植物同化物分配及其模型研究综述

目前生态系统模型模拟中所用的大多数同化物分配模型是经验性的。同化物分配对植物的生长、竞争及结构的形成有重要的影响,是植物生长的关键,也是植物生长模型中的薄弱环节。总结了影响同化物分配的因素：生理过程和环境因子。指出植物作为一个有机的整体,所有的生理过程都对其有影响,维管束作为各器官间的连接系统,以及同化物的运输管道,其性质对同化物分配有重要的影响。综述了环境因子特别是环境水分条件对同化物分配的影响。总结了以往研究中发现的、主要的同化物分配规律,指出同化物分配的模式极其复杂,分配过程完全是根据环境以及生长阶段变化而变化的、随机应变的过程。 对于同化物分配模型按照经验模型,目的性模型,源汇关系模型进行了总结归纳,分析指出：经验性模型应用最多但机理性差;功能平衡模型在模拟营养生长阶段同化物在条与根之间的分配很成功,但应用于其它器官之间很困难;最优化模型适于模拟平衡态下同化物的分配;源汇关系模型机理性最强,可模拟任何器官间的同化物分配,应用范围最广泛。 同化物研究取得了很大的进展,但研究中仍存在很多不足：对于各相关过程的研究存在不平衡性;整体水平上同化物分配的机理仍缺乏深入研究;同化物分配对于环境的响应方面的研究相对较弱;缺乏多环境因素的研究;缺乏长期的实验观测研究。作者认为环境与同化物分配相互关系的研究将成为日后研究中的热点问题。     

脱落酸对植物库强度的调节作用

脱落酸对植物库强度表现促进作用．这种作用与脱落酸促进同化物从韧皮部的卸出、库细胞对同化物的吸收以及同化物在库细胞内的代谢转化有关。文中讨论了脱落酸此类作用的可变性。     

叶幕PAR光能截留和分配对葡萄群体光合同化物源库关系的调控

 田间自然条件下在葡萄园群体水平上多年的研究证明：叶幕PAR光能截留率与葡萄群体净光合速率、叶幕和单叶PAR光能截留率与果实干物质总量占地上部生物量干重的百分比、与果实总糖产量占果实本身干物质总量的百分比、以及与果皮色素产量占果实本身干物质总量的千分比之间呈现显著或极显著的线性正相关关系。说明利用叶幕结构变异调节叶幕PAR光能截留和分配,可以对光合同化物源库关系和果实中物质代谢方向进行有效的调控。PAR光能截留率较高和分配合理的叶幕,不但通过较高的群体光合速率为产量和品质形成提供了丰富的同化物“源”,而且通过调节器官间“库”关系使同化物以较高的比例流向果实,同时使果实中物质代谢过程有利于合成构成品质的要素。     

留营养枝对棉株同化物生产,运转,分配及产量的影响

运用＾１４Ｃ示踪技术研究了留营养支棉株＾１４Ｃ同化物生产运转分配规律。结果表明：留营养枝与否对全株＾１４Ｃ总同化量基本没有影响,但留营养２枝棉株果枝叶的相对光合强度（以放射性比强度表示）降低;主茎叶、果枝叶的＾１４Ｃ同化量显著降低;营养２叶具有较高的光合作用强度和向外输送＾１４Ｃ同化物的转运速率,在＾１４Ｃ同化物生产运转分配中占有很重要的地位。留营养枝棉株＾１４Ｃ同化物的转运速率,在＾１４Ｃ同化     

