What is Phytochrome?

Phytochrome is an extremely important plant growth regulator that functions in the red end of the visible light spectrum. While it does not have a role in photosynthesis, phytochrome controls internodal elongation and a plant’s ability to measure day length (photoperiodism). The best understood of the plant-signaling compounds, phytochrome has two active states: phytochrome red (Pr) absorbs light from ~650nm to 670nm, and phytochrome far-red (Pfr) absorbs light at ~705nm to 740nm. Note that the Pfr absorption is outside of the PAR spectrum range.

The ratio between Pr and Pfr, which converts back and forth depending on the light the plant receives, affects the plant’s physical shape including its height. Plants use phytochrome to sense the amount of red and far-red light they are receiving.

Short-day plants such as cannabis/hemp also rely on phytochrome to initiate flowering. Flowering begins when a sufficient quantity of Pfr converts back to the Pr form, a process that requires about 12 hours of uninterrupted darkness. That’s why short-day plants grown outdoors begin to flower when day lengths shorten after the summer solstice, and why indoor growers switch to a 12-hours-on/12-hours-off light cycle for flowering short-day plants.

On the research front, growers have been experimenting with phytochrome to extend “day” length during the flowering phase. Why lengthen the day? So that your plants have more time to turn light into carbohydrates and then use those carbohydrates to grow stronger stems and bigger yields. The concept is to increase yields by keeping the lights on for 13 or 14 hours and then finishing the light cycle with far-red light only for periods ranging from a few seconds to a few minutes. This short period of far-red light jumpstarts the Pfr-to-Pr conversion process, allowing the plants to convert enough Pfr-to-Pr during a shortened night cycle to continue vigorous flowering.

The Role of Phytochrome in Plant Growth

1. Seed Germination: Phytochrome influences seed germination by sensing the quality of light during the early stages of plant growth. Red light (R) promotes germination, while far-red light (FR) inhibits it. This mechanism ensures that seeds only germinate when they are exposed to suitable light conditions, improving the plant's chances of survival.

2. Photomorphogenesis: Phytochrome controls photomorphogenesis, the process by which plants change their growth patterns in response to light. When a plant senses red light, it grows tall and slender with open, elongated stems and large leaves. Conversely, under far-red light, it becomes shorter and stockier with compact growth, which can be advantageous for certain crops.

3. Flowering: Phytochrome also plays a crucial role in the regulation of flowering in plants. It detects the duration of daylight and controls the transition from vegetative growth to reproductive growth. This is especially significant for farmers and horticulturists, as it helps them optimize flowering times for crop production.

4. Shade Avoidance: Plants have evolved a shade avoidance response, where they grow taller and allocate resources to reach for more light when they sense the presence of nearby competing plants. Phytochrome mediates this response by detecting changes in the light quality and quantity.

How does Valoya Innovate?

Valoya Inc. is at the forefront of providing innovative lighting solutions for horticulture and agriculture. Understanding phytochrome and its role in plant growth is instrumental in designing and implementing effective lighting strategies. Here's how Valoya Inc. harnesses the power of phytochrome in its products:

1. Spectrum Tuning: Valoya's lighting solutions offer spectrum tuning capabilities, allowing growers to adjust the light spectrum to match specific growth stages and crop types. This enables precise control over phytochrome-mediated responses, promoting healthy and efficient plant development.

2. Photoperiod Control: Valoya's lighting systems allow growers to manipulate photoperiods by providing the right balance of red and far-red light, ensuring optimal flowering and vegetative growth for different crops.

3. Energy Efficiency: By leveraging phytochrome knowledge, Valoya Inc. designs energy-efficient LED lighting systems that target the exact light wavelengths necessary for plant growth, reducing energy consumption while maximizing yields.