玉米籽粒类型及其与成粒的关系

玉米雌穗总粒数在抽丝后18d决定;败育粒在抽丝后8-28d决定;抽丝后3-4d内抽出花丝的,基本上能成为有效粒。高产栽培时,措施及气候因素对晚败粒及雌穗中下部败育粒的影响显著。     

花期弱光胁迫对玉米穗粒数的影响

为明确花期弱光对玉米穗粒数的影响规律,采用人工遮光模拟弱光胁迫,设置抽雄始期和吐丝期持续10 d60%和90%两个不同遮光强度的弱光处理,研究了花期弱光对雌穗小花受精、结实,干物质积累及其向雌穗分配的影响。结果发现,花期弱光胁迫导致玉米地上部总干物质日增重量降低,干物质分配到雌穗的比例减少,雌穗生长变慢,受精结实率降低,影响程度随遮光率的增加而增大。抽雄始期60%和90%遮光处理10 d后恢复自然光照结实率较处理结束时的受精率均明显提高,吐丝期60%和90%遮光处理10 d后恢复自然光照结实率较处理结束时的受精率降低和持平。抽雄始期光照不足导致穗粒数较对照下降57%~91%;吐丝始期光照不足导致穗粒数较对照下降43%~81%。无论对于抽雄始期还是吐丝期,遮光处理期间的日平均光合有效辐射强度在穗粒形成中作用最大,其次为处理期间的地上部总干物质日增重。对于吐丝期,处理期间的日平均温度对穗粒数也具有直接的正效应。     

花期弱光胁迫对玉米穗粒数的影响

为明确花期弱光对玉米穗粒数的影响规律,采用人工遮光模拟弱光胁迫,设置抽雄始期和吐丝期持续10 d60%和90%两个不同遮光强度的弱光处理,研究了花期弱光对雌穗小花受精、结实,干物质积累及其向雌穗分配的影响。结果发现,花期弱光胁迫导致玉米地上部总干物质日增重量降低,干物质分配到雌穗的比例减少,雌穗生长变慢,受精结实率降低,影响程度随遮光率的增加而增大。抽雄始期60%和90%遮光处理10 d后恢复自然光照结实率较处理结束时的受精率均明显提高,吐丝期60%和90%遮光处理10 d后恢复自然光照结实率较处理结束时的受精率降低和持平。抽雄始期光照不足导致穗粒数较对照下降57%⁹1%;吐丝始期光照不足导致穗粒数较对照下降43%91%;吐丝始期光照不足导致穗粒数较对照下降43%⁸1%。无论对于抽雄始期还是吐丝期,遮光处理期间的日平均光合有效辐射强度在穗粒形成中作用最大,其次为处理期间的地上部总干物质日增重。对于吐丝期,处理期间的日平均温度对穗粒数也具有直接的正效应。     

孕穗前期叶面喷赛苗旺对冬小麦穗粒数和粒质量的影响

为探讨孕穗前期叶面喷施赛苗旺对小麦穗粒数和粒质量的调控效应,以半冬性小麦品种郑麦379为供试材料,在冬小麦孕穗前14 d,以叶面喷清水为对照,研究叶面喷赛苗旺对冬小麦穗粒数和粒质量的影响。结果表明,在孕穗前14 d,喷施赛苗旺可抑制冬小麦败育阶段基部和中部穗位的小花败育速率,显著提高该部位的小花数,对顶部穗位小花的败育速率和小花数影响不大。与对照相比,在基部穗位,两试验点喷赛苗旺处理的小花败育速率分别显著降低23.30%、21.96%,小花数分别显著增加1.60、1.31个;在中部穗位,两试验点喷赛苗旺处理的小花败育速率分别降低31.65%、33.72%,小花数分别显著增加3.80、4.07个。对产量及其构成因素进一步分析发现,与对照相比,两试验点喷施赛苗旺处理穗数、千粒质量均有所提高,但不显著,穗粒数和产量分别显著提高11.85%、13.13%和7.50%、7.08%。综上说明,在冬小麦发育中后期,叶面喷施赛苗旺主要通过提高冬小麦基部和中部穗位的穗粒数来提高产量,且效果显著。     

抽雄期水分胁迫对玉米籽粒产量及其果穗性状的影响

以不同抗旱性玉米品种为试材，在不同强度水分胁迫下，玉米穗粒数的减少是抽雄开花期产量降低的主要限制因子，而秃尖增长和行粒数减少是穗粒数降低的主要因素。说明干旱导致雌穗发育受阻，花期不遇，籽粒败育率增加，抗旱性强的品种维持产量的能力较强。     

