Relationships between early vigour, grain yield, leaf structure and stable isotope composition in field grown barley

Fast growth and early development in barley are used in breeding programmes to improve the water use efficiency and transpiration efficiency of this crop in Mediterranean conditions. Here, we examine the use of several simple traits based on the structure and stable isotope composition of seedling leaves to assess differences in early vigour, phenology and grain yield, and also the interaction with low temperatures in barley. A set of 260 F₈ lines of two-row barley (Hordeum vulgare L.) derived from the cross of Tadmor and WI 2291 were cultivated in two locations in northwest Syria. Total chlorophyll content on an area basis (SPAD) and specific leaf dry weight (SLDW) were measured in recently fully expanded intact leaves of seedlings. Total leaf area and total dry weight per seedling were evaluated in the same seedlings. The stable isotope compositions of carbon and nitrogen (δ¹³C and δ¹⁵N, respectively) were analyzed in the same leaves on a subset of 75 genotypes. Number of days from planting to heading and grain yield were recorded at both sites. The grain yield measured at both locations was positively correlated with the SPAD value of seedlings, but showed no relationship with SLDW. Days to heading was negatively correlated with SPAD values. Regarding early vigour, a negative relationship between the SLDW and the total leaf area of seedlings was observed. However, no relationship between the δ¹³C of seedlings and early vigour was observed, except when only the genotypes most resistant to low temperatures (i.e. showing the highest SPAD values) were considered. This subset of genotypes showed negative relationships between δ¹³C and either total leaf area or total dry weight. In addition, δ¹⁵N was negatively correlated with SPAD only within the high-SPAD genotypes. This suggests that within the genotypes resistant to low temperatures, those with higher chlorophyll content assimilate more nitrogen from nitrate.     

Assessing leaf pigment content and activity with a reflectometer

This study explored reflectance indices sampled with a 'leaf reflectometer' as measures of pigment content for leaves of contrasting light history, developmental stage and functional type (herbaceous annual versus sclerophyllous evergreen). We employed three reflectance indices: a modified normalized difference vegetation index (NDVI), an index of chlorophyll content; the red/green reflectance ratio ( R _RED: R _GREEN), an index of anthocyanin content; and the change in photochemical reflectance index upon dark–light conversions (ΔPRI), an index of xanthophyll cycle pigment activity. In Helianthus annuus (sunflower), xanthophyll cycle pigment amounts were linearly related to growth light environment; leaves in full sun contained approximately twice the amount of xanthophyll cycle pigments as leaves in deep shade, and at midday a larger proportion of these pigments were in the photoprotective, de-epoxidized forms relative to shade leaves. Reflectance indices also revealed contrasting patterns of pigment development in leaves of contrasting structural types (annual versus evergreen). In H. annuus sun leaves, there was a remarkably rapid increase in amounts of both chlorophyll and xanthophyll cycle pigments along a leaf developmental sequence. This pattern contrasted with that of Quercus agrifolia (coast live oak, a sclerophyllous evergreen), which exhibited a gradual development of both chlorophyll and xanthophyll cycle pigments along with a pronounced peak of anthocyanin pigment content in newly expanding leaves. These temporal patterns of pigment development in Q. agrifolia leaves suggest that anthocyanins and xanthophyll cycle pigments serve complementary photoprotective roles during early leaf development. The results illustrate the use of reflectance indices for distinguishing divergent patterns of pigment activity in leaves of contrasting light history and functional type.     

Tissue-Specific Features of Pigment Biogenesis in Coleoptiles of Greening Etiolated Seedlings of Cereals

Biogenesis of the pigment apparatus was studied in coleoptiles of postetiolated barley seedlings (Hordeum vulgare L.) and triticale (Triticale), differing in chlorophyll content, during growing in a “ light-darkness” regime with a 16-h photoperiod. Photoactive protochlorophyllide with a fluorescence maximum at 655 nm (Pchlide655), which accumulates in coleoptiles of etiolated seedlings, was converted in the light into a chlorophyll pigment with a fluorescence maximum at 690 nm (excitation at 440 nm, temperature ?196°C). The spectral transition 690 nm → 675 nm forms was completed in darkness for 15 min illumination. There was almost no resynthesis of new portions of Pchlide655 in coleoptiles under darkness conditions, even after a 5–6-h darkness period after brief illumination of seedlings with flashes of white light. Chlorophyllide (Chlide) formed from Pchlide655 was not esterified and was destroyed both in the light (4 h, 1.0–1.5 klx) and darkness. In coleoptiles of greening etiolated seedlings, chlorophyll formation started only by 24 h of illumination. The instability of the chlorophyll pigment formed after etiolation indicates that plastids of coleoptiles do not contain the system of chlorophyll biosynthesis centers typical of leaves, which are bound to membranes and protect pigment from destruction.     

