对植物血红蛋白功能的新发现——调节NO的生物活性

血红蛋白在植物中广泛存在,对其功能的研究也不断深入。最新研究发现植物血红蛋白除具有运载氧、感应氧等生理功能外,还对植物诸多代谢活动发挥重要的调控作用,而这一作用主要通过调节信号分子NO的生物活性来实现。综述了在正常生长及胁迫条件下,植物血红蛋白对NO生物活性的调节作用,着重阐述缺氧条件下植物血红蛋白在解除NO毒害,再生NAD(P) 及维持能量水平等方面的功能及其机制。植物血红蛋白功能的这一新发现对研究不同条件下NO信号转导途径的调节机制具重要意义。     

一氧化氮在植物生长发育和抗逆过程中的作用研究进展

NO不仅在植物的抗病过程中发挥重要作用,同时也参与植物生长、发育和对干旱、高盐、高温、低温等非生物胁迫的响应等过程。该文对近年来国内外有关NO在植物生长、发育、非生物胁迫抗性过程中的作用及其与植物激素之间的互作关系等方面的研究进展进行综述,为相关研究提供信息和资料。     

植物FLOWERING LOCUS T/TERMINAL FLOWER1基因家族的研究进展

植物FLOWERING LOCUS T/TERMINAL FLOWER1(FT/TFL1)基因家族是一个进化上高度保守的基因家族,它在植物的花发育过程中具有重要作用:其成员FT基因编码的蛋白产物是可以长距离转运的成花激素,在花形成过程中起关键作用;另一成员TFL1基因则在花序的形成和维持过程中起重要作用.本文就近年来国内外对植物FT/TFL1基因家族的结构、成员,以及各个成员在花发育转换过程中的功能等研究现状进行综述,并对该基因家族的研究前景提出展望.     

调控植物花发育的MYB类转录因子研究进展

MYB转录因子是植物中最大的转录因子家族之一,在植物生长发育的各环节发挥重要作用。植物花发育是植物生殖生长过程中最为重要的过程。我们通过对大量文献的总结,简要综述了MYB类转录因子的结构和功能,重点对MYB类转录因子在植物花发育过程中的调控机理做综合阐述。     

植物MADS-box 基因FRUITFULL(FUL)研究进展

植物MADS-box基因家族的不同成员在植物生长发育过程中起着非常重要的作用。拟南芥MADS-box 基因FRUITFULL(FUL) 在控制拟南芥开花时间、花分生组织分化、茎生叶形态以及心皮和果实的发育中起到重要作用。其他植物中,FUL的同源基因也在调控花发育,果实发育以及叶片发育等方面各自起到重要作用。本文综述了FUL基因及其同源基因的表达模式和功能,并就其在农作物及果树育种上的潜在应用价值进行了讨论。     

气孔发育机制及其内外调控因子的研究进展

气孔是植物与外界环境进行气体与水分交换的重要通道,调节着植物的蒸腾与光合作用。在长期进化过程中,植物通过调节气孔行为和气孔发育机制来适应环境变化。不同植物气孔系的形成方式不尽相同,但过程均受到气孔发育信号网络系统的调节作用。近年来关于气孔发育机制的研究层出不穷,现重点综述各类转录因子、信号肽以及环境因子和植物激素对气孔发育的调节作用。该领域的研究为在微观层面揭示植物对环境变化的适应机制提供了科学基础。     

脱落酸在植物花发育过程中的作用

植物激素脱落酸(ABA)对植物的生长发育具有多方面的调节作用,比如种子休眠、萌发,营养生长,环境胁迫反应等。大量研究显示,ABA也参与了植物的成花调控。影响植物成花调控的环境因子,包括光周期变化、春化作用、干旱等均会导致植物体内ABA代谢的变化。本文从调控植物开花的4条主要途径与植物体内ABA代谢变化之间的相互关系,花芽分化时期ABA在植物叶芽和花芽中的动态分布以及离体培养条件下ABA对花芽分化的影响等方面总结了ABA与植物花发育这一领域的最新研究进展。对ABA在植物成花诱导和花发育中的作用进行了综合分析。     

