Chlorophyll Fluorescence Characteristics Research Articles

Effects of lanthanum nitrate on growth and chlorophyll fluorescence characteristics of Alternanthera philoxeroides under perchlorate stress

To investigate the effects of exogenous lanthanum (La) on Alternanthera philoxeroides (Mart.) Griseb under perchlorate stress, changes in the growth and physiological parameters were investigated in solution culture experiments under controlled conditions. Different concentrations of La (NO3)3 were used in our study. It was shown that 0.1 and 0.5 mg/L La3+ alleviated the inhibition effect of perchlorate on A. philoxeroides, including relative growth yield, dry weight of different organs, leaf area and root activity. And La3+ prevented decline in the relative chlorophyll content and chlorophyll fluorescence parameters including Fv/Fm, Fv′/Fm′, ΦPSII and ETR induced by perchlorate stress. Moreover, 0.5 mg/L La3+ showed an optimal mitigative effect, while excess La3+ (5.0 mg/L) led to synergistic effect on stress. Correlation analysis revealed a significant positive relationship between growth indexes and the chlorophyll fluorescence parameters, root activity and relative chlorophyll content (p<0.05). The results suggested that appropriate concentration of La3+ could effectively alleviate growth inhibition and injury of A. philoxeroides caused by perchlorate stress, and the mitigative effect of La3+ might be achieved by improving root activity, maintaining chlorophyll content and promoting photochemical efficiency of photosystem II of A. philoxeroides under perchlorate stress.

Growth, gas exchange, and water-use efficiency response of two young apple cultivars to drought stress in two scion-one rootstock grafting system

The combination of two scion-one rootstock was used for two apple cultivars, ‘Pink Lady’ and ‘Qinguan’, budded on the same, one-year-old Malus hupehensis (Pamp.) Rehd. to reduce the impact of root and pot size and in order to understand the growth, water-use efficiency (WUE), and chlorophyll fluorescence characteristics. The two-scion grafted trees were planted in plastic pots under two water regimes, i.e. 70% field capacity (FC) and 55% FC. Results indicated that different scions were affected differently by drought stress. ‘Pink Lady’ had higher net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) compared with ‘Qinguan’ under both water treatments. However, ‘Qinguan’ had lower minimal fluorescence (F0), higher maximum fluorescence (Fm), and higher maximum photochemical efficiency of photosystem II (Fv/Fm) than ‘Pink Lady’ at 55% FC. Moreover, ‘Qinguan’ had larger shoot dry mass (ShDM) and higher intrinsic WUEI than ‘Pink Lady’ under both water status. Gas-exchange and growth parameters, except for PN and scion diameter, were significantly affected by the cultivar and water treatment. At 70% FC, ShDM was significantly correlated with WUEI. Moreover, WUEI was negatively linearly correlated with gs at either 70 or 55% FC. These results might indicate that ‘Pink Lady’ was more sensitive to drought than ‘Qinguan’. ‘Qinguan’ apple was able to improve WUE more than ‘Pink Lady’ under both well-watered and drought conditions. The growth parameters and photosynthetic capacity of two different scions showed that the combination of double scion-one rootstock might eliminate the influences of the rootstock and pot size.

Effects of Nitrogen Fertilizer Level on Chlorophyll Fluorescence Characteristics in Flag Leaf of Super Hybrid Rice at Late Growth Stage

To compare the effects of slow-release nitrogen fertilizer at six different levels on the flag leaf chlorophyll fluorescence characteristics of super hybrid rice, a field fertilization experiment was conducted with super hybrid rice Y Liangyou 1 as a test material. The photosynthetic electron transport rate (ETR), effective quantum yield (EQY), photochemical quenching coefficient (qP), and non-photochemical quenching coefficient (NPQ) of flag leaves were measured at the initial heading, full heading, 10 d after full heading and 20 d after full heading stages. Results showed that the values of ETR, EQY and qP increased with rice development from initial heading to 20 d after full heading, whereas the NPQ decreased. During the measured stages, ETR, EQY and qP increased initially and then decreased as nitrogen application amount increased, but they peaked at different nitrogen fertilizer levels. The maximum ETR and EQY values appeared at the treatment of 135 kg/hm2 N. In conclusion, the optimum nitrogen amount for chlorophyll fluorescence characteristics of super hybrid rice was 135-180 kg/hm2.

