Pollen Grain Germination Research Articles

Auxin abolishes inhibitory effects of methylcyclopropen and amino oxyacetic acid on pollen grain germination, pollen tube growth, and the synthesis of ACC in petunia

As established by us earlier, ethylene behaves as a regulator of germination, development, and growth of male gametophyte during the progamic phase of fertilization. However, the mechanisms of the regulation of these processes remain so far unstudied. It is believed that the main factor providing variety of the ethylene responses is its interaction with other phytohormones. According to our working hypothesis, ethylene controls germination of pollen grains (PGs) and growth of pollen tubes (PTs) by interacting with auxin, which, as the available data indicate, is likely a key regulator of plant cell polarization and morphogenesis and one of the factors modulating the biosynthesis of ethylene at the level of ACC-synthase gene expression. In the present work, on germinating in vitro male gametophyte and the pollen-stigma system for petunia (Petunia hybrida L.) effects of phytohormones (ethylene and IAA) and known blockers repressing ethylene reception (1-methylcyclopropene, 1-MCP), the synthesis of ACC (amino oxyacetic acid, AOA) and transport IAA (triyodbenzoynaya acid, TYBA) on PGs germination, PTs growth and the synthesis of ACC were investigated. According to the data obtained, exogenous ethylene and IAA stimulated both PGs germination and PTs growth. 1-MCP and TYBA completely inhibited the first process, whereas IAA abolished the inhibitory action of 1-MCP and AOA on both the above processes. Etrel only partially weakened the inhibitory effect of TYBA. Examination of ACC synthesis modulation with AOA showed that IAA does not affect the level of ACC in germinating in vitro male gametophyte and nonpollinated stigmas, while this phytohormone insignificantly raised the level of ACC and abolished the inhibitory effect of AOA on its synthesis in the pollenstigma system. Pollination of stigmas with the pollen preliminarily treated with 1-MCP led to 2.5-fold decline in both the rate of PT growth and the level of ACC. At the same time, IAA abolished the inhibitory action of 1-MCP recovering the synthesis of ACC and growth of PTs to the control values. All these results, taken together, provide evidence for the interaction of the signal transduction pathways of ethylene and auxin at the level of ACC biosynthesis in the course of germination and growth of petunia male gametophyte during the progamic phase of fertilization.

Boric acid in germination of pollen grains and fruit set of peach cultivars in subtropical region

The pollination and fertilization process directly affects the crop yield of peach. Previous studies have shown that some cultivars lack consistent cropping (yield variation) in subtropical regions. The application of boric acid at flowering can minimize this problem. This study quantified the germination of pollen grains and fruit set on 18 cultivars of peach in a subtropical region when treated with boric acid at bud. The initial spray treatments were three concentrations of boric acid (400 mgL-1, 800 mgL-1 and 1,200 mgL-1) plus a control treatment of water. Treatments were sprayed on the shoots when the flower buds were flower bud swelling on early maturing cultivars Aurora 2 and Docura 2. There is a cultivar difference where ‘Aurora 2’ had a negative effect from the application of boric acid on the percentage of germinated pollen grains and fruit set. ‘Docura 2’ has a positive results at the concentration of 400 mgL-1 of boric acid. In a follow-up experiment with 18 cultivars, using only the water control and 400 mgL-1 boric acid treatment, boron increases pollen grain germination and fruit set for some cultivars. The increase in germination and fruit set varies significantly among the cultivars. The concentration of 400 mgL-1 of boric acid increases pollen germination and fruit set, but not in all cultivars.

Flower anatomy related to blooming development of Berberis microphylla G. Forst Berberida microphylla G. Forst (berberidaceae)

Berberis microphylla G. Forst. is a Patagonian native shrub commonly named “calafate”, which has a growing economic potential due to its dark blue berries that are consumed fresh, as jams and preserves, and are used for the production of soft drinks and ice cream. Moreover, the fruits have a high content of carbohydrates, phenols and antioxidants. The objective of this work was to show the changes observed in the flower from the emergence in relation to the floral phases and the importance that they have on pollination and fertilization. During the anthesis, the nectar is excreted inside and outside of the petal through the epidermis of the secretory tissue. The epidermis of the stigma is papillae with cells of greater length in the periphery of this structure simulating an additional ring. Secretory tissue is also present on the area of the fusion carpel. During anthesis, the epidermis glands of the stigma showed active secretion and these conditions favor pollen grain germination. Germinated pollen grains were observed after 12 hours of pollination and ten days later the pollen tube reached the ovule area. Pollen tube grew surrounded the ovules and probably some of them already accomplished the fertilization.

