基于器官生物量构建植株形态的玉米虚拟模型

探讨了基于玉米器官生物量模拟其形态的方法,并应用2000年田间试验数据提取了玉米节间、叶鞘和叶片的形态构建参数。基于玉米虚拟模型生物量分配模块模拟的器官生物量积累和建立的形态构建方法与提取的参数,模拟了2001年玉米不同生长阶段的器官形态,模拟结果与田间试验数据吻合较好。应用本模型实现了玉米生长过程中植株各个器官形态变化以及植株高度、叶面积动态的模拟,并实现了植株形态的可视化。     

夏玉米叶片水分变化与光合作用和土壤水分的关系

叶片是光合作用的重要器官,其含水量的变化必将影响光合作用,但关于叶片水分变化对光合作用的影响报道较少。以华北夏玉米为研究对象,利用三叶期不同水分梯度的持续干旱模拟试验资料,分析夏玉米叶片水分变化及其与叶片净光合速率和土壤水分的关系。结果表明:夏玉米叶片净光合速率对叶片水分变化的响应显著且呈二次曲线关系,叶片含水量约为70.30%时,叶片净光合速率为零;叶片含水量与土壤相对湿度呈非直角双曲线关系,叶片最大含水量约为85.14%。研究结果可为准确描述叶片水分变化对光合作用的影响及客观辨识夏玉米干旱的发生发展及监测预警提供参考。     

气候变暖对华北平原玉米叶片形态结构和气体交换过程的影响

未来全球变暖对农田生态系统产生的影响不仅可能改变整个陆地生态系统的碳平衡状态,更重要的是还关系到全球的粮食安全问题。然而,目前有关农作物对全球变暖响应和适应性机理的研究还很少见,尤其是缺少通过农田原位增温实验探讨作物叶片形态结构及其气体交换过程对增温的响应和适应性机理的研究。利用典型农田生态系统的实验增温平台,研究了未来全球气候变暖对我国华北平原重要农作物玉米叶片的形态、结构特征(解剖及亚显微结构)以及气体交换参数所可能产生的影响。研究结果显示,实验增温分别使玉米叶片的宽度和厚度减少了4%(P=0.017)和10%(P0.001)。然而,实验增温却导致叶绿体长度和宽度显著增加46%(P0.001)和50%(P0.001),从而使叶绿体的剖面面积显著增加了141%(P0.001)。另外,研究结果还显示,实验增温分别增加了玉米叶片的净光合速率52%(P=0.019)、气孔导度163%(P=0.001)以及蒸腾速率81%(P=0.017);同时,实验增温使玉米叶片的暗呼吸速率显著降低了24%(P=0.006),但却并没有对细胞间CO2浓度和水分利用效率产生显著的影响。因此,研究结果表明,未来气候变暖不仅会直接改变玉米叶片的形态和结构特征,同时还可能对玉米叶片的功能(例如光合和呼吸等关键生理生化过程)产生显著的影响。     

玉米冠层的数学描述与三维重建研究

采用Lang提出的原理开发了空间坐标仪。利用该仪器测定玉米冠层的空间坐标,以此提出了应用一般二次方程描述玉米叶曲线和叶形的数学方法,方程的系数由最小二乘回归方法得到,其中叶曲线系数由叶片主脉坐标决定,叶形系数由沿叶长方向叶宽测定值决定。从而使应用较少参数描述真实的玉米群体结构成为可能。另外,还实现了玉米冠层的计算机三维重建,为农业生态系统研究提供了新的手段。     

玉米冠层的数学描述与三维重建研究

采用Lang提出的原理开发了空间坐标仪。利用该仪器测定玉米冠层的空间坐标,以此提出了应用一般二次方程描述玉米叶曲线和叶形的数学方法,方程的系数由最小二乘回归方法得到,其中叶曲线系数由叶片主脉坐标决定,叶形系数由沿叶长方向叶宽测定值决定。从而使应用较少参数描述真实的玉米群体结构成为可能。另外,还实现了玉米冠层的计算机三维重建,为农业生态系统研究提供了新的手段。     

丝状真菌形态控制及其在发酵过程优化中的应用

丝状真菌广泛用于发酵产业,在液体深层发酵过程中,其生长形态与产物种类及产量间存在重要关联,成为发酵过程调控的热点。采用数学模型解释丝状真菌的形态发育与调控机制,是近年来工程学界颇为关注的研究手段。本文结合自己的工作着重解释丝状真菌各种生长形态的生长机理及形态发育的数学描述方式,以及如何采用数学模型描述丝状真菌发酵过程中产物、形态及环境的关联,最终实现形态的控制,完成生物发酵过程优化。具体包括:1)丝状真菌的生长机制;2)形态发育数学模型在发酵过程优化中的应用;3)控制丝状真菌形态的策略。     