Safety of herbicide Sigma Broad on Radix Isatidis (Isatis indigotica Fort.) seedlings and their photosynthetic physiological responses

The study was performed to explore the safety of sulfonylurea herbicide Sigma Broad (mesosulfuron-methyl and iodosulfuron-methyl sodium) on Radix Isatidis (Isatis Indigotica Fort.) seedlings and the photosynthetic physiological response of the crop to the herbicide. Through pot experiment, biological mass, leaf area, photosynthetic pigment content, photosynthetic rate, chlorophyll fluorescence characteristics, and P700 parameters of Radix Isatidis seedlings were analyzed 10days after Sigma Broad treatment at 5th leaf stage. The results showed that biological mass, leaf area, total chlorophyll, chlorophyll a, chlorophyll b, and carotenoids content, Pn, transpiration rate, stomatal conductance, PSII maximum quantum yield, PSII effective quantum yield, PSII electron transport rate, photochemical quenching, quantum yield of regulated energy dissipation in PS II, maximal P700 change, photochemical quantum yield of PS I, PS I electron transport rate, and quantum yield of non-photochemical energy dissipation due to donor side limitation in PS I decreased with increasing herbicide dosages, whereas chlorophyll a/b, stomatal limitation value, initial fluorescence, quantum yield of non-regulated energy dissipation in PS II and quantum yield of non-photochemical energy dissipation due to accepter side limitation in PS I increased. In conclusion, treatment with Sigma Broad higher than 13.48gai/ha was extremely unsafe to Radix Isatidis seedlings, which might be associated with damage of chloroplast, PS II and PS I structure, electron transport and its distribution between PS II and PS I, and decreased photosynthesis caused by the herbicide.

Genotypic difference in salinity tolerance in quinoa is determined by differential control of xylem Na+ loading and stomatal density

Quinoa is regarded as a highly salt tolerant halophyte crop, of great potential for cultivation on saline areas around the world. Fourteen quinoa genotypes of different geographical origin, differing in salinity tolerance, were grown under greenhouse conditions. Salinity treatment started on 10 day old seedlings. Six weeks after the treatment commenced, leaf sap Na and K content and osmolality, stomatal density, chlorophyll fluorescence characteristics, and xylem sap Na and K composition were measured. Responses to salinity differed greatly among the varieties. All cultivars had substantially increased K+ concentrations in the leaf sap, but the most tolerant cultivars had lower xylem Na+ content at the time of sampling. Most tolerant cultivars had lowest leaf sap osmolality. All varieties reduced stomata density when grown under saline conditions. All varieties clustered into two groups (includers and excluders) depending on their strategy of handling Na+ under saline conditions. Under control (non-saline) conditions, a strong positive correlation was observed between salinity tolerance and plants ability to accumulate Na+ in the shoot. Increased leaf sap K+, controlled Na+ loading to the xylem, and reduced stomata density are important physiological traits contributing to genotypic differences in salinity tolerance in quinoa, a halophyte species from Chenopodium family.

Photosynthetic and antioxidant responses of Liquidambar formosana and Schima superba seedlings to sulfuric-rich and nitric-rich simulated acid rain

To study whether differential responses occur in photosynthesis and antioxidant system for seedlings of Liquidambar formosana, an acid rain (AR)-sensitive tree species and Schima superba, an AR-tolerant tree species treated with three types of pH 3.0 simulated AR (SiAR) including sulfuric-rich (S-SiAR), nitric-rich (N-SiAR), sulfate and nitrate mixed (SN-SiAR), we investigated the changes of leaf necrosis, chlorophyll content, soluble protein and proline content, photosynthesis and chlorophyll fluorescence characteristics, reactive oxygen species production, membrane lipid peroxidation, small molecular antioxidant content, antioxidant enzyme activities and related protein expressions. Our results showed that SiAR significantly caused leaf necrosis, inhibited photosynthesis, induced superoxide radical and hydrogen peroxide generation, aggravated membrane lipid peroxidation, changed antioxidant enzyme activities, modified related protein expressions such as Cu/Zn superoxide dismutase (SOD), l-ascorbate peroxidase (APX, EC 1. 11. 1. 11), glutathione S transferase (GST, EC 2. 5. 1. 18) and Rubisco large subunit (RuBISCO LSU), altered non-protein thiols (NPT) and glutathione (GSH) content in leaves of L. formosana and S. superba. Taken together, we concluded that the damages caused by SiAR in L. formosana were more severe and suffered from more negative impacts than in S. superba. S-SiAR induced more serious damages for the plants than did SN-SiAR and N-SiAR.

