C3和C4植物光合途径的适应性变化和进化

高等植物大多为C₃植物, C₄植物和景天酸代谢(Crassulacean acid metabolism, CAM)植物是由C₃植物进化而来的。C₄途径的多源进化表明, 光合途径由C₃途径向C₄途径的转变相对简单。该文分析研究了植物光合途径的进化前景, 指出C₄植物是从C₃植物进化而来的高光效种类, 且地质时期以来降低的大气CO₂浓度和升高的大气温度以及干旱和盐渍化是C₄途径进化的外部动力。C₃植物的C₄途径的发现说明植物的光合途径并非是一成不变的, C₃和C₄植物的光合特征具有极大的可塑性, 某些环境的变化会引起植物光合途径在C₃和C₄途径之间转变。C₃植物具有的C₄途径是环境调控的产物, 是对逆境的适应性进化结果, 因而光合途径的转变也适用于干旱地区植被的适应性生存机理研究。该文还利用国外最新的C₄光合进化模型介绍了植物在进化C₄途径中所经历的7个重要时期(从分子基础到形态基础、结构基础, 再到物质代谢水平、光合酶活水平, 直到C₃和C₄途径协调运转时期, 最后达到形态与功能最优化阶段), 并结合全球气候变化的特点对国内外相关领域的研究进行了分析, 总结了植物光合途径的适应性转变和进化的研究成果, 为今后的相关工作提出建议。     

华南地区3个棕榈藤种光合途径的判别

C3植物uT以通过转入C4植物基因而具备C4植物光合特性,从而提高产量.有鉴于此,本文通过测定我国华南地区分布的黄藤(Daemonorops margarttae(Hance)Becc.)、单叶省藤(Calamus simplicifolius C.F.Wei)和白藤(C.tetradactylus Hance)等3个棕榈藤种苗木和成年植株叶片的叶绿素含量、气孔密度、磷酸烯醇式丙酮酸羧化酶(phosphoenolpyruvate carboxylase,PEPC)、丙酮酸磷酸二激酶(pyruvate phosphate dikinase,PPDK)和稳定碳同位素比值等指标以判别3个藤种的光合途径,为棕榈藤转入C4植物基因工作提供理论依据.结果表明,3种藤种苗木和成年植株的叶绿素含量和气孔密度比常见C3植物和C4植物高,但叶绿素a/b值、叶片上下表面气孔比值、PEPC酶活性、PPDK酶活性和稳定碳同位素比值等指标均较低,与常见C3植物的对应指标相当或略低,而远小于常见C4植物,因此认为黄藤、单叶省藤和白藤等3个藤种是C3植物.     

C3和C4植物的氮素利用机制

提高植物的氮素利用效率(NUE)不仅有利于保障全球粮食安全, 也是实现农业可持续发展的重要途径。近半个世纪以来, 植物氮素利用机理研究已取得重要进展, 但NUE的调控机制仍不明确, NUE的提高仍然十分有限。高等植物集光合碳素同化和氮素同化于一体, 只有碳氮代谢相互协调, 才能维持植物体内的碳氮平衡, 保证植物正常生长发育。由于C₃和C₄植物的光合氮素利用率(PNUE)存在差异, 对氮素的利用效率也会存在差异。为了更有效地提高作物的NUE, 须更全面地了解C₃和C₄植物对氮素吸收、转运、同化和信号转导等关键因子的功能和调控机制。此外, 面对大气CO₂浓度增高和全球气候变暖条件下的植物碳氮同化及其机理的研究也不容忽视。该文综述了C₃和C₄植物氮素利用关键因素的差异及其调控机制, 并对提高C₃禾本科作物氮素利用效率的遗传改良途径进行了展望。     

