POLLEN LONGEVITY AND STIGMA PRE-EMPTION IN CLARKIA

The ability of pollen to effect seed set decreases with age when stored at room temperature or on the plant, but not when stored at 5 C. Seed set declines rapidly with pollen stored 10 days or more at room temperature. Seed set declines rapidly with pollen stored 4 days or more on the plant. The degree of pollen germination on the stigma and the number of pollen tubes in the style correlate positively with seed set. Pollen germination on the stigma and pollen tube growth in the style are strongly correlated with seed set for pollen stored at room temperature, but not, or only weakly, correlated for pollen stored at 5 C. In the latter case, seed sets are lower than expected, indicating a possible viability reduction associated with a post-pollination function. Inviable pollen grains temporarily interfere with normal pollen germination on the stigma. Essentially no seeds are produced when in viable pollen, immediately followed by viable pollen, is placed on a fresh stigma. However 27 to 65 seeds are produced when in viable pollen, followed in 1 to 6 days by viable pollen, is placed on fresh stigmas. New stigma surface is exposed at the center as expanding stigma surfaces carry the interfering inviable pollen toward the edge of the stigma.     

蝴蝶兰红花系品种杂交种子形态及胚培养研究

对21个蝴蝶兰自交或杂交组合的种子形态进行观察和无菌培养,结果表明,蝴蝶兰不同组合的种子形态有一定差异,平均种子长、宽及种胚长、宽分别为0.292±0.025 mm、0.073±0.003 mm及0.151±0.009 mm、0.069±0.003 mm。种子萌发率及萌发所需时间因组合而异,平均萌发率为72.4%,原球茎及第一片叶出现所需时间分别为22±3 d、78±6 d,杂交组合启动萌发早、萌发率高。种子启动萌发所需时间、萌发率与果实、种子大小相关不显著,而种子启动萌发所需时间与种胚长、宽呈极显著负线性相关,表明种胚越大,萌发越快。     

Conservation of the germination capacity of pollen grains in three varieties of maize (Zea mays L.)

Maize pollen longevity is short under natural conditions, and the seed yield is hampered by poor synchronisation between pollen shed and ovule maturity. Hybridization during stress conditions could be improved if pollen is collected and stored for use at appropriate times. This study was initiated to determine the optimum conditions for in vitro maize pollen germination. The method of pollen conservation and its viability over time was also part of the study. The pollen from three Zea mays cultivars (Exp₁ 24 and 5057, two inbred lines, and Tuxpeño sequía which is an open pollinated cultivar) were used in this study. The conservation was evaluated using three different methods: room temperature, the refrigerator (+10°C), and deep‐freezing at ?20°C. Two base culture media (Brewbaker &; Kwack, Heslop‐Harrison) were used for in vitro pollen germination. The effects of saccharose concentrations, incubation and desiccation times, were also evaluated. Results from this study showed that, Heslop‐Harrison medium was better than Brewbaker and Kwack or and with pollen germination. Pollen stored in a refrigerator (+10°C) varying desiccation times, yielded the following findings: for a short conservation time (10 days maximum), there is no need for a prior desiccation. For a medium conservation time (between 16 days and 20 days), five to six hours desiccation time are needed to obtain maximum germination for inbred line Exp₁ 24 and for the composite variety Tuxpeño sequía respectively. It was also determined that, at room temperature, maize pollen could germination is longer than 24?hours. The use of deep‐freezer at ?20°C did not yield any consistent result. In vivo germination test in a maize field will be necessary to confirm the above in vitro germination.     

Effects of prior self-pollination on outcrossed seed set in tristylous Pontederia sagittata (Pontederiaceae)

The potential inhibitory effects of incompatible pollen on outcrossed seed set were investigated in mass-flowering, self-incompatible, tristylous Pontederia sagittata. Prior application of self pollen, followed after 2, 4, or 6 h by compatible pollen, was conducted on five genotypes of each of the three style morphs under uniform glasshouse conditions. The greatest reductions in seed set occurred in pollinations of the long-styled (L) morph at the 6 h time interval. Smaller reductions were also found for this treatment in the mid-styled (M) morph. No significant reductions in seed set were observed in the short-styled (S) morph or in the other morphs at shorter time intervals. Observations of pollen germination and pollen tube growth indicated that the lack of inhibitory effects in the S morph may occur because relatively few pollen grains adhered to stigmas in selfpollinations. In the L and M morphs, early germination of self pollen may cause physical clogging of the stigma and style, resulting in a reduced number of compatible pollen tubes in styles. Observations of the structural integrity of styles indicated that prior germination of self pollen resulted in more rapid onset of pistil senescence, particularly in the L morph. These influences may contribute to the morph-specific differences in seed set observed following prior self-pollination of outcrossed flowers. The negative effects of incompatible pollen are likely to be most evident where ecological factors cause delays in the delivery of outcross pollen to stigmas.     

