水稻穗上不同粒位籽粒胚乳结构及其结实期灌溉方式对它的调控作用
袁莉民, 展明飞, 章星传, 王志琴, 杨建昌*
扬州大学农学院 / 江苏省作物遗传生理国家重点实验室培育点 / 江苏省粮食作物现代产业技术协同创新中心, 江苏扬州225009;
*通信作者(Corresponding author): 杨建昌, E-mail: jcyang@yzu.edu.cn, Tel: 0514-87979317

第一作者联系方式: E-mail: lmyuan@yzu.edu.cn

摘要

为探明水稻穗上不同粒位胚乳结构形成特征及结实期灌溉方式对它的调控作用, 本研究以籼稻扬稻6号和粳稻武运粳24为材料, 运用扫描电镜观察了穗上不同部位籽粒胚乳结构的形成动态。自抽穗至成熟设置保持浅水层(CK)、轻干-湿交替灌溉(WMD)和重干-湿交替灌溉(WSD) 3种灌溉方式, 观察了干湿交替灌溉方式对水稻产量和籽粒胚乳结构的影响。结果表明, 灌浆过程中稻米胚乳结构的形态建成顺序是, 上部穗籽粒早于中部穗籽粒更早于下部穗籽粒, 一次枝梗籽粒早于二次枝梗籽粒, 穗上早开花的籽粒早于迟开花的籽粒。与CK相比, 结实期WMD可以明显提高水稻产量; 其穗下部籽粒胚乳的淀粉体排列更紧密, 籽粒背部淀粉粒嵌挤甚至粘连。在WSD下, 稻米胚乳淀粉体排列疏松, 体积减小, 粒径差异增大, 相互间隙增大。灌溉方式对胚乳结构的影响, 因粒位而异, 以下部穗二次枝梗籽粒的腹部最为显著。表明水稻穗上不同部位籽粒胚乳结构形成与花后天数有密切关系; 结实期WMD可以改进穗下部籽粒胚乳结构, WSD则会使胚乳结构变差。灌浆期土壤水势-20 kPa 可作为改善稻米胚乳淀粉结构的节水灌溉低限指标。

关键词: 水稻; 粒位; 胚乳结构; 淀粉粒; 灌溉方式
Endosperm Structure of Grains at Different Positions of Rice Panicle and Regulation Effect of Irrigation Regimes on It during Grain Filling
YUAN Li-Min, ZHAN Ming-Fei, ZHANG Xing-Chuan, WANG Zhi-Qin, YANG Jian-Chang*
Jiangsu Key Laboratory of Crop Genetics and Physiology / Co-Innovation Center for Modern Production Technology of Grain Crops, Yangzhou University, Yangzhou 225009, Jiangsu, China;
Abstract

In this study, an indica cultivar Yangdao 6 and a japonica cultivar Wuyunjing 24 were used to observe the changes in endosperm structure of grains at different positions of panicle with scanning electron microscope. Three irrigation treatments, namely shallow water layer (CK), alternate wetting and moderate drying (WMD), and alternate wetting and severe drying (WSD), were designed to investigate the effect of irrigation regimes on grain yield and grain endosperm structure. The endosperm structure formation in grains was earlier at the upper part of panicle than at the mid part of panicle, and earlier than at the lower part of panicle; the formation was earlier on a primary branch than on a secondary branch, and earlier in superior grains than in inferior grains. Compared with CK, WMD significantly increased grain yield. The starch granule in endosperm of grains at the lower part of panicle showed more compact arrangement, and that in the back part of grains was more crowded and even more adhered each other under WMD than under CK. Under WSD, the endosperm structure in grains showed that the starch granule arrangement was looser, the granule volume was decreased, and the differences in granule size and the gap between granules were increased, relative to those under CK. The effect of irrigation regimes on endosperm structure varied with grain positions, which was the most significant on the belly of grains at the secondary branch located at the lower part of panicle. The results suggest that the formation of endosperm structure in the grains at different parts of panicle is closely related to days after anthesis. WMD may improve, whereas WSD deteriorate, the endosperm structure of grains at the lower part of rice panicle. Soil water potential -20 kPa can be used as the low limit of soil water potential index in the water-saving irrigation for improving endosperm structure in grains during the grain filling period of rice.

Keyword: rice; grain position; endosperm structure; starch granule; irrigation regimes

籽粒灌浆是水稻粒重和品质形成的关键时期。水稻籽粒中的主要成分为胚乳淀粉, 胚乳淀粉粒结构(淀粉粒大小及其排列状况)直接关系到籽粒的充实和稻米的品质[1, 2, 3, 4]。通过遗传改良和栽培技术的改进促进稻米胚乳淀粉粒结构的发育是获取水稻高产优质的重要途径之一。水稻不同品种间以及同一品种同一穗上不同粒位间的灌浆速率和充实程度有较大的差异[1, 2]。一般早开花的强势粒灌浆速率大, 胚乳中淀粉粒排列紧密, 籽粒充实度好; 晚开花的弱势粒灌浆速率小, 胚乳中淀粉粒排列疏松, 籽粒充实度和外观品质等较差[3, 4]。前人对于不同粒位间灌浆特性的研究多限于强、弱势粒的粒重比较[5, 6, 7, 8, 9], 很少涉及穗上不同部位籽粒胚乳淀粉形态结构差异的观察分析。有关籽粒灌浆过程中胚乳结构形成的动态变化及其调控的研究, 尚未见报道。

