Photosynthetic Action Spectra of Scots Pine Needles of Different Ages from Seedlings Grown under Different Nursery Conditions

Photosynthetic action spectra of pine needles have been measured with an automatic recording method. A thin longitudinal cut from the flat surface of the needle was placed on top of an oxygen sensor and illuminated with monochromatic light in the range 400–700 nm. Good correspondence between absorption and action spectra was obtained in the range 550–700 nm. In the blue part of the spectrum photosynthetic efficiency was low compared with absorption. This low effect in blue light is probably due to screening absorption by photosynthetically inactive carotenoids. One-year-old needles showed a higher effect in the blue part of the spectrum than did current year needles. Needles from seedlings grown in the open had a lower photosynthetic effect in the blue part than needles from seedlings grown in a greenhouse. Pigment analyses support the idea that these differences are due to differences in the ratio chlorophylls/total carotenoids and/or differences in the composition of the carotenoid pigments.     

Seasonal Changes in the Levels of Some Cellular Components in the Abscission Zone of Coleus Leaves of Different Ages

The present study with intact petioles of Coleus of varyingages suggests an involvement of the phenomenon of mobilizationwith the abscission process. There was a gradual increase inthe levels of chlorophyll and nucleic acids and also solublenitrogen compounds in the proximal tissues with the approachof abscission with a concomitant decrease of these substancesin the distal tissues. This increase of metabolites in the proximaltissues was clearer in petioles at the first node than at thefourth node suggesting a lesser degree of metabolic activityof the proximal tissues in older petioles. The change of levelsof chlorophyll and nucleic acids and also of soluble nitrogenwas more marked in winter than in summer months. The application of NAA to petioles of the third node; just afterdeblading (i.e. in the auxin-inhibited stage 1), not only stoppedthe decline of nucleic acid levels (particularly RNA) at thedistal tissues but also caused an increase of nucleic acidsover the initial levels. This effect was more pronounced insummer than in winter months. If the initially inhibitory concentration of NAA was appliedin the auxin-promoted stage 2 of abscission, instead of an increase,there followed a quicker rate of decrease in nucleic acids (particularlyRNA). This effect was also more prominent in summer.     

Changes in the Constitution of Thylakoid Membranes in Spruce Needles During an Open-top Chamber Experiment

The goal of the presented paper was to study the emission effects of natural air pollutants on the protein complexes of the thylakoid membrane. The tests were carried out in the frame of a long-term experiment in which spruce trees kept in open-top chambers with unfiltered ambient-air were compared to spruce trees in chambers with purified-air. The reaction centres of photosystem I (P-700), cytochrome f, cytochrome b-563, cytochrome b-559, as well as the oxidation speed of the antennae chlorophylls were quantified. The concentrations of the cytochromes f and b-563 indicate a marked annual rhythm with decreased concentrations during the summer months. The spruce trees in chambers with ambient-air showed a smaller amount of the studied redox components in relation to 1000 molecules of chlorophyll than did the spruce trees in chambers exposed to purified-air. In addition, increased oxidation speed of antennae chlorophylls could be observed on the isolated thylakoid membranes of the spruce trees in chambers with ambient-air conditions. A relationship between the oxidation speed and the ozone concentration of the ambient air could be observed, i.e. with increasing ozone levels the oxidation of the antennae chlorophylls accelerated. However, the damage occurred only with a temporary delay (the so-called memory effect). In case of the cytochromes f and b-563 (components of the cytochrome b₆f-complex), a chamber effect related to changed light conditions became obvious when comparing spruce trees kept in chambers to trees left in their natural surrounding. The reduced photosynthetically active radiation — it is reduced in the chambers by 10 ? 30% — led to a decrease of both cytochromes. In spite of the effects due to the chambers, the results indicate that ozone could be an effective damage factor and this will be of importance with regard to the situation in the low mountain range of Germany.     

