Can plants survive without photosynthesis?
While this might be debatable, I believe that light is the ‘heart’ of a vertical farm and will be the key tool to advance modern crop production. Vertical farms rely on artificial light to provide the energy that plants need to grow, and without it, the plants would not survive. But plants do not only use light as their primary source of energy, light also influences how a plant grows and develops. One of the key benefits of vertical farming is the ability to control the quality, spectrum and intensity of light. By changing light, we can influence, and possibly fully control, the development of plants in an indoor growth farm. This means we can e.g. change the shape or architecture of a plant, control when it flowers and when it starts producing fruit or vegetables. We could even influence the taste and quality of fruits and vegetable. Plants and light are inseparable. Or are they?
Plants are masters of adaption. As sessile organisms, all kinds of unique adaption strategies have evolved among the plant kingdom. Today, we talk about a special group of plants. There are plants that have evolved unique mechanisms to obtain energy and nutrients without the need for sunlight. This group of plants does not (you probably guessed it…) photosynthesize. These are called heterotrophic plants. In fact, there are more than 3,000 plant species that are non-photosynthetic. These plants gain their energy by, for example, parasitizing other plants (such as climbing vines or lianas) or by forming a symbiosis with fungi to indirectly access nutrients from other plants. The latter are called mycoheterotrophs. Plants of the genus Monotropa such as the ghost plant (or Indian pipe plant, M. uniflora) or pinesap (M. hypopytis) are mycoheterotrophic plants, which are exploiting fungi to receive nutrients from nearby trees.
As you can see: this extreme change in lifestyle caused various changes in plants of the genus Monotropa. These plants are very pale, which is why M. uniflora is also called the ghost plant. This is because they lack chlorophyll, the pigment that allows plants to absorb light and convert it into energy through photosynthesis. As these plants don’t photosynthesize, they don’t need chlorophyll. Also, leaves are rarely seen. As a result, it does not produce its own food and instead relies on a symbiotic relationship with fungi in the soil. The fungi extract nutrients from the surrounding plants and then pass them on to M. uniflora.
Let’s have a look how these plants gain their nutrition. As stated before: the relationship between M. uniflora and fungi is known as myco-heterotrophy, where the plant benefits from the fungus's ability to extract nutrients from other plants. The fungus forms a mutualistic relationship with the roots of nearby trees, absorbing sugars and other nutrients from the tree's roots. The fungus then passes some of these nutrients on to M. uniflora, which it can use for its own growth and reproduction. Despite its unusual appearance and lack of photosynthesis, M. uniflora plays an important role in the ecosystem. Its symbiotic relationship with fungi helps to enrich the soil, providing vital nutrients for other plants and animals in the area. But the ghost plant is also beneficial for humans. The plants are not toxic or poisonous, but have a bitter taste and are not considered an attractive or desirable food. However, the plant has been used for medicinal purposes by some indigenous cultures, but its safety and efficacy for these purposes have not been scientifically established.
And where can you find these fascinating plants? Monotropa uniflora prefers to grow on moist and shaded forests and can be found in Asia, North and South America. However, you don’t need to travel this far to admire the Indian ghost pipe in nature. Monotropa hypopitys (‘pinesap’) is a close relative growing in the temperate regions of the Northern Hemisphere and can be found in Europe. So better don't eat it, if you find it in a forest ;)
Have you been wondering if plants that do not photosynthesize still have photoreceptors?
Briefly: what are photoreceptors?
Plant photoreceptors are specialized proteins that are sensitive to light and play a key role in regulating various aspects of plant growth and development. Photoreceptors are responsible for detecting changes in light intensity and wavelength, and passing this information to other parts of the plant. Light can influence the activity of photoreceptors, leading to changes in gene expression, the growth of certain tissues, and the timing of various metabolic processes. This ability to detect and respond to light is a critical aspect of the adaptability of plants, and it allows them to optimize their growth and reproduction in response to changes in their environment.
Interestingly, some plants that do not photosynthesize have photoreceptors. However, the presence of photoreceptors does not necessarily mean that a plant can photosynthesize. In the case of non-photosynthetic plants (such as our beloved M. uniflora) photoreceptors may be involved in regulating aspects of their growth and reproduction, such as the timing of flowering or the direction of shoot growth.
While the exact function of photoreceptors in non-photosynthetic plants is not yet fully understood, it is clear that light still plays an important role in their lives. Light can influence the growth and development of non-photosynthetic plants (similarly as in photosynthetic plants) by affecting the activity of their photoreceptors and regulating various metabolic processes. For example, light may stimulate the growth of certain tissues or alter the expression of specific genes, influencing the overall growth and development of the plant.
Monotropa uniflora is indeed a fascinating plant that demonstrates the incredible adaptability and diversity of plants. Despite its unusual appearance and lack of chlorophyll, this plant is able to survive and thrive by forming a symbiotic relationship with fungi, demonstrating the importance of symbiotic relationships in the natural world.
Schelkunov, M. I., Penin, A. A., & Logacheva, M. D. (2018). RNA-seq highlights parallel and contrasting patterns in the evolution of the nuclear genome of fully mycoheterotrophic plants. BMC genomics, 19(1), 1-16.