春小麦结实特性对穗粒数的影响

试验以19个春麦品种为材料,试图探讨影响春麦穗粒数的生育阶段。结果表明,小花数多是穗粒数多的必要不充分条件;受精前的退化小花数相对来说要少于受精败育数和成胚后籽粒的退化数,也即受精前的退化小花数并不是限制穗粒数的主要因子;增加小花数同时减少小花的退化、减少受精败育数和成胚退化数是现阶段提高春麦穗粒数的关键。对于穗粒数多于40粒的品种减少小花数的退化提高可育小花数是增加穗粒数的关键;对于穗粒数在30￣40粒之间的品种减少成胚后籽粒的退化是提高穗粒数的关键;对于穗粒数低于30粒的品种,要增加受精前的小花数,同时要针对不同的品种,采取措施减少受精败育数或成胚后籽粒的退化数才能有效地提高穗粒数。     

玉米秃尖的研究：Ⅱ.玉米雌穗不同部位小花,籽粒的分化发？…

本以８个在杂交后代表现出不同秃尖程度的自交系及其组配的一套８×８的双列杂交组合为材料，研究了雌穗不同部位小花吐丝的时间次序及其籽粒分化发育的特征。表明：雌穗中下部的小花吐丝最早最快，库容大，活力强，授粉后小花发育几乎没有败育籽粒，而雌穗中上部的小花除易出现退化花和未受精花外，还有较多的授粉小化发生籽粒的败育，可能与其抽丝畔锭较慢，和库处于弱势位有关。     

不同时期遮光对玉米籽粒生产能力的影响及籽粒败育过程的观察

通过对玉米植株进行分期遮光试验,认为;雌穗小花分化期至籽粒快速灌浆始期是影响玉米穗粒数的关键时期;雌穗小花分化期至籽粒快速灌浆高峰期是玉米植株产量形成的关键时期;吐丝期是决定单株产量和穗粒数的临界期;对百粒重有显著影响的时期是胚乳游离核期和快速灌浆期;果穗顶部籽粒比中、下部籽粒发育较迟,当中、下部籽粒进入快速灌浆期时,顶部籽粒则停止干物质积累,成为败育粒。     

吐丝前高温胁迫对不同耐热型夏玉米产量及穗发育特征的影响

【目的】吐丝前高温是影响玉米雌雄穗发育的重要因素之一,对玉米产量形成至关重要。探明吐丝前高温胁迫对玉米产量及雌雄穗发育进程的影响,为玉米稳产高产提供保障。【方法】以花粒期耐热型玉米品种郑单958和热敏感型玉米品种联创808为供试材料,采用盆栽试验,在第9片叶展开期至吐丝期,移入人工智能温室进行高温胁迫（最高温度/最低温度为40/30℃）,对照的最高温度/最低温度为35/25℃,研究高温胁迫对不同耐热型玉米产量、雌雄穗生长发育及外观形态结构、花粉花丝微观结构和光合特性的影响。【结果】第9片叶展开期至吐丝期高温胁迫显著降低了夏玉米穗长、行粒数、穗粒数和粒重,进而导致产量显著下降。与对照相比,高温胁迫下郑单958和联创808行粒数分别降低22.21%和24.59%,穗粒数分别降低29.85%和27.80%,千粒重分别降低24.04%和17.47%,导致籽粒产量分别降低44.98%和40.88%,差异均达显著水平。高温胁迫抑制了2个玉米品种雌雄穗发育,雌、雄穗干重和雌穗长度显著降低,光合性能显著降低,开花吐丝间隔期（ASI）拉长。高温胁迫后,郑单958和联创808吐丝期雄穗干重分别降低39.42%和15.60%,雌穗干重分别降低22.50%和15.56%,穗位叶净光合速率分别降低48.70%和56.48%,开花吐丝间隔期（ASI）分别达7 d和6 d,雌穗吐丝时间推迟是ASI拉长的主要原因。高温胁迫对玉米花粉及花丝表面超微结构均产生了明显影响,2个玉米品种花粉粒表面均出现干缩褶皱,外壳出现网状纹突起,萌发孔内陷;玉米花丝表面褶皱,花丝毛数明显降低,且存在的花丝毛几乎全部倒伏于花丝表面上,造成花丝接受花粉面积减少,且郑单958花粉花丝受损程度明显重于联创808。【结论】第9片叶展开期至吐丝期高温胁迫,对耐热型品种郑单958的产量形成、光合特性和雌雄穗发育的影响均高于热敏感型品种联创808。第9片叶展开期至吐丝期高温胁迫导致粉花丝微观形态受损,抑制雌雄穗发育,显著降低玉米光合能力,使得穗粒数和粒重减少,籽粒产量显著降低。因此,生产中适宜玉米品种的选用需参考不同区域高温逆境易发生阶段来确定。     

