Transport intensity

Van der Weij compared the transport system with a conveyor-belt and used the term capacity (Kapazitdt) to describe the load of a unit length of this belt ( die Kapazitat..., d.h. die Stoffmenge, welche jedes cm des Trans-portbandes enthalten kann, van der Weij 1932, p 482). This expression has led to some confusion in the literature. The term capacity has been used, misleadingly, in the sense of transport intensity or maximum intensity. Since it means length density , the term transport density has been proposed, and this term will be used in this article (Kaldewey 1968 a). 

From Eq. (2) it is evident that the cross-sectional area of the plant part examined may be taken as unity. Transport intensity therefore means mass transfer across the total cross-sectional area. This now is probably the only appropriate unit which auxin transfer of a plant part may be referred to, although evidence is increasing from surgical and autoradiographic studies that the different cell types contribute very differently to the total amount of auxin transported (see Sect. 3.3.6). Thus, the calculation of a specific mass transfer (Canny 1960, p 509, Kaldewey 1967b, p 487), i.e., mass transfer per unit area (e.g., flux mm of the plant part s cross section), may well be misleading since the specific area is not known. However, comparisons of specific fluxes in similar plant parts of different size may give information of their efficiency. 

In early auxin transport studies, the straight line was drawn by eye and the time intercept determined from graphical extrapolation. This subjective method has occasionally led to misinterpretations. For instance, from data thus treated, van der Weij (1932) concluded that the transport velocity remained constant in varying temperatures, and that the observed increase in transport intensity was due to an increase in transport density. However, statistical treat-... 

The transport intensity corresponds to the slope of the straight line, thus... 

DEWEY 1957, 1964), with radioactive lAA and to follow its behavior in the plant, left as intact as possible. The natural auxin source was replaced by a lanolin paste containing lAA (in this case, " C-IAA). The new auxin source sustained natural elongation and growth movements of the stalk (Kaldewey 1957, 1962, 1965b). Seven hours later, the axis of the plant was cut several centimeters below the apex and supplied at the cut end of its base with agar receivers, twice each for 15-min periods. Then, a 5-mm section was excised and stood on fresh agar receivers to allow all the mobile auxin to move out, and the new basal cut surface of the remaining axis was successively supplied with another pair of receivers for 15-min periods. The radioactivity collected in the 15-min receivers and the section receivers, respectively, allowed an estimation of the transport intensity and transport density. It was possible, therefore, to calculate the transport velocity from these quantities [see Eq. (2)]. Further, auxin immobilized within the 5-mm sections could be determined by extraction (see Fig. 3.6). 

Short-term application of auxin to the apical cut surface of coleoptile sections, combined with an estimation of auxin accumulation with time in basal receivers which were replaced at brief intervals, was demonstrated by van der Weij (1932, p442ff) to be a means of calculating transport velocity. He observed that the auxin export rate (i.e., the transport intensity) increased initially to a maximum and then decreased. He assumed that the arrival time of the peak of transport intensity was the period of time needed by the auxin stream to traverse the segment. The velocity thus estimated (8mmh" ) was similar to the values of about 10mmh obtained with the intercept method. When labeled hormones became available, such pulse experiments were refined and modified. The duration of the pulse application could be reduced to 60 s (Shen-Miller 1973 a, b) and the receivers could be changed with great frequency to improve the estimation of the peak. 

Fig. 3.6. Transport and distribution of radioactivity originating from 2- C-IAA, applied to decapitated apices of geoepinastically bent flower stalks of Fritillaria meleagris L. The transport characteristics have been evaluated by the short-term collecting method (see Sect. 3.3.2.2). The transport intensity was calculated from the radioactivity collected in agar receivers applied for two 15-min periods to the basal cut surface of a 5-cm explant, continuously supplied with an auxin paste source. The cut was separated by a mica plate into upper and lower halves or the convex and concave sides of the bent axis. After the second collection period, a 5-mm section was excised and radioactivity similarly collected from the new cut surface, and so forth up to the apex. The excised 5-mm sections were separated in upper and lower halves and placed individually on agar receivers for 1 h, to determine the transport densities. They were then exhaustively extracted with ethanol to give the immobilized fractions. (Mean values of four plants, data from Kaldewey 1968 b)...

Lateral redistribution of auxin in epinastic main and side shoots of Coleus and petioles of different species as postulated by Lyon (1963 a, b, 1965 a, b) would be the equivalent of a supplementary auxin source for the receiving half of the axis and it may cause an increase in the transport intensity in that half However, this is not a suitable explanation in the case of Fritillaria, since regions of increasing transport intensity do not coincide in upper and lower halves, in spite of the fact that overall intensity does increase basipe-tally initially. Thus an alternative explanation for the intensity alterations might be that an exchange may exist between the mobile and immobile auxin fractions, and that this may take place between the cytoplasm and the vacuoles. 

The examples mentioned so far point to considerable flexibility of the auxin transport system. This view is also supported by the observation of oscillations of electric potential moving down Avena coleoptiles after illumination or after the supply of auxin (Newman 1959, 1963), by the report of fluctuations of lAA movement in segments of oat coleoptiles after blue light illumination (Thornton and Thimann 1967), and in individual plant parts, by the demonstration of even more pronounced oscillations of the export rate of radiocarbon from auxin-depleted segments of oat and corn coleoptiles, supplied with labeled lAA (Hertel and Flory 1968). It is further supported by previously mentioned (see Sect. 3.3.3.4) experiments of Shen-Miller (1973a), where rhythmic fluctuations of the lAA transport intensity in intact coleoptiles of oat and corn were observed, moreover the rhythmicity was out of phase between the upper and lower halves of geostimulated coleoptiles (Shen-Miller 1973b, p 169). 

What practical steps can organisations take to improve the transport-intensity of their supply chains ... 

Product design can impact transport-intensity through the physical characteristics of the product, its density, the choice of materials (including packaging materials), the ease of recycling, reuse and end-of-life disposal. 

Clearly different transport modes have different impacts on carbon and other emissions. The design of vehicles and vessels is also increasingly influenced by the need to improve fuel efficiency. There are also arguments for increasing the size of vehicle or the vessel to achieve lower transport intensity per unit. For example, new-generation container ships such as the Emma Maersk. 

Research has highlighted that vehicle capacity is often poorly utilised. It is suggested that empty running because of the lack of return loads means that up to a third of the trucks on the roads of Europe are running empty More use of shared distribution, better vehicle routing and scheduling, and better loading can also dramatically improve transport-intensity. 

If standard, generic products can be shipped in bulk from their point of origin and then assembled, customised or configured for local requirements nearer the point of use, there may be an opportunity to reduce overall transport-intensity. 

A further irncentive to reduce the transport-intensity arises from the continued upward pressure on oii-Pased fuei costs, which wiii oniy intensify as oii reserves become depieted. 

Today s supply chains are more energy intensive than before because they are more transport intensive than they used to be. There are a number of reasons for this including ... 

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