Effect Of Low-Temperature Water Stress At Reproductive Stage On Growth And Nitrogen Metabolism Of Root In Cold-Region Japonica Rice

Heilongjiang province is an important japonica rice main production area and commercial japonica rice base in China,which has 3.81 million hectares cultivation area of japonica rice and 22.553 million tons total output,accounting for 10.9% of the total rice production in 2016.The stable and high yield of japonica rice in Heilongjiang province.It is an important guarantee of national food security,especially grain ration security.As the japonica rice main production area,Heilongjiang Province has frequently occurred cold damage,and has become one of the main restriction factors in the development of rice.The reproductive stage is a vital period of yield formation in rice,which is sensitive to temperature.During this period,low temperature damage seriously affects the growth and development of process,physiological and biochemical characteristics and yield formation process of rice.As the main organ of water and nutrient absorption,the growth condition and activity ability of rice root system play a vital role in the growth of rice.Nitrogen metabolism plays an important role in maintaining the balance between other metabolic pathways and physiological functions,and is one of the key basic metabolic pathways in plants.Two japonica rice varieties Dongnong 428 and Songjing 10 were used in this experiment.Low-temperature water stress was used to simulate natural cold damage in field conditions.We study the effect of low-temperature water stress at reproductive stage on morphology and nitrogen metabolism of root in cold region japonica rice.In order to ascertain the relationship among root growth,root nitrogen metabolism and yield in cold region japonica rice under low temperature stress at reproductive stage.In order to reveal the response nitrogen metabolism of root in cold-region japonica rice to low-temperature water stress at reproductive stage.Thus this research could enrich the physiological basis of nitrogen metabolism of japonica rice in cold-region,and provide the theoretical foundations of cold tolerance physiology of japonica rice in cold-region.The follows are the main conclusions from this study:1.Low-temperature water stress at reproductive stage inhibited the elongation and development of root in cold-region japonica rice,and also accelerated root senescence in cold-region japonica rice from full heading to maturity stage.Compared with the control,root length density,root volume,root surface area and root average diameter in cold-region japonica rice decreased during and after low-temperature water stress at reproductive stage,and the reductions gradually increased with the extension of low-temperature water stress time,and there are differences among treatments.The above-mentioned indexes in cold region japonica rice were no significant difference under low-temperature water stress with 3 days,and significantly decreased under low-temperature water stress with 6-15 days.The reduction of root length density,root volume and root surface area of Dongnong 428 was lower than those of Songjing 10 under low-temperature water stress,and the difference of reductions gradually increased with the extension of the low-temperature water stress time.This is one of the reasons why the yield of Dongnong 428 reductions less than that of Songjing 10.2.The physiological activity of roots in cold-region japonica rice were inhibited during low-temperature water stress at reproductive stage,and still inhibited after low-temperature water stress.Compared with the control,root oxidation activity and root bleeding intensity in cold-region japonica rice decreased during and after low-temperature water stress at reproductive stage,and the reductions gradually increased with the extension of low-temperature water stress time,and there are differences among treatments.The differences in root activity were not significant(except for root bleeding intensity of Songjing 10),and significantly decreased under low-temperature water stress with 6-15 days.The reductions of root oxidation activity and root bleeding intensity of Dongnong 428 was lower than that of Songjing 10 under low-temperature water stress,and the difference of reductions gradually increased with the extension of the low-temperature water stress time,This may be the reason why the nutrients transformation of Dongnong 428 roots is higher than that of Songjing 10.3.The changes of nitrate reductase(NR)activity of root in cold-region japonica rice varied with the number of stress days during low-temperature water stress at reproductive stage.Compared with the control,the NR activity of root in cold region japonica rice increased under the low-temperature water stress with 3-6 days,and significantly decreased under low-temperature water stress with 9-15 days,and the reductions gradually increased with the extension of the low-temperature water time.The NR activity of root in the cold region japonica rice from full heading stage to waxy stage significantly decreased after low-temperature water stress at reproductive stage,and the difference of reductions gradually increased with the extension of the low-temperature water stress time,and there are differences among treatments.Dongnong 428 can maintain higher NR activity of root than Songjing 10.4.Compared with the control,the key enzyme activities of ammonium assimilation of root in cold region japonica rice increased during and after low-temperature water stress at reproductive stage,and the enhancements gradually increased with the extension of the low-temperature water stress time,and there are differences among treatments.The glutamine synthetase(GS),glutamine-oxoglutarate aminotransferase(GOGAT)and glutamate dehydrogenase(GDH)activity of root in Dongnong 428 were no significant different under low-temperature water stress with 3 days,while those indexes in Songjing 10 significantly increased,and this indexes in cold region japonica rice significantly decreased under low-temperature water stress with 6-15 days.The increase of GS and GOGAT activity of root in Dongnong 428 was lower than that in Songjing 10 during and after low-temperature water stress,and the increase of GDH activity of root was greater than that of Songjing 10.5.Compared with the control,the glutamic oxaloacetic transaminase(GOT)and glutamic-pyruvic transaminase(GPT)of root in cold region japonica rice increased during and after low-temperature water stress at reproductive stage,and the enhancements gradually increased with the extension of the low-temperature water stress time,and there are differences among treatments.The GOT activity of root in Dongnong428 significantly increased under low-temperature water stress with 6-15 days,and the GOT activity of root in Songjing10 significantly increased under low-temperature water stress with 9-15 days.The GPT activity of root in Dongnong428 significantly increased under low-temperature water stress,and the GPT activity of root in Songjing10 significantly increased under low-temperature water stress.The increase of GOT and GPT activity of root in Dongnong 428 was greater than that in Songjing 10 during and after low-temperature water stress.6.Compared with the control,the total N accumulation and proportion of N distribution to shoot in cold region japonica rice decreased after low-temperature water stress at reproductive stage,and the reductions gradually increased with the extension of the low-temperature water stress time,and there are differences among treatments and varieties.The Root N content per unit root length and nitrogen dry matter production efficiency in cold-region japonica rice increased during and after low-temperature water stress at reproductive stage,and the enhancements gradually increased with the extension of the low-temperature water stress time,and there are differences among treatments and varieties.7.Compared with the control,the root dry weight,shoot dry weight and root-to-shoot ratio in cold-region japonica rice decreased during and after low-temperature water stress at reproductive stage,and the reductions gradually increased with the extension time of the low-temperature water stress,and there are differences among treatments and varieties.Compared with the control,the root and shoot dry weight in cold-region japonica rice were no significant different under low-temperature water stress with 3 days,and significantly decreased under low-temperature water stress with 6-15 days.The reductions of root and shoot dry weight in Dongnong 428 was lower than that in Songjing 10 during and after low-temperature water stress..8.Compared with the control,the yield and yield components in cold-region japonica rice decreased after low-temperature water stress at reproductive stage,and the reductions gradually increased with the extension time of the low-temperature water stress,and there are differences among treatments and varieties.The reduction of above-mentioned indexes of Dongnong428 was lower than that of Songjing 10,and the decline range of Dongnong 428 and Songsong 10 was 3.64%-43.05% and 17.79%-51.75%,respectively.The yield component with no significant of D3 treatment under low-temperature water stress correlated with the root morphology and vitality with no significant of D3 treatment during and after low-temperature water stress.The reason for the strongly cold tolerance of Dongnong 428 higher than that of Songjing 10 is that the higher root length density,root dry weight,root activity and root NR activity of Dongnong 428 under low-temperature water stress.It makes the nitrogen accumulation and the dry weight of aboveground in Dongnong 428 plant higher.Ultimately it makes the reduction of yield in Dongnong 428 lower than that in Songjing 10.