吐丝前高温胁迫对不同耐热型夏玉米产量及穗发育特征的影响

【目的】吐丝前高温是影响玉米雌雄穗发育的重要因素之一,对玉米产量形成至关重要。探明吐丝前高温胁迫对玉米产量及雌雄穗发育进程的影响,为玉米稳产高产提供保障。【方法】以花粒期耐热型玉米品种郑单958和热敏感型玉米品种联创808为供试材料,采用盆栽试验,在第9片叶展开期至吐丝期,移入人工智能温室进行高温胁迫(最高温度/最低温度为40/30℃),对照的最高温度/最低温度为35/25℃,研究高温胁迫对不同耐热型玉米产量、雌雄穗生长发育及外观形态结构、花粉花丝微观结构和光合特性的影响。【结果】第9片叶展开期至吐丝期高温胁迫显著降低了夏玉米穗长、行粒数、穗粒数和粒重,进而导致产量显著下降。与对照相比,高温胁迫下郑单958和联创808行粒数分别降低22.21%和24.59%,穗粒数分别降低29.85%和27.80%,千粒重分别降低24.04%和17.47%,导致籽粒产量分别降低44.98%和40.88%,差异均达显著水平。高温胁迫抑制了2个玉米品种雌雄穗发育,雌、雄穗干重和雌穗长度显著降低,光合性能显著降低,开花吐丝间隔期(ASI)拉长。高温胁迫后,郑单958和联创808吐丝期雄穗干重分别降低39.42%和15.60%,雌穗干重分别降低22.50%和15.56%,穗位叶净光合速率分别降低48.70%和56.48%,开花吐丝间隔期(ASI)分别达7 d和6 d,雌穗吐丝时间推迟是ASI拉长的主要原因。高温胁迫对玉米花粉及花丝表面超微结构均产生了明显影响,2个玉米品种花粉粒表面均出现干缩褶皱,外壳出现网状纹突起,萌发孔内陷;玉米花丝表面褶皱,花丝毛数明显降低,且存在的花丝毛几乎全部倒伏于花丝表面上,造成花丝接受花粉面积减少,且郑单958花粉花丝受损程度明显重于联创808。【结论】第9片叶展开期至吐丝期高温胁迫,对耐热型品种郑单958的产量形成、光合特性和雌雄穗发育的影响均高于热敏感型品种联创808。第9片叶展开期至吐丝期高温胁迫导致粉花丝微观形态受损,抑制雌雄穗发育,显著降低玉米光合能力,使得穗粒数和粒重减少,籽粒产量显著降低。因此,生产中适宜玉米品种的选用需参考不同区域高温逆境易发生阶段来确定。     

Segregation of form, color, movement, and depth: anatomy, physiology, and perception

Anatomical and physiological observations in monkeys indicate that the primate visual system consists of several separate and independent subdivisions that analyze different aspects of the same retinal image: cells in cortical visual areas 1 and 2 and higher visual areas are segregated into three interdigitating subdivisions that differ in their selectivity for color, stereopsis, movement, and orientation. The pathways selective for form and color seem to be derived mainly from the parvocellular geniculate subdivisions, the depth- and movement-selective components from the magnocellular. At lower levels, in the retina and in the geniculate, cells in these two subdivisions differ in their color selectivity, contrast sensitivity, temporal properties, and spatial resolution. These major differences in the properties of cells at lower levels in each of the subdivisions led to the prediction that different visual functions, such as color, depth, movement, and form perception, should exhibit corresponding differences. Human perceptual experiments are remarkably consistent with these predictions. Moreover, perceptual experiments can be designed to ask which subdivisions of the system are responsible for particular visual abilities, such as figure/ground discrimination or perception of depth from perspective or relative movement--functions that might be difficult to deduce from single-cell response properties.     

Mineralogy, petrology, and surface features of lunar samples 10062,35, 10067,9, 10069,30, and 10085,16

The primary rocks are a sequence of titanium-rich basic volcanics, composed of clinopyroxene, plagioclase, and ilmenite with minor olivine, troilite, and native iron. The soil and microbreccias are respectively loose and compacted mixtures of fragments and aggregates of similar rocks, minerals, and glassy fragments and spheres. Impact events are reflected by the presence of shock metamorphosed rock fragments, breccias, and glasses and their resulting compaction to form complex breccias, glass-spattered surfaces, and numerous glass-lined craters. Chemistry of the glasses formed by the impact events is highly variable, and the high iron and nickel content of a few moundlike features suggests that at least some of the projectiles are iron and nickel-rich meteorites.     

