It is important in the long term to explore and exploit the potential of plant traits contributing to the nitrogen (N) absorption efficiency of rice. Root is primary organ for rice to explore and utilize N nutrient. However, little knowledge is known about the relationship between N accumulation and rice root traits. A solution culture experiment was conducted in 2001 and 2002, using eighty eight and one hundred and twenty two conventional indica rice varieties, respectively. A total of 13 traits responsible for morphology and physiological activity of rice roots was measured at heading stage while dry matter accumulation and N accumulation were determined both at heading and maturity. The tested rice varieties were classified into 6 types based on their N accumulation at maturity by the MinSSw method, and the differences of root traits between the types were analyzed to investigate the main root traits that significantly affected the N accumulation level. The average N accumulation of different types of rice varieties varied significantly, from 10.40 to 25.13 g·m^-2 in 2001, and from 8.53 to 33.31 g·m^-2 in 2002, respectively. Both whole growth duration and N uptake per day significantly affected N accumulation at maturity with the determinant coefficient ranged from 0.960 to 0.996, and the latter was more important than the former. N accumulation was closely correlated to number of adventitious roots per plant, root dry weight per plant, total length of adventitious roots per plant, total root absorption area per plant, root active absorption area per plant and total α-NA oxidizing amount of roots per plant, other than the traits for single adventitious root or root activity per unit dry weight. Polynomial stepwise regression analysis showed that N accumulation at maturity was significantly influenced by root dry weight per plant, ratio of shoot to root, number of adventitious roots per plant and total length of adventitious roots per plant (R²＝0.429－0.591). Morphological and physiological evidence in this study provided some prospects for improvement of root traits to improve N accumulation in indica rice.

2001和2002年，在群体水培条件下，分别以国内外不同年代育成的籼稻代表品种88个和122个为材料，测定植株的干物重、全氮含量以及13个有关根系性状，采用组内最小平方和的动态聚类方法对供试籼稻品种成熟期的氮素累积量进行聚类，分析不同氮素累积量类型籼稻品种根系有关性状的差异以及影响籼稻品种氮素累积量的主要根系性状。结果表明：(1) 供试籼稻品种成熟期氮素累积量差异很大，2001年A、B、C、D、E、F类籼稻品种的氮素累积量分别为10.40、13.47、16.17、18.50、20.72、25.13 g·m^-2，2002年分别为8.53、12.44、15.80、19.87、25.15、33.31 g·m^-2，类型间的差异均达显著水平；（2）全生育期天数和每日氮素吸收量对品种成熟期氮素累积量均有显著影响（R²= 0.960～0.996），并且后者显著大于前者；（3）成熟期氮素累积量与单株不定根数、单株根干重、单株不定根总长、单株根系总吸收面积、单株根系活跃吸收面积、单株根系α-NA氧化量等全株根系性状关系密切，与单条不定根长、单条不定根粗、单条不定根重等单条不定根性状和单位干重根系总吸收面积、单位干重根系活跃吸收面积等单位干重根系活性指标关系不密切；（4）多元逐步回归分析表明，单株根干重、冠根比、单株不定根数和单株不定根总长是影响籼稻品种氮素累积量的主要根系性状（R²=0.429～0.591）。

