Piriformospora indica colonization promotes the root growth of Dimocarpus longan seedlings

As a mutualistic endophyte, the host range of Piriformospora indica is very broad and its promoting effects on host plant growth and development have been increasingly reported. In this study, we investigated the influence of P. indica colonization on the growth of longan (Dimocarpus longan Lour.) seedlings and found that the root length and root number, chlorophyll content in leaf, and flavonoid contents in both leaf and stem of P. indica colonized longan seedlings were significantly higher than those of the noncolonized controls. To reveal its promoting mechanism, activities of several antioxidant enzymes, contents of some antioxidant related molecules and phytohormones were measured. Results showed that the peroxidase (POD) activity (indicator of rooting ability) and indole-3-acetic acid (IAA, a root growth promoting phytohormone) content in P. indica colonized roots were both significantly higher than controls. Moreover, P. indica colonization reduced the accumulations of hydrogen peroxide (H2O2), malondialdehyde (MDA) and jasmonic acid (JA) in longan roots. Our results indicated that P. indica colonization improved the rooting ability of longan through inducing the IAA biosynthesis and POD activity, facilitated and accelerated the root growth by reducing H2O2 accumulation and suppressing the JA accumulation.