Fuerst E Patrick, James Matthew S, Pollard Anne T, Okubara Patricia A
Department of Crop and Soil Sciences and Western Wheat Quality Laboratory, Washington State University, Pullman, WA, United States.
Department of Crop and Soil Sciences, Washington State University, Pullman, WA, United States.
Front Plant Sci. 2018 Jan 23;8:2259. doi: 10.3389/fpls.2017.02259. eCollection 2017.
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 strain .1 was relatively rapid in wild oat ( L.) isoline "M73," with >50% decay after 8 days with almost no decay in wheat ( 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 .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 .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 .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 .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.
种子具有完善的被动物理和化学防御机制，可保护其食物储备免受导致腐烂的生物体和食草动物的侵害。然而，很少有研究评估休眠种子对病原体的潜在生化防御。致病菌株.1引起的颖果腐烂在野生燕麦（L.）近等基因系“M73”中相对较快，8天后腐烂率超过50%，而小麦（L.）品种RL4137几乎没有腐烂。因此，相对于小麦，这种真菌菌株具有选择性使野生燕麦腐烂的潜力。为了研究防御酶活性，将野生燕麦和小麦颖果与.1一起培养2 - 3天。将整个颖果在测定试剂中培养以测量外在防御酶活性。在两种植物中，多酚氧化酶、外切几丁质酶和过氧化物酶在整个颖果中被诱导，但草酸氧化酶减少。为了评估防御酶活性是否从颖果表面释放，用缓冲液冲洗颖果并测量渗滤液中的酶活性。多酚氧化酶、外切几丁质酶和过氧化物酶有显著活性，但草酸氧化酶没有，从颖果中被浸出。在所评估的野生燕麦和小麦基因型中，防御酶反应在质量上相似。虽然整个颖果中的绝对酶活性通常比渗滤液中的高，但.1对多酚氧化酶、外切几丁质酶和过氧化物酶的相对诱导程度在颖果渗滤液中更大，这表明诱导活性中有不成比例的量从颖果表面释放到环境中，这与其假定的防御作用一致。这里研究的特定防御酶不太可能在这两种基因型对.1腐烂的不同易感性中起关键作用，因为与小麦相比，在更易感的野生燕麦中防御酶活性更高。结果与以下假设一致：（1）休眠种子能够对病原体产生复杂反应；（2）多种防御酶参与多种植物物种的反应；（3）有可能鉴定出能够选择性使杂草种子腐烂而不损害作物种子的真菌，这一概念可能适用于田间杂草管理。虽然早期关于种子防御的工作证明了被动防御的存在，但这项工作表明休眠种子也相当敏感，能够响应病原体激活并释放防御酶。
