水稻叶片生育过程中RubisCO活性与光合、光呼吸的关系

水稻生育过程中,ＲｕＢＰ羧化酶活性与光合速率、ＲｕＢＰ加氧酶活性与光呼吸速率、ＲｕＢＰ羧化酶活性与加氢酶活性以及光合速率与光呼吸速率之间是相关的。籼型品种与粳型品种间酶活性的高低及光合、光呼吸速率的高低基本一致,籼型三系杂交稻（Ｆ１）无明显的光合优势。酶的羧化活性的高低只在一定范围内与光合速率的高低平行。在正常生育条件下,酶蛋白的数量不是水稻光合速率的限制因子。     

Source of glycolate and cyclic changes in photosynthetic and photorespiratory activity during the development of barley leaves

¹⁴CO₂ assimilation, RuBP earboxylase and PEP carboxylase activities show cyclic changes during the development of barley leaves. Cyclic changes, but in phase opposition with respect to carboxylating enzymes, are shown by RuBP oxygenase, phosphoglycolate phosphatase, glycolate oxidase and nitrate reductase activities. The oxygenase function of RuBP carboxylase appears to be the primary source of glycolate in young leaves, whereas in old ones glycolate could be supplied from some source in addition to RuBP oxygenase activity.     

Cycloheximide causes increased accumulation of translatable mRNA for tyrosine aminotransferase and tryptophan oxygenase in livers of cortisol-treated rats.

Messenger RNA activities for two cortisol-inducible enzymes, tyrosine aminotransferase and tryptophan oxygenase, have been determined by translation in a wheat germ system. The effects of cycloheximide on the two mRNA activities have been evaluated. Cortisol leads to an increase of the translatable mRNAs for tyrosine aminotransferase and tryptophan oxygenase with a maximum at approximately 6 h. Cycloheximide was administered 4 h after treatment with cortisol; 2 h later, the activities of tyrosine aminotransferase and tryptophan oxygenase mRNA had increased five-fold and two-fold, respectively, compared to the activities reached with cortisol alone. Thereafter the amount of the two translatable mRNAs declined, though 14 h after cortisol administration the mRNA activities were still several fold higher than in control animals. Application of alpha-amanitin together with cycloheximide did not prevent an increased accumulation of specific translatable mRNAs. The increase in tyrosine aminotransferase and tryptophan oxygenase activity by cortisol was immediately blocked by cycloheximide. Whereas tryptophan oxygenase activity rapidly declined after cycloheximide application, tyrosine aminotransferase activity remained at the same level. Approximately 4 h thereafter, both enzyme activities increased again.     

Influence of Temperature on the Ratio of Ribulose Bisphosphate Carboxylase to Oxygenase Activities and on the Ratio of Photosynthesis to Photorespiration of Leaves

Lehnherr, B., Mächler, F. and Nösberger, J. 1985.Influence of temperature on the ratio of ribulose bisphosphatecarboxylase to oxygenase activities and on the ratio of photosynthesisto photorespiration of leaves.—J. exp. Bot. 36: 1117–1125. Rates of net and gross photosynthesis of intact white cloverleaves were measured by infrared gas analysis and by short termuptake of ¹⁴CO₂ respectively. Ribulose bisphosphate carboxylaseoxygenase (RuBPCO) was purified from young leaves and kineticproperties investigated in combined and separate assays. Theratio of carboxylase to oxygenase activities was compared withthe ratio of photosynthesis to photorespiration at various temperaturesand CO₂ concentrations. The ratio of photosynthesis to photorespiration at 30 Pa p(CO₂)was consistent with the ratio of carboxylase activity to oxygenaseactivity when each was measured above 20 °C. However, theratio of photosynthesis to photorespiration increased with decreasingtemperature, whereas the ratio of carboxylase to oxygenase activitywas independent of temperature. This resulted in a disagreementbetween the measurements on the purified enzyme and intact leafat low temperature. No disagreement between enzyme and leafat low temperature occurred, when the ratio of photosynthesisto photorespiration was determined at increased CO₂ concentrations. The results suggest an effect of low temperature and low CO₂concentration on the ratio of photosynthesis to photorespirationindependent of the enzyme. Key words: Ribulose bisphosphate carboxylase oxygenase, photorespiration, temperature     

Benzylaminopurine induced changes in photosynthesis and photorespiration of barley plants

Benzylaminopurine (BA) caused an enhancement of chlorophyll and protein content and a reduced elongation of primary barley leaves. BA did not change the rhythmic pattern of¹⁴CO₂ fixation and activities of RuBP carboxylase, RuBP oxygenase, glycolate oxidase and phosphoglycolate phosphatase, but the enzyme activities were enhanced and the level of¹⁴CO₂ fixation was reduced. Light/dark¹⁴CO₂ evolution ratio was affeoted by BA only in older leaves. BA acts sequentially on the activities of photosynthetic and photorespiratory enzymes.     

