Photodynamic Herbicides - Chlorophyll Biosynthesis and Technological Applications - page 390

Table 17.8 Tetrapyrrole accumulation and ALA content of washed morningglory leaf sections of
various ages following ALA treatment (2lbs per acre)
ALA content and tetrapyrrole accumulation after 15 h dark-incubation

10-day old 15-day old 20-day old

C T C T C T

Tetrapyrrole
or % injury nmoles per g fresh weight

ALA 0.1 0.3 0.2 0.1 0.1 0.0 0.2 0.0 0.1 0.0 0.2 0.0

Mp(e) 0.0 0.0 0 7 0.3 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0

Pchlide a 1.6 0.2 9.0 4.2 0.5 0.1 2.9 1.6 0.2 0.0 1.0 0.0

% Injury 0 0 0.0 83.3 16.7 0.0 0.0 61.1 19.2 0.0 0. 0 55.6 14.0

LSD (0.05)
age

ALA ¼ 0.04

Mp(e) ¼ 0.15

Pchlide a ¼ 2.2

Injury ¼ 3.5

LSD (0.05)
treatment

ALA ¼ 0.03

Mp(e) ¼ 0.12

Pchlide a ¼ 1.8

2.5
Values are means of six replicates. Photoperiodic damage was assessed 10 days after treatment
(Reproduced from Kulur 1996 )

Injury ¼

old plants (Table 17.8 , Fig. 17.6 ). Also, as in whole, unwashed leaves, photody-
namic damage appeared to parallel tetrapyrrole accumulation as 10-day old
seedlings exhibited higher photodynamic damage (83.3 %),

than 15-day old

(61.1 %) and 20-day old plants (55.6 %).
Thus the key experiment that gave insight about the interaction of ALA
availability, tetrapyrrole metabolism and tissue age was the experiment just
described, involving washed leaf sections. The small amounts of ALA detected
in treated leaves of all ages were not significantly different from one another
(Table 17.8 ,Fig. 17.6 ). Yet, ALA-treated younger leaves accumulated signifi-
cantly higher amounts of tetrapyrroles than older ones (Table 17.8 ,Fig. 17.6 ). In
other words, the same amount of metabolically active ALA was detected in
young and old washed leaf sections, but younger leaves accumulated more
tetrapyrroles than older ones. This lead to several conclusions that are discussed
below.
The detection of very small amounts of ALA, and much larger amounts of
tetrapyrroles in young leaves is compatible with the notion that exogenous ALA
translocates rapidly to inner tissues, where it is rapidly converted to tetrapyrroles.
The rapid translocation of ALA to inner tissues is mandatory for the support of the
observed high rates of tetrapyrrole biosynthesis and accumulation. In this case, the
detection of very small amounts of ALA accumulation in the inner tissues can best
be explained by its rapid conversion to tetrapyrroles.