Estimation of Primary Productivity by Chlorophyll a in vivo Fluorescence in Freshwater Phytoplankton

Primary productivity in marine waters is widely estimated by the measurements of ¹⁴C incorporation, the underwater light climate, and the absorption spectra of phytoplankton. In bio-optical models the quantum efficiency of carbon fixation derived from ¹⁴C incorporation rates, the photosynthetically absorbed radiation derived from the underwater light climate, and the phytoplankton absorption spectra are used to calculate time- and depth-integrated primary productivity. Due to the increased sensitivity of commercially available fluorometers, chlorophyll a in vivo fluorescence became a new tool to assess the photosynthetic activity of phytoplankton. Since fluorescence data yield only relative photosynthetic electron transport rates, a direct conversion into absolute carbon fixation rates is not possible. Here, we report a procedure how this problem can be adressed in freshwater phytoplankton. We adapted a marine bio-optical model to the freshwater situation and tested if this model yields realistic results when applied to a hypertrophic freshwater reservoir. Comparison of primary productivity derived from ¹⁴C incorporation to primary productivity derived from Chl a fluorescence showed that the conversion of fluorescence data into carbon fixation rates is still an unsolved problem. Absolute electron transport rates calculated from fluorescence data tend to overestimate primary production. We propose that the observed differences are caused mainly by neglecting the package effect of pigments in phytoplankton cells and by non-carbon related electron flow (e.g., nitrogen fixation). On the other hand, the ¹⁴C incorporation rates can be artificially influenced by "bottle effects", especially near the water surface, where photoinhibition, photorespiration, and Mehler reaction can play a major role.     

Low growth temperature-induced changes to pigment composition and photosynthesis in Zea mays genotypes differing in chilling sensitivity

The effects on pigment composition and photosynthesis of low temperature during growth were examined in the third leaf of three chilling-tolerant and three chilling-sensitive genotypes of Zea mays L. The plants were grown under a controlled environment at 24 or 14 °C at a photon flux density (PFD) of 200 or 600 μ mol m^–2 s^–1. At 24 °C, the two classes of genotypes showed little differences in their photosynthetic activity and their composition of pigments. At 14 °C, photosynthetic activity was considerably reduced but the chilling-tolerant genotypes displayed higher photosynthetic rates than the chilling-sensitive ones. Plants grown at 14 °C showed a reduced chlorophyll (Chl) a + b content and a reduced Chl a / b ratio but an increased ratio of total carotenoids to Chl a + b . These changes in pigment composition in plants grown at low temperature were generally more pronounced in the chilling-sensitive genotypes than in the tolerant ones, particularly at high PFD. Furthermore, at 14 °C, all the genotypes showed increased ratios of lutein, neoxanthin and xanthophyll-cycle carotenoids to Chl a + b but a reduced ratio of β -carotene to Chl a + b , especially at high PFD. At 14 °C, the chilling-tolerant genotypes, when compared with the sensitive ones, were characterized by higher contents of β -carotene and neoxanthin, a lower content of xanthophyll-cycle carotenoids, a lower ratio of xanthophylls to β -carotene, and less of their xanthophyll-cycle carotenoid pool in the form of zeaxanthin. These differences between the two classes of genotypes were more pronounced at high PFD than at low PFD. The results are discussed in terms of the relationship that may exist in maize between pigment composition and the capacity to form an efficient photosynthetic apparatus at low growth temperature.     

Intra-tissue Characteristics of Chloroplasts in the Lamina and Petiole of Mature Winter Leaf of Arum italicum Miller

Abstract: Laminae and petioles from mature winter leaves of Arum italicum were studied in order to obtain information on the sun—shade intra-tissue properties of chloroplasts. This inference was based on the: (1) micro- and submicroscopic characteristics of the chloroplasts, (2) cytochemical localizations of functional PS I and PS II, (3) pigment patterns and compositions, (4) immunolocalization of Rubisco, and (5) net photosynthesis. It was inferred that all the chloroplasts across the lamina had adaptations to intermediate shade conditions, without a sun-shade dimorphism between the palisade and the spongy tissues. In the petiole, where normally-structured chloroplasts were surprisingly present in the entire thickness of the organ, a structural and chemical dimorphism was found between the outer chlorenchyma and the inner aerenchyma where intermediate shade-type and extreme shade-type chloroplasts were present, respectively. However, some anomalies in the pigment composition were noted chiefly in the inner aerenchyma (low concentrations of β-carotene and lutein, absence of zeaxanthin, presence of unusual pigments, for instance lutein epoxide, lutein cis-isomer, and chlorophyllide a). The Rubisco immunolabelling in the outer chlorenchyma of the petiole was similar to that in the lamina, while it was very scant in the inner aerenchyma. Net photosynthesis in the petiole was about 75% of that recorded in the lamina. These data suggest that the petiole of the mature winter leaf of A. italicum closely co-operates with the lamina for enhancing light capture and utilization.     