缺镁胁迫对纽荷尔脐橙叶绿素荧光特性的影响

以1年生枳砧纽荷尔脐橙为材料,测定不同叶龄叶片相对叶绿素含量和荧光参数,研究缺镁胁迫对叶片叶绿素合成与荧光特性的影响。结果显示,随着叶位的升高,低镁组和无镁组秋梢叶片(老叶)的相对叶绿素含量、<em>F_v/F_m</em>呈明显增加趋势,而春梢叶片(新叶)的相对叶绿素含量、<em>F_v/F_m</em>差异不显著;随着缺镁胁迫程度的增大,叶片相对叶绿素含量、<em>F_v/F_m</em>、光响应能力(<em>ΔF_v/F_m</em>、<em>qP</em>和<em>rETR</em>)均呈降低趋势,而非光化学淬灭(<em>qN</em>)呈升高趋势,低镁组老叶、新叶及无镁组新叶与对照差异不显著(<em>P</em>>0.05),而无镁组老叶与对照差异显著(<em>P</em><0.05)。表明,缺镁胁迫严重时不仅会导致纽荷尔脐橙老叶光合能力降低,也会导致其新叶光合能力降低;短期缺镁胁迫对老叶光合能力的影响显著大于新叶,而且这种差异随着缺镁程度的增大而呈增大趋势。因此,在夏季高光照条件下缺镁纽荷尔脐橙老叶易发生光抑制,缺镁严重时甚至会产生光伤害,导致叶片早衰。;Magnesium (Mg), an essential nutritional element for citrus growth and development, plays an important role in maintaining chloroplast structure, activating a variety of enzymes and improving crop yield and quality. In recent years, with the increased rate of NPK fertilizer application and the decreased rate of manure application, many Newhall navel orange orchards in Gannan in Jiangxi Province, the south of Hunan Province and the north of Guangxi Province have suffered leaf chlorosis due to Mg deficiency. This has become one of the important factors in the South region impeding the yield and quality of citrus fruit. The purpose of the present study is to explore the influence of Mg deficiency stress on chlorophyll synthesis and the fluorescence characteristics of Newhall navel orange (<em>Citrus sinensis</em> Osbeck) at different foliar ages. The experimental materials were one-year-old Newhall navel orange plants grafted onto trifoliate orange rootstock. The plants were grown in sand:perlite (1:1, v/v) medium and irrigated with deionized water for 24 days to stimulate new root growth. Plants were then irrigated every other day for two months with half-strength Hoagland's nutrient solution containing three Mg concentrations: 0 mmol/L (Mg-deficiency, DM), 0.1 mmol/L (low-Mg, LM) or 1 mmol/L (control) MgSO₄. After Mg deficient treatment for two months, a portable chlorophyll meter (SPAD-502) was used to determine the relative amount of leaf total chlorophyll content at different foliar ages. Simultaneously, using a Pulse-Amplitude-Modulation (PAM-2500) fluorometer, the maximum quantum efficiency of photochemistry in photosystem II in the dark (<em>F_v/F_m</em>) was calculated for the three treatments at different foliar ages. In addition, the rapid light response curves of the leaves were determined <em>in situ</em> with a PAM-2500 fluorometer to obtain the chlorophyll fluorescence characteristic parameters, including the effective quantum yield of photosystem II (<em>ΔF_v/F_m</em>), photochemical quenching (<em>qP</em>), non-photochemical quenching (<em>qN</em>) and relative electron transport rate (<em>rETR</em>). Results from recent studies showed that in low-Mg and Mg-deficient treatments, SPAD readings and <em>F_v/F_m</em> in last year's autumn flush leaves increased remarkably with the rising of leaf position, whereas those in this year's spring flush leaves were not statistically significant among leaf positions. SPAD readings, <em>F_v/F_m</em> and light response ability (<em>ΔF_v/F_m</em>, <em>qP</em>, <em>rETR</em>) decreased as the levels of Mg reduced, but <em>qN</em> increased. For chlorophyll fluorescence characteristics of last year's autumn flush leaves, the Mg-deficient treatment was remarkably different compared with the control, whereas there was no significant difference between the low-Mg treatment and the control. For chlorophyll fluorescence characteristics of this year's spring flush leaves, no significant differences were observed among the low-Mg, Mg-deficiency and control treatments. These findings suggested that Mg deficiency stress caused obvious decrement of photosynthetic capacity in last year's autumn flush leaves, and reduction of photosynthetic capacity in this year's spring flush leaves. In addition, short-term Mg deficiency would have a greater adverse effect on last year's autumn flush leaves depending on the degree of Mg deficiency stress. Therefore, under high irradiance in summer, Mg deficiency would make last year's autumn flush leaves of Newhall navel orange sensitive to photoinhibition. Severe Mg deficiency could even cause light-induced damage leading to the occurrence of premature senility (e.g. chlorosis).

