The key to helping plants grow is to understand the mechanisms behind and inside their growth, to learn why they decided to sprout at one time over another and why flowering at one point happened and not at another time. Due to these processes being intrinsic to the life cycle of the plant, tied up in not just reproduction, but also growth and development, one can imagine just how many complicated genetic, epigenetic, proteomic, and other systems are working in the background to control all of that.
The Complexity Of A Plant
Scientists have to work piece by piece, unraveling the ties that bind each segment of a plant’s infrastructure in order to better comprehend the whole of its activities. This can be as simple as trying to figure out the function of a single gene, which itself in turn may balloon out into being the main component in a complicated multi-locus signaling or hormonal pathway, or by going more broad and trying to determine how larger groups of cells in particular plant structures work together.
To begin looking into the latter, scientists often start with a more direct process of the plant that they want to learn more about and then use that to determine which cellular parts are involved in it.
Waking Up Seed Dormancy
For researchers at the University of Birmingham, they wanted to unwrap the cycle of seed dormancy, whereby a planted seed decides it is an appropriate time to sprout.
Past investigation has found that this process has far greater complexity than it seems to on its face. The plant takes into account current and past temperature variations, soil conditions being suitable for a growth cycle, the amount of sunlight available in its location and its needed direction for stalk growth in order to grow toward available sunlight, and many other factors.
How a simple seed is capable of doing all of this is what the researchers wanted to find out. A hypothesis that had been proposed is that, after seed dispersal from the mother plant, the seed’s responses are controlled by a set of antagonistically acting factors. These are a set of some controlling systems that keep the seed within a narrow range of acceptable growth times, pushing against each other for a desired outcome until one wins out based on environmental conditions.
Not As Simple Of A Process
Thus, if all the different factors are not aligned perfectly, the seed will not sprout. Further research found that this was indeed the case, with a set of two antagonistic hormones being the culprits, abscisic acid pushing the dormancy of the seed and gibberellin pushing its germination. Since both of these hormones are fairly common in the plant, there must be a certain threshold of amount needed for either one to start acting on its developmental processes.
Or, at least, that’s what scientists previously thought, until this current study proposed something different. Rather than being a simple one way switch being fought between the two hormones, the actual underlying system involved is much more complicated.
It is not these two hormones directly that controls this process. Instead, a specialized set of cells, two sets actually, act as a sort of brain processing unit specifically for controlling germination. Do note that this is just a comparative symbol, plants don’t have brains, but that’s the closest way to describe this set of cells for this specific process.
The Plant Brain For Germination
This “decision-making center”, as the study refers to it, is located in the developing root system of the seed, a part called the embryonic radicle. In translation, this is the “embryonic root”, the beginning of a plant’s roots that emerge from the seed embryo. The structural composition of these two sets of cells is remarkably similar to how animal brain systems are set up, though for a similar, yet very different and more precise purpose.
Bifurcated into a two-pronged group of cells for information processing, this system in humans makes up the brain and is used to create a time delay in signals between the two halfs, reducing sensory noise from one’s environment so the body is not overwhelmed and can focus on specific tasks.
For seedlings, these cell structures are used to filter through environmental stimuli above the seed, to sense temperatures, and to use hormonal mechanisms to end dormancy once conditions are met. The two previously mentioned hormones are used by this decision center to activate that action when the time has come.
The location of the embryonic radicle and the enclosed decision making cells seems to match the areas in other plants, beyond the model organism Arabidopsis used in this experiment, where germination is started. The mechanisms and hormones used are not always the same, but the location seems to be equivalent across plants as the cellular area where seed growth is begun.
Controlling Seeds Through Controlled Temperatures
The next step the scientists took was to test this ability of filtering out noisy environmental inputs by applying variable temperatures and other responses to see how the Arabidopsis seeds were affected. What they found was that variable temperatures were far faster at inducing seed growth rather than the commonly believed method of a cold time period stimulation.
This means that using proteomic and hormonal mapping, researchers should be able to determine the best series of inputs to regulate germination and rapidly speed up growth time periods from the point of seed planting. This can also allow synchronization of growth periods between different types of plants, allowing harvests to occur at the same time.
For farmers, controlling how quickly germination happens means more yields on an annual basis and also control over when the growing plants are exposed to pests, allowing a reduction in herbicide use by controlling when seed growth happens to avoid pest outbreaks. For plant growing in general, this new research should be a boon to allow more variable handling of plant growth in different seasons.
Combined with genetic alterations and continued visualization of protein output and hormone circulation, plant growers may soon have an even more intimate understanding with their plants and their life cycles.
Photo CCs: Micro photography from Wikimedia Commons