不同水分管理下优质稻花后植株碳氮流转与籽粒生长及品质的相关性

以桂华占、八桂香为材料,在干湿交替灌溉、亏缺灌溉、淹水灌溉3种水分条件下,研究优质稻花后植株碳氮流转与籽粒生长及品质的相关性。结果表明:不同水分管理下,桂华占和八桂香花后碳氮流转与籽粒的生长间存在密切相关。主要表现在:(1)茎鞘和叶片干物质转运对籽粒干物质积累的贡献率为16.86%～25.68%,花后茎叶干物质运转速度和运转率与籽粒起始灌浆势呈显著甚至极显著正相关;籽粒最大灌浆速率、活跃灌浆期、持续灌浆时间与叶片干物质运转速度和运转率呈极显著正相关,与茎鞘干物质运转速度和运转率呈极显著负相关;(2)茎鞘碳同化物转运对籽粒的产量和淀粉产量的贡献率则为干湿交替灌溉>亏缺灌溉>淹水灌溉;但叶片碳同化物转运对籽粒的产量和淀粉产量的贡献率则为淹水灌溉>亏缺灌溉>干湿交替灌溉;茎叶可溶性糖积累量的减少和籽粒直链淀粉含量和积累量增加是同步的,且茎叶可溶性糖积累量快速递减期(花后3～12d)与直链淀粉含量和积累量快速递增期(花后6～12d)同步;(3)茎鞘和叶片氮素转运对籽粒氮素积累的贡献率为44.05%～117.66%,叶片总氮转运对籽粒氮素积累的贡献率大于茎鞘,茎鞘和叶片氮同化物对籽粒氮素的贡献率以淹水灌溉处理的最大,亏缺灌溉处理的次之,干湿交替灌溉处理的最小。     

灌水对不同品种小麦茎和叶鞘糖含量及产量的影响

以冬小麦品种济麦20和泰山22为材料,设置全生育期不灌水(W0)、灌冬水+拔节水(W1)、灌冬水+拔节水+开花水(W2)、灌冬水+拔节水+开花水+灌浆水(W3)4个处理,研究不同灌水处理对小麦倒二茎节间和叶鞘中水溶性碳水化合物含量和籽粒产量的影响.结果表明:两品种W0处理灌浆初期倒二茎节间和叶鞘的可溶性总糖、聚合度(DP) ≥4和DP=3的果聚糖含量最高,灌浆后期的果糖含量最高,这有利于倒二茎节间和叶鞘水溶性碳水化合物的积累与降解,从而提高千粒重,灌水处理间比较,济麦20的W1处理在灌浆初期倒二茎节间和叶鞘的DP≥4、DP=3果聚糖含量和灌浆中后期的可溶性总糖、果糖含量最高,其籽粒产量也最高;泰山22的W2处理在灌浆初期倒二茎节间和叶鞘的DP≥4、DP=3果聚糖含量最高,灌浆后期的果糖含量高于W1处理,其籽粒产量也最高,品种间比较,泰山22灌浆阶段的倒二茎节间和叶鞘的可溶性总糖、DP≥4果聚糖含量和灌浆后期的果糖含量高于济麦20.两品种的籽粒产量对水分处理的响应不同,济麦20的籽粒产量在W0和W1条件下高于泰山22,在W2和W3条件下低于泰山22.本试验中,济麦20的W1处理和泰山22的W2处理有利于倒二茎节间和叶鞘中水溶性碳水化合物的积累与降解,其籽粒产量显著高于其他处理,分别是两品种的最优水分处理.     

小麦鞘、叶在籽粒形成与成熟过程中的作用

1.小麦叶片、叶鞘的干重消长呈单峰曲綫变化;同一叶位的叶鞘,干重高峰出現較叶片迟,下降持续时間也較叶片长,“和尚麦”最后二叶鞘能延至籽粒成熟期。 2.剪除鞘叶的試驗証明,剪除的时期愈早,减低粒数、粒重愈多,叶片和叶鞘的叶位愈高,影响也愈大。 3.从叶片、叶鞘衰老时期的早晚、干重的消长变化,以及不同时期进行剪叶剪鞘所引起的籽粒生长变化都証明,同一叶位的叶片与叶鞘对籽粒形成的影响,先是叶片的作用較大,然后才是叶鞘的影响。     