枫杨幼苗对土壤水分"湿-干"交替变化光合及叶绿素荧光的响应

以盆栽1年生枫杨幼苗为实验材料,通过人工设置土壤水分来模拟三峡库区消落带不同土壤水分对枫杨幼苗的光合参数、光合色素含量、叶绿素荧光特性等的影响。试验设置4个处理组,分别为常规供水、常规供水-轻度干旱-复水、水淹、水淹-轻度干旱-复水,3个处理期分别为前期(0-33 d)、中期(34-63 d)、后期(64-78 d)。结果表明,不同的水分处理显著地影响了枫杨幼苗"表观性"的气体交换、光合色素含量和水分利用效率等特性,但相较而言对枫杨幼苗"内在性"的叶绿素荧光特性影响较小,且影响的结果和程度因处理组和指标而异。78 d时,除胞间CO₂浓度(<em>Ci</em>)、叶绿素a/叶绿素b、光化学猝灭值(<em>qP</em>)和非光化学淬灭值(<em>qN</em>)外,水淹组(FL组)的各项指标在4个处理组中都为最低值;"湿-干"交替组(FD组)的净光合速率(<em>Pn</em>)、蒸腾速率(<em>Tr</em>)、气孔导度(<em>Gs</em>)及总叶绿素含量则表现出先降低复水后显著增加的趋势;DR组的变化趋势与FD组类似,但变化的幅度较FD组小。研究发现,枫杨幼苗面对不同水分状况呈现出了一定的敏感特性,但随着胁迫时间的延长其无论是从光合、水分利用还是叶绿素荧光特性方面都表现出积极的响应,较能适应干旱、水淹、"湿-干"交替等多种环境胁迫,且在胁迫解除后能够迅速恢复生长,可以考虑用于三峡库区消落带的植被重建。;The Three Gorges Dam has created a new riparian zone which is called 30m-water-level fluctuating zone of the Three Gorges Reservoir of the Yangtze River. Altered ecosystems of the riparian zone can disrupt the hydrological regime by reducing inundation, or creating longer term submergence, which adversely affects riparian vegetation, and in particular, the native plant species. Chinese wingnut (<em>Pterocarya stenoptera</em>) is a dominant native riparian tree species in the Three Gorges Reservoir region, and thus has to face the modified riparian environment. In order to shed light on the impacts of soil water regimes in this region on the Chinese wingnut, 4 water treatments were imposed on 1-year-old seedlings of Chinese wingnut for more than 2 months. The water treatments included normal water supply (CK), normal water supply-light drought-normal water supply (DR), flooding (FL) and flooding-light drought-normal water supply (FD), which simulated the modified hydrological regime in the riparian zone of the Three Gorges Reservoir region. The treatment of 3 stages for DR and FD groups lasted 33, 30 and 15 days respectively. The effects of water treatments on photosynthetic parameters, photosynthetic pigment contents and chlorophyll fluorescence characteristics of Chinese wingnut seedlings were investigated after 0, 33, 63 and 78 days of water treatment. The results showed that net photosynthetic rate (<em>Pn</em>), stomatal conductance (<em>Gs</em>), transpiration rate (<em>Tr</em>), photosynthetic pigment contents (chlorophyll a, chlorophyll b and carotenoid) and water use efficiency (<em>WUE</em>) of Chinese wingnut seedlings were reduced significantly in DR, FL and FD treatments as compared to CK. However, the chlorophyll fluorescence features of Chinese Wingnut seedlings in these three treatments were slightly reduced comparable to that of CK. Compared to other three treatments, seedlings in FL group were adversely influenced dramatically. At the end of the treatment, the <em>Pn</em> of Chinese wingnut seedlings under FL treatment was reduced by 65.9%,<em>WUE</em> was reduced by 65.7%, and total chlorophyll content was reduced by 68.7% comparing with that of CK. In contrast to CK group,<em> Pn</em>, <em>Tr</em>, <em>Gs</em> and total chlorophyll in FD groups were also decreased significantly in the beginning of the treatment due to flooding and drought, but they were increased significantly after rehydration. The seedlings in DR groups showed similar but lower variation as to those of FD. The results suggested that the seedlings of Chinese wingnut were sensitive to soil water stress including flooding and drought, although they showed obvious tolerant ability to water stress in terms of the characteristics of morphology, photosynthesis, water use efficiency and chlorophyll fluorescence. Additionally, all of them showed excellent recovery ability after stress being released. Therefore, Chinese wingnut might be suitable to the modified hydrological regime caused by the Three Gorges Dam, and thus could be applied to vegetation reconstruction in the water-level fluctuating zone of the Three Gorges Reservoir for its adaption to drought, flooding and flooding-drought alternative variation.

