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the higher tetrapyrrole content of 10 and 15-day old leaves was due to more active
tetrapyrrole metabolism in younger leaves rather than ALA availability.
Photodynamic damage appeared to parallel tetrapyrrole accumulation as 10-day
old seedlings exhibited higher photodynamic damage (96.28 %), than 15-day old
(83.8 %) and 20-day old seedlings (62.86 %).
17.10.2 ALA Content, Tetrapyrrole Accumulation
and Photodynamic Damage in Unwashed
Morningglory Primary Leaf Sections
To confirm that differences in tetrapyrrole accumulation in morningglory seedlings
of different ages were due to differences in active tetrapyrrole metabolism rather
than ALA availability, the ALA treatment experiment (see above) was repeated
with the following modification. Instead of monitoring tetrapyrrole accumulation
and ALA content on one leaf and photodynamic damage on other leaves, tetrapyr-
role and ALA analysis were performed on a small leaf section and photodynamic
damage was evaluated on the remaining leaf parts. It was conjectured that such an
approach would minimize sampling errors and give a more accurate picture of what
is going on.
Tetrapyrrole and ALA analyses were similar to those described earlier for whole
leaves, except that in this case unwashed leaf sections were used for analysis. After
the plants were sprayed at a rate of 2lbs ALA per acre, and placed in darkness
overnight, two small sections of the primary leaf were cut from each of the six
plants. The tissue sections were pooled, weighed and, frozen in liquid nitrogen for
tetrapyrrole analysis. Next, a second leaf section was removed from each plant. The
leaf sections were pooled and used for ALA determination. In this manner, about
two third of the primary leaf from each plant was removed for analysis. Photody-
namic damage was assessed on the remaining one-third leaf sections.
As was observed with unwashed whole leaves, the amount of ALA detected in
ALA-treated seedlings was significantly higher in treated leaves of all ages in
comparison to controls. Again, the amounts of ALA detected in treated leaves of
all ages were not significantly different from one another (Table 17.7 , Fig. 17.5 ).
These results confirmed that under our growth conditions, leaf age had no bearings
on ALA penetration to active sites of tetrapyrrole metabolism.
As was observed with whole leaves, ALA-treated plants accumulated signifi-
cantly higher amounts of tetrapyrroles than untreated ones (Table 17.7 , Fig. 17.5 ).
Here again, the accumulated tetrapyrroles consisted mainly of Pchlide a . In this
case too the accumulation of Pchlide a was age-dependent and the amount of
tetrapyrroles accumulated by 10 and 15-day old plants was higher than in 20-day
old plants (Table 17.7 , Fig. 17.5 ). Together with the ALA content data (see above)
these results confirmed that the higher tetrapyrrole content in 10 and 15-day old
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