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Brunetti on plant secondary metabolites

Jerry BrunettiJerry Brunetti's lecture was titled "Achieving the holy grail of crop health: Plant secondary metabolites".  That probably sounds a bit yawn-worthy if you're not a plant geek, but it turns out his talk was my favorite from the conference so far.  (In the interest of full disclosure, though --- I am a plant geek.)

So, what are plant secondary metabolites, and why should we care about them?  The term refers to every chemical that makes up a plant except for the big three --- carbohydrates, fats, and proteins.  The scent of a flower, the spiciness of a pepper, and the color of an apple are all plant secondary metabolites.  So are the chemicals released by caterpillar-nibbled trees to warn the next tree down the lane to build anti-caterpillar chemicals proactively, as well as the attractants emitted by plant roots to tempt soil microorganisms to stop by.

The chemicals that give plants intriguing tastes are all plant secondary metabolites, and so are compounds like lycopene and salicylic acid, which help prevent prostate cancer and heart attacks, respectively.  Brunetti explains that there are tens of thousands of plant secondary compounds produced for reasons that include attracting pollinators and seed dispersers, defending the plant from ultraviolet light and herbivores, and communicating with plants, insects, and soil microorganisms.

Plant secondary metabolitesThe fact that so many of the compounds impact our health (positively or negatively) is merely a side effect from the plants' point of view.  Plants create secondary metabolites because the chemicals make their lives easier --- since a tree can't run away from problems or travel to find true love, it has to repel the one and attract the other.  (Sounds like my life on the farm....)

But production of these chemicals comes at a cost.  Plants constantly have to weigh the pros and cons of using their limited energy to make carbohydrates, fats, and proteins --- allowing them to grow and reproduce --- or to make secondary metabolites of various sorts.  In the wild, plants usually create a bit of both, focusing on secondary metabolites more when they're subtly stressed, but not so injured that they're wilting away.

In an agricultural setting, the stakes are different.  Farmers try to protect our crops from all problems, which means the plants have little reason to produce secondary metabolites and can simply grow big and tall.  While that means more pounds of vegetables on our plates, the lower concentrations of secondary metabolites make the food less tasty and nutritious.  Maybe that's why vineyard keepers believe the best wine comes from grapes that had to struggle a little?

Strawberry micronutrient deficiencyIn addition to lacking the incentive to make secondary metabolites, some cultivated plants also lack the ability.  Micronutrients like boron, copper, aluminum, manganese, and zinc are all essential for the production of secondary metabolites but chemical farmers figure crops can get by without micronutrients as long as they're well dosed up with some 10-10-10.  I guess that's why I was able to taste a micronutrient deficiency in my strawberries --- the lack of minerals relates directly to the secondary metabolites that we Weekend Homesteaderperceive as flavor.

 So how do you grow the most delicious and nutritious fruits and vegetables possible?  Simply feed the soil well-rounded organic amendments like compost and mulch, and don't wipe out every last disease and pest.  You'll get lower yields, but what you do grow will be richer in flavor and nutrition.

Learn to grow healthy plants from the ground up in Weekend Homesteader.



This post is part of our ACRES conference lunchtime series.  Read all of the entries:





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This is great. I've always believed that you can only get out what you put in. This is the clearest, most scientific explanation of why homegrown (specifically compost-grown) tastes better.
Comment by Jessie : Improved Thu Apr 12 15:34:18 2012
Jessie --- Glad you enjoyed the post! I wasn't sure if I had summed up his inspiring talk well enough to get the gist across, but it sounds like I did. :-)
Comment by anna Thu Apr 12 16:37:15 2012
I haven't much to add to the discussion, I'm afraid, but I did want to second Jessie's enjoyment of this post! I found it both enlightening and useful, so much so that I put a link in my favorites so that it will be easy to find again! :) Thank you for sharing!
Comment by Ikwig Thu Apr 12 21:14:44 2012
Ikwig --- Thanks for your kind words! I'm so glad the post hit a nerve.
Comment by anna Fri Apr 13 11:09:35 2012
OK. I'll give you taste, Anna, but you haven't proved your point about nutrition. Having practiced medicine for 40 yrs, I'v never seen a patient suffering from Boron Deficiency. I know that this is America where the rule is that if one is good, then two must be better, but even commercial produce with levels of certain nutrients lower than organic counterparts still have plenty of them to keep us in good health. Remember that nutritional studies claiming some factor in food prevents this or that condition are based on shoddy "questionaire studies" that rely on the subjects' reminiscences of their diet over the past several decades compared to their health status today. None are prospective studies and certainly not double blind. Extrapolations from that data deserve little credibility.
Comment by doc Sun Apr 15 15:04:27 2012
Doc --- But I'm not just talking about the concentrations of micronutrients in the food here. I'm talking about the compounds that the plants turn them into (such as lycopene, etc.), which in many cases have been shown to reduce the risk of various ailments. I haven't read the medical literature, but I'm pretty sure that there have been double blind studies covering the effects of secondary compounds like resveratrol.
Comment by anna Sun Apr 15 17:12:32 2012
It's all mythology. For instance, they use some questionaire study to find that people who claim to eat more tomatoes have lower rates of, say, prostate cancer. Some researcher has the fantasy that's it must be the lycopene and not one of the other 19,999 chemicals in tomatoes, maybe because somebody else found that rats fed huge amounts of lycopene have less liver cancer, as if we can extrapolate liver cancer in rats to prostate cancer in humans.... The logistics of nutritional studies are a problem. Double blind, prospective studies are too difficult to do because you can't control subjects' diets strictly enough for long enough to show any differences (even if there really would be a difference) ... We know that plants make many beneficial chemicals, but consumming the plant rather than the refined, concentrated pharmaceutical is rarely adequate. How much moldy bread, for instance, would you need to eat to cure your pneumonia?...There's no such thing as "good nutrition," only adequate nutrition and bad nutrition.
Comment by doc Mon Apr 16 18:56:05 2012