浮游植物在不同光质和光强激发下的叶绿素荧光特性

浮游植物在不同光质和光强激发下的叶绿素荧光特性

Fluorescência da clorofila a em plantas de pessegueiro da cultivar maciel enxertada sobre diferentes porta-enxertos

O objetivo deste trabalho foi avaliar características da fluorescência da clorofila a em plantas de pessegueiro da cv. Maciel enxertadas em seis porta-enxertos. As análises da fluorescência da clorofila a, do índice de clorofila e do comprimento das folhas iniciaram-se após o período invernal e foram repetidas até aproximadamente 150 dias, totalizando seis coletas. O início da ontogenia das folhas foi caracterizado por alguns parâmetros de fluorescência mais elevados. Elevada pluviosidade, ocorrida entre os dias 61 e 112 do início do experimento, foi fator ambiental que causou maior alteração nos parâmetros do Teste JIP, principalmente aqueles relacionados ao fotossistema I. O índice de clorofila não foi influenciado pelo efeito das associações copa x porta-enxerto. Queda nos valores de PI TOTAL foram verificadas no período de maior precipitação, comportamento que foi independente dos porta-enxertos, exceto para as plantas enxertadas no porta-enxerto 'Rubirá', que apresentaram menores danos ao aparato fotossintético. De maneira geral, os porta-enxertos estudados, em combinação com a cv. Maciel, não afetaram a absorção e o aproveitamento da energia luminosa pelo sistema fotossintético.

Two-photon excitation chlorophyll fluorescence lifetime imaging: a rapid and noninvasive method for in vivo assessment of cadmium toxicity in a marine diatom Thalassiosira weissflogii

We demonstrate that a two-photon excitation fluorescence lifetime imaging technology can rapidly and noninvasively assess the cadmium (Cd)-induced toxic effects in a marine diatom Thalassiosira weissflogii. The chlorophyll, an intrinsic fluorophore, was used as a contrast agent for imaging of cellular structures and for assessment of cell toxicity. The assessment is based on an imaging-guided statistical analysis of chlorophyll fluorescence decay. This novel label-free imaging method is physically based and free of tedious preparation and preprocessing of algal samples. We first studied the chlorophyll fluorescence quenching induced by the infrared two-photon excitation laser and found that the quenching effects on the assessment of Cd toxicity could be well controlled and calibrated. In the toxicity study, chlorophyll fluorescence lifetime images were collected from the diatom samples after exposure to different concentrations of Cd. The alteration of chloroplast structure at higher Cd concentration was clearly identified. The decay of chlorophyll fluorescence extracted from recorded pixels of high signal-to-noise ratio in the fluorescence lifetime image was analyzed. The increase of average chlorophyll fluorescence lifetime following Cd treatment was observed, indicating the Cd inhibition effect on the electron transport chain in photosynthesis system. The findings of this study show that the temporal characteristics of chlorophyll fluorescence can potentially be utilized as a biomarker for indicating Cd toxicity noninvasively in algal cells.