民勤绿洲—荒漠过渡带植物叶性状的研究

以民勤绿洲—荒漠过渡带20种主要植物为研究对象,通过对叶片6个功能性状的测定,分析荒漠植物叶性状的变异及相关性,比较不同功能群植物叶性状的差异性,探讨荒漠植物对环境的适应性,为该地区植被的恢复和重建提供理论依据。结果表明：①叶性状存在种间差异且变异程度不同,变异范围为14.11%~47.63%,叶绿素含量（ChlC）变异系数最大,叶片全氮含量（LCC）变异系数最小。②叶干物质含量（LDMC）与ChlC、LCC均呈极显著正相关（P＜0.01）,ChlC与LCC呈极显著正相关（P＜0.01）,其他叶性状间相关性不显著。③不同功能群植物叶性状存在显著差异。其中,豆科植物叶片LDMC、ChlC、LCC极显著高于藜科植物（P＜0.01）。草本植物叶片比叶面积（SLA）极显著高于灌木植物叶片（P＜0.01）。一年生植物叶片SLA、LNC显著高于多年生植物（P＜0.05）;多年生植物叶片LDMC极显著高于一年生植物（P＜0.01）;多年生植物叶片C含量显著高于一年生植物（P＜0.05）。C₃植物叶片LDMC、ChlC显著高于C₄植物（P＜0.05）;C₄植物叶片δ¹³C极显著高于C₃植物 （P＜0.01）;C₃植物叶片LCC极显著（P＜0.01）高于C₄植物。     

The Australasian grass flora in a global context

Australia's flora and fauna have long been considered unique, but whether this applies to its grasses is less known. This study characterises the Australasian grass flora biogeographically. We investigate the distribution of C₃ and C₄ grass genera across four continents and construct broad profiles of their grass flora. We use endemism to examine global patterns of specialisation, and inter-continental distributions as indicators of dispersal, using databases constructed over twenty years. We examined Australasian patterns with regard to endemicity and shared groups and categorised all of the region's genera into four age classes, from Australia's separation from Gondwana to the present. Globally, each continent presented a unique profile and C₄ grasses were more widely shared than C₃. Australasia's grasses equally comprise C₃ and C₄ genera; it shared two thirds of its C₄ types with other continents, whereas C₃ types split evenly between shared and endemic. Australasia shared relatively few genera with just one neighbour (7% C₃, 13% C₄), primarily with EurAsia. Australasian grass genera and species were either endemic or globally widespread, and 88% of C₃ and 93% of C₄ species were derived from lineages that originated elsewhere. We conclude Southeast Asia was the gateway for dispersal into Australasia, akin to rainforest taxa exchanges which increased from c12 Ma, with about 65% of Australasia's grass genera arriving in the past 3.5 Ma. The strong presence of C₄ grasses in Australasia implies they have infiltrated a wide range of ecosystems, many probably occupied by ancient taxa with which they had not co-evolved.     

不同光合类型牧草对干旱-复水的光合生理响应及生长适应策略

基于干旱频率增加、强度增大这一全球降水变化背景, 探究干旱-复水条件下不同功能群(C₃和C₄)植物的光合生理响应及生长适应策略有助于预测降水格局变化条件下草地的植被组成和生态系统功能。该研究采用盆栽实验, 以松嫩草地生长的一年生C₃ (4种)和C₄ (3种)牧草为实验材料, 设置了对照、中度干旱和重度干旱3个水分处理水平, 在干旱末期及复水期对植物进行气体交换、生物量和比叶质量的测量。在干旱条件下, 各物种净光合速率和气孔导度均呈下降趋势, 水分利用效率呈上升趋势。干旱对不同植物光合指标的影响存在功能群差异, 随干旱程度的增加C₄植物逐渐丧失光合优势, 重度干旱对C₄植物净光合速率的影响较C₃植物更加明显。由于干旱条件下C₃植物光合固碳主要受气孔限制而C₄植物主要受代谢限制, 因此复水后C₄植物净光合速率恢复速度较C₃植物慢。干旱条件下, 各物种的生物量降低, 根冠比和比叶质量升高, 干旱对C₃植物各生长指标的影响均大于C₄植物; 复水处理后, C₃植物生物量随干旱强度增加呈下降趋势, 而C₄植物的生物量与对照相比无显著差异。     

Ionic iridium-gold and rhodium-gold perfluorobenzenethiolato binuclear complexes: syntheses and solution behavior

By reacting [(C₅Me₅)M(SR_F)₂] (forM = Ir, Rf = C₆F₅ (1a) or C₆F₄H-p (1b); for M = Rh, Rf = C₆F₅ (2a) or C₆F₄H-p (2a)) in toluene with Na[AuCl₄], ionic binuclear compounds with the general formula [(C₅Me₅)M(μ-SR_F)₂AuCl₂]Cl for M = Ir, R = C₆F₅ (3a) or C₆F₄H-p (3a); for M = Rh, R_F = C₆F₅ (4a) or C₆F₄H-p (4b) can be obtained, together with small amounts of [(C₅Me₅)₂Rh₂(μ-SR_F)(μ-Cl)₂]Cl (R_F = C₆F₅ (5a) or C₆F₄H-p (5b)) as by-products when 2a and 2b were used.     