灵武长枣果实同化物韧皮部卸载和运输途径研究

韧皮部卸载和韧皮部后运输在调节同化物在果实中的分配和积累方面起着至关重要的作用,而且很大程度上决定着果实的产量和质量。为探讨灵武长枣果实同化物韧皮部卸载和运输途径,以4个时期灵武长枣果实为实验材料,对各个发育时期果实维管束的显微结构进行观察,并综合运用荧光染料活细胞示踪与激光共聚焦扫描显微镜技术实时观察果实内韧皮部同化物卸载路径的变化,为灵武长枣果实同化物积累和品质调控奠定基础。结果显示：(1)膨大前期不仅果实的韧皮部中具有明显的CF绿色荧光,同时在周围薄壁细胞中也分布着CF绿色荧光,筛管伴胞复合体和周围薄壁细胞之间存在着共质体联系。(2)快速膨大期,CF绿色荧光主要局限于果实的韧皮部中,在韧皮部周围薄壁细胞中分布较少,筛管伴胞复合体与周围薄壁细胞之间主要以共质体隔离为主,但也存在着一定的共质体联系。(3)着色期和完熟期,CF绿色荧光局限于果实的韧皮部中,在韧皮部周围薄壁细胞中基本没有CF绿色荧光,果实筛管伴胞复合体与周围薄壁细胞之间是共质体隔离状态,但引入CFDA的同时引入具有质膜通透作用的洋地黄皂苷时,周围薄壁细胞中CF绿色荧光分布明显增加。研究认为,灵武长枣在膨大前期果实韧皮部同化物为共质体卸载途径,快速膨大期果实主要以质外体途径运输同化物,但也通过共质体卸出同化物,着色期和完熟期果实通过质外体途径运输同化物。     

研究种子同化物卸出的微注射法和空种皮杯法

MicroinjectionTechniqueandEmptySeedCoatTechniquefortheStudyofAssimilateUnloadinginSeedsDAIYu－Ling,ZHANGShu－Qiu,YANGShi－Jie,LOUCheng－Hou（CollegeofBiologicalScinces,ChinaAgriculturalUniversity,Beijing100094）对光合同化物卸出的研究,常采用一些间接方法如标记C引入、放射自显影等来显示同化物的分配。发育的大豆种子、胚和种皮间没有共质体联系,从茎叶运来的同化物先从种皮卸出到包围幼胚的质外体空间,再被幼胚吸收,是一种研究同化物卸出的好材料。1983年,美国的Thorne和Rainbird[3]用大豆、…     

光合同化物韧皮部卸载途径和机制

介绍近年来同化物在库器官中的卸载途径、机制和研究方法的研究进展,并简略讨论了该领域研究所面临的问题。     

苹果山梨醇脱氢酶的基因表达、组织分布和活性调控

木本蔷薇科植物光合作用产物以山梨醇为主。成熟叶片中合成的山梨醇运输到果实等库器官后不是作为储存形式而是被转化为其它形式的糖参与代谢。NAD-依赖的山梨醇脱氢酶(EC 1.1.1.14)催化山梨醇转化为果糖,是苹果等植物库器官分解利用山梨醇的关键酶,其含量和活性直接影响光合同化物在不同组织器官间的分配,关系到果实产量和品质。本文对苹果NAD-依赖的山梨醇脱氢酶的基因表达、组织分布以及酶活性调控等方面的研究进展进行了综述和讨论。     

小麦磷酸丙糖转运器的特性及其对同化物分配的调节

磷酸丙糖转运器(tnose phosphate/phosphatetranslocator,TPT)是源、库间光合产物分配的第一调控部位,研究TPT的特性及其对同化物分配的调节,对于提高光合作用同化物利用效率有着重要意义.我们首先采用Percoll密度梯度离心从小麦(Triticum aestivum L.)叶片中分离制备了完整性达91%以上、具有较高纯度的完整叶绿体.利用TPT不可逆抑制剂[H3]2-DIDS标记和SDS-PAGE,以及小麦TPT抗体进行Western blotting分析,证明TPT蛋白仅存在于叶绿体被膜中,约占被膜总蛋白的15%,其分子量为35 kD,而在液泡膜和线粒体膜上不存在.采用硅油离心法研究TPT对磷酸二羟丙酮(dihydroxyacetone phosphate,DHAP)、磷酸烯醇式丙酮酸(phosphoenolpyruvate,PEP)、葡萄糖-6-磷酸(glucose-6-phosphate,G6P)与Pi的反向运输动力学的结果表明,DHAP/Pi的最大运输活性最高,PEP/Pi次之,G6P/Pi最低.TPT与这些运输底物的Km值由小至大,分别为DHAP、Pi、PEP和G6P,证明TPT的最适运输底物为DHAP.用DIDS处理时,TPT对DHAP运输活性的抑制达95%.TPT运输活性受到抑制时,可导致叶绿体内大量积累淀粉.TPT在调控小麦叶绿体同化产物的分配中起着重要作用,在保证卡尔文循环正常运转的前提下,通过TPT外运到胞质中参与蔗糖合成和其他代谢活动的磷酸丙糖(triose phosphate,TP)约占93.6%,而用于叶绿体内合成淀粉的TP仅占6.4%.生理条件下其功能是高效率地把大部分光合同化产物TP及时运出叶绿体到胞质中,用于合成蔗糖并运输到其他库器官的需要.     

