Greenfield Lucy M, Hill Paul W, Paterson Eric, Baggs Elizabeth M, Jones Davey L
School of Natural Sciences, Bangor University, Gwynedd, LL57 2UW UK.
The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH UK.
Plant Soil. 2020;456(1):355-367. doi: 10.1007/s11104-020-04719-6. Epub 2020 Sep 23.
The capacity of plant roots to directly acquire organic nitrogen (N) in the form of oligopeptides and amino acids from soil is well established. However, plants have poor access to protein, the central reservoir of soil organic N. Our question is: do plants actively secrete proteases to enhance the breakdown of soil protein or are they functionally reliant on soil microorganisms to undertake this role?
Growing maize and wheat under sterile hydroponic conditions with and without inorganic N, we measured protease activity on the root surface (root-bound proteases) or exogenously in the solution (free proteases). We compared root protease activities to the rhizosphere microbial community to estimate the ecological significance of root-derived proteases.
We found little evidence for the secretion of free proteases, with almost all protease activity associated with the root surface. Root protease activity was not stimulated under N deficiency. Our findings suggest that cereal roots contribute one-fifth of rhizosphere protease activity.
Our results indicate that plant N uptake is only functionally significant when soil protein is in direct contact with root surfaces. The lack of protease upregulation under N deficiency suggests that root protease activity is unrelated to enhanced soil N capture.
植物根系直接从土壤中获取寡肽和氨基酸形式的有机氮的能力已得到充分证实。然而，植物难以获取土壤有机氮的主要储存库——蛋白质。我们的问题是：植物是主动分泌蛋白酶以促进土壤蛋白质的分解，还是在功能上依赖土壤微生物来承担这一作用？
在有无无机氮的无菌水培条件下种植玉米和小麦，我们测量了根表面的蛋白酶活性（根结合蛋白酶）或溶液中外源的蛋白酶活性（游离蛋白酶）。我们将根蛋白酶活性与根际微生物群落进行比较，以评估根源蛋白酶的生态意义。
我们几乎没有发现游离蛋白酶分泌的证据，几乎所有蛋白酶活性都与根表面相关。缺氮条件下根蛋白酶活性未受到刺激。我们的研究结果表明，谷类作物根系贡献了根际蛋白酶活性的五分之一。
我们的结果表明，只有当土壤蛋白质与根表面直接接触时，植物对氮的吸收才具有功能意义。缺氮条件下蛋白酶未上调表明根蛋白酶活性与增强土壤氮捕获无关。
