Effects of freezing stress on leaf structure and physiological indices of Brassica napus L.with different cold resistance
In this study,different cold-tolerant Brassica napus L.growing in northern China were treated with freezing to compare their physiological differences.The strong cold-tolerant line 2016TS(G)10 and the weak cold-tolerant variety Tianyou 2288 as the materials were subjected to freezing at-2℃.The plant morphology,leaf micro-structure and ultrastructure were observed,and the relative electrical conductivity(REL),malondialdehyde(MDA),soluble protein(SP),soluble sugar(SS),proline(Pro)content,net photosynthesis rate(Pn),inter-cellular carbon dioxide(Ci),and chlorophyll content were measured.The results showed that the most significant differences in plant morphology and survival rate between the strong cold-tolerant line 2016TS(G)10 and the weak cold-tolerant variety Tianyou 2288 were observed when exposed to-2℃.The physiological indicators of the two ma-terials,including REL,MDA,SP,SS,Pro content,Pn,Ci,chlorophyll a,chlorophyll b content,and chlorophyll a/b,changed in a similar trend,but the SP and SS content of the strong cold-tolerant line 2016TS(G)10 were 5.10%and 29.69%higher than those of in Tianyou 2288(P≤0.01),respectively,and the REL and MDA content were 4.8%and 17.9%lower(P≤0.01).The chloroplast structure of 2016TS(G)10 remained intact,with a more accumulation of starch grains,while the chloroplasts of Tianyou 2288 were broken and degraded,with no presence of starch grains.After being recovered at room temperature for 48 hours,the 2016TS(G)10 exhibited a stronger re-covery in plant morphology and Pn.Therefore,the cold tolerance of northern strong winter rapeseed should be eval-uated under freezing stress ranging from 0℃to-4℃.The stability and number of chloroplasts,especially the accu-mulation of starch granules,is an important factor affecting the cold resistance of winter rapeseed planted in north-ern China.