Associated growth of C3 and C4 desert plants helps the C3 species at the cost of the C4 species

C3 desert plant Reaumuria soongorica (RS-C3) and C4 desert plant Salsola passerina (SP-C4) may exist either in individual or in associated communities. Carbon isotope composition, leaf water potential, gas exchange and chlorophyll fluorescence characteristics of the individual and associated communities were compared with reveal, whether the associated growth represent an advantage under harsh habitat. The results showed that the δ13C values of leaves of RS-C3 and SP-C4 across different habitats fluctuated, respectively, from −24 to −27 ‰ and from −14 to −16 ‰. Leaf water potential of RS-C3 was lower than SP-C4 all day long, growing either individually or associated with the C3 plant. When associated with the C4 plant, the net photosynthetic rate of the RS-C3 increased, and the photosynthetic rate of the partner SP-C4 decreased. The transpiration rates of the associated RS-C3 and SP-C4 were both lower than in their individual colonies. In associated communities, in RS-C3, the maximal photochemical efficiency, the effective photochemical efficiency, the relative electron transport rate, the photochemical quenching of PS II increased, and the non-photochemical quenching of PS II decreased; all these parameters changed oppositely in the SP-C4 plant. This shows that, in the associated community, the C4 plants might facilitate adaptation of the RS-C3, while SP-C4 plant can adapt to the harsh environment through their own specialties. The association favored the expression of natural photosynthetic characteristics and survival of RS-C3, while retarded the growth of SP-C4. Associated growth decreases the transpiration rate of the whole community; it is conducive to improve its water use efficiency.

Non-invasive quality determination of spinach under simulated sale conditions and prediction of possible changes

Chlorophyll fluorescence, especially the optimum quantum yield Fv/Fm, is used to quantify the physiological state of plants, because stress, infections or wilting may lower the optimum quantum yield. The characteristics of chlorophyll fluorescence have attracted our attention for its use to determine the quality of spinach, because the measurement of Fv/ Fm during storage can be performed quickly and non-destructively, delivering information about spinach quality and its sale suitability. Applicability of modern techniques for quick and non-invasive in vivo determination of such parameters as quality and freshness of spinach under simulated sale conditions was tested in our study. In this experiment, application of chlorophyll fluorescence for quantification of quality as well as physical and physiological changes which occur in fresh products was verified. The experiment was conducted on spinach, a product characterized by rapid appearance of postharvest losses. Spinach was harvested as leafy vegetable for direct consumption and stored for 5 days (16 h in a cooling room at 2-4°C, 96-98% relative humidity, followed by 8 h at room temperature: ca 22oC, 65% relative humidity). Variants were represented by different cultivation conditions (fertilizer, leaf application of Previcur, CaCl2 and Cerone). The investigations revealed that fresh mass losses in the postharvest phase could be described by changes of Fv/Fm spinach leaves adapted to darkness by a linear relationship of parameters (r=0.77). The disadvantage of chlorophyll fluorescence measurement was the less precise determination of the critical loss of fresh mass of 3%. Instead, losses of 4 to 5% resulted in a the decrease of optimum quantum yield below the critical value of 0.80, which indicates the occurrence of postharvest stress. Leaf application

Effects of different light intensities on chlorophyll fluorescence characteristics and yield in lettuce

