Thank you Jon and Harrison - I had received a private response to my question with links to two articles which I post here for anyone else that might be following along - neither are as technical as the attached paper.
http://www.nyshs.org/pdf/fq/2000-Volume-8/Vol-8-No-3/MCP-Facts,-Speculation,-and-How-Could-it-Affect-the-New-York-Apple-Industry.pdf http://www.chemistry-blog.com/2011/10/12/fruit-ripening-how-does-it-work/ After repeated readings and a bit of thought, here is my current take home. 1. Ethylene is not the sole regulator of ripening in apples, but would be considered the largest single regulator. 2. Ethylene switches on several different genes controlling various aspects of ripening apples. Ethylene activated genes may produce enzymes which break chemical bonds associated with cell walls, leading to the cell wall loss of integrity and on to softening fruit. Etc. 3. Low internal ethylene production/concentration in certain varieties of apple is not the determining factor of long keeping, crispy flesh - ethylene receptor sites in a fruit are saturated at relatively low levels of ethylene, maybe as low as 10 ppm while the internal ethylene concentrations in common varieties are in the 100's of ppm. 4. Low ethylene generation in certain varieties may be correlated/associated with a physiology that is less sensitive to the effects of ethylene generally (few or mutated ethylene triggered genes?) 5. There is a lot unknown... Please feel free to challenge my interpretation - it's oversimplified I know, and some of it may just be wrong. I need to read thru the Harb paper several more times to do it justice, tho I feel like I'm getting a bit deeper understanding with each reading. I also note that we (as fruit growers, researchers, consumers) are up against the limitations of language as we discuss fruit quality - "firm" is not a scientific term - HoneyCrisp is not 'firm' in comparison to Arkansas Black- Mitch Lynd uses the word 'crispy' to describe HoneyCrisp - Red Delicious can be 'crisp', but is never 'crispy' - Miller at OSU has demonstrated that there is a physiological difference between Red Delicious (and the other common varieties) and HoneyCrisp in the way the fruit's flesh cleaves during chewing - Red Delicious et. al. break apart between cells, with cells remaining more or less intact, while in HoneyCrisp (and a few others) the cells break open (explosively crisp!), releasing the cell contents and providing the much sought after crunch. Reading the current active thread about 'HoneyCrisp prices' demonstrates how difficult it is for language to precisely describe aspects of quality. "...reflect the failure of traditional pressure testers to adequately measure crispness rather than firmness." Harp et.al. (the attached paper) - "There is no mechanical test that can sort out what people like." Miller, Ohio presentation 1/19/14 regards David Doud grower, IN On Jan 30, 2014, at 4:29 PM, Jon Clements wrote: > ---------- Forwarded message ---------- > From: "Wright, Harrison" <harrison.wri...@agr.gc.ca> > To: "Nichols, Doug" <doug.nich...@agr.gc.ca>, > "apple-crop-boun...@virtualorchard.net" > <apple-crop-boun...@virtualorchard.net> > Cc: "DeLong, John" <john.del...@agr.gc.ca> > Date: Thu, 30 Jan 2014 20:47:52 +0000 > Subject: RE: [apple-crop] ethylene > Hello Doug, I will add my two cents and attempt to answer David's questions, > for what it is worth. > > There is quite a range in the amount of ethylene that different apple > cultivars produce; in general though, they all have a similar signature: > immature fruit have little ethylene, sudden ethylene synthesis spurs > maturation and then this synthesis fades as the fruit begins to senesce. > > I think there likely is a trend between low ethylene fruit generally holding > firmness and high ethylene fruit going soft. Other examples could be Gala > fruit have low ethylene and stay firm and Macs and Cortland have high > ethylene and go soft. Whether this is cause and effect or a matter of > correlation, I am not sure; my hunch is it is complex and more the latter. > > It is an interesting question as to whether if you exposed a Honeycrisp apple > to high ethylene whether it too would go soft. My guess is you might have a > modest effect (same way that you can add a ripe banana to other green > climacteric fruit to more quickly ripen them), but it will not turn the > Honeycrisp into, say, a Mac because there are many other variables. > > I attached a recent paper comparing Honeycrisp to Macs. They found many > differences between the two besides just the peak climacteric ethylene > levels. ACC (the precursor to ethylene) was much higher in Honeycrisp than > Mac, suggesting there might be a limiting step there. When the two cultivars > were at similar ethylene levels, the expression of genes associated with > ethylene synthesis, ethylene perception and signal transduction were actually > much higher in Honeycrisp than in Mac (contrary to what you might think). > However, at comparable ethylene levels the expression of genes associated > with cell wall metabolism (breaking down cell walls and so