An analysis of the age-related decline in testicular steroidogenesis in the rat

The effect of aging in rats on serum and intratesticular testosterone levels, microsomal steroidogenic enzyme activities and microsomal cytochrome P-450 was studied. Serum testosterone levels were highest in 11-wk-old rats, declined at age 16 wk and further declined between ages 7 and 21 mo. Intratesticular testosterone levels in 21-mo-old rats were significantly lower than those of the other groups. The activity of 17 alpha-hydroxylase and C17-20 lyase, as well as cytochrome P-450, decreased significantly in 21-mo-old rats. The activity of 17 beta-hydroxysteroid oxidoreductase increased from 11 wk to 16 wk of age and then declined by 21 mo of age to the levels of 11-wk-old animals. Similar changes in delta 5-3,3-hydroxysteroid dehydrogenase coupled with delta 5-delta 4 isomerase activities were observed, but were not statistically significant. These results suggest that the decline in testosterone production in old rats is predominantly a result of decreased oxygenase activity. Inasmuch as oxygenases are gonadotropin dependent, our results support the hypothesis that gonadotropin deficiency is the major factor responsible for Leydig cell dysfunction in old rats. Further, the decline in the ratio of 17 alpha-hydroxylase to C17-20 lyase with aging suggests that other factors affect these enzymes as well as the reduction in cytochrome P-450.     

Light-dependent modulation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity in the genus Phaseolus

Modulation of the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in low light and darkness was measured in A) 25 genotypes from the four cultivated species of Phaseolus (P. vulgaris, P. acutifolius, P. lunatus and P. coccineus), B) 8 non-cultivated Phaseolus species, and C) the related species Macroptileum atropurpureum. The activity ratio of Rubisco (the ratio of initial and total Rubisco activities, which reflects Rubisco carbamylation), and the molar activity of fully-activated Rubisco (which primarily reflects the inhibition of Rubisco activity by carboxyarabinitol 1-phosphate, CA1P) were assayed in leaves from the cultivated species sampled at midday in full sunlight, in low light at dusk (60 to 100 mol photons m^-2s^-1), and after at least 4 h in darkness. Dark inhibition of Rubisco molar activity was compared in both cultivated and non-cultivated species. In all cultivated genotypes, a significant reduction of the activity ratio of Rubisco was measured in leaves sampled at low light; however, the molar activity of fully activated Rubisco was not greatly reduced in these low light samples. In darkened leaves, molar activities substantially declined in most Phaseolus species with 11 of 13 exhibiting greater than 60% reduction. In P. vulgaris, the reduction of molar activity was extensive (greater than 69%) in all genotypes studied, which included wild progenitors as well as ancient and advanced cultivars. These results indicate that at low light late in the day, modulation of Rubisco activity is primarily through changes in carbamylation state, with CA1P playing a more limited role. By contrast in the dark, binding of CA1P dominates the modulation of Rubisco activity in Phaseolus in a pattern that appears to be conserved within a species, but can vary significantly between species within a genus. The degree of CA1P inhibition in Phaseolus was associated with phylogenetic affinities within the genus, as the species with extensive dark-inhibition of Rubisco activity tended to be more closely related to each other than to species with reduced inhibition of Rubisco activity.Abbreviations CA1P carboxyarabinitol 1-phosphate - CABP carboxyarabinitol bisphosphate - PFD photon flux density between 400 and 700 nm - Rubisco ribulose-1,5-bisphosphate carboxylase/oxygenase     

Effects of CO2, O2 and temperature on a high-affinity form of ribulose diphosphate carboxylase-oxygenase from spinach

A high-affinity form of ribulose diphosphate carboxylase, observed transiently in spinach-leaf extracts soon after extraction, was inhibited by O₂ competitively with respect to CO₂. Analogously, the ribulose diphosphate oxygenase activity for this form was inhibited by CO₂, competitively with respect to O₂. For each gas, the K_m for the reaction in which it was a substrate was similar to its K_i for the reaction it inhibited. The Arrhenius activation energy for the oxygenase reaction was 1.5 times that of the carboxylase. These characteristics are consistent with ribulose diphosphate oxygenase being the enzymatic reaction responsible for synthesizing the substrate for photorespiration and with the concept that the balance between photosynthesis and photorespiration of leaves is a reflection of the ratio between the two activities of this bi-functional enzyme.     

