Pollen Water Content Research Articles

Studies on Pollen Morphology, Pollen Vitality and Preservation Methods of Gleditsia sinensis Lam. (Fabaceae)

Gleditsia sinensis Lam. (Fabaceae) is an endemic species in China, which has a wide range of ecological functions and high economic value. G. sinensis belongs to androdioecy, and the stamens of perfect flowers are aborted, meaning that a perfect flower is a functional female flower. Understanding the dynamic process of flowering and the characteristics of pollen morphology effectively determine the viability of pollen vitality, and the suitable conditions for short-term storage of pollen can provide theoretical basis and technical reference for hybrid breeding and germplasm conservation of G. sinensis. In this study, the male plants of G. sinensis in Guiyang area were used as research materials. The flowering dynamic process of male flowers was recorded through field observation. The morphology of pollen was observed and analyzed with a scanning electron microscope (SEM). The germination characteristics of pollen were studied with an in vitro germination method, and the pollen vitality was also determined using four staining methods. The effects of different storage temperatures and water contents on pollen germination rate were discussed. The results showed that the male flowers of G. sinensis had a short, single flowering period, lasting 2–3 days from the opening to the shedding. The dynamic opening process of a single flower was artificially divided into five stages. Pollen grains of G. sinensis are oblate spheroidal, tricolporate with equatorial elongated endoapertures and the sporoderm surface is reticulate. The MTT (Thiazolyl Blue Tetrazolium Bromide) staining method could accurately and quickly determine the pollen vitality of G. sinensis. The highest pollen germination rate was 65.89% ± 3.41%, and the length of the pollen tube was 3.96 mm after cultured in 15% sucrose + 100 mg/L boric acid + 20 mg/L calcium chloride for 24 h. It was necessary to collect the pollen at the big bud stage, which was conducive to improving the efficiency of pollen collection because the pollen had been mature with high pollen vitality at this stage. When it came to pollen preservation, the pollen germination rate was significantly affected by storage time, storage temperature and pollen water content. The pollen still had high vitality after being stored at −80 °C for 30 days when the moisture content of the pollen decreased to 9%, and the pollen germination rate only decreased by 28.84% compared with that before storage. In conclusion, this study has comprehensively and systematically studied the morphology, vitality determination and preservation methods of the pollen of G. sinensis, providing a theoretical basis for the cross regional breeding and the conservation and utilization of germplasm resources.

Impact of drying and cooling rate on the survival of the desiccation-sensitive wheat pollen

Key messageFast-drying and cooling induce fast intracellular water loss and reduced ice-crystal formation, which may promote the formation of intracellular glasses that might improve the likelihood of wheat pollen survival.Long-term storage of pollen is important for the fertilization of spatially or temporally isolated female parents, especially in hybrid breeding. Wheat pollen is dehydration-sensitive and rapidly loses viability after shedding. To preserve wheat pollen, we hypothesized that fast-drying and cooling rates would increase the rate of intracellular water content (WC) removal, decrease intracellular ice-crystal formation, and increase viability after exposure to ultra-low temperatures. Therefore, we compared slow air-drying with fast-drying (dry air flow) and found significant correlations between pollen WC and viability (r = 0.92, P < 0.001); significant differences in WCs after specific drying times; and comparable viabilities after drying to specific WCs. Fast-drying to WCs at which ice melting events were not detected (ΔH = 0 J mg−1 DW, < 0.28 mg H2O mg−1 DW) reduced pollen viability to 1.2 ± 1.0%, but when drying to 0.39 mg H2O mg−1 DW, some viable pollen was detected (39.4 ± 17.9%). Fast cooling (150 °C min−1) of fast-dried pollen to 0.91 ± 0.11 mg H2O mg−1 DW induced less and a delay of ice-crystal formation during cryomicroscopic-video-recordings compared to slow cooling (1 °C min−1), but viability was low (4.5–6.1%) and comparable between cooling rates. Our data support that the combination of fast-drying and cooling rates may enable the survival of wheat pollen likely due to (1) a reduction of the time pollen would be exposed to drying-related deleterious biochemical changes and (2) an inhibition of intracellular ice-crystal formation, but additional research is needed to obtain higher pollen survival after cooling.

