Biomedical subjects

Dale R Walters

Publications and source records attributed to Dale R Walters.

8 recordsLinked to original sources

PubMed2006

Plants and biotrophs: a pivotal role for cytokinins?

Plants infected with biotrophic fungal pathogens exhibit reduced photosynthetic rates, nutrient mobilization towards infection sites and, in interactions where discrete pustules are formed, green islands are induced. The ability of cytokinins to mobilize nutrients towards sites of application and to delay senescence led researchers to speculate that cytokinins might be involved in nutrient mobilization and green island formation in plants infected with biotrophic fungi. There is evidence that the reduction in photosynthesis in infected leaves results from early increases in invertase activity, leading to carbohydrate accumulation and the downregulation of photosynthetic metabolism. In this Opinion article, we propose that these seemingly disparate changes in host physiology in infected plants are the result of cytokinin-induced increases in invertase activity occurring early on in the host-pathogen interaction.

Cytokinins↗

PubMed2006

Rapid accumulation of trihydroxy oxylipins and resistance to the bean rust pathogen Uromyces fabae following wounding in Vicia faba.

BACKGROUND AND AIMS: Insect damage to plants leads to wound-activated responses directed to healing of damaged tissues, as well as activation of defences to prevent further insect damage. Negative cross-talk exists between the jasmonic acid-based signalling system that is activated upon insect attack and the salicylic acid-based system frequently activated following pathogen infection. Thus, insect attack may compromise the ability of the plant to defend itself against pathogens and vice versa. However, insect herbivory and mechanical wounding have been shown to reduce fungal infections on some plants, although the underlying mechanisms remain to be defined. This work examines the effects of mechanical wounding on rust infection both locally and systemically in the broad bean, Vicia faba and follows changes in oxylipins in wounded leaves and unwounded leaves on wounded plants. METHODS: The lamina of first leaves was wounded by crushing with forceps, and first and second leaves were then inoculated, separately, with the rust Uromyces fabae at various times over a 24 h period. Wounded first leaves and unwounded second leaves were harvested at intervals over a 24 h period and used for analysis of oxylipin profiles. KEY RESULTS Mechanical wounding of first leaves of broad bean led to significantly reduced rust infection in the wounded first leaf as well as the unwounded second leaf. Increased resistance to infection was induced in plants inoculated with rust just 1 h after wounding and was accompanied by rapid and significant accumulation of jasmonic acid and two trihydroxy oxylipins in both wounded first leaves and unwounded second leaves. The two trihydroxy oxylipins were found to possess antifungal properties, reducing germination of rust spores. CONCLUSIONS: These results demonstrate the rapidity with which resistance to pathogen infection can be induced following wounding and provides a possible mechanism by which pathogen infection might be halted.

Animals↗

PubMed2005

Local and systemic changes in arginine decarboxylase activity, putrescine levels and putrescine catabolism in wounded oilseed rape.

* Here we report the effect of mechanical wounding on putrescine biosynthesis and catabolism in oilseed rape (Brassica napus ssp. oleifera). * The lamina of first leaves was wounded by crushing with forceps, and first and second leaves were harvested at various intervals over a 24 h period. Levels of free polyamines were measured and activities of enzymes of polyamine biosynthesis and catabolism were assayed in the harvested tissue. * Mechanical wounding of the first leaves led to significant, but transient, increases in arginine decarboxylase (ADC) activity and levels of free putrescine in the wounded first leaf and in unwounded second leaves. The increased putrescine appeared to be the result of a combination of increased ADC activity, coupled with reduced putrescine catabolism, as activity of the oxidative enzyme diamine oxidase was significantly reduced following wounding, both locally and systemically. * The role of the increased free putrescine in the wound response of oilseed rape is not known, although the possibility that it is used to form putrescine conjugates is worthy of further investigation.

Amine Oxidase (Copper-Containing)↗

PubMed2004

Synthesis and antifungal activity of five classes of diamines.