In vitro germination and viability of pea pollen grains after application of organic nano-fertilizers

The objective of this study was to evaluate the influence of two organic nanofertilizers, Lithovit and Nagro, on in vitro germination, pollen tube elongation and pollen grain viability of Pisum sativum L cv. Pleven 4. The effect of their application was high and exceeded data for the untreated control (44.2 and 47.23 % regarding pollen germination and pollen tube elongation, respectively), as well as the effect of the control organic algal fertilizer Biofa (17.5 and 27.9 %, respectively). Pollen grains were inoculated in four culture media. A medium containing 15% sucrose and 1% agar had the most stimulating impact on pea pollen grains. Pollen viability, evaluated by staining with 1% carmine, was within limits of 74.72-87.97%. The highest viability of pollen grains was demonstrated after the application of Nagro organic nano-fertlizer.

Metabolic Control of Tobacco Pollination by Sugars and Invertases.

Pollination in flowering plants is initiated by germination of pollen grains on stigmas followed by fast growth of pollen tubes representing highly energy-consuming processes. The symplastic isolation of pollen grains and tubes requires import of Suc available in the apoplast. We show that the functional coupling of Suc cleavage by invertases and uptake of the released hexoses by monosaccharide transporters are critical for pollination in tobacco (Nicotiana tabacum). Transcript profiling, in situ hybridization, and immunolocalization of extracellular invertases and two monosaccharide transporters in vitro and in vivo support the functional coupling in supplying carbohydrates for pollen germination and tube growth evidenced by spatiotemporally coordinated expression. Detection of vacuolar invertases in maternal tissues by these approaches revealed metabolic cross talk between male and female tissues and supported the requirement for carbohydrate supply in transmitting tissue during pollination. Tissue-specific expression of an invertase inhibitor and addition of the chemical invertase inhibitor miglitol strongly reduced extracellular invertase activity and impaired pollen germination. Measurements of (competitive) uptake of labeled sugars identified two import pathways for exogenously available Suc into the germinating pollen operating in parallel: direct Suc uptake and via the hexoses after cleavage by extracellular invertase. Reduction of extracellular invertase activity in pollen decreases Suc uptake and severely compromises pollen germination. We further demonstrate that Glc as sole carbon source is sufficient for pollen germination, whereas Suc is supporting tube growth, revealing an important regulatory role of both the invertase substrate and products contributing to a potential metabolic and signaling-based multilayer regulation of pollination by carbohydrates.

Dissimilarity based on morphological characterization and evaluation of pollen viability and in vitro germination in Passiflora hybrids and backcrosses

Brazil is considered the main center of the genetic diversity and greatest worldwide producer of passion fruit. Passionfruit woodiness virus (Cowpea aphid born mosaic virus) is an important pathogenic agent of the passion fruit crop, causing severe losses in yield. Wild species of Passiflora are valuable sources of genetic resistance to this disease. Interspecific crosses are a promising method to incorporate resistance genes in commercial species (Passiflora edulis Sims.), despite problems with male sterility in developed hybrids. The objective of the present work was to study the dissimilarity based on morphological characteristics, and the viability and in vitro germination of pollen grains of progenitors, F1 hybrids, as well as progenies of the first generation of backcross BC1 [(P. edulis × P. cincinnata) × P. edulis]. Analysis of the severity of the viral disease showed that most genotypes were considered as susceptible to highly susceptible. The resistant hybrids did not show symptoms of foliar deformation. Cluster analysis showed two major groups; one represented by P. cincinnata and the second group by the hybrids and recurrent progenitor P. edulis. Morphological characterization of the hybrids showed phenotypic variation as to the color and shape of flowers, although the descriptors used were not able to show these differences. As expected, the progenitors (P. edulis and P. cincinnata) presented higher percentages of pollen viability, followed by the BC1-H45 progenies. The progenies of the BC1 will also be evaluated in the future with molecular markers aiming to accelerate the selection of hybrids with higher percentages of the genome of the recurrent parent.

Physiological influence of silica on germinating pollen as shown by Raman spectroscopy.