METHOD FOR DRYING MAIZE POLLEN

Pollen managements consisted of suitable harvest timing, pollen drying to a certain misture content, pollen viability testing, and pollen storage. Maize pollen was sensitive to desiccation. This experiment was aimed to determine preservation technique in reducing pollen water content while maintaining its viability. Maize variety which used in this research was BIMA 3 as male line hybrid maize. Pollen viability testing used potassium iodide (KI) 1%. This experiment used randomized block design with 3 factors and 2 replicates, i.e. boron (H3BO3) fertilizers (0 and 3 kg ha-1 ), drying techniques (MgCl2, silica gel, zeolite, preservation in air-cond room (18±1 °C; RH43%), and drying periods (0, 2, 4, 6, 8 hours). The observation response of this experiment were viability and pollen weight changing. The result showed that there is no interaction between three factors to observation response, while drying technique and drying period combinations showed interactions to observation response. Pollen maize drying used silica gel for 4 hours was able to decline much pollen weight and maintain pollen viability better than other techniques.

WATER CONTENT OF MIXED HONEY BEES-COLLECTED POLLEN

The knowledge of the water content of pollen is important to determine the amount of protein content, lipids, sugars, minerals and other components in the dry matter. The water content of mixed honey bee-collected pollen was determined by a method of drying. A table of the water content in the mixed pollen from different harvesting periods was made. The percentage of water content in the mixed bee-collected pollen samples ranged between 12.3% and 26.6% and the average was 18.8%. Pollen from different harvesting periods has different water content. There are also differences among the same months during three years. The average value of water content for each year is also different. According to the results, can’t be said during which season (spring, summer, autumn) the pollen has higher or lower water content. Ecological factors, especially rainfalls, can also affect water content.

Pollen has higher water content when dispersed in a tricellular state than in a bicellular state

ABSTRACT Pollen is generally dispersed in a sexually immature and somewhat dehydrated, metabolically quiescent state. Yet, in some species, pollen at anthesis is well-hydrated and metabolically active, and in 30 % of angiosperms pollen is dispersed after having formed its sperm cells. Pollen water content and sexual maturity may be correlated, either because both are subject to trade-offs between dispersal viability and post-pollination performance, or because the traits display developmental linkages. We inferred relative water content of sexually immature (“bicellular”) and sexually mature (“tricellular”) pollen of 30 species of angiosperms using a hydration index (HI) that ranges from zero to one, based on how near fresh pollen volume is to its minimal (dehydrated) or maximal (hydrated) volume. Tricellular pollen had 30 % higher HI than bicellular pollen (P < 0.005), after controlling for initial pollen size (larger pollen had higher HI; P < 0.05). A literature survey of 344 species indicated that the tricellular and hydrated states were strongly associated, although all four trait state combinations were present (P < 0.0001). Our results suggest that a common mechanism for the repeated origins of tricellular pollen has been via the loss of controlled pollen dehydration, which enables either accelerated or extended pollen development.

Pollen drying and storage for hybrid seed production of cucumber (Cucumis sativus L.)

