Abschlussbericht Projekt: „Verminderung der ... - BLE

tail. Mechanosensitive channels physically connect the extracellular matrix with the cytoskeleton
(Wang et al. 1993). Signal transformation and signal transduction occurs only
when the cytoskeleton is connected to the cell surface (Chen and Ingber 1999). These conditions
are present in turgid cells. Pressure increase within a given unit raise channel opening
of about 10 %, whereas maximal possible elastic changes of cell membranes increase
the channel opening only about with 2% (Garrill et al. 1996). Therefore, the cultivar specific
arrangement of the cytoskeletal components and local distortions in the lipid bilayer
might influence channel opening. The number and the arrangement of the mechanosensitive
channels in the membrane may determine quantitative response of the cell to qualitative
signals (Garrill et al. 1996). The activity of mechanosensitive channels is also regulated
by the mass of amyloplast and the protoplast, which exert a mechanical impact on the
cell membrane (Garrill et al. 1996). Normally, thus gravisusceptores regulates growth and
cell wall properties (Garrill et al. 1996; Soga et al. 2004) but the mass of amyloplast and
therefore the mass of starch might also influence mechanosensitive channel opening in
tuber cells if the tubers are exposed to mechanical impact.
Conclusion
Given cultivars displayed a range of tubers differing in their starch concentration. Variations
of the starch concentration within one cultivar, as shown in the distribution of tubers
in different specific gravity ranges, might have more effect on blackspot bruising then
variations in the starch concentration between cultivars, which corresponded e.g. to results
of the cv. Gala compared to the cv. Renate very well. Blackspot bruise occurred if the related
enzymatic reaction was able to proceed, which was possible when individual cell
membranes of cell organelles were open and released components. Membrane opening
might be realised by mechanosensitive channels. Channel opening (Ghazi et al. 1998) as
well as blackspot formation passed, if impact exceeded individual stress thresholds
(Baritelle and Hyde 2003). Independent of the availability of chemical components, which
determine bruise colour, the resistance of the mechanosensitive channels to opening, depended
on the cell mass determined particularly by the amount of starch molecules. Starch
in the amyloplast loaded the cell weight and activated mechanosensitive channels and sensing
might occur outside the plasma membrane as also described by Sack (1997). Tubers
with higher starch concentration are less resistant to blackspot bruise. Therefore the aim of
a potato crop management should be among others the generation of uniform tubers with
similar starch concentrations within each cultivar or plant.
References
Alvarez, M.D., D.E.J. Saunders, and J.F.V. Vincent. 2000. Fracture properties of stored
fresh and osmotically manipulated apple tissue. European Food Research and
Technology 211: 284-290.
Baritelle, A., and G.H. Hyde. 2003. Effect of the specific gravity and cultivar on the impact
sensitivity of potatoes. Postharvest Biology and Technology 29: 279-286.
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