The process of silicification in plants and the biochemical effects of silica in plant tissues are largely unknown. To study the molecular changes occurring in growing cells that are exposed to higher than normal concentration of silicic acid, Raman spectra of germinating pollen grains of three species (Pinus nigra, Picea omorika, and Camellia japonica) were analyzed in a multivariate classification approach that takes into account the variation of biochemical composition due to species, plant tissue structure, and germination condition. The results of principal component analyses of the Raman spectra indicate differences in the utilization of stored lipids, a changed mobilization of storage carbohydrates in the pollen grain bodies, and altered composition and/or structure of cellulose of the developing pollen tube cell walls. These biochemical changes vary in the different species.

Exogenous IAA and ABA stimulate germination of petunia male gametophyte by activating Ca2+-dependent K+-channels and by modulating the activity of plasmalemma H+-ATPase and actin cytoskeleton

To date, the molecular mechanisms underlying the osmoregulation of pollen grains (PGs) related to the maintenance of their water status and allowing pollen tubes (PTs) to regulate concentrations in them of osmolytes and transmembrane water transport remain to be not so far characterized. In the present work, the data on the participation of IAA and ABA in the osmoregulation of germinating in vitro petunia male gametophyte were obtained. It has been established that the growth-stimulating effect of these phytohormones is due to their action on intracellular pH (pHc), the membrane potential of plasmalemma (PM), the activity of PM H(+)-ATPase, K(+)-channels in the same membrane and organization of actin cytoskeleton (AC). Two possible targets of the action of these compounds are revealed. These are represented by (1) PM H(+)-ATPase, electrogenic proton pump responsible for polarization of this membrane, and (2) Ca(2+)-dependent K+-channels. The findings of the present work suggest that the hormone-induced pHc shift is involved in cascade of the events including the functioning of pH-dependent K+-channels. It was shown that the hormoneinduced hyperpolarization of the PM is a result of stimulation of electrogenic activity of PM H(+)-ATPase and the hormonal effects are mediated by transient elevation in the level of free Ca(2+) in the cytosol and generation of reactive oxygen species (ROS). The results on the role of K(+) ions in the control of water-driving forces for transmembrane water transport allowed us to formulate the hypothesis that IAA and ABA stimulate germination of PGs and growth of PTs by activating K(+)-channels. In addition, the studies performed showed that the AC of male gametophyte is sensitive to the action of exogenous phytohormones, with to more extent to the action of IAA. As judged by the action of latrunculin B (LB) the AC may serve as the determinant of the level of endogenous phytohormones that most likely participate in the regulation of the polar growth of PTs impacting on the pool of F-actin in their apical and subapical zones.

ОСОБЕННОСТИ РАЗВИТИЯ МУЖСКОГО ГАМЕТОФИТА СОСНЫ ОБЫКНОВЕННОЙ PINUS SILVESTRIS L. В УСЛОВИЯХ ГОРОДСКОЙ СРЕДЫ

<p>The peculiarities of the development of the male gametophyte of Pinus silvestris L. in the urban environment were studied. Quality of pollen was evaluated by laboratory experiments through germination at the nutrient medium and by histochemical staining to determine the presence of redox enzymes. It was shown that pollen viability is closely linked to climatic and weather conditions during the period of microsporogenesis and mass pollination. Atmospheric pollution affected the pollen significantly. Low temperatures and high humidity in the background of the weak capacity of self-purification of the atmosphere led to a reduction of the potential pollen viability. The ability of the pollen grains to germinate was reduced, the number of abnormal pollen tubes was increased, and the proportion of cells containing active peroxidase was decreased. We revealed a close positive correlation between the frequency of germinated pollen grains and the presence of active peroxidase, as well as a negative correlation between the percentage of colored pollen and the frequency of pollen tube anomalies, which confirmed the role of peroxidase activity not only in the induction of pollen germination, but also the formation of pollen tubes.<br />A ranking of the urban territory on the strength of unfavorable environmental factors has been carried out. The reaction of male gametophyte of pine allowed us to consider it as a biological indicator of unfavorable ecological situation in the urban environment.</p>

Determination of cardinal temperatures for sugar apple ( Annona squamosa L.)