Chlorophyll Fluorescence as a Possible Tool for Salinity Tolerance Screening in Barley (Hordeum vulgare L.)

The application of chlorophyll fluorescence measurements to screening barley (Hordeum vulgare L.) genotypes for salinity tolerance has been investigated. Excised barley leaves were cut under water and incubated with the cut end immersed in water or in a 100-mM NaCl solution, either in the dark or in high light. Changes in rapid fluorescence kinetics occurred in excised barley leaves exposed to the saline solution only when the incubation was carried out in the presence of high light. Fluorescence changes consisted of decreases in the variable to maximum fluorescence ratio and in increases in the relative proportion of variable fluorescence leading to point I in the Kautsky fluorescence induction curve. These relative increases in fluorescence at point I appeared to arise from a delayed plastoquinone reoxidation in the dark, since they disappeared after short, far-red illumination, which is known to excite photosystem I preferentially. We show that a significant correlation existed between some fluorescence parameters, measured after a combined salt and high-light treatment, and other independent measurements of salinity tolerance. These results suggest that chlorophyll fluorescence, and especially the relative fluorescence at point I in the Kautsky fluorescence induction curve, could be used for the screening of barley genotypes for salinity tolerance.     

Long-term effects of blue or red light on ATP and ADP contents in primary barley leaves

Levels of ATP and ADP were studied in primary leaves of barley (Hordeum vulgare L. cv. Viner) seedlings grown under blue (BL) or red light (RL) of various irradiances. In mature leaf segments, BL stimulated a greater accumulation of adenylates than RL. Transfer of barley seedlings from RL to BL for 48 h caused about a twofold increase in the content of adenylates, probably due to de-novo synthesis of adenine nucleotides. Weak BL was found to stimulate an increase in the adenylate content and a higher irradiance enhanced the stimulatory effect. The adenylate content increased markedly from the base towards the tip of barley leaves grown under BL but not in those grown under RL. However, the adenylate content was higher in the basalmost segment of barley leaves grown under RL, indicating that the action of RL on adenylate content proceeded more rapidly than that of BL. The same conclusion could be drawn from the results of experiments with de-etiolated leaves. A linear relationship was established between the maximum rate of CO₂ fixation and the ATP or ADP content in mature segments of primary barley leaves. The possible involvement of two photoreceptors, phytochrome and cryptochrome, in the long-term light regulation of the total content of adenylates in primary barley leaves is discussed.Abbreviations BL blue light - Chl chlorophyll - RL red light     

不同海拔对七子花叶片色素含量、含水量及比叶面积的影响

通过比较浙江大盘山不同海拔(A1:550~660 m,A2:700~800 m,A3:900~990 m,A4:1 000~1 015 m,A5:1 020~1 100 m)七子花(Heptacodium miconioides)叶片色素含量、含水量及比叶面积变化,探讨不同海拔对七子花生长的影响。结果表明,随着海拔的升高,叶绿素含量(包括叶绿素a、叶绿素b、叶绿素a+b)先增加后减少,在A3达最高值;叶绿素a/b比值、类胡萝卜素含量变化呈先低后高,在A3降至最低;比叶面积及叶片含水量,在较高海拔A4、A5都明显下降。七子花通过叶片色素、比叶面积、干重和含水量的变化以适应高海拔环境。     

The influence of salinity on cell ultrastructures and photosynthetic apparatus of barley genotypes differing in salt stress tolerance