The worldwide demand for Romaine lettuce (Lactuca sativa L.) is increasing. Regulation measures of supplementary or shading light are often used in the production of lettuce in some regions. However, inconsistent results on light saturation point of lettuce from previous studies did not facilitate the regulation of light intensity. In the present study, the effects of different light intensities on chlorophyll fluorescence characteristics and yield in lettuce were investigated. The results show that in the 100 and 800μmolm−2s−1 treatments, the values of qP, ΦPSII, and ETR were low, resulting in low light use efficiency and plant yield in lettuce. In the 200, 400, and 600μmolm−2s−1 treatments, the values of qP, ΦPSII, and ETR were high, resulting in high light use efficiency and plant yield in lettuce. Light-use efficiency in the 200μmolm−2s−1 treatment was the highest, whereas plant yield in the 600μmolm−2s−1 treatment was the highest. No significant difference in plant yield was observed between the 400 and 600μmolm−2s−1 treatment. In addition, judging by the values of Fv/Fm, the lettuce samples were under rather serious stress in the 800μmolm−2s−1 treatment, whereas they were under mild stress in the 600μmolm−2s−1 treatment. Based on these results, an optimal regulation strategy of light intensity that can maximize economic benefits for lettuce growers in some regions of the world is proposed. That is the range of 400–600μmolm−2s−1 is a recommendable light intensity for production of certain types of lettuce, and light intensity of 400μmolm−2s−1 can be an optimal value of supplementary light for winter greenhouse production of certain types of lettuce in higher latitudes, while light intensity of 600μmolm−2s−1 can be an optimal value of shading light for late spring and early autumn production of certain types of lettuce in lower latitudes.

Chlorophyll fluorescence characteristics throughout spring triticale development stages as affected by fertilization

Little is known about the response of spring triticale (× Triticosecale Wittm.) chlorophyll fluorescence parameters (Fo – initial fluorescence intensity, Fm – maximal fluorescence, Fv/Fm – maximum quantum yield of photosystem II) to nitrogen fertilization. We investigated after-effects of basic (N60P60K60 and N120P120K120) and additional (N30 and N60) fertilization on chlorophyll fluorescence characteristics at four main phonological development stages of spring triticale under field conditions. Both additional nitrogen (N) rates soon after application induced short-acting stress on both basic fertilization backgrounds only in dry weather conditions. Initial fluorescence intensity exhibited direct relationship (R2=0.52) with an additional nitrogen rate only at the beginning of booting (BBCH 31) in dry 2008. The correlation of maximal fluorescence with additional nitrogen rate was significant during the whole experimental period. Maximum quantum yield of photosystem II directly correlated with both basic and additional nitrogen fertilization from flag leaf stage (BBCH 37) to completion of flowering (BBCH 69) in 2008. Initial fluorescence intensity decreased after spring triticale heading stage.

Brassinosteroid alleviates phenanthrene and pyrene phytotoxicity by increasing detoxification activity and photosynthesis in tomato

The present study was carried out to investigate the effects of exogenously applied 24-epibrassinolide (BR) on growth, gas exchange, chlorophyll fluorescence characteristics, lipid peroxidation and antioxidant systems of tomato seedlings grown under different levels (0, 10, 30, 100 and 300 μM) of phenanthrene (PHE) and pyrene (PYR) in hydroponics. A concentration-dependent decrease in growth, photosynthetic pigment contents, net photosynthetic rate (Pn), stomatal conductance (Gs), maximal quantum yield of PSII (Fv/Fm), effective quantum yield of PSII ( Φ PSII), photochemical quenching coefficient (qP) has been observed following PHE and PYR exposure. By contrast, non-photochemical quenching coefficient (NPQ) was increased. PHE was found to induce higher stress than PYR. However, foliar or root application of BR (50 nM and 5 nM, respectively) alleviated all those depressions with a sharp improvement in the activity of photosynthetic machinery. The activities of guaicol peroxidase (GPOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) as well as content of malondialdehyde (MDA) were increased in a dose-dependent manner under PHE or PYR treatments. Compared with control the highest increments of GPOD, CAT, APX, GR and MDA by PHE/PYR alone treatments were observed following 300 μM concentration, which were 67%, 87%, 53%, 95% and 74% by PHE and 42%, 53%, 30%, 86% and 62% by PYR, respectively. In addition, both reduced glutathione (GSH) and oxidized glutathione (GSSG) were induced by PHE or PYR. Interestingly, BR application in either form further increased enzymatic and non enzymatic antioxidants in tomato roots treated with PHE or PYR. Our results suggest that BR has an anti-stress effect on tomato seedlings contaminated with PHE or PYR and this effect is mainly attributed by increased detoxification activity.

