水稻品质性状的遗传改良及其关键科学问题

改善稻米品质是水稻遗传改良及基础研究的重要目标。破解控制稻米重要品质性状形成的调控机制,对稻米品质改良和品种选育具有十分重要的意义。近十多年来,稻米品质功能基因组研究成果为其遗传改良提供了丰富的功能基因、有效的功能性分子标记及良好的改良策略。但是,稻米品质本身由多个性状构成,且各品质性状间、品质与产量性状间、品质与环境间均互相影响,极大地限制了稻米品质的遗传改良。因此,文中提出了未来水稻品质性状基础研究及遗传改良的六个关键科学问题。     

稻米品质形成的气候生态条件评价及我国地域分布规律

在多品种、多试点的田间分期播种和人工气候箱控温、遮光处理等试验的基础上,通过对影响稻米品质诸气候生态因子的相对重要程度及稻米品质形成与水稻灌浆结实期前30d的日均温度、日均太阳辐射间的关系进行分析,首先建立了稻米品质的温度评价函数,然后用分段法构建了稻米品质的日均太阳辐射量订正函数,将上述两式结合,则可得某一地稻米品质气候生存条件的综合评价函数。利用该公式,在全国选若干代表点计算其稻米品质的评价指标值,并以此为基础,分双季早籼、单季粳稻与双季早粳、双季晚粳4大类型描绘出我国不同气候生态条件下稻米品质的地域分布框架图。     

稻米淀粉品质形成的关键酶及其分子生物学研究进展

稻米淀粉的形成是影响水稻产量和品质的决定性因素之一。因此, 开展稻米淀粉形成过程中所涉及关键酶的研究是非常必要的。随着分子生物学技术的快速发展, 有关稻米淀粉品质的研究也越来越深入, 并取得了较大进展。该文对水稻淀粉品质形成过程中的关键酶及其分子生物学研究进展进行了较为详尽的综述, 主要包括ADP葡萄糖焦磷酸化酶、淀粉合成酶、淀粉分支酶和淀粉去分支酶等, 并对该领域的发展趋势进行了展望。     

稻米淀粉品质形成的关键酶及其分子生物学研究进展

稻米淀粉的形成是影响水稻产量和品质的决定性因素之一。因此,开展稻米淀粉形成过程中所涉及关键酶的研究是非常必要的。随着分子生物学技术的快速发展,有关稻米淀粉品质的研究也越来越深入,并取得了较大进展。该文对水稻淀粉品质形成过程中的关键酶及其分子生物学研究进展进行了较为详尽的综述,主要包括ADP葡萄糖焦磷酸化酶、淀粉合成酶、淀粉分支酶和淀粉去分支酶等,并对该领域的发展趋势进行了展望。     

稻米品质形成的生理基础研究进展

综述了水稻(Oryza sativa L)米质形成的生理基础的研究进展,主要包括稻米品质形成期的源库特征、淀粉合成的关键酶以及淀粉粒的形态、结构及其糊化特性等几个内容,从植物生理学角度来揭示稻米品质形成的规律有着重要的理论意义.     

稻麦两熟地区机插水稻品质形成的播期效应

合理播期是机插稻实现高产、优质稻米生产的关键技术。本文研究了播期对粳型超级稻和籼粳交水稻机插方式下稻米品质形成特征的影响,为机插稻高产、优质稻米生产提供依据。结果表明:稻米糙米率、精米率、整精米率随播期推迟而升高,碾米品质变优,但早播稻糙米产量、精米产量、整精米产量显著高于晚播稻(P0.05);不同播期的稻米垩白粒率、垩白度变异较大,均随播期推迟而下降,早播与晚播间差异达显著水平(P0.05);外观品质改善,推迟播期,稻米直链淀粉含量降低,胶稠度变短,峰值黏度、热浆黏度、最终黏度、崩解值呈规律性下降,消减值变化幅度较大,逐渐升高,糊化温度波动较小,RVA谱变劣,稻米蒸煮食味品质变差;稻米蛋白质含量及蛋白质产量均随播期推迟而下降(P0.05),营养品质变差;机插粳稻适期早播,易取得高的糙米、精米、整精米及蛋白质产量,提升营养品质及蒸煮食味品质,改善米粉RVA谱特征,但降低稻米碾米品质和外观品质。因此,麦茬机插稻于5月26—31日播种,是实现较优品质稻米较高产量的最佳时期。     

