碳酸氢盐处理下桑树和构树的生长、光合和抗逆性差异

为探究喀斯特生境中,在碳酸氢盐的胁迫下HCO^-₃对植株生长及生理特性的影响,该文以构树和桑树幼苗为研究对象,对不同浓度NaHCO₃溶液(0、15、30 mmol·L^-1)处理下植株的生长情况、光合能力、抗氧化酶活性、渗透调节物质含量和细胞膜系统损伤情况进行研究。结果表明:(1)在HCO^-₃处理下,构树和桑树的生长和光合能力均受到抑制,叶片细胞内均发生显著的抗氧化和抗渗透胁迫生理响应。(2)HCO^-₃对构树和桑树生长的抑制作用与其浓度有关,并有显著差异性(P<0.05)。(3)30 mmol·L^-1 HCO^-₃处理对植株生长、光合、抗氧化酶系统和渗透调节系统的抑制作用以及植物细胞的损伤情况要显著强于15 mmol·L^-1 HCO^-₃处理的效果。(4)同等浓度的HCO^-₃处理下,构树的生长、光合能力、抗氧化酶活性、渗透调节物质含量显著高于桑树,其叶片细胞损伤情况显著低于桑树。综上结果均表明,构树对碳酸氢盐胁迫的耐受能力要优于桑树。该研究为阐明桑科植物对喀斯特环境适应机制提供科学支撑。     

Photosynthetic response of three climber plant species to osmotic stress induced by polyethylene glycol (PEG) 6000

We examined the photosynthesis response to osmotic stress in three climber plant species, Pharbitis nil (Linn.) Choisy, Lonicera japonica Thunb, and Parthenocissus tricuspidata (Sieb.et Zucc.) Planch. All climber plants were exposed to osmotic stress induced by polyethylene glycol (PEG) 6000 at 4 levels (slight, moderate, severe osmotic and the control) for 30?days. Photosynthesis response was determined by measuring leaf photosynthesis, chlorophyll fluorescence, carbonic anhydrase activity and stable carbon isotope ratios. P. nil maintained high photosynthetic activity under long-term moderate osmotic stress due to both stable photosystem II photochemical efficiency and high carbonic anhydrase activity. L. japonica maintained high photosynthetic activity under long-term moderate stress due to high carbonic anhydrase activity rather than photosystem II photochemical efficiency. P. tricuspidata tolerated only short-term moderate osmotic stress and long-term slight osmotic stress because its response was mainly stomatal limitation, with the lowest photosynthetic activity and hardly any carbonic anhydrase activity. Carbonic anhydrase activity was inversely correlated with stable carbon isotope ratios. The regulation by carbonic anhydrase was probably the reason for P. nil and L. japonica to tolerate long-term moderate osmotic stress. The selection on the species should consider the differential adaptation mechanism to osmotic stress during the development of drought-resistant plants.     

贵州喀斯特森林三种植物对不同坡位环境的光合生理响应

该研究以贵州普定喀斯特森林中、下坡位生长的构树( Broussonetia papyrifera)、朴树( Celtis sinensis)和光滑悬钩子( Rubus tsangii)为材料,通过对碳酸酐酶( CA)活性、光合作用日变化、净光合速率对CO2与光的响应曲线、叶绿素荧光特性以及稳定碳同位素组成等指标的测定,进而对比分析三种植物不同的光合生理响应特性。结果表明：构树光合作用过程的无机碳源既可来自大气中的CO2,也可以在气孔部分闭合的情况下利用细胞内的HCO3－,下坡位的构树较高的CA活性使其利用HCO3－的效率会更高,并能在较低光强下具有较高的光能利用效率。这可能与下坡位的构树具有较高的CA活性有关,对下坡位具有更好的适应性。朴树光合无机碳的同化能力最低,且光合无机碳源较单一,主要利用大气CO2,其较慢的生长速率使其对无机碳的需求最低,且能保持较稳定的无机碳同化速率。相对来说,中坡位的朴树具有相对较高的净光合速率和光能利用效率,对中坡位表现出较好的适应性。光滑悬钩子主要利用大气中的CO2进行光合作用。中坡位的光滑悬钩子具有较强的光能利用效率,并表现出较高的净光合速率,光滑悬钩子对中坡位同样表现出较好的适应性。该研究结果为喀斯特生态脆弱区植被重建过程中树种的选择及合理配置提供了科学依据。     

