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  • #41
If the plant's sex doesn't change, at what point during it's growth is the sex determined? In the seedling stage, or as it enters sexual maturity? In other words, when do I need to abuse my plants to get more females?
 
  • #42
I wonder whether it's causative or correlative. For example, in many reptiles, gender is a direct result of temperature during incubation. So the environment causes gender selection. However in humans, for example, male and female sperm appear to be differently suited to various conditions, so workers at nuclear power plants have disproportionately high numbers of female? children.

So with the example of rafflesiana, does the exposed position cause seedlings to become male, or is it that only male seedlings can survive those conditions...?
 
  • #43
Hi all:

Similar events have been shown with alligators in the Florida Swamps where the proportion of female alligators is greater than the male population and this was shown to be due to exposure of dioxines in the water. Somehow sewage water is mixing with swamp water and causing more female alligators to be around. Please note that in this case, i am almost certaint that the alligators do have sex determining chromosomes.
I guess we are jumping too much amongst reptiles, humans, and plants

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Gus
 
  • #44
[b said:
Quote[/b] (agustinfranco @ Mar. 22 2006,3:21)]I guess we are jumping too much amongst reptiles, humans, and plants

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Gus
Good! I'll toss in fish
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. There was a study on the fish in the river near Denver, Colo. not too long ago into why there were so many fish with both male and female reproductive organs. In some parts of the river, there were very few male fish at all. Seems that female hormones were passing through the wastewater treatment plants into the river. The high hormone levels are thought to be due to the increase in the use of estrogen for variouse treatments from infertility to low bone calcium in women.

To get this back on topic, I suggest we use the water from tha river to water our Neps to see if that will increase the number of female plants being grown.

Sometimes my genious scares me!
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  • #45
So with the example of rafflesiana, does the exposed position cause seedlings to become male, or is it that only male seedlings can survive those conditions...?
Good question, Hamish, and I don't believe the book addressed that point. in fact, Clarke claims it was inconclusive and really required more investigation. I believe they found similar ratios in N. ampullaria. I will check when i get home.
 
  • #46
Very interesting and educational, to me at least.


N
[b said:
Quote[/b] ]So with the example of rafflesiana, does the exposed position cause seedlings to become male, or is it that only male seedlings can survive those conditions...?

I know exactly the places Charles made those observations on N. rafflesiana, I was with him. Rarely a female to be seen. The pure white silica sand around reflects the heat and makes it almost unbearable for people. Light levels are incredible and it's so bright that on a sunny day sunglasses are a must, otherwise you can hardly open your eyes to squint. Conditions there have been constant for many years, so it's probable that the plants experienced that harshness from the seed.

However... in areas where a sudden trauamatic event has taken place to turn otherwise pristine forest into a disaster zone, such as occurs when whenever man intervenes, large plants will immediately flower and I believe more females than males appear. This contradicts the theory that a stressed plant will produce a male flower since it takes less nutrients to prduce pollen than fruit.

Here's another piece of anecdotal information: we have 71 large stock plants of different clones of N. ampullaria 'Brunei red' 'Harlequin' and 'Williams red' in cossetted conditions in the nursery which we've been trying to flower for years. Only one has flowered there so far and it happens to be a male. We took 6 plants out of the nursery into full sun and stressed them severely. 5 of the 6 have now flowered - all female. What are the chances of that sexual expression being random?
 
  • #47
Hi Rob:

Nice example to make us think hard about the nature of these plants!. If I were you, i'd expose another 6 plants to the same conditions and if all 6 are still female, you have made a big discovery! If not, i guess you should have bought a lottery ticket!
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Gus
 
  • #48
I did my homework.
According to Clarke, Christopher Frazier actually did a study at two sites using N. rafflesiana, ampullaria and gracilis as the study plants. The two sites had both 'closed' and 'open' microenvironments. In the 'open' areas, 100% of rafflesiana was male, and 83% of gracilis was male. there were no ampullarias growing in the 'open' areas. In the closed areas, females accounted for more than 50 percent of the flowering plants, with the number hovering around 60 percent+. This fits in precisely with Rob's plants grown 'close' and then exposed to 'open', the larger population of females reveal themselves-when stressed. Frazier noted the need for females to expend more energy bearing fruit and seed and would thus require a more nurturing environment. The males could tough it out on the white sand. He also noted that the male flowers in the open were more accessible to potential pollinators-higher visibility, and produced less sugar than the females. He suggests its to get the pollinator to the male flower just long enough to pick up the pollen, and then find the larger quantities of sugar at the female flower, spend more time at the female, assuring pollination.
 
  • #49
This from a quick trawl of the net - seems a number of mechanisms are possible

How is sex determined in dioecious plants?

Nitesh Pati Tiwari, Allahabad

More than 90 per cent of flowering plants produce perfect flowers that have both male and female reproductive organs.

