Endre Lehoczki

Paraquat and atrazine co-resistance in Conyza canadensis (L.) Cronq.

Abstract A biotype of Conyza canadensis (L.) Cronq. from a vineyard subjected to repeated paraquat and triazine herbicide treatment and a wild type from an adjacent ruderal area were examined for resistance to paraquat and atrazine. CO 2 fixation was reduced by paraquat for 3 hr, but thereafter it was strongly stimulated in the resistant biotype, while that of the susceptible biotype remained inhibited. The fluorescence quenching measurements show that paraquat inhibited both biotypes at the level of isolated chloroplasts. Paraquat quenched fluorescence in intact leaves during the first hour of treatment. Fluorescence quenching ceased in the resistant biotype within 24 hr of paraquat treatment. The I 50 with paraquat in the resistant biotype was 170 times higher than that of the susceptible biotype in measurements of fluorescence induction quenching at 24 hr. There were no chlorophyll bleaching and chlorophyll/protein damage in the resistant biotype incubated with paraquat, in marked contrast to the susceptible biotype. The ultrastructure of the chloroplasts in the paraquat-treated leaves of resistant plants was similar to that of the untreated ones. Plastids of the susceptible biotype were disrupted, with considerable rearrangement of the lamellar system, after paraquat application. Superoxide dismutase, ascorbate peroxidase, catalase, and reduced glutathione levels in the total cell extracts were slightly lower in the resistant biotype, but there was a slightly higher level in the extracts of the susceptible biotype in the presence of paraquat. The paraquat-resistant biotype had co-resistance to atrazine as demonstrated through fluorescence induction measurements. The resistance ratio to atrazine was 300. From these results it was concluded that C. canadensis displays co-resistance to paraquat and atrazine; the data indicate that resistance to herbicides with different modes of action can be developed.

Correlation between linolenic-acid deficiency in chloroplast membrane lipids and decreasing photosynthetic activity in barley

Abstract Barley plants having chloroplasts with a gradually diminished linolenic and a gradually increased linoleic acid content (a gradually reduced linolenic-to-linoleic acid ratio) were grown by the application of sublethal doses of the pyridazinone compound SAN 9785. The photosynthetic properties of the leaves and of the chloroplasts isolated from the leaves were studied. SAN 9785 caused only minor changes in the chlorophyll and total lipid contents of the chloroplasts. The liposomes prepared from the chloroplast membrane lipids exhibited a lower level of fluidity, as revealed by fluorescence polarization measurements using diphenylhexatriene. A strong correlation was established between the modified chemical composition of the thylakoid membranes (altered linolenic-to-linoleic acid ratio) and (i) the relative intensity of the short-wavelength fluorescence bands of the low-temperature emission spectra; (ii) the normalized increment of fluorescence (F i − F 0 ) (F m − F 0 ) from fluorescence induction curves of intact leaves; (iii) the CO2-fixation activity of intact leaves; (iv) the Hill reaction rate of isolated chloroplasts; and (v) the degree of coupling between electron transport and photophosporylation. The results suggest that the presence of a sufficient amount of linolenic acid associated with chloroplast membrane lipids is essential for the functioning of the electron-transport chain and coupled phosphorylation. There seems to be a linolenic-to-linolenic acid ratio threshold value of 2 for satisfying coupling. SAN 9785 treatment also caused the chlorophyll-protein complex of the reaction centre of Photosystem I to decrease in quantity, suggesting a stabilizing role of the lipid environment in the assembly and organization of Photosystem-I particles.

Characterization of a Triple (Atrazine-Pyrazon-Pyridate) Resistant Biotype of Common Lambsquarters (Chenopodium album L.)

Summary Pyridate resistance was not a problem in maize fields (in area of Ipolytarnooc) in Hungary until we found a triple (atrazine, pyrazon and pyridate)-resistant common lambsquarters ( Chenopodium album L.) population (it is to be remarked that we do not find single pyridate-resistant populations of Chenopodium album L.). Before the evolution of triple resistance, pyridate herbicides had been applied for 2–3 years against atrazine-resistant Chenopodium album and Amaranthus retrojlexus . The triple resistant biotype of Chenopodium album showed the following characteristics: 1) 500μM atrazine and pyrazon caused no alteration in the fluorescence-transient kinetics in the APPR biotype. In contrast, 500μM pyridate had a strong effect on the rise in fluorescence in the APPR biotype. The degree of resistance of the APPR biotype in case of atrazine was at a high level. At the same time the degree of resistance towards pyridate was at a low level. 2) A 100 μM pyridate concentration caused 44% inhibition in nitrite reductase activity in the chloroplasts of the APPR biotype. 3) The APPR biotype had similar aesterase and very similar malate dehydrogenase zymograms. 4) The APPR biotype was extremely ineffectual and was not competitive with the S biotype. 5) Pyridate resistance was not totally stable in the APPR biotype.

Chemical compositions and physical states of chloroplast lipids related to atrazine resistance in Conyza canadensis L.

