Tropisms:
– Early experiments on phototropism using coleoptiles showed that plant cells on the darker side elongate more.
– Charles Darwin and his son Francis discovered that coleoptiles bend towards light when their tips are exposed.
– The Cholodny-Went model explains the phototropic and gravitropic properties of emerging shoots of monocotyledons.
– Auxin, a plant growth hormone, is synthesized in the coleoptile tip and causes asymmetric growth in response to light or gravity.
– Coleoptiles exhibit strong geotropic reaction, always growing upward and correcting direction after reorientation.
Physiology:
– Coleoptile acts as a hollow organ with stiff walls, surrounding the young plantlet and the primary source of the gravitropic response.
– It rapidly senesces after the shoot emerges, similar to the creation of aerenchyma in other parts of the plant.
– The coleoptile emerges yellowish-white from an imbibed seed before developing chlorophyll the next day.
– Changes induced by white light increase water potential in epidermal cells and result in coleoptile elongation.
– Adventitious roots from the coleoptile node quickly surpass the seminal root in volume and thickness.
Anaerobic germination:
– In waterlogged conditions, some plants like rice can undergo anaerobic germination.
– The coleoptile acts as a snorkel, providing the seed access to oxygen.
– Anaerobic germination allows the seed to survive in low-oxygen environments.
– This adaptation is crucial for plant survival in flooded areas.
– The coleoptile plays a vital role in ensuring oxygen supply to the germinating seed.
References:
– Coleoptiles are discussed in ScienceDirect Topics.
– Charles Darwin’s work on coleoptiles is mentioned in his book “The Power of Movement in Plants.”
– Studies have shown the importance of basipetal auxin transport for gravitropism in roots.
– Research has highlighted the role of coleoptiles as gravi-guiding systems in germinating grass seedlings.
– Various studies have explored the biophysical basis of cell elongation and organ maturation in coleoptiles.
External links:
– Wikimedia Commons has media related to Coleoptiles.
– Additional information can be found at the provided Wikipedia link.
– The topic falls under the category of plant anatomy.
– The article includes a short description and is distinct from Wikidata.
– Commons link is locally defined for easy access.
Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing stem in seedlings and eventually, allows the first leaf to emerge. Coleoptiles have two vascular bundles, one on either side. Unlike the flag leaves rolled up within, the pre-emergent coleoptile does not accumulate significant protochlorophyll or carotenoids, and so it is generally very pale. Some preemergent coleoptiles do, however, accumulate purple anthocyanin pigments.
Coleoptiles consist of very similar cells that are all specialised to fast stretch growth. They do not divide, but increase in size as they accumulate more water. Coleoptiles also have water vessels (frequently two) along the axis to provide a water supply.
When a coleoptile reaches the surface, it stops growing and the flag leaves penetrate its top, continuing to grow along. The wheat coleoptile is most developed in the third day of the germination (if in the darkness).