Breakdown of self-incompatibility during pistil development in Lycopersicon peruvianum by modified bud pollination

Summary Stylar self-incompatibility barriers in L. peruvianum can be avoided if pollen germination and growth through immature pistils is promoted under specific environmental conditions approximately 2–3 days before the initiation of anthesis. Since immature stigmas lack sufficient exudate for pollen germination, the sandwiching of a thin layer of pollen germination medium between the stigma and a mineral oil layer containing pollen allows precocious pollen germination and some compatible pollen tube growth through the style. This procedure is rapid, inexpensive, applicable in the field, and makes efficient use of pollen. Consistent though low seed yields have been obtained. A high proportion of aborted seed, seedling lethals, and aberrant seedling phenotypes in selfed progeny indicate the presence of strong post-zygotic barriers to such selfing. No evidence for a reduction in the strength of the SI response with increasing pistil age was observed.     

Studies on flower longevity in Digitalis

Flower lifespan was terminated by corolla abscission 5–6 days after stigma opening in the unpollinated flower. Increased pollen loads produced increased seed set and reduced flower longevity progressively to a minimum of one day after pollination with pure pollen. Weakening of the abscission zone was detectable 8 h after pollination, whilst the pollen tubes were still within the stigmatic zone, suggesting that a stimulus, moving at 4 mm h^–1 minimum, was transmitted through the style and ovary. Soon after pollination removal of the stigma prevented the pollination-induced corolla abscission. Later it was necessary to remove the stigma and upper style, and later still the whole style to delay abscission. The progressive induction of the stigma and style took place at a rate of 1.5 mm h^–1, in advance of the pollen tubes which grew at 0.75 mm h^–1. It was not possible to reproduce the pollination effects by application of indoleacetic acid (IAA) to the stigma or the style.Abbreviation IAA Indoleacetic acid     

The effects of pollen load size and donor diversity on pollen performance, selective abortion, and progeny vigor in Mirabilis jalapa

The influence of pollen competitive environment on pollen performance (pollen germination, stigmatic penetration, and pollen tube growth rate), the maturation or abortion of initiated fruit, seed size, and seedling vigor was explored by manipulating the size and diversity of stigmatic pollen loads on Mirabilis jalapa. All aspects of pollen performance significantly increased with the number of pollen grains on a stigma or pollen tubes in a style, but was not influenced by the diversity of pollen donors. Plants tended to mature single-ovulate fruits that came from flowers where pollen load size and diversity were greatest and aborted those where these were lowest. No plants from seeds resulting from pollinations with a single pollen grain survived, but other fitness measures were mostly determined by maternal plant. The data suggest that pollen performance is influenced by pollen competitive environment, and both the genetic diversity of the pollen load and number of competing pollen tubes are important determinants of seed/fruit abortion.     