Examples of five classes of diamines were synthesized and tested for antifungal activity. Two classes, the bis(cyclohexylmethyl)diamines and the bis(benzyl)diamines, were most effective in reducing mycelial growth of the oat leaf stripe pathogen Pyrenophora avenae Ito & Kuribay when used at a concentration of 250microM. The bis(benzyl)diamine BBD5 and the hydroxypyridylethylamine HPE2 both reduced powdery mildew infection of barley seedlings by greater than 70% when applied as a post-inoculation spray at 250 microM. Several of the compounds examined, and especially BBD5 and HPE2, reduced the formation of spermidine but greatly increased spermine levels. These changes in P avenae treated with BBD5 and HPE2 were also accompanied by greatly elevated activity of polyamine oxidase. It is suggested that the antifungal activity of these compounds may be related to the accumulation of spermine and specifically to its toxicity.

Benzylamines↗

PubMed2004

Potassium phosphate induces systemic protection in barley to powdery mildew infection.

In laboratory tests, treatment of the first leaves of barley (Hordeum vulgare L cv Golden Promise) with potassium phosphate led to significant reduction in infection of the second leaves with the powdery mildew fungus Blumeria graminis f sp hordei Marchal, with a 25 mM treatment giving 89% reduction in infection. Although the optimal interval between phosphate treatment of the first leaves and mildew inoculation of the second leaves was 2 days, significant protection was still obtained if the interval was increased to 12 days. Protection against powdery mildew infection was not as effective when the potassium phosphate was applied as a seed treatment or root drench. Phosphate treatment of the first leaves led to significant increases in activities of phenylalanine ammonia lyase (PAL), peroxidase and lipoxygenase in second leaves. Enzyme activities, especially PAL and peroxidase, were increased further when second leaves of phosphate-treated plants were inoculated with powdery mildew. Phosphate treatment of the first leaves did not adversely affect plant growth and, in a field trial, 25 mM potassium phosphate provided 70% control of mildew and gave a small increase in grain yield.

Enzyme Activation↗

PubMed2003

Polyamines and plant disease.

The diamine putrescine and the polyamines spermidine and spermine are found in a wide range of organisms from bacteria to plants and animals. They are basic, small molecules implicated in the promotion of plant growth and development by activating the synthesis of nucleic acids. Polyamine metabolism has long been known to be altered in plants responding to abiotic environmental stress and to undergo profound changes in plants interacting with fungal and viral pathogens. Polyamines conjugated to phenolic compounds, hydroxycinnamic acid amides (HCAAs), have been shown to accumulate in incompatible interactions between plants and a variety of pathogens, while changes in the diamine catabolic enzyme diamine oxidase suggest a role for this enzyme in the production of hydrogen peroxide during plant defence responses. More recent work has suggested a role for the free polyamine spermine in the hypersensitive response of barley to powdery mildew and particularly in tobacco to TMV. The prospects for the genetic manipulation of HCAA levels in plants as a means of both defining their role in plant defence and in the generation of disease resistant plants is discussed briefly.

Amides↗

PubMed2003

Antifungal activity of some deoxyhypusine synthase inhibitors (short communication: plant mycology and crop protection).

Several inhibitors of deoxyhypusine synthase were examined for antifungal activity. All compounds, used at concentrations of 1.0 mM or less, reduced mycelial growth of the oat leaf stripe pathogen Pyrenophora avenae grown on solid media. Four of the compounds completely inhibited fungal growth, 4a doing so at a concentration of only 0.61 mM. Inhibition of fungal growth afforded by some of the compounds was more marked than was reflected by the radial growth measurements.

Antifungal Agents↗

PubMedDate not supplied

Altered growth and polyamine catabolism following exposure of the chocolate spot pathogen Botrytis fabae to the essential oil of Ocimum basilicum.

Biomass of the fungal pathogen Botrytis fabae in liquid culture amended with two chemotypes of the essential oil of basil, Ocimum basilicum, was reduced significantly at concentrations of 50 ppm or less. The methyl chavicol chemotype oil increased the activity of the polyamine biosynthetic enzyme S-adenosylmethionine decarboxylase (AdoMetDC), but polyamine concentrations were not significantly altered. In contrast, the linalol chemotype oil decreased AdoMetDC activity in B. fabae, although again polyamine concentrations were not altered significantly. However activities of the polyamine catabolic enzymes diamine oxidase (DAO) and polyamine oxidase (PAO) were increased significantly in B. fabae grown in the presence of the essential oil of the two chemotypes. It is suggested that the elevated activities of DAO and PAO may be responsible, in part, for the antifungal effects of the basil oil, possibly via the generation of hydrogen peroxide and the subsequent triggering of programmed cell death.

Adenosylmethionine Decarboxylase↗