种植方式对夏玉米光合生产特征和光温资源利用的影响

为研究套种与直播两种种植方式对夏玉米光合生产特征和光温资源利用的影响,选取郑单958和登海661为研究对象,设置3个播期,密度为67500株·hm^-2,以地上干物质积累量和作物生长速率、叶面积指数、穗位叶的单叶光合速率来评价夏玉米的光合生产特征;以Richards模型拟合籽粒灌浆过程;结合气象数据计算夏玉米光能利用率.结果表明：直播处理比套种处理籽粒产量增加1.17%～3.33%（P<0.05）,但千粒重显著降低;生育期随播期提前而延长;直播条件下叶面积指数和单叶光合速率在灌浆前期显著高于套种,但灌浆后期下降较快;与套种相比,直播开花前和开花后具有较高的干物质积累量和较快的作物生长速率.Richards模型解析表明,直播处理达到最大灌浆速率的时间明显早于套种,起始势较套种高,但灌浆期、活跃灌浆期和灌浆速率最大时的生长量均低于套种;与套种相比,直播处理生育期间总积温和总辐射量分别减少150～350 ℃·d和200～400 MJ·m^-2,但籽粒光能利用率较套种提高10.5%～24.7%.因此,直播较套种有优势,在夏玉米大田生产条件下,重视叶片的光合生产特征,延缓叶片衰老,有利于提高夏玉米的光能利用率,进一步挖掘增产潜力.     

灌浆期热胁迫对小麦不同绿色器官光合性能的影响

以4个冬小麦（Triticum aestivem L.）品种（“JD8”、“Jing411”、“Centurk”和“Tam202”）为材料,研究灌浆期热胁迫对旗叶叶片、旗叶鞘、穗下节间、护颖、外疑和芒的光合性能和籽粒产量的影响。结果表明：灌浆期对泪科进行热锻炼也能增加其耐热性且各绿色器官间耐热性差异显。耐热性较强的器官为穗下节间、旗叶鞘和护颖;热敏感器官为旗叶叶片、外颖和芒。热胁迫条件下,穗下节间1旗叶鞘和护颖的细胞膜热稳定性强,光系统Ⅱ原初光能转换效率（Fv/Fm）下降速率以及叶绿素和类胡萝卜素降解速率均低于旗叶叶片、外颖和瓦,穗的净光合速率下降幅度小于旗叶。热胁迫过程中,相对耐热品种“JD8”各器官上述光合参数的下降速度均显低于其他3个热敏感品种。     

小麦灌水时期与灌水量对花后果聚糖积累与转运及水分利用效率的影响

于2004-2005年和2005-2006年冬小麦生长季,在山东泰安和兖州进行田间试验,研究不同灌水时期和灌水量处理对冬小麦开花后倒二节间果聚糖积累与转运和水分利用效率的影响.结果表明：全生育期不灌水促进了灌浆后期倒二节间贮藏果聚糖向籽粒的转运.在拔节期和开花期各灌水60 mm,可提高开花后旗叶的光合速率和同化物输入籽粒量及其对籽粒的贡献率,拔节期、开花期和灌浆期各灌水60 mm或拔节期和开花期各灌水90 mm,灌浆后期旗叶的光合速率显著降低,营养器官花前贮藏同化物转运量及其对籽粒的贡献率升高,花后同化物输入籽粒量及其对籽粒的贡献率降低,灌浆后期倒二节间的聚合度（DP）≥4、DP=3果聚糖滞留量增加,不利于果聚糖向籽粒的转运.两个生长季中,拔节期和开花期各灌水60mm处理的小麦籽粒产量较高,水分利用效率最高.拔节期、开花期和灌浆期各灌水60 mm或拔节期和开花期各灌水90 mm,小麦籽粒产量无显著变化,水分利用效率降低.     

黄土高原地膜春小麦地上干物质累积与转运规律

通过2个生长季的大田试验,研究了黄土高原半干旱地区地膜与露地春小麦地上干物质累积、转运规律.结果表明:与露地春小麦相比,地膜春小麦单株最大叶面积增加17.16%,最大绿叶面积峰值早出现6 d,开花前干物质积累量高8.97%;地膜春小麦叶片、茎秆、颖壳穗轴的输出率分别比露地春小麦高3.23%～3.67%、3.53%～4.55%和1.80%～3.63%;其转换率分别比露地春小麦高0.12%～0.46%、0.92%～1.90%和0.35%～0.87%;各非经济器官输出的干物质对籽粒干物质的贡献率比露地春小麦高1.9%～2.7%;地膜春小麦籽粒起始生长势、最大生长速率、活跃生长期均高于露地春小麦;而达最大生长速率的天数短于露地小麦;地膜春小麦籽粒灌浆期具有较强的生长势,灌浆速率快,灌浆时间长,最终表现为粒重高、产量增加36%.     