Nitrogen is the most important input required in rice production although over use of N causes so many environment problems. It is well known that N use efficiency is varied in different rice genotypes. Therefore, it is important to explore and exploit the potential contributing to the N use efficiency. As an integral part of plant organs, rice root plays an important role in absorption and utilization of N from soil and fertilizer. In this research, a field experiment with 225 kg ha-1 N fertilizer application was carried out in 2006 on the farm of Yangzhou University, Jiangsu province, China. A total of 12 rice genotypes ( 6 N-efficient and 6 N-inefficient ) selected from 120 rice cultivars grown in Yangzhou during 2004 and 2005 were adopted to investigate the charac-teristics of root morphology and physiology in rice types with different N use efficiencies. Relationship between N use efficiency and indexes of root morphology and physiology was also analyzed. The results showed that at different growth stages, the indexes of root morphology and physiology including the root dry weight, root volume, total absorbing surface area of root, active absorbing surface area of root, ratio of active absorbing surface area to total absorbing surface area in N efficient rice type were obviously higher than those in N inefficient rice type. At the critical stage of productive tillering and the stage of elongating, the ratio of root to shoot in N efficient rice type was significantly higher than that in N inefficient rice type while the trend was con-trary at the stages of heading and maturing. Before the stage of maturing, the root oxidation ability of α-NA in N efficient rice type was superior to that in N inefficiency rice type while at the stage of maturing the root oxidation ability of α-NA in N efficient hybrid rice was appreciably lower than that in some N efficient rice cultivars. N use efficiency positively correlated to all the above morphological and physiological indices at all growth stages, with the exception of negatively correlation to the ratio of root to shoot at the stage of heading and maturing. It could be concluded that the root morphology is good and the root is vigorous in N efficient rice type, its morphological and physiological characteristics ensures the efficient absorption and utilization of N in all its life, and proper ratio of root to shoot and the harmonious growth of root and shoot can also improve the efficiency of N absorption and utilization.

Abstract

This study was designed to elucidate the relationship between root chemical signals and the quality of rice. Various rice genotypes were used. Zeatin (Z) + zeatin riboside (ZR), abscisic acid (ABA), 1-aminocylopropane -1-carboxylic acid (ACC), and organic acids in roots during grain filling and the appearance quality, cooking/eating quality were investigated. The correlations among them were analyzed. The results showed that Z + ZR concentrations in the roots at mid- and late-grain-filling stages were significantly and positively correlated with the gel consistency and alkali spreading value (r = 0.72^* – 0.90^**), whereas negatively correlated with the amylose content (r = −0.68^* – −0.78^**). ABA concentrations in roots at mid-grain-filling stage were significantly and negatively correlated with the gel consistency and alkali spreading value (r = −0.90^** – −0.91^**), and positively correlated with the amylose content (r = 0.87^**). ACC concentrations in root exudates at mid-grain-filling stage were very significantly correlated with the percentage of chalky grains and chalkiness (r = 0.97^** − 0.98^**), and those at late-grain-filling stage were significantly correlated with chalkiness and chalky size (r = 0.69^* −0.96^**). The more the malic acid and succinic acid exuded from roots for a cultivar, the greater the breakdown values and the smaller the setback values in the starch profile, and the results were reversed for a cultivar with more tartaric acid and citric acid exuded from roots during the grain-filling period. The cultivar with more lactic acid in exudates had smaller gel consistency and alkali spreading values, but had greater amylose content. When roots were treated with exogenous ZR, ABA, and ACC during grain filling, effects of the chemicals on the rice quality were consistent with the relationships of the endogenous hormones (Z + ZR, ABA, and ACC) with the quality indexes. Using rape cake as organic fertilizer can increase the concentrations of malic acid and succinic acids exuded from roots as well as the breakdown value in starch profile and reduce the setback value. The results suggest that root chemical signals play important roles in the formation of rice quality, and rice quality could be improved through regulating the signals.

Cultivars of early rice with heat resistance: Nongda 228 and 082, and those with heat sensitivity: Molizhan and Xeiqingzao B were used to study the ATPase activity of plasma membrane and NH₄⁺ absorption rate in roots under high temperature stress. The results indicated that under high temperature stress, H⁺-ATPase and Ca²⁺-ATPase activities of plasma membrane were increased in roots of Nongda 228 and 082 while declined in roots of Molizhan and Xeiqingzao B, with significant differences between them by Duncan’s method test. The protein content in all cultivars declined under high temperature stress. The NH₄⁺ absorption rate had no change in the cultivars with heat resistance but declined in the cultivars with heat sensitivity under high temperature.