Of the remaining plant species, about half are monoecious, producing male and female flowers on the same plant and the rest are dioeceous, producing male and female flowers on separate plants. Plants have developed several interesting mechanisms for determination of sex.

Silene latifolia is the most well studied dioeceous plant for sex determination mechanisms. In this species, sex determination is by sex chromosomes similar to that in many animals; males are XY and females are XX.

In male and female plants, female and male reproductive organs do initiate respectively but are aborted early in flower development. The Y-chromosomes are thought to carry genes that promote male development and suppress female development. A similar mechanism has also been reported in the bryophyte Marchantia.

Papaya can produce male, female and hermaphrodites depending on the genotype of a single sex determining locus. This locus is thought to be clustered with several genes that play a role in sex determination.

Cucumber is usually monoecious producing female flowers at the top of the inflorescence and male flowers at the bottom. It has been found that sex is determined by the concentration gradient of the plant hormone ethylene, which acts to promote female sex.

In Maize, a gradient of the plant hormone gibberellic acid regulates the emergence of the male and female inflorescences. Hormone gradients in these species are genetically determined by two or three different genetic loci.

In addition to the above mechanisms, in the fern Ceratopteris, sex determination is epigenetically determined by a pheremone.

All individuals are hermaphrodites and developed individuals secrete the pheromone so as to masculinise the surrounding juvenile plants.
 
  • #50
Interesting. Rob, in your observations with Charles, were most of the plants flowering? What I'm getting at is if 50% of the plants were flowering, and 100% of them were male in that location, we still don't know the gender of the unflowering ones. If all plants were flowering then it is a much more interesting scenario.
 
  • #51
I only just caught back up with this as I was out most of last week.

To clear things up somewhat (I hope):

First off I want to note that I am speculating in relation to Neps. Most of the info I am going off is what I remember from what popped up on the web when I was having a conversation with James Cokendorfer (not sure on that spelling) a few years back and the majority of that was related to Cannibis because those people seem really happy to talk about it all over the place.

What I found was that the sex of Cannibis (and therefore I assumed dioecious plants) is determined early in growth by exposure to "stress" and once determined it would not naturally switch. So in the case of Cannibis, if the early germinated seedlings encounter any kind of "stress" like less than ideal water levels or light levels or heat then the majority of them will turn out male. The flip side being that germinated seedlings under ideal conditions will all be female. The causative agents responsible for this were concentration gradients between GA3 (like the Maize note above) and one other that I think was called cytochinin or something like that. Males would develope under low GA3 levels and females under high GA3 levels (compared to the cytochinin).

I was discussing this with James because we were talking about seeing if it would be possible to get an already committed plant to "switch" sex for the purpose of cross breeding for greater genetic viability with N. clipeata. The theory was that if there were more pure female clones than male clones that perhaps one or some of the females (or cutting from the females) could be induced to "switch" sex thereby providing a new pollen donor and a larger gene pool. I don't know if James ever tried to follow through with it though... Maybe I should drop him a line...
 
  • #53
I never did a proper survey but used to forage around for seeds a lot and definitely noticed a lot more males than females amongst exposed and therefore probably stressed plants. I would say that pretty much all the mature plants would be in flower together, usually during Dec-Feb. Even taking into account that the male flowers have more color and are therefore more visible at a distance, I am nearly sure this is the case. However I don't have any empirical evidence for this although it was an impression gained as a result of literally hundreds of visits to the areas concerned. I always used to accept it as the normal state of affairs.
 
  • #54
Rob,
You mention that they all bloom about the same time in a Dec-Feb time frame. Would this put the seedpods ripening and splitting just before, or at the beginning of the rainy season? (talking about raffs, amps,-Sarawak and Brunei lowlanders.)
 
  • #55
[b said:
Quote[/b] (Trent @ Mar. 30 2006,9:13)]Rob,
You mention that they all bloom about the same time in a Dec-Feb time frame. Would this put the seedpods ripening and splitting just before, or at the beginning of the rainy season? (talking about raffs, amps,-Sarawak and Brunei lowlanders.)
Hi,
I cant say anything about Borneo,
but only regarding bloom and germination time:
last year I had a sudden burst of flowers on my plants, that was about oct, and I made a cross. everything went smoothly. And the rainy season came in together with the time of fruit splitting. Within 2 weeks of sowing, more than 50% germinated and grew very well.
the plants had flowered at the very beginning of the monsoon period. Which lasted about ... I think 2+ months, then got hotter, but now its raining quite frequently again...
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hope this helps.
thanks
 
  • #56
hi all, i observed in one specific location of raffs,gracilis,mirabilis,ampullaria and the hybrids flowered in september,october ( before the monsoon arrives ) and seed pods would ripen and "exploded" during the moonsoon/rain season ie january and february.

There is no specific flowering season. Last weekend i was passing by a country road and I saw some mirabilis,gracilis and ampullaria were flowering. Some already bearing female seeds.In 2 months time they will matured and coincide with the driest time of the year ( may,june, july ).

Robert
 
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