The purpose of this thread is to provide Future4200 users with a better understanding of plant photoperception. My approach is to (1) add posts that serve as an educational resource for this community, and (2) answer relevant questions (when I am able to) that are posted in the thread.
Let’s start here:
Because plants are sessile organisms, their evolution includes an impressive array of mechanisms for detecting and responding to the continuous environmental changes that all plants encounter throughout their life cycle. From a plants perspective, these real-time changes in its micro-climate occur 24/7, 365 days a year, regardless of whether they are grown indoors or outdoors. It is important to note that these mechanisms for perceiving real-time changes in a plants micro-climate exist in wild plant species and in all cultivated crop species (e.g., cannabis).
To the best of our knowledge, humans have been cultivating different crop species for ~10,000 years. My guess is that farmers have suffered headaches and frustration for an equally-long period of time, when their crops exhibit variable yields and product quality due to the ever-changing micro-environments that all crops encounter year after year.
Greenhouses and indoor farms are nothing less than an attempt to minimize changes in a crop’s micro-climate and thereby achieve more reproducible crop yields and product quality. That said, plants are far more in tune with their environments than humans often appreciate, such that virtually EVERYTHING a human does in a greenhouse or indoor grow room perturbs these highly-controlled environments in ways that plants will perceive and respond to. Yield and terpene profiles from plants grown indoors are particularly relevant examples.
For reasons I may never understand, I have always viewed a plant’s hyper-sensitivity to its micro-climate as an opportunity (instead of a headache). Along these lines, I have always thought that understanding how plants perceive and respond to micro-climates provides us with the opportunity to manipulate a plant’s micro-climate in ways that increase that crop’s yield and/or product quality (hence this new thread). To put this another way, knowledge is power.
Your plants sense very small changes in temperature, soil moisture, day length, stress factors, humidity, wind speed, vibrations, pressure/altitude, light intensity (e.g., shading), light quality (i.e, the spectrum of incident light), the direction of incident light, overwatering, herbivore abundance/predation, soil bacteria populations, and likely every other environmental variable you can think of.
Because nearly all plants rely on light to make their energy (via photosynthesis), it should not surprise us that plants are exquisitely and continuously (24/7, 365) sensitive to surprisingly small changes in their ever-changing light environment. Along these lines, I have always enjoyed sharing the fact that an extremely small light pulse - equivalent to one-tenth of one flash from one firefly - is able induce changes in the biochemical processes in some plant cells.
I hope you are now asking yourself two questions:
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How is it that plants continuously monitor and respond to their ever-changing light environment?
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How can we leverage different light environments at different times in the cannabis plant’s life cycle to improve yield and/or product quality without adversely impacting other cannabis traits that determine cannabis crop value?
The answer to the first question is photoperception via three, and perhaps four, classes of proteinaceous plant photoreceptors, which appear to exist in all plant cells. Yes, root cells too. This is quite different from photoperception in animals. Generally speaking, animals (including humans) have a localized photoperception system, with their photoreceptors localized to an ocular system, i.e. eyes, which are a direct extension of the animal brain. Plant photoperception is very different. Instead of a localized vision system like animals, plants have a completely decentralized system of photoperception. In other words, virtually every cell in a plant can “see” and all of these plant cells monitor and respond to changes in their incident light in real time.
Three classes of plant photoreceptors have been well-documented in the scientific literature, and they allow plants to continually monitor changes in red/far-red light, blue light, and UV light (tangentially, humans are completely unable to see UV light). A possible fourth class of green-light photoreceptors might also exist in plants; it has become increasingly clear that plants have some green-light responses. That said, the protein photoreceptors - if they exist at all - and the gene/genes that encode these proposed green-light receptors remain poorly understood.
The purpose of this post was to set the stage for the thread. Mostly, it contains what I refer to as background material for this topic. Future posts will be shorter… much shorter.
Next up: The phytochrome photoreceptors, which plants use to detect changes in red and far-red light.
Why start with the phytochrome photoreceptors? Because plant phytochromes have long been known to control seasonal flowering (aka photoperiodic flowering). In addition, photoperception by plant phytochromes is known to be a key determinant of resource allocation in plants and resource allocation in plants is a key factor in driving higher yields in all crops (including cannabis).