Coleoptile and coleorhiza are the layers of the sheath emerging from monocot sheets. They occur in the seed before the germination of the seed. Coleorhiza is the sheath-like structure which connects coleoptile and primary roots. Coleorhiza stays in the soil but coleoptile emerges from the soil. Before discussing the difference between coleoptile and coleorhiza, let us discuss each term individually.
Coleoptile is the protective sheath-like structure which covers the pointed shoot in monocotyledons; this is the main function of Coleoptile. Examples for the monocotyledons are grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. Coleoptile has two vascular bundles one on each side.
Coleoptile lacks chlorophyll, so it is generally pale yellow in colour and some of them have anthocyanin pigment which imparts purple colour. Coleoptile consists of similar cells which are specialized to fast stretch growth. These cells don't divide but they increase their size by accumulating more water. Water vessels in the coleoptile help them to provide water supply.
Once the coleoptile reaches the surface it stops growing. In a later stage, the flag leaves penetrate the top layer of coleoptile and continue to grow along. Coleoptile consists of the cells which are very similar and specialized to fast stretch growth.
Coleoptile is a hollow organ having stiff walls which surround the young plantlet. The first coleoptile emerges, appearing yellowish white from the seed before developing into chlorophyll on the next day. Coleoptile grows and produces chlorophyll only for the first day, then it degrades and later due to water potential it grows. Coleoptile length is divided into an irreversible fraction, and a reversible fraction or elastic shrinking. White light increases the water potential in the epidermal cell and decreases the osmotic pressure.
Coleoptile was used to conduct early experiments on phototropism. It showed that plants grow towards light because plants on the darker side elongate more compared to the lighter side. Coleoptiles bend towards light only when their tips are exposed by Charles Darwin and his son Francis.
Coleorhiza is also known as Coleorhiza and root sheath and it is the layer of tissue (sheath-like structure) which surrounds the root in the seed. This is the main function of Coleorhiza which is seen in monocotyledons. Coleorhiza is the first thing which grows out of the seed during germination. Primarily it grows through cell elongation.
Some of the important differences of coleoptile and coleorhiza are discussed below.
After going through coleoptile and coleorhiza functions, definitions individually and then discussing the difference between them. We can conclude that the main difference is between the type of growth and occurrence.
1. Why Are Coleoptiles and Coleorhiza Absent in Dicots?
Answer. Coleoptile and coleorhiza are necessary for monocotyledons to protect the plumule and radicle of the root respectively. Coleoptile protects shoot apex and leaves enclosing them when they are below the soil and also helps in emerging out of the soil. Coleorhiza protects the root cap and radical till they come out of the seed.
2. How Cotyledons are Formed?
Answer. Cotyledons are formed during the process called embryogenesis. During this process, even root and shoot meristems are formed so they are present in seed prior to the germination.
There are two types of cotyledons one is monocotyledons( having one cotyledon) and the other is dicotyledons( having one or more cotyledons).
3. What is the Meaning of Radicle?
Answer. The first part of the seed to come out during the process of germination is called the radicle. Radicle is the embryonic root of the plants which grows down the soil.
4. What are the Primary Parts of the Seed?
Answer. Seed mainly consists of three main parts: embryo, endosperm and seed coat. The embryo is the young multicellular organisms, Endosperm is the source of stored food and the seed coat consists of one or more protective layers which protect the seed.