ABSTRACT The sugar apple is highly dependent on the pollination and fruit tree pollen performance is crucial for successful fertilization and fruit set. The objective of this study was to determine the cardinal temperatures for in vitro pollen grains germination and evaluate the effect of temperature on pollen tube growth of sugar apple. The experimental design was in a completely randomized with eight treatments (10, 15, 20, 25, 30, 35, 40 and 45 ºC), four replicates and each plot was constituted by two slides per parcel. The cardinal temperatures were determined by evaluating in vitro germination of pollen grains and pollen tube growth in standard culture medium. It also assessed the pollen tube growth and the percentage of germination in vitro depending on the type of pollen grain arrangement (monad, dyad, triad and tetrad). In vitro germination of pollen grains and pollen tube growth varied significantly with temperature. The maximum germination recorded (48.13%) and the maximum lengths of pollen tubes (536.45 μm) were obtained when pollen grains were cultivated at 25 ºC. The estimated cardinal temperatures were 9.7, 26.9 and 44.2 ºC. Among the pollen grain arrangements, tetrads pollen grains were observed in higher proportions, however, monads pollen grains presented higher germination percentage.

Actin3 promoter reveals undulating F-actin bundles at shanks and dynamic F-actin meshworks at tips of tip-growing pollen tubes

ABSTRACTThe dynamic actin cytoskeleton of pollen tubes is both the driver of the tip growth and the organizer of cell polarity. In order to understand this fast re-arranging cytoskeletal system, we need reliable constructs expressed under relevant promoters. Here we are reporting that the Lifeact reporter, expressed under the pollen-specific Actin3 promoter, visualizes very dynamic F-actin elements both in germinating pollen grains and tip-growing pollen tubes. Importantly, we have documented very active actin polymerization at the cell periphery, especially in the bulging area during pollen germination and in the apical clear zone. Expression of the Lifeact reporter under control of the pollen-specific Actin3 promoter revealed 2 new aspects: (i) long F-actin bundles in pollen tube shanks are dynamic, showing undulating movements, (ii) subapical ‘actin collars’ or ‘fringes’ are absent.

Pollen limitation is not the rule in nival plants: A study from the European Central Alps.

Seed output of high-mountain plants in the uppermost life zones is highly variable. One possible reason might be pollen limitation due to inadequate pollinator services. We tested this hypothesis for the insect-pollinated species Cerastium uniflorum, Ranunculus glacialis, and Saxifraga bryoides, which have their distribution center in the subnival and nival zone of the European Central Alps. We recorded insect visitors and determined their impact as pollinators. By analyzing pollination success and seed set following natural and saturating hand pollination, the magnitude of quantitative and qualitative pollen limitation was assessed. Anthomyiid and muscid flies had the highest pollination impact for R. glacialis and S. bryoides and syrphids for C. uniflorum. Natural stigma pollen load was highly variable in individual flowers of all species, but in most cases the number of conspecific pollen grains clearly exceeded the number of ovules to be fertilized. There was also a surplus in germinated pollen grains, whereas the pollen tube to ovule ratio was only sufficient in R. glacialis (2.6 on average) and S. bryoides (1.3), but not in C. uniflorum (0.6). Accordingly, seed to ovule ratio was around 0.8 in R. glacialis, 0.7 in S. bryoides but 0.4 in C. uniflorum. In C. uniflorum, saturating pollination slightly increased seed set. Regression analyses revealed that natural pollination success was more frequently limited by quality than by quantity. Our results do not support the idea of chronic, widespread pollen limitation in the subnival but rather fit into the concept of parental optimism by overinvesting in the number of ovules as an adaptation to variable resource availability.

Winning in style: Longer styles receive more pollen, but style length does not affect pollen attrition in wild Clarkia populations.

One proposed function of long styles is to intensify selection among male gametophytes relative to short styles. If so, given sufficient competition, longer styles will have higher rates of pollen tube attrition (failure to reach the style base) within the style than shorter ones. Alternatively, style length may influence pollen receipt, which itself may affect attrition rates. We tested these predictions by collecting senescing styles from wild populations of two insect-pollinated Clarkia species. We examined the number of pollen grains adhering to the stigma, length of styles, and rates of attrition from the stigma surface to the stigma-style junction (SSJ), from the SSJ to the style base, and from the stigma surface to the style base. Multivariate analyses estimated the independent effects of pollen grains per stigma, the number of pollen tubes at the SSJ, and style length on attrition. Style length was generally positively correlated with pollen receipt, and the number of pollen grains per stigma was positively correlated with all three attrition rates. In neither species was any attrition rate affected by style length independent of the number of pollen grains per stigma. Pollen attrition was mediated by style length, but the function of style length was primarily to increase the number of germinating pollen grains, which affected attrition rates either through stigma clogging or pollen-pollen interactions. Style length may have a direct effect on pollen receipt due to the stigma's position relative to pollinator body parts, but traits correlated with style length may also directly affect pollen receipt.

