The Photostability of Different Chlorophyll Forms in Dark Grown Leaves of Wheat

The effect of denaturing treatments on the stability against high intensity irradiation (red light, 700 W m^?2) was investigated in vivo for various chlorophyll forms in wheat. Three pigment forms were investigated: the 650-form (protochlorophyllide) present in dark grown leaves; the 684-form (chlorophyllide) formed within 5 s after photoreduction of the 650-form; and the 673-form (chlorophyll), into which the 684-form has been transformed 25 min after photoreduction of the 650-form. (The pigment forms are denoted by their absorption maxima in the red region before denaturation.) Two denaturing treatments were used: heat treatment (water of 55°C for 2 min) and freezing and thawing (freezing in liquid nitrogen followed by thawing in water of 25°C). Heat treatment as well as freezing and thawing caused a shift in the absorption peak of the two nonesterified pigment forms. The peak of of the chlorophyllide 684-form shifted to 673 nm and that of the protochlorophyllide 650-form to 636 nm. The absorption maximum of the chlorophyll 673-form was not affected by the above treatments. Heat treatment as well as freezing and thawing had profound effects on the structural organization of the plastid pigments, as shown by a decrease in the photostability. For the 684-form, heat treatment reduced the photostability by a factor of about 14 (half-life in strong light changed from 170 s to 12 s). Freezing and thawing also reduced the photostability, although the effect was less pronounced (c. 3–4 times decrease in half-life). Upon transformation of the chlorophyllide 684-form into the chlorophyll 673-form (the Shibata-shift) the pigments became less sensitive to light, and were no longer “aggregated” by heat treatment. The “aggregating” effect of freezing and thawing was still present after the Shibata shift. The results thus verify a clear difference in structural organization of the 684-form and the 673-form, since the two pigment forms were differently affected by heat treatment. The 650-form behaved similarly to the 684-form, although it appeared to be slightly less aggregated by heat treatment. — The decrease in photostability, caused by heat treatment of the 684-form, changed the kinetics for the photodecomposition from a first towards a second order reaction.     

The Photostability of Different Chlorophyll Forms in Dark Grown Leaves of Wheat

The stability against high intensity irradiation (red light, 700 W m^?2) was investigated for the chlorophyll(ide) pigments formed after the primary photoreduction of the protochlorophyll(ide) in dark grown leaves of wheat. After photoreduction, most of the chlorophyll(ide) exists in a form with an absorption maximum at 684 nm. This form is gradually transformed into a form with an absorption maximum at 673 nm (the Shibata shift). It was possible to ascribe a specific photostability to each of the pigment forms. This photostability was higher for the 673-form than for the 684-form. A red-shift in the absorption maximum following upon the Shibata shift, reflects the successive transformation of the 673-form into other pigment forms, which were quite photostable at the intensity used.     

Stacking Capacity and Chlorophyll Forms of Thylakoids in Normal and Mutant Maize Chloroplasts of Different Granum Content

Stacking of chloroplast lamellae, isolated from normal and carotenoid mutant chloroplasts of maize (Zea mays L.), was determined after a high-salt treatment. Stacking of isolated lamellae under favourable ionic conditions was almost identical with that occurring in intact chloroplasts; thus, differences in granum content could be attributed to the architectural properties of lamellae. Gaussian analyses, performed on the red band of room temperature absorption spectra, have shown that chloroplasts with lamellae of high stacking capacity contain relatively more Chl a₆₆₂ than chloroplasts containing lamellae of low stacking capacity. The presence of Chl a_705–708 was characteristic of preparations containing considerable amounts of stroma lamellae.     