One of the major problems in hybrid seed production of cucumbers is the low pollen production and low pollen viability. This research was mainly dealt with pollen handling in order to maintain its viability during storage, which was carried out in three steps. Male parental of 'KE014' was planted at Production Farm of East West Seed Indonesia Ltd. in Jember, East Java, Indonesia during March to September 2012. In a first step, male flowers were harvested and pollen was extracted and dried for 24 h during which the water content and pollen viability was monitored. In a second step the dried pollen was stored in an ultra-freezer (-79±2°C) for 56 days and its viability was also monitored every 7 days. The third step was the pollination of a female parental stock to produce hybrid seed. The experiments were arranged in three replications with completely randomized design. Results showed that pollen water content decreased significantly during the first 8 h of drying from 12.05 to 6.71% while the pollen viability increased from 10.16 to 25.60%. Prolonged pollen drying time up to 24 h did not substantially reduce the water content. Pollen dried for 8 h was able to maintain its viability during 56 days of storage in ultra-freezer (-79±2°C) better than those undried or dried longer. The fruit set and seed set got from pollination with undried and stored pollen (11.0 and 23.0%, respectively) was lower than fruit set and seed set got with dried and stored pollen (ranged 46.5-58.9 and 52.0-67.8%, respectively). Using stored pollen (undried or dried) for pollination in hybrid seed production yielded in lower number of filled seed per fruit than using fresh pollen. Hybrid seed germination got from pollination with dried and stored pollen was slightly higher (98.36-99.63%) than those got from undried and stored pollen (95.58%), nevertheless all of them were high quality seeds. Thus, using the stored pollen for pollination in cucumber hybrid seed production would reduce seed yield but not seed quality.

Wind-induced mechanical rupture of birch pollen: Potential implications for allergen dispersal

Mechanical rupture of pollen grains after a mechanical shock against a solid surface was tested as a new approach to one of the mechanisms related to the release of allergen loaded particles from pollen. Birch pollen was aerosolized and sent into an impactor to mimic a shock against a surface (trees, soil, walls, etc.) at wind speeds of atmospheric-relevance. Small particles in the range of 1–2.5µm were released subsequently to pollen impaction. The number of particles released increased with the velocity of impaction and with the water content of pollen. Damaged grains were observed by transmission electron microscopy and released particles are most likely cytoplasmic granules. This mechanism of pollen rupture and/or discharge may be of great importance in urban environment and may significantly contribute to thunderstorm-related allergic asthma and other associated pollen subparticles IgE mediated diseases.

Kinetic of NO2 uptake by Phleum pratense pollen: Chemical and allergenic implications

Phleum pratense pollen was exposed to NO2 in a reactor allowing a continuous analysis of NO2 concentration by FTIR. The uptake coefficient of NO2 on pollen was calculated postulating a first order kinetic reaction and a value of (1.1 ± 0.1) × 10−7 was determined. NO2 uptake was faster when the pollen water content was increased and when the pollen was pre-treated with ozone. The effect of NO2 exposure on pollen allergic properties was investigated by quantifying Th2- and Th1-associated chemokines in a model of human dendritic cells. Cellular analysis clearly showed that cells exposed to fumigated pollen favored the production of chemokines known to promote Th2-cell responses. Altogether these data demonstrate that NO2 uptake by pollen directly correlates with increased Th2 response in human cells, and are in favor of the involvement of NO2 pollution in the increase of allergic diseases.

Biophysical characteristics of maize pollen: Variability during emission and consequences on cross-pollination risks

Modelling of cross-pollination risks using physical-based model of pollen dispersal requires estimations of pollen viability rate as well as settling velocity distribution of viable pollen grains at emission. These two biophysical characteristics are mainly determined by pollen water content. Three years of experiments were carried out to measure biophysical characteristics of pollen at different times of emission within the day. In a first part, we proposed a simple model to predict pollen water content at emission as a function of air vapour pressure deficit. We found that by setting a constant duration of pollen dehydration in the anthers the model predicts accurately pollen water content variations at emission. In a second part, we related pollen water content and settling velocity distribution of viable and non-viable pollen grains. We used with success settling velocity distribution as a proxy to estimate fraction of spheroid pollen, water content distribution of spheroid pollen and pollen viability rate. In addition, we validated with success the estimations of viability rate. In a third part, based on above models, we estimated the effects of air humidity on cross-pollination risks.

