Leaves: Take a Closer Look! A look beyond the surface!

If we think of a plant as a city, then all the different parts of the plant would represent the different functioning parts of that city. The xylem and phloem serve as the highways transporting goods around, the roots are the local port for incoming materials, and the leaves are the manufacturing and production centres. By thinking in these terms we can, with greater ease, visualise the importance of the leaves. If the manufacturing and production centres of a city are shut down or not producing, then the city soon grinds to a halt. If this happens, then the city would quickly shut down and turn into a ghost town. With this in mind, we can see that leaves are the single most important part of a plant. Without the leaves the plant cannot produce energy or materials for production, and without production there is no growth or development, which means no yield! So let’s look a little further into these important little powerhouses of production so we can understand a little more about what they do, and more importantly, how we can increase their output to ultimately give us a greater yield! Before we dive in too deep, it will help if we have a quick tour of our manufacturing and production facilities (the leaves) as this will help us better understand how and why our little factories are so important. Sunlight Into Energy Without sunlight, life on earth could not exist. It warms us, and through plants, ultimately supplies the rest of life on earth with food, which is, after all, our energy. Plants convert this radiant energy (light) into a plant-usable form of energy through a complex series of reactions involving, primarily, carbon dioxide and a unique compound called rubisco. This combination ultimately yields sugar, which in turn provides the energy for other reactions that take place inside the plant. One of the primary functions of the leaves (our manufacturing centres) is the conversion of light energy into a plant useable form of sugar. The more light the leaves can process, the more sugar or energy the plant can manufacture, which, in turn can significantly influence the rate of growth and development of your plant, ultimately increasing your yield! So how does this occur? What happens inside the leaf? Can we measure this to see if our little factories are indeed producing more? The Leaf Surface This is the outside of our manufacturing centre, much like the outside of a building. The leaf surface stops unwanted things from getting in - such as fungi, viruses, etc. - thus allowing for the exchange of gas and water. Like most manufacturing centres, however, all the action takes place on the inside. So let’s have a look at Figure 1 which is a cross-section of a leaf showing all of the important features. Then let’s go inside for a more detailed examination of what goes on inside your leaves. Description of Function 1. Upper epidermis. This is a single layer of cells that are quite transparent and permit most of the light that strikes them to pass through to the underlying cells. The upper surface is covered with a waxy, waterproof cuticle, which serves to protect against pathogens and to prevent excessive water loss. 2. Palisade layer. This consists of one or more layers of cylindrical cells that are filled with chloroplasts and carry on most of the photosynthesis in the leaf. 3. Spongy layer. Situated beneath the palisade layer. Although the spongy layer contains some chloroplasts, their main function seems to be the temporary storage of sugars and amino acids synthesized in the palisade layer. They also aid in the exchange of gases between the leaf and the environment. Chloroplast Cells and Mitochondria For our lesson today we are going to primarily look at the features associated with energy conversion and energy production. The Palisade layer is where almost all the energy conversion action takes place. These specialised cells are primarily responsible for the conversion of light energy into a source the plant can use: sugar, or more specifically, glucose. The palisade cells contain, within them, specialised photoreceptive organelles called chloroplasts. It is these little fellows that actually perform the conversion of light energy into chemical energy. So we can think of the palisade layer as the power station for the plant, producing the raw energy that the manufacturing centres (mitochondria cells, etc.) will need, in conjunction with their raw materials (water, mineral elements etc) to produce the goods (hormones, enzymes, etc) that the plant needs to grow and develop. We can see that this is not unlike a typical manufacturing centre where our raw materials together with an energy source are used to produce the things the city needs to function and grow. Foliar Performance Nutrition Knowing a little more about the leaves of our plant and how they work together with how very important they are, should lead us to two very obvious and important questions. Can we access or influence the production process of the leaves? Can we measure this to see if our little factories are indeed producing more? Well I am happy to say the answer is a resounding yes - but not in a way you might think. Knowing the leaves are the primary influencing factor in the growth and development of your plants will lead you to the obvious realisation that almost everything you have been doing or supplying to your plants is a direct (or indirect) attempt to maximise the output of these little powerhouse performers, your leaves. You provide your plants with ample light (to hopefully maximize the amount of light energy your plants can convert), you provide your plants with ample food (raw materials for manufacture) and often you provide your plants with supplements (specialised manufacturing materials) in an attempt to, as you now know, influence the output of these factories (leaves) in a positive way. How Can We Get More from Our Plants Have you ever thought that the best way to increase the output of your plants was through the direct insertion of specialised materials exactly to where we now know they are required, inside the leaves of your plant? My guess is you have at some stage thought that this might be a good way to get your plant to produce more. Well guess what? It is a good idea; in fact it is a fantastic idea because it is the only way you can truly gain any significant or meaningful effects from applying specialised materials (performance supplements) to your plants.

