Midday depression in photosynthesis: Effect on sucrose-phosphate synthase and ribulose-1,5-bisphosphate carboxylase in leaves of Prosopis juliflora (Swartz) DC

The midday depression in net photosynthetic rate (PN) and stomatal conductance (gs) in Prosopis juliflora was studied in relation to two key enzymes of carbon metabolism. Diurnal gas exchange measurements carried out in autumn on P. juliflora showed a pronounced depression in PN and gs along with a decrease in apparent carboxylation efficiency (CE*) during midday. The activities of sucrose-phosphate synthase (SPS) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) also showed large diurnal fluctuations. Initial RuBPCO activity (that present in vivo) and total activity (fully carbamylated activity) increased gradually with increase in irradiance, in the morning reaching a maximum by 08:00 h. The RuBPCO activity declined sharply during midday due to decrease in initial activity. The drop in the % activation of RuBPCO indicated that the deactivation of RuBPCO was achieved via a decarbamylation mechanism. There was a marked similarity in the diurnal patterns of SPS activity and the PN. During a diurnal rhythm, SPS activity increased after irradiation, reaching a maximum at 08:00 h and then declined during midday. Diurnal fluctuations in SPS activity could be due to the changes in the amount of protein (changes in Vmax) as well as to the changes in kinetic properties (changes in Vlim). Hence the midday decline in photosynthesis is closely associated with the regulation of RuBPCO and SPS activities.     

Diurnal regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity and its content in Norway spruce needles

Diurnal changes of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activity and its content were measured to find the mechanism of RuBPCO activity regulation in Norway spruce needles. Both initial and total RuBPCO activities as well as the activation state had a typical pattern with two peaks in the morning and afternoon, respectively, and a midday depression. On the 19 October, RuBPCO content decreased during the day from 3.1 to 1.4 g m⁻², while on the 20 October it was approximately constant both in the morning and in the afternoon (2.7 g m⁻²). Neither initial nor total activity of RuBPCO copied irradiances. Relatively low morning and evening values of total activities indicate that nocturnal inhibitor CA1P is important in Norway spruce. However, the midday depression of total activity indicates that besides CA1P there function some other inhibitors of RuBPCO. In addition, the diminution of RuBPCO content during the day may indicate repression of its gene expression.     

Diurnal and Seasonal Changes in Prunus Amygdalus Gas Exchanges

Diurnal courses in net photosynthetic rate (PN), stomatal conductance (gs), leaf water potential (), internal CO2 concentration (ci), and water use efficiency (WUE) were studied as season progressed, in relation to environmental factors in field grown Prunus amygdalus. In sun leaves PN reached maximum between 09:00 to 11:00 h and subsequently declined when high temperature and low humidity occurred. An increase was observed late in the afternoon. A decrease in gs and was found as season progressed in both years of measurements. In periods of high evaporative demand, was very low, however, it did not explain the reductions of PN in all the three periods (spring, early and late summer). Midday depression of PN and gs seemed to be related with leaf temperature (Tl) and high irradiance. Increase in ci and F0 and decrease in Fv/Fm found between 12:00 and 14:00 h corresponded to the decrease in PN. Therefore, a transient modification of photosynthetic machinery might be considered. WUE was negatively correlated with vapour pressure difference of leaf to air, that decreased during the day. The September values, higher than in the previous months, were due to the lower seasonal decreases in PN than in gs.     

Light Regulation of Diurnal Variation of Sucrose-Phosphate Synthase in Potato

Light regulation of diurnal variation of sucrose-phosphate synthase (SPS) activity was studied in potato leaves during pre-tuber initiation stage. SPS activity was greatest at 14:00 and coincident with highest irradiance [2 000 μmol(PAR) m-2 s-1], and lowest at 18:00 during lowest irradiance (200 μmol m-2 s-1). In contrast, fructose-1,6-bisphosphatase (FBPase) activity was greatest at 12:00 (irradiance 1 700 μmol m-2 s-1). Inhibition of SPS activity by phosphorylation was least at 14:00 and highest at 18:00. Considerable inhibition was also observed at 10:00. SPS showed hyperbolic saturation kinetics in response to varying UDP-glucose concentrations. Diurnal variation of SPS activity was due to a change of affinity for its substrate (Km), but not due to change of Vmax. Phosphate (Pi) decreased the activation state of SPS. Inhibition by Pi was most severe under limiting UDP-glucose concentration. Sensitivity towards Pi inhibition at limiting substrate concentration was highest at 18:00 and lowest at 14:00. Change of tissue phosphate concentration followed the opposite pattern to that of diurnal variation of SPS activity and irradiance, being highest at 18:00 and lowest at 14:00. A dual mode of regulation is considered to exist for diurnal variation of potato leaf SPS: covalent modification and effector (Pi) regulation. Thus the change of tissue phosphate concentration may play a pivotal role in regulating potato leaf SPS. This revised version was published online in July 2006 with corrections to the Cover Date.     