青藏高原东缘61种常见木本植物种子萌发特性及其与生活史的关联

为了评价亚高山地带木本植物种子萌发对策及其与生活史关联, 该文对青藏高原东缘61种常见木本植物的种子萌发特征以及种子萌发与种子大小、扩散方式、海拔及生境的关系进行了调查分析。结果表明: 1) 61种植物的种子萌发率呈现偏斜、双峰分布。6种植物(9.8%)的种子萌发率大于80%, 13种(21.3%)的萌发率在60%~80%之间, 9种(14.8%)的萌发率在40%~60%之间, 8种(13.1%)的萌发率在20%~40%之间, 25种(41%)的萌发率小于20%, 其中8种植物的种子萌发率为零, 显示了该生境中木本植物的种子以休眠、低萌发率或连续稳定的萌发对策占优势, 以避免不利的环境因素。2)种子扩散方式是决定61种木本植物种间萌发率变异(R² = 24.1%, p < 0.001) 和萌发开始时间变异(R ²= 21.3%, p < 0.01) 的主要因素; 种子大小、母体植株的海拔和生境对种子萌发率和萌发开始时间几乎没有影响(p > 0.05); 风扩散的种子比脊椎动物扩散和无助扩散的种子有更高的萌发率(F = 9.219, p < 0.001) 和较早的萌发开始时间(F = 6.772, p < 0.01)。说明植物生活史特征如种子萌发与扩散方式之间存在固有而紧密的联系, 扩散能力强的种子(如风扩散)由于能散布到较远而空旷的生境, 可能避免了各种有害因素或个体竞争, 因而种子以较强的萌发能力进行拓殖; 扩散能力弱的种子(如无助扩散)由于其散布距离较近, 种子以休眠或降低萌发的方式来避免个体或同胞竞争以及各种有害因素, 以获得最大的生态利益并确保物种延续。     

Regulation of developmental pathways in cultured microspores of tobacco and snapdragon by medium pH

The regulation of developmental pathways in cultured microspores of tobacco (Nicotiana tabacum L) and snapdragon (Antirrhinum majus L) by medium pH is described for the first time. Unicellular tobacco and snapdragon microspores developed into normal, fertile pollen when cultured in media T1 and AT3 at pH 7.0 and 25°C for 6 and 8 days, respectively. First, pollen mitosis was asymmetric and mature pollen grains were filled with starch granules and germinated upon transfer to a germination medium. However, when tobacco and snapdragon microspores were cultured in media T1 and AT3, respectively, at pH 8.0–8.5 for 4–6 days at 25 °C, the frequency of symmetric division increased significantly with the formation two nuclei of equal size, and the gametophytic pathway was blocked, as seen by the lack of starch accumulation and the inhibition of pollen germination. The transfer of these microspores to embryogenesis medium AT3 at pH 6.5 resulted in the formation of multicellular structures in both species and, in tobacco, in the formation of embryos and plants. In order to understand the possible mechanisms of the action of high pH, sucrose metabolism was analysed in isolated microspores of tobacco cultured at various pH values. Invertase (EC 3.2.1.26) activity in microspores was maximal at pH 5.0 and strongly decreased at higher pH, leading to a slow-down of sucrose cleavage. At the same time the incorporation of ¹⁴C-labelled sucrose from the medium into microspores was drastically reduced at high pH. These data suggest that isolated microspores are not able to metabolise carbohydrates at high pH and thus undergo starvation stress, which was shown earlier to block the gametophytic pathway and trigger sporophytic development.     

Low-temperature stratification strategies and growth regulators for rapid induction of Paris polyphylla var. yunnanensis seed germination

The seeds of Paris polyphylla var. yunnanensis are deeply dormant, and they remain dormant for 18 months or longer in their natural environment. Periodic exposure of the seeds to a low-temperature of 4 °C broke the dormancy in about 16 weeks (112 days). The most effective temperature stratification scheme was an interval of 14 days at 4 °C and 14 days at 22 °C. Both GA₃ and ethephon significantly enhanced the germination rate during the stratification treatment. The seed coat, particularly the mesophyll outer layer of the seed coat, strongly inhibited the germination. With removal of the seed coat and exposure of the uncoated seeds to 600 mg/l GA₃ for 48 h before the temperature stratification of 14 days at 4 °C and 14 days at 22 °C for 112 days, a germination percentage as high as 95.3% of the seeds was attained in about 160 days.     

异叶苦竹花粉管生长及双受精过程

以异叶苦竹为材料,采用扫描电镜、荧光显微镜技术及传统的石蜡制片技术,解剖观察其花粉管生长途径及双受精过程。结果表明:(1)授粉后,花粉在柱头上吸水膨胀,约30 min即可萌发。(2)授粉1～2 h后花粉管可达到花粉长度的5～10倍,花粉管在柱头分支中进一步伸长,并开始伸入花柱中生长。(3)授粉后5 h,大量花粉管沿引导组织进入花柱基部与子房顶部之间的子房壁,有少量花粉管在子房壁与外珠被之间的缝隙中生长。(4)授粉后8 h,少量花粉管到达珠孔端。(5)授粉后15～18 h,精核与极核融合,形成初生胚乳核;精、卵核融合,形成合子。(6)授粉后20～30 h,仍可在花柱中见到大量呈束状的花粉管。(7)授粉后48 h,子房内的大部分花粉管出现解体,大多数花粉死亡。研究认为,精细胞到达胚珠的时间为8 h。     