模拟干旱胁迫下构树和桑树的生理特征比较

在不同浓度聚乙二醇(PEG 6000)的处理下,测定构树和桑树的碳酸酐酶活性、光响应曲线、二氧化碳响应曲线和叶绿素荧光等指标,比较它们的抗干旱能力.结果表明:(1)构树的碳酸酐酶活力变化不显著,而桑树的碳酸酐酶活力不同的PEG 6000浓度间差异较大.(2)构树的净光合速率受PEG 6000的影响较小,而桑树受到抑制较...     

Comparison of carbonic anhydrase activity among various species of plantlets

During plant tissue culture, the culture container is small and sealed; the concentration of CO₂ in the microenvironment is relatively low. The plantlet growth is restrained for the shortage of CO₂ in the culture container. Carbonic anhydrase is a zinc-containing metalloenzyme that catalyzes the reversible conversion of bicarbonate to CO₂. The determination of carbonic anhydrase of leaves from Atractylodes lancea (thunb.) DC, Orychophragmus violaceus (L.) O.E. Schulz, Brassica juncea (L.) Czern.et Coss. cv. Luzhousileng, Brassica campestris L. cv. Chuanyou No.8, Brassica napus L cv. Oro, Brassica carinata Braun, Raphanus sativa L. var. raphanistroides Makino and their plantlets indicates that the carbonic anhydrase activity of leaves from both plantlets and fields varies from plant species to plant species, the carbonic anhydrase activity of leaves of Atractylodes lancea (thunb.) DC is the lowest among those plants, and the leaves of all plantlets are lower in carbonic anhydrase activity than the same species of plants from fields. The comparison of the growth rates of those plantlets shows that their relative growth rates are significantly different, plantlets of Atractylodes lancea have the slowest relative growth rate among those plants, and plantlets of Brassica juncea have the greatest relative growth rate. The relationship between RGR of plantlets and their CA activities is a significant linear function. It seems that there was certain correlation between carbonic anhydrase activities of plants and their growth rates. It suggests that in vitro, the greater the carbonic anhydrase activity of plantlet is, the higher its net photosynthetic rate, and the faster its growth rate. Those results offer a foundation to a rational medium choice in plant tissue culture.     

Mechanisms of inorganic carbon acquisition in two estuarine Rhodophyceans: Bostrychia scorpioides (Hudson) ex Kützing Montagne and Catenella caespitosa (Withering) L. M. Irvine

Marine macroalgae possess a range of mechanisms to increase the availability of CO₂ for fixation by ribulose-1,5-bisphosphate carboxylase/oxygenase. Of these, possession of a periplasmic or external carbonic anhydrase and the ability to use bicarbonate ions is widely distributed. The mechanisms of carbon acquisition were studied in two estuarine red macroalgae Bostrychia scorpioides and Catenella caespitosa using a range of techniques. pH-drift and CO₂-depletion experiments at constant pH suggested that CO₂ is the main source of inorganic carbon in both species. Inhibitors indicated that internal and external carbonic anhydrase were present in both species. Inhibitors also suggested that uptake of bicarbonate is unlikely to be present (P < 0.05).     

Role of Photosynthetic Reactions in the Activity of Carbonic Anhydrase in Synechococcus sp. (UTEX 2380) in the Light : Inhibitor Studies Using the O-Exchange in C/O-Labeled Bicarbonate

