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Fig. 26.1.
The results of experiments with wound-type 2.
Numbers
show the pattern of the
activity of chymotrypsin added to leaf extracts of
leaf 1
, the oldest true leaf, and
leaf 2
,
and are expressed as a percentage of unwounded control plant samples;
low
values indicate
high
proteinase inhibitor activity. The
arrows
show the pattern of movement of the dye
Lucifer Yellow CH (
LY
) from a droplet placed on the surface of the lamina of cotyledon 1
(the cotyledon facing the observer when the plant was positioned with leaf 1 pointing to
the right), through which a clean cut was made using a razor blade. (Reproduced from
Rhodes et al. 1999, with the permission of Oxford University Press, copyright of the Annals
of Botany Company)
when cotyledon 1 was cut the LY entered the right side of leaf 1 and the left
side of leaf 2 (Fig. 26.1); the pattern was reversed when cotyledon 2 was
cut. The patterns of dye movement are directly linked to the architecture
of the xylem. Thus, there was an observable reversal of flow in the xylem
out of the wounded leaf, which could carry chemical elicitors to the rest of
the plant. The distribution pattern of this hydraulic dispersal in the xylem
coincided with the pattern of PI induction.
To track the movement of water in the xylem following other types of
wounding, LY was injected into the lamina of a cotyledon, a procedure
that did not cause systemic PI activity. Both a large mechanical wound
(wound-type 4) and a heat wound (wound-type 5) when applied to injected
cotyledon 1 caused uptake of LY by the xylem; flow of LY into leaves 1 and
2 followed the pattern already described for a cut across a droplet of LY
on the lamina of cotyledon 1 (Fig. 26.1). The pattern was reversed when
cotyledon 2 was injected and severely wounded. These severe wounds were
accompanied by electrical activity, whose pattern coincided with the pat-
ternofflowofLY.SeverewoundstocotyledonsinducedhighlevelsofPI
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