Through what mechanism do Trichos reject their own pollen?

[Halcyon Daze]

Yeah, so I was wondering how they actually do it? How exactly do Cacti do it?

Hoping to lure some of the old dogs out of their lairs.

Cheers!

Edited June 21, 2013 by Halcyon Daze

[Evil Genius]

PH i think. If the PH´s not right, fertilisation does not happen. Selfsterile cacti can be tricked into accepting their own pollen by messing with the PH.

[Stillman]

got any articles? Thats sounds very interesting.

[Auxin]

That sounds very unlikely. The pH range wouldnt be very wide and I've never heard of people repeatedly finding genetically distinct cacti unequivocally of the same species that cant cross. That would mean if the achievable pH range were even a broad ±0.5 from the average the difference would have to be precise to less than 0.01 of a pH, probably closer to 0.001 to give each plant its own pH 'barcode'. The tiniest environmental fluctuation (like a bushfire 100 kilometers off, or rabbit pee 100 meters off) would bring it outside that range and trigger selfing.

It was my vague and crude understanding that it came down to protein markers on the pollen grains that told a plant if it was self or other.

Sometimes pollen from a 'other' with distinct dominant traits is killed with ethanol or UVC and mixed with self pollen to trick a plant into opening up its defenses and allowing a selfing event to occur. Thats the simplified version of what I've read in papers about various non-cactus crop families, anyway.

In the demonstrated cases of calcium hydroxide promoting selfing, if apomixis has been ruled out, it could be that the extreme of pH just fucked up marker or receptor.

Achievable pollen tube length can also be relevant if flower morphology is significantly different.

[Halcyon Daze]

I found a good paper and I wish I had more time to read it right now.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2643390/pdf/160S72.pdf

What Auxin is saying about the protein markers is therefore probably right for cacti. I say probably because self-incompatibility is just one of the many basic aspects of the cactaceae that still seems to lack any detailed research. But it seems 'legit' and certainly a likely scenario.

So here's my best bet so far.

The self-fertilization barrier in cacti is indeed prezygotic, (and homomorphic), with compatibility being determined before a zygote is ever formed.

These mechanisms are the two most likely candidates in cacti.

1. The inhibition of germination of self-pollen on the stigmatic surface. -Some plants use the control of pollen germination as a way to prevent self-pollination.

2. The inhibition of growth of self-pollen tubes in the style. Growth of a pollen tube in the style is arrested (through the degradation of the pollen tube RNA) when the S allele carried by the pollen matches (proteins of) one of the two S alleles carried by the pistil.

-Germination and growth of the pollen tube involve molecular signaling between stigma and pollen. In self-incompatibility in plants, the stigma of certain plants can molecularly recognize pollen from the same plant and prevent it from germinating. (wikipedia)

I'm going with number 2 anyway.

I also like Auxins postulation that the extreme of pH of calcium hydroxide just 'fucks up' the marker or receptor.
Cacti can really take a lot of abuse

Edited June 21, 2013 by Halcyon Daze

[shortly]

I'm leaning toward inhibition of germination of self-pollen on the stigmatic surface at least for most of the columnar cacti genera i've tinkered with.

EG's cement tech or devitalized pollen (either with ethanol or microwave) from a related species or an unrelated clone if available, mixed with self pollen all produce fruits from selfed matings.

Albeit under sized fruit with few seeds (also somewhat small) compared with out crossed matings.

[Auxin]

But what isnt clear, as far as I've seen, is if those fruit contain seed that result from selfing or apomixis (agamospermy).

It would be a easy thing to test, take a breeding pair whos progeny will be obvious hybrids and just do the cement tek but using the other pollen in place of the self pollen. If the offspring are hybrids the selfing tek is quite possibly selfing, but if the calcium hydroxide altered hybridization produces selfed-looking offspring its almost certainly also causing apomixis in the selfing attempts.