夜间高温胁迫对水稻叶片光合机构的影响

The net photosynthetic rate (Pn), the apparent quantum yield (AQY), the photochemical efficiency of PSⅡ(Fv/Fm), the quantum yield of PSⅡ electron transport (Ф PSⅡ) and the coefficient of photochemical quenching (qp) were decreased in rice (Oryza sativa L.) leaves under high nocturnal temperature (42±1) ℃ stress, but the relative reduction state of PSⅡ (1-qp) was increased. With the increment of stress time, the chlorophyll content and the binding degree of chlorophyll-protein complex declined gradually, the O2(superoxide radical) production rate and H2O2 content in leaves elevated. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) increased for 2-3 days under high temperature stress yet decreased afterwards. The results showed that the photosynthetic efficiency declined in rice leaves under high nocturnal temperature stress with concurrent emergence of the symptom of oxidative damage. The gradual increase of the SOD, POD and CAT activities, as well as that of the ratio of Pr (photo-respiration rate) to Pr+Pn and non-photochemical quenching of chlorophyll fluorescence (NPQ) indicates that those mechanisms related to the changes of these parameters may play an important role in protecting rice leaves from oxidative damage under high nocturnal temperature stress.     

Photosynthesis in leaves of <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> L. infected with tobacco mosaic virus

In tobacco leaves inoculated with tobacco mosaic virus (TMV), changes in chlorophyll (Chl) and carotenoid contents, parameters of slow Chl fluorescence kinetics, i.e. the maximum quantum yield of photosystem (PS2) photochemistry F_v/F_m, the effective quantum yield of photochemical energy conversion in PS2 Φ₂, ratio of quantum yields of photochemical and concurrent non-photochemical processes in PS2 F_v/F₀, non-photochemical quenching (NPQ), and photochemical activities of isolated chloroplasts from systemically infected tobacco leaves were investigated. We compared two successive stages of infection, the first in the stage of vein clearing at 9^th day post inoculation (dpi) and the second at 22^nd dpi when two different regions, i.e. light- (LGI) or dark-green (DGI) islands in the infected leaf were apparent and symptoms were fully developed. These two different regions were measured separately. The Chl and carotenoid contents in infected leaves decreased with a progression of infection and were lowest in LGI in the second stage. Also the ratio of Chl a/b declined in similar manner. The maximum quantum yield of PS2 photochemistry F_v/F_m, was decreased in the following order: first stage, DGI, and LGI. The same is true for the ratio F_v/F₀. The decrease of Φ₂ in infected leaves declined as compared to their controls. On the contrary, NPQ increased in infected leaves, the highest value was found in the first infection stage. Photochemical activities of the whole electron transport chain in isolated chloroplasts dramatically declined with the progression of symptoms, the lowest value was in LGI. Similarly, but to a lesser extent, the activity of PS2 in isolated chloroplasts decreased in infected leaves. Generally, the most marked impairment of the photosynthetic apparatus was manifested in the LGI of infected leaves.     

Effects of Nitrogen Nutrition on Nitrogen Partitioning between Chloroplasts and Mitochondria in Pea and Wheat

