The Development of Chloroplast Ultrastructure and Hill Reaction Activity During Leaf Ontogeny in Different Maize (Zea Mays L.) Genotypes

Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Development of Chloroplast Ultrastructure and Hill Reaction Activity During Leaf Ontogeny in Different Maize (Zea Mays L.) Genotypes

Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts.     

Relative sensitivity of various spectral forms of photosynthetic pigments to leaf senescence in wheat (Triticum aestivum L.)

The change in the characteristics of the absorption spectrum of chloroplasts which were isolated from the mature and senescing primary wheat leaves, was examined at various wavelengths in which the photosynthetic pigments mostly absorb. Chlorophyll (Chl) a was observed to be relatively more sensitive to leaf senescence than Chl b and carotenoids. Furthermore, the various spectral in vivo forms of Chl a, did not degrade to a similar extent; the far red absorbing forms of Chl a including species that absorb maximally at 692 nm (Chl a-692), 700 nm (Chl a-700) and 708 nm (Chl a 708) were found to be extremely sensitive to senescence induced losses. Both attached and detached senscing primary wheat leaves exhibited nearly similar pattern in the loss of photosynthetic pigments which suggests that the loss in long wavelength absorbing forms of Chl a is a selective indicator of leaf senescence.     

墨兰幼叶和成熟叶不同部位叶绿体超微结构和光合作用

墨兰试管苗植株成熟叶片叶绿体基粒较发达,类囊本膜垛叠较紧密。幼叶叶绿体中少有亲锇颗粒,成熟叶的叶绿体中往往既有亲锇颗粒又有淀粉粒。幼叶中基粒数目比成熟叶的少,叶绿体也比成熟叶的小。幼叶的光合放氧速率比成熟叶的低。幼叶中叶尖部叶绿体最大而叶基部最小,但叶尖部的光合放氧速率比叶基部小。成熟叶中叶绿体大小及光合放氧速率区别不明显。通过对各部位叶绿素含量的测定发现,叶绿素含量与光合放氧速率之间没有正相关性     

The Distinctive Pattern of Photosystem 2 Activity,Photosynthetic Pigment Accumulation,and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content of Chloroplasts along the Axis of Primary Wheat Leaf Lamina

Wheat (Triticum aestivum L. cv. Sonalika) seedlings were grown in Hoagland solution. Primary leaves were harvested at 8, 12, and 15 d and cut into five equal segments. Contents of photosynthetic pigments and proteins, and photosystem 2 (PS2) activity increased from base to apex of these leaves. Chlorophyll (Chl) content was maximum at 12 d in all the leaf segments, but PS2 activity showed a gradual decline from 8 to 15 d in all leaf segments. In sharp contrast, the CO₂ fixation ability of chloroplasts increased from 8 to 15 d. CO₂ fixation ability of chloroplasts started to decline from base to apex of 15-d-old seedlings, where the content of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RuBPCO-LSU) increased acropetally. RuBPCO-LSU content was maximum in all the leaf segments in 12-d-old seedlings. This shows a distinctive pattern of PS2, Chl, CO₂ fixation ability of chloroplasts, and RuBPCO-LSU content along the axis of leaf lamina during development and senescence. RuBPCO-LSU (54 kDa) degraded to fragments of 45, 42, 37, 19, and 16 kDa products which accumulated along the leaf axis during ageing of chloroplasts. Thus the CO₂ fixation ability of chloroplasts declines earlier than PS2 activity and photosynthetic pigment contents along the leaf lamina.     

The polarity of endogenous regulatory substances inBryophyllum crenatum leaves and stems

In isolated leaves ofBryophylluni crenatum the intensity of marginal bud formation decreases from the apex towards the blade base, which is associated with the decreasing content of enioganous gibberallins. As proved by Dostál (1930), the formation of marginal buds on transversely divided blade of the isolated leaf increases in comparison with the non-divided control leaf. The results of our experiments have revealed that the increase in the formation of marginal buds in the blade transversely divided into the apical, middle and basal parts is connected with the increasing level of endogenous gibberellins, especially in the apical part. This rising level appears as early as 7 days following blade division,i.e. at the time preceding the formation of marginal bud bases. InBryophyllum crenatum plants the level of endogenous cytokinins was estimated in apical, middle and basal leaves, as well as in adjacent internodia. Maximum content was found out in the leaves from the middle stem part, which is probably associated with the capacity of this part to form marginal buds spontaneously also in intact plants. However, prior to flowering the maximum of cytokinin activity is shifted to the apical stem part.     

