镉与萘复合胁迫对红树植物白骨壤幼苗萌芽及生长的影响

为探讨白骨壤(Avicennia marina)幼苗对重金属镉(Cd)和多环芳烃萘(Nap)复合胁迫的响应,采用砂基栽培,对其幼苗的萌芽和生长进行了研究。结果表明,Cd、Nap复合胁迫对白骨壤萌芽的抑制效应较单一胁迫明显,胁迫前期幼苗成活率提高,胁迫后期则降低。胁迫栽培45 d,10 mg L~(–1)的Nap在叶形态、茎高及各器官生物量上能够减轻Cd胁迫的影响,但增强对根长的抑制作用,10 mg L~(–1) Nap-25 mg L~(–1) Cd处理的叶面积、叶长、叶宽、茎高及全株生物量分别比25 mg L~(–1) Cd处理的提高9.6%、7.9%、7.4%、5.1%和20.2%,但根长则比150 mg L~(–1) Cd处理的下降11.1%。至胁迫栽培90 d,各处理间幼苗器官及全株生物量无显著影响,复合胁迫对叶形态、茎高和根长等的抑制作用要强于单一Cd胁迫。因此,随着复合胁迫时间的延长,Cd和Nap对白骨壤幼苗的生长由拮抗效应转变为协同效应。     

EFFECT OF 4'-CHLOROGLUTARANILIC ACID ON GROWTH AND DEVELOPMENT OF SUNFLOWER SEEDLINGS

The potential growth-regulating properties of 4'-chloroglutaranilic acid (CGA) as well as oxygen and nitrogen isosteres were examined in whole-plant bioassay systems utilizing sunflower seedling (Helianthus annuus L.). Test systems included both soil-grown plants and hydroponic studies. Foliar applications of CGA produced growth inhibition which was detectable within 24 hr and which persisted for at least 30 days. Direct application to roots produced a growth inhibition which was 15% greater than foliar applications. Foliar or root application at 10^-5 m or greater concentrations produced gross changes in leaf morphology. Total plant-height inhibition was principally associated with stem growth in an area located between primary leaves and the shoot meristem. CGA was found to be 32 % less active than IAA as a growth promoter, but was 76 % more active than IAA as a growth inhibitor; the most severely affected organ was the leaf and the least affected was the root system. Leaves from soil-grown plants treated wth a 10^-3 m foliar application of CGA possessed several abnormalities. These included an increase in thickness and dry weight, a reduction in chloroplast starch vacuoles, extractable starch, soluble hexoses, and soluble proteins.     

The relevance of seed size in modulating leaf physiology and early plant performance in two tree species

The size of seeds and the microsite of seed dispersal may affect the early establishment of seedlings through different physiological processes. Here, we examined the effects of seed size and light availability on seedling growth and survival, and whether such effects were mediated by water use efficiency. Acorns of Quercus petraea and the more drought-tolerant Quercus pyrenaica were sowed within and around a tree canopy gap in a sub-Mediterranean forest stand. We monitored seedling emergence and measured predawn leaf water potential (Ψ_pd), leaf nitrogen per unit area (N_a), leaf mass per area, leaf carbon isotope composition (δ¹³C) and plant growth at the end of the first summer. Survival was measured on the next year. Path analysis revealed a consistent pattern in both species of higher δ¹³C as Ψ_pd decreased and higher δ¹³C as seedlings emerged later in the season, indicating an increase in ¹³C as the growing season is shorter and drier. There was a direct positive effect of seed size on δ¹³C in Q. petraea that was absent in Q. pyrenaica. Leaf δ¹³C had no effect on growth but the probability of surviving until the second year was higher for those seedlings of Q. pyrenaica that had lower δ¹³C on the first year. In conclusion, leaf δ¹³C is affected by seed size, seedling emergence time and the availability of light and water, however, leaf δ¹³C is irrelevant for first year growth, which is directly dependent on the amount of seed reserves.     

