Pollen size-number trade-off and pollen-pistil relationships in Pedicularis (Orobanchaceae)

Current patterns of floral design in Pedicularis must have undergone an evolutionary process of interacting among components of floral traits, and then formed internal relationships among these traits. To detect such correlations, which may provide insight to understand flower evolution, 40 Pedicularis species representing all corolla types of the genus were studied. Results show that, interspecifically, pollen size correlates negatively with pollen number, but positively with pistil length. This suggests that plants evolve an optimal pollen size, which balances the advantages of large pollen size for gametophytic competition against the fecundity disadvantages of fewer pollen grains. In contrast to sex allocation theory, this study does not find a trade-off, but an interspecific positive correlation between pollen and ovule number. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the lack of negative correlation between male and female function.This work was supported by the State Key Basic Research and Development Plan, China (Grant No. G2000046804) to YHG. The authors would like to thank Peter K. Endress and two anonymous reviewers for providing critical comments and helpful suggestions, Qing-Feng Wang, Jing-Yuan Wang and Jin-Ming Chen for their helpful suggestions. Shi-Guo Sun, Jing Xia, and Qian Yu are thanked for their assistance in both the field work and laboratory phases of the project.     

Pre‐zygotic reproductive isolation between two synchronopatric Opuntia (Cactaceae) species in the Brazilian Chaco

• Opuntia (Cactaceae) is known for high rates of hybridization and ploidisation, resulting in the formation of new species. The occurrence of two sympatric and closely related species of Opuntia, O. elata and O. retrorsa, in Brazilian Chaco enabled us to test the hypothesis that pre‐zygotic reproductive isolation mechanisms operate in both species.
• We monitored the flowering period, as well as floral biology, and compared the morphological variation of floral structures through measurements, performed intra‐ and interspecific cross‐pollination tests, and recorded the guild of floral visitors and pollinators.
• Flowering was seasonal and highly synchronous. Floral biology exhibits similar strategies, and although floral morphology differs significantly in many of the compared structures, such morphological variation does not result in the selection of exclusive pollinators. Floral visitors and pollinators are oligolectic bees shared by both species. Opuntia elata and O. retrorsa are self‐compatible. While interspecific cross‐pollination (bidirectional) resulted in germination, the pollen tube did not penetrate the stigma.
• Opuntia elata and O. retrorsa are closely related; however, they are isolated and do not hybridise in Brazilian Chaco. We found that both have weak pre‐pollination barriers, but that they are strongly isolated by pollen–pistil incompatibility, i.e. post‐pollination barrier.

     

Single-nucleus sequencing deciphers developmental trajectories in rice pistils

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2个果梅品种雌蕊分化进程及相关生化指标分析

为了解果梅(Prunus mume Sieb.et Zucc.)雌蕊分化进程及其败育机制,采用石蜡切片法观察了不同时期果梅品种‘龙眼’(‘Longyan’)和‘大嵌蒂’(‘Daqiandi’)花芽纵切面的解剖结构,并对2个品种不同时期花器官发育状况、花芽百分率、花芽纵径和横径以及花芽中的可溶性糖、可溶性蛋白质和淀粉含量进行了测定分析.结果显示:雌蕊分化期、雌蕊分化末期及盛花期,品种‘龙眼’的不完全花比例均显著小于品种‘大嵌蒂’,其中,盛花期‘龙眼’不完全花比例仅为5.0％,而‘大嵌蒂’不完全花比例高达76.3％.品种‘龙眼’雌蕊分化过程经历未分化期、分化初期、分化期及分化末期4个阶段,且最终有95.0％的花芽在分化末期能顺利形成完全花;品种‘大嵌蒂’雌蕊分化过程则包含未分化期、分化初期、分化期、解体期、解体后修复期和分化末期6个阶段,且仅有23.7％的花芽能形成完全花.雌蕊分化的不同阶段2个品种花芽纵径和横径的变化与其分化进程基本一致.品种‘龙眼’完全花的可溶性糖和可溶性蛋白质含量均高于品种‘大嵌蒂’的完全花和不完全花、淀粉含量则低于后两者;品种‘大嵌蒂’不完全花的可溶性糖和可溶性蛋白质含量最低、淀粉含量则最高,与2个品种的完全花有显著差异.综合分析结果表明:品种‘大嵌蒂’的花芽在12月中上旬停止伸长生长、雌蕊分化停滞直至逐渐解体,这一时期即为品种‘大嵌蒂’雌蕊败育的关键时期;导致果梅雌蕊选择性败育的原因可能与花芽中大分子营养物质的分解代谢有关.     

Diurnal pollen tube growth rate is slowed by high temperature in field-grown Gossypium hirsutum pistils

For Gossypium hirsutum pollination, germination, and pollen tube growth must occur in a highly concerted fashion on the day of flowering for fertilization to occur. Because reproductive success could be influenced by the photosynthetic activity of major source leaves, we hypothesized that increased temperatures under field conditions would limit fertilization by inhibiting diurnal pollen tube growth through the style and decreasing subtending leaf photosynthesis. To address this hypothesis, G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures while at the same developmental stage (node 8 above the cotyledons). Collection and measurement were conducted at 06:00, 09:00, 12:00, 15:00, and 18:00 h on August 4 (34.6 °C maximum air temperature) and 14, 2009 (29.9 °C maximum air temperature). Microclimate measurements included photosynthetically active radiation, relative humidity, and air temperature. Pistil measurements included pistil surface temperature, pollen germination, pollen tube growth through the style, fertilization efficiency, fertilized ovule number, and total number of ovules per ovary. Subtending leaf measurements included leaf temperature, photosynthesis, and stomatal conductance. Under high temperatures the first measurable pollen tube growth through the style was observed earlier in the day (12:00 h) than under cooler conditions (15:00 h). Also, high temperature resulted in slower pollen tube growth through the style (2.05 mm h⁻¹) relative to cooler conditions (3.35 mm h⁻¹), but there were no differences in fertilization efficiency, number of fertilized ovules, or ovule number. There was no effect of sampling date on diurnal photosynthetic patterns, where the maximum photosynthetic rate was observed at 12:00 h on both dates. It is concluded that, of the measured physiological and reproductive processes, pollen tube growth rate showed the greatest sensitivity to high temperature under field conditions.     

