Phytoalexin

About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.

Expression of Biphenyl Synthase Genes and Formation of Phytoalexin Compounds in Three Fire Blight-Infected Pyrus communis Cultivars.

Abstract: Pear (Pyrus communis) is an economically important fruit crop. Drops in yield and even losses of whole plantations are caused by diseases, most importantly fire blight which is triggered by the bacterial pathogen Erwinia amylovora. In response to the infection, biphenyls and dibenzofurans are formed as phytoalexins, biosynthesis of which is initiated by biphenyl synthase (BIS). Two PcBIS transcripts were cloned from fire blight-infected leaves and the encoded enzymes were characterized regarding substrate specificities and kinetic parameters. Expression of PcBIS1 and PcBIS2 was studied in three pear cultivars after inoculation with E. amylovora. Both PcBIS1 and PcBIS2 were expressed in ‘Harrow Sweet’, while only PcBIS2 transcripts were detected in ‘Alexander Lucas’ and ‘Conference’. Expression of the PcBIS genes was observed in both leaves and the transition zone of the stem; however, biphenyls and dibenzofurans were only detected in stems. The maximum phytoalexin level (~110 μg/g dry weight) was observed in the transition zone of ‘Harrow Sweet’, whereas the concentrations were ten times lower in ‘Conference’ and not even detectable in ‘Alexander Lucas’. In ‘Harrow Sweet’, the accumulation of the maximum phytoalexin level correlated with the halt of migration of the transition zone, whereby the residual part of the shoot survived. In contrast, the transition zones of ‘Alexander Lucas’ and ‘Conference’ advanced down to the rootstock, resulting in necrosis of the entire shoots.

[60] Plant cell wall polysaccharides that activate natural plant defenses

Abstract: Publisher Summary In recent years studies of the insect-induced proteinase inhibitors in plant leaves and of fungal-elicited phytoalexin synthesis in cotyledons and seedlings have demonstrated that plant cell walls contain within their polysaccharide structures informational components that can activate synthesis of these types of defensive chemicals. The chapter discusses preparation of pectin fragments, derived from tomato leaves and from soyabean cell walls, which are inducers of defense responses in plants. The chapter also discusses preparation of oligouronides with purification of the proteinase inhibitor inducing factor (PIIF) activity by digestion of pectic polysaccharides with tomato polygalacturonase. A galacturonic acid-rich polysaccharide that possesses phytoalexinelicitor activity in soybeans can also be prepared by partial acid hydrolysis of soybean cell walls. The preparation and characterization of this polyuronide is qualitatively similar to the procedure for the preparation of trifluoroacetic acid (TFA) PIIF. There is detailed discussion about the preparation of plant cell walls, and isolation of the endogenous elicitor of phytoalexins from soybean cell walls.

Host/parasite interaction in blackspot disease of roses caused by Diplocarpon rosae Wolf

Abstract: SUMMARY The utilization of amino acids by Diplocarpon rosae Wolf was investigated and compared with amino acid compositions of leaves of resistant and of tolerant roses. No amino acid appeared to determine resistance of roses to blackspot on a nutritional basis, but phenylalanine marginally increased resistance when taken up by wounded leaves of resistant or tolerant varieties. There is an accumulation of phenolic compounds in response to infection by D. rosae. Most phenolic compounds are toxic to D. rosae in vitro, particularly ellagic acid and p-coumaric acid, but their presence and quantity in healthy rose leaves could not be related to disease resistance. Inhibition of germination on rose leaves of conidia of the fungus was determined in a manner that suggested production of a phytoalexin. It is suggested that resistance of roses to D. rosae may be related to accumulation of polyphenols and possibly to the production of a phytoalexin.

Phytoalexin production and the resistance of lucerne (Medicago sativa L.) to Verticillium albo-atrum

Abstract: The production of phytoalexins (determined as sativan and medicarpin) in leaf diffusates, leaf tissue and stem segments of lucerne cultivars resistant and susceptible to infection by Verticillium albo-atrum has been determined. No relationship between resistance and the formation of the antifungal compounds by leaves was observed. With stem segments, however, both the rates and amounts of phytoalexin synthesis were directly related to host resistance.

A Blast Lesion Mimic Mutant of Rice

Abstract: Plant reacts to pathogen attack by activating multiple defense mechanisms as a result from the interaction of resistance gene in the plant and a corresponding avirulence gene in the pathogen. Interaction of the resistance and avirulence genes would stimulate a signalling cascade leading to the activation of defense mechanisms; hypersensitive response (HR), production of reactive oxygen species, cell wall fortification, accumulation of salicylic acid and phytoalexin, and induction of PR genes (reviewed in Bent, 1996; Hammond-Kosack and Jones, 1996).