Compensatory growth and photosynthetic responses of <Emphasis Type="Italic">Pharbitis purpurea</Emphasis> seedlings to clipped cotyledon and second leaf

Leaf tissue damaging to seedlings can limit their subsequent growth, and the effects may be more extensive. Compensatory photosynthesis responses of the remnant cotyledon and primary leaf of Pharbitis purpurea to clipping and the effect of clipping on seedling growth were evaluated in a pot-cultivated experiment. Three treatments were conducted in the experiment, which were clipped cotyledon (CC), clipped second leaf (CL), and control group (CG). The area, thickness, mass, and longevity of the remaining cotyledon of CC exhibited over-compensatory growth. In contrast, seedlings of CC had under-compensatory growth in seedling height, root length, seedling mass, and root to shoot ratio. However, the traits of remnant cotyledon and seedling in CL treatment exhibited equal-compensatory growth. Net photosynthetic rate of the cotyledon of CC was significantly higher than those of CL and CG treatments, and the diurnal changes in photosynthetic rates showed significantly different patterns which were unimodal curve (CC) and bimodal curve (CL and CG), respectively. There was no significant difference between CL and CG treatment. Net photosynthetic rate of the primary leaf of CL was significantly higher than that of CG treatment. However, the photosynthetic rates of primary leaves of CL and CG treatments showed similar photosynthetic patterns characterized by a bimodal curve. P. purpurea seedlings used a compensatory growth strategy in the remaining cotyledon or the primary leaf to resist leaf loss and minimize any adverse effects.     

Effects of Manganese Toxicity on the Growth and Gene Expression at the Seedling Stage of Soybean

In order to investigate the effects of Manganese (Mn) toxicity stress on the growth and gene expression at the seedling stage of soybean, soybean seedlings were treated with normal Mn concentration (5 μmol/L MnSO₄) and excess Mn concentration (100 μmol/L MnSO₄) by the method of hydroponic culture in this study. When soybean was subjected to Mn toxicity stress, excessive Mn could affect seedling growth, root development, the number of Mn oxide spots in leaves, and the Mn accumulation content in different parts of soybean. With the increase of exogenous Mn concentration and the prolongation of culture time, the shoot and root biomasses of soybean decreased significantly, but the plant height of soybean had no obvious effects. The total root length, root surface area and root volume of soybean decreased significantly, but the taproot length, taproot tip length and root diameter did not change significantly. The number of Mn spots in the primary leaves (first leaf) was significantly more than that in the old leaves (second leaf) and the youngest leaves (fourth leaf). The Mn concentration in leaves was significantly higher than that in roots, and the Mn concentration in the old leaves was significantly higher than that in youngest leaves with the method of inductively coupled plasma atomic emission spectrometry (ICP-AES). Moreover, the results in the present study suggested that the 10 selected genes were significantly up-regulated or down-regulated by Mn toxicity in the old and young leaves by quantitative real-time PCR (qRT-PCR) analysis. This indicates that these genes might be important in the process of regulation in old and young leaves of the physiological responses and ion transporting to Mn toxicity stress.     

The Relationship between the Growth of the Primary Leaf and of the Coleoptile in Seedlings of Avena and Triticum

Partial inhibition of extension growth of the primary leaf occurswhen whole Triticum seedlings are immersed in aerated solutionsof IAA but is replaced by growth promotion when sucrose is addedto the external solution. In seedlings in which the coleoptilehas been excised, IAA increases the growth of the leaf bothwith and without additional sucrose. Inhibition of the leaf by moderate concentrations of IAA nolonger occurs when the seedling is detached from the endosperm.Sucrose added to the external solution raised the percentageelongation of the coleoptile almost to the level of that attainedin intact seedlings without additional carbohydrate. It alsoenabled the leaf to show a positive growth response with IAA. The results indicate that in intact seedlings treated with IAAthe growth of the primary leaf is markedly diminished owingto diversion of carbohydrate to the coleoptile if the growthof the latter is promoted as a result of the treatment. Whenthe competition of the coleoptile for carbohydrate is diminishedor eliminated, acceleration of the growth of the primary leafby IAA becomes apparent. In addition to the endogenous rhythm, with a period close to24 hours, induced in the growth-rate of the coleoptile whenseedlings of Avena are transferred from red light to darkness,a similar rhythm, with a slightly longer period, is inducedin the growth-rate of the primary leaf. This rhythm persistsin elongating leaves so long as they remain within the coleoptile.It can be recorded for at least 100 hours in deseeded seedlings. When intact seedlings of Avena are immersed for one hour inrelatively high concentrations of IAA and then transferred todistilled water for 18 hours, the elongation of the coleoptileis greater and the inhibition of the leaf is less than whenthey are transferred to humid air. Sections of the leaf of Triticum showed a slight increase inelongation in concentrations of IAA up to 5 mg./l., but no evidencewas obtained that sections of leaf and coleoptile exert any.influenceon each other's elongation when floated together on solutionsof IAA.     

