Pit (botany)

As pits thin spots or recesses are referred to in the secondary wall of plant cells in plant anatomy, which serve the mass transfer between adjacent cells. The totality of the dots and their arrangement is called stippling.

Function

In plant cells with primary walls unlignified a substance exchange between the cells, to a particle size of 5 nm is possible. As the lignification of the cell walls, which improves their strength properties, the permeability is greatly reduced. To ensure a lateral mass transfer to the neighboring cell dots are used where it is required, is applied.

When pressure change in the cell lumen, it may degenerate into a Tüpfelverschluss.

Construction

A dot consists of a Tüpfelhöhle and a Tüpfelmembran ( closing skin). In most cases, two pits are opposite, so that a Tüpfelpaar arises. There is only the Tüpfelschließhaut consisting of the middle lamella and the primary wall thin layers between two adjacent cells. It limits the Tüpfelhöhle toward the neighboring cell while the cell lumen towards the cave is open. Depending on the design of Tüpfelhöhle three types of wells can be distinguished: bordered pits, semi- bordered pits and simple pits.

Bordered pits

Bordered pits, that is, both sides bordered pits occur between dead water-conducting and firming cells ( tracheids, tracheae ). In contrast to the simple pit the secondary wall of the middle class ( middle lamella primary wall ) stands out in the bordered pits and vaulted them as edge bead. Thus, the Tüpfelkanal be flared to a Tüpfelkammer whose round is referred to slit-like opening as Porus in the cell lumen. From the lumen of view, the curvature of the edge bead around the pore is emerging as a yard.

The Tüpfelmembran is thickened at the bordered pits of the Pinaceae in the middle of a circular torus (Latin, upholstery ). The edge of the torus is fringed. The fringes graduate into threads that form a mesh-like Margo (Latin, edge ), which is permeable to liquids.

Bordered pits in the xylem of angiosperms have a slit-like opening and no torus on the closing skin. In some dicots, there are sculptured bordered pits in which the cavity of the Tüpfels is studded with wart-like formations. In the walls of the libriform fibers are oblique columnar pits, where the columns of a Tüpfelpaares are rotated relative to each other.

One side bordered pits

Limits and parenchyma tracheids / drums with each other, occur on one side of bordered pits. For them, the Tüpfelhohlraum on the part of parenchymal cell consists of a channel on the opposite side it has the form of a Tüpfelkammer. As with the simple wells also as missing both the central thickened portion ( torus ) and the porous nature of the membrane peripheral regions ( Margo ). The number and shape of the one side minutely bordered pits in the intersection areas is of great importance in the determination of softwoods. With regard to the shape of Pori on the part of Längstracheiden be distinguished:

Window-: large-scale, almost the entire cross-field surface filling Pori
Pinoide pits: oval to roundish Pori with reduced edge beads
Piceoide pits: slotted, the Hofumriss overlapping Pori
Cupressoide pits: lenticular, the Hofumriss non-overlapping Pori
Taxodiode pits: oval to rounded, the Hofumriss non-overlapping Pori.

Simple pits

By simple pits parenchymal cells communicate with each other. The Tüpfelhohlraum is formed in these wells as a channel. By Tüpfelmembran run through plasmodesmata as designated cytoplasmic strands that serve the mass transfer. The places where pits occur later are seen in the primary wall as thin spots. They are traversed by plasmodesmata tight and are called primary Tüpfelfeld.

One-sided pits

Unilateral dots or blind dots have no Komplementärtüpfel in the adjacent cell. They lead to intercellular spaces or end at the middle class. Probably it is for them to incompletely formed pits without any function.

History

The first pictures of pits found in 1675 Malpighi and Leeuwenhoek in 1722. Lange were they regarded as warts or holes in the wall and called pores. Ludolph Christian Treviranus spoke of stippled or dotted vessels. Hugo von Mohl in 1828 recognized that this is not a pore, but thin spots to wells.