Polarity cell wall growth

Fig. 1. Model of polar cell wall expansion in filamentous fungi. Vesicles with cell wall components and proteins are transported to the tip. An actin-myosin-based system is important in establishing polar growth through transport of the micro-vesicles to the cell surface. The cell wall at the apex is plastic but it hardens as the matrix of glucans and chitin crystallizes...

More detailed matrix of proposed positive correlations (indicated by ) between (a) the effect of changes in CMT numbers along periclinal cell walls in shoot tissue in relation to growth rate, and (b) changes in CMT orientation in relation to cell or organ growth polarity... 

A hypothesis on the nature and aetion of this protein ean be made as an extension of the hypothesis or provisional model of Green (1963) based upon his studies of polarization in the cell of Nitella. He postulates that polarized growth places a maximum strain upon the cell in the direction of polarization. The cytoplasm adjacent to the cell wall is believed to contain long elements, presumably fibrous structural proteins, which are flow-oriented by the distortions of elongation itself. Since their orientation is disturbed by the action of colchicine, they are believed to be related to or even identical with the spindle fiber protein. 

In resting neutrophils it is estimated that there are about 11-23 microtubules per cell, with a diameter of approximately 25 nm and a wall width of 5 nm. They are long, tubular structures made by the helical formation of tubulin molecules, which are either a- or /3-subunits, each with a relative molecular mass of 55 kDa (Fig. 4.9). Each subunit is present in equimolar amounts in a tubulin molecule, and these subunits exist as dimers of one a- and one /3-subunit. Because microtubules are polar, growth of the fibre is biased towards one end, termed the plus end. A number of microtubule-associated proteins (MAPs) affect the dynamic shape of the microtubule, and in the resting neutrophil about 35-40% of the tubulin pool is assembled, whilst the remainder can be assembled very rapidly after cell stimulation. 

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