Developmental Changes in Amounts of Thylakoid Components in Plastids of Barley Leaves

Changes in the amounts of several components of the photosyntheticelectron-transport system during greening of etiolated barleyleaves were studied on a "per plastid" basis. P700 and Q_A, whichwere initially absent from etioplasts, appeared 2 h after thestart of illumination in complete complexes of PS I and PS II,respectively. From 6 h, they increased rapidly in amount witha constant stoichiometric ratio of 1:1. Amounts of Cyt f, Cytb₆, Cyt b-559 and FeS, initially present in etioplasts at levelsthat were one-third to half of those in mature chloroplasts,also increased rapidly after 6 h of illumination. The molarratio of Cyt f, Cyt b₆ and Cyt b-559 was the same in etioplastsand in mature chloroplasts, namely 1:2:2. After 4 h of illumination,levels of FeS increased at nearly the same rate as those ofthe PS I complex. The increase in levels of all components wasmarked after 6 h of illumination, probably due to the energysupplied by developing plastids that had just become photosyntheticallycompetent. The results are discussed in relation to the timeof appearance of chlorophyll-protein complexes and photochemicalactivities. ¹ Present address: Department of Botany, Faculty of Science,Kyoto University, Kyoto, 606-01 Japan.     

Protoplasmic Changes in Cambial Cells Induced by a Tracheid-Differentiation Factor from Pine Needles

Direct differentiation of ‘dormant’ fusiform cambialcells (fees) into tracheids in stem cuttings of Pinus contortaDougl. was investigated by light and transmission electron microscopy.In cuttings from which all but one pair of needles had beenremoved, differentiation occurred close to the needle tracewithout prior cell division or expansion. The highly osmiophillic,granular cytoplasm of differentiating fees exhibited numerousmitochondria, dictyosomes and endoplasmic reticulum (ER) cisternaeand was enriched with vesicles and polyribosomes. The protoplasmdid not become highly vacuolated, as it normally does, untildifferentiating tracheids were approaching maturation. During differentiation, secondary walls were deposited in feesas ribs of annular and spiralled thickenings and also as borderedpit-likestructures devoid of margo and torus and lacking the typicallamellar structure of secondary-xylem tracheids. The fee plasmamembrane at sites of secondary-wall growth was in dynamic flux,dilated vesicles derived from both ER and dictyosomes apparentlyfusing with it at these locations. In addition, electron-denseblebs were invariably plasma membrane-associated and appearedto be exocytotic; these blebs became rare during autolysis andthey were never seen in non-differentiating cells. Depositionof oriented nascent cellulose microfibrils appeared to occurin the absence of associated cortical microtubules. As secondary-walldeposition neared completion, vacuoles derived from rough ERgrew and fused; concomitantly, the protoplasm disappeared resultingin fully autolysed tracheids. Auxin (indol-3-ylacetic acid, IAA) promoted the gel-like protoplasmof dormant fees to became highly vacuolated, and cell divisionand expansion followed; however, tracheid differentiation didnot occur. Polyribosomes, rough ER, and dictysomes were lessabundant than in differentiating fees and the cytoplasm of auxin-treatedfees was fine grained and less densely stained. The electron-denseexocytotic blebs found at the plasmalemma in differentiatingfees were not induced by IAA treatment. Fees of control cuttingsenlarged somewhat and became more vacuolated but otherwise remaineddormant. Key words: Cambium, exocytosis, Gymnospermae, ultrastructure, xylogenesis     

雪松松针挥发油化学成分及抗氧化活性研究

采用水蒸气蒸馏法提取雪松松针挥发油,利用气相色谱-质谱联用技术分析其化学成分。使用维生素C为阳性对照,以DPPH自由基、ABTS自由基和羟基自由基清除作用为指标评价挥发油的抗氧化活性。从雪松松针挥发油中鉴定了37种化学成分,占挥发油总量的95.10%,以烃类和醇类为主;挥发油对DPPH自由基、ABTS自由基和羟基自由基有明显的清除作用,其IC₅₀分别为0.30、0.22及0.96 μg·mL^-1,且呈现一定的量效关系。可见,雪松松针挥发油中含有多种有应用价值的化学成分,具有显著的抗氧化活性。     

Light-induced Changes in the Conformation and Configuration of the Thylakoid Membrane of Ulva and Porphyra Chloroplasts in Vivo

The ultrastructural basis of light-induced transmission and light scattering changes of thalli of Ulva and Porphyra were investigated by high resolution electron microscopy and microdensitometry. The results show that upon illumination of dark thalli (a) a reduction in thickness of thylakoid membranes (conformational change), (b) a more regular ordering, and (c) flattening of the thylakoids (configurational changes) have occurred. An explanation for the observed conformational and configurational changes was proposed in terms of correlated changes in ionic environment and osmotic properties of chloroplasts in vivo which are initiated by photosynthetic reactions.     

