How long does it take for pollen to germinate and fertilize the ovum?
Seeing no takers, I’ll take a shot at this. Probably David Z knows better than most but I don’t recall him telling explicitly about in vivo studies. There will be variation depending on the vigor of the pollen and the length of the styles. I think we know with fair confidence that within a few hours, pollen is not washed off by water. So germination and initial growth is prompt if the stigma is receptive. Artificial germination is quick and followed by rapid elongation of the pollen tube. But that is without tissue resistance.
Actually measuring this would take a lot of sectioning and microscopy of styles. You’d want a very fertile pollen donor and mother plant. One alternative strategy would be to pollinate one day with a particular pollen donor, then some time later cut the top off the styles so that only pollen that had moved its nucleus down the tube would make seeds. That would at least give you the rate of something.
Another factor is that chemical reactions double for every 10 C, so that day and night temperatures could really affect this. So you might need a controlled environment too.
I give up.
I think we know with fair confidence that within a few hours, pollen is not washed off by water.
Thanks Larry, that was what I was looking for.
Hi Judith and Larry!!
Great question!! I’m on the same page as you Larry. I’m not sure. Great point that with the resistance of the style pollen tube growth is much slower than in just sugar / boric acid water. I suspect probably a day or two to get down. This summer I hope to do a little study with Kathy Zuzek following pollen tube growth in some rose styles related to self and cross compatibility. Years ago I did similar work in potato. We’ll pollinate and then fix flowers at different points in time. The styles are softened in a high pH solution and a special dye that fluoresces under UV light is used. The styles are squashed on a slide and we can see the plugs along the way that are made to keep the nuclei going down the tube and not moving back up. We can get an indication of how far the tubes are based on these dots that fluoresce in the style.
Hopefully we can get it to work.
Here’s a related question I have wondered about. It’s my understanding that pollen grains vary in size according to ploidy–the higher the ploidy the larger the pollen grain. Would that make it difficult for a higher-ploidy pollen grain to get down the pollen tube of a diploid flower?
Thanks,
Betsy
Minnesota zone 4
I’ve read this before, but it is not entirely relevant. Pollen tubes are not mere mechanical structures that respond linearly to temperature. They are tiny plants with their own adaptations. For some species they are adapted to pollination at low temperatures (night blooming plants) while those of other species favor heat.
Takatsu, et al. (2001) made a detailed study of pollination of Gladiolus tristis. They found that the pollen tubes grow fastest at about 20C, but that fertilization was more successful at 15C.
They did not mention the relevant fact that G. tristis becomes fragrant in the dark, and is pollinated by night-flying moths in the wild.
Some other Gladiolus spp. are normally pollinated during the day.
Regarding roses, Heslop-Harrison (1921) reported:
There remained then the operations of Diptera and Hymenoptera to be considered. I therefore got up earlier, at 4 a.m. (GMT), before any insects were at work, when I found that even then every newly expanded > R. pimpinellifolia > had its stigmas powdered with pollen from its own overarching stamens. At the same time those of > R. mollis, R. omissa > and > R. Lintoni > were quite untouched. A little later even their anthers dehisced, after which, unless insect guests performed the necessary operation, on the maturing of the innermost stamen whorls curved over and deposited their precious dust. In many cases indeed even this curving motion as a mode of self-pollination proved superfluous, for almost without exception, as the flowers mature, several stamens are locked between the stigma heads so that their pollen, as it is shed, of necessity falls on the adjacent stigmas. By one method or another, therefore, in default of outside agencies, self-pollination is automatic.
In the species mentioned, pollen tubes must be adapted to the cool of early morning. Other species, such as R. gigantea of Burma, presumably have pollen tubes that favor more warmth.
In hybrids, we have something else to consider. If the pollen tubes of one parent favor low temperatures, while those of the other parent like heat, we may expect some degree of segregation in the hybrid’s pollen. And if this does occur, we might get different results according to the temperature at which the pollen is used. In other words, if we use the hybrid’s pollen on some flowers in the wee hours of the morning, and then on other flowers of the same seed parent later in the day, the offspring from the two rounds of pollination may differ in various ways due to linkage between “genes for temperature adaptation” and genes affecting other traits.
Karl, of course you are right. I should have said “ceteris paribus” as Heslop-Harrison would have done. Enzymes obey the rule of doubling activity per 10 C pretty well when isolated. But some undergo cooperative changes that may lead to a much different temperature response than the simple one mentioned. Mix a hundred or more different enzymes making a pollen tube and moving the nucleus and you get the average effect you mention.
One important consideration perhaps in the work of H-H is that once-blooming roses bloom in summer when days in the U.K. are very long, especially as you move northward. So he’s really talking about sunrise time, depending on whether daylight saving or double daylight is the time base being used. And actual temperature in the flower may depend on solar warming to a considerable degree. So during the actual growth of the pollen tube it might be mostly in daylight hours and warmer than for a night pollinated plant.
Very challenging problem. Need real data. I wish David luck this summer.
Enzymes obey the rule of doubling activity per 10 C pretty well
Not to thread this needle too finely but don’t the underlying thermodynamics, order and mechanism of a given reaction govern the change in the rate of that reaction with the enzymes simply lowering the activation energy?
Judith,
As a follow on to your question, have we determined the life of pollen? When collected and stored in a film canister, how long will it be effective? I realize that fresh is better, but that is not always feasible. I do leave the canisters in the fridge overnight, and have frozen some, i.e., mixing the left over from the year so I have something to use at the start of the next season on some early bloomers. I have had mixed results from that, but nothing worth jumping up and down about.
