Organismal Capillary

An organismal capillary (OC) will be defined as a capillary having the following two properties  

The internal surface of the capillary bears excess negative fixed charges when in contact with an electrolyte at neutral pH. 

The internal surface of the OC may be conceived, to get a geometrical picture, as covered by a few layers of structured water while the polar residues of the phospholipids protrude further out, in the bulk phase of the 

FIGURE 1. A basic transport unit that has been successively constructed beginning with the bathing media, Bq and and a bicellular symplast with a plasmodesma. See text for further details. 

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The results obtained in the last two sections will now be discussed and summarized. In Section 2.4 a question was raised whether it is possible to have a mechanism by which a pmf between two cells can be used to drive nutrients towards the cell which extrudes H actively. Using the concept of proticity we have arrived at the conclusion that it is possible to achieve this if the path is an organismal capillary. While the process of injection and ejection of H in relation to the cells of plant tissues will be discussed in Section 5, the events within the OC have been worked out in this section. It has been shown, that the flow of proticity in one direction induces a flux of at the internal surface of the OC in the opposite direction. In an ideal case, which corresponds to a high surface conductance of the layer, the anions on the two sides of the OC stay where they are, merely exchanging the counterions, and K, at the sides where the and... 

In the basic transport unit of Fig. 1, Mq and Mi were required to be permeable to and water and to enable H" to enter them and move along their internal surfaces by the specific transport mechanism described in Section 3.1. In Section 3.5, the apoplasm between Mq and Mq was also assumed to show proton conduction. Thus two xylem conduits with their walls in contact with each other constitute, together with the pits between them as the organismal capillaries, a variation of the basic transport unit. The wall phase without the pits may be considered as having an appreciably lower conductance for H", K", and water, while the pits form... 

The transport system of the sieve tubes is also a multiplet of generalized transport units (pTU) with the sieve plate pores as organismal capillaries. Though the sieve tubes are thin as such, the dependence of the hydraulic conductivity, on the fourth power of the radius, makes the distinction between them and the pores essential. The effects of occlusion on gw are difficult to calculate but the general features of the sieve tube system permit one to surmise that it has been made to cope with adverse hydrostatic gradients of variable but often large magnitudes. 

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