Robert Lannoye

Cold-Resistant and Cold-Sensitive Maize Lines Differ in the Phosphorylation of the Photosystem II Subunit, CP29

The effects of low temperature on the relative contributions of the reaction center and the antenna activities to photosystem II (PSII) electron transport were estimated by chlorophyll fluorescence. The inhibition of PSII photochemistry resulted from photo-damage to the reaction center and/or a reduced probability of excitation energy trapping by the reaction center. Although chill treatment did not modify the proportion of the dimeric to monomeric PSII, it destabilized its main light-harvesting complex. Full protection of the reaction center was achieved only in the presence of the phosphorylated PSII subunit, CP29. In a nonphosphorylating genotype the chill treatment led to photoinhibitory damage. The phosphorylation of CP29 modified neither its binding to the PSII core nor its pigment content. Phosphorylated CP29 was isolated by flat-bed isoelectric focusing. Its spectral characteristics indicated a depletion of the chlorophyll spectral forms with the highest excitation transfer efficiency to the reaction center. It is suggested that phosphorylated CP29 performs its regulatory function by an yet undescribed mechanism based on a shift of the equilibrium for the excitation energy toward the antenna.

Correlation between Heat Tolerance and Drought Tolerance in Cereals Demonstrated by Rapid Chlorophyll Fluorescence Tests

Summary Drought and heat tolerances were measured in intact leaves of a large number of genotypes of durum wheat ( Triticum durum Desf.), barley ( Hordeum vulgare L.) and triticale ( Triticum durum L. × Secale cereale L.) using rapid in vivo chlorophyll fluorescence tests. The high temperature (T p ) corresponding to maximal F o -fluorescence in leaf samples heated at a rate of 1 ưC min −1 was used to estimate the relative heat tolerance. On the other hand, drought tolerance was measured by the reduction of the photochemical quenching of chlorophyll fluorescence (q Q ) after a short desiccation treatment. The data indicate a very wide range of genotypic adaptation to drought and heat in cereals. The two types of tolerance were, however, closely related: the most heat tolerant cereal varieties were also the most drought tolerant ones. The results presented in this paper also provide a good example of the usefulness and the simplicity of modulated chlorophyll fluorescence measurements as rapid screening tests for stress tolerance in crop plants.

Chlorophyll fluorescence induction: A sensitive indicator of water stress in maize plants

SummaryThis investigation shows that the chlorophyll fluorescence induction phenomenon provides a simple non destructive method for investigating effects of drought on plants. Drastic reduction of the maximum (P) to the minimum (0) chlorophyll fluorescence ratio and strong inhibition of the slow fluorescence induction transients were observed in maize submitted to water stress sufficient to dehydrate leaves to 68% of original water content. The P/0 value and the typical PSMT induction sequence were restored following the removal of drought conditions. However, the slow quenching of chlorophyll fluorescence to the steady-state (T) remained noticeably altered, indicating irreversible damage on the chloroplastic membranes.

Aluminum effects on photosynthesis and elemental uptake in an aluminum-tolerant and non-tolerant wheat cultivar

Abstract The effects of aluminum (Al) on photosynthesis and elemental uptake were studied in two wheat cultivars (Triticum aestivum L. cvs Yecora E, Nestos) differing in their tolerance to Al. Concentrations of calcium (Ca), magnesium (Mg), potassium (K), and iron (Fe) in the plant tissues of both cultivars grown in nutrient solutions (pH 4.5) decreased at all Al levels (0, 37.1, 74.1, and 148 μM). The tolerant cultivar Yecora E retained larger concentrations of all elements measured in roots and above ground parts compared with the non tolerant cultivar Nestos. Concentrations of Ca and Mg in leaves of the cultivar Nestos under high Al treatment were within the deficiency range. Changes in the shape of the chlorophyll fluorescence induction curves showed that Al‐stress altered thylakoid photofunctioning even in the more tolerant cultivar. Aluminum stress resulted in partial inhibition of photosynthetic electron transport at photosystem II and closure of photosystem II reaction centers. Chloroplast element...

Evolution of enzyme activities and microbial populations during composting of cattle manure

SummaryPopulation changes in the levels of mesophilic and thermophilic fungi and actinomycetes were studied during composting of cattle manure.Activities of urease, phosphatase, and cellulase were also followed. The results obtained in a bench-scale composter were compared with those obtained during pile-composting. The consequences of disturbances in the composting process were studied during a bench-scale operation. Our results indicate the potential usefulness of enzyme measures as indexes of accuracy of real composting.