Sucrose and jasmonic acid interact in photosynthetic pigment metabolism and development of potato (Solanum tuberosum L. cv. Sante) grown in vitro

Potato (Solanum tuberosum L., cv. Sante) plantlets grown from stem node culture on medium supplemented with 90 mM sucrose accumulated lower amounts of photosynthetic pigments per mg dry weight in comparison to those grown on 30 mM sucrose. Addition of 0.1, 1 or 10 µM jasmonic acid (JA) to the medium resulted in a decrease of chlorophylls and carotenoids in the plantlets grown on either sucrose concentration. JA treatment induced de-epoxidation of violaxanthin to antheraxanthin and zeaxanthin only in those plantlets grown on a higher amount of sucrose in which hyperhydric symptoms were observed. The synergistic effect of JA and sucrose was clearly demonstrated in the plantlets grown on 90 mM sucrose and 1 µM JA. This was possibly due to overaccumulation of sucrose, the consequence of the most developed root system, and/or to stimulated water and solute transport by other mechanisms.     

Changes in the quantities of violaxanthin de-epoxidase,xanthophylls and ascorbate in spinach upon shift from low to high light

Zeaxanthin, a carotenoid in the xanthophyll cycle, has been suggested to play a role in the protection against photodestruction. We have studied the importance of the parameters involved in zeaxanthin formation by comparing spinach plants grown in low light (100 to 250 mol m^-2 s^-1) to plants transferred to high light (950 mol m^-2 s^-1). Different parameters were followed for a total of 11 days. Our experiments show that violaxanthin de-epoxidase decreased between 15 and 30%, the quantity of xanthophyll cycle pigments doubled to 100 mmol (mol Chl)^-1, corresponding to 27 mol m^-2, and the rate of violaxanthin to zeaxanthin conversion was doubled. Lutein and neoxanthin increased from 50 to 71 mol m^-2 and from 16 to 23 mol m^-2, respectively. On a leaf area basis, chlorophyll and -carotene levels first decreased and then after 4 days increased. The chlorophyll a/b ratio was unchanged. The quantity of ascorbate was doubled to 2 mmol m^-2, corresponding to an estimated increase in the chloroplasts from 25 to 50 mM. In view of our data, we propose that the increase in xanthophyll cycle pigments and ascorbate only partly explain the increased rate of conversion of violaxanthin to zeaxanthin, but the most probable explanation of the faster conversion is an increased accessibility of violaxanthin in the membrane.     

光质和光周期对山白兰苗木生长、生理的影响

为筛选出山白兰(Michelia baillonii)苗木培育过程中适宜的光环境，该研究以一年生山白兰幼苗为试验材料，设置12、16 h·d^-1两个光周期，配合使用红蓝复合光(8R1B、6R1B)、红蓝紫绿复合光(8R1B1P1G、6R1B1P1G)4种光质和白光(W)对照，采用双因素随机区组试验设计和隶属函数法，探讨了山白兰苗木生长、光合色素、内源激素含量对不同光质和光周期处理的响应规律。结果表明：(1)光质、光周期及其交互作用对山白兰苗高增长量、叶面积、叶绿素a、玉米素(ZR)、脱落酸(ABA)的含量、内源激素比值[IAA/ABA、(IAA+GA₃+ZR)/ABA]等均有显著影响(P<0.05)。(2)16 h·d^-1光周期有利于苗高增长量、叶面积、苗木质量指数、生物量、叶绿素a、生长素(IAA)、ZR的含量、内源激素比值的提高。(3)当光周期为16 h·d^-1时，8R1B处理下的苗高增长量、叶面积和苗木质量指数均最大，分别为21.84 cm、158.39 cm²和2...     

THE WAVELENGTH DEPENDENCE OF MASSIVE CAROTENE SYNTHESIS IN DUNALIELLA BARDAWIL (CHLOROPHYCEAE)1

Dunaliella bardawil Ben-Amotz & Avron accumulates high concentrations of β-carotene when grown under high light intensity. The β-carotene is composed mainly of 9-cis and all-trans β-carotene. Accumulation of β-carotene and an increase in the ratio of the 9-cis to the all-trans isomer are strongly dependent on the light intensity under which the algae are cultivated but are independent of light quality within the photosynthetically active radiation range. Cells grown under continuous red (>645 nm) or white light of 500 W·m^?2 reach a value of about 32 pg β-carotene·cell^?1 and a ratio of 9-cis to all-trans β-carotene of around 2, whereas cells grown under low red or white light intensity of 25 W·m^?2 contain about 3 pg·cell^?1 and a ratio of isomers of around 0.3.     

微生物黄色素的研究进展

对来源于微生物的天然黄色素的研究进行了详细概述, 尤其对红曲黄色素的生产、安全性以及黄色素的合成代谢机理研究进行了详细论述, 最后对红曲黄色素的应用前景及其未来研究重点进行了展望, 并对研究中存在的问题进行了分析。     

Possibilities of subunit localization with fluorescent protein tags and electron microscopy examplified by a cyanobacterial NDH-1 study

Cyanobacterial NDH-1 is a multisubunit complex involved in proton translocation, cyclic electron flow around photosystem I and CO₂ uptake. The function and location of several of its small subunits are unknown. In this work, the location of the small subunits NdhL, -M, -N, -O and CupS of Synechocystis 6803 NDH-1 was established by electron microscopy (EM) and single particle analysis. To perform this, the subunits were enlarged by fusion with the YFP protein. After classification of projections, the position of the YFP tag was revealed; all five subunits are integrated in the membrane domain. The results on NDH-1 demonstrate that a GFP tag can be revealed after data processing of EM data sets of moderate size, thus showing that this way of labeling is a fast and reliable way for subunit mapping in multisubunit complexes after partial purification.