSUE-CULTURED STRAWBERRY FOLLOWING TRANSPLANTING.

Strawberry plantlets (Fragaria X ananassa Duch. cv. Kent) were submitted to a factorial arrangement of 2 photosynthetic photon fluxes (PPF) (80 and 150 μmol·m-2·s-1, PAR) and 2 CO2 concentrations (330 and 3000 ppm) during the in vitro rooting stage. Leaves were tagged and placed in a growth chamber tor acclimatization. Photosynthetic capability of leaves from different origins was determined by measuring the initial and total activity of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (rubisco), but the contribution of Phosphoenolpyruvate carboxylase (PEPCase) to fixation was also examined High CO2 concentration and PPF significantly increased fresh weight and surface area in vitro and after 4 weeks ex vitro. Improved growth was not the result of increased autotrophy in vitro since initial rubisco activity was 10 times lower than that of de novo formed leaves and declined under high CO2 and PPF. Carbon dioxide concentration and PPF had no effect on total activity of rubisco. Low activation state and total activity of rubisco in in vitro leaves is the cause of poor photosynthetic activity in vitro Persistent in vitro leaves after 4 weeks of acclimatization did not have higher total activity of rubisco, but the activation state was 4 times larger than the corresponding activity in vitro which might thus provide for non-negligible contribution to photosynthetic carbon assimilation. The possible inhibition of photosynthesis by the presence of sugar in the medium is discussed.

Endogenous opioids and ventilatory adaptation to prolonged hypoxia in goats

To investigate whether endogenous opioid peptides mediate time-dependent changes in ventilatory control during prolonged hypoxia, we studied four adult goats at rest during 14 days at simulated high altitude in a hypobaric chamber (P B∼450 Torr). Arterial PCO 2 fell during the first several hours of hypoxia, remained stable over the next 7 days, and then rose slightly (but without statistical significance) by day 14. Ventilatory responsiveness to CO 2 increased during the first week of hypoxia. By day 14, while still greater than control, the ventilatory response to CO 2 was less than that observed on day 7. Immunoactive β-endorphin levels in plasma and CSF did not change during the 14-day period. Administration of naloxone on day 14 did not restore the ventilatory response to CO 2 to the level observed during the first week of acclimatization. We conclude that in adult goats, time-dependent changes in ventilatory response to CO 2 during acclimatization to prolonged hypoxia are not primarily attributable to alterations in endogenous opioid peptide activity.

Cigarette smoking as a risk for cardiovascular disease. Part VI. Compensation with nicotine availability as a single variable.

In a biochemical investigation of human smoking behavior with filter cigarettes with high draw resistance that varied only in nicotine yield, we attempted to determine which nicotine levels provide desired nicotine intake with a minimum of physiologic and biochemical consequences. Twelve prescreened subjects were divided into two study groups and supplied with cigarettes that varied in nicotine delivery. Both groups were initially monitored while smoking their usual cigarette. At the following visit, smokers in group 1 received incremental increases and smokers in group 2 received incremental decreases in nicotine levels in assigned cigarettes. All subjects were monitored upon first exposure, after 1 week of acclimatization to each experimental cigarette, and upon return to their usual brands. Subjects in both groups were unable to compensate fully for their nicotine uptake from the lowest nicotine cigarette. In subjects in group 1, new nicotine baselines began to develop after 1 week of acclimatization to cigarettes containing 0.9 and 1.3 mg nicotine. New baseline nicotine levels were also noted in subjects receiving decreases in nicotine (group 2) after smoking the cigarette containing 1.3 mg nicotine for 1 week. Carboxyhemoglobin concentrations did not differ from those measured after the usual-brand cigarettes. Plasma cotinine concentrations increased as nicotine content per cigarette increased, except when subjects smoked a 1.3 mg nicotine cigarette. Plasma thiocyanate levels did not vary in either group. Systolic and diastolic blood pressures were generally not different from control values.

Neurophysiological Problems in Snow Bound High Altitude Areas

A series of studies have been conducted to evaluate the neurophysiological responses in young healthy soldiers during acclimatization at 3,500m altitude in Western Himalayas. The responses of autonomic nervous system, electroencephalogram hypothalamic thermoregulatory efficiency, orthostatic tolerance, sleep profile and effects of sleep deprivation have been studied in fresh inductees during three to five weeks of acclimatization at high altitude and compared with those of one year acclimatized lowlanders and high altitude natives. Physiological significance of these neurophysiological responses in the process of altitude adaptation is discussed in the light of current knowledge in the field.