转玉米PEPC基因水稻中有限的C4光合微循环及其生理作用

用转PEPC基因水稻(Oryza sativa L. subsp.japonica Kitaake)和原种水稻Kitaake为材料,研究了不同基因型水稻叶片中的C4光合微循环及其功能.通过测定与光合C4途径有关的关键酶,如磷酸烯醇式丙酮酸羧化酶(PEPC)、NADP -苹果酸酶(NADP -ME)、NADP -苹果酸脱氢酶(NADP -MDH)和丙酮酸磷酸双激酶(PPDK),说明原种水稻叶片中具有完整的C4光合酶体系;用外源OAA或MA饲喂叶切片或叶绿体后明显增加光合速率,证明原种水稻中具有一个有限的光合C4微循环.将玉米的PEPC基因导入原种水稻后,可大幅度提高光合C4微循环的速率.测定不同基因型的CO2交换速率,看出水稻中C4光合微循环的增强有提高净光合速率(Pn)和降低光呼吸速率/净光合速率(Pr/Pn)比值的作用.叶绿素荧光特性分析表明,C4光合微循环的增强伴随着PSⅡ电子传递效率(Fv/Fm)和光化学猝灭(qP)的增加以及非光化学猝灭(qN)的降低;这些结果为通过基因工程手段提高作物光合效率的遗传育种提供了科学根据.     

Photosynthetic traits in C3 and C4 grassland species in mesocosm and field environments

The North American tallgrass prairie is composed of a diverse mix of C₃ and C₄ plant species that are subject to multiple resource limitations. C₄ grasses dominate this ecosystem, purportedly due to greater photosynthetic capacity and resource-use efficiency associated with C₄ photosynthesis. We tested the hypothesis that intrinsic physiological differences between C₃ and C₄ species are consistent with C₄ grass dominance by comparing leaf gas exchange and chlorophyll fluorescence variables for seven C₄ and C₃ herbaceous species (legumes and non-legumes) in two different settings: experimental mesocosms and natural grassland sites. In the mesocosms, C₄ grasses had higher photosynthetic rates, water potentials and water-use efficiency than the C₃ species. These differences were absent in the field, where photosynthetic rates declined similarly among non-leguminous species. Thus, intrinsic photosynthetic advantages for C₄ species measured in resource-rich mesocosms could not explain the dominance of C₄ species in the field. Instead, C₄ dominance in this ecosystem may depend more on the ability of the grasses to grow rapidly when resources are plentiful and to tolerate multiple limitations when resources are scarce.     

东北草原区C3、C4植物的生态分布及其适应盐碱环境的生理特性

用5种实验方法对东北草原区233种植物光合类型进行鉴定,并对其相对分布随纬度变化关系及其与土壤含盐量和PH值的关系进行分析.在此基础上对几种典型C₃、C₄牧草适应于盐碱环境的生理特点进行深入研究结果表明,在所鉴定的233种植物中,C₃植物有144种,隶属于28科94属,C₄植物有89种;隶属于17科55属,在高纬度地区C₃植物表现出更高的生长优势,在纬度较低和盐碱化区域,C₄植物分布具相对优势.尤其在盐碱化程度较重的地区,C₄植物成为明显的优势种,分布上的差别决定于它们对环境适应机制上的差异C₃植物对盐碱环境适应机制主要通过积累脯氨酸等有机溶质进行渗透调节,而C₄植物主要通过液泡中离子区域化积累作用进行调节,并且与C₃植物相比对盐碱环境具更强的适应能力.     

Transformation of steroids by Bacillus strains isolated from the foregut of water beetles (Coleoptera:Dytiscidae): I. Metabolism of androst-4-en-3,17-dione (AD)

Two Bacillus strains were isolated from the foregut of the water beetle Agabus affinis (Payk.) and tested for their steroid transforming ability. After incubation with androst-4-en-3,17-dione (AD), 13 different transformation products were detected. AD was hydroxylated at C₆, C₇, C₁₁ and C₁₄, resulting in formation of 6β-, 7-, 11- and 14-hydroxy-AD. One strain also produced small amounts of 6β,14-dihydroxy-AD. Partly, the 6β-hydroxy group was further oxidized to the corresponding 6-oxo steroids. In addition, a specific reduction of the Δ⁴-double bond was observed, leading to the formation of 5-androstane derivatives. In minor yields the carbonyl functions at C₃ and C₁₇ were reduced leading to the formation of 3ξ-OH or 17β-OH steroids. EI mass spectra of the trimethylsilyl and O-methyloxime trimethylsilyl ether derivatives of some transformation products are presented for the first time.     