firmness) was much > lower in Honeycrisp than in Mac; this is why the Honeycrisp stay firm. How > this correlates with the low ethylene in Honeycrisp (and the buildup of ACC), > I'm not exactly sure. Also, as an aside, it is my experience that a lot of > the ethylene that is sometimes produced is often overkill; I'm not sure why > this is (maybe off-gassing prompts other neighbouring fruit on the tree in > nature to mature at more or less the same time; again, positive feedback?). > In other words, it is my belief that if you took a Mac and you somehow > managed to keep the internal ethylene to no more than 50 ppm, maybe even 5 > ppm, it would go soft just as fast as a fruit that was allowed to go up to > 500 ppm). Now, 1-MCP, a site blocker, not necessarily a synthesis inhibitor > (though it does decrease synthesis too) complicates this relationship. > > It is believed that 1-MCP binds the ethylene receptor sites. I believe the > fruit will still undergo a typical climacteric peak, but the peak will likely > be lower and the time it takes greatly protracted. For example, I just took > some Macs out of storage the other day. On day 1 the control fruit averaged > an internal ethylene content after 4 months of storage of about 250 ppm; the > 1-MCP fruit were less than 1 ppm for comparison. After a 7 day shelf life the > control fruit had increased to about 800 ppm internal ethylene; the 1-MCP > fruit had also increased, but only averaged around 50 ppm (though to be fair > they were all over the place and ranged from about 4 to 400 ppm - that Mac > with 1-MCP at 400 ppm? Still firm...). For some things (pears or avocados, or > an immature apple) a full rate of 1-MCP may work TOO good; these fruit will > never mature and will turn brown before they fully ripen. As far as David's > assumption about 1-MCP timing, my understanding is the same, ethylene > synthesis needs to have begun, but you want to catch it before it takes off. > Ethylene synthesis involves a positive feedback loop. I believe timing is > essential; as I mention before, if you pick the apples too early, my > understanding is, like pears, if the ripening process has not already been > set in motion, those immature fruit treated with 1-MCP will likely remain > immature fruit until they whither up and turn brown. Do not get me wrong; > treated at the right time 1-MCP is remarkable chemical that probably was the > salvation of a number of cultivars. > > I hope this helps and I have not steered you wrong. > > Harrison > > -----Original Message----- > From: Nichols, Doug > Sent: January-30-14 1:07 PM > To: Wright, Harrison; Wright, Harrison > Cc: DeLong, John > Subject: FW: [apple-crop] ethylene > > FYI > > -----Original Message----- > From: apple-crop-boun...@virtualorchard.net > [mailto:apple-crop-boun...@virtualorchard.net] On Behalf Of David Doud > Sent: January-12-14 10:58 AM > To: Apple-Crop > Subject: [apple-crop] ethylene > > So - help me understand the differences in ethylene physiology in different > apples - I am familiar with textbook graphs and the climateric respiration > pattern that is a generalized explanation for maturity/senescence in apples, > but there are apples that don't seem to fit that pattern, specifically > GoldRush and HoneyCrisp, where ethylene production/concentrations do not seem > to spike, but seem to 'peak' at a low level of 1-5ppm rather than spiking to > 10's to 100's of parts per million - > > GoldRush and HoneyCrisp are also associated with maintaining firm, crisp > flesh quality over a long storage life (at least the fraction of HC that > don't bitter pit or soft rot or decline from any of the several other > maladies to which it is subject) - is the low ethylene synthesis the > explanation for this? If HoneyCrisp is exposed to high concentrations of > ethylene does it then soften and age like a 'normal' apple? Or is there > something else going on? > > MCP binds to ethylene receptor sites and so prevents ethylene from having its > normal effect on respiration and maturation - does the treated fruit still > exhibit the climateric peak in ethylene generation? But the ethylene is > unable then to have its effect because of the blocked sites? From what I have > gathered, MCP is applied at some point after significant ethylene production > has initiated, but likely before production has peaked. > > Thanks for any input, feel free to correct any misconceptions on my part, I > won't take anything personally - > > David Doud > grower, Indiana > -15F last week > > _______________________________________________ > apple-crop mailing list > apple-crop@virtualorchard.net > http://virtualorchard.net/mailman/listinfo/apple-crop > > > > > -- > Jon Clements > aka 'Mr Honeycrisp' > UMass Cold Spring Orchard > 393 Sabin St. > Belchertown, MA 01007 > 413-478-7219 > umassfruit.com > <(Harb et al) Mac and Honeycrisp softening related to wall enzyme activity > (2012).pdf>_______________________________________________ > apple-crop mailing list > apple-crop@virtualorchard.net > http://virtualorchard.net/mailman/listinfo/apple-crop
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