植物蔗糖合成的分子机制

高等植物中,光合同化产物主要是以蔗糖的形式从源向库运输的。近十几年来,随着生物技术的发展,许多与碳水同化产物代谢有关的基因已经被分离,同时多种植物遗传转化体系的建立使在植物中改变基因活性成为现实,对转基因植株的生理生化分析进一步增加了植物中对碳水同化产物合成、分配、运输以及利用等方面的认识。本文就CO2固定,同化产物分配,蔗糖合成三个方面介绍近年来利用基因工程对植物源活性调控及改善的研究进展。     

Photoassimilate partitioning in nodulated soybean II. The effect of changes in photoassimilate availability shows that nodule permeability to gases is not linked to the supply of solutes or water

It is concluded that the permeability of the soybean nodule to gases is not linked to the supply of solutes or water via the phloem to the nodule. Nodule respiration and nitrogenase activity were less affected by diel variation and shading treatments than partitioning to the nodule, as assessed using a non-invasive ¹¹C-based technique. Thus C import to the nodule was not matched to C requirement by the nodule. Transit times of tracer to, and within, the nodulated root increased under conditions of reduced photosynthetic rate. The increase in transit time was interpreted as a reduction in the flux of phloem sap. Thus the fluxes of both water and C to the nodule decreased following a reduction in photosynthetic rate. The change in partitioning of recent photosynthate to soybean roots and nodules in response to changes in photoassimilate availability was also used to assess the 'priority' of these sinks. Partitioning from the leaf to the root system was greatly decreased when photoassimilate availability was limited, indicating that root system priority is lower than that of the shoot, as reported for other systems. However, partitioning of tracer arriving in the root system between the nodulated and non-nodulated zones of the root was not affected by changes in photoassimilate availability, as caused by diel change, shading, or steaming of branch roots. Thus although nodules are sinks of high sink 'activity', they have 'priority' equal to that of other root sinks. It is suggested that there are similar phloem unloading kinetics, despite the very different metabolic destiny of the carbohydrate within the two organs.     

MassFlowDyn I: A Carbon Transport and Partitioning Model for Root System Architecture

Carbon partitioning is important for understanding root developmentbut little is known about its regulation. Existing models suggestthat partitioning is controlled by the potential sink strength.They cannot, however, simulate hierarchical uptake other thanby using absolute priorities. Moreover, they cannot explainthat the changes in photoassimilate partitioning result fromchanges in photosynthesis. In this paper we present a modelof phloem sieve circulation, based on the model of Minchin etal. (Journal of Experimental Botany44: 947–955, 1993).The root system was represented by a network of segments towhich meristems were connected. The properties of the segmentswere determined by the differentiation stage. Photoassimilateimport from each organ was assumed to be limited by a metabolicprocess and driven by Michaelis–Menten kinetics. The axialgrowth was proportional to meristem respiration, which drivesthe flux of new cells required for root elongation. We usedthe model to look at trophic apical dominance, determinate andindeterminate root growth, the effect of the activity of a rooton competition with its neighbours, and the effect of photoassimilateavailability on changes in partitioning. The simulated phloemmass flow yielded results of the same order of magnitude asthose generally reported in the literature. For the main wellvascularized axis, the model predicted that one single apicalmeristem larger than its neighbouring laterals, was enough togenerate a taprooted system. Conversely, when the meristem oflaterals close to the collar had a volume similar to that ofthe taproot, the predicted network became fibrous. The modelpredicted a hierarchical priority for organ photoassimilateuptake, similar to that described in the literature, duringthe decline in photosynthetic activity. Our model suggests thatdeterminate growth of the first laterals resulted from a localshortage of photoassimilate at their meristem, as a result ofthe limited transport properties of the developed roots. Copyright2000 Annals of Botany Company Münch theory, phloem transport model, photoassimilate-partitioning, root growth, root system architecture, translocation     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: III. RELATIONSHIP BETWEEN GROWTH RATE OF INDIVIDUAL TUBERS, TUBER WEIGHT AND STOLON GROWTH PRIOR TO TUBER INITIATION