干湿交替灌溉技术(alternate wetting and drying irrigation, AWD)是一种重要的节水灌溉技术, 其主要技术特点是在水稻生育过程中, 在一段时间里保持水层, 自然落干至土壤不严重干裂再灌水, 再落干, 再灌水, 如此循环。目前该项技术在亚洲各主要水稻生产国都得到了大面积推广与应用, 取得了显著的节水效果[10, 11, 12, 13, 14, 15, 16]。但有关结实期干湿交替灌溉如何影响水稻穗上不同粒位籽粒胚乳结构缺乏研究。以上问题的深入探讨对提高水稻产量和品质有重要意义。本研究以典型的籼、粳稻品种为材料, 运用扫描电镜观察籽粒灌浆过程中胚乳结构形成的动态以及穗上不同部位籽粒淀粉粒结构的分布特点, 探讨结实期干湿交替灌溉方式对它的调控作用, 以期为水稻高产优质栽培提供理论和实践依据。

1 材料与方法
1.1 试验材料与处理

1.1.1 试验1 水稻穗上不同粒位籽粒胚乳结构的观察 试验于扬州大学农学院实验农场进行。供试材料为籼稻品种扬稻6号和粳稻品种武运粳24。前茬作物为小麦, 土壤质地为沙壤土, 耕作层含有机质2.04%、有效氮106.2 mg kg-1、速效磷28.5 mg kg-1、速效钾93.6 mg kg-1。全生育期施尿素420 kg hm-2, 按基肥∶ 分蘖肥∶ 穗肥 = 4∶ 2∶ 4施用。5月10日至12日播种, 6月8日至10日移栽至大田。株、行距为17 cm × 20 cm, 每穴2株苗, 小区面积为5.1 m × 4.2 m。重复4次, 随机区组排列。田间管理按常规高产栽培。

1.1.2 试验2 结实期灌溉方式对不同粒位籽粒胚乳结构的调控 供试材料和试验地点同试验1, 分别种植于土培池和大田。土培池由水泥制成并填满土, 每个池的长、宽、高分别为8 m、1.5 m和0.3 m, 共9个。土培池和大田的土壤质地、土壤养分含量即施氮量同试验1。5月10日至12日播种, 6月8日至10日移栽。株、行距为17 cm × 20 cm, 每穴2株苗。除结实期土壤水分(灌溉)处理外, 其余田间管理按当地常规高产栽培。灌浆期间(8月16日至10月6日)各候(每5 d)的平均气温分别为27.3° C、27.2° C、26.8° C、25.2° C、24.6° C、23.5° C、22.6° C、22.2° C、21.3° C和20.7° C, 适宜水稻灌浆结实。自抽穗(50%穗伸出剑叶叶鞘)至成熟, 设置3种灌溉方式处理: (1)保持浅水层(CK); (2)自浅水层自然落干至土壤水势-20 kPa, 然后灌1~2 cm水层(人工用桶加水)再落干, 如此循环, 简称轻干-湿灌溉(T1); (3)自浅水层自然落干至土壤水势-40 kPa, 然后灌1~2 cm水层再落干, 如此循环, 简称重干-湿灌溉(T2)。裂区设计, 以水分处理为主区, 品种为裂区(小区)。土培池试验小区面积为5.7 m2, 大田试验为18.0 m2, 重复3次。在T1和T2处理的小区内安装真空表式土壤负压计(中国科学院南京土壤研究所产)监测土壤水势。土壤负压计陶土头埋设深度为离地表15~20 cm。大田试验在各小区间以塑料薄膜包埂。土培池和大田均有遮雨设施。

1.2 测定项目与方法

1.2.1 水稻胚乳结构观察 以穗顶部第1至第3朵颖花开花定为开花始日。

于开花始日选取各品种或处理120~150个同日始花、生长整齐一致的穗子挂牌标记, 从中选取10个穗从上午8:00到下午3:00观察穗上颖花开花日序, 并记录在穗上的位置。分别于花后5 d、10 d、15 d、20 d、25 d、30 d、35 d 7个时期取样, 各时期取样穗5~8个。按开花日序所对应的穗上枝梗部位及粒位分类取样。扬稻6号和武运粳24一个稻穗一般有11~12个一次枝梗, 穗顶端的3~4个一次枝梗为穗上部, 穗中部的4个一次枝梗为穗中部, 穗基部的4个一次枝梗为穗下部(图1)。分别取穗上部、中部和下部各1个一次枝梗及其中部二次枝梗, 按稻穗结构模式图将一次枝梗上的第1至第6粒分成6个粒位, 一次枝梗上的第1、第2、第3、第4、第5、第6位籽粒称第1粒、第2粒、· · · · · · 、第6粒, 将二次枝梗上第1至第3粒或4粒分成3个或4个粒位, 同样, 二次枝梗上的第1粒位、第2粒位、· · · · · · 、第4粒位籽粒称第1粒、第2粒、· · · · · · 、第4粒。将穗上同一部位、同日开花的籽粒合并, 作为一个样本, 剔除未受精的空粒, 用于观察水稻胚乳结构。