Polyester and nylon powders used as pollen diluents preserve pollen germination and tube growth in controlled pollinations

Pollen acquisition for seed production, breeding programs and supplemental pollination can be costly and difficult. The identification of dry particulates for use as pollen diluents would facilitate the use of limited amounts of pollen and aid in accurate pollen application and dispersion. Four powders - Rilsan ES, polyester, wheat flour, and Lycopodium spores - were evaluated as pollen diluents using petunia as a model system. Diluents were combined with petunia pollen at a 5:1 (v/v) ratio. Two types of studies were conducted: (1) storage studies evaluated the viability of pollen combined and held with diluent for different durations; and (2) in vivo studies evaluated pollen tube growth in the styles of flowers pollinated with pollen-diluent mixtures. Pollen germination was not affected when stored as pollen-diluent mixtures for 4 days. Slight detrimental effects on pollen germination were observed after 6 days storage with Rilsan ES powders. Pollination with all the pollen-diluent mixtures resulted in fewer pollen tubes growing in the style compared to controls diluted with heat-killed pollen instead of diluent powders. Lycopodium-pollen mixtures were the most inhibitory, providing only 8% of the tube numbers observed in controls. Pollen mixed with polyester powders, Rilsan ES powders or wheat flour had tube numbers ranging from 47 to 61% of the control, but still had 175 or more pollen tubes per style, which would be sufficient for high rates of seed set in petunia. Wheat flour-pollen mixtures tended to clump and degrade pollen flow. Rilsan ES and polyester were identified as two promising pollen diluent powders that can facilitate accurate metering and distribution of pollen, produce large numbers of pollen tubes, and maintain pollen viability under storage.     

花冠对紫茉莉繁殖适合度的影响

以授粉后具花闭合特性的紫茉莉为研究材料,通过在不同天气状况下作去花冠和存留花冠处理,观察花冠对花粉活力、柱头可授性及结实率等繁殖特性的影响。结果表明:紫茉莉自然存留花冠比去花冠的花粉活力、柱头可授性、柱头上的花粉数及柱头上花粉萌发率各指标达最高值的时间重叠性更强,并以阴天存留花冠的最强。存留花冠通过这种时间的重叠性来保证花粉在柱头上的萌发,产生了有利的繁殖适合度。越晚去花冠结实率越高,结实率呈现花闭合自然存留花冠>花冠闭合期去花冠>散粉初期去花冠>花冠展开期去花冠的规律。因此,花冠对紫茉莉繁殖适合度具有利影响。紫茉莉花冠的存留提高了繁殖适合度,增强了对环境的适应能力。     

The effects of time,temperature and plant variety on pollen viability and its implications for gene flow risk

• Pollen viability affects the probability that a pollen grain deposited on a plant's stigma will produce a viable seed. Because a mature seed is needed before a gene flow event can occur, pollen viability will influence the risk of escape for genetically engineered (GE) crops.
• Pollen viability was measured at intervals for up to 2 h following removal of the pollen from the anthers. It was quantified at three temperatures and for different alfalfa varieties, including both conventional and Roundup Ready (RR) varieties. Pollen viability was assessed using in vitro germination.
• Time since removal from the anthers was the most prevalent factor affecting pollen viability in alfalfa. Pollen viability declined with increasing time at all three temperatures and for all varieties tested. Pollen viability was not affected by temperatures ranging between 25 and 37 °C and did not vary among plant varieties, including conventional and RR varieties.
• Bee foraging behaviour suggested pollen viability within the first 10 min following pollen removal from a flower to most affect seed production. Pollen longevity was predicted to have little impact on seed set and gene flow. Linking pollinator behaviour to pollen viability improved our understanding of its impact on gene flow risk.