小麦籽粒灌浆特征及影响因素的研究进展

本文对小麦籽粒灌浆特征及影响因素研究进展进行了综述。小麦籽粒灌浆过程中,粒重的增长进程(即灌浆进程)呈“S”型变化趋势,目前通常用Logistic生长方程、Richards生长方程和三次多项式方程对该“S”型曲线进行模拟。这些方程中的参数,如灌浆持续期、最大灌浆速率、平均灌浆速率、最大粒重等均表征着一定的生物学意义,其中灌浆速率主要由遗传控制,灌浆持续期主要取决于环境因素。从现有文献看,灌浆速率是决定籽粒重量的关键性参数,而灌浆持续期与籽粒重量间的相互关系仍有待进一步研究。小麦开花时有相当数量的贮藏性物质以非结构碳水化合物形式贮藏在叶片、茎鞘和茎秆中,在籽粒灌浆期间分解并向籽粒转移,对籽粒重量的贡献率达1／3以上,描述物质转移的指标包括干物质转移量、干物质转移效率和转移干物质对籽粒的贡献率等,小麦遗传特性、养分供应水平和气候条件均影响小麦灌浆期间的物质转移,如杂种小麦的干物质转移效率和转移干物质对籽粒的贡献率均明显高于亲本,适量增施氮肥能够促进开花后营养器官贮存光合产物向籽粒中的运转,提高籽粒可溶性糖含量,灌浆期间受到干旱胁迫时,转移干物质对籽粒的贡献率明显增加;环境温度、光照、土壤水分和养分(特别是氮素)状况对小麦灌浆过程及相关参数有显著影响。过去虽然对小麦灌浆过程进行了大量卓有成效的研究工作,但是,在籽粒灌浆过程中收获指数的动态变化、植物营养调控对根冠关系、灌浆过程和物质转移的影响、田间个体和群体调控及不同高产栽培模式下灌浆过程及物质转移的差异、灌浆过程和物质转移与品质形成的相互关系等方面的研究资料比较缺乏;在灌浆过程中繁殖体大小等级结构的变化、蘖群中优势蘖穗籽粒灌浆特征与非优势蘖穗籽粒灌浆特征和物质转移的差异、不同穗位籽粒灌浆特征间的差异、灌浆过程与植物体氮素气态损失间的关系等领域的研究资料更加缺乏。而这些问题的研究,对进一步深入了解小麦灌浆过程,丰富小麦籽粒和品质形成理论,指导高产优质小麦育种,实现高产优质高效小麦栽培等具有十分重要的理论和实践意义。     

不同品质类型小麦非叶光合器官光合荧光特性研究

以强筋(郑麦9023)、中筋(新麦13)和弱筋(豫麦50)型小麦品种为试材,测定了它们非叶光合器官的叶绿素含量、荧光动力学参数、净光合速率及对籽粒的贡献率.结果显示,不同品质类型小麦非叶光合器官叶绿素含量表现为旗叶鞘>穗下节间>芒>穗部颖片,各非叶光合器官开花18d后叶绿素含量均表现为弱筋小麦>中筋小麦>强筋小麦;弱筋小麦的非叶光合器官在灌浆前期具有较高的Fv/Fm、ΦPSⅡ值,在灌浆后期其Fv/Fm和ΦPSⅡ值下降幅度显著小于强筋小麦并有较高的净光合速率;非叶光合器官对籽粒的相对贡献率依次为穗部>旗叶>节鞘,且对弱筋小麦籽粒的贡献率高于中筋和强筋小麦,其中节鞘和穗对弱筋小麦粒重的相对贡献率分别为15.7%和35.4%.研究表明,弱筋小麦豫麦50的非叶光合器官能维持较较强的光合能力,生产更多的光合产物,花后形成的光合产物对其粒重的增加起重要作用.     