The role of the photosystems in the exchange of ¹⁸O between species of inorganic carbon and water was studied in suspensions of the cyanobacterium Synechococcus sp. (UTEX 2380) using membrane-inlet mass spectrometry. This ¹⁸O exchange is caused by the hydration-dehydration cycle of CO₂ and is catalyzed by carbonic anhydrase. We observed the complex ¹⁸O exchange kinetics including dark-light-dark transients in suspensions of whole cells and found these to be identical to the ¹⁸O exchange kinetics of physiologically fully active spheroplast preparations. There was no enhancement effect of inorganic nitrogen on inorganic carbon accumulation. Membrane preparations exhibited no uptake of inorganic carbon and very little carbonic anhydrase activity, although these membranes were photosynthetically fully competent. DCMU, the inhibitor of photosystem II, eliminated almost entirely the ¹⁸O exchange activity of whole cells in the light. But this effect of DCMU could be reversed by addition of the electron donor couple 3,6-diaminodurene/ascorbate, suggesting the involvement of photosystem I in the events leading to ¹⁸O exchange. Iodoacetamide, an inhibitor of CO₂ fixation, enhanced the ¹⁸O exchange in whole cell suspensions and inhibited neither the uptake of inorganic carbon nor the dehydration of bicarbonate in the light. The proton carrier carbonylcyanide m-chlorophenylhydrazone and the inhibitors diethylstilbestrol and N,N′ -dicyclohexyl carbodiimide affecting the membrane potential, totally abolished ¹⁸O exchange in the light. From ¹⁸ O-labeled inorganic carbon experiments we conclude that one of the roles of photosystem I is to provide the active uptake of inorganic carbon into the cells, where carbonic anhydrase catalyzes the interconversion between CO₂ and HCO₃⁻ resulting in the ¹⁸O exchange from inorganic carbon to water.     

14C Fixation by Leaves and Leaf Cell Protoplasts of the Submerged Aquatic Angiosperm Potamogeton lucens: Carbon Dioxide or Bicarbonate?

Protoplasts were isolated from leaves of the aquatic angiosperm Potamogeton lucens L. The leaves utilize bicarbonate as a carbon source for photosynthesis, and show polarity; that is, acidification of the periplasmic space of the lower, and alkalinization of the space near the upper leaf side. At present there are two models under consideration for this photosynthetic bicarbonate utilization process: conversion of bicarbonate into free carbon dioxide as a result of acidification and, second, a bicarbonate-proton symport across the plasma membrane. Carbon fixation of protoplasts was studied at different pH values and compared with that in leaf strips. Using the isotopic disequilibrium technique, it was established that carbon dioxide and not bicarbonate was the form in which DIC actually crossed the plasma membrane. It is concluded that there is probably no true bicarbonate transport system at the plasma membrane of these cells and that bicarbonate utilization in this species apparently rests on the conversion of bicarbonate into carbon dioxide. Experiments with acetazolamide, an inhibitor of periplasmic carbonic anhydrase, and direct measurements of carbonic anhydrase activity in intact leaves indicate that in this species the role of this enzyme for periplasmic conversion of bicarbonate into carbon dioxide is insignificant.     

植物光合作用限制因素与植被生产力研究进展

随着全球气候变化的加剧,陆地生态系统中植物光合作用限制影响程度的增加已成为降低全球植被净初级生产力的主要因素。系统了解植物光合作用限制因素是科学评估植被生产力的重要前提,也是缓解植物光合作用限制,增加植物光合碳同化能力的先决条件。对植物光合作用限制因素进行了系统解析,分析了光合作用三种限制因素生化限制(Biochemical limitation,l_b)、气孔限制(Stomatal limitation,l_s)、叶肉限制(Mesophyll limitation,l_m)的环境响应,重点讨论了叶肉限制及其影响机理,述评了光合作用限制定量分析方法及改善措施,最后以提高植被生产力为驱使目标,对未来植物光合作用限制因素研究提出以下内容：(1)基因工程技术与系统生物学数据相结合提高植被生产力;(2)气孔响应速度对植物光合作用的影响机制;(3)水通道蛋白(Aquaporin, AQPs)和碳酸酐酶(Carbonic anhydrase, CAs)感知环境信号变化的驱动基因。以期为未来气候变化背景下,深入认识和降低植物光合作用限制,提...     