     

干旱胁迫下白刺花种子大小与萌发对策

种子大小与种子萌发及其与环境因子的关系是植物种子萌发对策研究中的重要科学问题之一。采用PEG模拟干旱法研究不同干旱胁迫强度(0,5%,10%,15%,20%)下,白刺花(Sophora davidii)种子萌发进程、种子大小与种子萌发及种子命运的关系。结果表明:不同干旱胁迫下,白刺花种子具有相似的萌发进程,但中度干旱处理(10%PEG)萌发率显著高于零干旱(0%PEG)和重度干旱处理(P0.05),重度干旱处理(20%PEG)种子萌发开始时间晚于零干旱和中度干旱处理;种子大小与种子萌发开始时间的关系表现为零干旱处理下呈极显著负线性关系,中度干旱处理(5%PEG,10%PEG)下无相关关系,重度干旱处理(15%PEG,20%PEG)下呈负二次曲线关系;种子大小对种子命运的影响表现为零干旱处理有利于大、小种子萌发和小种子休眠,中度干旱处理(10%PEG)增加中等种子萌发、大种子休眠和小种子死亡风险,重度干旱处理(15%PEG,20%PEG)增加大种子死亡风险、中等种子和小种子休眠。综合分析表明,白刺花种子大小与萌发行为及种子命运的关系具有较强的环境依赖性,即种子萌发行为表现为顺境下种子越大萌发越快,逆境下小种子和大种子较中等种子萌发更快;种子命运表现为顺境增加种子死亡的风险,中度干扰有利于种子萌发,逆境则有利于种子休眠。     

The effect of petal-size manipulation on pollen removal,seed set,and insect-visitor behavior in Campanula americana

We investigated the effect of petal-size variation in tall bellflower, Campanula americana, on pollen removal rates, seed set, and pollinator behavior. Pollen removal, seed set, and the behavior of two bee visitors (Bombus and Halictus) were assessed in flowers that had 0%, 50%, or 100% of their petal lobes removed. Pollen removal rates did not differ significantly among the three treatment groups, probably due to the presence of an ineffective (ugly) pollinator (Halictus), which quickly removed pollen from completely reduced flowers. Seed set was significantly positively correlated with petal size. Bumblebees discriminated against reduced flowers, thereby lowering pollen movement to reduced flowers. Halictid bees rarely contacted stigmatic surfaces and thus pollen delivery to reduced flowers was limited. The presence of an ugly pollinator probably obscured the effect of petal reduction on pollen receipt, thus masking the impact of attractive structures on male fitness. Given the positive relationship between seed set and petal size, we caution against ascribing expenditure on attractive structures exclusively to male function. In plants with many olules, expenditure on attractive structures may affect seed set.     

The relationship of the female reproductive success of Eucalyptus globulus to the endogenous properties of the flower

Low capsule and seed set is a major factor limiting seed production in Eucalyptus globulus seed orchards. Controlled pollination studies showed that the reproductive success (number of seeds produced per flower pollinated) was primarily determined by the female. We aimed to identify the factors contributing to the differences in reproductive success between female genotypes in terms of the physical and anatomical properties of the flower. We studied pairs of genotypes of high and low reproductive success from each of three races (Furneaux Group, Strzelecki Ranges and Western Otways) growing in a seed orchard. Controlled pollinations were performed on six females and along with flower physical measurements, pollen tube growth and seed set were assessed. Overall tree reproductive success was positively correlated with flower size, ovule numbers, style size, cross-sectional area of conductive tissue within the style (all of which were inter-correlated) and the proportion of pollen tubes reaching the bottom of the style. Significant positive correlations of reproductive success and flower physical properties between different ramets of the same genotypes across seasons suggests a genetic basis to the variation observed. The majority of pollen tube attrition occurred within the first millimetre of the cut style and appeared to be associated with differences in style physiology. When examined as pairs within races the difference in reproductive success for the Western Otways pair was simply explained by differences in flower size and the number of ovules per flower. Physical features did not differ significantly for the Strzelecki Ranges pair, but the proportion of pollen tubes reaching the bottom of the style was lower in the less reproductively successful genotype, suggesting an endogenous physiological constraint to pollen tube growth. The difference in reproductive success between the females from the Furneaux Group was associated with a combination of these factors.     