Abstract A comparison of the chemical composition and physical states of chloroplast lipids, of atrazine-resistant (R) and sensitive (S) biotypes of Conyza canadensis L. (horseweed), in the rosetta stage showed: (1) the R biotype contains lower amounts of polar lipids in its thylakoids, as expressed on a chlorophyll basis, than the S biotype. (2) The chloroplasts of the R biotype have higher contents of monogalactosyl diacylglycerol (MGDG) and lower contents of digalactosyl diacylglycerol (DGDG) and phosphatidylglycerol (PG), than those of the S biotype. (3) The chloroplast total lipids exhibit a higher degree of unsaturation in the R biotype. This is due to a higher level of linolenic acid, and a lower level of palmitic acid in the glycolipids. The fatty acid compositions of the phospholipids, except that of PG, do not differ significantly. (4) The lipid matrix of the thylakoid membranes of the R biotype is more fluid than that of the S biotype, as measured by the fluorescence polarization technique. The results are discussed in terms of whether these differences are responsible for the herbicide resistance.

Xanthophyll Cycle Patterns and in vivo Photoinhibition in Herbicide-Resistant Biotypes of Conyza canadensis

Summary The xanthophyll cycle and in vivo photoinhibition were investigated in the herbicide-susceptible (S), paraquat-resistant (PQ-R), atrazine-resistant (Atr-R) and paraquat-atrazine co-resistant (PQAtr-R) biotypes of Conyza canadensis using both low-(LLG) and high-light-grown (HLG) plants. HPLC revealed markedly reduced levels of zeaxanthin under photoinhibitory conditions in atrazine-resistant (Atr-R and PQAtr-R) biotypes as compared with the S and PQ-R biotypes. The variable chlorophyll fluorescence (F v ) decrease and constant fluorescence (F o ) increase revealed an enhanced susceptibility to in vivo photoinhibition in Atr-R and PQAtr-R biotypes. LLG plants were more susceptible than HLG plants to in vivo photoinhibitory treatment. It is suggested that the increased susceptibility to photoinhibition in Atr-R and PQAtr-R biotypes of C. canadensis is a consequence not only of D1 protein mutation, but also possibly of a lower rate of violaxanthin to zeaxanthin de-epoxidation.

Characterization of intermediate biotypes in atrazine-susceptible populations of Chenopodium polyspermum L. and Amaranthus bouchonii thell. in Hungary

Abstract Intermediate biotypes for atrazine herbicide resistance in Chenopodium polyspermum and Amaranthus bouchonii were characterized by a peculiar chlorophyll fluorescence induction curve. The intermediate biotypes were isolated from progenies of susceptible plants in maize grown in alternate years without atrazine. The lethal dose in seedling treatments was lower than that of the resistant plants but higher than for susceptible plants. Atrazine at 10 μM was near the I50-value for in vivo nitrite reductase activity in both intermediate biotypes. The activity of nitrite reducttase in the intermediate biotypes was about 75% of that of susceptible biotypes. These characteristics of intermediate biotypes were maternally inherited in crosses.

Cerulenin-induced Changes in Lipid and Fatty Acid Content of Chloroplasts in Detached Greening Barley Leaves.

Measurements were made of the monogalactosyl diglyceride, digalactosyl diglyceride, total phospholipid, and total fatty acid contents, the fatty acid compositions of the glycerolipids of plastids from detached barley leaves before and after 72 hours of greening in the presence or absence of the fatty acid biosynthesis inhibitor cerulenin. At the final stage of greening the incorporation of 1-(14)C-acetate into leaf tissue and that of U-(14)C-galactose into chloroplast galactolipids as well as the ultrastructure of chloroplasts were also studied. Cerulenin caused a marked reduction in the rate of accumulation of chloroplast lipids and fatty acids during the greening period. In addition, specific alterations were observed in the fatty acid composition of monogalactosyl diglyceride, phosphatidyl choline, and phosphatidyl inositol following cerulenin treatment, the possible reasons of which are discussed. 1-(14)C-acetate incorporation into leaf slices was only slightly reduced in cerulenin-treated leaves after 72 hours of greening, whereas nearly 3 times as much U-(14)C-galactose incorporated into chloroplast galactolipids as in the control. The chloroplasts of cerulenin-treated leaves displayed a marked membrane deficiency, probably due to the shortage of galactolipids.

Light Dependence of Thermostability of Photosynthetic Apparatus

PS II is one of the most sensitive component of the photosyntehtic apparatus to different environmental stresses. Heat stress causes the hyperfluidization of the thilakoid membranes, the deactivation of PS II including the dissociation of LHC from the core complexes and inactivation of oxygen evolving system(1). The heat sensitivity of plants can be caracterized by the thermostability of PS II measured by temperature-dependent changes of initial fluorescence (Fo) of dark adapted leaves (2). In parallel with the heating, the initial level of fluorescence yield increases intensively above a critical temperaure (Tc). The Fo vs T curve and the critical temperaure depend on the composition and physical state of the thylakoid membranes (3). It seems that the thermostability of the photosynthetic apparatus of preilluminated plants is higher than of the untreated samples, which manifests in the upshift of Tc measured on dark adapted leaves (4).