植物原生质体的游离和融合

通过原生质体融合进行体细胞杂交已或为研究植物遗传和育种的一个潜在新途径。在本报道中,我们描述了用酶法将小麦、大麦、玉米、红花和蚕豆等作物的叶片和根尖细胞游离成大量的完整的原生质体的方法。观察了在降低原生质体悬浮液的渗透浓度下,小麦、玉米及蚕豆的同源融合的过程。这种融合过程可在数分钟内完成。在上述植物中以小麦和玉米的同源融合率较高,分别达到15％和22％。还描述了获得诱发种间融合的方法。利用硝酸钠和降低渗透稳定剂浓度时,于蚕豆叶片和红花根尖的远缘种间原生质体间获得了融合体。诱发融合率达4％强。同时也观察到小麦叶片和红花根尖原生质体间的融合。     

小麦根系三维形态建模及可视化

作物三维形态建模和可视化技术是数字植物研究的重要组成部分,本文旨在构建基于形态特征参数的小麦根系三维形态模型,并实现小麦根系生长的可视化.基于小麦根系生长的可视化技术框架,首先构建了小麦根轴的三维显示模型,包括根轴生长模型、分枝几何模型和根轴曲线模型;然后结合根系拓扑结构,确定相应的图元,利用根系形态模型输出的形态特征参数,对整个小麦根系进行三维重构;最后基于OpenGL图形平台,综合纹理映射、光照渲染、碰撞检测等真实感处理手段,实现了小麦根系生长的三维可视化表达.结果表明：模型输出的根系真实感较强,能较好地实现不同品种、水分和氮素条件下小麦根系的三维可视化表达.研究结果为进一步建立完整的可视化小麦生长系统奠定了技术基础.     

中国特有种丹霞梧桐的新分布区和形态特征修订

为完善丹霞梧桐(Firmiana danxiaensis)的形态描述,对丹霞和喀斯特地貌4个分布点的植株宏观形态特征进行了比较研究。结果表明,丹霞梧桐的叶柄、叶片、花序、雄蕊、蓇葖果、花萼等特征与其原始文献的描述明显不同,且原始描述缺少败育雄蕊、败育子房、及花萼、果皮、种皮在发育过程中的颜色变化等特征。因此,对丹霞梧桐形态描述进行了修订或补充,并提供图片资料。     

玉米生长周期内植硅体的变化研究

植物不同组织部位的植硅体形态、组合研究有助于准确鉴定考古地层植硅体来源植物的具体种类以及组织部位;生长周期内植硅体形态、组合变化研究有利于探讨植硅体的形成机制,认识植硅体形态组合变化与环境因子之间的关系,科学解释土壤及沉积物植硅体古植被、古环境信息。玉米变种亚航0919在生长的初期,尤其是前3片真叶,含比重较高的3片以上的多铃型植硅体;随着玉米生长天数增加及生长温度的升高,第4—5片真叶3片以上多铃型植硅体消失,哑铃型植硅体含量逐渐增加,尖型及棒型植硅体含量有所降低,叶片哑铃型植硅体长度(L)及宽度(W)有增加的趋势;相同生长阶段,叶片与叶脉植硅体组合及大小显著不同,叶脉相对叶片含较低比重的哑铃型植硅体、较高比重的十字型和椭圆-哑铃型植硅体,叶脉中哑铃型植硅体小于叶片中的。玉米叶片植硅体形态、组合在生长季节内的变化主要与植物的成熟阶段及生长环境温度的变化有关,其植硅体形态、大小和组合,尤其是哑铃型植硅体大小能够响应温度变化。     

玉米根系分布空间和空间密度分布的数学模型

应用重积分研究了土壤层中散根型和直根型玉米根系的分布空间,同时研究了玉米根系的空间密度分布．     

Computational studies of shape memory alloy behavior in biomedical applications

BACKGROUND: Nowadays, shape memory alloys (SMAs) and in particular Ni-Ti alloys are commonly used in bioengineering applications as they join important qualities as resistance to corrosion, biocompatibility, fatigue resistance, MR compatibility, kink resistance with two unique thermo-mechanical behaviors: the shape memory effect and the pseudoelastic effect. They allow Ni-Ti devices to undergo large mechanically induced deformations and then to recover the original shape by thermal loading or simply by mechanical unloading. METHOD OF APPROACH: A numerical model is developed to catch the most significant SMA macroscopic thermo-mechanical properties and is implemented into a commercial finite element code to simulate the behavior of biomedical devices. RESULTS: The comparison between experimental and numerical response of an intravascular coronary stent allows to verify the model suitability to describe pseudo-elasticity. The numerical study of a spinal vertebrae spacer where the effects of different geometries and material characteristic temperatures are investigated, allows to verify the model suitability to describe shape memory effect. CONCLUSION: the results presented show the importance of computational studies in designing and optimizing new biomedical devices.     