Chloroplast development and the synthesis of chlorophyll and protochlorophyllide in Zostera transferred to darkness

Intact plants and isolated leaves of Zostera capricornii Martens ex Aschers were transferred from daylight to darkness. Substantial amounts of chloropyll a and b continued to accumulate in immature and mature tissue in the same ratio as in the light and were incorporated into chlorophyll-protein complexes in the thylakoids. A small amount of protochlorophyllide also accumulated in immature tissue in the dark. Proplastids and immature chloroplasts continued to develop into mature chloroplasts in the dark in the normal manner but prolamellar bodies, which are a conspicuous feature of immature chloroplasts, took longer to disperse than in the light. Protochlorophyllide accumulation and prolamellar-body formation were not correlated. The results indicate that Zostera has a genetic capacity for dark chlorophyll synthesis which is expressed in immature and mature leaf tissue and enables this plant to continue synthesising chlorophyll and assembling chloroplasts at night.Abbreviations Chl chlorophyll - T _o time of transfer to darkness     

Changes in distribution of nucleoids in developing and dividing chloroplasts and etioplasts ofArena sativa

Summary Nucleoid distribution in chloroplasts and etioplasts at the different developmental stages was examined with the first leaves ofAvena sativa by using a DNA-specific fluorescent probe, 46-diamidino-2-phenylindole (DAPI). In light-grown first leaves, three types of plastid nucleoid distribution were recognized. 1. Peripheral distribution in undeveloped chloroplasts which contain only a few thylakoids in the middle region of the leaf sheath. 2. Ring-like arrangement along the rim of developing and dividing young chloroplasts, of which grana were composed of four to eight layers of thylakoids, at the base of the leaf blade. The plane of the nucleoids' ring is in parallel with the face of the thylakoids. 3. Scattered distribution of 10 to 20 discrete spherular nucleoids in the stroma of fully developed chloroplasts, of which grana were composed of up to 20 thylakoids, in the regions of the middle and the tip of the leaf blade. In dark-grown first leaves two types were recognized. 1. Peripheral distribution in developing and dividing young etioplasts in the leaf sheath and the base of the leaf blade. 2. Scattered distribution of 10 or more discrete spherular nucleoids in fully developed etioplasts, containing extended prothylakoids, in the regions of the middle and the tip of the leaf blade. Ring-like arrangement of nucleoids was not observed in any etioplasts. The results indicates that spatial arrangement of plastid nucleoids dynamically changes in close relationship with the development of the inner membrane systems of plastids.     

竹柏2种颜色叶片的光合特性研究

为了解竹柏(Podocarpus nagi)的光合特性,以3 a生全绿叶和花叶竹柏为材料,测定其光合色素含量和气体交换参数。结果表明,全绿叶竹柏叶片的叶绿素a、叶绿素b、类胡萝卜素、叶绿素a+b、叶绿素a/b和叶绿素a+b/类胡萝卜素均显著高于花叶竹柏;全绿叶竹柏叶片的初始量子效率、最大光合速率和暗呼吸速率均显著高于花叶,而光饱和点和光补偿点均显著低于花叶;全绿叶竹柏叶片的初始羧化效率、光合速率、CO2饱和点和光呼吸速率均高于花叶,而CO2补偿点低于花叶。2种颜色叶片的气孔导度、蒸腾速率和水分利用效率均随着光合有效辐射的增大而增大,且均表现为全绿叶花叶,而胞间CO2浓度则相反,表现为花叶全绿叶。因此,全绿叶竹柏利用弱光的能力强于花叶竹柏,而花叶竹柏利用强光的能力更强,在园林绿化配置中,可根据2种颜色叶片的光合特性合理配置。     

High irradiance and water stress induce alterations in pigment composition and chloroplast activities of primary wheat leaves