水稻Rubisco和RCA的日变化及其细胞定位

采用免疫胶体金标记电镜技术对水稻(Oryza satova subsp.indica cv.浙农952)叶片中的Rubisco及其活化酶(RCA)进行细胞器定位和定量,同时用免疫扩散法进行叶片含量分析,研究了这两种酶含量及活力的日变化。结果表明Rubisco主要分布于叶绿体,RCA分布于叶绿体和线粒体中;光合速率(Pn)、Rubisco初始活力和RCA活力与光合日变化密切相关;在光照最强的13时,出现光合“午休”,叶绿体中Rubisco的密度有一定程度降低,而全叶的总Rubisco保持稳定,Rubisco初始活力也有明显的“午休”,这意味着体内Rubisco的活力除受RCA调节外,可能还与叶绿体中Rubisco的分布有关。RCA活力变化与叶绿体中RCA含量变化较为一致,表明RCA在叶绿体中的分布对调节其本身活力和Rubisco活性有重要作用。     

Diurnal and Seasonal Modulation of Sucrose Phosphate Synthase Activity in Leaves of Prosopis juliflora

Diurnal changes of sucrose-phosphate synthase (SPS) activity in different seasons were measured in Prosopis juliflora (Swartz) DC. leaves. SPS activity showed large variations with two distinct peaks, one around 09:00 and another at 21:00. The diurnal pattern was apparently not due to circadian rhythm since the activities were directly related to the changes in environmental parameters (irradiance, temperature, and leaf to air vapour pressure deficit) in different seasons. During the day, the enzyme showed changes in kinetic properties, differential sensitivity to allosteric modulators, differential response to ATP concentration, to concentration of endogenous sucrose, and to protein phosphatase inhibitors. These results taken together indicate the modulation of SPS in synchrony with photosynthesis and suggest the existence of multiple levels of modulation, presumably as an adaptive response to changing environmental extremes. This revised version was published online in July 2006 with corrections to the Cover Date.     

水稻Rubisco和RCA的日变化及其细胞定位

采用免疫胶体金标记电镜技术对水稻(0ryza sativa subsp.indica cv.浙农952)叶片中的Rubisco及其活化酶(RCA)进行细胞器定位和定量,同时用免疫扩散法进行叶片含量分析,研究了这两种酶含量及活力的日变化.结果表明Rubisco主要分布于叶绿体,RCA分布于叶绿体和线粒体中;光合速率(Pn)、Rubisco初始活力和RCA活力与光合日变化密切相关;在光照最强的13时,出现光合"午休",叶绿体中Rubisco的密度有一定程度降低,而全叶的总Rubisco保持稳定,Rubisco初始活力也有明显的"午休",这意味着体内Rubisco的活力除受RCA调节外,可能还与叶绿体中Rubisco的分布有关.RCA活力变化与叶绿体中RCA含量变化较为一致,表明RCA在叶绿体中的分布对调节其本身活力和Rubisco活性有重要作用.     

Diurnal resting in brown lemurs in a dry deciduous forest, northwestern Madagascar: implications for seasonal thermoregulation

