Primary pit field

The plasmodesmata may be aggregated in primary pit fields or in the pit membranes between pit pahs. The plasmodesmata appear as narrow canals (2 pm) lined by a plasma membrane and are traversed by a des-motubule, a tubule of endoplasmic reticulum. The plasmodemata are dynamic altering their dimensions and are functionally diverse. For example, whereas some transport endogenous plant transcription factors, others transport numerous proteins from companion cells to enucleated sieve elements. 

The normal structure of the cell wall is broken by pits. Changes appear already in the growth period of the cell. For instance, early stages of pit formation in softwoods are visible in the primary wall just before the cell reaches its final dimensions (primary pit fields). The microfibril network is loosened and new microfibrils are oriented around these points. The structure in the middle of the circles is tightened and the radially oriented microfibril bundles finally form a netlike membrane, permeable to liquids (margo) (Fig. 1-17). The central, thickened portion of the pit membrane... 

Key N, nucleus NE, nuclear envelope Nu, nucleolus NV, nucleolar vacuole P, plastid V, vacuole Chr, chromatin CW, cell wall PPF, primary pit field. 

High nitrate concentrations can cause methaemoglobinaemia (blue-baby syndrome) in bottle-fed infants. This condition is also associated with the simultaneous presence of bacterial contamination. The primary approach to managing nitrate contamination is prevention, particularly for rural wells, which are the major problem with regard to methaemoglobinaemia. In particular, protection of wells from runoff from fields and siting of manure stores, pit latrines and septic tanks will help to prevent contamination with nitrate and microbial pathogens. 

Field exposure tests (e g. the TAPPI program in pulp bleach washers) and electrochemical current decay tests show pits to propagate more rapidly in JS777. JS700 is therefore the recommended alloy where pitting or crevice corrosion is the primary concern. 

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