Spectroscopic and electrical properties of the [W(C3Se5)3] anion complex (C3Se5 = 1,3-diselenole-2-selone-4,5-diselenolate) and the oxidized species

[NBuⁿ₄]₂[W(C₃Se₅)₃] (C₃Se₅²⁻ = 1,3-diselenole-2-selone-4,5- diselenolate(2−)) was prepared by the reaction of Na₂[C₃Se₅] with WCl₆ in ethanol, followed by addition of [NBuⁿ₄]Br. The cyclic voltammogram in dichloromethane exhibits two oxidation peaks at −0.04 and +0.03 V (versus SCE). The complex reacted with [Fe(C₅Me₅)₂][BF₄], iodine or [TTF]₃[BF₄]₂ (TTF^·+ = the tetrathiafulvalenium radical cation) in acetonitrile to afford the oxidized complexes [Fe(C₅Me₅)₂]_0.5[W(C₃Se₅)₃], [NBuⁿ₄]_0.1[W(C₃Se₅)₃] and [TTF]_0.5[W(C₃Se₅)₃], respectively. Current-controlled electrochemical oxidation of the complex in acetonitrile gave [NBuⁿ₄]_0.6[W(C₃Se₅)₃]. The oxidized complexes exhibit electrical conductivities of 4.7×10 ⁻⁵−1.5×10⁻³ S cm⁻¹ at room temperature measured for compacted pellets. Electronic absorption, IR and ESR spectra of these complexes are discussed.     

Photosynthetic carbon metabolism in Panicum milioides, a C3-C4 intermediate species: Evidence for a limited C4 dicarboxylic acid pathway of photosynthesis

Panicum milioides, a naturally occurring species with C₄-like Kranz leaf anatomy, is intermediate between C₃ and C₄ plants with respect to photorespiration and the associated oxygen inhibition of photosynthesis. This paper presents direct evidence for a limited degree of C₄ photosynthesis in this C₃-C₄ intermediate species based on:

1. (a) the appearance of 24% of the total ¹⁴C fixed following 4 s photosynthesis in ¹⁴CO₂-air by excised leaves in malate and aspartate and the complete transfer of label from the C₄ acids to Calvin cycle intermediates within a 15 s chase in ¹²CO₂-air;

2. (b) pyruvate- or alanine-enhanced light-dependent CO₂ fixation and pyruvate stimulation of oxaloacetate- or 3-phosphoglycerate-dependent O₂ evolution by illuminated mesophyll protoplasts, but not bundle sheath strands; and

3. (c) NAD-malic enzyme-dependent decarboxylation of C₄ acids at the C-4 carboxyl position, C₄ acid-dependent O₂ evolution, and ¹⁴CO₂ donation from [4-¹⁴C]C₄ acids to Calvin cycle intermediates during photosynthesis by bundle sheath strands, but not mesophyll protoplasts.

However, P. milioides differs from C₄ plants in that the activity of the C₄ cycle enzymes is only 15 to 30% of a C₄ Panicum species and the Calvin cycle and phosphoenolpyruvate carboxylase are present in both cell types. From these and related studies (Rathnam, C.K.M. and Chollet, R. (1979) Arch. Biochem. Biophys. 193, 346–354; (1978) Biochem. Biophys. Res. Commun. 85, 801–808) we conclude that reduced photorespiration in P. milioides is due to a limited degree of NAD-malic enzyme-type C₄ photosynthesis permitting an increase in pCO₂ at the site of bundle sheath, but not mesophyll, ribulosebisphosphate carboxylase-oxygenase.     