Remarkable changes were observed in chlorophyll (Chl) (a+b), carotenoids (Car), and protein content of leaves and fluorescence emission, polarisation, excitation energy transfer, lipid peroxidation and DCPIP photoreduction activity in isolated chloroplasts of wheat leaves grown under moderate irradiance (MI, 15 W m⁻², control) and subsequently exposed to high irradiance stress (HIS, 250 W m⁻²), water stress (WS, 5 % aqueous polyethylene glycol-4000 solution) and HIS+WS simultaneously, during mature and senescence phase. In the stress exposed samples the Chl, Car and protein contents and kinetics of Hill activity significantly declined. Decrease in excitation energy transfer and increase in membrane polarisation and accumulation of malondialdehyde (MDA) in chloroplasts were also observed. The effect was more pronounced when the seedlings were treated with HIS+WS simultaneously. These observations suggest additive and a possible synergetic action of HIS and WS causing faster loss of pigments and protein content, intense changes in membrane properties including photochemical function, compared to samples exposed to either of the stresses individually.     

Physiological and Biochemical Changes during Seed Filling in Relation to Leaf Senescence in Soybean

Field experiments with Glycine max (L.) Merr. cv. Ludou 11 and Ludou 4 were conducted to evaluate changes in photosynthetic rate, antioxidative enzyme activity, soluble protein, chlorophyll (Chl) and carotenoid (Car) contents in relation to leaf senescence during seed filling period. Photosynthetic rate, soluble protein content, catalase and peroxidase activities were the highest at 25 days after flowering (DAF). Chl a, Chl b and Car contents reached the maximum at 15 DAF and rapidly decreased after 33 DAF.     

Maize F<Subscript>1</Subscript> hybrid differs from its maternal parent in the development of chloroplasts in bundle sheath,but not in mesophyll cells: Quantitative analysis of chloroplast ultrastructure and dimensions in different parts of leaf blade at the beginning of its senescence

The quantitative changes of chloroplast ultrastructure and dimensions in mesophyll (MC) and bundle sheath (BSC) cells, associated with the onset of leaf senescence, were followed along the developmental leaf blade gradient of the third leaf of maize (Zea mays L.). To ascertain whether the rapidity of structural changes associated with the transition of chloroplasts from mature to senescent state is a heritable trait, the parental and the first filial generations of plants were used. The heterogeneity of leaf blade, associated with the development of maize leaf (with the oldest regions at the apex and the youngest ones at the base) was clearly discernible in the ultrastructure and dimensions of chloroplasts; however, there were differences in the actual pattern of chloroplast development between both genotypes as well as between both cell types examined. While the course of MC chloroplasts’ development at the onset of leaf senescence in maize hybrid followed that of its parent rather well, this did not apply for the BSC chloroplasts. In this case, each genotype was characterized by its own distinguishable developmental pattern, particularly as regards the accumulation of starch inclusions and the associated changes of the size and shape of BSC chloroplasts.     

Light regulation of photosynthetic membrane structure,organization, and function

The light environment during plant growth determines the structural and functional properties of higher plant chloroplasts, thus revealing a dynamically regulated developmental system. Pisum sativum plants growing under intermittent illumination showed chloroplasts with fully functional photosystem (PS) II and PSI reaction centers that lacked the peripheral chlorophyll (Chi) a/b and Chl a light-harvesting complexes (LHC), respectively. The results suggest a light flux differential threshold regulation in the biosynthesis of the photosystem core and peripheral antenna complexes. Sun-adapted species and plants growing under far-red-depleted illumination showed grana stacks composed of few (3–5) thylakoids connected with long intergrana (stroma) thylakoids. They had a PSII/PSI reaction center ratio in the range 1.3–1.9. Shade-adapted species and plants growing under far-red-enrichcd illumination showed large grana stacks composed of several thylakoids, often extending across the entire chloroplast body, and short intergrana stroma thylakoids. They had a higher PSII/PSI reaction center ratio, in the range of 2.2–4.0. Thus, the relative extent of grana and stroma thylakoid formation corresponds with the relative amounts of PSII and PSI in the chloroplast, respectively. The structural and functional adaptation of the photosynthetic membrane system in response to the quality of illumination involves mainly a control on the rate of PSII and PSI complex biosynthesis.     

