Department of Crop and Soil Sciences, Washington State University Pullman, WA, USA.
Root Disease and Biological Control Research Unit, United States Department of Agriculture - Agricultural Research Service, Washington State University Pullman, WA, USA.
Front Plant Sci. 2014 Dec 10;5:689. doi: 10.3389/fpls.2014.00689. eCollection 2014.
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 the plant defense enzyme, polyphenol oxidase (PPO), when wild oat (Avena fatua L.) caryopses and seeds were challenged with seed-decaying Fusarium fungi. These studies suggest that dormant seeds are capable of mounting a defense response to pathogens. The pathogen-induced PPO activity from wild oat was attributed to a soluble isoform of the enzyme that appeared to result, at least in part, from proteolytic activation of a latent PPO isoform. PPO activity was also induced in wild oat hulls (lemma and palea), non-living tissues that cover and protect the caryopsis. These results are consistent with the hypothesis that seeds possess inducible enzyme-based biochemical defenses arrayed on the exterior of seeds and these defenses represent a fundamental mechanism of seed survival and longevity in the soil. Enzyme-based biochemical defenses may have broader implications since they may apply to other defense enzymes as well as to a diversity of plant species and ecosystems.
种子休眠和抗腐烂是基本的生存策略，使种子种群能够在很长一段时间内发芽。种子具有物理、化学和生物防御机制，可保护其食物储备免受腐烂诱导生物和草食动物的侵害。在这里，我们假设种子也具有基于酶的生化防御机制，这是基于在受到腐烂真菌的野生燕麦（Avena fatua L.）颖果和种子的挑战时，植物防御酶多酚氧化酶（PPO）的诱导。这些研究表明，休眠种子能够对病原体发起防御反应。来自野生燕麦的病原体诱导的 PPO 活性归因于该酶的可溶性同工型，该同工型似乎至少部分来自潜伏 PPO 同工型的蛋白水解激活。在野生燕麦的外壳（内稃和外稃）中也诱导了 PPO 活性，外壳是覆盖和保护颖果的非生活组织。这些结果与种子具有排列在种子外部的可诱导酶基生化防御的假设一致，这些防御代表了种子在土壤中生存和长寿的基本机制。基于酶的生化防御可能具有更广泛的意义，因为它们可能适用于其他防御酶以及多种植物物种和生态系统。
