Time-lapse imaging of self- and cross-pollinations in Brassica rapa

Background and Aims

Pollination is an important process in the life cycle of plants and is the first step in bringing together the male and female gametophytes for plant reproduction. While pollination has been studied for many years, accurate knowledge of the morphological aspects of this process is still far from complete. This study therefore focuses on a morphological characterization of pollination, using time-series image analysis of self- and cross-pollinations in Brassica rapa.

Methods

Time-lapse imaging of pollen behaviour during self- and cross-pollinations was recorded for 90 min, at 1 min intervals, using a stereoscopic microscope. Using time-series digital images of pollination, characteristic features of pollen behaviours during self- and cross-pollinations were studied.

Key Results

Pollen exhibited various behaviours in both self- and cross-pollinations, and these were classified into six representative patterns: germination, expansion, contraction, sudden contraction, pulsation and no change. It is noteworthy that in ‘contraction’ pollen grains shrunk within a short period of 30–50 min, and in ‘pulsation’ repeated expansion and contraction occurred with an interval of 10 min, suggesting that a dehydration system is operating in pollination. All of the six patterns were observed on an individual stigma with both self- and cross-pollinations, and the difference between self- and cross-pollinations was in the ratios of the different behaviours. With regard to water transport to and from pollen grains, this occurred in multiple steps, before, during and after hydration. Thus, pollination is regulated by a combination of multiple components of hydration, rehydration and dehydration systems.

Conclusions

Regulated hydration of pollen is a key process for both pollination and self-incompatibility, and this is achieved by a balanced complex of hydration, dehydration and nutrient supply to pollen grains from stigmatic papilla cells.     

八种广西特有报春苣苔属植物开花生物学特性研究

广西是报春苣苔属植物的世界分布中心,特有种较多。该研究针对线叶报春苣苔(Primulina linearifolia)、条叶报春苣苔(P. ophiopogoides)、刺齿报春苣苔(P. spinulosa)、大根报春苣苔(P. macrorhiza)、线萼报春苣苔(P. linearicalyx)、癞叶报春苣苔(P. leprosa)、桂中报春苣苔(P. guizhongensis)、百寿报春苣苔(P. baishouensis),八种广西特有种的开花物候期、开花动态、子房发育情况、花粉活性等开花生物学特性进行了研究。结果表明:(1)八种广西特有报春苣苔属植物在野外及人工环境下部分种在花期、单株开花量、单花开放持续时间具有显著性差异。人工栽培植株在单株开花量、单花开放持续时间要优于野生植株。(2)不同物种的单花花期长短不同,为3～14 d。雄蕊在花蕾阶段已经基本完成生长。雌雄蕊成熟期不一致,雄蕊先于雌蕊成熟。(3)花冠半开放至完全打开阶段的花粉活性最高,均在90%以上。(4)花冠完全开放阶段的柱头可授性最强。(5)自花授粉不能结实,异花授粉可正常结实,自交种子发芽率在80%以上。综上结果不仅为解决珍稀物种的繁殖障碍和保存种质资源提供了数据支持,而且对后续提高报春苣苔属的杂交育种成功率具有重要意义。     

Personal stigma in schizophrenia spectrum disorders: a systematic review of prevalence rates,correlates, impact and interventions

A systematic electronic PubMed, Medline and Web of Science database search was conducted regarding the prevalence, correlates, and effects of personal stigma (i.e., perceived and experienced stigmatization and self‐stigma) in patients with schizophrenia spectrum disorders. Of 54 studies (n=5,871), published from 1994 to 2011, 23 (42.6%) reported on prevalence rates, and 44 (81.5%) reported on correlates and/or consequences of perceived or experienced stigmatization or self‐stigma. Only two specific personal stigma intervention studies were found. On average, 64.5% (range: 45.0–80.0%) of patients perceived stigma, 55.9% (range: 22.5–96.0%) actually experienced stigma, and 49.2% (range: 27.9–77.0%) reported alienation (shame) as the most common aspect of self‐stigma. While socio‐demographic variables were only marginally associated with stigma, psychosocial variables, especially lower quality of life, showed overall significant correlations, and illness‐related factors showed heterogeneous associations, except for social anxiety that was unequivocally associated with personal stigma. The prevalence and impact of personal stigma on individual outcomes among schizophrenia spectrum disorder patients are well characterized, yet measures and methods differ significantly. By contrast, research regarding the evolution of personal stigma through the illness course and, particularly, specific intervention studies, which should be conducted utilizing standardized methods and outcomes, are sorely lacking.     