Developmental pathways for shaping spike inflorescence architecture in barley and wheat

Grass species display a wide array of inflorescences ranging from highly branched compound/panicle inflorescences to unbranched spike inflorescences. The unbranched spike is a characteristic feature of the species of tribe Triticeae, including economically important crops,such as wheat and barley. In this review, we describe two important developmental genetic mechanisms regulating spike inflorescence architecture in barley and wheat.These include genetic regulation of(i) row-type pathway specific to Hordeum species and(ii) unbranched spike development in barley and wheat. For a comparative understanding, we describe the branched inflorescence phenotypes of rice and maize along with unbranched Triticeae inflorescences. In the end, we propose a simplified model describing a probable mechanism leading to unbranched spike formation in Triticeae species.     

玉米叶片持绿性研究进展与对策

叶片持绿性(stay green或non-senescence)与植物叶片衰老相关,影响植物生长及生物产量。叶片持绿性相关研究主要集中于拟南芥等模式植物,玉米中的研究相对落后,但该研究对玉米产量、品质、抗病等具有重要意义。本文对玉米叶片持绿性的研究进展进行了综述,包括玉米叶片持绿性概念、评价指标、生理生化特性、遗传特性、基因/QTL定位等。提出了玉米持绿性研究存在的问题与相关对策。     

Proton and copper adsorption to maize and soybean root cell walls

A surface complexation model which has been used to describe inner-sphere complexation on metal oxide surfaces was applied to the adsorption of Cu by isolated cell walls of 4-day and 28-day-old maize (Zea mays L. cv WF9 × Mo17) and 21-day-old soybean (Glycine max [L.] Merr. cv Dare) roots. Concentration dependence of the titration data prevented the determination of unique pK and capacitance values for the 4-day maize cell walls, though mean values obtained for the intrinsic pK of the titratable carboxyl groups were 3.0 (4-day maize), 3.6 (28-day maize), and 3.0 (21-day soybean) as determined by potentiometric titration with either NaOH or HCl in 20 millimolar NaCl. The constant capacitance model was applied to Cu sorption data from rapid batch equilibrium experiments in an ionic medium of 20 millimolar NaClO₄. Speciation calculations indicated that the formation of a bidentate surface complex was sufficient to describe the experimental data for all three types of plant material, with only one value for the pK and capacitance density. The intrinsic constants of Cu complexation by a neutral site are: log K = −0.3 ± 0.1, −0.2 ± 0.3, and 0.9 ± 0.1 for 4-day and 28-day maize, and 21-day soybean, respectively. The integral capacitance density parameter, which describes the relationship between surface charge density and electrical potential, is several times larger than for crystalline mineral surfaces. This result indicates that the surface electrical potential remains low even when the surface charge density is high. Such behavior is characteristic of gels and porous oxides.     

The measurement and modelling of the mechanical properties of human skin in vivo--II. The model

The stress-strain relationship for human skin in vivo has a characteristic non linear shape even for low loads. Considerations are given on the basis of which a structural model has been selected, in which the mechanical properties of corrugated collagen fibrils are involved. It is found that such a model can describe the experimental stress-strain relationship surprisingly well with only three free parameters. These parameters are related to basic collagen fibril properties such as stiffness, diameter and waviness. The role of elastin is likely to be negligible for the purely elastic properties of human skin in vivo.     

How a Plant Builds Leaves

A leaf develops from a few cells that grow, divide, and differentiate to form a complex organ that is precisely positioned relative to its neighbors. How cells communicate to achieve such coordinated growth and development is the focus of this review. We discuss (1) how the stem cells within the shoot meristem gain competence to form organs, (2) what determines the positioning and initiation of new organs, and (3) how the new organ attains its characteristic shape and polarity. Special emphasis is given to the recent integration of mathematics and physics in the study of leaf development.     

DNA sequence and shape are predictive for meiotic crossovers throughout the plant kingdom

A better understanding of genomic features influencing the location of meiotic crossovers (CO s) in plant species is both of fundamental importance and of practical relevance for plant breeding. Using CO positions with sufficiently high resolution from four plant species [Arabidopsis thaliana , Solanum lycopersicum (tomato), Zea mays (maize) and Oryza sativa (rice)] we have trained machine‐learning models to predict the susceptibility to CO formation. Our results show that CO occurrence within various plant genomes can be predicted by DNA sequence and shape features. Several features related to genome content and to genomic accessibility were consistently either positively or negatively related to CO s in all four species. Other features were found as predictive only in specific species. Gene annotation‐related features were especially predictive for maize, whereas in tomato and Arabidopsis propeller twist and helical twist (DNA shape features) and AT /TA dinucleotides were found to be the most important. In rice, high roll (another DNA shape feature) and low CA dinucleotide frequency in particular were found to be associated with CO occurrence. The accuracy of our models was sufficient for Arabidopsis and rice (area under receiver operating characteristic curve, AUROC  > 0.5), and was high for tomato and maize (AUROC  ? 0.5), demonstrating that DNA sequence and shape are predictive for meiotic CO s throughout the plant kingdom.