Cytological basis for a tetraspory in Cupressus sempervirens L. megagametogenesis and its implications in genetic studies

 The processes of megasporogenesis and early megagametogenesis were cytologically investigated in Cupressus sempervirens L. in order to elucidate, at the cellular level, the origin of the megagametophyte. After pollination, sporogenous tissue developed in the chalazal region of the nucellus, but only one megaspore mother cell differentiated and divided meiotically without cell-wall formation. This led to the development of a cell with four nuclei which directly functioned as a megaspore. The C. sempervirens megagametophyte is thus tetrasporic, in contrast to the majority of conifers where the megagametophyte is monosporic. The consequenses of this observation are discussed from a genetics point of view. Received: 15 August 1997 / Accepted: 19 September 1997     

Insights into a hydration regulating system in Cupressus pollen grains

Background and Aims

Hydration, rupture and exine opening due to the sudden and large expansion of intine are typical of taxoid-type pollen grains. A hemispheric outgrowth external to the exine was observed on Cupressus and Juniperus pollen grains before the intine swelling and exine release. However, the actual existence of this permanent or temporary structure and its precise role in pollen hydration is still being debated. The aim of this paper is to collect information on the actual presence of this peculiar outgrowth on the surface of the Cupressus pollen grain, its structure, composition and function.

Methods

Pollen grains of several Cupressus species were observed using various techniques and methodologies, under light and fluorescence microscopy, phase-contrast microscopy, confocal microscopy, scanning electron microscopy, and an environmental scanning electron microscope. Observations were also performed on other species with taxoid-type pollen grains.

Key Results

A temporary structure located just above the pore was observed on Cupressus pollen grains, as well as on other taxoid-type pollens. It is hemispheric, layered, and consists of polysaccharides and proteins. The latter are confined to its inner part. Its presence seems to regulate the entrance of water into the grains at the beginning of pollen hydration.

Conclusions

The presence of a temporary structure over the pore of taxoid-type pollen grains was confirmed and its structure was resolved using several stains and observation techniques. This structure plays a role in the first phases of pollen hydration.     

水分胁迫对重庆石灰岩地区不同龄级柏木(Cupressus funebris Endl.)幼苗气体交换的影响

通过盆栽水分胁迫试验,采用美国Li-COR公司生产的Li-6400便携式光合测定分析仪,对比研究了水分胁迫对重庆石灰岩地区不同龄级柏木幼苗气体交换的影响。结果表明:水分胁迫降低了两种年龄柏木幼苗的净光合速率、蒸腾速率和气孔导度,1年生幼苗的净光合速率下降的幅度大于5年生幼苗。1年生幼苗的胞间CO2浓度随着水分胁迫强度的增加而升高,而气孔限制值下降,5年生幼苗在重度干旱前,胞间CO2浓度随着水分胁迫强度的增加而降低,气孔限制值上升,但重度干旱后,趋势与1年生幼苗相同,由这些指标的变化趋势分析得出,1年生幼苗的净光合速率的下降是由非气孔限制因素引起的,而5年生幼苗在重度干旱前净光合速率的下降是由气孔限制因素引起,而在重度干旱后转为非气孔因素。1年生幼苗的水分利用效率随着水分胁迫的加剧而降低,5年生幼苗水分利用效率呈上升趋势,说明5年生幼苗更能适应干旱胁迫。干旱胁迫降低了一年生柏木幼苗的表观量子产额、羧化效率以及最大净光合速率即光合能力,但光补偿点、CO2补偿点、光呼吸和暗呼吸却随着水分胁迫的加剧而升高。对于5年生幼苗,干旱胁迫对其表观量子效率、光补偿点、光呼吸及光合能力的影响基本与一年生幼苗一致。但羧化效率、CO2补偿点呈先降后升的趋势,而暗呼吸却先升后降,说明适度的干旱(未遭受重度干旱之前)提高了柏木的CO2利用能力,但因呼吸消耗较多的光合产物还是导致了其光合能力的降低,但降低的程度较一年生幼苗小,表现为对干旱环境更好的适应能力。     

Variation and inheritance of resistance to cypress aphid, Cinara cupressi Buckton in Cupressus lusitanica Miller

Cupressus lusitanica seedlings from open-pollinated seeds of 18 families were inoculated with day-old first instar Cinara cupressi. Aphid survival was used to determine the genetic basis and inheritance of resistance to the insect. There was marked variation in aphid survival both between and within families. An individual-tree narrow-sense heritability of 0.76 ± 0.30 shows strong additive genetic control which could allow effective selection and breeding for resistance. Resistant parents produced resistant progeny while susceptible parents produced susceptible progeny. There were notable exceptions as some susceptible parents produced highly resistant progeny, indicating that they had acquired pollen from resistant neighbours. Recovery of aphid damaged trees is evident implying that care should be taken in selecting for resistance. The strong additive variance and potentially high heritability indicate that one cycle of selection may yield a resistant population, while intraspecific crossing may give better results. Implications of the results in a C. lusitanica breeding programme are discussed.     

Nuclear and cell fusion cause polyploidy in the megagametophyte of common cypress, Cupressus sempervirens L.