野菊与菊花杂交中花粉活力和柱头可授性及胚胎发育研究

应用石蜡制片、活体压片、光学显微镜及扫描电子显微镜观察等方法,研究了四倍体河南云台山野菊(Dendranthema indicum)与栽培菊花'钟山金山'(D.grandiflorum 'Zhongshanjinshan')种间杂交中父本花粉活力、花粉在柱头萌发、花粉管生长及胚胎发育情况等.结果发现,父本云台山野菊的花粉活力在授粉时为12%左右.人工授粉后的不同时间,在柱头上都观察到正常萌发的花粉粒,且花粉管都能进入柱头,其中,在授粉后0.5 h时,平均每柱头有5.9粒花粉萌发;12 h时,为59.9粒;而24和48 h时,则分别降为47.1和35.7粒.此外,在授粉后8、10、12和15 d时,分别在49.1%、40.8%、39.7%和38.5%子房内观察到正常发育的胚胎,最终杂交结实率为44.8%,而母本自然开放结实率为52.3%.研究表明,授粉前其多数母本雌蕊发育良好、授粉后多数花粉能在柱头正常萌发和花粉管正常生长,在受精后大部分胚胎发育正常是野菊与栽培菊种间杂交较高结实率的重要保证,而授粉前父本较低的花粉活力对杂交结实率影响不大.     

Self-incompatibility in a distylous species of Rubiaceae: is there a single incompatibility response of the morphs?

Heterostyly is a genetically controlled floral polymorphism usually associated with an incompatibility system. This set of features is known to occur in several angiosperm families, but some aspects of its biology has not been well studied. The present study investigates cellular aspects of the pollen–pistil interaction after compatible and incompatible pollinations of Psychotria nuda, to increase our knowledge of heteromorphic self-incompatibility (HetSI). The use of bright field, fluorescence and transmission electron microscopy methods allowed us to demonstrate that pollen tubes behave differently after incompatible and compatible pollinations. Pollen tubes were particularly distinct after incompatible pollinations of L- and S-morph flowers. Relative to compatible pollen tubes, incompatible L-morph tubes had a drastic reduction in cellular contents, but no cell rupture. Incompatible S-morph tubes exhibited dense cytoplasm in apical regions, as well as in other regions, accompanied by a rupture of the apex. These results support the hypothesis that L- and S-morph flowers have different incompatibility mechanisms during HetSI.     

Reproductive biology of Boswellia serrata, the source of salai guggul, an important gum-resin

Detailed studies were carried out on the phenology, floral biology, pollination ecology and breeding system of Boswellia serrata Roxb. (Burseraceae) the source of 'salai guggul'. The trees remain leafless during the entire period of flowering and fruiting. The inflorescence is a terminal raceme and produces up to 90 bisexual, actinomorphic flowers. On average a flower produces 10 044 ± 1259 starch-filled pollen grains. About 85% of the fresh pollen grains are viable; the pollen to ovule ratio is 3348 : 1. The stigma is of the wet papillate type. The style is hollow with three flattened stylar canals filled with a secretion product. The stylar canals are bordered by a layer of glandular canal cells. The inner tangential wall of the canal cells shows cellulose thickenings. The ovary is trilocular and bears three ovules, one in each locule. Flowers offer nectar and pollen as rewards to floral visitors. The giant Asian honey bee ( Apis dorsata ) and A. cerana var. indica (Indian honey bee) are the effective pollinators. The species is self-incompatible and the selfed pollen tubes are inhibited soon after their entry into the stigma. Self-pollen tubes develop a characteristic 'isthmus' as a result of enlargement of the tube soon after emergence through the narrow germ pore. Cross-pollinated flowers allowed normal pollen germination and pollen tube growth, and resulted in fruit- and seed-set. Under open pollination fruit-set was only about 10%. Although manual cross-pollinations increased fruit set, it was only up to about 20%. Low fruit set appears to be the result of inadequate cross-pollination and other constraints, presumably limitation of available nutrients.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 73–82.     

Pollen-pistil size correlation and pollen size-number trade-off in species of Argentinian Nyctaginaceae with different pollen reserves

Data on pollen and pistil traits from 14 Argentinean Nyctaginaceae species with starch or lipids as pollen reserves are presented. We expect differences in the traits between these two groups of species, but the same pattern within each group for (a) the relationship between pollen size and pistil length assuming that pollen tube length is predetermined by provisions in the pollen independently of the pollen reserve type, and for (b) a trade-off between size and number because available resources for male function are not unlimited. In particular we expect that (a) species with longer pistils will have larger pollen grains, (b) pollen grain size and the number of pollen grains per flower will be negatively correlated. Significant differences in the mean pollen number per flower and mean pollen size were observed between species with different pollen reserve type but not for pistil length. Then, correlation analyses were performed for species with starchy pollen or with pollen with lipids separately. Pollen size - pistil length correlation was positive and significant for species with starchy pollen but not for species with pollen with lipids. On the other hand, pollen size - number correlation was not significant for both starchy and oil-rich species. Results suggest that pollen reserve type would be a relevant factor that constraint pollen size in species of Nyctaginaceae, and that this pollen trait should be considered when studying pollen-pistil relationships, mainly between species of those families with mixed pollen reserves.