Effect of the combined supplementation of diets with increasing levels of fish and linseed oils on yolk fat composition and sensorial quality of eggs in laying hens

Yolk fatty acid (FA) concentrations and egg quality were evaluated with respect to the inclusion of different levels of marine fish oil (MFO) and linseed oil (LO) in a basal diet. Ten diets were arranged factorially with two levels of MFO addition (15 and 17 g/kg) and five levels of linseed oil (1, 2, 3, 4 and 5 g/kg). Two commercial feeds with no n-3 FA sources added, or containing 15 g MFO/kg served as controls for egg sensorial quality traits. Type of diet did not affect egg production traits, nor total fat content in yolk or saturated and monounsaturated FA concentration in yolk fat. An increase in the inclusion of MFO from 15 to 17 g/kg increased (P<0.05) egg yolk content of total n-3 FA, C_20:5 n-3 and C_22:6 n-3 by 3.3, 9.8 and 3.5%, respectively. Linseed oil addition increased linearly (P<0.001) the level of total n-3 FA and the proportion of C_18:3 n-3, C_20:5 n-3, C_22:5 n-3 and C_22:6 n-3 retained in yolk fat by respectively 131, 12.0, 6.9 and 20.7% between extreme diets. Efficiency of retention of n-3 FA decreased (P<0.001) with dietary level of n-3 FA, and with the dietary ratio of MFO to LO. Both MFO and LO addition decreased (P<0.001) C_20:4 n-6 to C_18:2 n-6 ratio in yolk. Sensorial quality of eggs was not affected by treatments and did not differ with respect of that obtained in commercial n-3 FA enriched eggs. No interaction was found between LO and MFO addition for any of the traits studied. Regression equations have been calculated in order to predict efficiency of retention and yolk fat content of LC n-3 and n-6 FA from dietary characteristics.     

Intermolecular Re---H·H---X hydrogen bonding (X = N, C) involving ReH5(PPh3)3

Ab initio (B3LYP) calculations show that PD·H---ReH₄(PH₃)₃ (PD = Proton donor) interactions follow the order PD = pyrrole > NH₃ > HCCH > C₂H₄ > CH₃---H 0 and decrease with the pK_a of the PD. For equivalent pK_a's, NH interacts more strongly than CH. However, intermolecular hydrogen-bonding of the M---H·H---C type is too weak to be detected experimentally in FTIR or UV-vis studies between ReH₅(PPh₃)₃ and PhCCH, C₆F₅H or PhCHCl₂.     

C60-fullerenides of ytterbium and lutetium

Cp^#₂Yb (Cp^#=C₅H₄(CH₂)₂NMe₂) has been obtained by reaction of YbI₂(THF)₂ with 2 equiv. of C₅H₄(CH₂CH₂NMe₂)K in THF. The X-ray structure analysis shows a bent structure with intramolecular coordination of both nitrogen atoms to ytterbium. The reaction of C₆₀-fullerene with Cp^#₂Yb leads to the formation of the fullerenide derivative [Cp^#₂Yb]₂C₆₀, which shows an ESR signal in the solid state and in THF solution at room temperature (solid: ΔH = 50 G, G = 1.9992; solution: ΔH = 10 G, G = 2.0001) and a magnetic moment of 3.6 BM. The lutetium fullerenides CpLu(C₆₀)(DME) (3) and Cp^*Lu(C₆₀)(DME)(C₆H₅CH₃) (4), (Cp = η⁵−C₅H₅, Cp^* = η⁵−C₅Me₅), were obtained by reaction of C₆₀ with CpLu(C₁₀H₈) (DME) and Cp^*Lu(C₁₀H₈) (DME) in toluene. Both complexes are paramagnetic (μ_eff = 1.4 and 0.9 BM) and exhibit temperature-dependent ESR signals (293 K: g = 1.992 and 2.0002 respectively).     

Summer monsoon intensity controls C4/C3 plant abundance during the last 35 ka in the Chinese Loess Plateau: Carbon isotope evidence from bulk organic matter and individual leaf waxes

The natural abundance of C₃ and C₄ plants is affected by multiple environmental factors including temperature, moisture balance and atmospheric pCO₂. The relative importance of these factors is a subject of considerable debate, and may vary in different natural ecosystems. Previous studies generally focus on single loess sequences in the Chinese Loess Plateau, and conflicting conclusions on C₄/C₃ have been reached when studying carbon isotope ratios in carbonate and organic matter. In this paper we report a comprehensive carbon isotopic characterization of total organic carbon (TOC) and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the Chinese Loess Plateau (CLP). The five coring sites encompass large gradients of annual mean temperature (9.2–13.9 °C) and precipitation (402–673 mm), allowing us to assess the controlling mechanisms on C₄/C₃ plant ratios. Glacial–interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility. Our results demonstrate that increased C₄/C₃ ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites. We conclude C₄ abundance increases from the last glacial to the Holocene in response to greater monsoon activity and that the C₄ expression is suppressed in the cold and drier intervals.     