Potato plants (Solanum tuberosum L.) were grown in water culture.About 14 d after tuber initiation no significant differenceswere found between apical and basal tuber parts in ¹⁴C-uptakeand partitioning into various fractions from ¹⁴C-labelled photosynthate.Thus, the fresh weight of these tubers could be used as a parameterfor the sink size. The ¹⁴C-content per tuber (sink strength)20 h after ¹⁴CO₂-supply to the foliage was significantly correlatedwith the tuber fresh weight. No correlation was found betweenthe ¹⁴C-concentration of the tuber (sink activity; ct. min^–g^– fr. wt.) and tuber fresh weight. Consequently, tuberfresh weight (sink size) per se must have been a factor whichinfluenced sink strength. Stolon parameters characterizing theirgrowth prior to tuber initiation (e.g. stolon volume) and theircapacity for photosynthate transport (diameter, length) weremeasured at the time of tuber initiation. Significant correlationswere found between these stolon parameters and subsequent growthof individual tubers. Anatomical studies on the proportion ofvarious tissues in the cross sectional area of stolons supportthe idea of a negative relation between growth of individualtubers and transport resistance in the phloem of the stolons.It is concluded that in the initial phase of tuber growth, mainlyfactors outside of the tuber determine its growth rate. In laterstages of tuber growth, when the sink strength increases, thecompeting strength of individual tubers for photosynthate isdominated mainly by factors within the tuber itself, such astheir sink size and sink activity. Key words: Potato tuber, sink size, tuber initiation, transport resistance     

Effect of Reduction of Sink Strength in Developing Seeds on Vein Loading Patterns of Photoassimilate in Source Leaves of Pisum sativum L

The effect of sink strength reduction in developing seeds onvein loading of photoassimilate has been studied in Pisum sativumL. The sink strength was manipulated by means of the ‘openseed coat technique’. Sink strength of the operated ovuleswas controlled by the osmolality of a substitute medium replacingthe embryo. A high osmolality of the medium (400 mM mannitol)or a low osmolality of the medium (without mannitol) was usedto maintain a high or low sink strength, respectively. To studythe effect of sink strength reduction on vein loading, macro-autoradiographywas used. After applying ¹⁴CO₂ to the source leaf for 10 to20min autoradiographs of plants with different sink strengthshowed differences in distribution of ¹⁴C-photoassimilate overthe mesophyll and the veins. Under low sink strength conditionsvein loading of ¹⁴C-photoassimilate was reduced. After longertime spans (40 to 60 min) no clear differences in vein loadingwere visible in the autoradiographs. However, measurement of¹⁴C in plant parts along the path of transport from source tosink showed a decrease of the rate of export of ¹⁴C from thesource leaf under low sink strength conditions. Apparently,accumulation of ¹⁴C-photoassimilate into the phloem and exporttowards sink regions can be reduced by lowering the sink strength.A signal must have been transferred from sink all the way tothe source regions. The mechanism of such a signal is discussed. Key words: Pisum sativum, phloem loading, photoassimilate transport, seed development, sink-source interactions     