Inside-out flowers of Lacandonia brasiliana (Triuridaceae) provide new insights into fundamental aspects of floral patterning.

Background and Aims. A recently described Brazilian species, Lacandonia brasiliana, shares with its longer established putative sister species from Mexico, L. schismatica, inverted floral patterning (carpels surrounding stamens) that is almost unique among angiosperms. We present a detailed ontogenetic study of L. brasiliana for comparison with other members of the tribe Triurideae (Triuridaceae) to explore the possible evolutionary origins of “inside-out” flowers.Methods. Wild-source populations of L. brasiliana were compared morphologically and ontogenetically with related species of Triurideae, using light and scanning electron microscopy.Key Results. Relatively few morphological differences separate flowers of L. brasiliana and L. schismatica. Both species have tepals with late-developing subapical appendages. In both species, the three central (almost sessile) anthers develop precociously with respect to the carpels; the anthers remain closed, and fertilization is achieved via pollen-tube growth from germinating pollen grains of the same cleistogamous flower. Carpels are initiated on fascicles.Conclusions. The close similarity between the two Lacandonia species makes it unlikely that they arose independently from two separate homeotic transformation events; they could either represent sister species or two populations of a single disjunct species. Our study underlines the problematic generic and species boundaries within Triurideae. We present an evolutionary scenario of character evolution in Triuridaceae. The inside-out Lacandonia flower could have resulted from a stabilized homeotic transformation; this hypothesis is not in conflict with constrasting theories of the origin of the Triuridaceae flower, which coincided with a shift to unisexuality. The unisexual yet highly plastic flowers that are typical of Triuridaceae could have pre-adapted the origin of the extraordinary Lacandonia morphology.

Establishment of growth medium and quantification of pollen grains and germination of pear tree cultivars

To support breeding programs of pear tree, on the selection of cultivars to subtropical area in Brazil, the objective of this research was to adjust the growth medium basic to pollen grain germination. The pollen grains of 'D'Agua' cultivar were spread on the surface of Petri dishes containing 20 ml of culture medium in accordance with the following sequential experiments: 1) agar (4; 6; 8 and 10 g L-1) and pH (3,5; 4,5; 5,5 and 6,5); 2) sucrose (0; 30; 60 and 90 g L-1); 3) calcium nitrate (0; 200; 400 and 800 mg L-1); 4) boric acid (0; 400; 800 and 1200 mg L-1); 5) temperature of incubation (15; 20; 25 e 30 oC) and 6) emission time of the pollen tube (0; 1; 2; 3; 4; 5 and 6 hours after inoculation). After incubation, the germination rate of pollen grains of nine pear cultivars ('Rocha', 'Abate Fetel', 'Packham's Triumph', 'Atago', 'Hosui', 'Primorosa', 'Triunfo', 'Seleta' and 'D'Agua') was evaluated, and number of stamens, the number of pollen grains per anther and per flower. The protocol for germination of pollen grains of pear tree consist in the culture medium have to be solidified with 10 g L-1 agar, being the pH measured to 5,2 , added with 90 g L-1 sucrose, 145 mg L-1 calcium nitrate and 700 mg L-1 boric acid, with incubation temperature of 23 oC. The readings germination percentage should be performed after five hours of incubation. The pollen grain 'Rocha' cultivar showed higher germination percentage.

<b>Morphology and viability of castor bean genotypes pollen grains

The objective of this work was to characterize the morphology and viability of the pollen of 15 genotypes of castor bean (Ricinus communis L.) and to generate information that can assist in the selection of highly promising male parents for future use in genetic improvement programs aimed at producing seeds for oil extraction. Acetolysis and scanning electron microscopy was used to characterize the morphology of the pollen. The viability of the pollen grains was estimated by in vitro germination and colorimetric analysis (acetocarmine 2% and 2, 3, 5-triphenyltetrazolium chloride 1%). For the in vitro germination, pollen grains were grown in 10 types of solidified culture medium consisting of different concentrations of sucrose, boric acid, calcium nitrate, magnesium sulfate and potassium nitrate. The pollen grains had the following characteristics: medium size, isopolar and subspheroidal shape, radial symmetry, circular ambit, 3-colporate, elongated endoapertures, tectate exine and granulated sexine. The acetocarmine dye overestimated pollen viability. The media M5 and M8 were the most efficient at promoting the germination of pollen grains. The studied genotypes had high levels of viability and can therefore be used as male parents in genetic improvement programs.

