Even Aristotle got it wrong. He thought plant roots convert soil into wood and grow that way. Plants resemble bizarre upside down animals. Their superior mouth parts (roots) are located in an inferior position. According to Aristotle, plants are ‘lower’ level living things. They are the first basic steps in procession of life from the inanimate to the animate (animals). Plants don’t move and are without ‘sensory soul’ but still have ‘souls’. Plants do not have any excrement, do not have real sexes, do not impregnate.
Many of these misconceptions about plants are still with us. We think of them as rather passive landscape elements. This is obviously not true. Plants exhibit quite a curious suit of adaptations such as the crown shyness observed in certain forest communities or ability to count as documented in Venus fly trap. Using secondary metabolites and secretions through their flowers and extrafloral nectaries they can manipulate the behavior of animals interacting with them. Perhaps the first comprehensive treatise that set the stage for understanding of plant responses is Charles Darwin’s book on plant movements.
In this documentary by the California Academy of Science, researchers at ETH Zurich, the Swiss Federal Institute of Technology, demonstrate that plant perception can be quite elaborate. Some parasitic plants such as the dodder (Cuscuta) from the morning glory family (Convolvulaceae) can search for other plants nearby, and can use this information to either grow toward or away from their neighbors. Whole genome sequences of two cuscuta species have been published in 2018.
The second plant in the documentary is the purple devil (Solanum atropurpureum) from the nightshade family (Solanaceae) which employs a two tiered response against the herbivores. For large caterpillars the ultra long spines are effective as constitutive (always on) defense. These caterpillars sooner or later will spear themselves to death while feeding. For small caterpillars however the plant uses a facultative (induceable) chemical defense that switches on when it senses that it gets munched.
Ever since plants evolved to split water as a part of their photosynthetic light reactions life and physical environment on our planet became a very different place with its oxygen enriched atmosphere. There’s clear evidence that colonization of the land was first achieved by plants around 700 million years ago. Starting from the Devonian period, evolution of vascularization lead to efficient root systems and robust tall crowns and evolution of river systems through stabilized soil and evapotranspiration dominated habitats such as the rain forests.
The two plants highlighted in this short documentary provide fascinating examples for complex defenses that have evolved as a co-evolutionary arms race between the herbivores and their plant prey. The plant adaptations will most certainly continue to amaze us as we study and learn more about them.
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