The objective of this study was to quantitatively analyze the change patterns of rice root morphological characteristics based on image analysis method in pot experiments with different nitrogen rates, water regimes, and rice cultivars in different years. WinRhizo software (WR) was used as the root image analysis tool, and two modes of LM and T200 were used to measure the root diameter and adventitious root length under two ranges of root diameter as 0–0.30 mm and 0.25–1.80 mm, respectively. The measurement results from WR were compared with those from Image-Pro Plus 6.0 software (IP). Then, the diameter ranges of different types of root were determined. On the basis of the dataset from WR, the statistical analysis were performed on rice root morphological characteristic indices, including dry weight, total volume, total surface area, total adventitious root length and number per plant at different growth stages. The results were as follows: (1) The average NRMSEs between WR (LM and T200) and IP for root diameters were 5.44% and 10.95%. (2) The diameter range of fine lateral root was circumscribed within 0.03–0.10 mm for all the experiments, coarse lateral and adventitious root were circumscribed within 0.10-0.30 and 0.30-1.40 mm for V1 (Nipponbare) and V2 (Wuxiangjing 14), but 0.10–0.25 and 0.25–1.65 mm for V3 (Yangdao 6). Following this method, the NRMSEs for adventitious root length measured by WR and IP were 10.78%–12.01%. (3) All indices increased rapidly in the growth process and reached or approached the maximum at heading, then increased slowly or decreased after heading. There were significant differences between treatments with different nitrogen rates from tillering to maturing on all indices. Increasing nitrogen rate accelerated the growth of roots, and especially enhanced the proportion of adventitious roots. Properly control of irrigation could promote the growth of roots and increase the proportion of lateral roots. All indices of V3 were significantly higher than these of other cultivars, and there were no significant differences between V1 and V2. The results indicated that it was feasible to measure morphological indices of different types of rice root by WR with different modes, and the methods used in this paper have a good accuracy and reliability. These results could provide a support for the quantitative analysis on root morphology of rice or other crops.

利用图像分析方法定量研究水稻根系形态特征指标的变化规律。通过实施不同水氮处理和不同品种的水稻桶栽试验，选用WinRhizo (WR)软件的不同模式(LM和T200)分析根系图像，分别提取根直径范围0~0.30 mm和0.25~1.80 mm的根系形态数据，并与基于Image-Pro Plus 6.0软件(IP)的根直径和不定根长的测量结果进行比较分析；确定了3种水稻品种不同类型根直径的范围；对不同生育时期水稻根长、根体积、根表面积、根系干重和不定根数量等水稻根系形态特征指标变化差异，以及分枝特征进行了分析。结果表明：(1)基于WR软件LM和T200模式下的根直径测量结果与基于IP软件的测量结果之间NRMSE分别为5.44%和10.95%。(2)界定细分枝根直径范围为0.03~0.10 mm，扬稻6号(V3)粗分枝根和不定根分别为0.10~0.30 mm和0.30~1.65 mm，而日本晴(V1)和武香粳14(V2)分别为0.10~0.25 mm和0.25~1.40 mm，不定根长与IP测量结果进行比较，其NRMSE为10.78%~12.01%。(3)各指标抽穗前增长迅速，之后增长减缓或衰老下降；不同氮肥处理间各指标分蘖至成熟均差异显著，增施氮肥可促进根系生长，明显提高不定根比例；适当控水可促进根系生长，明显提高分枝根比例；品种V3自分蘖期到成熟期各指标均显著高于V1和V2，V1与V2间差异不显著。本研究表明，本方法具有较好的精度和可行性，为推进水稻或其他作物根系的定量研究提供了参考。

