Suppression of ROS generation mediated by higher InsP3 level is critical for the delay of seed germination in lpa rice

Abstract

The breeding of low phytic acid (lpa) crop is considered as an effective strategy to improve crop nutrition, but these crops have an inferior performance in seed germination. In this paper, two rice genotypes, cv. 9311 and its lpa mutant (9311-lpa), were used to clarify the relationship of InsP3 and ROS concentration in sprouting seeds with the occurrence of retarded seed germination for lpa crop. Results showed that the inferior performance of seed germination for 9311-lpa was mostly characterized by the delay of seed germination progression, with insignificant difference in seed germination rate between the two genotypes after a longer imbibition duration. The retarded seed germination of 9311-lpa was closely associated with the genotypic difference in InsP3 and ROS concentrations in germinating seeds, with the considerably higher InsP3 level and lower ROS concentration for 9311-lpa relative to the wild type. Under an appropriate range of concentration, exogenous H2O2 treatment promoted seed germination, while the activator of InsP3 (m-3M3FBS) had an inhibitory effect on seed germination. The delay of seed germination occurred mainly as the results of the higher InsP3 level and the lower ROS concentration in the germinating seeds of 9311-lpa. Furthermore, the germinating seeds of 9311-lpa had relatively lower activities of ROS scavenging enzymes (SOD, CAT, POD, and APX) and ROS generating enzyme (NOX) than those of the wild type. m-3M3FBS significantly suppressed NOX activity and NOX transcripts in sprouting seeds, which then resulted in the lowered ROS generation in sprouting seeds and the decreased seed germination rate. Thus, the retarded seed germination of 9311-lpa, with lower ROS level in germinating seeds, was mostly caused by the weaker ability of ROS generation in the presence of higher InsP3 level, rather than the effective detoxification of ROS burst during seed germination.