被子植物系统学中花发育研究的进展及对今后研究的思考

从花发育研究的方法、花发育与被子植物花部结构的多样性、花发育与被子植物的系统发育以及 花发育的分子遗传学等四个方面对近年来被子植物系统学中花发育研究的主要进展作一综述,例举了 一些重要结果。同时,对该领域今后研究的方向和应注意的一些问题作了简要评论。作者认为植物的 形态结构可以看作是一个时空过程,在系统学研究中对花部性状的分析和认识应该树立动态的观点。 今后应该从动态的角度开展被子植物花的发生和发育以及性状在不同类群间的比较等方面的广泛研究,并加强对在被子植物花的起源和演化中起重要作用的花部同源异型现象的发育过程的观察。     

一氧化氮在植物抗病反应中的信号作用

近年来的研究发现,一氧化氮(nitricoxide,NO)在植物抗病反应中具有重要作用,本文概述了植物中NO的来源、NO在植物抗病反应中的信号传导作用、NO与植物中其它信号分子之间的相互作用以及NO的研究进展。     

一氧化氮对植物细胞基因表达和代谢产物合成的影响机制

一氧化氮(NO)作为一种气体信号分子,在植物体内具有多种生理功能,许多研究逐步揭示了NO在植物发育、新陈代谢和疾病响应等方面的分子机制。内源和外源NO都可以使植物组织或悬浮细胞基因表达发生变化,高通量的基因表达的研究,如转录分析等,为信号网络通路分析提供了有力的证据。我们简要综述了NO的合成途径,并讨论了次生代谢产物及细胞程序性死亡过程中依赖NO调控的相应基因及蛋白的变化,揭示了NO是一种重要的植物信号分子,有较高的研究价值。     

Flower bud differentiation and development in fruiting and non-fruiting shoots in relation to fruit set in apricot (Prunus armeniaca L.)

Situations of high flower bud drop and low fruit set without apparent causes are common in fruit trees. The term flower quality has been coined to explain differences among flowers in their capacity to set fruit, but the causes underpinning these differences are largely unknown. This lack of knowledge is based on the fact that these differences are established a posteriori and there are no criteria to determine a priori what will make a flower to set a fruit or to drop. In this work, we profit from the empirical knowledge that there are fruiting and non-fruiting shoots to explore to which extent flower bud differentiation and bud development will affect the subsequent fruit set. For this purpose, the processes from flower bud differentiation to fruit set were sequentially analyzed in both types of shoots, over 2 years. More than half of the buds from long shoots aborted development and dropped before flowering. At anthesis, most of the remaining flowers showed underdeveloped pistils that failed to sustain pollen germination or pollen tube growth along the pistil. This unsuccessful development resulted in clear differences in fruit set between both types of branches. These results highlight that flower bud differentiation and development play an important role for fruit set and that developmental timing appears critical to reach anthesis with a fully developed pistil.     

Asynchronous development of stigmatic receptivity in the pear (Pyrus communis; Rosaceae) flower

While stigma anatomy is well documented for a good number of species, little information is available on the acquisition and cessation of stigmatic receptivity. The aim of this work is to characterize the development of stigma receptivity, from anthesis to stigma degeneration, in the pentacarpellar pear (Pyrus communis) flower. Stigma development and stigmatic receptivity were monitored over two consecutive years, as the capacity of the stigmas to offer support for pollen germination and pollen tube growth. In an experiment where hand pollinations were delayed for specified times after anthesis, three different stigmatic developmental stages could be observed: (1) immature stigmas, which allow pollen adhesion but not hydration; (2) receptive stigmas, which allow proper pollen hydration and germination; and (3) degenerated stigmas, in which pollen hydrates and germinates properly, but pollen tube growth is impaired soon after germination. This developmental characterization showed that stigmas in different developmental stages coexist within a flower and that the acquisition and cessation of stigmatic receptivity by each carpel occur in a sequential manner. In this way, while the duration of stigmatic receptivity for each carpel is rather short, the flower has an expanded receptive period. This asynchronous period of receptivity for the different stigmas of a single flower is discussed as a strategy that could serve to maximize pollination resources under unreliable pollination conditions.     

