Photodynamic Herbicides - Chlorophyll Biosynthesis and Technological Applications - page 389

leaves was more likely due to more active tetrapyrrole metabolism in younger
leaves than to ALA availability.
Also, as in whole, unwashed leaves, photodynamic damage appeared to parallel
tetrapyrrole accumulation as 10-day old seedlings exhibited higher photodynamic
damage (100 %), than 15-day old (89.7 %) and 20-day old plants (64.1 %).
Altogether the above results confirmed the conclusions drawn from the analysis
of unwashed whole leaves.
17.10.3 ALA Content, Tetrapyrrole Accumulation
and Photodynamic Damage in Washed
Morningglory Primary Leaf Sections
To further confirm that differences in tetrapyrrole accumulation in morningglory
seedlings of different ages was due to differences in active tetrapyrrole metabolism
rather than ALA availability, the above experiment was repeated with the following
modification. Instead of monitoring tetrapyrrole accumulation and ALA content on
unwashed leaf sections, tetrapyrrole and ALA analyses were performed on washed
leaf sections, and photodynamic damage was evaluated on the remaining leaf parts.
It was conjectured that such an approach would give a more accurate picture of the
size of the active ALA pool inside the leaf tissue by eliminating the contribution of
metabolically inactive surface ALA that did not penetrate the tissue. As a conse-
quence a better evaluation of the relationship between ALA metabolic availability
and photodynamic damage may be obtained.
Tetrapyrrole and ALA analyses were similar to those described earlier for
unwashed leaf sections, except that in this case washed leaf sections were used
for analysis. In other words, after the plants were sprayed and placed in darkness
overnight, the leaves were washed with distilled water before excising the leaf
sections.
Contrary to what was observed with unwashed leaf sections, the difference in
ALA content between control and ALA-treated seedlings although statistically
significant was extremely small (Table 17.8 , Fig. 17.6 ). This in turn indicated that
the higher ALA concentrations observed in ALA-treated plants in comparison to
controls, in unwashed leaves and leaf sections were probably due to traces of
metabolically inactive ALA that remained on the unwashed leaf surface. As pointed
out below, it also shed additional light about the interaction of ALA availability,
tetrapyrrole biosynthesis and leaf age.
As was observed with unwashed leaf material, ALA-treated plants accumulated
significantly higher amounts of tetrapyrroles than untreated ones (Table 17.8 ,
Fig. 17.6 ). Most of the accumulated tetrapyrroles consisted 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