Nitrogen partitioning among proteins in chloroplasts and mitochondria was examined in pea (Pisum sativum L.) and wheat (Triticum aestivum L.) grown hydroponically with different nitrogen concentrations. In pea leaves, chloroplast nitrogen accounted for 75 to 80% of total leaf nitrogen. We routinely found that 8% of total ribulose-1,5-bisphosphate carboxylase/oxygenase adhered to thylakoids during preparation and could be removed with Triton X-100. With this precaution, the ratio of stroma nitrogen increased from 53 to 61% of total leaf nitrogen in response to the nitrogen supply, but thylakoid nitrogen remained almost constant around 20% of total. The changes in the activities of the stromal enzymes and electron transport in response to the nitrogen supply reflected the nitrogen partitioning into stroma and thylakoids. On the other hand, nitrogen partitioning into mitochondria was appreciably smaller than that in chloroplasts, and the ratio of nitrogen allocated to mitochondria decreased with increasing leaf-nitrogen content, ranging from 7 to 4% of total leaf nitrogen. The ratio of mitochondrial respiratory enzyme activities to leaf-nitrogen content also decreased with increasing leaf-nitrogen content. These differences in nitrogen partitioning between chloroplasts and mitochondria were reflected in differences in the rates of photosynthesis and dark respiration in wheat leaves measured with an open gas-exchange system. The response of photosynthesis to nitrogen supply was much greater than that of dark respiration, and the CO₂ compensation point decreased with increasing leaf-nitrogen content.     

Changing ribulose diphosphate carboxylase/oxygenase activity in ripening tomato fruit

Tomato fruit (Lycopersicum esculentum Mill) from green, pink, and red stages were assayed for changes in the activity of ribulose diphosphate carboxylase and oxygenase, phosphoenolpyruvate carboxylase, changes in the levels of glycolate and respiratory gas exchange. The ribulose diphosphate carboxylase activity decreased as the fruit ripened. By comparison, the ribulose diphosphate oxygenase activity increased during the transition from the green to the pink stage, and declined afterward. The changes in the endogenous glycolate levels and the respiratory gas exchange, as observed at different stages of ripening, resembled the changes in the ribulose diphosphate oxygenase activity. The utilization of glycolate in further metabolic activity may result in the formation of peroxidases required for the onset of ripening.     

CERTAIN ENZYMATIC ACTIVITIES OF NORMAL AND MOSAIC INFECTED TOBACCO PLANTS

The lower leaves of tobacco plants were inoculated with leaf mosaic virus and the activities of oxygenase, peroxidase, catalase, and invertase were followed in leaves of comparable age at intervals of 2 or 3 days over a period of 21 days. The inoculated leaves exhibited a great decrease relative to normal tissue in the activity of oxygenase and peroxidase on the 6th day. Younger leaves showed this minimum at a progressively later date. A great decrease in the activities of these enzymes was attained by the 14th to the 18th day. This maximum was followed by a decrease. Catalase exhibited an increased activity which reached a maximum at about the 8th day. A second maximum was observed on the 16th to the 18th day. Invertase reached a minimum, relative to normal plants, on about the 8th day. A second minimum was approached on the 16th to the 18th day. These data show that profound disturbances in the physiology of infected plants occur many days before the leaf juice attains an infectious concentration of virus. The observed activities could not be due therefore to metabolic activities of the virus particles themselves. Since infectivity is attained only after a period of profound physiological disturbance, it seems possible that the virus protein develops as a product of abnormal metabolism.     

Co<Subscript>2</Subscript> assimilation and chlorophyll fluorescence in green <Emphasis Type="Italic">versus</Emphasis> red <Emphasis Type="Italic">Berberis thunbergii</Emphasis> leaves measured with different quality irradiation

Photosynthesis, photorespiration, and chlorophyll (Chl) fluorescence in green and red Berberis thunbergii leaves were studied with two different measuring radiations, red (RR) and “white” (WR). The photosynthetic and photorespiration rates responded differently to the different radiation qualities, which indicate that the carboxylase and oxygenase activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were affected. Differences in photosynthetic rate between the two color leaves were less under RR than under WR. However, this reduced difference in photosynthetic rate was not correlated with the stomatal response to the measuring radiation qualities. Compared with the WR, the RR reduced the differences in dark-adapted minimum and maximum fluorescence, steady-state fluorescence, light-adapted maximum fluorescence, and actual photochemical efficiency (Φ_PS2) of photosystem 2 (PS2), but enlarged the difference in non-photochemical quenching between the two color leaves. Differences in both maximum quantum yield of PS2 and ratio of Φ_PS2 to quantum yield of CO₂ fixation between the two color leaves were similar under the two measuring radiations. To exclude disturbance of radiation attenuation caused by anthocyanins, it is better to use RR to compare the photosynthesis and Chl fluorescence in green versus red leaves.     

Ribulose diphosphate carboxylase/oxygenase. IV. Regulation by phosphate esters.