Growth,photosynthetic pigment content and oil yield ofPogostemon cablin grown under sun and shade conditions

Patchouli (Pogostemon cablin Benth.) plants grown under shade (LI) showed an increased height due to internodal elongation, leaf area, leaf area index, and chlorophyll (Chl)b, Chl (a+b) and carotenoid (Car) contents compared to the plants grown in sunlight (HI). The number of branches and green leaves decreased under LI treatment, with a marginal variation in the patchouli oil yield. A comparison between the relative contents of photosynthetic pigments indicated that Chlb and Car accumuled preferentially over Chla in the LI grown plants.     

Response of photosynthesis and chlorophyll fluorescence quenching to leaf dichotocarpism in Ligustrum vicaryi, an ornamental herb

Net photosynthetic rate of yellow upper leaves (UL) of Ligustrum vicaryi was slightly, but not significantly higher than that of green lower leaves (LL). Diurnally, maximum photochemical efficiency of photosystem 2, PS2 (F_v/F_m) of LL did not significantly decline but the UL showed fairly great daily variations. Yield of PS2 of UL showed an enantiomorphous variation to the photosynthetically active radiation and was significantly lower than in the LL. Unlike F_v/F_m, the efficiency of energy conversion in PS2 and both non-photosynthetic and photosynthetic quenching did not differ in UL and LL. Significant differences between UL and LL were found in contents of chlorophyll (Chl) a, b, and carotenoids (Car) and ratios of Chl a/b, Chl b/Chl (a+b), and Car/Chl (a+b). Leaf colour dichotocarpism in L. vicaryi was mainly caused by different photon utilization; sunflecks affected the LL.     

Ultrastructural localization of photosynthetic activity in thylakoids during chloroplast development in maize

The localization of photosynthetic activity in developing maize (Zea mays L.) chloroplasts was studied in situ by two electron-microscopic-cytochemical methods. The activity of photosystem I was detected by photooxidation of 3,3-diaminobenzidine (DAB) and the activity of the photosystem II by photoreduction of thiocarbamyl nitrotetrazolium blue (TCNBT). During the transformation of proplastids into chloroplasts, at the base of the leaf blade the DAB reaction appeared before the TCNBT reaction. A positive DAB reaction was observed in the single thylakoids of plastids in cells located only about 0.5 mm above the base. Dark, osmiophilic DAB polymers accumulated in the lumina of the thylakoids. Plastid envelopes and tubules of the prolamellar bodies in immature chloroplasts were DAB-negative. In fully differentiated leaf tissue the DAB reaction was intense in the thylakoids of bundle-sheath chloroplasts, as well as in the stroma thylakoids and the peripheral grana thylakoids of mesophyll chloroplats. The photoreduction of TCNBT started in leaf tissue about 1 mm above the base. Dark granular material of reduced TCNBT appeared mostly in the partitions of grana, i.e. interthylakoidally, but some granules were also attached to the stroma thylakoids. The membranes of plastid envelopes and the tubules of prolamellar bodies showed a negative TCNBT reaction. Young bundle-sheath chloroplasts contained some reduced TCNBT in their grana; these deposits largely disappeared in the course of further differentiation. In mature leaf tissue the photoreduction of TCNBT was conspicuous in the grana of mesophyll chloroplasts, but very weak in the single thylakoids and in the granal rudiments of bundle-sheath chloroplasts.Abbreviations DAB 3,3-diaminobenzidine·4 HCl - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PS(I,II) photosystem (I,II) - TCNBT thiocarbamyl nitrotetrazolium blue chloride     

Effects of Phytoplasma Infection on Pigments, Chlorophyll-Protein Complex and Photosynthetic Activities in Field Grown Apple Leaves