Species-specific effect of UV-B radiation on the temporal pattern of leaf growth

Recent molecular and physiological studies have demonstrated that ultraviolet‐B radiation (UV‐B) can affect some of the processes involved in leaf growth, but the phases of leaf growth affected have not been clearly delimited. We used functional growth analysis to assess the effects of UV‐B radiation on the time course of leaf growth in seedlings of two birch species (Betula pendula and Betula pubescens). Our aim was to identify the phase(s) of leaf development affected by UV‐B radiation. In a greenhouse study, 1‐year‐old birch seedlings were subjected to three daily doses of supplemental UV‐B radiation treatments (UV‐B⁺) and no UV‐B radiation controls (UV‐B^?). Leaf growth measurements every 2 days were complemented by assessment of other functional traits over a 4‐week period at the start of the growing season. Using fitted curves, we were able to determine that the rate of leaf expansion was slowed by the UV‐B⁺ treatment in leaves of B. pendula because of a slower maximum leaf growth rate compared with plants under the UV‐B^? controls, but that compensation toward the end of the period of expansion negated this difference when leaves reached their final size. UV‐B⁺ had little effect on the rate of B. pubescens leaf growth despite a larger reduction in leaf final size due to UV‐B⁺ than occurred in B. pendula leaves. In conclusion, effective regulation ameliorated the effects of UV‐B radiation on leaf and seedling growth in B. pendula, whereas in B. pubescens, reductions in leaf final size under UV‐B⁺ were consistent with a slightly reduced rate of height growth.     

Maize (Zea mays L.) seedling leaf nuclear proteome and differentially expressed proteins between a hybrid and its parental lines

To better understand the underlying molecular basis of leaf development in maize, a reference map of nuclear proteins in basal region of seedling leaf was established using a combination of 2DE and MALDI‐TOF‐MS. In total, 441 reproducible protein spots in nuclear proteome of maize leaf basal region were detected with silver staining in a pH range of 3–10, among which 203 spots corresponding to 163 different proteins were identified. As expected, proteins implicated in RNA and protein‐associated functions were overrepresented in nuclear proteome. Remarkably, a high percentage (10%) of proteins was identified to be involved in cell division and growth. In addition, comparative nuclear proteomic analysis in leaf basal region of highly heterotic hybrid Mo17/B73 and its parental lines was also performed and 52 of 445 (11.69%) detected protein spots were differentially expressed between the hybrid and its parental lines, among which 16 protein spots displayed nonadditively expressed pattern. These results indicated that hybridization between two parental lines can cause changes in the expression of a variety of nuclear proteins, which may be responsible for the observed leaf size heterosis.     

Estimation of the whole-plant CO2 compensation point of tobacco (Nicotiana tabacum L.)

The whole-plant CO₂ compensation point (Γ_plant) is the minimum atmospheric CO₂ level required for sustained growth. The minimum CO₂ requirement for growth is critical to understanding biosphere feedbacks on the carbon cycle during low CO₂ episodes; however, actual values of Γ_plant remain difficult to calculate. Here, we have estimated Γ_plant in tobacco by measuring the relative leaf expansion rate at several low levels of atmospheric CO₂, and then extrapolating the leaf growth vs. CO₂ response to estimate CO₂ levels where no growth occurs. Plants were grown under three temperature treatments, 19/15, 25/20 and 30/25°C day/night, and at CO₂ levels of 100, 150, 190 and 270 μmol CO₂ mol⁻¹ air. Biomass declined with growth CO₂ such that Γ_plant was estimated to be approximately 65 μmol mol⁻¹ for plants grown at 19/15 and 30/25°C. In the first 19 days after germination, plants grown at 100 μmol mol⁻¹ had low growth rates, such that most remained as tiny seedlings (canopy size <1 cm²). Most seedlings grown at 150 μmol mol⁻¹ and 30/25°C also failed to grow beyond the small seedling size by day 19. Plants in all other treatments grew beyond the small seedling size within 3 weeks of planting. Given sufficient time (16 weeks after planting) plants at 100 μmol mol⁻¹ eventually reached a robust size and produced an abundance of viable seed. Photosynthetic acclimation did not increase Rubisco content at low CO₂. Instead, Rubisco levels were unchanged except at the 100 and 150 μmol mol⁻¹ where they declined. Chlorophyll content and leaf weight per area declined in the same proportion as Rubisco, indicating that leaves became less expensive to produce. From these results, we conclude that the effects of very low CO₂ are most severe during seedling establishment, in large part because CO₂ deficiency slows the emergence and expansion of new leaves. Once sufficient leaf area is produced, plants enter the exponential growth phase and acquire sufficient carbon to complete their life cycle, even under warm conditions (30/25°C) and CO₂ levels as low as 100 μmol mol⁻¹.     