A hydroponic experiment was conducted to elucidate the difference in growth and cell ultrastructure between Tibetan wild and cultivated barley genotypes under moderate (150 mM NaCl) and high (300 mM NaCl) salt stress. The growth of three barley genotypes was reduced significantly under salt stress, but the wild barley XZ16 (tolerant) was less affected relative to cultivated barley Yerong (moderate tolerant) and Gairdner (sensitive). Meanwhile, XZ16 had lower Na⁺ and higher K⁺ concentrations in leaves than other two genotypes. In terms of photosynthetic and chlorophyll fluorescence parameters, salt stress reduced maximal photochemical efficiency (F _v/F _m), net photosynthetic rate (Pn), stomatal conductance (Gs), and intracellular CO₂ concentration (Ci). XZ16 showed relatively smaller reduction in comparison with the two cultivated barley genotypes. The observation of transmission electron microscopy found that fundamental cell ultrastructure changes happened in both leaves and roots of all barley genotypes under salt NaCl stress, with chloroplasts being most changed. Moreover, obvious difference could be detected among the three genotypes in the damage of cell ultrastructure under salt stress, with XZ16 and Gairdner being least and most affected, respectively. It may be concluded that high salt tolerance in XZ16 is attributed to less Na⁺ accumulation and K⁺ reduction in leaves, more slight damage in cell ultrastructure, which in turn caused less influence on chloroplast function and photosynthesis.     

Photosynthetic responses of sun- and shade-grown barley leaves to high light: is the lower PSII connectivity in shade leaves associated with protection against excess of light?

In this study, we have compared photosynthetic performance of barley leaves (Hordeum vulgare L.) grown under sun and shade light regimes during their entire growth period, under field conditions. Analyses were based on measurements of both slow and fast chlorophyll (Chl) a fluorescence kinetics, gas exchange, pigment composition; and of light incident on leaves during their growth. Both the shade and the sun barley leaves had similar Chl a/b and Chl/carotenoid ratios. The fluorescence induction analyses uncovered major functional differences between the sun and the shade leaves: lower connectivity among Photosystem II (PSII), decreased number of electron carriers, and limitations in electron transport between PSII and PSI in the shade leaves; but only low differences in the size of PSII antenna. We discuss the possible protective role of low connectivity between PSII units in shade leaves in keeping the excitation pressure at a lower, physiologically more acceptable level under high light conditions.     

Detection of the photoactive protochlorophyllide-protein complex in the light during the greening of barley.

A photoactive protochlorophyllide-protein complex with absorbance and fluorescence maxima at 648 and 653 nm was detected in greening barley leaves without any re-darkening. The variations of the amplitudes of the absorbance and the fluorescence of the photoactive protochlorophyllide with greening time at two different light intensities indicate a close relationship between the rate of chlorophyll synthesis and the amount of the complex during the first hours. The chlorophyllide resulting from photoreduction during greening has an absorbance maximum at 684 nm, which shifts towards a shorter wavelength within a few seconds, indicating rapid liberation of the pigment from the enzyme. We conclude that chlorophyll accumulation proceeds through continuous regeneration and phototransformation of the photoactive complex.     

SPAD chlorophyll meter reading can be pronouncedly affected by chloroplast movement

Non-destructive assessment of chlorophyll content has recently been widely done by chlorophyll meters based on measurement of leaf transmittance (e.g. the SPAD-502 chlorophyll meter measures the leaf transmittance at 650 and 940 nm). However, the leaf transmittance depends not only on the content of chlorophylls but also on their distribution in leaves. The chlorophyll distribution within leaves is co-determined by chloroplast arrangement in cells that depends on light conditions. When tobacco leaves were exposed to a strong blue light (about 340 μmol of photons m⁻² s⁻¹), a very pronounced increase in the leaf transmittance was observed as chloroplasts migrated from face position (along cell walls perpendicular to the incident light) to side position (along cell walls parallel to the incoming light) and the SPAD reading decreased markedly. This effect was more pronounced in the leaves of young tobacco plants compared with old ones; the difference between SPAD values in face and side position reached even about 35%. It is shown how the chloroplast movement changes a relationship between the SPAD readings and real chlorophyll content. For an elimination of the chloroplast movement effect, it can be recommended to measure the SPAD values in leaves with a defined chloroplasts arrangement.     

