#skotomorphogenesis

[whats-in-a-sentence]

PIFs promote etiolated development in the dark (skotomorphogenesis) primarily by serving as transcriptional activators of dark-induced genes (Figure 16.13A), and also by repressing some light-induced genes (Figure 16.13B).

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.

[thomaspoems]

Skotomorphogenesis (January 8th, 2021)

Every time it snows I cry

because I remember the Magnolia

that lost its flowers waiting for another year of light

The white like a melody or picture

or a freezing maternal hand

strips the warmth from my body

The floating corpses in the sky

let down their frozen hair

in bleached braids that disappear in my palms

The Evergreen tells me why I can’t seem to leave here

as I touch its etiolated skin forgotten underneath the

sheath of winter

Snow was a mirror I saw too much in

and its brightness vanished in the dark like mine did

[onelittleglobetrotter-blog]

THE WORLD OF PLANTS is a very different world...

Can plants see? This is the first question I would like to address. To many of us, plants are boring little green immobile organisms that do not do much. But we know that without plants, there would be any life on earth today as we know. We know that they take up CO2 and convert it into O2, but so what, you’d say. 

You see, plants actually CAN “see” in a molecular sense. But they haven’t evolved vision the way we did. 

Learning about the molecular basis of the responses of plants is the key. By identifying specific genes involved in a particular process, we can access the instruction manual of how a particular process works. By working with DNA sequences, we can even obtain information of how a particular process evolved. 

Light is the most important environmental cue for plants. Plants are able to sense the direction, intensity and colour of light and thus use light as the source of what the environment they live in is like. Light is important for plants because it is necessary component for the process of photosynthesis, however, it is also the most important environmental cue that can help plants maintain almost all their physiological needs. The information from light is used to learn about their environment. 

So at WHAT LEVEL can plants sense the light? Is it an entire plant that must see the light, an organ? Or maybe a single cell? The answer is all of the above. Even a single cell of a plant can respond to light by expressing certain sets of genes. The point is that, the entire plant does not have to ‘see’ the light for gene expression to be altered. 

The responses of plants to light can thus occur at all levels but are also very complex. A single cell can respond by altering its gene expression and chloroplast development. An organ can respond by either inhibiting its growth (hypocotyl/stem) or leaf development. And the organism as a whole can respond by altering its development, such as floral development. 

NO LIGHT? Etiolation is the process in which a plant grows in the dark. The plant will only develop a chloroplast when it is sensible to do so. It has only a limited amount of reserves so its priority is to grow in height to reach the source of light. 

But as soon as it sees the light, de-etiolation will take place and the plant will switch from skotomorphogenesis (growing in the dark) to a new developmental process, photomorphogenesis, in which it will begin developing the chloroplast and the cotyledons can become the first leaf of the plant upon germination. Thus upon sensing the light, the plant will stop growing in height and begin transforming its etioplasts and plastids into functioning chloroplasts. The genes involved in this process are actually light regulated and are FROM TWO DIFFERENT GENOMES! This means two different genomes, the chloroplast genome and its actual genome must be activated as soon as light is available to the plant. 

Growth strategies of the plant are also regulated by the availability of light. A plant can remain in the vegetative state using the cues from light. The transition from vegetative state to inflorescence to reproductive state (flowering) can be initiated by sensing the length of the days (as days become longer in the spring) and warmer temperature, however, this is different for different species and some species will enter the reproductive state when days become shorter. 

SHADE AVOIDANCE, right so you got out of the soil and you’re all ready to sense the light but shit, you’re under a huge oak tree. What now? Plants can sense the ratio of different wavelengths and thus be aware if they are other competing species for light around them or if they are alone in an open field. They can do this by sensing the ratio of red light to far-red. If the ratio is large, the plant has access to lots of red light and thus can stop growing in height to absorb what it needs. However, if the ratio is low, this must mean they are other species ‘neighbours’ around the plant so it should probably continue to grow in height to avoid being in shade. Experiments show that even when there are no neigbours, the plant might continue to grow in height if we apply the ratio of red: far-red low, tricking the plant into growing, as the wavelength of light availability is lower. 

NEXT: the receptors responsible for sensing the light.   

[whats-in-a-sentence]

Hook formation and maintenance in the dark result from ethylene-induced asymmetric growth (Figure 18.27A). (...) During the seedling response to ethylene, the transverse pattern of microtubule alignment in the cells of the hypocotyl is disrupted, and the microtubules switch over to a longitudinal orientation (Figure 18.27B).

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.

[whats-in-a-sentence]

det2 loss-of-function mutants have reduced levels of brassinosteroids, resulting in a de-etiolated appearance of the seedling even when grown in the dark (Figure 18.26).

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.

[whats-in-a-sentence]

In contrast, light-grown seedlings have shorter, thicker hypocotyls, open cotyledons, and expanded leaves with photosynthetically active chloroplasts (Figure 18.25).

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.