Keywords: plants, Arabidopsis, cryptochromes, phototropins, redundancy, phototropism, photosynthesis, gravitropism, communication
While some people may talk to their plants, we don’t hear the plants talking back. Plants lack a brain and vocal cords; so, they cannot speak. They have no beliefs or thoughts. The Bible records that God created plants according to their kinds.1 Yet, in a biblical context, plants are not considered to be alive in the same sense as animals or people.2 Instead, plants were created before them to provide food for life on earth.3
Plants were created with the ability to make seeds and reproduce.4 This is one reason why plants are classified as alive in the modern biological sense. The ability to reproduce ensures a constant food source for animals and people. Although plants cannot speak, they were created to be able to respond to their environment, and, in a sense, communicate.
Plants require sunlight to grow and produce food. They also need moisture and other nutrients that are present in soil. Why do roots grow down into the soil? Why do stems and leaves naturally grow towards the sunlight? What cause them to make chlorophyll so they turn green? What influences when plants flower? Detailed studies of a small flowering plant, Arabidopsis thaliana, are beginning to shed some light on the subject.
“Seeing” the Light
Arabidopsis produces several different types of molecules that can sense light. One type of molecule, phytochromes, senses light around the red end of the spectrum.5 Other types of molecules, cryptochromes and phototropins, can detect light in the blue end of the spectrum.6 Five phytochromes (phyA through phyE), two cryptochromes (cry1 and cry2), and two phototropins (phot1 and phot2) have been identified in this plant.7
It is interesting that Arabidopsis has several types of molecules that detect light and several of each type of molecule. There is some redundancy in this system. For example, although each of the five different phytochromes has some unique roles,8 they also have overlapping roles. This overlap, or redundancy, allows the plant to be able to develop even if the gene for one of the phytochromes becomes damaged. Redundancy provides a built in safety mechanism by allowing a second system to take over in the event the first one fails. This strategy is often used by human engineers to make their products more fail-safe.
Responding to the Light
Plants need to be able to do more than detect light; they must be able to respond to it. After a phytochrome molecule is activated by light, it travels to the nucleus of the cell to send the message along. In the nucleus it interacts with other molecules which adjust the outputs of a variety of genes.9 This allows the plant to respond to the light in an appropriate way.
Plants need to be able to do more than detect light; they must be able to respond to it.
Growing plants can bend toward the light, a phenomenon known as phototropism. For this response, plants use information from light sensing molecules to adjust the amount of various growth factors. Auxin is a plant hormone that stimulates cell growth. Other molecules tend to inhibit cell growth. By adjusting the relative amounts of these substances, the dark side of the plant can grow longer, bending the plant towards the light.10
Plants respond to light throughout their life cycle. Seed germination can be affected by light as well as temperature. Light is necessary for seedlings to become established. It slows hypocotyl elongation, expands cotyledons, and begins chlorophyll production.11 Light is necessary for photosynthesis and influences the location of chloroplasts, stomatal opening, and leaf positioning to keep this process efficient.12
For efficient growth and reproduction, the light signaling pathway must be integrated with other signaling cascades. For example, plants have an internal circadian clock, which is made up of multiple interconnected feedback loops. These two pathways interconnect so plants can coordinate photosynthesis and metabolism with day/night cycles. The time of flowering is influenced by changes in day length and temperature. This requires proper interaction between light signaling, temperature signaling, and circadian clock pathways.13 This complex internal communication makes use of logic and operational features much like human programmers use in computers.
Sending Roots down Deep
Gravity is the primary signal used for roots to grow down into the soil. This growth response to gravity is called gravitropism. New discoveries highlight the “complexity of a highly redundant gravity-signalling process in roots.”14 Other environmental factors, including moisture15 and light, also affect root growth. It has been shown that white or blue light results in negative phototropism in roots.16 In other words, roots tend to grow away from white or blue light. Interestingly, red light results in positive phototropism in roots.
While only a portion of these complex signaling pathways are understood, it is readily apparent that the programming involved is astounding. The use of complex logical circuits, redundancy, and other design features clearly implies that an amazing Programmer created plants. Yet the communication doesn’t end within the plant. Plants are also able to use information to affect the world around them.
Communication with Microbes
Bacteria and other microbes inhabit the world around (and in) us. In order for plants to grow well and defend against disease, they must be able to interact with these microbes appropriately. Some microbes, such as symbiotic bacteria and fungi, are helpful to the plant. The plant is designed to establish relationships with these types of microbes. Other microbes can be harmful. Plants are designed to defend themselves against these pathogenic microbes.
Ironically, in plants, the same group of compounds that is used to identify symbiotic microbes so healthy relationships can be established is also used to identify pathogens so the plant can defend itself. These compounds, lectins, are proteins that are able to bind to carbohydrates. The portion of the molecule involved in binding is highly variable, much like immunoglobins in our immune system. This allows for specific recognition so the right molecule can be responded to in the right way. Scientists are still working to discover details on how plants determine which response to use once a microbe has been identified.17
A World Dependant on Proper Relationships
Jesus used plants to teach his disciples on numerous occasions.18 There are still many things we can learn from plants today. The incredible design of plants inspires a sense of awe for the God who is Designer of designers and the Programmer of programmers.19 We are able to catch a glimpse of God’s abundant provision and foresight as we begin to understand the complex communication necessary for plants to grow and reproduce. We also see the importance of healthy relationships.
The Bible teaches that God is triune. That is, while there is only one God, He has always existed as three distinct persons: Father, Son, and Holy Spirit. All three persons exist in harmonious relationship with each other. This relational aspect of God’s nature is reflected in the world He created. Microbes, plants, animals, and humans all live in relationship with each other. Originally, all relationships were very good.20 However, when humans sinned, relationships were severely damaged. This included our relationship with God, with each other, and with the world around us.21
In the Bible, God has communicated with us on how our broken relationships can be restored. God the Son came as Christ to reconcile us to God by paying the penalty for our sins through His death.22 We have instructions on how to maintain healthy relationships with each other.23 For those who repent and follow Christ, there will be a new heavens and new earth where we live forever in harmonious relationship with our Maker.24