Defense Enzyme Responses in Dormant Wild Oat and Wheat Caryopses Challenged with a Seed Decay Pathogen
نویسندگان
چکیده
Seeds have well-established passive physical and chemical defense mechanisms that protect their food reserves from decay-inducing organisms and herbivores. However, there are few studies evaluating potential biochemical defenses of dormant seeds against pathogens. Caryopsis decay by the pathogenic Fusarium avenaceum strain F.a.1 was relatively rapid in wild oat (Avena fatua L.) isoline "M73," with >50% decay after 8 days with almost no decay in wheat (Triticum aestivum L.) var. RL4137. Thus, this fungal strain has potential for selective decay of wild oat relative to wheat. To study defense enzyme activities, wild oat and wheat caryopses were incubated with F.a.1 for 2-3 days. Whole caryopses were incubated in assay reagents to measure extrinsic defense enzyme activities. Polyphenol oxidase, exochitinase, and peroxidase were induced in whole caryopses, but oxalate oxidase was reduced, in response to F.a.1 in both species. To evaluate whether defense enzyme activities were released from the caryopsis surface, caryopses were washed with buffer and enzyme activity was measured in the leachate. Significant activities of polyphenol oxidase, exochitinase, and peroxidase, but not oxalate oxidase, were leached from caryopses. Defense enzyme responses were qualitatively similar in the wild oat and wheat genotypes evaluated. Although the absolute enzyme activities were generally greater in whole caryopses than in leachates, the relative degree of induction of polyphenol oxidase, exochitinase, and peroxidase by F.a.1 was greater in caryopsis leachates, indicating that a disproportionate quantity of the induced activity was released into the environment from the caryopsis surface, consistent with their assumed role in defense. It is unlikely that the specific defense enzymes studied here play a key role in the differential susceptibility to decay by F.a.1 in these two genotypes since defense enzyme activities were greater in the more susceptible wild oat, compared to wheat. Results are consistent with the hypotheses that (1) dormant seeds are capable of mounting complex responses to pathogens, (2) a diversity of defense enzymes are involved in responses in multiple plant species, and (3) it is possible to identify fungi capable of selective decay of weed seeds without damaging crop seeds, a concept that may be applicable to weed management in the field. While earlier work on seed defenses demonstrated the presence of passive defenses, this work shows that dormant seeds are also quite responsive and capable of activating and releasing defense enzymes in response to a pathogen.
منابع مشابه
Polyphenol oxidase as a biochemical seed defense mechanism
Seed dormancy and resistance to decay are fundamental survival strategies, which allow a population of seeds to germinate over long periods of time. Seeds have physical, chemical, and biological defense mechanisms that protect their food reserves from decay-inducing organisms and herbivores. Here, we hypothesize that seeds also possess enzyme-based biochemical defenses, based on induction of th...
متن کاملSeed dormancy and responses of caryopses, embryos, and calli to abscisic Acid in wheat.
Preharvest sprouting of wheat (Triticum aestivum L.) is associated with inadequate seed dormancy. Although abscisic acid (ABA) has often been suggested to play a central role in developing seed, its involvement in dormancy of mature seed lacks firm experimental evidence and endogenous ABA levels are not well correlated with germinability. We examined genotypic and temporal variation in wheat se...
متن کاملبررسی تاثیر عصاره الکلی آفتابگردان( Helianthus annuus ) بر جوانه زنی، رشد رویشی و فعالیتهای انزیمی یولاف وحشی ( Avena ludoviciana)
In order to evaluate the allelopatic potential of sunflower alcoholic extract against winter wild oat (Avena ludoviciana) at germiantion and vegetative growth stage two expriments were coducted in Islamic Azad University, Shoushtar branch at 2012. Both expriments were laid out according to Completely Randomized Design with five replications and treatments were various concentration of sunflower...
متن کاملبررسی ویژگیهای برگ و نسبت ریشه به ساقه در تداخل اندامهای زیرزمینی و هوایی گندم زراعی ( Triticum aestivum ) و تراکمهای مختلف یولاف وحشی ( Avena fatua )
A pot experiment was designed to investigate the effects of full, above and below ground interactions of wheat with wild oat on leaf characteristics and root to shoot ratio. This experiment was conducted as a factorial based on randomized complete design with four replications. The treatments included four interference levels (above ground, below ground, above and below ground and check wheat a...
متن کاملبررسی ویژگیهای برگ و نسبت ریشه به ساقه در تداخل اندامهای زیرزمینی و هوایی گندم زراعی ( Triticum aestivum ) و تراکمهای مختلف یولاف وحشی ( Avena fatua )
A pot experiment was designed to investigate the effects of full, above and below ground interactions of wheat with wild oat on leaf characteristics and root to shoot ratio. This experiment was conducted as a factorial based on randomized complete design with four replications. The treatments included four interference levels (above ground, below ground, above and below ground and check wheat a...
متن کامل