Isolation and Characterization of Phosphatase from Thylakoid Membranes of Spinach Chloroplasts

A phosphatase from thylakoid membrane of spinach (Spinacia oleracea L. ) chloroplasts was isolated with the methods of extraction with n-ButanoL centrifugation at 100000 g for 30 min and chromatographic separation through DEAE-Cellulose (DE 52) column.The phosphatase catalyzed hydrolysis of phosphate monoesters (4-nitrophenyl phosphate). The optimal pH for enzyme catalysis was below 7. The peak rate of the enzyme reaction was obtained when it was incubated at 60℃ for 15 min. The phosphatase was inhibited by ATP and phosphate. The results from SDS-PAGE showed that the preparation of enzyme was composed of two proteins.     

Thylakoid Membrane Protein Kinase Activity as a Signal Transduction Pathway in Chloroplasts

Photosynthetica - In plants external stimuli are perceived through a cascade of signals and signal transduction pathways. Protein phosphorylation and de-phosphorylation is one of the most important...     

Carbohydrate Accumulation in Siberian Spruce Needles of Various Ages

The content of mono- and oligosaccharides, hemicelluloses, and water-soluble polysaccharides was studied in Siberian spruce (Picea obovata Ledeb.) needles of various ages. Accumulation of carbohydrates during the growth period and the ratio of their individual fractions were determined by the proportions between the growth rate and assimilate export in developing needles. Throughout the growth period, the content of monosaccharides in needles of all ages was much higher than that of oligosaccharides. Unlike the period of active growth, the dormancy period was characterized by a wider diversity of oligosaccharides and their rather high content. Hemicelluloses that accumulated during the previous growth season and water-soluble polysaccharides of 2- and 3-year-old needles were involved into metabolism at the time of active growth of current-year needles. Analysis of carbohydrate accumulation in 1- to 9-year-old needles showed that the monosaccharide concentration was higher in needles of the first two years. The content of hemicelluloses A and B and water-soluble polysaccharides was higher in older needles. During the growth period, the assimilates of 2- and 3-year-old needles were partly used for the formation of young needles. The increase in relative content of polysaccharides during needle senescence reflects the involvement of photosynthetic products into the secondary pool of carbon metabolites.     

Thylakoid Membrane Protein Kinase Activity as a Signal Transduction Pathway in Chloroplasts

In plants external stimuli are perceived through a cascade of signals and signal transduction pathways. Protein phosphorylation and de-phosphorylation is one of the most important transduction paths for the perception of signals in plants. The highest concentrations of plant phospho-proteins are located in chloroplasts. This facilitates the protection of thylakoid membranes from stress-induced damage and augments adaptive strategies in plants. In this review, the protein kinases associated with phosphorylation of thylakoid membrane protein, and the adaptive changes in thylakoid membrane architecture and developmental cues are given. The presence of membrane bound kinases in thylakoid membranes have evolutionary implications for the signal transduction pathways and the photosynthetic gene expression for thylakoid membrane protein dynamics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Chlorophyll Synthesis in Dark-Grown Pine Primary Needles