SOURCE-SINK RELATIONSHIPS IN THE BLADE OF ALARIA ESCULENTA (LAMINARIALES,PHAEOPHYCEAE)1

The translocation of ¹⁴C-labelled photoassimilate was studied in blades of the kelp, Alaria esculenta (L.) Grev., which had been surgically modified to produce source and sink regions of various sizes. Thirty cm above the blade base a 2.5 cm dia. section of the blade received a 1 h pulse of H¹⁴CO₃^?. Efflux of ¹⁴C-labelled photoassimilate from this “source disc” was monitored over the next 8 days using a Geiger-Müller detector probe. Accumulation of ¹⁴C-labelled solutes by a “sink disc” of similar diameter, 20 cm below the source disc, was also monitored. Rate of ^l4C efflux from the source disc was governed by two factors: (1) total sink size and (2) feed-back from competing sources. In the latter case, source export was depressed if the portion of the blade, just distal to the source disc, was present. While the initial ¹⁴C influx rate into the sink disc was greater when competing sinks were present, the total accumulation of ¹⁴C-photoassimilates was 2–3 times higher in the sink disc when competing sources were not present. Basipetal translocation velocity (1.3–1.7 cm h^?1) was unaffected by competing sources and sinks.     

Identification of actively filling sucrose sinks

Certain actively filling plant sucrose sinks such as a seed, a tuber, or a root can be identified by measuring the uridine diphosphate and pyrophosphate-dependent metabolism of sucrose. Sucrolysis in both active and quiescent sucrose sinks was tested and sucrose synthase was found to be the predominant sucrose breakdown activity. Sucrolysis via invertases was low and secondary in both types of sinks. Sucrose synthase activity dropped markedly, greater than fivefold, in quiescent sinks. The tests are consistent with the hypothesis that the sucrose filling activity, i.e. the sink strength, of these plant sinks can be measured by testing the uridine diphosphate and pyrophosphate-dependent breakdown of sucrose. Measuring the initial reactions of sucrolysis shows much promise for use in agriculture crop and tree improvement research as a biochemical test for sink strength.     

A Fruit Growth Model Dependent on Both Carbon Supply and Inherent Fruit Characteristics

A mathematical model of carbon accumulation by growing fruitis presented. The model implicitly incorporates the conceptsof sink activity and sink size but avoids the need to stipulatesink strength. In addition to sink activity and size, carbonaccumulation depends on characteristics such as photosynthesisand respiration of the fruit itself as well as carbon supplyvia the peduncle attachment. Simulations with prescribed limitationsof carbon supply show similar results to field observations.The proposed model coupled with a carbon distribution/supplymodel could simulate the growth of individual fruit within aheterogeneous canopy.Copyright 1999 Annals of Botany Company Fruit growth, model, carbon partitioning, source:sink, relative growth rate.     

Effective carbon partitioning driven by exotic phloem-specific regulatory elements fused to the Arabidopsis thaliana AtSUC2 sucrose-proton symporter gene

Background  

AtSUC2 (At1g22710) from Arabidopsis thaliana encodes a phloem-localized sucrose/proton symporter required for efficient photoassimilate transport from source tissues to sink tissues. AtSUC2 plays a key role in coordinating the demands of sink tissues with the output capacity of source leaves, and in maintaining phloem hydrostatic pressure during changes in plant-water balance. Expression and activity are regulated, both positively and negatively, by developmental (sink to source transition) and environmental cues, including light, diurnal changes, photoassimilate levels, turgor pressure, drought and osmotic stress, and hormones.     

Long Distance Transport in Macrocystis integrifolia: III. MOVEMENT OF THO

Movement of THO and tritium-labeled photoassimilate was studied in intact fronds and frond cuttings of Macrocystis integrifolia following labeling of a mature blade by tritiated water. Both THO and tritium-labeled assimilate moved from the source blade to sink areas at velocities comparable to those recorded earlier for ¹⁴C- and ³²P-labeled compounds. In intact fronds and frond cuttings, THO and tritium-labeled assimilate showed a declining gradient with increasing distance from the source. In the exudate collected from the basal cut end of the frond, there was a marked increase in radioactivity with time in the photoassimilate, but no such gradient was evident for THO. These results support the idea that, although both tritium-labeled assimilate and THO move in the sieve elements, THO is rapidly exchanged with water in the tissues surrounding the sieve elements. Finally, it is shown that THO is transported to the sink and there “unloaded”; indeed, it can move out of the plant itself. The data on velocity and directionality of transport as well as unloading of THO at the sink are discussed, along with computations on specific mass transfer, and favor the idea that Münch's pressure-flow hypothesis is applicable in Macrocystis for long distance translocation of photoassimilates.