John
I prefer, of course, to use very fresh pollen, immediately released. I generally keep it in a cup in the house once it’s released, rather than having it be exposed to our 100 degree temps, and consider it trash once the color fades (two days-ish). Totally not scientific, but that’s my method. I do freeze pollen on occasion and use the same gauge as a marker to whether it is still viable. In April, I used some 1 year old frozen Julia Child & Easy Does It pollen this year and both seem to have taken, as the hips are maturing nicely. Most of the other pollens I had frozen lost their color so I did not use them.
Don, you have a fine humor in this thread. Or is it a fine thread with this humor? Anyway, yes you’re right but most chemical reactions tend to behave in the way described, unless they are diffusion-controlled. So we were able to estimate whether a breakdown of nasty chemicals by a plant was limited by diffusion to the plant, or reaction via an enzyme, based on how much the reaction increased as we grew plants at temperatures from 15-30 C.
My main point originally is a simple one. Growth of pollen tubes has a lot of things affecting it and probably temperature is important. so what works as a rate estimation in central Texas in May would likely be very different from Alberta, or Edinburgh in July.
Hi John!!
That is a great question about pollen viability over time. A number of years ago I did a study with Kathy Zuzek and Stan Hokanson trying to see if we can use pollen temperature treatment to try to favor gametes conferring greater hardiness. We generated different populations using the same parents to compare for hardiness, but resources became very limited and we didn’t get to that step. Anyways, we were able to look at pollen viability over different storage temps and durations. The colder the better to maintain it more like fresh. Even for short term use, I put my canisters in the freezer since doing this. A typical household freezer I think is about -20F or so.
Here is the abstract:
ROSE POLLEN VIABILITY OVER TIME AT VARYING STORAGE TEMPERATURES
Authors: D.C. Zlesak, K. Zuzek, S.C. Hokanson
Keywords: pollen competition, pollen germination, pollen tube length, Rosa
Abstract:
The ability to store rose pollen allows for greater flexibility when crossing asynchronously flowering parents. However, storage conditions and duration may lead to gametophytic selection and affect the resulting sporophytic populations. The objective of this study was to compare degradation of rose pollen stored for relatively short (two weeks) and long durations (52 weeks) at -80°C, -20°C, and 4 or 7.5°C. Results will be directed towards the longer-term objective of determining if gametophytic selection for cold tolerance is occurring by comparing sporophytic populations for cold hardiness. Rose selection 1B30 was chosen as the male because it is a cross of non-winter hardy × hardy (USDA cold hardiness zone 4) parents and should contain genes segregating for cold hardiness. Pollen was air dried, sealed in canisters, and placed at the designated temperatures. A hanging drop pollen germination assay (1.5% sucrose, 40ppm boric acid) was used to determine percent pollen germination (%PG) (after four hours) and pollen tube length (PTL) (after two hours). Over the 52- and two-week storage periods, seven and two pollen germination readings were made, respectively. On June 29, 2004, 52 and two weeks after storage treatments commenced, PTL and %PG data were taken and 24 pollinations per treatment (including a fresh pollen control) were made onto Rosa × ‘Bucbi’ (Carefree BeautyTM). Pollen germination quickly declined at 4 or 7.5°C, and after two and 52 weeks of storage %PG, PTL, and achene number per hip were generally greater at -80°C than -20°C. Achene number per hip was significantly correlated with PTL (r=0.86), but not with %PG, nor was %PG significantly correlated with PTL. Pollen tube length appeared to be predictive of fertilization ability and can be used to select pollen lots to maximize seed set and monitor treatment effects on pollen for pollen competition studies.
Larry,
The Himalayan trait in mammals involves a mutation that inhibits melanin synthesis at higher temperatures (near core body temperature). Only the cooler parts of the body (the “points”) are fully pigmented. I take it that the relevant enzyme is inactive (or much less active) at higher temperatures.
Similarly, vernalization in many plants proceeds more rapidly near 0 C that at 15 C. Similarly, potatoes kept in cold storage become sweeter because the starch is broken down more rapidly at lower temperatures. There may be more involved than just the activity of enzymes, of course.
vernalization in many plants proceeds more rapidly near 0 C that at 15 C. Similarly, potatoes kept in cold storage become sweeter because the starch is broken down more rapidly at lower temperatures. There may be more involved than just the activity of enzymes, of course.
I would guess, for vernalization, a phytochrome-related switching mechanism and for starch conversion in potato a simple shift in equilibrium constants.
Judith asked a practical question, though, and to answer her I suggest that, in the presence of adequate irrigation, in warm to hot, dry weather give it a day and in cool to cold, damp weather give it two days.
As for pollen management, bone dry pollen stored in a freezer is viable all season long.
Actually the potato sweetening is a terribly complex signaling pathway that takes considerable time to set in. I took a quick google look last night. No one really knows how it works but interfering RNA etc will control some enzymes that are part of the challenge. Different cultivars of potato really differ in how much they do it.
Vernalization depends on inducing enzymes that methylate or acetylate DNA or the histones in combination with it. It is a highly regulated, multi-signal pathway and only incidentally about temperature (it is a measure of winterness, telling when it is safe to grow again and it somehow integrates the degree-days of cooling so that the plant pops forth not too early and not too late.). It is equivalent to day length response in many ways. In temperate climates short days and cool temperatures go together. But not in San Diego. So I predict there are roses, or other flowers that quit blooming there, even if it isn’t cold enough to stop them.