Decreased activity has been reported in both nocturnal and diurnal primates during the prolonged dry season in western Madagascar, and this has been interpreted as a reaction to the severe environment, with its food scarcity and/or thermal stress. Several day-active lemurs rest more as trees defoliate, although the reason for this is unclear. To understand the mechanism underpinning the diurnal resting of lemurs in seasonal deciduous forests, I observed common brown lemurs (Eulemur fulvus fulvus) for one year in Ankarafantsika National Park, northwestern Madagascar. In Ankarafantsika, despite high fruit availability during the dry season, brown lemurs are known to engage in diurnal resting. To examine the effects of thermal factors and defoliation on lemur inactivity, I recorded the activity of a troop at 1 min intervals, hourly ambient temperature, daily rainfall, and weather during observations (06:00-18:00). I quantified the amount of leaves biweekly for 680 trees. I tested correlations between percentages of resting time and each factor across hours during the day and across seasons. During the rainy season, resting time did not differ between sunny and cloudy days, and lemurs were active throughout the daytime. At the hourly level during the dry season, lemurs rested exclusively at midday, apparently at peak sunlight intensity rather than at peak ambient temperature. At seasonal level, percentages of total resting time from 08:00 to 16:00 were greater during dry season (81.9%) than during rainy season (62.6%), and percentages increased as ambient temperatures increased. Defoliation was related to seasonal decrease in weekly rainfall, which served as an index of water retained in the forest. Defoliation probably reflected aridification as well as the penetration of sunlight into the forest. Diurnal resting increased as both the amount of leaves and weekly rainfall decreased seasonally. These results suggest that heat stress under dry conditions may promote resting. Diurnal resting may function as behavioral thermoregulation to avoid overheating and to minimize water loss via excessive evaporative respiration.     

The Pattern of Changes in Photosynthetic Apparatus in Response to Cold Acclimation and De-acclimation in Two Contrasting Cultivars of Oilseed Rape

In spring and winter cultivars of oilseed rape (Brassica napus var. oleifera), acclimation of photosynthetic apparatus to cold was connected with the increase in activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and sucrose-phosphate synthase (SPS). Conversely, cold de-acclimation entailed the decline of RuBPCO and SPS activities. The rate of this photosynthetic de-acclimation might depend on day temperature. On the other hand, temperature rise during de-acclimation (identical during the day and night) resulted in the improvement of photosynthetic activity measured by means of chlorophyll fluorescence. An increase in SPS activity (and even transitory increase in RuBPCO activity) was observed when the elongation growth rate (EGR) accelerated during de-acclimation. Throughout re-acclimation, plants with high EGR were unable to maintain or recover higher photosynthetic capacity, despite the fact that SPS activity remained high or even increased during re-acclimation.     

Diurnal changes in maize leaf photosynthesis : I. Carbon exchange rate, assimilate export rate, and enzyme activities

Diurnal changes in photosynthetic parameters and enzyme activities were characterized in greenhouse grown maize plants (Zea mays L. cv Pioneer 3184). Rates of net photosynthesis and assimilate export were highest at midday, coincident with maximum irradiance. During the day, assimilate export accounted for about 80% of net carbon fixation, and the maximum export rate (35 milligrams CH₂O per square decimeter per hour) was substantially higher than the relatively constant rate maintained through the night (5 milligrams CH₂O per square decimeter per hour). Activities of sucrose phosphate synthase and NADP-malate dehydrogenase showed pronounced diurnal fluctuations; maximum enzyme activities were generally coincident with highest light intensity. Reciprocal light/dark transfers of plants throughout the diurnal cycle revealed that both enzymes were deactivated by 30 minutes of darkness during the day, and they could both be substantially activated by 30 minutes of illumination at night. During 24 hours of extended darkness, sucrose phosphate synthase activity declined progressively to an almost undetectable level, but was activated after 1.5 hours of illumination. Thus, the diurnal fluctuation in maize sucrose phosphate synthase can be explained by some form of light modulation of enzyme activity and is not due to an endogenous rhythm in activity. No diurnal fluctuations were observed in the activities of NADP-malic enzyme or fructose 6-phosphate-2-kinase. Phosphoenolpyruvate carboxylase was activated by light to some extent (about 50%) when activity was measured under suboptimal conditions in vitro. The results suggested that the rates of sucrose formation and assimilate export were closely aligned with the rate of carbon fixation and the activation state of sucrose phosphate synthase.     

Age-specific changes of acidity, phosphoenolpyruvate carboxylase, ribulose-1,5-bisphosphate carboxylase/oxygenase, abscisic acid and leaf water potential in Mesembryanthemum nodiflorum

