Analysis Of Acetochlor Tolerance In Root Of Brassica Napus And Triticum Aestivum

Acetochlor is one of the most heavily used herbicides in our country, which can effectively control weeds and safe to Brassica napus L., while it is forbidden in wheat fields because it is unsafe even though the dosage is lower than prescription. This investigation was carried out to study the influence of acetochlor on seedling root morphology, root tip anatomical structure as well as physiological metabolism in B. napus and Triticum aestivum L. by using acetochlor hydroponic experiments. Concentrations of acetochlor were 0, 0.01, 0.1, 1, 10 and 100 mg/L. Results can be used to reveal the mechanism of different acetochlor tolerance in 2 crops and provide basis for save application. Main results are as follows:(1) Root morphology results showed that the inhibition of T. aestivum root length, root dry weight, lateral root number, root hair length and density were greater than B. napus. Root phytotoxicity sympotoms of T. aestivum: under 0.01 mg/L acetochlor treatment, lateral root number was obviously depressed; under 0.1 mg/L acetochlor treatment, root dry weight and root hair length were restrained; under 1 mg/L acetochlor treatment, root twisted, hard and turned brown, root hair density lessened, root hair distributed unevenly; under 100 mg/L acetochlor treatment, the first root stopped grow and there was no lateral root observed. However, root length, root dry weight, lateral root number, root hair length and density were restrained when acetochlor concentration over 1 mg/L. In terms of the significance of root morphological response, tolerant concentration of B. napus is over 10 times that of T. aestivum.(2) Anatomical results indicated that under 1 mg/L and 10 mg/L acetochlor treatment, root tip internal structure of B. napus and T. aestivum showed different reactions: B. napus root tip shortened and thickened, its meristem zone width, layer number and thickness of cortical cells increased, but its root cap, meristem zone, quiescent center, vascular cylinder and vessel were normal; while T. aestivum root cap shape became close to the arc, the boundary of internal structure blurred, cell gap increased and cell arrangement disorded, shape of root cap changed, cell staining of meristem zone cells was light, dividing phase of meristem zone cells decreased, length of meristem zone shortened, volume of quiescent center cells enlarged and cell shape was similar to meristem zone cells, meanwhile, the casparian strips obviously thickened, diameters of vascular cylinder and vessel increased, pericycle cells severely lignified. We believe that the thickness of casparian strip contributes to preventing the absorption of acetochlor, alleviating the damage to leaves, which is an adaptive response; the depression of meristem zone cell mitotic activity is the main reason why root morphology shortened, lignification of pericycle cells is the direct reason why there is no lateral root in T. aestivum.(3) Physiological metabolism results indicated that MDA content, membrane permeability, soluble sugar content and proline content were rised with the increase of acetochlor concentration. The variation tendency of membrane permeability was quite different: membrane permeability of B. napus was unchanged until acetochlor concentration reached 100 mg/L, while that of T. aestivum was significantly rised at 0.1 mg/L acetochlor treatment, so the tolerance concentration of B. napus membrane permeability was over 1000 times that of T. aestivum. In addition, the amount and rate of proline accumulation of B. napus were greater than T. aestivum. Moreover, soluble protein, SOD, POD and CAT activities of B. napus were uptrended continuously, while that of T. aestivum were increased firstly and then delined.The above results indicated that physiological metabolism is more sensitive to morphology, different tolerance on root tip membrane permeability is the main reason why acetochlor tolerance is significantly different in root of B. napus and T. aestivum, besides, differences in proline content and antioxidant enzyme level are also factors.