Phytochrome-controlled extension growth of Avena sativa L. seedlings

The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of P_fr, the far-red light absorbing form of phytochrome (e.g., by [P_fr]0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by P_fr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to P_fr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by P_fr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of P_fr established at the onset of darkness rather than by the actual P_fr level present during the growth period.Abbreviation P_fr far-red light absorbing form of phytochrome     

不同产地苦楝苗期生长节律研究

苦楝在我国分布广泛,具有丰富的遗传变异性。为进一步做好苦楝种源筛选和良种选育工作,该文对不同产地苦楝实生苗生长性状和各阶段的生长特点进行了比较分析,初步揭示了苦楝苗期生长规律。以15个产地的1年生实生苗为试材,对苗高、地径、复叶生长及生物量积累等生长性状进行了观测分析,并用Logistics方程对生长节律进行了拟合。结果表明:(1)不同产地苦楝苗高、地径生长差异均达显著水平,根生物量、茎生物量及复叶相关性状差异均达极显著性水平;(2)苗高和地径生长均呈现慢-快-慢的S型生长规律,且均存在2次生长高峰,与苗高生长高峰出现时间相比,地径生长高峰出现时间较晚;(3)Logistic拟合方程的R²为0.976～0.994,均达到极显著相关水平,说明可用Logistic方程拟合苦楝的生长节律;(4)总体上地径速生期较苗高速生期长20～30 d,北方产地苗高和地径进入速生期和结束速生期的时间均早于南方产地,速生期苗高和地径累积生长量均超过总生长量的60%;(5)各生长指标均与纬度负相关,苗高、生物量及复叶面积与经度正相关,其他指标与经度负相关。综上结果表明,苦楝为全期生长型树种,各生长性状在产地间达显著差异水平,生长受纬度和经度双重控制,以纬度控制为主。     

Demography of the seedling bank of Manilkara zapota (L.) Royen,in a subtropical rain forest of Mexico

Selection of individuals in tropical trees, occurs mainly in the seedling phase, which in part explains the low densities of most species. The main objective of this work was to gain an insight into those factors that influence growth and survival of Manilkara zapota seedlings, one of the most abundant species in the lowland forests of Mexico and Central America. Eight 10-m² rectangular plots (5m×2m) were established, in which all < 35-cm-high M. zapota seedlings were marked, measured and enumerated at bimonthly intervals. In each census seedling height, number of leaves, length of largest leaf, type of damage and seedling death were registered. Seedling survival during 2 yr was high, reaching 82% including newly emerged seedlings. A maximum likelihood regression analysis showed that both number of leaves and length of largest leaf had a direct influence on seedling survival; however, neither type of damage nor seedling density and height had significant effect. Seedling height growth averaged 2.8 cm in the 2 yr of study. The combined effect of high seedling survival, reduced growth, and impact of physical damage mainly due to falling branches and leaves reveals the occurrence of a persistent seedling bank. Such a bank would contribute to recruitment of individuals in the juvenile and eventually in the adult stages. This seedling bank could explain the high density of individuals of M. zapota in the tropical forests of Mexico.     

