Expert Eye: Carbohydrates and Amino Acid Products
By Urban Garden Magazine ⋅ July 12, 2010 ⋅
What’s the big deal with carbohydrate and amino acid products these days? Are they being used or misused by growers? We asked Steve Berlow, a research consultant for Florigen Laboratories in BC, Canada to give us his insider perspective on the rise of carbohydrate and amino acid based products in the marketplace in recent years…
The hydroponics and indoor gardening industry is rapidly changing and evolving. Recently the pace of that change has become quite staggering with new products seeming to appear almost daily – nowhere is this more prominent than in the field of plant nutrition. In the last few years the hydroponic nutrient market has progressed from offering base nutrients and some phosphorus flowering boosters through to today’s market where a staggering (some might say ‘bewildering’) array of new technologies and theories are promoted.
Two product types that have been causing a lot of chatter in the growing community are carbohydrate (sugar) supplements and amino acid based additives. And for good reason. Sugars and amino acids are both interesting concepts in the context of plant nutrition and many experts consider them to be on the cutting edge. All sounds pretty exciting doesn’t it? But before you rush off and buy that next fancy-labelled bottle of sugary or amino acid goodness, you really should get your head around some basic facts concerning these substances and the ability of plants to make use of them.
Carbohydrates – Are They Really ‘Candy’ For Your Plants?
You’ve probably heard the hype about carbs: “Feed your plants supplemental carbs and turn them into Olympic Gold Medal winners!”
So a grower walks into their local store, decides to buy a big bottle of some sugary carb supplement, with the intention of deploying it on his next res change. The notion is that the plants will suck up the carbs and get a boost of ‘pure energy’ without having to go through the hassle of producing them as a product of photosynthesis.
Errrr, sorry to spoil the big carb party, but it’s not actually that straight forward. The carbohydrate supplement is definitely a case where theory got ahead of practice. In theory providing your plants with an array of simple and complex carbohydrates seems like a great idea. We all know that plants, driven by light energy and photosynthesis, produce sugar and starch. The plant uses this for growth and development. So the theory goes – if we supplement our nutrient solution with those very same sugars and starches, then the plant won’t have to make them all for itself and can therefore devote its energy to other things – such as making big flowers and fruits! Alternatively, if the plant is undergoing a period of physical stress (such as flowering or fruiting) then the supplementation of those sugars and starches will enable the plant to grow and develop at warp speed as we have removed a limiting factor. Unfortunately all this seems feasible in a text book but, as usual, these things are rarely as simple in real life.
Why not? Well, put simply, it’s one thing to supplement a plant with carbs in a lab, quite another to do so in vivo (real life – real situation.) You can inject carbs directly into a stem or a leaf, for instance, using laboratory techniques, but surely the crunch question is: can a plant uptake carbohydrates through its roots? I have been involved in research that aimed to determine whether plants could actually uptake and utilize carbohydrates and, if so, what could they uptake and utilize. Carbohydrates range in size from very small, simple structures like glucose or fructose through to enormously large, complex molecules like polysaccharides.
So – did I find that plants could uptake simple and complex carbohydrates? Other than some very simple, and small carbohydrates (e.g. plain table sugar or fructose / glucose) plants essentially cannot take up other more complex carbohydrates through their root zone. Why? It’s because of a unique little barrier in the roots called the Casparian strip – complete with his sidekick the endodermis. Essentially the Casparian strip forces everything, and that includes carbohydrates, through the endodermis to be actively selected or rejected for uptake.
Ready For The Science Bit? Introducing The Casparian Strip – Your Plant’s Very Own Homeland Security!
UG_2010-05_CasparianStrip_fInside the roots of your plants sits a very innocuous and extremely important band of cells – called the Casparian Strip. I like to think of this as a sort of “security guard” for your plant. It is used to block the passive flow of materials ( travelling between the cells), such as water and solutes into the main water carrying columns of the plant – the xylem and phloem. By doing this it forces everything to actively pass through or be rejected by the endodermis. Once within the epidermis, water passes through the cortex, mainly traveling between the cells. However, in order to enter the stele, it must pass through the cytoplasm of the cells of the endodermis. Once within the stele, water is free again to move between cells as well as through them. For solutes to pass through the endodermis they must be in inorganic, ionic form to be transported across to the stele. As you can see getting water and nutrients inside your plants is no easy process!
An interesting side note for people who grow with organic nutrients.
When you hear of the virtues of organic fertilizers, remember that such materials are unable to meet any nutritional needs of the plant until they have been degraded / converted into inorganic forms. Organic matter does play an important role in making good soil texture and rhizosphere health, but it can only meet the nutritional needs of the plant to the extent that it can yield inorganic ions. Once within the epidermis, only the inorganic ions pass inward from cell to cell.
Amino Acid supplements and supplementation – possible or possibilities?
