Tolerance Mechanism Of Rapeseed And Barley To Herbicide (ZJ0273) Stress And Development Of Spectroscopy Models For Physiological Parameters

Propyl 4-(2-(4,6-dimethoxypyrimidin-2-yloxy)benzylamino)benzoate (ZJ0273) is a novel herbicideused in the rapeseed field with the advantage of broad weeding spectrum. It is meaningful to study themode of action and tolerance mechanism of this new herbicide among crops and weeds for its extendedapplication. In this study, rapeseed (Brassica napus L. cv. ZS758) and barley (Hordeum vulgare L. cv.Huangqingluo) were investigated to clarify the tolerance mechanism within monocotyledon anddicotyledon species to ZJ0273 stress with various physiological measurements and microscopic analyses.In addition, several near-infrared spectroscopy (NIRS) models were developed to investigate for rapid andnon-destructive determination of physiological characters in rapeseed leaves under herbicide ZJ0273stress. The main results are as follows:1. The differential tolerance or susceptibility of four plant species viz. B. napus L. (rapeseed),Hordeum vulgare L. (barley), Malachium aquaticum (L.) Fries (water chickweed) and Alopecurusaequalis Sobol. (equal alopecurus), to various concentrations of ZJ0273, was studied based on the rate ofinhibition of acetolactate synthase (ALS) activity. B. napus was observed as the most tolerant among fourspecies in which ALS activity in vivo was hardly affected by ZJ0273 at 100 mg/L (recommended dose inthe rapeseed field). In contrast, Hordeum vulgare was found to be more susceptible while the two weedspecies exhibited moderate susceptibility as compared to Hordeum vulgare. However, ALS activity in vitrowas hardly inhibited by herbicide ZJ0273. In addition, there was a wide variation noted for in vivo ALSactivity among various parts of plants. The uppermost younger leaf seemed to be the most appropriatesample for evaluation, as it showed the highest level of ALS activity in the plant. Spatial and temporalvariations in ALS activity as affected by 100 mg/L ZJ0273 in water chickweed, rapeseed and barley alsosuggested that the synchronized sampling based on the tissue position is necessary to examine precisely,the difference in tolerance or susceptibility to ALS-inhibiting herbicide. The variant tendency of ALSactivity from different parts of plants within monocotyledons and dicotyledons to ZJ0273 treatmentsshowed differential response which revealed some possible mechanisms related to the altered absorptionand translocation of the herbicide. Furthermore, the tolerance among three species of Brassica suggestedthat B. rapa was the most susceptible and B. juncea was the most tolerant to the new herbicide ZJ0273.2. Response of seedling growth, root cell viability, mitosis, root and leaf cell structure andultrastructure of rapeseed and barley to herbicide ZJ0273 at germination stage was studied to define the action mechanism of this novel herbicide. The results indicated that both of rapeseed and barley seedlingsare very sensitive to ZJ0273 at germination stage and the application of 1 mg/L (optimum concentration) issafer for seedling growth. 10 mg/L ZJ0273 treatment can significantly inhibit seedling growth (especiallythe root elongation and development) and root viability. Besides, the inhibitive effects become intensifiedwith the increase of dosage and duration. Mitotic index of root-tip cells was declined and cell division wasstopped at metaphase after being treated by 100 mg/L ZJ0273, which shortened the meristematic zone andelongation zone in plant root tips. In addition, the cell development in maturation zone was also inhibited,which deferred the development of lateral root. ZJ0273 significantly inhibited the development of cell wall,vacuole, plastid and chloroplast in barley cells while induced the senescence (aging) of chloroplast inrapeseed cotyledon cells, which suggested that the effect of ZJ0273 on cell development is bifacial and itcould be exploited as a plant growth regulator. Furthermore, 100 mg/L ZJ0273 treatment obviouslyinhibited root cell viability and resulted in disintegration of cell and mitochondria membrane, as well asmore microbodies were observed in treated cells, which suggested that ZJ0273 might be activated withinthe microbodies and acting in mitochondria in plant cells. However, nucleus in root and leaf cells ofrapeseed and barley treated by ZJ0273 showed no significant change in comparison to that of control, asshown by the histochemical and transmission electron microscopy (TEM) demonstrations. Furthermore,chromosome number and shape in dividing cells treated by 100 mg/L ZJ0273 were also normal, whichindicated that this new herbicide hardly induced the tolerant weed mutants and it is helpful to itsapplication and commercialization in fields.3. The tolerance mechanism of rapeseed and barley to ZJ0273 stress was studied by measurements ofbiomass, antioxidants and photosynthetic characteristics. As above results shows, rapeseed is no moretolerant than barley at germination stage. In contrast, the tolerance of rapeseed seedlings at 5-leaf stage issignificantly higher than barley seedlings to ZJ0273, which showed that rapeseed seedlings were hardlyaffected by 100 mg/L treatment where as the inhibitive effect of ZJ0273 treatments at higherconcentrations on physiological characteristics recovered with the passage of time. However, barley wasmore susceptible which was reflected in lower biomass production even under at the lowest rate of 100mg/L of ZJ0273 and the enhanced inhibitive effect along with the increase of treatment concentrations anddurations. In the beginning, rapid increase and then sudden decline of leaf peroxidase (POD) andsuperoxide dismutase (SOD) activities under herbicide stress, indicated that ZJ0273 affected barleyantioxidant system more badly than rapeseed, as compared to the slight changes in rapeseed. In addition,ZJ0273 treatments hardly affected net photosynthesis (Pn) of rapeseed leaves but significantly inhibitedSPAD and Pn values of barley leaves, which indicated that the photosystemâ…¡of barley was paralyzed byinhibition effect of herbicide on non-photochemical quenching (NPQ) capability and finally, the biomass was reduced more significantly.4. Effect of herbicide ZJ0273 on plant agronomic characters, seed yield and quality of oilseed rapewas also compared in this study by treating at seedling stage and bolting stage, respectively. The resultsconfirmed that 100 mg/L ZJ0273 (recommended dose in the rapeseed field) promoted seed yield withslight effect on seed quality but significantly reduced rapeseed yield and affected seed quality whenapplied at seedling stage and bolting stage, respectively. The treatment at highest concentration of 1000mg/L applied at seedling stage mainly affected seed quality but badly reduced seed yield when was appliedat bolting stage, which indicated that rapeseed yield and seed quality are more sensitive to ZJ0273 atbolting stage than seedling stage. These results suggested that crop tolerance revealed some possiblemechanisms related to the altered absorption, translocation of the herbicide. In addition, treatmentapproach such as root application or leaf-spray was also possible reason that affected the herbicideinhibitive action according to its root-absorption trait. Thus, both of optimal leaf stage and treatmentapproach should be considered in field application of ZJ0273.5. Near-infrared spectroscopy (NIRS) was investigated for rapid and non-destructive determination ofvarious physiological characters in rapeseed leaves from different leaf-positions under herbicide stress.NIRS models of ALS activity, soluble, non-soluble, total protein and total amino acid contents weresuccessfully developed and the correlation coefficients of all models were higher than 0.9. Furthermore,the improved models with spectra preprocessed and efficient wavelength selected were obtained and theircorrelation coefficients were between 0.95-0.99.In conclusion, the above results contribute a lot to understand the differential tolerance mechanismamong monocotyledonous and dicotyledonous species (both the crops and weeds) to ZJ0273 stress whichare the basis of safe use of this new herbicide in field. The development of NIRS models in this studywould be helpful for further field analysis of using NIRS to monitor the growing states and biologicalproperties of oilseed rape under herbicide stress.