The Spectral Response of Light Dependent Chlorophyll b Formation

Dark grown seedlings of barley will obtain a high ratio chlorophyll a/chlorophyll b when exposed to intermittent light (1 min of incandescent light or one electronic flash every hour). Such material has been exposed to monochromatic light of different wavelengths for 1 h. The ratio a/b gets a minimum in light of 670 nm, indicating the highest rate of chlorophyll b formation at this wavelength. The possibility is discussed that the light absorber (and also precursor) could be a short-lived chlorophyll a form, existing prior to the forms in the Shibata-shift. Chlorophyll b formation in darkness is discussed from the findings that the rate of formation of chlorophyll b is higher in intermittent light than it should be, calculated from the rate in continuous light, where the saturation intensity is rather low.     

不同光环境和发育阶段美国山核桃叶的荧光性状研究

研究美国山核桃同一枝条不同叶位、苗木不同部位、不同方位叶片的叶绿素荧光特性,探讨不同光环境和发育阶段叶片的光合效率,旨在为其高效栽培提供科学依据.以湖南省永州市冷水滩采穗圃中的美国山核桃为试材,系统田间测定了两个品种同一枝条不同叶位、同株苗木不同部位、不同方位叶片叶绿素荧光参数(F0-初始荧光、Fm-最大荧光、Fv/Fm-PSⅡ原初光能转化效率、Fv/F0-PSⅡ潜在活性、Yield-光合量子产额、qp-光化学猝灭系数、qN-非光化学猝灭系数),并测定了苗木不同部位叶片基本性状.结果表明,同一枝条不同叶位、同株苗木不同方位叶片荧光参数末达显著差异,但仍表现一定的规律性;同株苗木不同部位叶片性状与荧光参数Yield、qN均存在显著或极显著差异.相关分析表明,苗木不同部位叶片的Yield、qN与部分叶片性状均呈显著或极显著相关.     

Properties of Oligomeric Forms of Phosphofructokinase from Chlorella kessleri Grown under Different Light Conditions

Fast protein liquid chromatography on Superose 6 of crude extracts from Chlorella kessleri, Fott et Novákóva, grown autotrophically in blue or in red light yields three different oligomeric forms of phosphofructokinase (PFK, EC 2.7.1.11). Their substrate affinities and responses to homotropic and heterotropic effectors are different. In vitro, the degree of oligomerization of the enzyme can be influenced by specific intermediates or cofactors. Its substrate, MgATP (10 mM/5 mM), and the negative effector, phosphoenolpyruvate (5 mM), both lead to some dissociation, while the second substrate, fructose-6-phosphate (5 mM), and the positive effector, inorganic phosphate (50 mM), have no effect. It is discussed whether formation or dissociation of oligomeric PFK forms in vivo result from alterations in the levels or in the intracellular distribution of effector molecules and whether such processes are involved in the different regulation of cell metabolism in blue or in red light.     

Urease Activity and Urea Gene Sequencing of Coccoid Forms of H. pylori Induced by Different Factors

Helicobacter pylori exists in two morphologic forms: spiral shaped and coccoid. The nonculturable coccoid forms were believed to be the morphologic manifestations of cell death for a long time. However, recent studies indicate the viability of such forms. This form of H. pylori is now suspected to play a role in the transmission of the bacteria and is partly responsible for relapse of infection after antimicrobial treatment. Urease activity of H. pylori is an important maintenance factor. Determination of urease activity and possible mutations in the DNA sequences of coccoid bacteria will hence contribute to the understanding of pathogenesis of infections, which these forms might be responsible for. In this study, our aim was to analyze the urease activity and investigate the urease gene sequences of coccoid H. pylori forms induced by different factors with respect to the spiral form. For this purpose, the urease activities of H. pylori NCTC 11637 standard strain and two clinical isolates were examined before and after transformation of the cells to coccoid forms by different methods such as exposure to amoxicillin, aerobiosis, cold starvation, and aging. The effects of these conditions on the urease gene were examined by the amplification of 411-bp ureA gene and 115-bp ureB gene regions by PCR technique and sequencing of the ureA gene. The urease activities of coccoid cells were found to be lower than those of the spiral form. ureA and ureB gene regions were amplified in all coccoid cells by PCR. Inducing the change to coccoid form by different methods was found to have no effect on the nucleotide sequence of the ureA gene. These results show that the urease gene region of coccoid H. pylori is highly protected under various mild environmental conditions.     