稻米品质的分子水平研究进展

随着分子生物学和各项技术的发展,稻米品质的研究取得了一些进展。从与稻米品质中的直链淀粉含量、胶稠度、垩白、糊化温度及碾磨品质有关的基因或QTL,ADP葡聚糖焦磷酸化酶、淀粉合成酶、分支酶及脱支酶在淀粉合成中的作用以及胚乳淀粉粒的形成、形态与结构等方面作了综述 。     

稻米外观品质性状遗传与分子定位研究进展

稻米外观品质主要是指稻米的粒形、垩白、透明度和籽粒色泽等,它不仅直接影响到人们的喜好,还与其他品质性状诸如蒸煮食用、加工等密切相关。因此,外观品质对稻米的商品价值有着十分重要的影响。本文从经典遗传与现代分子生物学两个方面对稻米主要外观品质的遗传研究进展进行了较全面的综述,包括粒长、粒宽、长宽比、粒厚、垩白、透明度和籽粒色泽等。综合近年来的遗传研究结果发现,大多数稻米外观品质性状都是由数量基因控制的。利用分子标记技术已将控制外观品质的QTL（qualitative trait locus）定位在不同的染色体上,为下一步的稻米外观品质改良提供了有利条件。     

转基因技术改良稻米淀粉品质的研究进展

淀粉是稻米胚乳的主要组成成分, 而淀粉含量和性质的差异又直接决定稻米的品质。早期关于稻米淀粉的研究局限于其组成成分、品种间含量的差异以及稻米淀粉合成的经典遗传学方面。随着现代分子生物学和转基因技术的发展, 稻米品质、淀粉的生物合成及其分子调控成为研究热点。随着淀粉合成相关基因的克隆、分子特性及其表达调控的研究取得了较大进展, 人们也开始尝试利用现代基因工程技术, 高效地改良稻米品质, 如提高或降低淀粉含量及改变支链淀粉的结构。本文从综述稻米淀粉的组成、结构和淀粉合成相关酶的研究进展入手, 探讨了转基因技术改良稻米品质的研究进展和发展前景。     

转基因技术改良稻米淀粉品质的研究进展

淀粉是稻米胚乳的主要组成成分,而淀粉含量和性质的差异又直接决定稻米的品质。早期关于稻米淀粉的研究局限于其组成成分、品种间含量的差异以及稻米淀粉合成的经典遗传学方面。随着现代分子生物学和转基因技术的发展,稻米品质、淀粉的生物合成及其分子调控成为研究热点。随着淀粉合成相关基因的克隆、分子特性及其表达调控的研究取得了较大进展,人们也开始尝试利用现代基因工程技术,高效地改良稻米品质,如提高或降低淀粉含量及改变支链淀粉的结构。本文从综述稻米淀粉的组成、结构和淀粉合成相关酶的研究进展入手。探讨了转基因技术改良稻米品质的研究进展和发展前景。     

水稻垩白的研究现状与改良策略

文章综合分析了水稻垩白与其他稻米品质性状的相关性、垩白形成机理、经典遗传以及分子遗传方面的国内外研究进展。表明垩白形成是一个复杂的生理过程, 与稻株“源-库”关系、籽粒灌浆动态以及胚乳内淀粉的合成与积累密切相关。垩白属于复杂的数量性状, 其遗传具有母体效应、胚乳效应以及细胞质效应, 还受环境条件的影响。在多条染色体上存在一些稳定表达的控制垩白性状的QTL, 其中3个与垩白形成相关的影响淀粉合成、淀粉代谢和果实发育的基因已被克隆。然而, 关于垩白的形成机制和调控网络目前仍不清楚。在育种实践中, 降低垩白仍是我国优质稻育种, 尤其是籼稻品质育种的主要目标之一。文章对今后稻米垩白的遗传研究方向及其改良措施进行了讨论。     