The pigment content of dark-grown primary needles of Pinus jeffreyi L. and Pinus sylvestris L. was determined by high-performance liquid chromatography. The state of protochlorophyllide a and of chlorophylls during dark growth were analyzed by in situ 77 K fluorescence spectroscopy. Both measurements unambiguously demonstrated that pine primary needles are able to synthesize chlorophyll in the dark. Norflurazon strongly inhibited both carotenoid and chlorophyll synthesis. Needles of plants treated with this inhibitor had low chlorophyll content, contained only traces of xanthophylls, and accumulated carotenoid precursors. The first form of chlorophyll detected in young pine needles grown in darkness had an emission maximum at 678 nm. Chlorophyll-protein complexes with in situ spectroscopic properties similar to those of fully green needles (685, 695, and 735 nm) later accumulated in untreated plants, whereas in norflurazon-treated plants the photosystem I emission at 735 nm was completely lacking. To better characterize the light-dependent chlorophyll biosynthetic pathway in pine needles, the 77 K fluorescence properties of in situ protochlorophyllide a spectral forms were studied. Photoactive and nonphotoactive protochlorophyllide a forms with emission properties similar to those reported for dark-grown angiosperms were found, but excitation spectra were substantially red shifted. Because of their lower chlorophyll content, norflurazon-treated plants were used to study the protochlorophyllide a photoreduction process triggered by one light flash. The first stable chlorophyllide photoproduct was a chlorophyllide a form emitting at 688 nm as in angiosperms. Further chlorophyllide a shifts usually observed in angiosperms were not detected. The rapid regeneration of photoactive protochlorophyllide a from nonphotoactive protochlorophyllide after one flash was demonstrated.     

Changes in Unsaturated Levels of Fatty Acids in Thylakoid PSII Membrane Lipids During Chilling-induced Resistance in Rice

Temperature is one of the abiotic factors limiting growth and productivity of plants. In the present work, the effect of low non‐freezing temperature, as an inducer of “chilling resistance”, was studied in three cultivars of rice (Oryza sativa L.), japonica cv. 9516 (j‐9516), the two parental lines of superhigh‐yield hybrid rice between subspecies, Peiai/E32 (ji‐PE), and the traditional indica hybrid rice Shanyou 63 (i‐SY63). Leaves of chill‐treated rice showed chilling‐induced resistance, as an increase of their low‐temperature tolerance was measured using chlorophyll fluorescence measurements, revealing a change in photosystem II (PSII) efficiency. After 5 d of exposure to 11°C under low light (100 μmol m^‐2 s^‐1), levels of unsaturated fatty acids in PSII thylakoid membrane lipids decreased during the initial 1‐2 d, then increased slowly and reached 99.2%, 95.3% and 90.1% of the initial value (0 d) in j‐9516, ji‐PE and i‐SY63, respectively, on the fifth day. However, under medium light (600 μmol m^‐2 s^‐1), all cultivars experienced similar substantial photoinhibition, which approached steady state levels after a decline in levels of unsaturated fatty acids in PSII thylakoid membrane lipids to about 57.1%, 53.8% and 44.5% of the initial values (0 d) in j‐9516, ji‐PE and I‐SY63 on the fifth day. Under either chilling‐induced resistance (the former) or low temperature photoinhibition (the latter) conditions, the changes of other physiological parameters such as D1 protein contents, electron transport activities of PSII (ETA), F_v/F_m, xanthophyl cycle activities expressed by DES (deepoxide state) were consistent with that of levels of unsaturated fatty acids in PSII thylakoid membrane lipids. So there were negative correlations between saturated levels of fatty acids (16:1(3t), 16:0, 18:0), especially the 16:1(3t) fatty acid on thylakoid membrane and other physiological parameters, such as D1 protein contents, ETA and (A+Z)/(A+V+Z). A specific role of desaturation of fatty acids and the photoprotective pigments of the xanthophyl cycle, leading to an acclimation response in thylakoid membrane lipids may be involved. We conclude that chilling‐induced resistance is accelerated by the unsaturation of thylakoid membranes, and the ability of rice plants to cold‐harden can be enhanced by genetic engineering.     

