Zoltán Szigeti

Photosynthetic activity of homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and rehydration

The functional state of the photosynthetic apparatus of flowering homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and subsequent rehydration was investigated in order to characterize some of the mechanisms by which resurrection plants survive drought stress. The changes in the CO2 assimilation rate, chlorophyll fluorescence parameters, thermoluminescence, fluorescence imaging and electrophoretic characteristics of the chloroplast proteins were measured in control, moderately dehydrated (50% water content), desiccated (5% water content) and rehydrated plants. During the first phase of desiccation the net CO2 assimilation decline was influenced by stomatal closure. Further lowering of net CO2 assimilation was caused by both the decrease in stomatal conductance and in the photochemical activity of photosystem II. Severe dehydration caused inhibition of quantum yield of PSII electron transport, disappearance of thermoluminescence B band and mainly charge recombination related to S2QA− takes place. The blue and green fluorescence emission in desiccated leaves strongly increased. It could be suggested that unchanged chlorophyll content and amounts of chlorophyll–proteins, reversible modifications in PSII electron transport and enhanced probability for non-radiative energy dissipation as well as increased polyphenolic synthesis during desiccation of Haberlea contribute to drought resistance and fast recovery after rehydration.

Effects of Pb and Cd on Cucumber Depending on the Fe-Complex in the Culture Solution

Summary Modifying effects of EDTA and citrate as Fe(III)-complexes on Pb-and Cd-toxicity were investigated with cucumber ( Cucumis sativus L.) grown in culture solution. Pb and Cd were applied in lO μM concentration. Pb and Cd inhibited the growth of plants with Fe-citrate but with Fe-EDTA only Cd did. Chlorophyll content of Cd-treated plants-independently on the Fe-complex-was very low similarly to the iron deficient plants. Pb is proved to inhibit the chlorophyll accumulation only in plants supplied with Fe-citrate. Photosynthetic activity of 6-week-old plants was characterized by in vivo CO 2 fixation. The highest activities were observed in the middle (third-fourth) leaf storeys, and decreased in the lower and higher leaf storeys. Cd caused more than 50 % inhibition of the photosynthetic activity when applied with Fe-EDTA. With Fe-citrate, the inhibition exceeded 90 %. The photosynthetic activities in the Pb-treated plants were not significantly different from the control plants. The amount of chlorophyll containing complexes, especially that of PS I was highly affected by Cd particularly in the lower leaves. The results correlate with 59 Fe translocation into the shoot. Fe translocation was stimulated by Pb in the presence of Fe-EDTA but it was inhibited in the presence of Fe-citrate. Cd completely inhibited Fe translocation from the root to the shoot with both chelators. It is concluded that strong iron deficiency has a great but not exclusive role in the observed symptoms, and that the quality of the chelator strongly influences the effects of these polluting metals.

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.

Role of light in the development of post-chilling symptoms in maize

Summary The effect of light (250 μmol m -2 s -1 ) on the appearance of post-chilling symptoms was investigated in cold-treated maize ( Zea mays L. hybrid Furio) seedlings using electrolyte leakage and chlorophyll fluorescence induction measurements as indicators. The longer the cold pretreatment (0.5 °C) in complete darkness, the more rapid the decrease in F v /F m and the increase in electrolyte leakage during cold treatment in the light. The most important difference in the changes in these two parameters is that the changes in F v /F m occur much earlier if the cold treatment is carried out in the light. These findings suggest that chilling stress in cold sensitive maize plants led to an increased susceptibility to photoinhibition at low temperatures. F v /F m and electrolyte leakage changed not only at low temperatures but also after a certain cold pretreatment period at normal temperature. When the seedlings were returned to 25 °C after various chilling periods in the dark both parameters showed that post-chilling symptoms appeared much more rapidly in the light than in the dark. By contrast to the change in F v /F m , where plants chilled for only two days exhibited differences in post-chilling changes in the light and dark, a substantial increase in electrolyte leakage was only observed after four days of cold pretreatment. These results suggest that photoinhibition has a role not only during the chilling period, but also in the appearance of post-chilling symptoms.

Multicolor Fluorescence Imaging of Leaves—A Useful Tool for Visualizing Systemic Viral Infections in Plants†

Multicolor fluorescence induced by UV light is a sensitive and specific tool that may be used to provide information about the primary and secondary metabolism of plants by monitoring signals of the chlorophyll fluorescence (Chl‐F) and blue‐green fluorescence (BGF), respectively. We have followed the systemic infection of Nicotiana benthamiana plants with the Pepper mild mottle virus (PMMoV) by means of a multicolor fluorescence‐imaging system, to detect differences between two strains of PMMoV during the infection process and to establish a correlation between the virulence and changes induced in the host plant. Changes in both BGF and Chl‐F were monitored. BGF increased mainly in the abaxial side of the leaf during pathogenesis and the corresponding images showed a clear vein‐associated pattern in leaves of infected plants. HPLC analysis of leaf extracts was carried out to identify compounds emitting BGF, and determined that chlorogenic acid was one of the main contributors. BGF imaging was able to detect viral‐induced changes in asymptomatic (AS) leaves before detection of the virus itself. Chl‐F images confirmed our previous results of alterations in the photosynthetic apparatus of AS leaves from infected plants that were detected with other imaging techniques. Fluorescence ratios F440/F690 and F440/F740, which increase during pathogenesis, were excellent indicators of biotic stress.

Improving on the 1.5-Approximation of a Smallest 2-Edge Connected Spanning Subgraph

We give a

An Improved Approximation Algorithm for Minimum Size 2-Edge Connected Spanning Subgraphs

\frac{17}{12}

Apparatus and Method for Rapid Determination of Photosynthetic CO2 Fixation of Leaves

-approximation algorithm for the following NP-hard problem: Given a simple undirected graph, find a 2-edge connected spanning subgraph that has the minimum number of edges. The best previous approximation guarantee was

Hypergraph connectivity augmentation

\frac{3}{2}

Are either SOD and catalase or the polyamines involved in the paraquat resistance of Conyza canadensis

. If the well-known