In common cypress, Cupressus sempervirens L., the megagametophyte persists in mature seeds as a polyploid endosperm containing cells with even and odd series of DNA contents: 1C, 2C, 3C, 4C, 5C etc., where C is the amount of DNA in the haploid genome. In this study, cytometrical, histological and cytochemical investigations were performed in order to determine the behavior of megagametophyte nuclei during the reproductive cycle. Unexpected nuclear alterations due to a continuous process of nuclear fusion were observed in the megagametophyte, leading to polyploidization and consequently to intense food-reserve synthesis. During the free nuclear stage, the megagametophyte exhibited only sporadic nuclear fusion and limited food-reserve production. When cellularization took place, multinucleated compartments were observed in which nuclei fused, producing odd and even series of DNA contents as proved by flow-cytometric analysis. This polyploidization process considerably increased after fertilization and during embryo development, and was accompanied by increased food-reserve synthesis. During these later stages, fusion mainly involved nuclei of contiguous cells and was preceded by the disintegration of their adjacent walls. Mitoses with incomplete phragmoplast differentiation were also observed to yield polyploid nuclei. Finally, in mature seeds the endosperm still exhibited multinucleate cells and fusion nuclei, and contained high amounts of storage products. The results are interpreted as an alteration of DNA contents in the megagametophyte cells in relation to specific metabolic activity during seed development. Received: 2 September 1998 / Accepted: 31 December 1998     

地钱,肾蕨和中山柏的NADP硫氧还蛋白系统

硫氧还蛋白(Td)是一类低分子量酸性蛋白,具有二硫键(-s-s-),通过氧化还原互变来参与很多反应(周志民等1986)。Td可被NADP-硫氧还蛋白还原酶(NTR)还原:     

岷江上游干旱河谷岷江柏的光合与水分生理特征干湿季对比研究

岷江柏（Cupressus chengiana）是干旱河谷地区的重要生态恢复物种,为探讨岷江柏对干旱河谷环境的适应策略,以生长于岷江上游干旱河谷自然生境中的岷江柏为研究对象,研究分析了其在湿季（7月）和干季（11月）的水分生理特征和光合生理特征。结果表明：（1）水分生理方面,相较于湿季,干季岷江柏的脯氨酸（Pro）、可溶性糖（SS）、过氧化物酶（POD）显著增加（P<0.05）,比叶重（LMA）、黎明水势（Ψ_pl）、正午水势（Ψ_ml）则显著下降（P<0.05）;（2）光合生理方面,相较于湿季,岷江柏在干季的气孔导度（G_s）、蒸腾速率（T_r）、饱和光下最大净光合速率（P_nmax）、初始羧化效率（CE）、光合能力（A_max）、CO₂补偿点（Γ）、光呼吸速率（R_p）、最大羧化速率（V_cmax）、最大电子传递速率（J_max）、磷酸丙糖利用率（TPU）、J_max/V_cmax、光能捕获效率（F_v''/F_m''）、PSII实际光化学效率（Ф_PSII）、光化学猝灭系数（qP）、电子传递效率（ETR）均显著下降（P<0.05）,而暗呼吸速率（R_d）、水分利用效率（WUE）、非光化学猝灭系数（NPQ）则显著上升（P<0.05）。干季,岷江柏采取增加水分获取能力并降低水分散失的水分利用策略、增加光合产物消耗策略、增加热耗散的光合器官保护策略等,以适应干季干旱、低温等环境胁迫,进而表现出较强的环境适应性。     

宜昌市郊不同龄级柏木人工林下植物组成与多样性变化

对宜昌市郊3个不同龄级柏木人工林林下植物物种组成和多样性变化的研究,结果表明,从幼龄林、中龄林到近熟林,林下灌木层由耐旱及强阳性种趋向耐旱性较强及中性种,且乔木种逐渐增加;林下草本层由以栗褐苔草和铺地龙为主趋向以蕨类为主;灌木层和草本层物种数量、香农—威纳指数、均匀度指数均呈增加趋势,而生态优势度呈下降趋势。说明实施封育恢复后柏木人工林呈进展演替趋势,但仍处于演替早期阶段。     

四川柏木人工林林下植被生物量与林分结构的关系

森林结构与林下植被生物量的关系是森林持续经营与森林碳计量监测的科学基础,但一直缺乏必要的研究。以四川柏木(Cupressus funebris)人工林为研究对象,揭示林下植被生物量(Wu)、灌木生物量(Ws)和草本生物量(Wh)与林分结构的关系,并试图构建区域性林下植被生物量估测的混合模型。结果表明:(1)乔、灌、草群体共12个结构因子中,灌木群体的平均基径(Ds)、盖度(Cs)、高度(Hs)、体积(Vs)与林下植被生物量关系更紧密,在林下植被生物量模型构建中更有效;(2)多模型拟合与比较表明,柏木林Ws最佳估算模型为Ws=0.0005V1.0411s(R2a=0.762,P0.001,n=40),而Wu的最佳估算模型为ln Wu=0.0158Hs+0.0111Cs-0.5358(R2a=0.695,P0.001,n=40),但对于Wh未能获得较为理想的估算模型(R2a0.410,P0.01,n=40);(3)林分密度(Du)整合进入多元线性模型提高了林下植被生物量的估测精度,ln Wu=a+b Du+c Hs+d Cs(R2a=0.721,P0.001,n=40)。研究为区域性林下生物量估测模型构建提供了新论据。