图1 水稻穗结构模式图Fig. 1 Schematic representation of a rice panicle

籽粒离穗后按袁莉民等[7]的方法制备扫描样品, 于FEI XL30-ESEM环境扫描电镜下观察、摄影并记录籽粒胚乳结构。

1.2.2 产量及其构成 成熟期从每小区取3个10穴, 考查每穗粒数、结实率和千粒重, 以土培池试验实收2.5 m2、大田试验实收5.0 m2计产。

2 结果与分析
2.1 不同粒位胚乳结构形成

2.1.1 花后5 d胚乳结构 除二次枝梗上的第2、第3、第4粒以及穗下部一次枝梗上的第2、第3粒子房尚未明显膨大外, 其他不同部位、不同粒位籽粒在胚乳细胞增殖的同时均已经开始了淀粉的累积, 此时, 发育米粒的断面上胚乳呈完全的裸露态, 低倍下不见细胞轮廓。淀粉体排列疏松, 可见复粒。穗上部一次枝梗第1粒为全穗最早开花者, 籼稻扬稻6号籽粒胚乳已经开始显露出不同部位的结构差异, 心部的充实状况最好, 复粒大小达约6.2~8.3 μ m, 但仍以单粒居多, 大小约1.05 μ m (图版I-1); 粳稻武运粳24上部一次枝梗第1粒胚乳淀粉尚未见有复粒, 单粒淀粉大小参差, 大的达1 μ m, 小的120 nm, 第2粒则更为滞后。扬稻6号穗下部一次枝梗第1粒胚乳(图版I-2), 复粒约1.99~3.87 μ m, 穗下部一次枝梗第2粒发育米粒已略有膨大, 胚乳淀粉粒约160~250 nm (图版I-3)。表明穗上愈是迟开花的籽粒, 其胚乳结构愈是疏松, 淀粉粒的体积愈小。武运粳24胚乳发育比扬稻6号迟缓。

图版I 花后5~10 d穗上不同部位籽粒胚乳结构
图1: 扬稻6号穗上部一次枝梗第1粒花后5 d背部; 图2: 扬稻6号穗下部一次枝梗第1粒花后5 d胚乳; 图3: 扬稻6号穗下部一次枝梗第2粒花后5 d胚乳; 图4: 武运粳24穗上部一次枝梗第1粒花后5 d胚乳; 图5: 武运粳24穗上部一次枝梗第5粒花后5 d胚乳; 图6: 扬稻6号穗上部一次枝梗第2粒花后10 d背部; 图7: 扬稻6号穗上部一次枝梗第6粒花后10 d腹部; 图8: 扬稻6号穗中部一次枝梗第2粒花后10 d背部。
Plate I Endosperm structure in the grains at different positions on a rice panicle at 5-10 d after flowering
Fig. 1: Endosperm structure of back of 1st grain on a primary branch at the upper parts on a panicle, at 5 d after flowering of Yangdao 6. Fig. 2: Endosperm structure of 1st grain on a primary branch at the lower parts on a panicle, at 5 d after flowering of Yangdao 6. Fig. 3: Endosperm structure of 2nd grain on a primary branch at the lower parts on a panicle, at 5 d after flowering of Yangdao 6. Fig. 4: Endosperm structure of 1st grain on a primary branch at the upper parts on a panicle, at 5 d after flowering of Wuyunjing 24. Fig. 5: Endosperm structure of 5th grain on a primary branch at the upper parts on a panicle, at 5 d after flowering of Wuyunjing 24. Fig. 6: Endosperm structure of back of 2nd grain on a primary branch at the upper parts on a panicle, at 10 d after flowering of Yangdao 6. Fig. 7: Endosperm structure of belly of 6th grain on a primary branch at the upper parts on a panicle, at 10 d after flowering of Yangdao 6. Fig.8: Endosperm structure of back of 2nd grain on a primary branch at the mid parts on a panicle, at 10 d after flowering of Yangdao 6.

2.1.2 花后10 d胚乳结构 穗上较早开花(穗上部一次枝梗)籽粒胚乳细胞分裂已结束, 胚乳细胞数目已定。此时, 发育米粒的断面上胚乳组织呈不完全的裸露态, 低倍下以心部为中央的2~4层放射状排列的细胞不裸露, 其外围至糊粉层呈完全的裸露态。淀粉体形态多样, 呈球形、椭球体形、棒状、肾形或不规则形状, 粒间间隙比花后5 d的小、体积则较之为大, 复粒大小平均约9.2 μ m, 单粒大小约1.96 μ m, 排列仍疏松(图版I-6, 7; II-1)。心部淀粉体排列明显比背部的紧密, 背部胚乳结构优于腹部。穗上愈是迟开花(穗基部二次枝梗)籽粒, 其发育米粒断面的裸露区域愈大, 胚乳结构愈是疏松, 复粒与单粒的体积愈小(图版I-8; II-2), 心、背、腹部的结构差异愈不明显。武运粳24穗下部一次枝梗第2、第3粒及其中部二次枝梗第2、第3粒子房仍未明显膨大即淀粉的累积仍微乎其微; 穗上较早开花籽粒胚乳复粒大小平均约13.0 μ m, 单粒大小约2.65 μ m, 淀粉粒平均体积比扬稻6号的大(图版II-3, 6), 穗上较迟开花籽粒的胚乳结构则明显疏松(图版II-4, 5, 7, 8)。2个供试品种籽粒胚乳结构穗上部位间差异及粒位间差异显著。

