Riboflavin induced tolerance against the root-knot nematode Melopidogyne graminicola in rice

Abstract

The role of plant hormones such as Salicylic acid, Jasmonic acid and Ethylene in plant defense has been largely investigated particularly in dicotyledonous plants. Riboflavin has also shown effects on plant physiology but its role in plant defense/tolerance is yet to be elucidated.

Rice plantlets were randomly grown in laboratory, sprayed with hormones and riboflavin 24 hours before their infection by the nematodes meloidogyne gramicola juvenile 2. Two types of infection experiments were done. The normal rice nipponbare susceptible to M. gramincola infection was used in the first while in the second series experiments four transgenics/mutants were used. The shoots length, roots length and the roots weight were measured. The numbers of galls per plant were counted under a stereomicroscope. The relative expression of the genes Osein2b, Oswrky 45, OsJAmyb and OsNPR1 was evaluated using the qRT-PCR method.

It was noticed that the plantlets treated with BTH significantly developed less galls compared to control (P = 0.000<0.05). This was also observed with ETHEPHON and MeJA spray (P =0.001 and P = 0.000 <0.005 respectively). The treatment with riboflavin didn’t show a significant effect (P = 0.61>0.05) in comparison with the control. However these plants grew taller enough with a strong roots system except for OsNPR1antisense line which developed more galls than others tested plants.

The foliar supply of riboflavin on rice significantly upregulated OsNPR1 in leaves and roots of rice plantlets. OsWRKY45 was also upregulated in both leaves and root samples.

Keywords: Riboflavin, systemic tolerance, transgenics/mutants, gene expression