Photoacoustic measurements of photosynthetic activities in intact leaves under copper stress

Abstract Photoacoustic spectroscopy was used to monitor Cu damage to photosynthesis by measuring photochemical energy storage (PES) at high frequency of 600 Hz and yield of O 2 evolution (Aox/Apt) at low frequency of 19 Hz in intact leaves of a Cu-tolerant ( Silene compacta ) and a non-Cu-tolerant ( Alyssum montanum ) species. The results indicated that Cu affected root growth (RRG), more severely than photoacoustic parameters in both species. Plants of S. compacta grown in lower Cu concentration revealed an enhancement phenomenon on RRG, PES and Aox/Apt, in contrast, plants of A. montanum revealed a slight decrease in the above mentioned parameters. A remarkable decline of PES and Aox/Apt for both species, was observed, at higher Cu concentrations, a fact considered to reflect inhibition of the photsynthetic e − flow in thylakoids. PES was less affected by Cu stress than O 2 evolution showing a differential sensitivity of two photosystems in Cu. Photosystem II (PSII) seemed to be more sensitive because of degradation and leakage of chloroplasts membranes, inducing a decline in yield of O 2 evolution. On the other hand, PES was appreciable because of cyclic e − transfer around the intact or less inhibited photosystem I (PSI).

Temperature dependence of delayed chlorophyll fluorescence in intact leaves of higher plants. A rapid method for detecting the phase transition of thylakoid membrane lipids

The temperature dependence of the yield of in vivo prompt and delayed chiorophyll fluorescence was investigated in maize and barley leaves. In the chilling-sensitive maize, delayed fluorescence at steady-state level showed a maximum near the temperature at which thylakoid membrane lipids undergo a phase transition as revealed by differential scanning calorimetry measurements. In the chilling-resistant barley, no phase transition was detected above 0°C and the delayed light emission varied in a monotonic fashion. It was shown that measurements of delayed luminescence intensity in vivo can provide a rapid and sensitive method for detecting the phase change of membrane lipids in intact leaves of chilling-sensitive plant species such as tomato, cotton, cucumber, castor bean or avocado. In contrast, the use of steady-state prompt chlorophyll fluorescence as an indicator of membrane fluidity change was not successful.

Reversible effects of moderately elevated temperature on the distribution of excitation energy between the two photosystems of photosynthesis in intact avocado leaves

Initial (Fo), maximum (Fm) and steady-state (Fs) levels of modulated chlorophyll fluorescence were measured in intact avocado leaves (Persea americana Mill.) during state 1-state 2 transitions using a combination of modulated and non-modulated lights with synchronized detection. Under normal temperature conditions (20°C), transition from state 2 to state 1 was associated with a substantial increase (about 20%) in Fm and Fo whereas the Fm/Fo ratio remained constant, reflecting increased absorption cross-section of PS II. On the contrary, at moderately elevated temperature (35°C), these fluorescence changes were very limited, indicating marked inhibition of the state regulation. The fraction of light distributed to PS II (β) was calculated from the Fo, Fm and Fs levels for both types of leaves. In control leaves, β varied from 48% (in state 2) to values as high as 58% (in state 1). In contrast, mild heat treatment resulted in β values close to 50% in both states, indicating the inability of heated leaves to reach extreme state 1. The results suggested that avocado leaves under moderately elevated temperature conditions are blocked in a state close to state 2. This effect was shown to occur in a non-injurious temperature range (as shown by the preservation of the (photoacoustically monitored) oxygen evolution activity) and to be rapidly reversed upon lowering of the temperature. Thermally induced development of state 2 (independent on the light spectral quality) could possibly be a protective mechanism to avoid photodamage of the heat-labile PS II by high light intensities which usually accompany heat stress in the field.

Correlation between the Banding Pattern and the Cell Wall Composition in Chara corallina: A Fourier Transform Infra-red Study

Summary The distribution of polymers and proteins in the cell wall of Chara corallina was investigated by means of a Fourier transform infra-red spectrophotometer connected to a microscope. The distribution of both carboxylic groups from pectins and amine groups from proteins is homogeneous in the acid band but not in the alkaline band. In the alkaline band there is a strong correlation between the amount of calcium carbonate and the various cell wall materials. Protons interact more strongly with carboxylate anions than calcium does.

The relationship between the yield factors for prompt and delayed fluorescence.

where J is the rate of chlorophyll singlet formation and @DF is the fluorescence yield of the chlorophyll molecules through which the delayed fluorescence exciton migrates before de-excitation. To understand the relationship between @DF and @, has important implications since it would reveal information about the extent of the migration of an exciton away from the trap from which it originated [2-51 . Unfortunately earlier studies designed to investigate the