图版II 花后10 d穗上不同部位籽粒胚乳结构
图1: 扬稻6号穗中部一次枝梗第5粒花后10 d背部; 图2: 扬稻6号穗下部一次枝梗第4粒花后10 d背部; 图3: 武运粳24穗上部一次枝梗第1粒花后10 d背部; 图4: 武运粳24穗上部一次枝梗第3粒花后10 d背部, 图5: 武运粳24穗中部一次枝梗第2粒花后10 d胚乳; 图6: 武运粳24穗中部一次枝梗第6粒花后10 d心部; 图7: 武运粳24穗下部二次枝梗第1粒花后10 d背部; 图8: 武运粳24穗下部二次枝梗第4粒花后10 d背部。
Plate II Endosperm structure in the grains at different positions on a rice panicle at 10 d after flowering
Fig. 1: Endosperm structure of back of 5th grain on a primary branch at the mid parts on a panicle, at 10 d after flowering of Yangdao 6. Fig. 2: Endosperm structure of 4th grain on a primary branch at the lower parts on a panicle, at 10 d after flowering of Yangdao 6. Fig. 3: Endosperm structure of back of 1st grain on a primary branch at the upper parts on a panicle, at 10 d after flowering of Wuyunjing 24. Fig. 4: Endosperm structure of back of 3rd grain on a primary branch at the upper parts on a panicle, at 10 d after flowering of Wuyunjing 24. Fig. 5: Endosperm structure of 2nd grain on a primary branch at the mid parts on a panicle, at 10 d after flowering of Wuyunjing 24. Fig. 6: Endosperm structure of 6th grain on a primary branch at the mid parts on a panicle, at 10 d after flowering of Wuyunjing 24. Fig. 7: Endosperm structure of back of 1st grain on a secondary branch at the lower parts on a panicle, at 10 d after flowering of Wuyunjing 24. Fig. 8: Endosperm structure of back of 4th grain on a secondary branch at the lower parts on a panicle, at 10 d after flowering of Wuyunjing 24.

2.1.3 花后15 d胚乳结构 穗上较早开花籽粒的断面在低倍镜下细胞以心部为中央呈放射状排列, 其中少数个别细胞裸露, 仅与糊粉层相邻的极小区域呈完全裸露态。背部的淀粉体排列较紧密(图版III-1), 裸露处无论是背腹, 其中的淀粉体排列仍疏松(图版III-2, 5, 6), 复粒大小扬稻6号约10.7 μ m, 武运粳24约11.2 μ m, 心部较为疏松, 腹部最疏松。穗上愈是迟开花的籽粒, 其发育米粒断面的裸露区域愈大, 胚乳结构愈是疏松, 复粒与单粒的体积愈小(图版III-3, 4, 7, 8), 心、背、腹部的结构差异愈不明显。籽粒胚乳结构部位间差异及粒位间差异显著, 最迟开花的穗下部二次枝梗第2、第3粒子房已膨大、淀粉已累积, 但其胚乳结构疏松。

图版III 花后15 d穗上不同部位籽粒胚乳结构
图1: 扬稻6号穗上部一次枝梗第1粒花后15 d背部; 图2: 扬稻6号穗上部一次枝梗第5粒花后15 d心部; 图3: 扬稻6号穗上部二次枝梗第2粒花后15 d背部; 图4: 扬稻6号穗下部一次枝梗第1粒花后15 d腹部; 图5: 武运粳24穗上部一次枝梗第5粒花后15 d心部; 图6: 图5籽粒腹部扁平细胞内胚乳; 图7: 武运粳24穗上部二次枝梗第2粒花后15 d胚乳; 图8: 武运粳24穗下部二次枝梗第2粒花后15 d胚乳。
Plate III Endosperm structure in the grains at different positions on a rice panicle at 15 d after flowering
Fig. 1: Endosperm structure of back of 1st grain on a primary branch at the upper parts on a panicle, at 15 d after flowering of Yangdao 6.Fig. 2: Endosperm structure of the center portion of 5th grain on a primary branch at the upper parts on a panicle, at 15 d after flowering of Yangdao 6. Fig. 3: Endosperm structure of back of 2nd grain on a secondary branch at the upper parts on a panicle, at 15 d after flowering of Yangdao 6. Fig. 4: Endosperm structure of belly of 1st grain on a primary branch at the lower parts on a panicle, at 15 d after flowering of Yangdao 6. Fig. 5: Endosperm structure of the center portion of 5th grain on a primary branch at the upper parts on a panicle, at 15 d after flowering of Wuyunjing 24. Fig. 6: Endosperm structure of belly of 1st grain on a primary branch at the upper parts on a panicle, at 15 d after flowering of Wuyunjing 24. Fig. 7: Endosperm structure of 2nd grain on a secondary branch at the upper parts on a panicle, at 15 d after flowering of Wuyunjing 24. Fig. 8: Endosperm structure of 2nd grain on a secondary branch at the lower parts on a panicle, at 15 d after flowering of Wuyunjing 24.