Doc --- Hmm, I can't say I agree with you. True, it's tough to do really scientifically rigorous studies on topics of human health for ethical reasons, but that doesn't mean we should ignore all of our stabs in the dark. Does that mean you also don't believe that cigarette smoke increases our risk of lung cancer because we, presumably, haven't stuck test subjects in a room for several years with measured levels of cigarette smoke vs. test subjects with no cigarette smoke? Just because we instead asked them how many packs a day they smoked and relied on their memories?

(It's also a bit unfair to compare the effects of penicillin used to cure a serious illness --- presumably you need a lot of it in one dose --- with compounds that boost your health in small amounts over extended periods of time.)

Comment by anna Mon Apr 16 20:51:17 2012

If you are looking at some type of measurable performance with regards to plant health and micronutrients (or some other amendment like foliar sprays) you should be able to do a BRIX test before and after the application. If the plant responds well, the BRIX level should increase. If not, then that particular amendment isn't currently beneficial to that particular plant. I don't know for sure, but I would expect that secondary metabolites would contribute to the overall BRIX measurement.

Personally I still see a few challenges with this approach. I don't have a refractometer available to see how practical this testing actually is. In addition, I don't have a lot of the same type of plant where it makes sense to apply a small dose of one amendment to one plant before I decide to apply it to the rest of that variety. Finally, I think that soil testing for trace elements is probably more exact to determine major deficiencies... then again it is very expensive and takes a long time to get the results when being sent to a distant lab. I'm sure that testing the soil every few years is worth the expense, but going back to the basics of adding compost and aged manure frequently will probably address the majority of problems.

Comment by David Wed Apr 18 14:41:04 2012

David --- Excellent point about having to have a lot of the same kind of plant to use brix most effectively. What intrigued me was the idea of monitoring a planting over time to see if the brix begins to decline, which would give me an idea I might need to topdress to ward off disease. The nice thing about brix vs. soil testing is that you can test the brix easily at home, so you can do it every day if you want to.

I'm still not totally sold, but I probably will eventually have to get one of those meters and experiment. :-)

Comment by anna Wed Apr 18 16:54:59 2012

Ha! I get so tired of being told that my experience in life is not quantifiable nor explainable. It's in your head. Nope, it's in the strawberry, or not as real world experience tells a different tale.

I grew up eating from about an acre garden, it was our main food source, then we moved into town and ate from the grocery store. I hated it. Said the milk tasted like colored water and bad water at that. Etc. etc. I was a pain to my parents. It's always nice to learn that there might be some science to be explored that might help me understand the why and wherefore of the changing taste.

(PS Many thanks to your geeky brother for the email replies button, for someone like me who is very behind in her garden blog reading... it's a help!)

Comment by c. Fri Apr 20 10:32:32 2012

c --- Isn't it crazy how insipid grocery store food tastes after you've eaten the real thing?

I've passed your thanks on to Joey! That should oil the gears for my next webpage request. :-)

Comment by anna Fri Apr 20 13:52:11 2012

Happy to help with the "leverage positive to encourage help from tech guy" side of things. :D

And yes, snobs call it "having a palate" sadly the world used to eat like that daily.

Comment by c. Fri Apr 20 21:05:59 2012