Effect of Carbonic Anhydrase Inhibitors on Inorganic Carbon Accumulation by Chlamydomonas reinhardtii

Membrane-permeable and impermeable inhibitors of carbonic anhydrase have been used to assess the roles of extracellular and intracellular carbonic anhydrase on the inorganic carbon concentrating system in Chlamydomonas reinhardtii. Acetazolamide, ethoxzolamide, and a membrane-impermeable, dextran-bound sulfonamide were potent inhibitors of extracellular carbonic anhydrase measured with intact cells. At pH 5.1, where CO₂ is the predominant species of inorganic carbon, both acetazolamide and the dextran-bound sulfonamide had no effect on the concentration of CO₂ required for the half-maximal rate of photosynthetic O₂ evolution (K_0.5[CO₂]) or inorganic carbon accumulation. However, a more permeable inhibitor, ethoxzolamide, inhibited CO₂ fixation but increased the accumulation of inorganic carbon as compared with untreated cells. At pH 8, the K_0.5(CO₂) was increased from 0.6 micromolar to about 2 to 3 micromolar with both acetazolamide and the dextran-bound sulfonamide, but to a higher value of 60 micromolar with ethoxzolamide. These results are consistent with the hypothesis that CO₂ is the species of inorganic carbon which crosses the plasmalemma and that extracellular carbonic anhydrase is required to replenish CO₂ from HCO₃⁻ at high pH. These data also implicate a role for intracellular carbonic anhydrase in the inorganic carbon accumulating system, and indicate that both acetazolamide and the dextran-bound sulfonamide inhibit only the extracellular enzyme. It is suggested that HCO₃⁻ transport for internal accumulation might occur at the level of the chloroplast envelope.     

Expression of Tobacco Carbonic Anhydrase in the C4 Dicot Flaveria bidentis Leads to Increased Leakiness of the Bundle Sheath and a Defective CO2-Concentrating Mechanism

Flaveria bidentis (L.) Kuntze, a C₄ dicot, was genetically transformed with a construct encoding the mature form of tobacco (Nicotiana tabacum L.) carbonic anhydrase (CA) under the control of a strong constitutive promoter. Expression of the tobacco CA was detected in transformant whole-leaf and bundle-sheath cell (bsc) extracts by immunoblot analysis. Whole-leaf extracts from two CA-transformed lines demonstrated 10% to 50% more CA activity on a ribulose-1,5-bisphosphate carboxylase/oxygenase-site basis than the extracts from transformed, nonexpressing control plants, whereas 3 to 5 times more activity was measured in CA transformant bsc extracts. This increased CA activity resulted in plants with moderately reduced rates of CO₂ assimilation (A) and an appreciable increase in C isotope discrimination compared with the controls. With increasing O₂ concentrations up to 40% (v/v), a greater inhibition of A was found for transformants than for wild-type plants; however, the quantum yield of photosystem II did not differ appreciably between these two groups over the O₂ levels tested. The quantum yield of photosystem II-to-A ratio suggested that at higher O₂ concentrations, the transformants had increased rates of photorespiration. Thus, the expression of active tobacco CA in the cytosol of F. bidentis bsc and mesophyll cells perturbed the C₄ CO₂-concentrating mechanism by increasing the permeability of the bsc to inorganic C and, thereby, decreasing the availability of CO₂ for photosynthetic assimilation by ribulose-1,5-bisphosphate carboxylase/oxygenase.     

Is carbonic anhydrase activity of photosystem II required for its maximum electron transport rate?

It is known, that the multi-subunit complex of photosystem II (PSII) and some of its single proteins exhibit carbonic anhydrase activity. Previously, we have shown that PSII depletion of HCO₃^?/CO₂ as well as the suppression of carbonic anhydrase activity of PSII by a known inhibitor of α?carbonic anhydrases, acetazolamide (AZM), was accompanied by a decrease of electron transport rate on the PSII donor side. It was concluded that carbonic anhydrase activity was required for maximum photosynthetic activity of PSII but it was not excluded that AZM may have two independent mechanisms of action on PSII: specific and nonspecific. To investigate directly the specific influence of carbonic anhydrase inhibition on the photosynthetic activity in PSII we used another known inhibitor of α?carbonic anhydrase, trifluoromethanesulfonamide (TFMSA), which molecular structure and physicochemical properties are quite different from those of AZM. In this work, we show for the first time that TFMSA inhibits PSII carbonic anhydrase activity and decreases rates of both the photo-induced changes of chlorophyll fluorescence yield and the photosynthetic oxygen evolution. The inhibitory effect of TFMSA on PSII photosynthetic activity was revealed only in the medium depleted of HCO₃^?/CO₂. Addition of exogenous HCO₃^? or PSII electron donors led to disappearance of the TFMSA inhibitory effect on the electron transport in PSII, indicating that TFMSA inhibition site was located on the PSII donor side. These results show the specificity of TFMSA action on carbonic anhydrase and photosynthetic activities of PSII. In this work, we discuss the necessity of carbonic anhydrase activity for the maximum effectiveness of electron transport on the donor side of PSII.     