针叶树越冬针叶光氧化与叶绿体超氧阴离子自由基

以Tiron为自旋探针,检出了越冬针叶叶绿体指示超氧阴离子自由基产生的TH~·ESR信号。此信号可由紫外辐射,也可由光合有效辐射产生。以单位叶绿素量为基数计算的信号强度比已报道的其它植物材料大2～3个数量级。红松叶绿体信号又大于其它针叶树。此信号可被外源SOD,抗坏血酸、乙醇和N_2抑制;随光照增加而增强,12月到次年5月期间又随时间而增强。上述结果表明红松针叶的冬季光氧化伤害与叶绿体中过量超氧阴离子自由基的产生有关。     

Kinetics of Freezing Damage in Apple Bark and Pine Needles

The time course of freezing damage in pine needles and in bark of apple trees was followed at different subzero temperatures. From these data the killing rate by freezing was determined for trees which differed in degree of cold hardiness. The activation energy of the killing reaction was also calculated. The killing rate was lowest in cold-acclimated trees, but the activation energy of the killing reaction was very high indicating a high degree of structured water in the cells. Non-acclimated trees showed uniform low values of the activation energy of the killing reaction at all subzero temperatures studied. It is suggested that intracellular supercooling could be a part of the mechanism of frost protection in cold-acclimated apple trees within the – 30 to – 20°C range, but not in the –20 to –10°C range.     

The Histological Components of the Phoniatrical Body-Cover Model in Minipigs of Different Ages

Pigs are models in human phoniatry. However, features of maturation and ageing have not been considered with regard to the so-called body-cover model in this species. Therefore, the glottis of “young” (2–3 months; n = 6) and “old” (4–7 years; n = 6) minipigs was investigated. Their cranial (CraF) and caudal (CauF) vocal folds were histomorphometrically and stratigraphically analysed with emphasis on their amounts of collagen structures and elastic fibres. A dense subepithelial layer (SEL) was a distinct feature of CraF and CauF of both age groups; it was spread upon the underlying loose, flexible “cover” like a fibro-elastic membrane. The “cover” was characterised by the so-called superficial layer (SL), which was distinctly loose in the “young” minipigs, but had a much denser texture in the “old” minipigs. Here, the SL was dominated by elastic fibres in the CraF, but was of mixed qualities (collagenous and elastic) in the CauF. The structural requirements for the SL’s function as a loose “cover” were thus met only in the “young” animals. A clearly demarcated intermediate layer (IL)—characterised by high amounts of elastic fibres (as in humans)—was only found in the CraF of the “young” animals. In the “old” animals, it had lost its demarcation. In the depth of the CraF of the “old” animals, many thick collagen fibre bundles were detected in a location equivalent to that of the vocal muscle in the CauF. The development of their large diameters was interpreted as part of the maturation process, thereby supporting the hypothesis of their functional importance as a component of the “body.” In the CauF, the amounts of collagen structures increased throughout the entire lamina propria, resulting in a loss of demarcated stratigraphical subdivisions in the “old” minipigs. This situation resembled that described in the vocal fold of geriatric humans.     

Thylakoid Protein Phosphorylation in Higher Plant Chloroplasts Optimizes Electron Transfer under Fluctuating Light