Age-induced changes in 1) nocturnal and diurnal acidity fluctuations that coincide with the ongoing environmental conditions, 2) the build up of abscisic acid (ABA) in plant roots and leaves during sunrise, midday, and sunset in all growing stages, 3) the changes in phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activities as key enzymes of the photosynthetic pathways of C3 and CAM, 4) leaf water potential (ψ1), and 5) Km and Vmax for PEPC to express its activity and affinity, were studied in Mesembryanthemum nodiflorum during transition from C3 to CAM mode of CO2 fixation. The acidity during sunset in mature stage was higher than in earlier stages and reflected the impact of environmental conditions on physiological and metabolic changes. Moreover, the higher acidity during sunrise and sunset was observed during the senescence than the mature stage; this might be due to CO2 release and oxygen intake during senescence induced ethylene formation that lead to increased malic acid formation. The ABA concentration was high in M. nodiflorum leaves, but stomatal closure was insensitive to elevated ABA concentrations recorded. Vmax of PEPC, Km, and the affinity of PEPC during later stages indicated the ability of PEPC to fix CO2 taking up at night in CAM cycle of M. nodiflorum. Less affinity during sunrise indicated inhibitory effect of malate on PEPC during the release of CO2. The second peak of PEPC activity before sunset caused CO2 fixation. The RuBPCO was inactive at night. Slight increase in ABA during sunset, and night drop in air temperature and increase in relative humidity reduced markedly transpiration rate without decreasing ψ1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diurnal variation in the P300 component of human cognitive event-related potential

Diurnal variation in the P300 component of the human cognitive event-related potential (ERP) was examined. The P300 component is considered to be a measure of neuroelectric activity related to cognitive functions such as attention allocation and information processing. Nine diurnally active healthy male subjects whose sleep-wake rhythms were synchronized prior to the experiment were studied. The P300 components oral temperature, heart rate, left- and right-hand grip strength, reaction time, subjectively rated sleepiness, attention level, and fatigue were measured at 08:00, 11:00, 14:00, 17:00, and 20:00. Significant diurnal variations in P300 latency, P300 amplitude, oral temperature, heart rate, left- and right-hand grip strength, subjectively rated sleepiness, and attention level were observed. The P300 latency at 08:00 was significantly longer than at 11:00, 17:00, and 20:00, while the P300 amplitude at 08:00 was significantly greater than at 17:00 and 20:00. The P300 latency was correlated positively with subjectively rated sleepiness and negatively correlated with subjectively rated attention level. These results suggest the existence of diurnal variation in human cognitive functions.     

DIURNAL VARIATION IN THE P300 COMPONENT OF HUMAN COGNITIVE EVENT-RELATED POTENTIAL

Diurnal variation in the P300 component of the human cognitive event-related potential (ERP) was examined. The P300 component is considered to be a measure of neuroelectric activity related to cognitive functions such as attention allocation and information processing. Nine diurnally active healthy male subjects whose sleep-wake rhythms were synchronized prior to the experiment were studied. The P300 components oral temperature, heart rate, left- and right-hand grip strength, reaction time, subjectively rated sleepiness, attention level, and fatigue were measured at 08:00, 11:00, 14:00, 17:00, and 20:00. Significant diurnal variations in P300 latency, P300 amplitude, oral temperature, heart rate, left- and right-hand grip strength, subjectively rated sleepiness, and attention level were observed. The P300 latency at 08:00 was significantly longer than at 11:00, 17:00, and 20:00, while the P300 amplitude at 08:00 was significantly greater than at 17:00 and 20:00. The P300 latency was correlated positively with subjectively rated sleepiness and negatively correlated with subjectively rated attention level. These results suggest the existence of diurnal variation in human cognitive functions. (Chronobiology International, 17(5), 669–678, 2000)     

Diurnal and seasonal cortisol, testosterone, and DHEA rhythms in boys and girls during puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07:45, 08:00, 08:30, 12:00, 16:50, and 21:00 h. The participants' ages ranged from 8-14 yrs, and each participant was tested three times at six-month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1-3) but not later puberty (stages 4-5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

云锦杜鹃叶片光合作用日变化特征

自然条件下, 对云锦杜鹃光合作用日进程和光响应进行了观测, 结果表明:夏季晴天云锦杜鹃阳叶净光合速率日进程曲线为"双峰"型, 光合效率午间明显降低。胞间CO₂ 浓度的日进程基本与净光合速率相反, 中午胞间CO₂ 浓度增高表明净光合速率午间降低主要受非气孔限制因素的影响。暗呼吸速率日进程呈单峰曲线, 中午最高。阴叶净光合速率在一天的大部分时间里变化不大。一天分时段光响应试验表明, 阳叶饱和光强和表观量子效率上午较高, 下午有所降低, 而光补偿点下午有所上升。阴叶的这些光合参数在上午和下午没有明显的变化。这些研究结果表明, 强光下光抑制的发生是引起云锦杜鹃阳叶光合效率午间降低的重要原因。逐步多元回归和通径分析表明, 光合有效辐射和空气温度是直接影响净光合速率日变化的主要因子。     

