exudate from those plants sprayed with L(+)-adenosine contained
43% more Ca2+, 32% more Mg2+, and 31% more K+
than exudate from water-sprayed controls (Table 111). This
study indicated that the signal that elicited the increased
pulse of cations was able to rapidly transverse a 4.0-mm gap
of water joining the shoots of the excised maize seedlings,
thus obviating the possibility of diffusion or translocation.
Single leaves centrally positioned on approximately 0.5-m
long cucumber plants were sprayed with either water or 100
pg L-' of L(+)-adenosine. Subsequently, the stem of the main
axis was excised at both basal and apical sites as indicated in
Figure 4. Analysis of exudates from the four locations (A-D)
showed that the major effect was on the exudate from the
base of the plant (A in Fig. 4); however, higher Ca2+ concentrations
also were found in the exudate from both basipetal
and acropetal sides of the apical cut on the main stem (Fig.
4, C and D).
A diffusion experiment using tomato plants was conducted
to investigate whether the signal elicited by L(+)-adenosine
moved both acropetally and basipetally within the plant.
Two central leaves, as shown in Figure 5, were sprayed with
L(+)-adenosine. An apical and basal leaf were excised within
5 s and placed in 5 mL of water for 5 min. The L(+)-adenosine
increased the Ca2+ and Mg2+ concentrations in the diffusate
from the petiole of apical leaves by 40 and 56%, respectively,
but decreased the K+ concentration by 21% (Fig. 5). The
concentration of a11 three ions in the diffusate from basal
leaves was lower in the L(+)-adenosine treatment.