Identification and localization of a thylakoid-bound carbonic anhydrase from the green algae Tetraedron minimum (Chlorophyta) and Chlamydomonas noctigama (Chlorophyta)

In order to broaden our understanding of the eukaryotic CO₂-concentrating mechanism the occurrence and localization of a thylakoid-associated carbonic anhydrase (EC 4.2.1.1) were studied in the green algae Tetraedron minimum and Chlamydomonas noctigama. Both algae induce a CO₂-concentrating mechanism when grown under limiting CO₂ conditions. Using mass-spectrometric measurements of ¹⁸O exchange from doubly labelled CO₂, the presence of a thylakoid-associated carbonic anhydrase was confirmed for both species. From purified thylakoid membranes, photosystem I (PSI), photosystem II (PSII) and the light-harvesting complex of the photosynthetic apparatus were isolated by mild detergent gel. The protein fractions were identified by 77 K fluorescence spectroscopy and immunological studies. A polypeptide was found to immunoreact with an antibody raised against thylakoid carbonic anhydrase (CAH3) from Chlamydomonas reinhardtii. It was found that this polypeptide was mainly associated with PSII, although a certain proportion was also connected to light harvesting complex II. This was confirmed by activity measurements of carbonic anhydrase in isolated bands extracted from the mild detergent gel. The thylakoid carbonic anhydrase isolated from T. minimum had an isoelectric point between 5.4 and 4.8. Together the results are consistent with the hypothesis that thylakoid carbonic anhydrase resides within the lumen where it is associated with the PSII complex. Received: 13 May 2000 / Accepted: 16 August 2000     

Carbonic Anhydrase-Deficient Mutant of Chlamydomonas reinhardii Requires Elevated Carbon Dioxide Concentration for Photoautotrophic Growth

A mendelian mutant of the unicellular green alga Chlamydomonas reinhardii has been isolated which is deficient in carbonic anhydrase (EC 4.2.1.1) activity. This mutant strain, designated ca-1-12-1C (gene locus ca-1), was selected on the basis of a high CO₂ requirement for photoautotrophic growth. Photosynthesis by the mutant at atmospheric CO₂ concentration was very much reduced compared to wild type and, unlike wild type, was strongly inhibited by O₂. In contrast to a CO₂ compensation concentration of near zero in wild type at all O₂ concentrations examined, the mutant exhibited a high, O₂-stimulated CO₂ compensation concentration. Evidence of photorespiratory activity in the mutant but not in wild type was obtained from the analysis of photosynthetic products in the presence of ¹⁴CO₂. At air levels of CO₂ and O₂, the mutant synthesized large amounts of glycolate, while little glycolate was synthesized by wild type under identical conditions. Both mutant and wild type strains formed only small amounts of glycolate at saturating CO₂ concentration. At ambient CO₂, wild type accumulated inorganic carbon to a concentration several-fold higher than that in the suspension medium. The mutant cells accumulated inorganic carbon internally to a concentration 6-fold greater than found in wild type, yet photosynthesis was CO₂ limited. The mutant phenotype was mimicked by wild type cells treated with ethoxyzolamide, an inhibitor of carbonic anhydrase activity. These observations indicate a requirement for carbonic anhydrase-catalyzed dehydration of bicarbonate in maintaining high internal CO₂ concentrations and high photosynthesis rates. Thus, in wild type cells, carbonic anhydrase rapidly converts the bicarbonate taken up to CO₂, creating a high internal CO₂ concentration which stimulates photosynthesis and suppresses photorespiration. In mutant cells, bicarbonate is taken up rapidly but, because of a carbonic anhydrase deficiency, is not dehydrated at a rate sufficiently rapid to maintain a high internal CO₂ concentration.     