Effect of waxy rice flour and cassava starch on freeze-thaw stability of rice starch gels

Repeatedly frozen and thawed rice starch gel affects quality. This study investigated how incorporating waxy rice flour (WF) and cassava starch (CS) in rice starch gel affects factors used to measure quality. When rice starch gels containing 0-2% WF and CS were subjected to 5 freeze-thaw cycles, both WF and CS reduced the syneresis in first few cycles. However CS was more effective in reducing syneresis than WF. The different composite arrangement of rice starch with WF or CS caused different mechanisms associated with the rice starch gel retardation of retrogradation, reduced the spongy structure and lowered syneresis. Both swollen granules of rice starch and CS caused an increase in the hardness of the unfrozen and freeze-thawed starch gel while highly swollen WF granules caused softer gels. These results suggested that WF and CS were effective in preserving quality in frozen rice starch based products.     

FLOURY ENDOSPERM16 encoding a NAD‐dependent cytosolic malate dehydrogenase plays an important role in starch synthesis and seed development in rice

Starch is the most important form of energy storage in cereal crops. Many key enzymes involved in starch biosynthesis have been identified. However, the molecular mechanisms underlying the regulation of starch biosynthesis are largely unknown. In this study, we isolated a novel floury endosperm rice (Oryza sativa) mutant flo16 with defective starch grain (SG) formation. The amylose content and amylopectin structure were both altered in the flo16 mutant. Map‐based cloning and complementation tests demonstrated that FLO16 encodes a NAD‐dependent cytosolic malate dehydrogenase (CMDH). The ATP contents were decreased in the mutant, resulting in significant reductions in the activity of starch synthesis‐related enzymes. Our results indicated that FLO16 plays a critical role in redox homeostasis that is important for compound SG formation and subsequent starch biosynthesis in rice endosperm. Overexpression of FLO16 significantly improved grain weight, suggesting a possible application of FLO16 in rice breeding. These findings provide a novel insight into the regulation of starch synthesis and seed development in rice.     

Effect of high temperature on fine structure of amylopectin in rice endosperm by reducing the activity of the starch branching enzyme

Rice (Oryza sativa L.) grain quality is affected by the environmental temperature it experiences. To investigate the physiological molecular mechanisms of the effect of high temperatures on rice grain, a non-waxy indica rice was grown under two temperature conditions, (29/35 degrees C) and (22/28 degrees C), during the ripening stage in two phytotrons. The activities and gene expression of key enzymes for the biosynthesis of amylose and amylopectin were examined. The activity and expression levels of soluble endosperm starch synthase I were higher at 29/35 degrees C than that at 22/28 degrees C. In contrast, the activities and expression levels of the rice branching enzyme1, the branching enzyme3 and the granule bound starch synthase of the endosperm were lower at 29/35 degrees C than those at 22/28 degrees C. These results suggest that the decreased activity of starch branching enzyme reduces the branching frequency of the branches of amylopectin, which results in the increased amount of long chains of amylopectin of endosperm in rice grain at high temperature.     

Some properties of starch branching enzyme from indica rice endosperm (Oryza sativa L.)

Starch branching enzyme (α-1,4-glucan: α-1,4-glucan-6-glycosyl transferase; EC 2.4.1.18) catalyzes the formation of the α-1,6-bond in branched starch molecules such as amylopectin. Some characteristics of starch branching enzyme in rice endosperm (Oryza sativa L.) were determined because of the importance of starch structure for rice quality. Two or three peaks of starch branching enzyme activity were resolved by anion-exchange chromatography of extracts from high amylose rice. The properties of rice starch branching enzyme were similar to those found for the enzyme from other plant sources except for a much lower molecular weight. Rice branching enzyme had an apparent molecular weight of 40 000 as estimated by gel permeation chromatography. Multiple forms of starch branching enzyme could also be resolved in milled rice, suggesting that relationships between starch quality and characteristics of starch branching enzyme could be examined in the mature grain after harvest.