Light Gradients and the Transverse Distribution of Chlorophyll Fluorescence in Mangrove andCamelliaLeaves

The light gradient and transverse distribution of chlorophyllfluorescence in mangrove andCamellialeaves, which have differentmorphological characteristics, were examined using a micro-fluorescenceimaging system reported previously (Takahashiet al., Plant,Cell and Environment17: 105–110, 1994). Epidermal cellsscattered light strongly, resulting in an increase in the fluencerate in epidermal cells. For theCamellialeaf, a light gradientwas formed by absorption of light by photosynthetic pigmentsassociated with the induction of chlorophyll fluorescence. Forthe mangrove leaf, a light gradient was formed by backward scatteredlight within a thick layer of non-assimilatory cells. Lightwith a low absorption coefficient (515 nm) penetrated deeperthan that with a higher absorption coefficient (477 nm and 488nm) in theCamellialeaf, while light of both wavelengths showedsimilar profiles in the mangrove leaf. In the mangrove leaves,scattered light declined significantly in the non-assimilatorycell layer which is in front of the assimilatory cells. Light,the intensity of which was reduced to approx. 10% of the maximum,was well scattered and induced a considerable amount of chlorophyllfluorescence in the assimilatory cells, which appear to be wellorganized to capture weak light.Copyright 1998 Annals of BotanyCompany fluorescence, intact leaf, light gradient, mangrove (Rhizophora mucronataLamk.),Camellia japonicaL.     

Changes in the Growth of Salvinia natans Induced by Cycles of Light and Darkness of widely Different Duration

The growth of Salvinia natans has been examined when clonalmaterial, maintained at a constant temperature (30 ^°C) receivesthe same amount of light energy per day but where the light-darkcycle of equal intervals varies in eight steps from 1 min to12 h. The area per leaf, the rate of leaf production, the netassimilation rate, and the relative growth-rate increase withthe lengthening of the cycle, but the leaf-area ratio is reduced.The magnitude of the changes differs between the criteria whilethe order of the response may be disparate between consecutiveintervals. In supporting experiments the same measurements weremade on plants subjected to a wide range of light intensitieswith a common photoperiod of 12 h. Here decreasing light intensityproduces similar trends to those recorded for increasing thelength of the cycle but the patterns of response may diverge.It was also established that the size of the stomatal pore isthe same in the light and in the dark. It is postulated thatvanations in the light-dark cycle may influence both the levelof photosynthetic activity and the pathways.     

水稻幼苗不同叶位的叶片叶绿素荧光和类胡萝卜素的生物合成对高光胁迫的响应

研究了水稻 (OryzasativaL .)幼苗叶片生长过程中叶绿素荧光和类胡萝卜素各组分含量的变化以及它们对高光胁迫的响应。结果表明 :随着叶片的衰老 ,光合速率、类胡萝卜素不同组分及总的类胡萝卜素含量和叶黄素循环库下降 ;不同叶龄的叶片经高光胁迫后 ,第 5叶 (成熟叶 )qN增加的幅度比第 6叶 (幼嫩叶 )和老叶 (第 3和 4叶 )大 ;与高光胁迫前相比 ,第 3、4、5和 6叶光系统Ⅱ激发压 (1-qP)分别增加了 4 4 %、5 7%、19%和 4 5 % ;第 5叶具有高胡萝卜素含量和高紫黄质到玉米黄质的转化 ,这与其呈现较强的抗高光胁迫相一致。水稻叶片抵御光抑制的能力与类胡萝卜素水平和类胡萝卜素的生物合成能力以及叶片所处的生长时期相关。     

Distribution of Chlorophyll between the Two Photoreactions in Photosynthesis of the Blue-Green Alga Anacystis nidulans Grown at Two Different Light Intensities