Carbon Balance of Peperomia obtusifolia Plants during Acclimatization to Low PPFD

Abstract The CO2 exchange rates of Peperomia obtusifolia A. Dietr. plants (tops and roots) were measured for 12-hour light and 12-hour dark cycles during 5 weeks of acclimatization at 30 µEs-1m-2. A carbon balance analysis of the data indicated that the growth conversion efficiency (Yg) remained constant (0.73 ± 0.1 and 0.77 ± 0.04 before and after acclimatization, respectively). The daily rate of substrate production from photosynthesis (ΔS/Δt) remained constant at 18 ± 2 mg C plant-1 24 hr-1, at the acclimatization photosynthetic photon flux density (PPFD), but the daily rate of synthesis of carbon into new material (ΔW/Δt) increased by 55% within the first week. The maintenance coefficient (m) decreased from 13.0 ± 0.9 to 7.4 ± 0.4 mg g-1 24 hr-1, and change in m may be a criterion for selection of plants that can be adapted for use at low PPFD. The light compensation point (LCP) was reduced during acclimatization, but its use underestimated the PPFD required for 24-hour plant maintenance because of failure to account for night-time respiratory losses. It is suggested that the PPFD at which ΔW/Δt is zero or slightly above is more reliable than the light compensation point for determining PPFD required for plant maintenance.

Light Compensation Points and Acclimatization of Four Tropical Foliage Plants1

Abstract Whole plant net CO2 exchange, light compensation points, and acclimatization were determined for Philodendron scandens Subsp. oxycardium (Schott) Bunt, Epipremnum aureum (Linden & Andre) Bunt (Pothos), Brassaia actinophylla Endl. and Dracaena sanderana Sander before and after 4 and 15 week acclimatization periods at 27 μE m−2 sec−1 (400-700 nm), for 12 hr/day. Philodendron scandens Subsp. oxycardium, E. aureum, B. actinophylla and D. Sanderana exhibited CO2 uptake rates of 0.53, 1.16, 1.18 and 0.50 mg CO2 dm−2hr−1, respectively, at 57 μE m−2 sec−l (3400 lx) after 15 weeks of acclimatization. Each species showed a significant increase in net CO2 uptake during the study period. Dark respiration decreased 63% in P. scandens Subsp. oxycardium, 71% in E. aureum, 53% in B. actinophylla and 64% in D. sanderana during the acclimatization period. The regression correlation coefficient of CO2 uptake with light intensity increased for each species during the study. At 15 weeks, P. scandens Subsp. oxycardium, E. aureum, B. actinophylla and D. sanderana exhibited r values of .95, .98, .96, and .91, respectively. Light compensation points decreased between week 1 and week 15 as follows: 33 to 7 μE m−2 sec−1 in P. scandens Subsp. oxycardium, 38 to 6 μE m−2 sec−1 in E. aureum, 14 to 4 μE m−2 sec−1 in B. actinophylla and 119 to 15 μE m−2 sec−1 in D. sanderana. As a result of acclimatization, all species exhibited increases in net CO2 uptake and decreases in dark CO2 evolution concomitantly indicating a reduction in dark respiration. Leaf area increase was negatively correlated with light compensation point. B. actinophylla had the highest leaf area increase with 2.16 dm2, E. aureum and P. scandens Subsp. oxycardium were intermediate with 1.08 and 0.96 dm2, respectively, while D. sanderana, the species with the highest light compensation point exhibited the lowest leaf area increase (0.44 dm2). Philodendron scandens Subsp. oxycardium, E. aureum, B. actinophylla, exhibited similarly rapid rates of acclimatization, while D. sanderana acclimatized much more slowly and had a significantly higher light compensation point.

Effect of photoperiod length on feedback sensitivity to estradiol in the female rat.

The effect of photoperiod on the negative feedback effect of estradiol on LH release was examined in this study. Female ARS/Sprague-Dawley rats were exposed to lighting schedules of 2, 8, 16 or 22 h of light per 24 h from 60 days of age until autopsy. After 5 to 6 weeks of acclimatization to the photoperiod, all rats were ovariectomized, given various treatments during the next 14 days and sacrificed on the 15th day. Treatments consisted of either daily injections of various doses of estradiol benzoate (EB) in sesame oil or of implantation of a Silastic capsule containing crystalline estradiol-17<i>β </i>(E₂) at the time of ovariectomy; in addition to untreated controls in each group, some animals received either oil injections or implantation of an empty Silastic capsule, as appropriate. At the time of autopsy, blood was taken for radioimmunoassay of serum LH and body and uterine weights were recorded. Untreated ovariectomized rats, and those receiving oil injections or an empty capsule implant, showed wide variations in serum LH levels; no significant effect of photoperiod length could be demonstrated. At low dose ranges of EB, very little effect on serum LH was seen. A dose-related effect was seen on relative uterine weight, and the response to EB was significantly greater (p < 0.05) in the 22 h photoperiod than in the others, but this effect was not seen at moderate or at presumptively high doses of estradiol. At these higher doses, however, there was a significant effect of photoperiod length on serum LH levels (p < 0.05). In both of these dose ranges, the longer the photoperiod, the higher the LH level at any given dose of estrogen. These results suggest that photoperiod length can alter the sensitivity of the LH control system to the negative feedback effects of estrogen: in the case of the rat, the shorter the photoperiod, the more sensitive the negative feedback system.