茄子野生近缘种托鲁巴姆试管微扦插繁殖技术研究

嫁接栽培是茄果类蔬菜防治土传病害和提高产量的重要措施之一。茄子野生近缘种托鲁巴姆(Solanums torvum)因综合抗性强,成为茄子和番茄嫁接的常用优良砧木。但是,由于托鲁巴姆种子的发芽率、发芽势和发芽指数较低,苗龄较长,限制了其在工厂化育苗中的大规模应用,因此迫切需要开发其他方法及相应技术体系提高托鲁巴姆的育苗效率,降低育苗成本。为优化托鲁巴姆微扦插技术,该研究探索并优化了试管内微扦插繁殖托鲁巴姆技术,以无菌播种获得初代无菌苗的茎段为外植体,通过在培养基中添加植物生长调节剂,对比不同浓度植物生长调节剂对托鲁巴姆微扦插繁殖过程中的影响。结果表明:(1)托鲁巴姆在不同培养基中,腋芽诱导、继代增殖和生根培养的效果存在显著差异,初代芽诱导的最佳培养基为MS+KT 0.5 mg·L^-1+IBA 0.1 mg·L^-1,出芽率达90%。(2)继代扦插最佳培养基为MS+IBA 0.4 mg·L^-1,培养30 d的增殖系数达6.11,植株长势健壮。(3)最佳生根培养基为1/2MS+IBA 0.2 mg·L^-1,生根培养30 d,单株一级根数4.56条,最长根长125.80 mm、根粗0.50 mm,根系发达。采用试管内微扦插技术繁殖托鲁巴姆种苗,操作简单,增殖系数较高,可满足快速繁育种苗的要求。该研究结果为托鲁巴姆的工厂化规模育苗提供了新途径。     

由细胞质雄性不育系（CMS）配制的小麦F1杂种优势形成机理的比较蛋白质组分析

分别以苗期（分蘖）、拔节期、抽穗期叶片和花粉母细胞减数分裂期、小孢子双—三核期、花粉粒时期的花药为材料,对由小麦CMS与恢复系杂交F1杂种优势形成机理作了比较蛋白质组分析。结果表明,F1杂种中有超亲、亲二型和低亲三种蛋白质表达类型出现,出现频率为亲二型＞低亲＞超亲。对这三种类型共17个蛋白质斑点作了质谱分析,其功能涉及DNA和蛋白质合成、能量代谢、环境防御,基因转座及光合作用等。苗期生长特性如叶鲜重、叶干重、叶片数,F1杂种倾向于双亲,没有观察到杂种优势现象,这与F1叶片中蛋白质表达多数呈亲二型相吻合。但F1中分蘖数多于双亲,因此其总鲜重、干重、总叶片数明显呈现出杂种优势,然而这种杂种优势现象与蛋白质组的变化是否有关需进一步研究。     

广西多穗柯叶片性状变异及幼苗生长量研究

多穗柯是一种珍贵天然野生药用植物,可以开发出保健食品色素和天然医用药品,广西的资源较丰富,该研究采集巴马、那坡、德保及田林等4个产地的多穗柯种子进行播种育苗,并跟踪调查测定一年生幼苗的叶片性状及幼苗生长量,并进行相关性分析。结果表明:(1)不同产地间叶片性状及幼苗生长指标均存在不同程度的差异,其中巴马与那坡、德保、田林在叶长、叶宽、叶面积、叶脉间距、叶鲜重、叶片干物质含量、叶片组织密度等叶片性状上的差异均达到显著水平,在株高、地径、单株干重、主根长、单株根干重及单株叶干重等生长指标上亦存在显著差异,且生长量是后3个产地的1~2倍;通过比较各产地的叶片保水力及植株净生长量,巴马的多穗柯植株耐旱性及生长速度优于其他三地。综合各性状表现,认为巴马的多穗柯苗期表现比较好,生长速度快,长势好,抗旱性较强,可作为多穗柯优良种源的初步选择。(2)8月份是多穗柯株高、地径的生长高峰期,建议此时应加强肥水管理,调节适宜的水肥光热条件,尽量延长幼苗的快速生长时间,以获得苗木的最大累积生长量。(3)叶片性状与幼苗生长量的相关性分析结果显示,叶面积与株高、地径、单株干重、单株根干重以及单株叶干重等呈极显著正相关,叶脉间距、叶绿素相对含量(SPAD)与株高、单株干重呈显著或极显著正相关,比叶面积与株高、地径呈显著负相关。因此,在以后的优株表型选择中,要优先考虑叶子大、叶脉间距宽、中老熟叶片叶色浓绿的植株。该研究结果为多穗柯优良种质资源的早期筛选提供了一定的依据。     

Growth stimulation inPhaseolus vulgaris L. induced by gamma irradiation of seeds

Gamma radiation in doses 0.13 to 0.77 C kg^-1 (0.5 to 3.0 kR) significantly (P ≥ 0.01) stimulated seed germination, seedling height, and length of primary leaves of French bean cv. ‘Blue Lake’; these doses did not affect chlorophyll content per leaf area unit. Doses of 1.16 to 1.93 C kg^-1 (4.5 to 7.5 kR) induced inhibition of the four parameters studied.     