2.1.4 花后20 d胚乳结构 穗上、中部较早开花籽粒发育米粒的断面与花后15 d的较为相似, 仅与糊粉层相邻的极小区域呈完全裸露态且裸露处可见细胞轮廓, 约2~3层细胞。此时糊粉层细胞活跃, 其内积累了大量的糊粉粒, 背部淀粉体排列较紧密, 有的因相互嵌挤而呈多面体形态, 复粒大小约17.4 μ m, 最大的达23.5 μ m, 最小的约6.21 μ m (图版IV-1, 2, 5)。淀粉体中淀粉粒呈多面体态这是排列紧密、间隙小的形态学表现, 但仍有至少0.35 μ m间隙。心部也较为紧密(图版IV-6), 膜性结构等胚乳细胞退化残迹较多, 但腹部仍疏松(图版IV-3)。穗上愈是迟开花的籽粒, 其发育米粒断面的裸露区域愈大, 胚乳结构愈疏松(图版IV-4, 7, 8), 复粒与单粒的体积愈小, 心背腹部的结构差异愈明显。胚乳结构穗上部位间差异及粒位间差异显著, 最迟开花的穗下部二次枝梗第2、第3粒胚乳结构仍最疏松。

图版IV 花后20 d穗上不同部位籽粒胚乳结构
图1: 扬稻6号穗上部一次枝梗第5粒花后20 d背部; 图2: 扬稻6号穗中部二次枝梗第1粒花后20 d背部; 图3: 扬稻6号穗中部二次枝梗第1粒花后20 d腹部; 图4: 扬稻6号穗下部二次枝梗第1粒花后20 d背部; 图5: 武运粳24穗上部一次枝梗第1粒花后20 d背部; 图6: 武运粳24穗上部一次枝梗第1粒花后20 d心部; 图7: 武运粳24穗中部一次枝梗第6粒花后20 d腹部; 图8: 武运粳24穗下部一次枝梗第4粒花后20 d腹部。
Plate IV Endosperm structure in the grains at different positions on a rice panicle at 20 d after flowering
Fig. 1: Endosperm structure of back of 5th grain on a primary branch at the upper parts on a panicle, at 20 d after flowering of Yangdao 6. Fig. 2: Endosperm structure of back of 1st grain on a secondary branch at the mid parts on a panicle, at 20 d after flowering of Yangdao 6. Fig. 3: Endosperm structure of belly of 1st grain on a secondary branch at the mid parts on a panicle, at 20 d after flowering of Yangdao 6. Fig. 4: Endosperm structure of back of 1st grain on a secondary branch at the lower parts on a panicle, at 20 d after flowering of Yangdao 6. Fig. 5: Endosperm structure of back of 1st grain on a primary branch at the upper parts on a panicle, at 20 d after flowering of Wuyunjing 24. Fig. 6: Endosperm structure of the center of 1st grain on a primary branch at the upper parts on a panicle, at 20 d after flowering of Wuyunjing 24. Fig. 7: Endosperm structure of belly of 6th grain on a primary branch at the mid parts on a panicle, at 20 d after flowering of Wuyunjing 24. Fig. 8: Endosperm structure of belly of 4th grain on a primary branch at the lower parts on a panicle, at 20 d after flowering of Wuyunjing 24.

2.1.5 花后25 d胚乳结构 上部穗一次枝梗第5、第6粒发育米粒断面裸露的细胞数目、位置不定, 各处细胞轮廓均明显, 背部和心部淀粉体排列紧密, 胚乳细胞退化残迹较多, 腹部淀粉体体积小, 排列不及背部和心部紧密, 心部淀粉体虽小但排列紧密(图版V-5~7), 穗上部一次枝梗上较早开花的强势粒腹部胚乳淀粉排列, 扬稻6号(图版V-1)的不及武运粳24(图版V-7)的紧密。穗上较迟开花的籽粒, 其各部位胚乳结构疏松, 复粒与单粒的体积小(图版V-2, 3, 8)。胚乳结构穗上部位间差异及粒位间差异显著, 最迟开花的穗中、下部二次枝梗第2、第3粒发育米粒断面为完全裸露态, 胚乳结构仍最疏松, 淀粉体体积小、间隙大且相互粘连(图版V-4), 这会阻碍后续灌浆物质的进入。较迟开花的穗中部二次枝梗第4粒穗下部一次枝梗第2、第3、第4粒胚乳心部与腹部结构疏松, 且淀粉粒上约有161.3 nm的小孔洞(图版V-3)。