温度对小麦籽粒形成过程中生理变化的影响

试验研究了温度对小麦籽粒形成过程中生理变化的影响,得到以下结果:1.小麦在开花到成熟处于日温相同(25℃)而夜温不同(20℃,10℃)的条件下,夜温低的处理籽粒灌浆期和成熟期比夜温高的处理延长10天。2.夜温低的处理绿色叶面积大、下部叶片衰亡较慢、叶片夜间呼吸强度低,有利于干物质的积累。因此茎鞘、叶、穗、籽粒和总干重都较高。开花到开花后17天植株干重的主要差异是茎鞘。开花17天以后到成熟,两个处理籽粒干重的差异逐渐增加。3.夜温低的处理,籽粒灌浆的物质来源较丰富,有利于晚开花的籽粒生长。由于灌浆的粒数较多,不仅小穗第一、二粒的粒重增加,第三粒的结实率和粒重也有所提高。4.夜温低的处理,茎、鞘和叶的含糖量比夜温高的处理大,以茎较为显著。籽粒生长前期淀粉含量低而醇溶性糖的含量高,接近成熟时两个处理的差异减小。5.在小麦籽粒灌浆盛期供给旗叶以 C~(14)O_2后;穗、穗下节和饲喂叶的局部温度改变(5—8℃,20—25℃)引起了同化产物运输分配情况发生变化。穗部降温对同化产物输入籽粒的抑制作用最大,饲喂叶次之。穗下节降温到5—8℃的影响不大。穗及饲喂叶降温有较多的放射性物质留存在饲喂叶中。6.不论是供给、输导或接受器官降温,受到低温影响的部分醇溶性物质的分布百分率皆增高;穗部降温的影响最大,饲喂叶次之,穗下节较小。穗部降温籽粒中的放射性约有65%在醇溶性部分,不降温的约有63%在稀酸水解部分;说明了5—8℃的低温阻碍籽粒中糖向淀粉等高分子物质的转化过程。7.本文对青海地区小麦干粒重较高的原因,夜温对小麦茎、鞘、叶和籽粒的生长,每穗粒重和粒数的关系等进行了分析和讨论;并指出改变温度或用其他方法增加粒重提高产量的可能。     

Contributions of root uptake and remobilization to grain zinc accumulation in wheat depending on post-anthesis zinc availability and nitrogen nutrition

Background and aims

Whether root Zn uptake during grain filling or remobilization from pre-anthesis Zn stores contributes more to grain Zn in wheat is subject to an on-going debate. This study investigated the effects of N nutrition and post-anthesis Zn availability on the relative importance of these sources.

Methods

Durum wheat plants were grown in nutrient solution containing adequate Zn (0.5?μM) and three different N levels (0.5; 1.5; 4.5?mM). One third of the plants were harvested when they reached anthesis. One half of the remaining plants were grown to maturity with adequate Zn, whereas the Zn supply to the other half was discontinued at anthesis. Roots, straw and grains were harvested separately and analyzed for Zn and N.

Results

Depending on the N supply, Zn remobilization from pre-anthesis sources provided almost all of grain Zn when the Zn supply was withheld at anthesis; otherwise up to 100?% of grain Zn could be accounted for by Zn taken up post-anthesis. By promoting tillering and grain yield and extending the grain filling, higher N supply favored the contribution of Zn uptake to grain Zn accumulation.

Conclusion

Remobilization is critical for grain Zn accumulation when Zn availability is restricted during grain filling. However, where root uptake can continue, concurrent Zn uptake during grain development, favored by higher N supply, overshadows net remobilization.     

Ontogenetic changes in photosynthetic capacity and dry matter production of flag wheat leaves during the grain filling period

The relationships between photosynthetic capacity and dry matter accumulation during the grain filling period have been studied in flag leaves of Triticum aestivum L., cv. Kolibri grown in Mediterranean field conditions. Particular importance has been given to assimilate accumulation in relation to the onset of senescence. During grain filling, the time course of specific dry weight (SDW) was similar in the blade and in the sheath. Variations in SDW were about six times larger in the sheath than in the blade. Minimum blade SDW values occurred during heading and at anthesis. Maximum blade SDW values were observed two weeks after anthesis. After this, SDW values decreased sharply. The dry matter increase per grain in the period from two weeks after anthesis to the end, was only about 25% of final grain dry weight. The importance of environmental constraints on maximum SDW values are discussed. Maximum SDW values occurred at the beginning of the period of rapid decline in blade net CO₂ assimilation rate and leaf nitrogen content, that is, at the beginning of senescence. On the other hand, the stomatal resistance to CO₂ and the development of senescence are not apparently related. The maximum blade dry weight increase (considering a value of zero at heading) was about 60 mg dry weight per g fresh weight. The possible relationships between dry matter accumulation and senescence onset are discussed.     

