The effects of differing cytokinin and auxin concentrations on resistance of tobacco (
Nicotiana tabacum
L.) tissue cultures to race 0 of
Phytophthora parasitica
var.
nicotianae
were examined. With 1 ...micromolar kinetin and either 11.5 micromolar indoleacetic acid or 1 micromolar 2,4-dichlorophen-oxyacetic acid, tissues from resistant cultivars exhibited a “hypersensitive” reaction to zoospores of the fungus and subsequently were colonized only slightly. With susceptible cultivars or with tissues from resistant cultivars supplied with higher cytokinin levels (
e.g.
10 micromolar kinetin), this hypersensitive reaction did not occur and tissues were heavily colonized. Benzylaminopurine and kinetin were particularly effective in eliminating both the hypersensitive reaction and disease resistance. Zeatin and 6-(3-methyl-2-butenylamino)purine were less effective. Increases in indoleacetic acid levels reversed the effects of high cytokinin concentrations. The balance of phytohormones apparently controls the host response to the fungus; thus, in this system, resistance or susceptibility can be studied without changing either host or fungal genotype.
The ability of synthetic peptides and polypeptides to act as substrates and/or inhibitors of pp60
c-
src
was examined. The random copolymer, poly(K
4Y) had a threefold lower specificity than poly(E
...4Y). Peptides containing lysine vs. glutamate were also found to have a lower substrate specificity (
V
max:
K
m ratio). In order to assess the substrate specificity of acidic peptides, an assay protocol using DEAE-membranes was developed. Peptides containing a (Y
XE)
5Y
XD motif (
X = G, A, V, P, or norvaline) were tested as inhibitors and substrates of pp60
c-
src
. The glycine-containing peptide was the best substrate having a specificity 16 000-fold higher than
5Val-angiotensin II, the most commonly used peptide substrate. Most of the peptides, except for the proline containing peptide, had
K
i values of 20–100 μM. In a series of (
XGE)
5
XGD peptides, where
X = Y or F, tyrosine at position 10 was found to be the preferred site for accepting a phosphate. Analogs in which the glycine was replaced with alanine indicated that loss of flexibility around position 10 was detrimental to substrate specificity. Results suggest that conformational requirements of the peptides tested was important and substrate specificity was a more sensitive parameter than binding as measured by
K
i values.
Radical Catholic liberation theology in Latin America is declining. The books reviewed here help analyze this trend from international, national, local, and individual perspectives. Analyses of local ...and individual factors have been the most fruitful so far. Moreover, they suggest that individual religious faith may be more important than institutional church politics for Latin American politics in the future.
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