图版V 花后25 d穗上不同部位籽粒胚乳结构
图1: 扬稻6号穗上部一次枝梗第1粒花后25 d腹部; 图2: 扬稻6号穗中部二次枝梗第2粒花后25 d背部; 图3: 扬稻6号穗中部二次枝梗第4粒花后25 d心部; 图4: 扬稻6号穗下部二次枝梗第2粒花后25 d胚乳; 图5: 武运粳24穗上部一次枝梗第7粒花后25 d心部; 图6: 武运粳24穗上部一次枝梗第7粒花后25 d背部; 图7: 武运粳24穗上部一次枝梗第7粒花后25 d腹部; 图8: 武运粳24穗中部一次枝梗第4粒花后25 d腹部。
Plate V Endosperm structure in the grains at different positions on a rice panicle at 25 d after flowering
Fig. 1: Endosperm structure of belly of 1st grain on a primary branch at the upper parts on a panicle, at 25 d after flowering of Yangdao 6. Fig. 2: Endosperm structure of back of 2nd grain on a secondary branch at the mid parts on a panicle, at 25 d after flowering of Yangdao 6. Fig. 3: Endosperm structure of the center of 4th grain on a secondary branch at the mid parts on a panicle, at 25 d after flowering of Yangdao 6. Fig. 4: Endosperm structure of 2nd grain on a secondary branch at the lower parts on a panicle, at 25 d after flowering of Yangdao 6. Fig. 5: Endosperm structure of the center of 7th grain on a primary branch at the upper parts on a panicle, at 25 d after flowering of Wuyunjing 24. Fig. 6: Endosperm structure of back of 7th grain on a primary branch at the upper parts on a panicle, at 25 d after flowering of Wuyunjing 24. Fig. 7: Endosperm structure of belly of 7th grain on a primary branch at the upper parts on a panicle, at 25 d after flowering of Wuyunjing 24. Fig. 8: Endosperm structure of belly of 4th grain on a primary branch at the mid parts on a panicle, at 25 d after flowering of Wuyunjing 24.

2.1.6 花后30~35 d至成熟 此期胚乳结构穗上不同部位、不同粒位间差异进一步缩小。穗上早开花的籽粒, 如上部穗一次枝梗第5、第6粒, 其背部的淀粉体排列愈加紧密甚至粘连, 细胞残迹明显减少, 心部也常常结构致密直至粘连, 腹部的淀粉粒无论单粒或复粒, 体积较前又有所增大, 相互间隙由较疏松渐趋紧密。穗上迟开花的籽粒, 各部位胚乳结构由疏松变紧密。总体上, 籼稻扬稻6号与粳稻武运粳24在灌浆过程中胚乳结构的变化趋势基本一致, 但武运粳24胚乳结构的发育要稍滞后于扬稻6号, 开花30 d后两品种间的差距才基本消失。

成熟期籽粒胚乳结构, 中部二次枝梗上迟开花的弱势籽粒的心部或腹部胚乳结构较为紧密, 但淀粉粒粒径差异较大(图版VI-2, 3), 尤其是下部二次枝梗上迟开花的弱势籽粒的心部或腹部或心腹部常常可见疏松胚乳结构, 如图版VI-8 (武运粳24)和图版VI-4 (扬稻6号)。一次枝梗上迟开花的弱势籽粒的腹部小淀粉体较多, 与背、心部比, 排列略显疏松, 淀粉体粒径差异大, 以中、下部一次枝梗第2粒最明显(图版VI-6)。其余籽粒胚乳结构均较紧密(图版VI-5, 7), 籽粒各部位的胚乳结构差异也不显著。常见因胚乳充实良好淀粉体排列紧密、嵌挤以至粘连的情形(图版VI-1)。

图版VI 成熟期穗上不同部位籽粒胚乳结构
图1: 扬稻6号穗中部一次枝梗第1粒成熟期背部; 图2: 扬稻6号穗中部二次枝梗第2粒成熟期背部; 图3: 扬稻6号穗中部二次枝梗第3粒成熟期腹部; 图4: 扬稻6号穗下部二次枝梗第3粒成熟期心部; 图5: 武运粳24穗上部一次枝梗第2粒成熟期心部; 图6: 武运粳24穗中部一次枝梗第2粒成熟期腹部; 图7: 武运粳24穗中部一次枝梗第5粒成熟期腹部; 图8: 武运粳24穗下部二次枝梗第2粒成熟期腹部。
Plate VI Endosperm structure in the grains at different positions on a rice panicle at maturity
Fig. 1: Endosperm structure of back of 1st grain on a primary branch at the mid parts on a panicle, at maturity of Yangdao 6. Fig. 2: Endosperm structure of back of 2nd grain on a secondary branch at the mid parts on a panicle, at maturity of Yangdao 6. Fig. 3: Endosperm structure of belly of 3rd grain on a secondary branch at the mid parts on a panicle, at maturity of Yangdao 6. Fig. 4: Endosperm structure of the center of 3rd grain on a secondary branch at the lower parts on a panicle, at maturity of Yangdao 6. Fig. 5: Endosperm structure of the center of 2nd grain on a primary branch at the upper parts on a panicle, at maturity of Wuyunjing 24. Fig. 6: Endosperm structure of belly of 2nd grain on a primary branch at the mid parts on a panicle, at maturity of Wuyunjing 24. Fig. 7: Endosperm structure of belly of 5th grain on a primary branch at the mid parts on a panicle, at maturity of Wuyunjing 24. Fig. 8: Endosperm structure of belly of 2nd grain on a secondary branch at the lower parts on a panicle, at maturity of Wuyunjing 24.

