Photodynamic Herbicides - Chlorophyll Biosynthesis and Technological Applications - page 373

Table 17.2 (continued)

%
Death

%
Death
ALA MOD A + N!

%
Death

Modulator
ID Modulator template Modulator

Pyrrole 309P 1-(Dimethylamino)pyrrole 38 0 94

Pyrrole 235P 1-(2-Cyanomethyl)pyrrole 63 0 88

Pyrrole 664P 1-Methyl-2-pyrrolecarboxylic

acid

63 0 88

Pyrrole 183P tert -Butyl 4-acetyl-3,5-dimethyl-

2-pyrrolecarb

31 100 88

Quinoline 1,004 6-Nitroquinoline 30 30 100

Quinoline 1,005 8-Nitroquinoline 30 100 100

Quinoline 819 5-Nitroquinoline 25 95 100

Quinoline 840 4,7 Phenanthroline 35 40 95

Quinoline 838 1,7 Phenanthroline 25 35 95

Percent death was monitored 10 days after Spraying
ALA ALA alone, Mod Modulator alone, A+M ALA + modulator, ID modulator identification
number in the database

light (light death) probably via singlet oxygen formation. Protoporphyrin is a
transient metabolite, which does not accumulate to any large extent in normal
tissues. It is an immediate precursor of protoheme which in turn is the prosthetic
group of cytochromes in mitochondria and chloroplasts. It is also the prosthetic
group of catalases and peroxidases.
Since non-chlorophyllous plant tissues such as roots consist of cells containing an
abundance of mitochondria, which in turn contain cytochromes and presumably an
active porphyrin-heme biosynthetic pathway, the issue was raised as to whether some
TDPH formulations would be effective against plant roots, in the same manner they
were effective against insects. In particular, it was interesting to determine whether
plant roots would be susceptible to TDPH dependent dark death since in their natural
environment in the soil, roots are usually shielded from light.
Chung and Rebeiz (unpublished) investigated the effects of ALA and four
modulators belonging to four different templates on excised and attached cucumber
roots. The results of these investigations are summarized below.

17.7.1 Effects of TDPH on Excised Cucumber Roots

Excised cucumber roots were incubated overnight in darkness with ALA and
modulators. At the end of dark incubation the tissue was analyzed for tetrapyrrole
accumulation and was exposed to light for evaluation of photodynamic damage.
The latter was evaluated visually, and polarographically by the decrease in oxygen
consumption of treated roots as compared to controls. Excised roots incubated with