β-Glucan synthetase II activity upon callose formation in the flower ofArabidopsis thaliana

Callose formation was observed in the pollens during flower development and pollen tube grown in the pistil ofA. thaliana. The accumulation of callose occurred in the tetrad in the flower bud and pollen tube. Therefore, the activity of β-glucan synthetase II (GS II), which is responsible for synthesizing the callose, was measured in the flowers on the same developmental stages. The enzyme activity was increased by about 10% while the level of callose contents was increased by about 70% in tetrads. Then, callose accumulation was increased during pollen tube growth by about 30% higher than the other stages and enzyme activity was detected, 30% more too. These results suggest that callose plays an important role in the growth of pollen and pollen tube by increasing GS II activity.     

Is non‐host pollen suitable for generalist bumblebees?

Current evidence suggests that pollen is both chemically and structurally protected. Despite increasing interest in studying bee–flower networks, the constraints for bee development related to pollen nutritional content, toxicity and digestibility as well as their role in the shaping of bee–flower interactions have been poorly studied. In this study we combined bioassays of the generalist bee Bombus terrestris on pollen of Cirsium, Trifolium, Salix, and Cistus genera with an assessment of nutritional content, toxicity, and digestibility of pollen. Microcolonies showed significant differences in their development, non‐host pollen of Cirsium being the most unfavorable. This pollen was characterized by the presence of quite rare δ7‐sterols and a low digestibility. Cirsium consumption seemed increase syrup collection, which is probably related to a detoxification mixing behavior. These results strongly suggest that pollen traits may act as drivers of plant selection by bees and partly explain why Asteraceae pollen is rare in bee generalist diet.     

The role of electrostatic forces in pollination

This paper reviews research on the role of electrostatic forces in pollination, both in natural and in agricultural systems. Researchers from various fields of biological studies have reported phenomena which they related to electrostatic forces. The theory of electrostatically mediated pollen transfer between insect pollinators and the flowers they visit is described, including recent studies which confirmed that the accumulated charges on airborne honey bees are sufficient for non-contact pollen detachment by electrostatic forces (i.e., electrostatic pollination). The most important morphological features in flower adaptiveness to electrostatic pollination were determined by means of two theoretical models of a flower exposed to an approaching charged cloud of pollen; they are style length and flower opening. Supplementary pollination by using electrostatic techniques is reported, and its possible importance in modern agriculture is discussed.     

Temperatures during flower bud development affect pollen germination,self‐incompatibility reaction and early fruit development of clementine (Citrus clementina Hort. ex Tan.)

• One of the key environmental factors affecting plant reproductive systems is temperature. Characterising such effects is especially relevant for some commercially important genera such as Citrus. In this genus, failure of fertilisation results in parthenocarpic fruit development and seedlessness, which is a much‐prized character. Here, we characterise the effects of temperature on flower and ovary development, and on pollen–pistil interactions in ‘Comune’ clementine (Citrus clementina Hort. ex Tan.).
• We examine flower bud development, in vitro pollen germination and pollen–pistil interaction at different temperatures (15, 20, 25 or 30 °C). These temperatures span the range from ‘cold’ to ‘hot’ weather during the flowering season in many citrus‐growing regions.
• Temperature had a strong effect on flower and ovary development, pollen germination, and pollen tube growth kinetics. In particular, parthenocarpic fruit development (indicated by juice vesicle growth) was initiated early if flowers were exposed to warmer temperatures during anthesis.
• Exposure to different temperatures during flower bud development also alters expression of the self‐incompatibility reaction. This affects the point in the pistil at which pollen tube growth is arrested and confirms the role of sub‐ and supra‐optimal temperatures in determining the numbers of pollen tubes reaching the ovary.