2.2 结实期干湿交替灌溉对水稻产量的影响

干湿交替灌溉对产量的影响因干的程度不同而有较大差异(表1)。无论是大田试验还是土培池试验, 均以轻干-湿灌溉(T1)的产量最高, 显著高于水层灌溉(CK)和重干-湿灌溉(T2)。重干-湿灌溉的产量显著低于CK。

表1 结实期干湿交替灌溉对水稻产量及其构成的影响 Table 1 Effect of alternate wetting and drying irrigation during grain filling on grain yield and its components of rice

由于本试验是在抽穗期才进行水分处理, 因此干湿交替灌溉对穗数和每穗粒数均无显著影响, 不同处理间产量的差异主要是由结实率和粒重的不同所造成的。即, 与CK相比, 轻干-湿灌溉显著提高了结实率和粒重, 重干-湿灌溉处理减产主要是由于结实率的降低, 两个品种的趋势一致(表1)。

2.3 结实期干湿交替灌溉对籽粒胚乳结构的影响

运用扫描电镜观察成熟稻米胚乳结构(图版VII)表明, 在轻干-湿交替灌溉方式下, 穗下部籽粒胚乳结构明显改进, 表现为籽粒的背部、心部和腹部各部位淀粉体排列更紧密(VII-2, 5), 背部嵌挤甚至粘连; 重干-湿交替灌溉方式下, 则会使稻米胚乳结构变差(VII-3, 6), 表现为淀粉体排列疏松, 体积减小, 粒径差异增大, 淀粉体相互间隙增大。同时, 灌溉方式对胚乳结构的这种改变因粒位而异, 以穗下部二次枝梗籽粒的腹部最显著, 2个品种的趋势一致(图版VIII)。

图版VII 结实期干湿交替灌溉对籼稻扬稻6号稻米胚乳结构的影响
图1: 对照组基部一次枝梗籽粒腹部; 图2: T1处理组基部一次枝梗籽粒腹部; 图3: T2处理组基部一次枝梗籽粒腹部; 图4: 对照组基部二次枝梗籽粒腹部; 图5: T1处理组基部二次枝梗籽粒腹部; 图6: T2处理组基部二次枝梗籽粒腹部; 图7: 对照组顶部二次枝梗籽粒背部; 图8: T2处理组顶部二次枝梗籽粒背部。
Plate VII Effect of alternate wetting and drying irrigation on the endosperm structure of the indica cultivar Yangdao 6
Fig. 1: Endosperm structure of belly of grain on a primary branch at the lower parts on a panicle, under CK (shallow water layer). Fig. 2 Endosperm structure of belly of grain on a primary branch at the lower parts on a panicle, under T1 (alternate wetting and moderate drying (WMD)). Fig. 3: Endosperm structure of belly of grain on a primary branch at the lower parts on a panicle, under T2 (alternate wetting and severe drying (WSD)). Fig. 4: Endosperm structure of belly of grain on a secondary branch at the lower parts on a panicle, under CK. Fig. 5: Endosperm structure of belly of grain on a secondary branch at the lower parts on a panicle, under T1. Fig. 6: Endosperm structure of belly of grain on a secondary branch at the lower parts on a panicle, under T2. Fig. 7: Endosperm structure of back of grain on a secondary branch at the upper parts on a panicle, under CK. Fig. 8: Endosperm structure of back of grain on a secondary branch at the upper parts on a panicle, under T2.

图版VIII 结实期干湿交替灌溉对粳稻武运粳24稻米胚乳结构的影响
图1: 对照组基部一次枝梗籽粒背部; 图2: T1处理组基部一次枝梗籽粒背部; 图3: T2处理组基部一次枝梗籽粒背部; 图4: 对照组基部一次枝梗籽粒腹部; 图5: T1处理组基部一次枝梗籽粒腹部; 图6: T2处理组基部一次枝梗籽粒腹部; 图7: 对照组基部二次枝梗籽粒背部; 图8: T2处理组基部二次枝梗籽粒背部。
Plate VIII Effect of alternate wetting and drying irrigation on the endosperm structure of the japonica cultivar Wuyunjing 24
Fig. 1: Endosperm structure of back of grain on a primary branch at the lower parts on a panicle, under CK (shallow water layer). Fig. 2: Endosperm structure of back of grain on a primary branch at the lower parts on a panicle, under T1 (alternate wetting and moderate drying (WMD)). Fig. 3: Endosperm structure of back of grain on a primary branch at the lower parts on a panicle, under T2 (alternate wetting and severe drying (WSD)). Fig. 4: Endosperm structure of belly of grain on a primary branch at the lower parts on a panicle, under CK. Fig. 5: Endosperm structure of belly of grain on a primary branch at the lower parts on a panicle, under T1. Fig. 6: Endosperm structure of belly of grain on a primary branch at the lower parts on a panicle, under T2. Fig. 7: Endosperm structure of back of grain on a secondary branch at the lower parts on a panicle, under CK. Fig. 8: Endosperm structure of back of grain on a secondary branch at the lower parts on a panicle, under T2.

