Inter-auricular distance: A morphological biomarker for ethylene production in the boot and coincidental grain loss of rice plant

Abstract

Inter-auricular distance (IAD) has been often used for physical calibration of defects in panicle emergence of rice plants induced by stress-prone environments or cytoplasmic male sterility genetic factors slackening male gametogenesis. Information is scant on the physiological relationship inherent between IAD, panicle enclosure, and spikelet filling despite the wide phenotypic diversity of rice cultural types. In the present study, IAD extension and grain filling pattern in the panicle of the main shoot of rice cultivars contrasting for spikelet sterility were assessed concerning physiological factors like assimilate homeostasis, ethylene evolution, and expression of ethylene signal transducers genes at the anthesis stage of development. The panicle retention time was longer and the concentration and expression of ethylene and its transducer protein genes respectively, were higher in high sterile cultivars compared to low sterile ones. Spikelets subjected to a high concentration of ethylene for a longer time interval filled poorly because of infringement of starch synthesis in the post-anthesis stage of development. Alternatively, faster release of panicle by enhanced IAD extension shortened the exposure time and marginalized inhibitory effects of ethylene on grain filling. Rapid IAD extension and attenuation of boot ethylene production could be beneficial for male gametogenesis and grain filling.