Intra-inflorescence variation in floral traits and reproductive success of the hermaphrodite Silene acutifolia

BACKGROUND AND AIMS: Intraspecific variation in floral components and reproductive success is often located at the intra-individual level. The arrangement of flowers within inflorescences may explain a great deal of this variation. The variation in number of ovules, fruit set, number of seeds per fruit, seed set, seed weight and seed germination is investigated at different positions within the inflorescence of Silene acutifolia. METHODS: Data were obtained in natural populations, and germination experiments were conducted in a germination chamber. KEY RESULTS: The number of ovules, fruit set, number of seeds, seed set and seed weight, showed a significant decline from early (primary) position to later (tertiary) position. The patterns of intra-inflorescence variation were consistent in different populations and years of study. Seed germination showed an opposite pattern, seeds from primary position showed the lowest germination percentages and seeds from tertiary position the highest, although the effect of position on germination was only marginally significant. There was significant among-population variation in number of ovules per flower. Fruit set also varied significantly among populations, with lower fruit set in the smaller and more isolated population. No significant among-population differences were detected in number of seeds per fruit and seed set. Seeds from the smallest and more isolated population (Arnado) were the lightest. Seed germination showed strong differences between populations, seeds from Arnado started to germinate later, and showed the lowest final germination percentages. CONCLUSIONS: Architectural effects or resource competition are the most commonly proposed hypothesis to explain these patterns. Data suggest that there is less pollen available to pollinate tertiary flowers, and that there is not enough outcross pollen in Arnado. The germination percentages suggest that there is variation in the source of pollen within inflorescences, with high probability of receiving outcross pollen in flowers from primary position, and higher probability of geitonogamous crosses in tertiary flowers.     

In vitro pollen maturation and successful seed production in detached spikelet cultures in wheat (Triticum aestivum L.)

Summary Two spring wheat genotypes (cv Orofen and Chinese Spring) were compared for their in vitro pollen maturation capacity in detached spikelet cultures in a defined solid medium. Under these in vitro conditions Chinese Spring produced normal trinucleate pollen in 66.8% and Orofen in only 37.5%. In both cultivars the pollen maturation process from the middle uninucleate stage took approximately 3 days longer in vitro than in vivo. The pollen maturation time depended on the microspore developmental stage at the time that the culturing started. The viability, germination capacity, and fertilizing ability of the in vitro matured pollen also differed between the two genotypes. The seed set achieved in vitro (averagely 12.8%) offers promise for the practical application of this method for producing controlled or selected offspring.     

Nectar replenishment and pollen receipt interact in their effects on seed production of Penstemon roseus

Resource supply and pollen delivery are often thought to equally limit seed production in animal-pollinated plants. At equilibrium, plants should show no response to experimental pollen supplementation because resources limit seed set above the current level of pollen attraction, while experimental reduction in pollen deposition below the equilibrium level would reduce seed set. The predicted equilibrium may be disrupted, however, if plants expend additional energy to replenish removed nectar. We investigated the combined effects of nectar removal and pollen delivery on female reproductive success of Penstemon roseus (Plantaginaceae), a hummingbird-pollinated plant that replenishes removed nectar. We first documented that the frequency of experimental nectar removal was correlated with total nectar secretion; and increased frequency of nectar removal resulted in increased female reproductive costs to the plant. Trade-offs between investing resources in nectar and investing resources in seeds were then investigated in two contrasting natural populations by removing nectar from flowers at increasing frequencies while simultaneously hand-pollinating flowers with increasing amounts of pollen. Seed set was lowest at low levels of pollen deposition, highest at medium-sized pollen loads, and intermediate when pollen loads were highest. At both sites, the frequency of nectar removal and pollen deposition had an interactive effect on seed production, in that intermediate levels of nectar removal result in the absolute highest seed set, but only at intermediate pollen loads. At high pollen loads, seed set was higher following little to no nectar removal, and at low pollen loads, all rates of nectar removal affected fecundity equally. Seed mass responded to nectar removal and pollination differently than did seed set. High levels of nectar removal and pollen delivery both lowered seed mass, with little interaction between main effects. Our findings are among the first to demonstrate that nectar replenishment costs and pollination intensity jointly affect seed production. This conflict between nectar replenishment costs and pollen-limiting factors results in trade-offs between pollinator attraction and seed provisioning. Thus, resource allocation towards nectar production should more often be considered in future studies of pollen limitation.