Toxic Effects Of Cadmium And The Regulation Of Toxicity Via External Application Of Plant Growth Regulators In Oilseed Rape (Brassica Napus)

Oilseed rape (Brassica napus) is a species belonging to the family Cruciferae. It consists of the genome C from Brassica oleracea and the genome A from Brassica campestris. It is interested to be applied as pioneer crop in remedying the arable fields that contaminated by the industry waste due mainly to its relatively huge biomass. At the mean while, it is also of particular importance in the study on the mechanism of plant tolerance to abiotic stress due to its allopolyploid nature. In this study, we investigated the toxic effect of cadmium in germination stage and the role of external plant growth regulators in alleviating the toxicity in 5-7 leaves plantlets of "Zheshuang 72", a local cultivar that has "double-low" seed quality. Our experimental results indicated that(1) Low cadmium concentration slightly promoted seed germination as well as root growth; whilst high cadmium concentration significantly inhibited seed germination and root growth.(2) The application of cadmium had negative effect on the activities of two enzymes, namely, the isocitrate and lipase, which play key role in seed germination.(3) The germinated seeds responded to increasing cadmium concentration with higher concentration of sucrose, but lower concentration of fructose. On the other hand, total saccharide content in germinated seeds decreased gradually in responding to increasing cadmium at first, but it increased when the cadmium concentration reached to a certain level.(4) Cadmium affected negatively on seedlings of oilseed rape in terms of chlorophyll content, weight of dried biomass. The degree of cadmium toxicity could be reflected by the alternation of activities of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) as well as MDA content.(5) The application of one of the following plant regulators, namely, jasmonic acid, abscisic acid, gibberellin, salicylic acid affected cadmium toxicity on rapeseed plantlets after a 10-day-treatment. JA and ABA were able to alleviate the cadmium toxicity, and their roles in regulating the plant tolerance to cadmium stress were the most obvious. GA took part in the tolerance to cadmium stress too, however, its effect was not comparable to those of JA and ABA. SA also played role in regulating the cadmium toxicity, however, in comparison to JA, ABA and GA, it did not alleviate the toxic symptom, but aggravated the toxic symptom, instead.