【Objective】 The goal of the research is to analyze the characteristics of root traits in conventional indica rice cultivars with large sink potential (SP). 【Method】 88 and 122 conventional indica rice cultivars were solution-cultured in 2001 and 2002, respectively. Dry matter weight (including root system, culm and sheath, leaves, panicle), root traits, root physiological activity, yield and its components were measured. The tested rice cultivars were classified into 6 types (i.e. A, B, C, D, E and F, A was the lowest, and F was the highest) based on their SP level by the MinSSw method, to study their differences of root traits, root physiological activity. 【Result】 Difference of SP of the cultivars used in this study was very large, the averages SP of A, B, C, D, E, and F were 426.37, 642.53, 770.96, 903.73, 1 064.32, 1 213.90 g?m-2 in 2001, and 359.36, 574.11, 764.98, 962.43, 1 200.11, 1 455.59 g?m-2 in 2002, respectively. The number of adventitious roots per unit area, total length of adventitious roots per unit area and root dry weight per unit area in large SP type variety was higher than that in small SP type variety, no significant differences of traits per adventitious and per unit root dry weight between different SP type cultivars were observed. Polynomial regression analysis showed that SP level was significantly influenced the length of adventitious roots per unit area, root dry weight per unit area, ratio of shoot to root at heading stages, root activity per unit area, and the determinant coefficient ranged from 0.423-0.578. Large SP could be reached by increasing the length of adventitious roots per unit area, dry weight per unit area, ratio of shoot to root at heading stage, root activity per unit area. 【Conclusion】 Root traits per unit area in large SP type variety are higher than that in small SP type variety, larg SP could be reached by increasing the length of adventitious roots per unit area, root dry weight per unit area, ratio of shoot to root at heading stages, root activity per unit area.

【目的】明确大库容量类型水稻品种根系性状的特征,为大库容量品种的根系遗传改良提供参考依据。【方法】在群体水培条件下,以国内、外不同年代育成的常规籼稻代表品种(2001年为88个、2002年为122个)为材料,测定干物重(包括根系)、根系性状和根系活性、产量及其构成因素等,采用组内最小平方和的动态聚类方法将供试品种按库容量从低到高依次分为A、B、C、D、E、F 6类,研究各类品种根系的基本特点。【结果】供试品种间库容量的差异很大(426%、817%)。A、B、C、D、E、F类品种的平均库容量,2001年分别为426.37、642.53、770.96、903.73、1 064.32、1 213.90 g?m-2,2002年分别为359.36、574.11、764.98、962.43、1 200.11、1 455.59 g?m-2;大库容量籼稻品种单位面积不定根数、不定根总长、根干重显著大于小库容量籼稻品种,但不同库容量类型品种间每条不定根性状、单位根重等根系性状差异不显著;多元回归分析表明,显著影响单位面积库容量的主要根系性状是单位面积不定根长、单位面积根干重、抽穗期冠根比和单位面积根系活性,决定系数为0.423～0.578。随着单位面积不定根长、单位面积根干重、抽穗期冠根比、单位面积根系活性的提高单位面积库容量显著增加。【结论】大库容量籼稻品种单位面积根系性状大于小库容量类型品种,单位面积不定根长、单位面积根干重、抽穗期冠根比、单位面积根系活性是显著影响单位面积库容量的主要根系性状。

Eighty-eight and one hundred and twenty two conventional indica rice cultivars were solution-cultured in 2001 and 2002, respectively. Dry matter weight (including root system, culm and sheath, leaves, panicle), root traits, root physiological activity, yield and its components were measured.The tested rice cultivars were classified into six types (i.e. A, B, C, D, E, and F, A was the lowest, and F was the highest) based on their panicle weight level by the MinSSw method, to study their differences of root traits, root physiological activity. Difference of panicle weight of the cultivars used in this study was very large (the ratio of the maximalpanicle weight to the minimumpanicle weight in 2001 and 2002 were 493% and 764%, respectively), the average of panicle weight was0.99, 1.56, 2.00, 2.54, 3.16, and 4.08 grams per panicle in 2001, and0.82, 1.38, 1.80, 2.38, 3.04, and 4.29 grams per paniclein 2002,respectively.Root dry weight per plant, total length of adventitious roots per plant, and total root absorption area per plantin large-panicle type cultivars higher than those in small-panicle type cultivars.Number of adventitious roots per panicle, root dry weight per panicle, length of adventitious roots per panicle, total root absorption area per panicle, root active absorption area per panicle, and root activity per paniclein large-panicle type cultivars were higher than those in small-panicle type cultivars. Polynomial regression analysis showed that panicle weight was significantly influenced by length of adventitious roots per panicle, root dry weight per panicle,ratio of shoot to root at heading stage,root activity per panicle,and the determinant coefficient ranged from 0.620 to 0.639. Largerpanicle weight could be reached by increasinglength of adventitious roots per panicle, root dry weight per panicle,ratio of shoot to root at heading stage,root activity per panicle.

