Abstract:

In order to explore the effect of low temperature during the flowering period in Brassica napus,Brassica napus L.GZhui(strong resistance to winter cold)and 10B(weak resistance to winter cold)were used as test materials,low-temperature stress (14 h, 12 ℃ at daytime; 10 h, 2 ℃ at nighttime) to these materials for 1, 2, 3, 4, 5 d, and normal environment(14 h,22 ℃ at daytime;10 h,18 ℃ at nighttime)as control,determine the changes of physiological indexes in bolting stem leaves and lower leaves under low-temperature stress,as well as pollen viability and stigma receptivity after the opening of flower buds of different length.The research results showed that the leaves of the two materials were slightly wilted after low-temperature treatment,and there was no obvious damage to the shape of the plants in all treatments,the changes of various physiological indexes of leaves after low-temperature treatment were more complicated,and the three antioxidant enzymes were sensitive to peroxidase(POD),and most of the antioxidant was significantly increased,lower leaves more than bolting stem leaves.The content of soluble sugar(SS)in osmotic adjustment substances changed significantly,GZhui increased significantly.Malondialdehyde(MDA)content increased significantly,10B more than GZhui,and the lower leaves and bolting stem leaves showed different performances.For flower buds larger than 6.0 mm,the pollen viability of the two materials was little affected by low-temperature treatment for 4 days.For less than 3.0 mm of flower buds,the development stopped and eventually died for more than 4 days of cold stress,and the pollen viability decreased significantly after 2—3 days of stress.After the flower buds of all levels,less than 6.0 mm were under low-temperature stress,the pollen viability of GZhui was higher than that of 10B,and the difference was obvious with the flower buds of 3.0—6.0 mm,so it was considered that the 3.0—6.0 mm flower buds could be used as an indicator for identifying different varieties of low-temperature tolerance during flowering.The performance of stigma receptivity was consistent with the trend of pollen vigor.The stigma receptivity of flower buds larger than 3.0 mm was not affected within 3 days of low-temperature treatment,and the receptivity of stigma more than 4 days of treatment was reduced;the flower buds smaller than 3.0 mm,the receptivity of stigma decreased to varying degrees within 3 days of low-temperature treatment.These results indicated that flower buds(smaller than 3.0 mm)were more sensitive to low temperature,resulting in reduced pollen vitality and stigma receptivity,and even abortion.

Key words: Brassica napus L., Flowering stage, Cold stress, Physiological activity, Pollen viability, Stigma receptivity