Effects of exogenous ABA and cytokinin on leaf photosynthesis and grain protein accumulation in wheat ears cultured <Emphasis Type="Italic">in vitro</Emphasis>

A detached culture system and steady-state ¹⁵N labeling technique were used to study the effects of exogenous ABA and ZR on photosynthetic characteristics, nitrogen remobilization and the activities of key enzymes for nitrogen metabolism in detached wheat parts during grain protein accumulation. The differences in net photosynthetic rate, chlorophyll content (SPAD value) and soluble protein content in the flag leaves of detached culture system between the treatments of ABA and ZR showed that ABA facilitates the post-anthesis senescence course compared to the ZR treatment. The differences in the changes of ¹⁵N amount in different organs in the detached culture system between the ABA and ZR treatments showed that nitrogen remobilization from vegetative organs to the grain is accelerated by the ABA treatment but is delayed by ZR. The activities of GS and GPT in grains treated with ABA were significantly higher than those with the control treatment at 5 DAC, but reduced significantly compared with control at 11 DAC. The two enzyme activities in grains were reduced significantly by ZR at 5 DAC and increased significantly at 11 DAC, compared with those treated with ABA. The above changes of enzyme activity showed that the ABA treatment hastens amino acid conversion into grains and protein accumulation in grains, whereas the ZR treatment delays these processes. A significant reduction in grain weight with ABA treatment is associated with the reduction of net photosynthesis, chlorophyll content, and soluble protein content in flag leaves. Compared with the control and ZR treatments, a significant increase in grain protein content with the ABA treatment may result from the accelerating effects of ABA on N remobilization, amino acid conversion into grains and protein accumulation in grains.     

Contribution of Pre-Anthesis Assimilates and Current Photosynthesis to Grain Yield,and their Relationships to Drought Resistance in Wheat Cultivars Grown Under Different Soil Moisture

We investigated the relative importance of pre-anthesis assimilates stored in plant parts, mainly in the stem, and post-anthesis photosynthesis to drought resistance in wheat (Triticum aestivum L.) cultivars Hongwangmai (drought resistant) and Haruhikari (drought sensitive) subjected to two soil moisture regimes: irrigated and non-irrigated. In the irrigated treatment, soil moisture was maintained near field capacity throughout the growing season, while in the non-irrigated treatment water was withheld from 81 d after sowing until maturity. Drought stress reduced grain yield of Hongwangmai and Haruhikari by 41 and 60 %, respectively. Remobilization of pre-anthesis assimilates to the grain (remobilization) was reduced by drought in Hongwangmai but increased in Haruhikari. The contribution of pre-anthesis assimilates to the grain decreased under non-irrigated treatment in Hongwangmai. However, under water stress, Hongwangmai maintained a higher net photosynthetic rate in the flag leaf than Haruhikari. These results indicated that maintenance of post-anthesis photosynthetic rate was related to drought resistance in Hongwangmai rather than to remobilization under drought stress.     

A proteomics view on the role of drought-induced senescence and oxidative stress defense in enhanced stem reserves remobilization in wheat

Drought is one of the major factors limiting the yield of wheat (Triticum aestivum L.) particularly during grain filling. Under terminal drought condition, remobilization of pre-stored carbohydrates in wheat stem to grain has a major contribution in yield. To determine the molecular mechanism of stem reserve utilization under drought condition, we compared stem proteome patterns of two contrasting wheat landraces (N49 and N14) under a progressive post-anthesis drought stress, during which period N49 peduncle showed remarkably higher stem reserves remobilization efficiency compared to N14. Out of 830 protein spots reproducibly detected and analyzed on two-dimensional electrophoresis gels, 135 spots showed significant changes in at least one landrace. The highest number of differentially expressed proteins was observed in landrace N49 at 20days after anthesis when active remobilization of dry matter was observed, suggesting a possible involvement of these proteins in effective stem reserve remobilization of N49. The identification of 82 of differentially expressed proteins using mass spectrometry revealed a coordinated expression of proteins involved in leaf senescence, oxidative stress defense, signal transduction, metabolisms and photosynthesis which might enable N49 to efficiently remobilized its stem reserves compared to N14. The up-regulation of several senescence-associated proteins and breakdown of photosynthetic proteins in N49 might reflect the fact that N49 increased carbon remobilization from the stem to the grains by enhancing senescence. Furthermore, the up-regulation of several oxidative stress defense proteins in N49 might suggest a more effective protection against oxidative stress during senescence in order to protect stem cells from premature cell death. Our results suggest that wheat plant might response to soil drying by efficiently remobilize assimilates from stem to grain through coordinated gene expression.     