Proactive strategies to avoid infectious disease

Infectious disease exerts a large selective pressure on all organisms. One response to this has been for animals to evolve energetically costly immune systems to counter infection, while another--the focus of this theme issue--has been the evolution of proactive strategies primarily to avoid infection. These strategies can be grouped into three types, all of which demonstrate varying levels of interaction with the immune system. The first concerns maternal strategies that function to promote the immunocompetence of their offspring. The second type of strategy influences mate selection, guiding the selection of a healthy mate and one who differs maximally from the self in their complement of antigen-coding genes. The third strategy involves two classes of behaviour. One relates to the capacity of the organisms to learn associations between cues indicative of pathogen threat and immune responses. The other relates to prevention and even treatment of infection through behaviours such as avoidance, grooming, quarantine, medicine and care of the sick. In humans, disease avoidance is based upon cognition and especially the emotion of disgust. Human disease avoidance is not without its costs. There is a propensity to reject healthy individuals who just appear sick--stigmatization--and the system may malfunction, resulting in various forms of psychopathology. Pathogen threat also appears to have been a highly significant and unrecognized force in shaping human culture so as to minimize infection threats. This cultural shaping process--moralization--can be co-opted to promote human health.     

Pollen-stigma interference in two gynodioecious species of Lamiaceae with intermediate individuals

BACKGROUND AND AIMS: Intermediate individuals (perfect flowers with very high degree of pollen abortion) in a gynodioecious plant species are very rare. A study is made of male-female relationships in each flower type and how floral characters can enhance the avoidance of 'pollen discounting' and 'self-pollination' in two gynodioecious species, Teucrium capitatum and Origanum syriacum. METHODS: The relationship between stigma receptivity and pollen viability was studied in two gynodioecious protandrous species of Lamiaceae, in addition to measuring some floral morphological characters over the life span of the flowers. KEY RESULTS: Three plant types in each species were found: plants bearing hermaphrodite (or male fertile) flowers (MF), female (or male sterile) flowers (MS) and intermediate flowers (INT). Plant types differed in flower size, with MS types being shorter than the other two types. There was no difference in style length among plant types in T. capitatum. Stigma receptivity decayed with floral age and was negative and significantly correlated with pollen viability in the two species, and positive and significantly correlated with style length in O. syriacum but only in MS flowers of T. capitatum. CONCLUSIONS: Reduction in size of floral characters is associated with male sterility, except style length in T. capitatum. MF flowers have two successive reproductive impediments: self-pollination and pollen-stigma interference. In both species, self-pollination is avoided by dichogamy (negative correlation between stigma receptivity and pollen viability), and pollen-stigma interference shows two different patterns: (1) style elongation in O. syriacum is characterized by a significant length increase, final MF dimensions are greater than those of MS dimensions, and style length is positively and significantly correlated with stigma receptivity; and (2) style movement in T. capitatum is characterized by a non-significant increase in style length, final MF floral dimensions are similar to those of MS dimensions, and there is no correlation between style length and stigma receptivity.     

Wind-dragged corolla enhances self-pollination: a new mechanism of delayed self-pollination

BACKGROUND AND AIMS: Delayed self-pollination is a mechanism that allows animal-pollinated plants to outcross while ensuring seed production in the absence of pollinators. This study aims to explore a new mechanism of delayed self-pollination facilitated by wind-driven corolla abscission in Incarvillea sinensis var. sinensis. METHODS: Floral morphology and development, and the process of delayed self-pollination were surveyed. Experiments dealing with pollinator and wind exclusion, pollination manipulations, and pollinator observations were conducted in the field. KEY RESULTS: Delayed self-pollination occurs when the abscising corolla driven by wind drags the adherent epipetalous stamens, thus leading to contact of anthers with stigma in late anthesis. There is no dichogamy and self-incompatibility in this species. The significantly higher proportion of abscised corolla under natural conditions as compared with that in wind-excluding tents indicates the importance of wind in corolla abscission. When pollinators were excluded, corolla abscission significantly increased the number of pollen grains deposited on the stigma and, as a result, the fruit and seed set. Only half of the flowers in plots were visited by pollinators, and the fruit set of emasculated flowers was significantly lower than that of untreated flowers in open pollination. This species has a sensitive stigma, and its two open stigmatic lobes closed soon after being touched by a pollinator, but always reopened if no or only little pollen was deposited. CONCLUSIONS: This delayed self-pollination, which involved the movement of floral parts, the active participation of the wind and sensitive stigma, is quite different from that reported previously. This mechanism provides reproductive assurance for this species. The sensitive stigma contributes to ensuring seed production and reducing the interference of selfing with outcrossing. The pollination pattern, which combines actions by bees with indirect participation by wind, is also a new addition to ambophily.     

