The Effects Of Different Nutrient Deficiencies On Vegetative Growth And The Expressions Of Root Growth-related Genes In Rapeseed Seedlings(Brassica Napus L.)

Nutrients are important for plant growth and development, nutrient deficiency severely inhibits the yield and quality of crops. Currently, researches concern about nutrient deficiency mainly focused on the effects of N deficiency, P deficiency, K deficiency, and B deficiency on the yield and shoot phenotype of rapeseed plant, respectively. However, the effects of different nutrient deficiencies on pigments content, roots morphological change, nutrients uptake and utilization is still unknown. Rapeseed cultivar ‘ZS11’ and the hydroponic system were employed to investigate the effects of different nutrient deficiencies in this study, including N, P, K, Ca, Mg, B, Fe, Cu and Zn deficiencies, on the symptoms of nutrient deficiency, pigments content, root morphological changes, and nutrients uptake and utilization of rapeseed seedlings. In addition, the expressions of several root growth-related genes were determined through q RT-PCR in root samples, which selected from the rapeseed seedlings under the treatments with significant root morphological changes. And the possible reasons for the morphological changes of rapeseed roots under nutrient deficiencies conditions were further analyzed. The main results were summarized as follows:(1) Rapeseed seedlings exhibited typical symptoms under different nutrient deficiencies, the growth of rapeseed seedlings were significantly affected by the deficiencies of macro-nutrients, such as N, P, K. Furthermore, the deficiencies of mid- and micro-nutrients, such as Ca, Mg, B, Fe, Cu, Zn, also inhibited the growth of rapeseed seedlings in some degree. Leaves showed different symptoms under different nutrient deficiencies, which were consistent to the changes of pigments content under different nutrient deficiencies conditions. The deficiencies of N、P、K、B、Fe markedly decreased the chlorophyll contents in young leaves of rapeseed, while N、P、B deficiencies dramatically increased the anthocyanin content of old leaves.(2) Nutrient deficiencies had significant influences on root morphology of rapeseed seedlings. N deficiency significantly increased rapeseed roots growth after 28 days treatments, as indicated by 130.7% and 68.4% increase in primary root length and total lateral root length, respectively. And P, Fe deficiencies also increased the length of lateral roots. While K, Ca and B deficiencies severely inhibited roots growth of rapeseed, as indicated by 33.8%、35.1%、41.4% and 88.6%、62.1%、80.8% decrease in primary and lateral root growth, respectively.(3) The concentration and content of nutrient elements in rapeseed seedlings were also affected by different nutrient deficiencies. Except for K and Fe, elements concentration showed increased trend among most of treatments, while N deficiency significantly decreased K and Fe concentration in the leaves. For another, elements content were decreased in the leaves of all treatments except Fe deficiency. Compared with the leaves, there were no significant difference among all elements concentration except Fe, Cu and Zn, however, the content of all elements exhibited decreased tendency. Of note, the concentration and content of Fe showed dramatic changes under different nutrient deficiencies. Iron concentrations were increased in the roots of all treatments, while Fe contents were significantly increased in the roots of N-, Ca-, and Mg-deficient seedlings.(4) Rapeseed roots exhibited significant and reversed morphological changes under N deficiency and B deficiency conditions. N deficiency promoted rapeseed roots growth, the expressions of several genes involved in cell wall metabolism were significantly up regulated by N deficiency in the roots, including EXPB, CESA, and XTH genes. However, the expressions of CESA and XTH were obviously reduced in N-deficient roots, these might inhibit the root growth of rapeseed seedlings. The expressions of these two genes showed opposite trend as root morphological changes.In this study, the effects of different nutrient deficiencies on vegetative growth, pigments content, roots morphological changes, nutrients uptake and utilization, and the expressions of several root growth-related genes were comprehensive and systematic analyzed. It will contribute to explain the possible reasons for the morphological changes of rapeseed roots under nutrient deficiencies conditions, and will provide a theoretical basis for the physiology and molecular mechanisms of rapeseed plants response to nutrient deficiency stress in the future.