Physiological mechanisms contributing to the increased water-use efficiency in winter wheat under deficit irrigation

Deficit irrigation in winter wheat has been practiced in the areas with limited irrigation water resources. The objectives of this study were to (i) understand the physiological basis for determinations of grain yield and water-use efficiency in grain yield (WUE) under deficit irrigation; and (ii) investigate the effect of deficit irrigation on dry matter accumulation and remobilization of pre-anthesis carbon reserves during grain filling. A field experiment was conducted in the Southern High Plains of the USA and winter wheat (cv. TAM 202) was grown on Pullman clay loam soil (fine mixed thermic Torretic Paleustoll). Treatments consisted of rain-fed, deficit irrigation from jointing to the middle of grain filling, and full irrigation. The physiological measurements included leaf water potential, net photosynthetic rate (Pn), stomatal conductance (Gs), and leaf area index. The rain-fed treatment had the lowest seasonal evapotranspiration (ET), biomass, grain yield, harvest index (HI) and WUE as a result of moderate to severe water stress from jointing to grain filling. Irrigation application increased seasonal ET, and ET increased as irrigation frequency increased. The seasonal ET increased 20% in one-irrigation treatments between jointing and anthesis, 32-46% in two-irrigation treatments, and 67% in three- and full irrigation treatments. Plant biomass, grain yield, HI and WUE increased as the result of increased ET. The increased yield under irrigation was mainly contributed by the increased number of spikes, and seeds per square meter and per spike. Among the irrigation treatments, grain yield increased significantly but the WUE increased slightly as irrigation frequency increased. The increased WUE under deficit irrigation was contributed by increased HI. Water stress during grain filling reduced Pn and Gs, and accelerated leaf senescence. However, the water stress during grain filling induced remobilization of pre-anthesis carbon reserves to grains, and the remobilization of pre-anthesis carbon reserves significantly contributed to the increased grain yield and HI. The results of this study showed that deficit irrigation between jointing and anthesis significantly increased wheat yield and WUE through increasing both current photosynthesis and the remobilization of pre-anthesis carbon reserves.     

Grain sink strength may be related to the poor grain filling of indica-japonica rice (Oryza sativa) hybrids

The physiological and biochemical factors contributing to poor grain filling of indica-japonica rice ( Oryza sativa L.) hybrids were studied by analyzing the role of grain sink strength in dry matter accumulation of grains of two types of rice cultivars, Yayou 2 (an indica-japonica hybrid) and Yanjing 2 (a japonica cultivar). Carbon dioxide enrichment and plant hormone application were imposed at anthesis and the number of endosperm cells, dry matter accumulation and the activities of some sugar-metabolizing enzymes of grains were measured during grain filling. In Yayou 2, strong-potential grains (SPGs) accumulated dry weight much earlier than weak-potential grains (WPGs), but this difference was not obvious for Yanjing 2. Carbon dioxide enrichment imposed after heading significantly stimulated dry matter accumulation of WPGs of Yayou 2, but had little influence on WPGs of Yanjing 2 and SPGs of both cultivars. Leaf sheath dry matter decreased steadily in both cultivars during early stages of grain filling and accumulated during the later stages. Carbon dioxide enrichment increased leaf sheath dry matter. Dry matter accumulated by grains was linearly related to the increases in endosperm cell numbers and the activities of sucrose synthase (SS) and ADP-glucose pyrophosphorylase (AGPase) in SPGs and WPGs of both cultivars. Application of either 6-benzyladenine or abscisic acid had no significant influences on both endosperm cell number and grain dry matter accumulation. These results suggest that grain sink strength, determined by both cell numbers, SS and AGPase activities in the endosperm control the dry matter accumulation of grains.