     

Nitric oxide is involved in growth regulation and re-orientation of pollen tubes

Nitric oxide (NO) controls diverse functions in many cells and organs of animals. It is also produced in plants and has a variety of effects, but little is known about their underlying mechanisms. In the present study, we have discovered a role for NO in the regulation of pollen tube growth, a fast tip-growing cellular system. Pollen tubes must be precisely oriented inside the anatomically complex female ovary in order to deliver sperm. We hypothesized that NO could play a role in this guidance and tested this hypothesis by challenging the growth of pollen tubes with an external NO point source. When a critical concentration was sensed, the growth rate was reduced and the growth axis underwent a subsequent sharp reorientation, after which normal growth was attained. This response was abrogated in the presence of the NO scavenger CPTIO and affected by drugs interfering in the cGMP signaling pathway. The sensitivity threshold of the response was significantly augmented by sildenafil citrate (SC), an inhibitor of cGMP-specific phosphodiesterases in animals. NO distribution inside pollen tubes was investigated using DAF2-DA and was shown to occur mostly in peroxisomes. Peroxisomes are normally excluded from the tip of pollen tubes and little if any NO is found in the cytosol of that region. Our data indicate that the rate and orientation of pollen tube growth is regulated by NO levels at the pollen tube tip and suggest that this NO function is mediated by cGMP.     

Distinct expression of members of the LHT amino acid transporter family in flowers indicates specific roles in plant reproduction

Sexual plant reproduction necessitates proper development of pollen, pollen germination and tube growth through various tissues of the pistil, the female organ of the flower. Finally, sperm cells are released to fertilize the female gametophyte. These processes require high metabolic activities of all tissues involved and rely on the delivery of nitrogen assimilates for success. However, transporters mediating nitrogen fluxes are mostly unknown. The presented work provides an expression analysis of members of the LHT amino acid transporter family in relation to pollen development and pollen–pistil interaction. Expression of Arabidopsis LHTs was analyzed during flower development and the location of LHT function resolved by transporter-GFP and promoter-GUS studies. GFP-LHT localization in onion cells indicates that all LHTs analyzed are targeted to the plasma membrane. We further showed that LHTs are expressed in anthers and male gametophytes where they are proposed to function in transport of amino acids for pollen development and maturation. Expression in germinating pollen, pollen tubes and transmitting tissue of the pistil points to a role of LHTs in support of the fertilization process. Overall, our study suggests that LHT function in flowers is cell or tissue specific, developmentally regulated and highly coordinated between male and female tissue.     

Better safe than sorry? A Fabaceae species exhibits unfavourable pollen properties for developing bee larvae despite its hidden anthers

Empirical evidence suggests that pollen chemistry plays an important role in shaping the pollen host spectra of many bee species. Although the underlying mechanisms are poorly understood, pollen diets of several plant taxa have experimentally been found to impede larval development of unspecialized bees. The pollen of all plant taxa, for which such a detrimental effect on bee larval development has been observed so far, is freely accessible in the flowers and thus easily harvestable for flower visitors, suggesting that this pollen might be chemically protected in order to reduce its loss to pollen-feeding animals. In the present study, we compared larval performance of five solitary bee species on pollen diets of the two Fabaceae species Onobrychis viciifolia and Lotus corniculatus, which have their anthers concealed inside the flowers, with that on control diets composed of host pollen provisions. As the complex flower morphology of the two Fabaceae species already considerably narrows the spectrum of pollen harvesting bee taxa, which might supersede costly chemical protection of the pollen, we expected bees that usually do not exploit Fabaceae to develop well on Onobrychis and Lotus pollen diets. Larval survival on the Onobrychis pollen diet was successful for all five bee species tested. In contrast, larval survival on the Lotus pollen diet was reduced in three species despite the fact that Lotus flowers are more difficult to exploit for pollen than Onobrychis flowers. We conclude that there is no trade-off between pollen concealment and pollen defence in Lotus and that pollen of morphologically complex flowers with a restricted visitor spectrum is not necessarily an easy-to-use nutritional source.