Diurnal and Seasonal Cortisol,Testosterone, and DHEA Rhythms in Boys and Girls during Puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07∶45, 08∶00, 08∶30, 12∶00, 16∶50, and 21∶00 h. The participants' ages ranged from 8–14 yrs, and each participant was tested three times at six‐month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1–3) but not later puberty (stages 4–5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

当归叶片光合参数日变化及其与环境因子的关系

在当归根茎膨大期,利用CI-310便携式光合仪,田间活体测定了当归的净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(Gs)、胞间CO2浓度(Ci)等光合生理生态因子,以及光合有效辐射(PAR)、田间CO2浓度(Ca)、相对湿度(RH)、大气温度(Ta)、叶温(TL)等环境因子的日变化。结果表明,当归Pn日变化曲线为"双峰"型,最高峰出现在10:00左右,次高峰出现在16:00左右,午间有明显的"午休"现象,气孔因素是导致其"午休"的主要原因。Tr、Gs和Ci的日变化曲线均为"双峰"型,最高峰出现在10:00,次高峰出现在17:00。当归叶片净光合速率随环境因子日变化最优逐步多元回归方程为yPn=14.3108 0.0076xPAR-0.5271xTL(R2=0.6601,P<0.05),TL和PAR是对光合速率直接影响最大的生态因子,而Ca、RH和Ta主要是通过TL而间接影响光合速率的变化。     

Diurnal variation in temperature, mental and physical performance, and tasks specifically related to football (soccer)

Football (soccer) training and matches are scheduled at different times throughout the day. Association football involves a variety of fitness components as well as psychomotor and game-related cognitive skills. The purpose of the present research, consisting of two separate studies, was to determine whether game-related skills varied with time of day in phase with global markers of both performance and the body clock. In the first study, eight diurnally active male association football players (19.1+/-1.9 yrs of age; mean+/-SD) with 10.8+/-2.1 yrs playing experience participated. Measurements were made on different days at 08:00, 12:00, 16:00, and 20:00 h in a counterbalanced manner. Time-of-day changes in intra-aural temperature (used as a marker of the body clock), grip strength, reaction times, flexibility (markers of aspects of performance), juggling and dribbling tasks, and wall-volley test (football-specific skills) were compared. Significant (repeated measures analysis of variance, ANOVA) diurnal variations were found for body temperature (p<0.0005), choice reaction time (p<0.05), self-rated alertness (p<0.0005), fatigue (p<0.05), forward (sit-and-reach) flexibility (p<0.02), and right-hand grip strength (p<0.02), but not left-hand grip strength (p=0.40) nor whole-body (stand-and-reach) flexibility (p=0.07). Alertness was highest and fatigue lowest at 20:00 h. Football-specific skills of juggling performance showed significant diurnal variation (p<0.05, peak at 16:00 h), whereas performance on the wall-volley test tended to peak at 20:00 h and dribbling showed no time-of-day effect (p=0.55). In a second study, eight diurnally active subjects (23.0+/-0.7 yrs of age) completed five test sessions, at the same times as in the first study but with a second session at 08:00 h. Test-re-test comparisons at 08:00 h for all components indicated good reliability. Intra-aural temperature showed a significant time-of-day effect (p<0.001) with mean temperature at 16:00 h (36.4 degrees C) higher than at 08:00 h (35.4 degrees C). There was no significant effect of chronotype on the temperature acrophase (peak time) (p>0.05). Diurnal variation was found for performance tests, including sit-and-reach flexibility (p<0.01) and spinal hyper-extension (p<0.05). Peaks occurred between 16:00 and 20:00 h and the daytime changes paralleled the temperature rhythm. Diurnal variation was also found for football-specific tests, including dribbling time (p<0.001, peak at 20:00 h) and chip test performance (p<0.01), being more accurate at 16:00 h (mean error=0.75 m) than at 08:00 h (mean error=1.01 m). Results indicate football players perform at an optimum between 16:00 and 20:00 h when not only football-specific skills but also measures of physical performance are at their peak. Body temperature peaked at a similar time, but positive mood states seemed to peak slightly earlier. While causal links cannot be established in these experiments, the results indicate that the diurnal variation of some aspects of football performance is affected by factor(s) other than body temperature alone.