Characterization and evaluation of Berberis microphylla G. Forst pollen grains

Berberis microphylla , commonly known as “calafate”, is a non-timber forest product native from Patagonia, and its berries possess highlighted nutraceutical value. The objective of this research was to describe the morphology and anatomy of pollen grains of Berberis microphylla G. Forst genotypes growing spontaneously on the island of Tierra del Fuego (Argentina), and evaluate their vitality and germination. Pollen grain diameter varied from 40 to 47.26 µm, the pollen grains of 124 and 201 genotypes being significantly smaller than the others. Vitality measured by DAPI methodol-ogy was also variable among genotypes, although always about 50%. In vitro germination of pollen grains measured one day after the flowers were collected was very high for some genotypes (near 80%), and then decreased after 21 days of storage, except for genotype 123 whose germination value increased from 44.34 to 69%. The significant variability found in pollen performance (size, viability and germination) among B. microphylla genotypes from a natural population could be interpreted as an enhanced survival strategy to maximize reproduction fitness, with a marked capacity of response to environmental changes. High viable pollen frequency together with germination percentages observed in all the geno-types tested could indicate a good fertilization process. The correlation observed between size and germination percent-age could be used as markers of pollen grain performance, paving the way for possible B. microphylla breeding.

Micronutrients and productivity of oilseed crops -A review

Micronutrients are essential for plant growth, but plants require relatively in smaller quantity. They include iron (Fe), manganese (Mn), zinc (Zn), boron (B), copper (Cu), molybdenum (Mo) chlorine (Cl). In oilseeds these micronutrients play a major role in translocation of photosynthates, increasing seed setting percentage, essential for translocation of sugar, germination of pollen grains, stigma receptivity, amino acid and protein synthesis which ultimately increase the productivity of oilseed crops.

Reproductive biology and pollen–pistil interactions in Passiflora species with ornamental potential

The objective of this work was to study the reproductive systems, pollen viability, and pollen–pistil interactions in 11 species of Passiflora. The reproductive systems were evaluated by the pollen/ovule ratio (P/O) and field pollination. Pollen viability was estimated by in-vitro germination of pollen grains and the colourimetric method with 2,3,5-triphenyltetrazolium chloride (TTC) and the pollen–pistil interactions through aniline blue fluorescence. According to the P/O ratio, Passiflora suberosa, Passiflora morifolia, Passiflora capsularis, and Passiflora tenuifila were classified as obligatory autogamous, Passiflora foetida was classified as facultative autogamous, and the other species as facultative allogamous. Controlled pollination under field conditions identified six self-incompatible (Passiflora edulis f. flavicarpa, Passiflora gibertii, Passiflora muchronata, Passiflora galbana, Passiflora racemosa, and Passiflora edmundoi) and five self-compatible (P. tenuifila, P. morifolia, P. capsularis, P. foetida, and P. suberosa) species. Interspecific hybridisations were successful for some combinations, and the fruits obtained produced fertile seeds. Regarding pollen viability, there were different responses among species. P. capsularis showed the highest in-vitro germination (80.1%) and stained pollen grains (96.2%). In self-incompatible species, the pollen–pistil interactions showed pollen tube inhibition due to the irregular deposition of callose, while, in self-compatible species, regular deposits of callose were observed. The results obtained from studies of the reproductive biology can aid in planning crosses and establishment of Passiflora breeding programs using compatible genotypes with expressive ornamental potential.

NYMPHAEA REVISITED: A PRELIMINARY COMMUNICATION

ABSTRACT A number of pollination syndromes within the genus Nymphaea are examined. Adaptive radiation has created a wide range, from beetle-pollination with production of solid food bodies for the visitors to pollination by small Hymenoptera and syrphid flies with production of a pool of stigmatic fluid in which, on the first day of anthesis when the flower is functionally pistillate, pollinators drown. In the latter category, there is striking sophistication in the features that ensure proper deposition and germination of the pollen grains. In the tropical water lilies examined, the sugar level of the stigmatic fluid was 1%-1.5% which is well below the threshold of perception for honeybees regardless of the nature of the sugar; fructose and glucose were present in roughly equal concentrations. In Nymphaea odorata, a temperate zone water lily, the sugar concentration was about 3%, a considerable part of which was sucrose; glucose and fructose were again present in almost equal concentrations. No obvious b...