Physiological and morphoanatomic analysis of cenostigma macrophyllum tul. (fabaceae) submitted to different concentrations of glyphosate
DOI:
https://doi.org/10.6008/CBPC2179-6858.2020.005.0017Keywords:
Pesticides, Cerrado, Herbicides, Caneleiro, PhotosynthesisAbstract
The aim was to identify the effects of glyphosate on Cenostigma macrophyllum in order to indicate possible bioindicating characteristics of the presence of the herbicide in plants. The study was conducted in a green house. The experiment consisted of 7 treatments, with 4 repetitions each, including 6 different doses of the herbicide: 25, 50, 100, 200, 400, 800g i.a. ha-1 and the control. The evaluations were performed on the leaf tip foliar of the median region of each plant. The values of photosynthesis (A), gas exchange (E), perspiration (gs) and the relation between internal (Ci) and external (Ca) concentration of CO2 (Ci/Ca) were determined. The same area was used to evaluate the fluorescence of chlorophyll a. The initial fluorescence (F0), maximum fluorescence (Fm), potential quantum yield (Fv/Fm), effective quantum yield (ΔF/Fm'), non photochemical dissipation (NPQ) and apparent electron transport rate (ETR) were determined. The sheets evaluated were collected to evaluate the concentration of chloroplastidic pigments, membrane permeability evaluation and morphoanatomical analysis. There was a reduction in A, gs and E values and an increase in Ci/Ca, indicating CO2 accumulation in the sub stomatic cavity. Glyphosate did not cause significant damage to the chlorophyll a fluorescence parameters, membrane degradation, as well as chloroplastid pigment content. Anatomical analysis indicated changes in the autofluorescence emission intensity of chlorophyll a. There was a reduction in the thickness of the adaxial epidermis, in the palisadic and spongy parenchymes and a reduction in the abaxial epidermis, differing significantly from the control in the first dose observed. The leaflets presented chlorosis and necrosis, besides the sprouting of twisted leaves in the highest dose. The reduction of gs and consequent reduction of E and A, may indicate the action of the herbicide in the guard cells, causing the closure of the stomas, however the increase in the Ci/Ca ratio indicates that these damages did not occur only in the stomas, probably there was a decrease in the diffusion of CO2 in the mesophilus or even damage or decrease in the amount of the enzyme Rubisco, responsible for the fixation of CO2 in the Calvin Cycle. The reduction of foliar tissues may have contributed to the deficiency of CO2 diffusion in mesophyll. Morphoanatomic responses have shown damage to chlorophyll and can be used as an early warning of possible future damage. The parameters evaluated in which it was possible to perceive the effect of the herbicide, indicated in case of biomonitoring with the studied species, were: gas exchange, chlorophyll autofluorescence emission and morphoanatomic analyses.
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