The Photosynthetic Characteristics in Chaling Common Wild Rice (Oryza rufipogon Griff.) under the Cold Stress

Abstract

Abstract'Chaling' common wild rice (CWR, Oryza rufipogon Griff.), found in Chaling county, Hunan province, China, is one of the only two wild rice populations grown northernmost in the world. Although the cold tolerance of 'Chaling' CWR is extremely strong, its photosynthetic characteristics under cold stress remain unknown. In this study, the photosynthetic parameters of leaves at tiller stage in 'Chaling' CWR were first determined under the conditions of cold stress (15 °C) and normal temperature (28 °C), and then compared with those in the standard rice cultivars including indica 'Guangluai 4', indica 'Y-Liangyou 1' (a Chinese hybrid rice with super high grain yield), and japonica 'Nipponbare' under the same temperature conditions. The results showed that the net photosynthetic rate, the total chlorophyll and total carotenoid contents, the maximum quantum yield of PSII, the apparent quantum yield, and the carboxylation efficiency in 'Chaling' CWR were all significantly higher than those in the standard rice cultivars under cold stress (P < 0.05). The ratios of these parameters in 'Chaling' CWR under cold stress to those under normal temperature condition were 47.9 ~ 84.9%, much higher than those in the standard rice cultivars, which were 3.1 ~ 73.8%. These results indicate that the photosynthetic characteristics of 'Chaling' CWR under cold stress are excellent. Our findings would have an enormous benefit if the trait of the cold stress tolerance of 'Chaling' CWR is transferred to the cultivated rice via the traditional breeding or molecular breeding.Keywords: apparent quantum yield, carboxylation efficiency, chlorophyll fluorescence, photosynthetic pigment, photosynthetic rate Abbreviations: A-C i curve -assimilation rate plotted against intercellular CO 2 concentration, AQY -apparent quantum yield, Car -carotenoids, CE -carboxylation efficiency, Chl -chlorophyll, CWR -common wild rice, F o -the minimal chlorophyll fluorescence value, F m -the maximum chlorophyll fluorescence value, F v /F m -variable to maximum fluorescence, P n -net photosynthetic rate.

Studies on the cold tolerance of ratoon ‘Chaling’ common wild rice

“…However, through this study, it is clear that under field conditions, even if ratoon 'Chaling' CWR was subjected to long-term low-temperature with ice and snow (the average daily mean temperature for continuous 22 days is − 1.0 °C, the average daily minimum temperature is − 1.7 °C, the average daily maximum temperature is 2.3 °C, and the extreme low temperature is − 4.7 °C), it can still safely overwinter, which is enough to support the conclusion that ratoon 'Chaling' CWR possesses strong cold tolerance and certain freeze resistance. Additionally, we found that the photosynthetic characteristics of 'Chaling' CWR under cold stress (15 °C) are superior to those of the standard rice cultivars including indica 'Guangluai 4' , indica 'Y-Liangyou 1' (a Chinese hybrid rice with super high grain yield), and japonica 'Nipponbare' at their tiller stages [11], and 'Chaling' CWR grows better than the standard rice cultivars under the cold stress. Therefore, the authors believe that 'Chaling' CWR is a valuable rice cold-tolerant germplasm which has potential utilization value in improving the cold tolerance of cultivated rice to keep its yield stable and high, and to widen its planting range of space and time, on the other hand, it is helpful to elucidate the physiological & metabolic basis and the molecular mechanism underlying its strong cold tolerance using ratoon 'Chaling' CWR as material to deepen the understanding of cold tolerance of Oryza plants.…”

“…More importantly, it is one of two wild rice populations grown northernmost in the word (the other population is 'Dongxiang' CWR, distributed in Dongxiang county, Jiangxi province, China, 28° 14′ N). Some achievements have been made on the studies of its geographical distribution and ecological environment characteristics, living habits, botanical characteristics and systematic classification, resistance to disease and pest, tolerance to abiotic stress, and photosynthetic characteristics [9][10][11][12][13][14][15]. However, the study on its cold tolerance is not enough in that only the cold tolerance of its seedling was evaluated [13], while the similar study of the other CWR populations, especially 'Dongxiang' CWR, is relatively more [16][17][18][19].…”

Identification of the blast resistance gene Picl(t) from Chaling common wild rice (Oryza rufipogon Griff.)

“…The Chaling O. rufipogon populations are located in the Huli wetland in Yaoshui town, Chaling County, Hunan Province, China (26°50′N, 113°40′E). It has been reported that Chaling common wild rice (CWR) contains some valuable traits, such as cold tolerance, high photosynthetic efficiency and disease resistance (Kang, Xu, Chen, Xu, & Chen, 2007; Li, Hou, Wei, & Sun, 2001; Mo & Xu, 2016). Although some Chaling CWR accessions showed resistance to rice blast and bacterial blight, few resistance genes have been identified.…”