铁皮石斛叶色突变体的叶绿体超微结构、光合色素和叶绿素荧光特性的研究

以铁皮石斛(Dendrobium officinale Kimura et Migo)(‘TP35’)经自然突变的白绿杂色突变体(‘TP-MA’)和太空诱变的绿黄杂色突变体(‘TP-MG’)为材料,研究不同光照强度(0、50、100μmol·m^-2·s^-1)处理后,植株叶片的叶绿体超微结构、光合色素含量以及叶绿素荧光动力学参数的变化规律,并阐明叶色突变体与正常植株光合特性的差异。结果显示,‘TP-MA’和‘TP-MG’的叶绿体形态均发生了一定程度的缺失,且叶绿体分布不均匀、无规则,基粒片层结构不完整且排列疏松,基本与其表型性状相一致。‘TP-MA’光合色素的含量和叶绿素荧光参数F v/F m、ΦPSⅡ及F v′/F m′等显著低于‘TP35’,但非光化学淬灭系数(NPQ和q P)则相对较高;‘TP-MG’的光合色素含量及叶绿素荧光参数均低于‘TP35’,但差异不显著,且对较强的光照(100μmol·m^-2·s^-1)条件具有一定的适应性。研究结果表明不同光强处理后,铁皮石斛叶色突变体的叶绿体结构和光合生理指标均发生了不同程度的变化,且对植株的叶绿素含量及荧光参数产生一定影响,过低和过高的光照强度均不利于植株的正常生长。     

不同剂量^137Cs-γ辐射对毛竹幼苗叶片叶绿素荧光参数的影响

利用不同剂量的137Cs-γ射线对毛竹（Phyllostachys heterocycla ‘Pubescens’）种子进行辐射, 测定实生苗叶片中的光合色素含量和叶绿素荧光参数等指标, 探讨辐射对毛竹幼苗生长的影响, 为筛选有利的突变单株奠定良好基础。结果表明：30或60 Gy的137Cs-γ射线辐射后, 毛竹幼苗的光合色素含量以及最大荧光强度（Fm）、可变荧光强度（Fv）、PSII最大光化学效率（Fv/Fm）、PSII的潜在活性（Fv/Fo）、PSII实际光化学效率（Yield）和表观光合电子传递速率（ETR）等荧光参数值均高于90 Gy辐射处理, 说明较低剂量辐射后PSII反应中心的能量捕获效率高, 且具有较强的光合能力; 而90 Gy的137Cs-γ射线辐射对毛竹的影响则与之相反。不同处理剂量之间叶片光能耗散程度以及表观光合电子传递速率-光合有效辐射（ETR-PAR）响应曲线的分析结果也进一步证实了以上结论。     

Gel observation chamber for rapid screening of root traits in cereal seedlings

A simple gel chamber is described for measurement of seedling root traits. Seedlings are located between two closely spaced flat layers of transparent gel, on plastic plates (at least one of which is transparent). Root system traits can be non-destructively recorded in two-dimensions using a flatbed scanner. Easily measured rooting traits include root length, elongation rate, longest root, deepest root, seminal root number, and angular spread of roots. Examples of wild, landrace, and cultivated barleys were grown in the gel chambers, between gel layers or in loosely packed soil. Root growth on the gel plates was similar to that in loose soil, with the cultivated barley having the most seminal axes (about 7), and widest angular spread of roots (about 120 °), and wild barley the fewest seminal axes (about 3), and narrowest angular spread of roots (about 40 °). Landrace barley lines tested were intermediate between wild barley and modern cultivars. Separate experiments were performed to study the effect of grain mass and grain size on these rooting traits. These experiments included parents of genetic mapping populations. Seminal root number was most strongly dependent on grain mass in the modern cultivar Chime. Grain size significantly influenced root number in the modern cultivar Derkado, the breeding line B83-12/21/5, and a selection from a landrace Tadmor, suggesting that grain size should be controlled in any screening exercise.     

Characterization of the Xanthophyll Cycle and Other Photosynthetic Pigment Changes Induced by Iron Deficiency in Sugar Beet (Beta vulgaris L.)

