School of Applied Biosciences, Kyungpook National University, Daegu, Republic of Korea.
BMC Microbiol. 2012 Jan 12;12:3. doi: 10.1186/1471-2180-12-3.
Endophytic fungi are little known for exogenous secretion of phytohormones and mitigation of salinity stress, which is a major limiting factor for agriculture production worldwide. Current study was designed to isolate phytohormone producing endophytic fungus from the roots of cucumber plant and identify its role in plant growth and stress tolerance under saline conditions.
We isolated nine endophytic fungi from the roots of cucumber plant and screened their culture filtrates (CF) on gibberellins (GAs) deficient mutant rice cultivar Waito-C and normal GAs biosynthesis rice cultivar Dongjin-byeo. The CF of a fungal isolate CSH-6H significantly increased the growth of Waito-C and Dongjin-byeo seedlings as compared to control. Analysis of the CF showed presence of GAs (GA1, GA3, GA4, GA8, GA9, GA12, GA20 and GA24) and indole acetic acid. The endophyte CSH-6H was identified as a strain of Paecilomyces formosus LHL10 on the basis of phylogenetic analysis of ITS sequence similarity. Under salinity stress, P. formosus inoculation significantly enhanced cucumber shoot length and allied growth characteristics as compared to non-inoculated control plants. The hypha of P. formosus was also observed in the cortical and pericycle regions of the host-plant roots and was successfully re-isolated using PCR techniques. P. formosus association counteracted the adverse effects of salinity by accumulating proline and antioxidants and maintaining plant water potential. Thus the electrolytic leakage and membrane damage to the cucumber plants was reduced in the association of endophyte. Reduced content of stress responsive abscisic acid suggest lesser stress convened to endophyte-associated plants. On contrary, elevated endogenous GAs (GA3, GA4, GA12 and GA20) contents in endophyte-associated cucumber plants evidenced salinity stress modulation.
The results reveal that mutualistic interactions of phytohormones secreting endophytic fungi can ameliorate host plant growth and alleviate adverse effects of salt stress. Such fungal strain could be used for further field trials to improve agricultural productivity under saline conditions.
内生真菌在植物激素的外分泌和缓解盐胁迫方面鲜为人知，而盐胁迫是全球农业生产的主要限制因素。本研究旨在从黄瓜根系中分离具有产植物激素能力的内生真菌，并鉴定其在盐胁迫条件下对植物生长和胁迫耐受的作用。
我们从黄瓜根系中分离出 9 株内生真菌，并在赤霉素（GA）缺陷型水稻品种 Waito-C 和正常 GA 生物合成水稻品种 Dongjin-byeo 上筛选其培养滤液（CF）。真菌分离株 CSH-6H 的 CF 显著促进了 Waito-C 和 Dongjin-byeo 幼苗的生长，与对照相比。CF 分析表明存在赤霉素（GA1、GA3、GA4、GA8、GA9、GA12、GA20 和 GA24）和吲哚乙酸。根据 ITS 序列相似性的系统发育分析，内生真菌 CSH-6H 被鉴定为拟青霉 LHL10 菌株。在盐胁迫下，与未接种对照植物相比，接种拟青霉显著提高了黄瓜茎长和相关生长特性。在宿主植物根系的皮层和周皮区也观察到拟青霉的菌丝，并成功地使用 PCR 技术重新分离。拟青霉的共生通过积累脯氨酸和抗氧化剂并维持植物水势来抵消盐胁迫的不利影响。因此，在共生体中，电渗析和对黄瓜植物的膜损伤减少。与胁迫相关的脱落酸含量的降低表明，与内生菌相关的植物受到的胁迫较小。相反，在内生菌相关的黄瓜植物中，内源 GA（GA3、GA4、GA12 和 GA20）含量的升高表明盐胁迫得到了调节。
结果表明，分泌植物激素的互惠共生内生真菌可以改善宿主植物的生长，缓解盐胁迫的不利影响。这种真菌菌株可用于进一步的田间试验，以提高盐胁迫条件下的农业生产力。
