Effects Of Cold Water Stress At Booting Stage On Physiology And Yield Formation Of Japonica Rice

Rice,as China’s main food crop,plays an important role in ensuring China’s food security.Heilongjiang Province is the main japonica rice producing area,but its geographical location is located in the northernmost part of China.The average annual temperature is low,resulting in frequent occurrence of low-temperature cold damage,which seriously affects grain production in Heilongjiang Province.Rice is a thermophilic crop,which is very sensitive to temperature at booting stage.Rice suffering cold stress during booting stage will affect normal physiological and metabolic processes,showing low seed setting rate and decreased yield.In this experiment,cold-sensitive japonica rice Songjing 10（SJ10）and cold-tolerant japonica rice Dongnong 428（DN428）were used as the test materials.Under the field conditions,the natural low temperature was simulated,and cold water irrigation treatments were carried out at booting stage for different days（0,5,10.15d）,denoted as D0,D5,D10,D15,to determine the antioxidant system,osmotic adjustment substance,photosynthetic characteristics,endogenous hormones,ultrastructure and yield formation rules of functional leaves and roots of japonica rice at booting stage,and systematically analyze the booting stage The effect of low temperature on the physiolo gical characteristics and yield formation of the above-ground and under-ground japonica rice in cold areas provides a reference for solving the problem of low-temperature cold damage at the booting stage of japonica rice in cold areas.（1）Compared with the control,under cold water stress at booting stage,the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）in SJ10,DN428 functional leaves and DN428 roots were significantly increased.And it increased with the extension of the number of days of cold water stress,showing D15>D10>D5.The increase of antioxidant enzyme activity in the roots of SJ10 with the extension of the number of days under cold water stress showed D10>D15>D5.After the end of cold water stress,the antio xidant enzyme activity in the functional leaves and roots of SJ10 and DN428 decreased rapidly first,then slowly.（2）Compared with the control,under cold water stress at booting stage,the content of reactive oxygen species in hydrogen peroxide（H₂O₂）,superoxide anion（O₂^-）,and malondialdehyde（MDA）in SJ10,DN428 functional leaves and roots increased significantly.Both increased with the increase of the number of cold water stress days,which showed that D15>D10>D5,and the content of active oxygen in SJ10 functional leaves and roots increased more than DN428.After the end of cold water stress,the content of reactive oxygen species in functional leaves and roots of SJ10 and DN428 decreased significantly.（3）Compared with the control,under cold water stress at booting stage,the contents of soluble sugar（SS）,soluble protein（SP）,and proline（Pro）osmotic adjustment substances in functional leaves and roots of SJ10 and DN428 increased,with the cold water stress As the number of days increased,it increased as D15>D10>D5,and the increase of DN428 osmotic adjustment substance during cold water stress was greater than that of SJ10.After cold water stress at booting stage,the contents of osmotic adjustment substances in functional leaves and roo ts of SJ10 and DN428 decreased significantly.（4）Chlorophyll a,chlorophyll b,carotenoids and total chlorophyll content of SJ10 and DN428 functional leaves showed an increasing trend and then a decreasing trend as the growth process progressed.The influence of cold water stress at booting stage on the total chlorophyll content of japonica rice in cold regions was more obvious.Under cold water stress,the total chlorophyll content was lower than that of the control,which was CK>D5>D10>D15.The photosynthetic rate（Pn）,transpiration rate（Tr）,intercellular CO ₂ concentration（Ci）,and stomatal conductance（Gs）of SJ10 and DN428 were significantly less than the control under each cold water stress treatment,and with the increase of cold water stress t ime,Pn,Tr,Ci,Gs also gradually declined.（5）In the SJ10 and DN428 functional leaves,the ABA content in the SJ10 functional leaves increased significantly with the increase of cold water stress time,and reached the maximum value under D15 treatment,while the DN428 functional leaves reached the maximum value under D5treatment.The ABA content in the root system was maximized under D15 treatment.The contents of IAA,GA₃ and ZR in functional leaves and roots of SJ10 and DN428 treatments were significantly smaller than that of the control,and showed a downward trend as the number of cold water stress days increased.（6）Under normal irrigation conditions,the chloroplast structure of SJ10 and DN428 is intact,and it is oval or spindle-shaped and clings to the cell wall,and the thylakoid layers are very clear.Under cold water stress at booting stage,the chloroplast structure of SJ10 and DN428 showed chaotic structure,swelling,and the internal thylakoid lamellar structure disintegrated or disappeared.Compared with the control,cold water stress significantly inhibited the anther development of japonica rice in cold regions.Cold water stress will destroy the anther structure,causing cavities in the pollen tube,and the tapetum will gradually disapp ear.The effect of cold water stress on chloroplast and anther ultrastructure of SJ10 was greater than that of DN428.（7）Compared with the control,the average filling rate（GRmean）and maximum filling rate（GRmax）of the strong and weak grains of SJ10 and DN428 decreased with the increase of cold water stress time.The number of days to reach the maximum filling rate（Tmax）and the duration of filling period（D）increased with the increase of cold water stress time at booting stage.Compared with weak grains,strong grains have higher GRmean and GRmax.Reaching Tmax is faster and D is shorter.In terms of varieties,under cold water stress at booting stage,the strong and weak grains of SJ10 under each treatment had higher Tmax and GRmean than DN428.（8）Compared with the control,the primary and secondary spikelets,total spikelet differentiation number and existing number of SJ10 and DN428 decreased with the extension of cold water stress time,and the degradation number and degradation rate increased wit h the extension of cold water stress time.From the degradation rate,it can be seen that the cold water stress at booting stage has a greater effect on SJ10 spikelet formation than DN428.（9）With the progress of the development of japonica rice in cold r egions,the total dry matter accumulation and grain dry matter accumulation of SJ10 and DN428 gradually increased.Compared with the control,under different cold water stress treatments,the total dry matter accumulation and grain dry matter accumulation were significantly lower than the control,and significantly decreased with the increase of cold water treatment time,the difference between the treatments was significant.The effect of cold water stress on the accumulation of dry matter in SJ10 was greater than that of DN428.（10）The yield decreased gradually with the increase of cold water stress time.Cold water stress at booting stage has a significant effect on the yield components of cold-season japonica rice.Compared with the control,the number of grains per panicle,seed setting rate,and 1000-grain weight of SJ10 and DN428 showed a gradual downward trend with the prolongation of low temperature stress.Judging from the decreasing extent of cold water stress at booting stage on the yield component factors of cold region japonica rice,cold water stress at booting stage has a greater influence on the seed setting rate and 1000-grain weight of cold region japonica rice.