In this work we characterize the changes induced by iron deficiency in the pigment composition of sugar beet (Beta vulgaris L.) leaves. When sugar beet plants were grown hydroponically under limited iron supply, neoxanthin and β-carotene decreased concomitantly with chlorophyll a, whereas lutein and the carotenoids within the xanthophyll cycle were less affected. Iron deficiency caused major increases in the lutein/chlorophyll a and xanthophyll cycle pigments/chlorophyll a molar ratios. Xanthophyll cycle carotenoids in Fe-deficient plants underwent epoxidations and de-epoxidations in response to ambient light conditions. In dark adapted Fe-deficient plants most of the xanthophyll cycle pigment pool was in the epoxidated form violaxanthin. We show, both by HPLC and by in vivo 505 nanometers absorbance changes, that in Fe deficient plants and in response to light, the de-epoxidated forms antheraxanthin and zeaxanthin were rapidly formed at the expense of violaxanthin. Several hours after returning to dark, the xanthophyll cycle was shifted again toward violaxanthin. The ratio of variable to maximum chlorophyll fluorescence from intact leaves was decreased by iron deficiency. However, in iron deficient leaves this ratio was little affected by light conditions which displace the xanthophyll cycle toward epoxidation or de-epoxidation. This suggests that the functioning of the xanthophyll cycle is not necessarily linked to protection against excess light input.     

PEG预处理对青稞种子萌发和幼苗生理特性的影响

选择国内外28份青稞品种材料幼苗第一片展开叶,分别测定其相对含水量和失水率,并选择其中对水分胁迫敏感与不敏感的材料各1份,研究不同浓度(5%～30%)聚乙二醇(PEG)预处理对青稞种子萌发、幼苗生长和生理特性的影响,探讨短期水分胁迫对青稞生长发育的调节作用。结果显示:(1)28个青稞材料中‘旱地紫青稞’幼苗叶片的相对含水量最高(60.16%)、‘大麻青稞’最低(38.98%),而离体失水率‘旱地紫青稞’最低(8.80%)、‘大麻青稞’最高(20.20%)。说明‘大麻青稞’对水分胁迫最敏感,而‘旱地紫青稞’最不敏感。(2)随着胁迫程度的增加,青稞种子的萌发率和生根率,幼苗的根长、苗高和鲜重均呈先增加后降低的趋势,‘旱地紫青稞’和‘大麻青稞’种子分别在15%和10%PEG处理下发芽和生根最佳且均与对照差异显著(P<0.05),两品种的幼苗根长、苗高和鲜重均在10%PEG处理下表现最佳,但‘大麻青稞’与对照差异不显著。(3)‘旱地紫青稞’幼苗叶片可溶性蛋白和叶绿素含量随PEG处理浓度增加而逐渐增加,而丙二醛含量和相对电导率则逐渐降低,并在30%PEG处理下效果差异极显著(P<0.01);‘大麻青稞’叶片可溶性蛋白和叶绿素含量随PEG处理浓度增加呈先增加后降低的趋势,丙二醛含量和相对电导率呈先降低后增加的趋势,并在20%PEG处理下最佳。研究表明,短时间低浓度PEG处理对青稞种子萌发、幼苗生长及可溶性蛋白、叶绿素、丙二醛含量和相对电导率等生理指标的改善均有一定的促进作用;高浓度PEG处理却具有抑制作用,且高浓度PEG胁迫条件下,耐旱性强比耐旱性弱品种的自我调控能力更强。     

Trade-off between leaf chlorophyll and betacyanins in Suaeda salsa in the Liaohe estuary wetland in northeast China

Aims Pigment composition is an important functional trait that can be affected by environmental factors. The objective of this study was to investigate the effect of soil salinity on pigment composition in Suaeda salsa by comparing chlorophyll and betacyanin content in the Liaohe estuary wetland, a typical coastal wetland in northeast China.Methods We investigated the plant biomass, percentage of red leaves and pigment content (chlorophyll a, chlorophyll b and betacyanins) in S. salsa in intertidal and supratidal zones of the upper, middle and lower reaches of the Liaohe estuary wetlands. The Na + content of both the soil and plant was also measured. Full analysis of variance and multivariate analysis were used to compare differences in pigment content and Na + content between the supratidal and intertidal zones.Important findings Pigment composition was significantly affected by soil salinity. With increasing soil salinity, the percentage of red leaves was higher in the intertidal zone than in the supratidal zone. In all three reaches, plants had lower chlorophyll a content and higher betacyanin content in the intertidal zone than in the supratidal zone. Compared to chlorophyll a, chlorophyll b was less sensitive to soil salinity. There were no differences in chlorophyll b content between the intertidal and supratidal zones in the upper and lower reaches. Furthermore, pigment composition was associated with both the plant tissue and soil Na + content. Compared to the supratidal zone, the intertidal zone had a higher Na + content in plants. There was a negative relationship between plant chlorophyll content and soil Na + content, but a positive relationship between betacyanin content and soil Na + content. Overall, the results indicated that there might be a trade-off between leaf chlorophyll and betacyanin content in S. salsa to maintain its growth and survival in high salinity environments.     

