Heat Stress Is More Damaging to Superior Spikelets than Inferiors of Rice (Oryza sativa L.) due to Their Different Organ Temperatures.

Guanfu Fu,Baohua Feng,Xiufu Zhang,Tingting Chen,Xia Zhao,Caixia Zhang,Longxing Tao,Qianyu Jin,Xueqin Yang,Yongjie Yang

doi:10.3389/fpls.2016.01637

Guanfu Fu, Baohua Feng + Show 8 more

Open Access

https://doi.org/10.3389/fpls.2016.01637

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Abstract

In general, the fertility and kernel weight of inferior spikelets of rice (Oryza Sativa L.) are obviously lower than those of superior spikelets, especially under abiotic stress. However, different responses to heat stress are seemed to show between the superior and inferior spikelet, and this response is scarcely documented that the intrinsic factors remain elusive. In order to reveal the mechanism underlying, two rice plants with different heat tolerance were subjected to heat stress of 40°C at anthesis. The results indicated that a greater decrease in fertility and kernel weight was observed in superior spikelets compared to inferior spikelets. This decrease was primarily ascribed to their different organ temperatures, in which the temperature of the superior spikelets was significantly higher than that of inferior spikelets. We inferred the differences in canopy temperature, light intensity and panicle types, were the primary reasons for the temperature difference between superior and inferior spikelets. Under heat stress, the fertility and kernel weight of superior and inferior spikelets decreased as the panicle numbers per plant were reduced, which was accompanied by significantly increasing the canopy temperatures. Thus, it was suggested that the rice plant with characteristic features of an upright growth habit and loose panicles might be more susceptible to heat stress resulting from their higher canopy and spikelets temperatures.

Highlights

Spikelets grown within the same panicle of rice (Oryza Sativa L.) can be classified as superior spikelets and inferior spikelets, in which the former are located on apical primary branches, while the latter are located on proximal secondary branches (Mohapatra et al, 1993; Ishimaru et al, 2003)
Heat stress occurring at anthesis caused more damage to the superior spikelets than the inferiors of rice, which was mainly ascribed to their different organ temperatures
Heat stress occurring at anthesis significantly increased spikelet sterility, and higher reduce were shown in superior spikelet than inferior, which was mainly ascribed to the remarkable decrease in pollen numbers on the stigma, as well as an increase in reactive oxygen species (ROS), especially for the superior spikelets

Summary

Introduction

Spikelets grown within the same panicle of rice (Oryza Sativa L.) can be classified as superior spikelets and inferior spikelets, in which the former are located on apical primary branches, while the latter are located on proximal secondary branches (Mohapatra et al, 1993; Ishimaru et al, 2003). The superior spikelets flower earlier, fill faster and produce larger and heavier grains. The inferior spikelets flower later, exhibit a slower rate of increase in dry weight during grain development and a lower grain weight than superior spikelets (Yang et al, 2006; Dong et al, 2014). The differences in spikelet fertility, kernel weight and grain quality between the superior and inferior spikelets are more exacerbated in large panicle rice, especially the super rice (Mohapatra et al, 2009; Zhang et al, 2009).

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