Department of Botany, University College of Science, Abdul Wali Khan University Mardan, Shankar Campus, Mardan, Pakistan,
Curr Microbiol. 2013 Nov;67(5):624-30. doi: 10.1007/s00284-013-0408-4. Epub 2013 Jun 21.
Nostoc, a nitrogen-fixing cyanobacterium, has great potential to make symbiotic associations with a wide range of plants and benefit its hosts with nitrogen in the form of nitrates. It may also use phytohormones as a tool to promote plant growth. Phytohormones [cytokinin (Ck) and IAA] were determined in the culture of an endophytic Nostoc isolated from rice roots. The strain was able to accumulate as well as release phytohormones to the culture media. Optimum growth conditions for the production of zeatin and IAA were a temperature of 25 °C and a pH of 8.0. Time-dependent increase in the accumulation and release of phytohormones was recorded. To evaluate the impact of cytokinins, an ipt knockout mutant in the background of Nostoc was generated by homologous recombination method. A sharp decline (up to 80 %) in the zeatin content was observed in the culture of mutant strain Nostoc AHM-12. Association of the mutant and wild type strain with rice and wheat roots was studied under axenic conditions. The efficacy of Nostoc to colonize plant root was significantly reduced (P < 0.05) as a result of ipt inactivation as evident by low chlorophyll a concentration in the roots. In contrast to the mutant strain, wild type strain showed good association with the roots and enhanced several growth parameters, such as fresh weight, dry weight, shoot length, and root length of the crop plants. The study clearly demonstrated that Ck is a tool of endophytic Nostoc to colonize plant root and promote its growth.
念珠藻是一种固氮蓝藻，具有与广泛的植物形成共生关系的巨大潜力，并以硝酸盐的形式为其宿主提供氮。它还可能利用植物激素作为促进植物生长的工具。在从水稻根部分离的内生念珠藻的培养物中确定了植物激素[细胞分裂素（Ck）和 IAA]。该菌株能够积累并向培养基中释放植物激素。生产玉米素和 IAA 的最佳生长条件是温度为 25°C 和 pH 值为 8.0。记录了植物激素积累和释放的时间依赖性增加。为了评估细胞分裂素的影响，通过同源重组方法在念珠藻的背景下生成了 ipt 敲除突变体。突变菌株 Nostoc AHM-12 的玉米素含量急剧下降（高达 80%）。在无菌条件下研究了突变体和野生型菌株与水稻和小麦根的关联。ipt 失活导致 Nostoc 定植植物根的功效显著降低（P < 0.05），这表现在根中的叶绿素 a 浓度较低。与突变体菌株相比，野生型菌株与根的关联良好，并增强了作物植物的几个生长参数，如鲜重、干重、茎长和根长。该研究清楚地表明，Ck 是内生念珠藻定植植物根并促进其生长的工具。