Chlorophyllase in <Emphasis Type="Italic">Piper betle</Emphasis> L. has a role in chlorophyll homeostasis and senescence dependent chlorophyll breakdown

Total chlorophyll content and chlorophyllase (chlorophyll-chlorophyllido hydrolase EC 3.1.1.14) activity in fresh leaves of Piper betle L. landrace KS was, respectively, twofold higher and eight fold lower than KV, showing negative correlation between chlorophyll and chlorophyllase activity. Specific chlorophyllase activity was nearly eightfold more in KV than KS. ORF of 918 nt was found in cloned putative chlorophyllase cDNAs from KV and KS. The gene was present as single copy in both the landraces. The encoded polypeptide of 306 amino acids differed only at two positions between the KV and KS; 203 (cysteine to tyrosine) and 301 (glutamine to glycine). Difference in chlorophyllase gene expression between KV and KS was evident in fresh and excised leaves. Up regulation of chlorophyllase gene by ABA and down regulation by BAP was observed in both the landraces; however, there was quantitative difference between KV and KS. Data suggests that chlorophyllase in P. betle is involved in chlorophyll homeostasis and chlorophyll loss during post harvest senescence.     

Temperature-dependent adjustment of the thermal stability of photosystem II in vivo: possible involvement of xanthophyll-cycle pigments

Moderately elevated temperatures induce a rapid increase in the heat and light resistance of photosystem II (PSII) in higher-plant leaves. This phenomenon was studied in intact potato leaves exposed to 35 °C for 2 h, using chlorophyll fluorometry, kinetic and difference spectrophotometry and photoacoustics. The 35 °C treatment was observed to cause energetic uncoupling between carotenoids and chlorophylls: (i) the steady-state chlorophyll fluorescence emission excited by a blue light beam (490 nm) was noticeably reduced as compared to fluorescence elicited by orange light (590 nm) and (ii) the quantum yield for photosynthetic oxygen evolution in blue light (400–500 nm) was preferentially reduced relative to the quantum yield measured in red light (590–710 nm). Analysis of the chlorophyll-fluorescence and light-absorption characteristics of the heated leaves showed numerous analogies with the fluorescence and absorption changes associated with the light-induced xanthophyll cycle activity, indicating that the carotenoid species involved in the heat-induced pigment uncoupling could be the xanthophyll violaxanthin. More precisely, the 35 °C treatment was observed to accelerate and amplify the non-photochemical quenching of chlorophyll fluorescence (in both moderate red light and strong white light) and to cause an increase in leaf absorbance in the blue-green spectral region near 520 nm, as do strong light treatments which induce the massive conversion of violaxanthin to zeaxanthin. Interestingly, short exposure of potato leaves to strong light also provoked a significant increase in the stability of PSII to heat stress. It was also observed that photosynthetic electron transport was considerably more inhibited by chilling temperatures in 35 °C-treated leaves than in untreated leaves. Further, pre-exposure of potato leaves to 35 °C markedly increased the amplitude and the rate of light-induced changes in leaf absorbance at 505 nm (indicative of xanthophyll cycle activity), suggesting the possibility that moderately elevated temperature increased the accessibility of violaxanthin to the membrane-located de-epoxidase. This was supported by the quantitative analysis of the xanthophyll-cycle pigments before and after the 35 °C treatment, showing light-independent accumulation of zeaxanthin during mild heat stress. Based on these results, we propose that the rapid adjustment of the heat resistance of PSII may involve a modification of the interaction between violaxanthin and the light-harvesting complexes of PSII. As a consequence, the thermoresistance of PSII could be enhanced either directly through a conformational change of PSII or indirectly via a carotenoid-dependent modulation of membrane lipid fluidity.Abbreviations and Symbols Fo and Fm initial and maximal level of chlorophyll fluorescence, respectively - Fv = Fm — Fo variable chlorophyll fluorescence - LHC(II) light-harvesting chlorophylla/b-protein complexes (of PSII) - photoacoustically measured quantum yield of photosynthetic oxygen evolution (in relative values) - _P fluorimetrically measured quantum yield of PSII photochemistry in the light - PFD photon flux density - q_E pH dependent quenching of chlorophyll fluorescence We thank Dr. J-L Montillet (CEA-Cadarache) for the use of his HPLC apparatus and Professor Y. Lemoine (University of Lille, France) for technical advice on HPLC.     

