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10 day-old seedlings exhibited higher photodynamic damage (100-87.5 %), than
15-day old (87.5-27.5 %) and 20-day old plants (55.7-50.2 %). In 10 and 15-day
old seedlings, higher concentrations of thioflavin T appeared to result in lower
levels of photodynamic injury. All in all, the enhancement of ALA translocation by
thioflavin T was not large enough to allow determination of the activity level of
tetrapyrrole biosynthesis in older leaf tissues.
17.11.2 Response of 20-Day Old Morningglory Leaves
to Conditions That Simulate Improved ALA
Penetration to Inner Tissues
Since the use of a desiccant failed to substantially improve ALA translocation to
inner tissue, and to shed additional light upon the activity level of tetrapyrrole
biosynthesis in older leaves, an alternative strategy was explored. It was
conjectured that if the older plant tissue was left in contact with a solution of
ALA overnight, enough ALA may translocate to the inner tissues and would result
in improved tetrapyrrole accumulation and concomitant photodynamic injury. This
would be true if the Chl biosynthetic pathway is as active in older leaves as in
younger ones (Table 17.10 ).
The amount of ALA detected in leaves incubated with ALA was significantly
higher than in control leaves (Table 17.10 ). It was also noticed that ALA content
in the treated leaves was much higher than that accumulated by leaves sprayed
Fig. 17.8 (continued) of washed leaf sections excised from control or treated seedlings. (a) ALA
content and photodynamic injury: CA ALA content of control, 2AA ALA content after treatment
with 2 lbs per acre of ALA, 0.5TAA ALA content after treatment with 0.5 lbs. per acre of
thioflavin T, 0.5TA ALA content after treatment with 0.5 lbs. per acre of thioflavin T and 2 lbs.
per acre of ALA, 2TAA ALA content after treatment with 2 lbs. per acre of thioflavin T, 2TA ALA
content after treatment with 2 lbs. per acre of thioflavin T and 2 lbs. per acre of ALA. (b)Mp
(e) accumulation and photodynamic injury, CM Mp(e) content of control, 2 AM Mp(e) content
after treatment with 2 lbs. per acre of ALA, 0.5TM Mp(e) content after treatment with 0.5 lbs. per
acre of thioflavin T, 0.5TAM Mp(e) content after treatment with 0.5 lbs. per acre of thioflavin T
and 2 lbs. per acre of ALA, 2TMMp(e) content after treatment with 2 lbs. per acre of thioflavin T,
2TAMMp(e) content after treatment with 2 lbs. per acre of thioflavin T and 2 lbs. per acre of ALA,
(c) Pchlide a accumulation and photodynamic injury, CP Pchlide a content of control, 2AP Pchlide
a content after treatment with 2 lbs. per acre of ALA, 0.5TP Pchlide a content after treatment with
0.5 lbs. per acre of thioflavin T, 0.5TAP Pchlide a content after treatment with 0.5 lbs. per acre of
thioflavin T and 2 lbs. per acre of ALA, 2TP Pchlide a content after treatment with 2 lbs. per acre
of thioflavin T, 2TAP Pchlide a content after treatment with 2 lbs. per acre of thioflavin T and 2 lbs.
per acre of ALA, CI Photodynamic damage in control leaves, 2AI Photodynamic damage in leaves
treated with 2 lbs. per acre ALA, 0.5TI Photodynamic damage in leaves treated with 0.5 lbs. per
acre thioflavin, 0.5TAI Photodynamic damage in leaves treated with 0.5 lbs. per acre thioflavin T
and 2 lbs. per acre ALA, 2TI Photodynamic damage in leaves treated with 2 lbs. per acre
thioflavin T, 2TAI Photodynamic damage in leaves treated with 2 lbs. per acre thioflavin T and
2 lbs. per acre ALA. All other abbreviations are as in Fig. 17.4
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