What is Endosperm Haustoria?
Endosperm haustoria refers to the elongated structures arising that penetrate the tissue of the seed and placenta. They are nutritive in function and help the endosperm absorb and metabolize nutrition. Such haustorium may arise from the chalazal end or micropylar end of the endosperm. Sometimes, haustoria may arise from both ends.
Endosperm with Chalazal Haustorium
The haustorium arises from the chalazal end. It arises as a worm-like structure that will coil. The elongating haustorium will be multinucleated in the initial stages but will develop a cell wall to form a multicellular structure.
- It is commonly seen in Iodinia rhombifolia, Macadamia temifolia, Magnolia obovata, etc.
- Echinocystis lobaa belonging to the Cucurbitaceae family has the longest endosperm
- Lomalia, has numerous funger-like projections from the cellular endosperm, in addition to its chalaza1 haustorium.
- In Crotolaria and Gravillea, the upper region of the endosperm develops a wall while the chalazal region remains free nucelate which will elongate to form the haustorium.
Endosperm with Micropylar Haustorium
In this type, the primary endosperm nucleus divides to form an upper larger and lower smaller chamber. The haustorium arises from the terminal region of the upper chamber. It is seen in Impatiens, Nemophila, and Hydrocera.
Endosperm with Chalazal and Micropylar Haustoria
Endosperm haurotia arises from both chalazal and micropylar ends in plants such as Nemophila, Melampynun, etc.
- In Nemophila, both ends develop haustorium and the one from the chalazal end develops lateral branches that connect to the placenta.
- In Melampyrum lineare, the chalazal haustorium is short and reaches the nucellum. The haustorium from the micropylar end is tubular and single-celled which will enlarge, and each integument tissue.
- The Chalazal haustorium of Klugia notaniana grows terminally and laterally to reach the sub-epidermal cells of the integument. The micropylar haustorium becomes functional only after the chalazal haustorium starts declining its activity.
Endosperm with Lateral Haustoria
The helobial endosperm in Monochoria develops a lateral haustorium developed from the free nuclei from the micropylar chamber. After, this will fuse with the enlarged body of the endosperm to form a compact mass endosperm.
Endosperm with Secondary Haustoria
Centranthera develops ephemeral haustoria from the micropylar and chalazal ends. Some endospermic cells near the micropyle form tubular outgrowths extending into the nucellus tissue to serve as a haustorium. This is called a secondary haustorium.
Haustoria Behavior of Embryo Sac
Haustoria development from the embryo sac is essential for those plants that do not produce an endosperm. The entire surface of the embryo sac is reported to be absorptive and can eventually absorb the nucellus and integument that surrounds it.
In some plants, the embryo sac shows pronounced growth from both micropylar and chalazal ends and completely absorbs the nucellar tissue. In such cases, the embryo sac may come in contact with the placenta to absorb nutrition.
Members of Loranthaceae develop elongated structures on both ends of their embryo sacs but the micropylar end may have slightly more vigorous growth in comparison.
Haustoria Formation
The zygotic cell of eukaryotes divides into a basal and an apical cell. The basal cell gives rise to the suspensor and the embryo is developed from the apical cell. While the basal cell undergoes multiple transverse divisions to form the long suspensor that pushes the developing embryo deeper into the ovule tissue.
The main function of the suspensor is to help the embryo go deeper into the ovular tissue and reach the nutritive tissue. Later it will disintegrate as the embryo matures.
In some plants, the suspensor gets modified into haustoria. Such modified structures are common in the members of Leguminosae. However, in Mimosae, the haustorium is absent so the embryo develops into a spherical structure without any major changes. There are several modifications seen in angiosperms.
- In Lupinus luteus, the suspensor is uniseriate and binucleate cells.
- In Cytisus laburnum, the suspensor cells are clustered into a bunch as seen in grapes.
- A long structure of 7 cells forms the suspensor in Omnis fruticosa.
At the same time, members of Orchidaceae and Podostemonaceae lack endosperm or have poorly developed endosperm. Here, the embryo develops suspensor haustoria. Such haustoria will be unicellular as in Cypripedium or uniseriate filament as in Habenaria. These uniseriate filaments may develop branches and enter the placenta to absorb nutrition.
References
- Sukumaran O R. Pre-Degree Botany. Murali Publications.
- Abraham P C. Anatomy, Embryology & Microtechnique. 1999. St. Mary’s Books & Publications.
- Paper – V – Anatomy and Embryology Unit – 4
- https://egyankosh.ac.in/bitstream/123456789/16388/1/Unit-4.pdf