Germination and seedling growth under anaerobic conditions in Echinochloa crus-galli (barnyard grass)*

Abstract Although rice has long been recognized to be uniquely adapted for growth in low oxygen environments of flooded rice fields, rice weeds of the Echinochloa crus-galli complex appear to be at least as well specialized for germination and growth under such unusual biological conditions. Seeds of two varieties of E. crus-galli germinate and grow for prolonged periods in a totally oxygen-free environment. E. crus-galli germinates as well as rice (Oryza sativa) under a total nitrogen atmosphere and produces as large a seedling in spite of its much smaller seed size. Like rice, the seedlings of E. crus-galli are unpigmented, the primary leaves do not emerge from the coleoptile and no root growth occurs without oxygen. Of particular interest is the ultrastructure of mitochondria from anaerobically-grown seedlings. Mitochondrial profiles from the primary leaf of seedlings grown continuously in nitrogen are very similar to those grown aerobically. The size and shape of the mitochondria are similar and the cristae are numerous and normal in appearance. This is in sharp contrast to previous studies of other species which have reported that mitochondria were vesiculate and tended to lose their normal fine-structure after similar periods without oxygen. Finally, based on ultrastructure and ¹⁴C labeling studies, anaerobically-grown seedlings are highly active metabolically, which may explain, at least for E. crus-galli var. oryzicola, its ability to germinate and emerge from flooded rice fields.     

Effect of soil matric potential on leaf water potential,diffusive resistance,growth and development ofGmelina arborea L. seedlings

Gmelina arborea L. seedling growth and diurnal stomatal opening (as measured by stomatal resistance) were studied at soil matric potential 0, -0.1 and -0.72 × 10^?5 Pa. Leaf area, leaf number, plant height and dry weights of the vegetative parts were significantly reduced as soil matric potential decreased from 0 to -0.72 × 10^?5 Pa. The growth responses followed the same trend as net assimilation rate and relative growth rate. The highest moisture stress induced leaf senescence and leaf fall. Leaf water potential decreased from - 2 × 10^?5 Pa to - 20 × 10^?5 Pa with increasing soil moisture stress. Results indicate that the diurnal stomatal opening is controlled by photon flux density when this species is grown at soil matrio potential 0 Pa. However, with decreasing soil matrio potential (- 0.10 and -0.72 × 10^?5 Pa) the internal plant water deficit appears to oontrol the stomatal opening.     

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi

A greenhouse assay to screen sunflower for resistance to Alternaria helianthi is described. A comparison of conditions led to the following standard conditions being recommended. The first or second pair of leaves of seedling plants at the V8 growth stage are inoculated using inoculum grown on sunflower leaf extract agar for 5–10 days at an inoculum density of 1–2 spores cm² of leaf tissue. A 48 h dew period should be applied to plants covered by a plastic tent. A dew period temperature of 26/26°C night/day and a post-dew period temperature relative to that experienced under local growing conditions should be applied. Lesions are measured 7 days after inoculation, and mean lesion size per plant is calculated. Mean lesion size of lines being tested is expressed as a proportion of the mean lesion size of a susceptible standard included in each screening experiment.     

Size dependence of leaf area and the mass of component organs during a course of self-thinning in a hinoki (Chamaecyparis obtusa) seedling population

The allometric equation, y=gx^h, was applied monthly to the relationships between two different dimensions of tree seedlings of hinoki cypress (Chamaecyparis obtusa) during a course of self-thinning from April 1990 to March 1991 to detect differences in biomass allocation among individuals. As the h-value in the allometry of crown length and seedling height was greater than unity for all seasons, crown ratio became greater as seedling height increased. Leaf weight ratio increased with increasing seedling size because the h-value in the allometry of leaf dry weight and whole seedling dry weight was greater than unity in every month. Therefore, smaller seedlings are disadvantageous to photosynthetic production by leaves. In contrast, the leaf area ratio was constant irrespective of seedling size because the h-value in the allometry of leaf area and whole seedling dry weight was nearly equal to unity in most seasons. In addition, because the h-value in the allometry of leaf area and leaf dry weight was less than unity in all seasons, specific leaf area decreased with an increase in leaf dry weight, indicating that smaller seedlings adapt to low light environments by possessing shade leaves. Root weight ratio decreased with increasing seedling size because the h-value in the allometry of root dry weight and whole seedling dry weight was less than unity in most seasons.