Values,technologies, and epistemology

The aim of this paper is to make possible dialogue between those who claim that technologies are coded with social, political, or ethical values and those who argue that they are value-neutral. To demonstrate the relevance of this bridge-building project, the controversy regarding agrifood biotechnology will be used as a case study. Drawing on work by L. H. Nelson about the nature of human knowledge-building enterprises and E. F. Kittay’s account of the relationally-constituted self, the argument will be made that all technologies embody the values of the communities that created them. Zahra Meghani is an assistant professor in the Department of Philosophy at the University of Rhode Island. Her research interests are philosophy of technology, feminist theory (especially feminist epistemology and feminist philosophy of science), normative ethics, practical ethics (especially health care ethics), disability issues, and political theory.     

Research and development, productivity, and inflation

R & D, through its effects on the rate of productivity increase, can significantly restrain the rate of inflation in the medium and long run. High rates of inflation damage the workings of the price system and impair the efficiency of practically all economic activities, including R & D. Findings suggest that the percentage increase between 1969 and 1979, in total real R & D expenditures, has been exaggerated due to the inadequacy of the gross national product deflator as applied to R & D.     

Beliefs,knowledge, and values held by inner-city youth about gardening,nutrition, and cooking

Changes in the US food system and an interest in changing dietary habits among youth have impelled numerous schools and communities to develop programs such as community gardens. Youth community gardens have the potential to positively influence dietary behaviors and enhance environmental awareness and appreciation. However, actual data supporting youth gardening and its influence are limited. The purpose of this study was to explore the effects of community gardens on youth dietary behaviors, values and beliefs, and cooking and gardening behaviors. Focus groups were conducted with inner-city youth living in Minneapolis/St. Paul, Minnesota and compared those involved in a youth garden program with those uninvolved in order to investigate whether the gardening program influenced their habits, beliefs, and values. Findings indicate that youth garden program participants were more willing to eat nutritious food and try ethnic and unfamiliar food than those not in the program. Additionally, it was apparent that garden participants had a stronger appreciation for other individuals and cultures and were more likely to cook and garden on their own than youth not involved in a garden program. The findings suggest that garden programs positively impact youth garden habits, food choice, social skills, nutrition knowledge, and cooking skills. Lauren Lautenschlager is currently a graduate student at the University of Minnesota and working toward obtaining her MS in nutrition and becoming a registered dietitian. She is interested in the education of youth on the food system. Chery Smith is an associate professor in the Department of Food Science and Nutrition at the University of Minnesota. Her research interests include the dietary behavior and nutritional status of low-income and homeless people, community and international nutrition, and food systems.     

Atmospheric halocarbons, hydrocarbons, and sulfur hexafluoride: global distributions, sources, and sinks

The global distribution of fluorocarbon-12 and fluorocarbon-11 is used to establish a relatively fast interhemispheric exchange rate of 1 to 1.2 years. Atmospheric residence times of 65 to 70 years for fluorocarbon-12 and 40 to 45 years for fluorocarbon-l1 best fit the observational data. These residence times rule out the possibility of any significant missing sinks that may prevent these fluorocarbons from entering the stratosphere. Atmospheric measurements of methyl chloroform support an 8-to 10-year residence time and suggest global average hydroxyl radical (HO) concentrations of 3 x 10(5) to 4 x 10(5) molecules per cubic centimeter. These are a factor of 5 lower than predicted by models. Additionally, methyl chloroform global distribution supports Southern Hemispheric HO levels that are a factor of 1.5 or more larger than the Northern Hemispheric values. The long residence time and the rapid growth of methyl chloroform cause it to be a potentially significant depleter of stratospheric ozone. The oceanic sink for atmospheric carbon tetrachloride is about half as important as the stratospheric sink. A major source of methyl chloride (3 x 10(12)grams per year), sufficient to account for nearly all the atmospheric methyl chloride, has been identified in the ocean.     

Fiber, food, fuel, and fungal symbionts

Virtually all plants of economic importance form mycorrhizae. These absorbing organs of higher plants result from a symbiotic union of beneficial soil fungi and feeder roots. In forestry, the manipulation of fungal symbionts ecologically adapted to the planting site can increase survival and growth of forest trees, particularly on adverse sites. Vesicular-arbuscular mycorrhizae, which occur not only on many trees but also on most cultivated crops, are undoubtedly more important to world food crops. Imperatives for mycorrhizal research in forestry and agriculture are (i) the development of mass inoculum of mycorrhizal fungi, (ii) the interdisciplinary coordination with soil management, plant breeding, cultivation practices, and pest control to ensure maximum survival and development of fungal symbionts in the soil, and (iii) the institution of nursery and field tests to determine the circumstances in which mycorrhizae benefit plant growth in forestry and agri-ecosystems.