The stimulation or inhibition of ribulose diphosphate oxygenase by a variety of compounds is compared with the reported effects on these compounds on the ribulose diphosphate carboxylase activity. A possible transition state analog of ribulose diphosphate, 2-carboxyribitol 1, 5-diphosphate, at a molar ratio of inhibitor to enzyme of 10 to 1, irreversibly inactivates the oxygenase and carboxylase activities. This is consistent with the hypothesis that there may be a single active site for both the carboxylase and oxygenase activities. Several compounds of the reductive pentose photosynthetic carbon cycle act as effectors of the ribulose diphosphate oxygenase in a manner complementary to their reported effect upon the carboxylase. Ribose 5-phosphate inhibits the oxygenase with an apparent Ki of 1.8 mM, but it is reported to activate the carboxylase; fructose 6-phosphate and glucose 6-phosphate act similarly but are less effective than ribose 5-phosphate. Fructose 1. 6-diphosphate stimulates the oxygenase at low magnesium ion concentrations. The stimulatory effect of 6-phosphogluconate on the oxygenase is associated with a 3-fold reduction of the Km (Mg2+). ATP inhibits the oxygenase but has been reported to stimulate the carboxylase; pyrophosphate acts in an opposite manner. From these results it appears that the ratio of carboxylase to oxygenase activity may be a variable factor with predictable subsequent alteration in the ratio between photosynthetic CO2 fixation and photorespiration.     

Is light quality involved in the regulation of the photosynthetic apparatus in attached rice leaves?

The regulatory effect of light quality on the photosynthetic apparatus in attached leaves of rice plants was investigated by keeping rice plants under natural light, in complete darkness, or under illumination with light of different colors. When leaves were left in darkness and far-red (FR)-light conditions for 6 days at 30°C, there was an initial lag in chlorophyll (Chl) content, Chl a/b ratio, and maximum photosystem (PS) II photochemistry that lasted until the second day; these then rapidly decreased on the fourth day. In contrast, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) rapidly disappeared with no lag under low or zero light conditions. By using spectrophotometric quantitation, it was determined that the PSII and PSI reaction centers were regulated by light quality, but cytochrome (Cyt) f was regulated by light intensity. However, the PSII heterogeneity was also strongly modified by the light intensity; PSIIα with the large antenna decreased markedly both in content and in antenna size. Consequently, the PSIIα/PSI ratio declined under FR-light because the low intensity of FR-light dominated over its quality in the modulation of the PSIIα/PSI ratio. An imbalance between them induced the generation of reactive oxygen species (ROS), although the ROS were scavenged by stromal enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). The activities of these stromal enzymes are also regulated by light quality. Thus, although the photosynthetic apparatus is regulated differently depending on light quality, light quality may play an important role in the regulation of the photosynthetic apparatus.     

Regulation and Localization of Key Enzymes during the Induction of Kranz-Less,C4-Type Photosynthesis in Hydrilla verticillata

Kranz-less, C4-type photosynthesis was induced in the submersed monocot Hydrilla verticillata (L.f.) Royle. During a 12-d induction period the CO2 compensation point and O2 inhibition of photosynthesis declined linearly. Phosphoenolpyruvate carboxylase (PEPC) activity increased 16-fold, with the major increase occurring within 3 d. Asparagine and alanine aminotransferases were also induced rapidly. Pyruvate orthophosphate dikinase (PPDK) and NADP-malic enzyme (ME) activities increased 10-fold but slowly over 15 d. Total ribulose-1,5-bisphosphate carboxylase/oxygenase activity did not increase, and its activation declined from 82 to 50%. Western blots for PEPC, PPDK, and NADP-ME indicated that increased protein levels were involved in their induction. The H. verticillata NADP-ME polypeptide was larger (90 kD) than the maize C4 enzyme (62 kD). PEPC and PPDK exhibited up-regulation in the light. Subcellular fractionation of C4-type leaves showed that PEPC was cytosolic, whereas PPDK and NADP-ME were located in the chloroplasts. The O2 inhibition of photosynthesis was doubled when C4-type but not C3-type leaves were exposed to diethyl oxalacetate, a PEPC inhibitor. The data are consistent with a C4-cycle concentrating CO2 in H. verticillata chloroplasts and indicate that Kranz anatomy is not obligatory for C4-type photosynthesis. H. verticillata predates modern terrestrial C4 monocots; therefore, this inducible CO2-concentrating mechanism may represent an ancient form of C4 photosynthesis.     

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.