Several proteins of photosystem II (PSII) and its light-harvesting antenna (LHCII) are reversibly phosphorylated according to light quantity and quality. Nevertheless, the interdependence of protein phosphorylation, nonphotochemical quenching, and efficiency of electron transfer in the thylakoid membrane has remained elusive. These questions were addressed by investigating in parallel the wild type and the stn7, stn8, and stn7 stn8 kinase mutants of Arabidopsis (Arabidopsis thaliana), using the stn7 npq4, npq4, npq1, and pgr5 mutants as controls. Phosphorylation of PSII-LHCII proteins is strongly and dynamically regulated according to white light intensity. Yet, the changes in phosphorylation do not notably modify the relative excitation energy distribution between PSII and PSI, as typically occurs when phosphorylation is induced by “state 2” light that selectively excites PSII and induces the phosphorylation of both the PSII core and LHCII proteins. On the contrary, under low-light conditions, when excitation energy transfer from LHCII to reaction centers is efficient, the STN7-dependent LHCII protein phosphorylation guarantees a balanced distribution of excitation energy to both photosystems. The importance of this regulation diminishes at high light upon induction of thermal dissipation of excitation energy. Lack of the STN7 kinase, and thus the capacity for equal distribution of excitation energy to PSII and PSI, causes relative overexcitation of PSII under low light but not under high light, leading to disturbed maintenance of fluent electron flow under fluctuating light intensities. The physiological relevance of the STN7-dependent regulation is evidenced by severely stunted phenotypes of the stn7 and stn7 stn8 mutants under strongly fluctuating light conditions.Several proteins of PSII and its light-harvesting antenna (LHCII) are reversibly phosphorylated by the STN7 and STN8 kinase-dependent pathways according to the intensity and quality of light (Bellafiore et al., 2005; Bonardi et al., 2005). The best-known phosphorylation-dependent phenomenon in the thylakoid membrane is the state transition: a regulatory mechanism that modulates the light-harvesting capacity between PSII and PSI. According to the traditional view, “state 1” prevails when plants are exposed to far-red light (state 1 light), which selectively excites PSI. Alternatively, thylakoids are in “state 2” when plants are exposed to blue or red light (state 2 light), favoring PSII excitation. In state 1, the yield of fluorescence from PSII is higher in comparison with state 2 (for review, see Allen and Forsberg, 2001). State transitions are dependent on the phosphorylation of LHCII proteins (Bellafiore et al., 2005) and their association with PSI proteins, particularly PSI-H (Lunde et al., 2000). Under state 2 light, both the PSII core and LHCII proteins are strongly phosphorylated, whereas the state 1 light induces dephosphorylation of both the PSII core and LHCII phosphoproteins (Piippo et al., 2006; Tikkanen et al., 2006). In nature, however, such extreme changes in light quality rarely occur. The intensity of light, on the contrary, fluctuates frequently in all natural habitats occupied by photosynthetic organisms, thus constantly modulating the extent of thylakoid protein phosphorylation in a highly dynamic manner (Tikkanen et al., 2008a).The regulation of PSII-LHCII protein phosphorylation by the quantity of light is much more complex than the regulatory circuits induced by the state 1 and state 2 lights. Whereas changes in light quality induce a concurrent increase or decrease in the phosphorylation levels of both the PSII core (D1, D2, and CP43) and LHCII (Lhcb1 and Lhcb2) proteins, the changes in white light intensity may influence the kinetics of PSII core and LHCII protein phosphorylation in higher plant chloroplasts even in opposite directions (Tikkanen et al., 2008a). Indeed, it is well documented that low light (LL; i.e. lower than that generally experienced during growth) induces strong phosphorylation of LHCII but relatively weak phosphorylation of the PSII core proteins. Exposure of plants to high light (HL) intensities, on the contrary, promotes the phosphorylation of PSII core proteins but inhibits the activity of the LHCII kinase, leading to dephosphorylation of LHCII proteins (Rintamäki et al., 2000; Hou et al., 2003).Thylakoid protein phosphorylation induces dynamic migrations of PSII-LHCII proteins along the thylakoid membrane (Bassi et al., 1988; Iwai et al., 2008) and modulation of thylakoid ultrastructure (Chuartzman et al., 2008). According to the traditional state transition theory, the phosphorylation of LHCII proteins decreases the antenna size of PSII and increases that of PSI, which is reflected as a quenched fluorescence emission from PSII. Alternatively, subsequent dephosphorylation of LHCII increases the antenna size of PSII and decreases that of PSI, which in turn is seen as increased PSII fluorescence (Bennett et al., 1980; Allen et al., 1981; Allen and Forsberg, 2001). This view was recently challenged based on studies with thylakoid membrane fractions, revealing that modulations in the relative distribution of excitation energy between PSII and PSI by LHCII phosphorylation specifically occur in the areas of grana margins, where both PSII and PSI function under the same antenna system, and the energy distribution between the photosystems is regulated via a more subtle mechanism than just the robust migration of phosphorylated LHCII (Tikkanen et al., 2008b). It has also been reported that most of the PSI reaction centers are located in the grana margins in a close vicinity to PSII-LHCII-rich grana thylakoids (Kaftan et al., 2002), providing a perfect framework for the regulation of excitation energy distribution from LHCII to both PSII and PSI.When considering the natural light conditions, the HL intensities are the only known light conditions that in higher plant chloroplasts specifically dephosphorylate only the LHCII proteins but not the PSII core proteins. However, such light conditions do not lead to enhanced function of PSII. Instead, the HL conditions strongly down-regulate the function of PSII via nonphotochemical quenching of excitation energy (NPQ) and PSII photoinhibition (for review, see Niyogi, 1999). On the other hand, after dark acclimation of leaves and relaxation of NPQ, PSII functions much more efficiently when plants/leaves are transferred to LL despite strong phosphorylation of LHCII, as compared with the low phosphorylation state of LHCII upon transfer to HL conditions.The delicate regulation of thylakoid protein phosphorylation in higher plant chloroplasts according to prevailing light intensity is difficult to integrate with the traditional theory of state transitions (i.e. the regulation of the absorption cross-section of PSII and PSI by reversible phosphorylation of LHCII). Moreover, besides LHCII proteins, reversible phosphorylation of the PSII core proteins may also play a role in dynamic light acclimation of plants. Recently, we demonstrated that the PSII core protein phosphorylation is a prerequisite for controlled turnover of the PSII reaction center protein D1 upon photodamage (Tikkanen et al., 2008a). This, however, does not exclude the possibility that the strict regulation of PSII core protein phosphorylation is also connected to the regulation of light harvesting and photosynthetic electron transfer. Moreover, the interactions between PSII and LHCII protein phosphorylation, nonphotochemical quenching, and cyclic electron flow around PSI in the regulation of photosynthetic electron transfer reactions remain poorly understood. To gain a deeper insight into such regulatory networks, we explored the effect of strongly fluctuating white light on chlorophyll (chl) fluorescence in Arabidopsis (Arabidopsis thaliana) mutants differentially deficient in PSII-LHCII protein phosphorylation and/or the regulatory systems of NPQ.     