3 讨论

稻米品质与籽粒灌浆过程密切相关, 籽粒灌浆过程即稻米品质的形成过程, 在此过程中, 以细胞为单位, 发生着一系列复杂的生物化学变化和结构变化。籽粒间灌浆过程的不同导致其胚乳结构不同, 因而导致其相互间米质的差异, 其结果导致稻米粒间品质差异[23]。因此, 稻米品质改良不仅仅是品质性状的总体水平问题, 而且其粒间品质差异也不应被忽视[17, 18]。过去对于胚乳细胞内结构的变化仅限于对个别品种的观察[9], 或仅限于强、弱势粒结构形成的比较研究[18]。本试验则系统研究了穗上不同部位、不同粒位籽粒灌浆过程中胚乳淀粉结构形成过程的差异, 这是前人研究未涉及的。本研究结果表明, 胚乳结构的形态建成顺序表现为上部穗籽粒早于中部穗早于下部穗籽粒, 一次枝梗籽粒早于二次枝梗籽粒, 这与穗上颖花开花的日序一致, 也与水稻穗上籽粒碾米品质、垩白等品质性状在粒间的差异基本一致[12, 20, 21, 22]。说明缩小穗上粒间胚乳淀粉结构的差异, 促进穗上迟开花特别是基部二次枝梗籽粒的胚乳淀粉发育, 改善这些籽粒的胚乳淀粉结构是获取水稻高产优质的重要途径。

籼稻和粳稻是普通栽培稻的2个亚种。在通常情况下, 籼稻的支链淀粉含量较低, 粳稻的支链淀粉含量较高[23]。王忠[24]观察到, 稻米胚乳淀粉粒的形态与其支链淀粉含量有密切关系, 一般支链淀粉含量低的品种淀粉粒棱角较锐, 淀粉体充实较好。本研究表明, 在胚乳淀粉发育的早期, 籼稻品种和粳稻品种的籽粒胚乳结构有一定差异, 胚乳淀粉发育以籼稻较早较快, 粳稻较迟较慢; 胚乳淀粉粒以籼稻较大较整齐, 粳稻较小差异较大。较早的研究认为, 籼稻胚乳淀粉发育前期有复粒, 粳稻则没有复粒[25, 26]。但近年的研究表明, 粳稻胚乳发育早期的淀粉粒也是复粒[27, 28]。前后观察结果的不一致, 可能与电子显微镜的分辨率和观察倍数有关: 因粳稻胚乳发育前期的淀粉粒小, 早期的电子显微镜分辨率较低, 不易辨认出复粒; 现在的电子显微镜分辨率较高, 提高观察倍率可分辨出复粒淀粉。但以上研究, 仅是对少数籼、粳稻品种的研究, 今后需要对更多的籼稻和粳稻品种进行观察, 以进一步明确其胚乳淀粉结构的发育特征。

水分是调控水稻产量和品质的重要因子。一些研究者[29, 30, 31, 32]指出, 结实期土壤水势控制在-15 kPa时, 稻米的加工品质和食味品质得到改善, 当土壤水势控制在-30 kPa时, 稻米的多数品质指标变劣, 并建议将土壤水势-15 kPa作为结实期水稻节水灌溉的低限指标。董明辉等[33]指出, 灌浆期土壤轻度落干(土壤水势在-15~ -30 kPa ) 有利于稻米品质的改善。Zhang等[34]观察到, 水稻灌浆期的低限土壤水势在-25 kPa时复水灌溉, 可以增加根系细胞分裂素的产生, 进而促进籽粒灌浆, 增加粒重。但有关干湿交替灌溉对稻米胚乳淀粉结构影响的研究, 尚未见报道。本研究表明, 无论在土培池试验还是大田试验, 当干湿交替灌溉的低限土壤水势为-20 kPa时, 结实率和千粒重明显较保持水层灌溉的CK提高, 胚乳结构显著改善; 当干湿交替灌溉的低限土壤水势为-40 kPa时, 胚乳淀粉结构会明显变差。说明轻干-湿交替灌溉可以改进穗下部籽粒胚乳结构, 而重-干湿交替灌溉则会劣化胚乳淀粉结构。综合本研究结果和以往他人研究结果, 建议将-20 kPa作为水稻结实期改善胚乳淀粉结构的低限土壤水势指标。但是否可作为水稻优质灌溉的指标, 有待深入研究。

4 结论

水稻穗上不同部位和不同粒位籽粒胚乳结构形成与花后天数有密切关系, 上部穗籽粒早于中部穗籽粒更早于下部穗籽粒, 一次枝梗籽粒早于二次枝梗籽粒, 穗上早开花的籽粒早于迟开花的籽粒, 并因籼、粳稻品种不同而有一定差异, 粳稻品种的胚乳结构发育迟于籼稻品种。结实期轻干-湿交替灌溉可以改善穗下部籽粒胚乳结构, 对穗上部籽粒胚乳结构影响很小, 重干-湿交替灌溉则会使胚乳淀粉结构变差。灌浆期土壤水势-20 kPa可作为改善水稻籽粒胚乳淀粉结构的节水灌溉的低限指标。

The authors have declared that no competing interests exist.

作者已声明无竞争性利益关系。

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