An example of flexistyly in a wild cardamom species (Amomum maximum (Zingiberaceae))

We studied the floral and pollination biology of Amomum maximum. Our observations suggest that flexistyly is present in this species, and stigmatic behavior is similar as reported for Alpinia species. Two phenotypes occur in a ratio of 1:1 in natural populations. No fruit set occurred in the unpollinated bagged plants. Significant differences in seed set between selfing and crossing manipulations demonstrate that inbreeding depression or partial self-incompatibility is apparent in this species. Despite the resemblance in floral behavior, there are still some differences between the previous studies and ours: with special floral design, the body size of legitimate visitors ranged wider in Amomum maximum than in Alpinia species; the presence of anther appendage is suggested to prevent competing and delayed selfing. This is the first report of flexistyly in a wild cardamom species, which is the second largest group in ginger family (Zingiberaceae).     

有花植物触敏柱头的闭合行为及其适应意义

有花植物触敏柱头的闭合行为一直是传粉生态学和进化生物学研究的热点问题之一。植物花的多裂片柱头在传粉者接触后迅速闭合的现象主要存在于玄参目的一些类群中。早在上个世纪初,植物学家就对花的柱头闭合现象进行过初步的研究,认为柱头闭合主要是由于花粉在柱头上萌发时吸收水分导致柱头细胞膨压降低而引起的;并对柱头闭合的适应性提出了一些假说。近年来,许多学者研究证实柱头闭合能促进花粉萌发及花粉管伸长,或减少花粉散出与柱头接受花粉间的相互干扰,提高传粉者访问过程中花粉的散播量,并且柱头的状态会直接影响传粉者的取食行为。到目前为止,对柱头闭合的机制及其避免自交的假说还存在许多争议。关于触敏柱头的闭合行为,尤其是其适应机制及其生态学意义还有待更加系统和深入的研究。本文概述了触敏柱头的研究进展,并对研究中尚存在的一些问题进行了讨论。     

白杨派树种雌蕊柱头可授性及其检测方法的研究

以银腺杨、毛新杨和银毛杨为材料,采用定期授粉观察以及联苯胺-过氧化氢染色等方法,对白杨派树种雌蕊柱头可授性进行了研究,结果表明:在温室水培条件下,白杨树种雌蕊柱头的可授期一般在1~3 d内,其中毛新杨雌蕊柱头可授期比银腺杨和银毛杨相对短些.但3个树种进入最佳授粉时期时的柱头开裂角度约为180°,此时柱头发亮且表面有大量分泌物存在;在适宜授粉时期内,用联苯胺-过氧化氢染色后柱头变蓝,并有气泡产生。在育种实践中,可根据柱头形态以及联苯胺-过氧化氢染色后柱头颜色变化和气泡产生情况及时判别有关白杨派树种最佳授粉时期。     

硅藻中国新记录种——帕瓦拉桥弯藻

在对湖南省硅藻多样性研究过程中,发现其中一采自湘江的桥弯藻种类具有以下鉴定特征:(1)细胞小,长度小于29 μm;(2)壳面略微呈背腹之分;(3)远缝端末梢向壳面背侧弯曲;(4)顶孔区很小,由1～3横列形态不同的两种类型孔纹组成,一种孔纹与壳面上的孔纹相似,呈狭缝隙状,另一种为圆形小孔,其内部开口上方有袋盖状硅质突出物覆盖;(5)壳面背侧中部处线纹密度每10 μm为10～12条、腹侧中部处每10 μm为11～13条,孔纹密度每10 μm为30～40个;(6)在靠近壳面腹侧中央区具有1～2个孤点。经与帕瓦拉桥弯藻(Cymbella pavanaensis A. Vigneshwaran et al.)模式种群相比较,该文确定上述桥弯藻即为帕瓦拉桥弯藻。该文提供了对帕瓦拉桥弯藻超微结构的更多清晰认识,扩大了其地理分布区域,且是该种在中国的首次报道。