Changes in Activities of Antioxidant Enzymes in Sunflower Leaves of Different Ages

Role of superoxide dismutase isozymes and other antioxidant enzymes was studied in relation to leaf age in sunflower (Helianthus annuus L. cv. ACC 1508) at pre-flowering and grain filling stages. Relative water content (RWC) did not change much in leaves of different age and at the two stages. Protein content declined continuously from the youngest to the oldest leaf, while chlorophyll (Chl) and carotenoids (Car) contents increased down to 7^th/9^th leaf and declined in subsequent older leaves. Protein, Chl and Car contents were higher at pre-flowering than at seed filling stage. Superoxide dismutase (SOD), its isozymes, and ascorbate peroxidase (APO) and catalase (CAT) activities were highest in the 9^th leaf and declined in subsequent older leaves. SOD and APO activities were higher at seed filling, except in oldest senescent (13^th, 15^th) leaves. Among SOD isozymes, Cu/Zn-SOD and Mn-SOD activities accounted for most of the total SOD, and only marginal activity was observed for Fe-SOD. Peroxidase activity increased from youngest to the oldest leaf at pre-flowering stage and down to 13^th leaf at seed filling stage. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detection of a Precursor Polypeptide of the Rapidly-Synthesized 32,000-Dalton Thylakoid Protein in Spinach Chloroplasts

Spinach chloroplast RNA was translated in a wheat germ cell-freesystem in the presence of [³⁵S]methionine or [³H]lysine, andthe products were analyzed by SDS polyacrylamide gel electrophoresisand fluorography. A polypeptide with molecular mass of 2,000-Dalarger than the 32,000-Da thylakoid protein was detected asa major product labeled by [³⁵S]methionine but not by [³H]lysine.Peptide mapping of this polypeptide showed a pattern very closeto that of the 32,000-Da protein synthesized in isolated chloroplasts.A better separation of this polypeptide from the 32,000-Da proteinwas observed in the electrophoresis on polyacrylamide gel includingurea at 8 M. Pulse-labeling of the isolated chloroplasts showedthe occurrence of the larger molecular weight form, which wasconverted to the mature size by a chasing incubation with coldmethionine. These results suggested that the 32,000-Da proteinof spinach is translated primarily as a high molecular weightprecursor in the chloroplasts, as has been reported for otherplant species. (Received March 30, 1985; Accepted April 23, 1985)