Metabolism of CO2 by leaves of different photosynthetic types of Neurachne species

Following a series of continuous exposures to ¹⁴CO₂ for different lengths of time, leaves from Neurachne munroi (C₄), N. minor (C₃-C₄) and N. tenuifolia (C₃| were estimated to assimilate 100%, 9% and 2–4%, respectively, of atmospheric CO₂ by the C₄ pathway. The percentage of ¹⁴C-label appearing in malate and aspartate in leaves of N. minor progressively increased with longer exposure times indicating that a significant proportion of its C₄ acids are formed as secondary products. In ¹⁴CO₂/¹²CO₂ pulse/chase experiments, the ¹⁴C-label in leaves of N. munroi was rapidly transferred from C₄ acids to sugar monophosphates plus sugar diphosphates, and finally to sucrose. In leaves of N. minor, the ¹⁴C-label was slowly metabolized from the C-4 carboxyl of malate and asparate (apparent half-time = 250 s), and the formation of C₄ acids as secondary products was again evident. ¹⁴C-label in serine/glycine accumulated to comparable magnitudes in both N. minor and in N. tenuifolia, but there was an initial lag phase in the accumulation of label in N. minor. C₄ photosynthesis is apparently of minimal importance in reducing photorespiration in N. minor, but leaf anatomical specializations and a possible compartmentation of photorespiratory metabolism may be of considerable importance.     

Surface lipid composition of C3 and C4 plants

The characteristic surface lipid compositions of several C₃ and C₄ plants are discussed. C₄ plants produce surface lipids (epicuticular waxes) made up of the ubiquitous classes of aliphatic compounds: free fatty acids, aldehydes, primary alcohols, alkanes and aliphatic linear esters. C₃ plants synthesize surface lipids comprising the ubiquitous classes and either of the two following groups of compound: (i) lβ-diketones, hydroxy lβ-diketones, alkan-2-ol esters; (il) ketones and secondary alcohols with the functional group in the middle of the hydrocarbon chain. These features are suggested to represent physioIogical characteristics of the plant and to be related to ecological adaptations. Wax class compositions might also be an ancillary method for defining the C₃ or C₄ mechanism of CO₂ assimilation in cases where uncertainty exists.     

Dialkyl-μ-ethylidene-μ-methylene-bis(pentamethylcyclopentadienyl)-dirhodium complexes: synthesis, spectra and decomposition reactions

The dialkyl-μ-ethylidene-μ-methylene-bis (pentamethylcyclopentadienyl)-dirhodium complexes [{(C₅Me₅)Rh}₂(μ-CH₂)(μ-CHMe) (R)₂] (4, P=Me; 5, Et; 6, n-Bu; 7, CH=CH₂; and 8, Z-CH=CHMe) have been prepared from RMgBr and [{(C₅Me₅)Rh}₂(μ-CH₂)(μ-CHMe)(X)₂] (2, X=Cl; 3, X=Br). Structures deduced from the NMR spectra show that the dialkyl complexes can exist in one trans and two cis forms. The decomposition of the dimethyl complex 4 is compared with that of the related di-μ-methylene complex; it reacts readily (30°C, MeCN solution) in the presence of one-electron oxidisers to give propene and methane and a little ethene and some butenes. Mass-spectrometric analysis of the ¹³C labelling in the organics originating from [{(C₅Me₅)Rh}₂(μ-CH₂)(μ-CHMe) (¹³CH₃)₂] shows that methane derives from the Rh---Me, ethene half from the ethylidene and half from coupling of Rh-methyl and a bridging methylene, while the propene arises almost entirely from the ethylidene and a rhodium methyl. The butenes come from coupling of ethylidene, methylene and a Rh-methyl, but only quite small amounts are formed; thus C+C coupling is the major decomposition path for the μ-ethylidenes, in contrast to the di-μ-methylene complexes where C+C+C coupling predominates. The divinyl complex [{(C₅Me₅)Rh}₂(μ-CH₂)(μ-CHMe) (CH=CH₂)₂] also underwent internal C+C coupling on reaction with AgBF₄ in MeCN to give a mixture of the allyl and methylallyl cations [(C₅Me₅)Rh(η³-CH₂CHCHR)(MeCN)]⁺(10, R=H; 11, R=Me).