在群体水培条件下，以国内、外不同年代育成的常规籼稻代表品种(2001年为88个、2002年为122个)为材料，测定干物重(包括根系)、根系性状和根系活性、产量及其构成因素等，采用组内最小平方和的动态聚类方法将供试品种按单穗重从低到高依次分为A、B、C、D、E、F 6类，研究各类品种根系的基本特点。结果表明，供试品种间单穗重的差异很大(两年分别相差493%和764%)，A、B、C、D、E、F类品种的平均单穗重，2001年分别为0.99、1.56、2.00、2.54、3.16、4.08 g，2002年分别为0.82、1.38、1.80、2.38、3.04、4.29 g。大穗型品种每株不定根总长、每株根干重、每株根系总吸收面积显著大于小穗型品种。大穗型品种每穗根数、每穗根重、每穗根长、每穗根系总吸收面积、每穗根系活跃吸收面积、每穗根系活性显著优于小穗型品种。多元回归分析表明，显著影响单穗重的主要根系性状是每穗根长、每穗根重、抽穗期冠根比、每穗根系总活力，决定系数为0.620~0.639。随着每穗根长、每穗根重、抽穗期冠根比、每穗根系总活力提高单穗重显著增加。

【Objective】 The root characteristics of C Liangyou rice combinations and the correlation between root characteristics and yield were studied. 【Method】 The root morphology, root physiology as well as the correlation between root characteristics and yield were studied by using seven C Liangyou rice combinations as experimental materials and Shanyou 63 as a control. 【Result】 The results showed that root dry weight, number of adventitious root , total length of adventitious root, total root volume, root growth abilities, total root absorption area,root active absorption area and root oxidation ability of the combination were significantly higher than those of the control Shanyou 63. Root dry weight, number of adventitious root , total length of adventitious root, total root absorption area,and root oxidation ability at the heading stage, and root growth abilities at the grain filling stage and the milking stage had a significant positive correlation with yield per plant. Stepwise regression indicated that the number of adventitious root and root oxidation ability at the heading stage were the main influencing factors of high yield of rice and could be regarded as reliable indicators for cultivation and management and genetic inprovement of rice. 【Conclusion】 It is concluded that root morphology is good and the root is vigorous in C Liangyou rice combinations at all stages, its morphological and physiological characteristics ensure the efficient absorption of nutrient and water in the whole growing period, which is the base leading to high yield of C Liangyou rice combinations. Strong root vigor at the late growing stage, and proper ratio of root to shoot and the harmonious growth of root and shoot are also the main causes leading to high yield of C Liangyou rice combinations.

【目的】揭示两系杂交水稻C两优系列组合的高产根系特征及根系与产量之间的关系。【方法】用两用核不育系C815S配制7个杂交组合,以汕优63为对照,对其根系形态和生理特性及其与产量的关系进行了研究。【结果】C两优系列组合的根系干重、不定根条数、不定根总长、根系总体积、发根力、根系总吸收面积、根系活跃吸收面积和根系a-NA氧化量显著高于对照汕优63。相关分析表明,抽穗期根系干重、不定根条数、不定根总长、根系总吸收面积、根系a-NA氧化量及灌浆期和乳熟期的发根力与单株产量呈极显著或显著正相关。逐步回归表明,抽穗期的不定根数量和根系a-NA氧化量是影响水稻高产的主要因素,可作为水稻高产栽培和水稻品种遗传改良的可靠指标。【结论】C两优系列杂交组合在整个生育期内比汕优63具有发达的根系和较强的根系活力,保证了其营养元素和水分的吸收,从而为高产奠定了基础。尤其是在生育后期仍保持较强的根系活力及地下部与地上部的和谐关系是其高产的重要原因。