Analysis of photosynthetic pigments and chlorophyll fluorescence characteristics of different strains of Porphyra yezoensis

The levels of photosynthetic pigments and chlorophyll fluorescence of Porphyra yezoensis strains selected from high-light environments were investigated. Sutong and Sulian strains originated from the same high-light environment but were selected from different sites on the Yellow Sea coast of Jiangsu Province, China. In January (a low temperature period), the Sulian strain and the WT (a widely cultivated strain) had higher levels of chlorophyll a, phycoerythrin, phycocyanin, and allophycocyanin, and higher actual photochemical efficiency of PSII (ΔF/Fm′) than the Sutong strain. This indicated that Sulian and the WT may have better adaptation to low temperature. In March (an optimal temperature period), Sutong had higher levels of photosynthetic pigments and higher ΔF/Fm′ than the WT and Sulian strains. This suggested that Sutong had higher light use efficiency at optimal temperatures and that most energy absorbed by PSII was used for photosynthetic electron transport. The differing areas of origin of these strains may have resulted in these differences in temperature adaptation.

Effect of water deficit and potassium fertilization on photosynthetic activity in cotton plants

Physiological mechanisms that can contribute to drought tolerance and the role of potassium fertilization in cotton were studied by evaluation of parameters describing photosynthetic performance. Gas-exchange and chlorophyll fluorescence characteristics were measured on leaves of two cotton genotypes, one drought sensitive (Nazilli 84-S) and the other drought tolerant (Sahin 2000), grown in field conditions in the Aegean region of Turkey under different regimes of water and potassium supply. It was shown that under drought conditions without potassium fertilization Sahin 2000 had a higher photosynthetic rate and stomatal conductance than Nazilli 84-S. Potassium fertilization to a great extent compensated for the inhibitory effect of drought on photosynthesis. Application of the JIP test by using chlorophyll fluorescence data revealed that the drought sensitive Nazilli 84-S was more responsive to potassium fertilization than Sahin 2000, as judged by a number of parameters representing quantum efficiency of the processes and energy fluxes in photosystem (PS) II. The observed decrease in photosynthetic CO2 assimilation in both cotton cultivars under drought conditions was not accompanied by any significant decrease in the electron transport flux in PSII and maximum quantum yield of primary photochemistry.

Photosynthetic acclimation to light in woody and herbaceous species: a comparison of leaf structure, pigment content and chlorophyll fluorescence characteristics measured in the field

Acclimation of foliage photosynthetic properties occurs with varying time kinetics, but structural, chemical and physiological factors controlling the kinetics of acclimation are poorly understood, especially in field environments. We measured chlorophyll fluorescence characteristics, leaf total carotenoid (Car), chlorophyll (Chl) and nitrogen (N) content and leaf dry mass per area (LMA) along vertical light gradients in natural canopies of the herb species, Inula salicina and Centaurea jacea, and tree species, Populus tremula and Tilia cordata, in the middle of the growing season. Presence of stress was assessed on the basis of night measurements of chlorophyll fluorescence. Our aim was to compare the light acclimation of leaf traits, which respond to light availability at long (LMA and N), medium (Chl a/b ratio, Car/Chl ratio) and short time scales (fluorescence characteristics). We found that light acclimation of nitrogen content per unit leaf area (N(area)), chlorophyll content per unit dry mass (Chl(mass)) and Chl/N ratio were related to modifications in LMA. The maximum PSII quantum yield (F(v) /F(m)) increased with increasing growth irradiance in I. salicina and P. tremula but decreased in T. cordata. Leaf growth irradiance, N content and plant species explained the majority of variability in chlorophyll fluorescence characteristics, up to 90% for steady-state fluorescence yield, while the contribution of leaf total carotenoid content was generally not significant. Chlorophyll fluorescence characteristics did not differ strongly between growth forms, but differed among species within a given growth form. These data highlight that foliage acclimation to light is driven by interactions between traits with varying time kinetics.

Characteristics of gas exchange and chlorophyll fluorescence in red and green leaves of Begonia semperflorens

To determine the effects of leaf colour on gas exchange and chlorophyll fluorescence, two genotypes of Begonia semperflorens with green leaves or red leaves were compared. The red leaves showed a high accumulation of anthocyanins and high absorbance at 282 and 537 nm while the green leaves exhibited a higher net photosynthetic rate and lower thermal dissipation of light energy. It seems likely that anthocyanins in the vacuoles restricted the absorption of green light to the chloroplasts, leading to a decrease in the efficiency of excitation capture by open PS 2 centres, photochemical quenching and CO2 assimilation.