Okay, after that bombshell, let’s take a look at Amino Acids. These are fascinating little things, these miniature building blocks of protein – body builders love them and, according to many growers, plants do too. So what roles do amino acids play in plant nutrition?
Table 1 shows the 21 Proteinogenic Amino Acids
Table 1 shows the 21 Proteinogenic Amino Acids
There are total of 21 Amino Acids used in the production of protein and you’ve probably seen most of them listed on the back of a bottle by now. They are known as Proteinogenic Amino Acids
Every chemical reaction or process that goes on inside a plant relies on protein. From photosynthesis through to hormone production, growth and development, stress – proteins are used by the plant for every aspect of its life, so we can see that amino acids are very important in the big scheme of things.
This importance has not escaped the attention of researchers or manufacturers of plant nutrients and additives. We are now seeing quite a few emerging products that contain these essential building blocks of life. One area being examined by both researchers and manufacturers are amino acids that are direct precursors to hormones. Tryptophan is one popular amino acid being researched as it is the direct precursor to IAA - a powerful growth hormone. Arginine is one of the precursors for cytokinins and is a major player in the production of flowers and fruits on a biochemical level. Other exciting roles of amino acids include their part in mitigating plant stress. Proline is produced by the plant in huge quantities during times of stress to assist with osmotic balance and to maintain a positive water status.
Amino acids are also used as a source of nitrogen in the root zone as they are delaminated by rhizosphere bacteria and fungi. The bacteria feed on the amino acids and in return nitrogen, in the form of ammonia, is released which can be absorbed by the plant. Ammonia is very rapidly absorbed and utilized by the plant and, in small quantities, is very beneficial to the support of rapid growth and development.
A new and very exciting and emerging area of amino acid research, and one that I am very actively involved in, is the role played by accumulated amino acids. In plants, the roles of accumulated amino acids varies from acting as an osmolyte, the regulation of ion transport, modulating stomatal opening, and detoxification of heavy metals. Amino acids also affect the synthesis and activity of enzymes, and most excitingly of all play a major role in gene expression!
So it’s readily apparent why plant nutrient manufacturers would be interested in the humble amino acid – they could be very useful to growers! As useful as might be, amino acids are also commonly misunderstood – just like the carbohydrates we looked at earlier. Once again theory is getting way in front of reality.
As with carbohydrates no one really looked at whether plants can take actively up amino acids through their roots. A major focus of my research is examining how or if plants can take up amino acids via their roots. One method is to feed plants a solution of radioactively labelled amino acids and then take special x-rays of the whole plant 24 hours later. You can actually visualize the extent of the amino acid uptake. In all of the experiments I’ve been involved in, almost none of the amino acid solution fed to the plants had been absorbed by the roots and transported to the leaves. So what’s at play here? Once again it’s the role of the Capsarian strip and endodermis coming into play and excluding the uptake of almost all of the amino acid solution fed to the plants. Amino acid supplementation does work to a minor extent – as some, but very few, of those root fed amino acids are absorbed by the plant. The exciting thing is that even that tiny amount that is absorbed positively affects the growth and development of plants.
So what did we learn?
Only simple sugars are absorbed by the plant root system. And only a very small amount of any amino acids supplied will ever be taken up by your plant’s root system. So what does that mean? Are carboyhydrate and amino acid producs a waste of your time? No – not exactly. Even when a small amount of amino acids are absorbed by the plant, we can get some positive effects. The simple sugars in your carbohydrate products do get absorbed. Others form a good source of food for beneficial bacteria in your root zone. So there are some benefits from using these types of products – just probably not to the degree that some of us may have hoped.
Feeding your plants carbohydrate and amino supplements is not a waste of your time or money – in fact many of those simple and complex carbohydrates serve as food for the friendly bacteria and fungi in your root zone. But don’t forget that your plant’s roots constantly exude simple and complex, carbohydrates, amino acids and proteins into the rhizospere and that those exudates serve as food and growth promoting compounds for many of the beneficial bacteria, fungi and micro organisms present in your plant’s rhizoshpere.
Root exudates are commonly divided into two classes. Low-molecular weight compounds – such as amino acids, organic acids, sugars, and other secondary metabolites and high molecular weight exudates – such as mucilage (polysaccharides or complex carbs) and proteins. The rhizospheric bacteria and fungi return the favor, in a symbiotic relationship, by breaking down complex products in the rhizosphere into ionic forms the plant can absorb as well as excreting protein and secondary signalling molecules of their own that benefit the plant by increasing its rate of growth and development.
In fact, much or all of the apparent success of carbohydrate and amino acids products are due to this inadvertent power feeding of your root zone friendlies and the symbiotic benefits they return to your plants.
http://urbangardenmagazine.com/2010/07/expert-eye-carbohydrates-and-amino-acid-products/
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