Carbonic Anhydrase-Dependent Inorganic Carbon Uptake by the Red Macroalga, Chondrus crispus

The rate of photosynthetic carbon uptake of Chondrus crispus Stack-house plants, at various CO₂ concentrations and pretreated with carbonic anhydrase (CA) inhibitors, was determined using an air-suspension, differential infra-red gas analyzer technique. It was found that the CA inhibitors, acetazolamide, dextran-bound acetazolamide (DBI, which does not permeate cell membranes), and subtilisin (a protease that attacks the cell surface) inhibit photosynthetic carbon uptake in C. crispus. Inhibition was greatest at low CO₂ concentrations, and decreased at CO₂ saturation. Acetazolamide inhibited carbon uptake to a greater extent than DBI. The data support the conclusion that C. crispus plants utilize HCO₃⁻ for photosynthesis, and that both cell-surface and internal CA are involved in the photosynthetic uptake of inorganic carbon.     

A modified pH drift assay for inorganic carbon accumulation and external carbonic anhydrase activity in microalgae

Threat of global warming due to carbon dioxide (CO₂) emissions has stimulated research into carbon sequestration and emissions reduction technologies. Alkaline scrubbing allows CO₂ to be captured as bicarbonate, which can be photochemically fixed by microalgae. The carbon concentrating mechanism (CCM), of which external carbonic anhydrase is a key component, allows organisms to utilise this bicarbonate. In order to select a suitable strain for this application, a screening tool is required. The current method for determining carbonic anhydrase activity, the Wilbur and Anderson assay, was found to be unsuitable as a screening tool as the associated error was unacceptably large and tests on whole cells were inconclusive. This paper presents the development of a new, whole cell assay to measure inorganic carbon uptake and external carbonic anhydrase activity, based on classical pH drift experiments. Spirulina platensis was successfully used to develop a correlation between the specific carbon uptake (C) and the specific pH change (dpH). The relationship is described by the following: C[mmol C (g dry algae)^?1?h^?1]?=?0.064?×?(dpH). Inhibitor and salt dissociation tests validated the activity and presence of external carbonic anhydrase and allowed correlation between the Wilbur and Anderson assay and the new whole cell assay. Screening tests were conducted on S. platensis, Scenedesmus sp., Chlorella vulgaris and Dunaliella salina that were found to have carbon uptake rates of 5.76, 5.86, 3.86 and 2.15 mmol C (g dry algae)^?1?h^?1, respectively. These results corresponded to the species' known bicarbonate utilisation abilities and validated the use of the assay as a screening tool.     

Effects of Acetazolamide (Diamox), Ethoxzolamide and High Levels of CO2 on Carbonic Anhydrase, Photosystem Activity, and Oxygen Evolution in Euglena gracilis

Investigations using steady-state culture conditions indicate that carbonic anhydrase activity is correlated to the photosynthetic rate in Euglena in some but not all circumstances. When cultures grown with 5% CO₂ were changed to air growth, the photosynthetic rate was independent of the carbonic anhydrase activity. While experiments using the inhibitor acetazolamide indicated a close correlation between photosynthetic capacity and carbonic anhydrase activity, the inhibitor was found to be nonspecific. Acetazolamide altered photosystem activities directly as measured by the photoreduction of DCPIP in chloroplast preparations, whole-cell fluorescence transients of chlorophyll a, and by whole chain photoelectron flow. Ethoxzolamide, another inhibitor of carbonic anhydrase, was also found to inhibit photosystem activities, i.e., the photoreduction of DCPIP, and in vivo photoelectron flow, at high concentrations. Cells grown in 5% CO₂ were less sensitive to the effects of acetazolamide than cells exposed to air. The rate of electron flow in chloroplasts from cells grown with 5% CO₂ and exposed to 10 mM acetazolamide was 2.5-fold faster than that of chloroplasts from air-grown cells exposed to the same concentration of inhibitor. The whole cell chlorophyll a fluorescence transients of cultures grown with high CO₂ were completely different from those of air-grown cells and also showed fewer effects on exposure to acetazolamide. These results suggest a reevaluation of the hypothesis that carbonic anhydrase activity regulates photosynthesis. It is also apparent that results from air-grown and 5% CO₂-grown cultures cannot be directly compared in such studies.     