The Long Inefficient Road vs the Direct Route Traditionally, every one of us has gone down the long slow traditional way by supplying their performance-based supplements to their plants via the roots. This works great for traditional elements such as Nitrogen, Phosphorus Calcium etc., but not so great for performance based specialist materials. Why? For two very good reasons. Firstly, most performance based supplements or specialised materials have a very low absorption level by the roots. During recent trials conducted at the University of British Columbia our Dutchmaster research team looked at which things the roots can absorb and translocate easily and efficiently. The results were amazing! What was found was that with the exception of very small molecules, elements and ions, etc. not much else was efficiently absorbed or translocated by the roots. Certainly things like enzymes, complex carbohydrates, proteins etc. were almost always completely blocked from uptake by a unique little barrier inside the root called the Casparian Strip. This strip is designed to prevent unwanted compounds, fungus and bacteria, etc. from entering the plant via the root zone. This protective barrier also prevents a lot of specialised materials from ever entering the root and being translocated to the leaves. Secondly, what does get absorbed is slowly moved from the roots to the leaves where they can then be used (translocated). This slow trickle feed also allows the plant’s “negative feedback” loops to function very efficiently. This feedback loop is a plants’ way of keeping everything in check. If, for example, a plant requires a particular hormone and you supply it with extra amounts of that hormone, the plant will then reduce its own production of that hormone to keep things in balance. The trick is to overwhelm or flood the plants negative feedback system so positive effects are produced before this feedback loop can compensate. Foliar application of the specialised materials, when the correct delivery agent is used, is the only way you can effectively introduce these materials in such volumes and with such speed that the plants negative feedback system is temporarily overwhelmed, and our desired growth or developmental patterns can be temporarily induced. So we can see that there are two paths to take when it comes to introducing performance-enhancing materials to our manufacturing centre, the leaves. The first is the long slow and inefficient way, via the roots, and the second is the very fast efficient way, with one very important proviso (and one you must never forget if you are to truly experience the benefits of foliar performance supplementation). Delivery Agents vs Wetting Agents For any foliar program to be completely effective you must be able to deliver your specialised materials inside the leaf of your plant. Now this is not as easy as it sounds because you first have to get past the protective waxy layer that surrounds every leaf. Once past this layer you must then get it inside the cells where all the action is taking place. Now this is not as simple as just “madly” spraying your plants with an enhanced solution, as most of what you apply to the leaves will never be absorbed. For many years it was believed that by allowing a solution to remain in contact with the leaf surface for an extended period of time, the effective absorption of that solution would take place through tiny openings in the leafs surface called the stomata. In my last article we examined how the plant uses the stomata to absorb and exchange gases (CO2, Oxygen) and to regulate water flow (transpiration). Modern research is now showing that only a tiny portion of what you spray can get inside the leaf surface via the stomata. In fact, typically less than 10% of the stomata uptake any solutes1*. This is then further compounded by the fact that even once taken up, most of the supplied material is immobilized on the inner side by ion exchange membranes2*. This certainly explains the very hit and miss effects of traditional foliar spraying when trying to facilitate enhanced growth patterns or development. “But I use a wetting agent,” I hear many of you say. This is good in that it will allow the solution to sit evenly on the leaf for an extended period of time, allowing a small amount of absorption but certainly not enough to effectively saturate and overwhelm a plants’ negative feedback system. The only way to effectively deliver large amounts of specialized elements inside the leaves of your plant is to use a very new type of product known as a “Delivery Agent”. The difference between a wetting agent and a delivery agent is very simple and very important. A wetting agent is designed to make water wetter, so that it sits more evenly over the leaf and extends the contact area and time when applied to a leaf. A delivery agent is also designed to do this - but - and it’s a big but - a delivery agent is primarily designed to actively translocate elements from the outside of the leaf surface to the inside, past the ion exchange membranes and directly to the cells where they are needed. Further, a delivery agent is designed to do this independently of the stomatal opening in the leaves. What you have with a specialized delivery agent is a unique opportunity to profoundly affect the development and growth patterns of your plant. This type of technology is very new but freely available in many hydroponic stores. Make sure you ask for a delivery agent and not a wetting agent if you want to be able to maximize the results from a specialised foliar spraying program. Figure 2 demonstrates the dramatic difference that using a delivery agent can make to the uptake efficiency of foliar applied nutritional supplements. The pictures you are looking at were conducted recently at the University of British Columbia’s Bio Imaging Centre by our chief research officer. They clearly show that the most effective way to saturate the cells of a leaf is through the use of a delivery agent. A specialised and very small sized dye was used to track movement into the leaf. If you look at the control (no dye) you can see the inside of the leaf section is red. This is because chlorophyll fluoresces red when viewed under a fluorescent microscope. The dye we are tracking is green, so the more green on the inside of the leaf the greater the uptake. You can see that on the leaves treated with the dye only, as well as on the leaves treated with the dye plus a wetting agent - is stuck mainly on the outside surface of the leaf whereas the leaf treated with the delivery agent plus dye is fully saturated. Well, we certainly have been exposed to a lot of new material and concepts in this article, so let’s quickly recap what we have discovered. We have seen that most of what happens to control the growth and development of a plant takes place inside the leaves. We have learned that you can alter the output of the leaves in a beneficial way through the use of specialised foliar supplements. Most importantly we learned that this type of foliar enhancement is now a reality thanks to research and technology.