Regulation Of Uniconazole Of Soybean Root At Seedling Stage Under Drought Stress

Drought is one of the major problems facing global agricultural production.Uniconazole is an efficient triazole plant growth regulator,which plays a key role in improving plant stress resistance.In order to clarify the effect of drought stress on the root system formation of soybean at seedling stage and the regulation effect of uniconazole after drought stress,drought-resistant variety Hefeng 50 and drought-sensitive variety Kenfeng 16 were used as materials.The root morphology,microstructure and ultrastructure,antioxidant enzyme system,osmotic regulation substance content,hormones content and stress-resistant gene expression were determined under continuous drought stress by using potting test to study the effect and mechanism of uniconazole on soybean root system at seedling stage under drought stress.The main results are as follows:1.With the prolongation of water cut-off time,the level of drought increased gradually.At120 h after treatment,the difference of root morphological indexes in each treatment of two soybean varieties reached the largest.The total root length,root surface area,root volume,root tip number,root average diameter and root dry weight in uniconazole soaking treatment of Hefeng 50 were 9.27 %,16.47 %,19.43 %,15.94 %,19.49 % and 21.50 % higher than those in water soaking treatment,respectively;6.10 %,12.80 %,38.51 %,10.28 %,12.48 % and 16.98 %higher than those in water soaking treatment of Kenfeng16.Uniconazole could effectively alleviate the inhibition of drought stress on root growth and development of two varieties.2.At 48 h after water cut-off treatment,the root microstructure in water soaking treatment of two soybean varieties showed that the diameter of middle column sheath,and the cross-sectional area of xylem and phloem decreased,cortical cells lose water and cause plasmolysis;at 96 h after treatment,columnar cells lose water and caused plasmolysis,vessel lignified and root morphology was shriveled and deformed,the xylem cells in water soaking treatment of Kenfeng 16 were shriveled seriously and could not observe the normal morphology.While the the diameter of middle column sheath,and the cross-sectional area of xylem and phloem were larger in uniconazole soaking treatment of two varieties than that in water soaking treatment.After 96 h after treatment,the whole root morphology did not shrink and deform.3.At 48 h after water cut-off treatment,the root ultrastructure in water soaking treatment of two soybean varieties showed that a large number of cavities and the cristaes reduction werefound in mitochondria and the nucleus were deformed;at 96 h after treatment,the outer membranes of mitochondria partly disappeared,the cavities and cristae disappeared became more obvious,the mitochondria internal degradation occurred and some contents exudated,the nucleolus disappeared,the chromatin condensed and marginalized.While,at 48 h after treatment,a few cavities and the cristaes reduction were found in the mitochondria,the nucleus were not affected in uniconazole soaking treatment of two soybean varieties;at 96 h after treatment,the phenomenon of cavities became more serious,but no degradation occurred inside,the nucleolar disappeared,the chromatin condensed and marginalized.4.Under drought stress condition,uniconazole soaking treatment could decrease the roots MDA content and relative conductivity of of Hefeng 50 and Kenfeng 16.The root SOD activity of the two varieties reached the maximum at 96 h and 72 h after treatment,SOD activity in uniconazole soaking treatment were 14.73 % and 15.69 % higher than water soaking treatment,respectively.The difference of POD,CAT,PPO activity reached the maximum at 120 h after treatment,the activity of POD,CAT,PPO in uniconazole soaking treatment of two varieties were49.36 %,41.28 %,71.02 % and 23.16 %,43.44 %,62.88 % than that in water soaking treatment,respectively.At 120 h after treatment,the content of soluble sugar,soluble protein,proline in uniconazole soaking treatment of two varieties were 49.36 %,41.28 %,71.02 % and 23.16 %,43.44 %,62.88 % higher than that in water soaking treatment,respectively.Uniconazole could alleviate the root oxidative damage and enhance drought resistance of two soybean varieties.5.At 48 h after water cut-off treatment,the contents of IAA and ABA in uniconazole soaking treatment of Hefeng 50 and Kenfeng 16 roots were 25.02 %,88.22 % and 23.88 %,15.69 % higher than that in water soaking treatment,respectively.At 96 h after treatment,the contents of IAA and ABA in uniconazole soaking treatment of Hefeng 50 root were 52.84 % and77.55 % higher than that in water soaking treatment;the contents of IAA in uniconazole soaking treatment of Kenfeng 16 root was 52.17 % higher than that in water soaking treatment.Under drought stress,uniconazole could decrease the GA3 content of Hefeng 50 root and increase the GA3 content of Kenfeng 16 root.At 96 h after treatment,the contents of ZT in uniconazole soaking treatment of Hefeng 50 and Kenfeng 16 roots were increased 76.00 % and 49.23 % than that in water soaking treatment.6.At 48 h after water cut-off treatment,for NAC transcription factors,the expression ofGmNAC003,GmNAC004,GmNAC015,GmNAC020 in uniconazole soaking treatment of Hefeng50 root were 1.76,3.14,3.11,1.49 times higher than that in water soaking treatment,respectively.The expression of GmNAC003,GmNAC004,GmNAC020 in uniconazole soaking treatment of Kenfeng 16 root were 1.77,1.09,1.61 times higher than that in water soaking treatment,respectively.For two-component system,the expression of Gm HK07,Gm RR01,Gm RR02 in uniconazole soaking treatment of Hefeng 50 root were 1.03,1.24,1.12 times higher than that in water soaking treatment,respectively.The expression of Gm HK07,Gm RR01,Gm RR16 and in uniconazole soaking treatment of Kenfeng 16 root were 1.72,1.12,1.95 times higher than that in water soaking treatment,respectively.The regulate effect of uniconazole was not obvious at 96 h after treatment.In conclusion,uniconazole alleviated the effect of drought stress on soybean root formation by promoting the growth and development of root system,reducing the damage of root structure and organelle,enhancing the activity of antioxidant enzymes,and increasing the content of osmotic regulators and hormones.