The synergistic effect of drought and light stresses in sorghum and pearl millet

The effects of drought stress and high irradiance and their combination were studied under laboratory conditions using young plants of a very drought-resistant variety, ICMH 451, of pearl millet (Pennisetum glaucum) and three varieties of sorghum (Sorghum bicolor)—one drought-resistant from India, one drought-tolerant from Texas, and one drought-sensitive variety from France. CO₂ assimilation rates and photosystem II fluorescence in leaves were analyzed in parallel with photosynthetic electron transport, photosystem II fluorescence, and chlorophyll-protein composition in chloroplasts isolated from these leaves. High irradiance slightly increased CO₂ assimilation rates and electron transport activities of irrigated plants but not fluorescence. Drought stress (less than −1 megapascal) decreased CO₂ assimilation rates, fluorescence, and electron transport. Under the combined effects of drought stress and high irradiance, CO₂ assimilation rates and fluorescence were severely inhibited in leaves, as were the photosynthetic electron transport activities and fluorescence in chloroplasts (but not photosystem I activity). The synergistic or distinctive effect of drought and high irradiance is discussed. The experiments with pearl millet and three varieties of sorghum showed that different responses of plants to drought and light stresses can be monitored by plant physiological and biochemical techniques. Some of these techniques may have a potential for selection of stress-resistant varieties using seedlings.     

The Role of External Carbonic Anhydrase in Inorganic Carbon Acquisition by Chlamydomonas reinhardii at Alkaline pH

The role of external carbonic anhydrase in inorganic carbon acquisition and photosynthesis by Chlamydomonas reinhardii at alkaline pH (8.0) was studied. Acetazolamide (50 micromolar) completely inhibited external carbonic anhydrase (CA) activity as determined from isotopic disequilibrium experiments. Under these conditions, photosynthetic rates at low dissolved inorganic carbon (DIC) were far greater than could be maintained by CO₂ supplied from the spontaneous dehydration of HCO₃⁻ thereby showing that C. reinhardii has the ability to utilize exogenous HCO₃⁻. Acetazolamide increased the concentration of DIC required to half-saturate photosynthesis from 38 to 80 micromolar, while it did not affect the maximum photosynthetic rate. External CA activity was also removed from the cell-wall-less mutant (CW-15) by washing. This had no effect on the photosynthetic kinetics of the algae while the addition of acetazolamide to washed cells (CW-15) increased the K_½^DIC from 38 to 80 micromolar. Acetazolamide also caused a buildup of the inorganic carbon pool upon NaHCO₃ addition, indicating that this compound partially inhibited internal CA activity. The effects of acetazolamide on the photosynthetic kinetics of C. reinhardii are likely due to the inhibition of internal rather than a consequence of the inhibition of external CA. Further analysis of the isotopic disequilibrium experiments at saturating concentration of DIC provided evidence consistent with active CO₂ transport by C. reinhardii. The observation that C. reinhardii has the ability to take up both CO₂ and bicarbonate throws into question the role of external CA in the accumulation of DIC in this alga.     

我国白裤瑶饲料植物的民族植物学研究

白裤瑶非常喜欢饲养和食用当地黑猪，对饲料植物的采集和管理具有独特而丰富的经验和知识。该研究旨在对白裤瑶地区饲料植物及其有关的本土知识进行民族植物学编目，在2019—2021年期间，该文作者多次前往当地进行饲料植物的民族植物学调查，利用了关键人物访谈、半结构式访谈和小组讨论，同时该研究还通过打分排序和统计植物利用频度来筛选出综合利用价值高的饲料植物。结果表明：(1)白裤瑶传统饲料植物共104种，隶属于42科85属；被引用植物种数最多的科是菊科(16种，占总种数的15.38%),其次为荨麻科(13种，占总种数的12.5%)。(2)枝叶(56.73%)、全草(26.92%)和叶(8.65%)为当地饲料植物的主要利用部位，大多数饲料植物是草本植物(88.46%),多数饲料植物(占总数的64.42%)一年四季都可以采集，保障了家猪食物来源充足。(3)饲料植物的主要加工方法是将其切碎或打碎后煮熟饲喂。(4)当地被受访者引用最多的物种是玉蜀黍、构树、番薯、桑、金荞麦、稻。(5)根据综合打分排序，在当地具有较高综合评价的饲料植物分别为构树、番薯、桑、金荞麦、南瓜。白裤瑶对饲料植物用于养猪的传统知识非常...