Photosynthetic light-harvesting function of carotenoids in higher-plant leaves exposed to high light irradiances

Exposure of barley (Hordeum vulgare L.) leaves to strong white light (1500 μmol photons · m⁻² · s⁻¹) decreased the quantum yield of photosynthetic oxygen evolution in green light preferentially absorbed by carotenoids (Φ-510) but not in red light exclusively absorbed by chlorophylls (Φ-650). This phenomenon was observed to be (i) rapidly induced (within a few minutes), (ii) slowly reversible in darkness (within about 1 h), (iii) insensitive to dithiothreitol and (iv) maximally induced by photon flux densities higher than about 1000 μmol · m⁻² · s⁻¹. Determination of the carotenoid composition of the major light-harvesting complex of PSII (LHCII) and analysis of the thylakoid membrane lipid fluidity before and after strong illumination of barley leaves in the presence or the absence of dithiothreitol showed that the light-induced decrease in the Φ-510/Φ-650 ratio did not require the physical detachment of carotenoids from the pigment antennae. Compared to barley plants grown under moderate light and temperature conditions, plants grown in sustained high irradiance at elevated temperature exhibited (i) a lower Φ-510/Φ-650 ratio, (ii) a reduced size of the functional PSII pigment antenna in green light (but not in red light) and (iii) a marked increase in the amount of free carotenoids found in non-denaturing Deriphat-containing electrophoretic gels of thylakoid membranes. Similarly, the Φ-510/Φ-650 ratio of the LHCII-deficient chlorina-f2 barley mutant was very low compared to the wild type. Separation and quantification of the cis/trans carotenoid isomers of barley leaves revealed that strong illumination did not induce pronounced cis-trans isomerization of xanthophylls. Taken together, the data suggest that the efficiency of energy transfer from carotenoids to chlorophylls varies with the light environment both in the short term and in the long term, with excess light energy noticeably inhibiting the photosynthetic light-harvesting function of carotenoids. The photoprotective significance of this carotenoid decoupling from the chlorophyll antennae is discussed. Received: 28 July 1997 / Accepted: 25 October 1997     

Differential Interaction Between PAV-like Isolates of Barley Yellow Dwarf Virus and Barley (Hordeum vulgare L.) genotypes

Four PAV-like isolates of barley yellow dwarf virus (BYDV) were identified as causing very severe (RG), severe (2t), moderately severe (3b) and mild symptoms (13t) in barley (Hordeum vulgare) cultivar Plaisant in a growth chamber at 25 days after inoculation. These isolates had different effects on a range of barley genotypes. Cultivar Vixen, which contains the Yd2 resistance gene, and 80–81BQCB10 were not affected by any isolate. Five other genotypes were significantly affected by at least one of the isolates. Line Ea52 (which is a mutant of the Japanese cultivar Chikurine Ibaraki) was more susceptible to BYDV-PAV than Chikurin Ibaraki 1. No serological differences were detected between the four isolates using monoclonal or polyclonal antibodies. Virus antigen concentration, estimated by enzyme-linked immunosorbent assay (ELISA), was correlated with the decrease in the shoot fresh weight for all isolates and all genotypes except for Vixen and 80–81BQCB10. In field tests, the severity of symptoms induced by the BYDV-PAV isolates was in accordance with that estimated in the growth chamber. However isolate 2t was more severe on cultivar Vixen and overcame the partial resistance of Chikurin Ibaraki 1 to the three other isolates. The results show that virus antigen concentration not only contributes to characterizing the resistance levels of barley genotypes but also the severity of BYDV-PAV isolates.