Figure 7. The area of the vascular tissue of the crease phloem compared to the total area of the crease vascular tissue, and to the rate of kernel weight gain of six wheat cultivars differing in final seed weight measured in two separate years. The regression through the data points of each comparison is presented.

Fructans can be found in the kernel free space (64). They probably are accumulated during megasporogenesis and after fertilization of the endosperm nucleus are excluded as new cells develop and they then end up in the free space. This appears likely because fructan was not labeled when 14C-sucrose was fed to the endosperm (64). In wheat kernels sink fructans then might have a reserve carbohydrate storage role rather than control of sucrose content as can be projected for stem tissue. The control point for movement into the kernel has been suggested as the companion cell sieve element unloading into the symplast of cells in the nucellar region (63). Under these conditions fructan interaction with membranes could be important for maintaining the osmotic component of the sucrose concentration gradient between the unloading region and the endosperm cells on the kernel (63, 65).

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