Anacystis nidulans was grown in white light of two different intensities, 7 and 50 W ·m^?2. The in vivo pigmentations of the two cultures were compared. The ratio phycocyanin/chlorophyll a was 0.96 for cells grown at 7 W · m^?2 and 0.37 for cells grown at 50 W · m^?2. Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared, using French press treatment and fractionated centrifugation. Algae grown in the irradiance of 50 W · m^?2 showed a chlorophyll a/P700 ratio of 260, while algae grown at 7 W · m^?2 had a value of 140. Corresponding PSI-particles showed values of 122 and 109 respectively. Light-induced absorption difference spectra measured between 400–450nm indicated different ratios between cytochrome f and P700 in the two algal cultures. Enhancement studies of photosynthetic oxygen evolution were carried out. When a background beam of 691 nm was superimposed upon a signal beam of 625 nm, good enhancement was observed for both cultures. With the wavelengths 675 and 691 nm together a pronounced enhancement could be detected only in algae grown at the higher light level. Absorption spectra recorded on whole cells at 77°K revealed a small shift of the main red chlorophyll a absorption peak caused by light intensity. It is proposed that the reduction of the phycocyanin/chlorophyll a ratio in high light-grown cells is accompanied by an increased energy distribution by chlorophyll a into PSII.     

Analysis of Chlorophyll Fluorescence by Means of Noisy Light

Linearization is an efficient means of detecting individualcomponents in complex fluorescence induction curves. In a previousinvestigation based on sine-waves (Hansen, Kolbowski, and Dau,1987) the components related to the plastoquinone pool, thehigh-energy state of the thylakoid membrane and the state 1-state2 transition controller could be identified. In this paper,binary noise is used as an alternative input signal which canalso allow linearization by mathematical tools. Comparison withexperiments using sine-waves shows that curve-fitting of thenoise experiments yields the same data as the sine-wave analysis.Further, some additional components were revealed as labelledby the related time-constants whose values depended on lightintensity (e.g. 5, 15, 20, 70, 85, 550 s for spinach at 2.5W m^–2). The advantages of noise analysis are a shorter measuring time and the availability ofan on-line criterion which indicates when a sufficient signal-to-noiseratio is reached. Key words: Chlorophyll fluorescence, correlation functions, linearization, noise, spinach, time-constants     

Reflected Far-Red Light Effects on Chlorophyll and Light-Harvesting Chlorophyll Protein (LHC-II) Contents under Field Conditions

The influence of various colors of soil cover (mulch) on the farred/red (FR/R) ratio in upwardly reflected light and on concentrations of chlorophyll (Chl) and light-harvesting Chl protein (LHC-II) were measured under field conditions. The FR/R ratios above green surfaces were higher than over white surfaces. Even though plants (Gossyplum hirsutum L. cv PD-1) were grown in full sunlight, those that received higher FR/R ratios in upwardly reflected light were taller and had thinner leaves with higher concentrations of Chl and LHC-II. A controlled environment experiment showed FR/R control of Chl and LHC-II concentrations. The results illustrate the importance of spectral distribution of reflected light on plant growth and a potential means of altering the chemistry of leaf crops under field conditions.     

Chlorophyll Degradation by Light in Leaf Discs in the Presence of Sugar

Leaf dises of Xanthium pensylvanicum floated on 0.01 M sucrose solutions inside Petri dishes incubated in a growth chamber at 22°G with illiumination of 3000 lux for 16 to 24 hours of light lost 90% of their chlorophyll. Similar dises floated on water under the same conditions lost 60% of their chlorophyll by the end of one week. chlorophyll degradation calculated as percent of the optical density of the original chlorophyll content accelerated with time. A minimum light intensity of 2000 lux is required for such degradation. Higher intensities accelerated chlorophyll degradation. Glucose, ribose, and xylose have effects similar to sucrose on chlorophyll destruction in the presence of light. chlorophyll degradation was found to be temperature sensitive. There is no difference in chlorophyll content in the presence or absence of sucrose at 10 °C.