Pollen carbohydrates and water content during development, presentation, and dispersal: a short review

Pollen accumulates starch reserves during development and the final stage of ripening. Before the anther opens, starch is totally or partially converted to pectins, glucose, fructose, sucrose, and to some unknown polysaccharides. Pollen is exposed to dispersing agents in an arrested developmental state which differs according to pollen water content. Pollen is classified as partially dehydrated or partially hydrated. The final water content may be reached before or after anther opening. Especially during exposure and dispersal, partially dehydrated pollen may interconvert soluble and insoluble reserves, modifying internal turgor pressure and hindering water loss or gain. Partially hydrated pollen is commonly devoid of mechanisms to conserve viability in time but has the advantage of quickly emitting pollen tubes on reaching the stigma.

Partially hydrated pollen : taxonomic distribution, ecological and evolutionary significance

The problem of the water content of pollen is reconsidered, especially the distinction between “partially hydrated pollen” (PH pollen), pollen with a water content greater than 30%, and “partially dehydrated pollen” (PD pollen), which has a water content of less than 30%. Both types have been found even in systematically contiguous groups or the same genus. Partially hydrated pollen, encountered in at least 40 families of angiosperms, has the advantage of germinating quickly, normally in a few minutes to less than an hour. Dispersal of highly hydrated pollen also occurs in orchids but for a different reason, i.e. to enable packaging of massulae. The disadvantage of pollen dispersed with a high water content is that water is readily lost and the pollen may desiccate and die unless it has biochemical or anatomical devices to retain water or phenological strategies, such as flowering when temperatures are not too high and when relative humidity is high. Most pollen of Gymnosperms and Angiosperms studied has, however, been found partially dehydrated.

Storage of Maize Pollen for Use in Haploid Production of Hexaploid Wheat

Viability of maize pollen after the drying and freezing process was estimated by its germination on maize silks. Secondly, frequencies of embryo formation were determined in crosses of hexaploid wheat with freeze-stored pollen of maize. Maize pollen germinated at frequencies ranging from 54.2 to 66.60/0 when pollen water content was reduced from 59.0% (fresh) to 9.50/0 . Pollen with a water content of 9.50/0 maintained viability and germinated at a frequency of 22.1% after four weeks of storage at - 80 °C. Embryos were successfully obtained in crosses of wheat with the maize pollen dried to 12.7 and 10.3% water content and stored for 13 weeks at - 80 °C. These embryo formation frequencies were 9.6 and 8.6% respectively. It was 22.2% in crosses with fresh pollen. All regenerated plants were wheat polyhaploids. These results suggest that stored maize pollen can be used for hexaploid wheat haploid production when and where fresh maize pollen is not available.

« Harmomegathy »: Un problema aperto e misconosciuto

Abstract « Harmomegathy »: a still open problem not yet well-known. - Wodehouse used the term « Harmomegathy » to indicate the form and volume change in pollen grains, due to water loss or assumption. Roundish and tricolporate grains in the anther become oval and decrease in volume during the dehydration preceeding anthesis. Viceversa during rehydration on the stigma they undergo the opposite process. Pollen water content at an thesis varies from species to species and it usually ranges between 10 and 20%; nevertheless in some families as Zingiberaceae and Araceae it is higher. Anther and pollen dehydrations are affected by environmental factors, such as humidity of air and temperature, before the anthesis and when pollen is suspended in air. Besides, to avoid the further loss of water during pollen flow, an oily layer derived from tapetum degeneration is deposited outside the pollen grains. During dehydration and rehydration pollen grains undergo a stress due to shape and volume changes expecially in the...

Storage of maize (Zea mays L.) pollen at −196°C in liquid nitrogen

The water content of pollen has a decisive influence on its storability in liquid nitrogen. Pollen with an initial high water content cannot be stored successfully at extremely low temperatures, so a certain degree of drying must be carried out before storage. Provided the viability of the pollen is not significantly reduced during drying, the pollen remains viable and fertile when kept at −196°C.