Changes in contents of pigments, chlorophyll-protein complex, and photosynthetic activities were investigated in field grown apple (Malus pumila Mill.) leaves infected by Apple Proliferation phytoplasma. The contents of chlorophyll a+b (Chl) and carotenoids (Car) markedly decreased in infected leaves. Similar results were also observed for content of total soluble proteins and ribulose-1,5-bisphosphate carboxylase activity. When various photosynthetic activities were followed in isolated thylakoids, phytoplasma infection caused a marked inhibition of whole chain and photosystem 2 (PS2) activity. Smaller inhibition of photosystem 1 (PS1) activity was observed even in severely infected leaves. The artificial exogenous electron donors, MnCl₂ diphenyl carbazide, and NH₂OH, did not restore the loss of PS2 activity in both mildly and severely infected leaves. Similar results were obtained by Chl fluorescence measurements. The marked loss of PS2 activity in infected leaves was due to the reduction of contents of chlorophyll and light-harvesting chlorophyll-protein 2 complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat shock increases thermotolerance of photosynthetic electron transport and the content of chloroplast membranes and lipids in wheat leaves

Preliminary heating of 15-16-day-old wheat (Triticum aestivum L.) plants for 3 h at 37–38°C (heat shock, HS) increased the tolerance of photosynthetic electron transport (determined as the reduction of 2,6-dichlorophenol indophenol by isolated chloroplasts) toward heating of leaves at 42–48°C in high light (100 klx). At the same time, HS did not affect the activity of the xanthophyll cycle reactions in the 30–48°C temperature range. HS exposure induced an increase in the thylakoid length, the number of grana, and the average number of thylakoids per granum. The volume of the thylakoid system increased 1.4-fold. Such indices as the total content of chlorophylls (a + b), the chlorophyll a/b ratio, as well as the contents of individual carotenoids, chloroplast membrane proteins, and the soluble leaf proteins remained unchanged. The de novo photosynthetic membrane formation was accompanied by the 1.5-fold increase in major chloroplast lipids. It was concluded that, in mature wheat chloroplasts, HS induced the formation of thylakoids characterized by a changed molecular structure and by increased lipid/protein and lipid/chlorophyll ratios.     

Effects of changes in growth temperature on photosynthesis and carotenoid composition in Zea mays leaves

The effects of changes in growth temperature on photosynthesis and carotenoid composition were examined in Zea mays L. leaves of different age and different developmental history. The plants were first grown at sub-optimal temperature (14°C) until the full development of the third leaf. At that time, the mature third leaf and the immature fourth leaf had a low chlorophyll (Chl) content, a low Chl a/b ratio, a high carotenoid/Chl a+b ratio, a high xanthophyll/β-carotene ratio, and about 80% of the xanthophyll cycle pool (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was in the form of zeaxanthin and antheraxanthin. When the temperature was increased from 14°C to 24°C for three days, increased Chl synthesis, accompanied by an increase in the Chl a/b ratio, took place. The ratios of lutein, neoxanthin, and V+A+Z to Chl a+b decreased markedly, whereas no significant changes appeared in the β-carotene/Chl a+b ratio. Furthermore, there was a sharp decrease in the xanthophyll/β-carotene ratio and most of zeaxanthin was converted to violaxanthin in the xanthophyll cycle. The third leaf and the tip segment of the fourth leaf, both expanded at 14°C, showed little difference in their pigment contents. However, the rate of CO₂ assimilation of the tip segment of the fourth leaf was nearly twice that of the third leaf on the third day at 24°C, while the photosynthetic activity was similar in both leaves before the transfer to 24°C. During the warm period at 24°C, new leaf tissue (basal segment of the fourth leaf and part of a fifth leaf) was formed. On the third day at 24°C, the pigment content of 24°C-grown leaf tissue did not differ much from that of 14°C-grown leaf tissue with the exception that the total carotenoid content was lower in the former as compared to the latter, mainly because of a lower V+A+Z content. The rate of CO₂ assimilation of 24°C-grown leaf tissue was comparable to that of the tip segment of the fourth leaf. Regardless of which leaf tissue is considered, reducing the temperature from 24°C to 14°C for 5 days slightly affected the pigment content, but violaxanthin was largely converted to zeaxanthin and antheraxanthin in the xanthophyll cycle. The results indicate that compared to old leaf tissue of mature leaves, physiologically younger leaf tissue of immature leaves is much more able to recover from depressions in the photosynthetic activity induced by growth at sub-optimal temperature when the plants experience optimal growth temperatures, but that factors other than the pigment content must determine this capability.     

Photosynthetic Characteristics of Chloroplasts of Primary Wheat Leaves Grown under Different Irradiance

The rate of accumulation of total chlorophyll (Chl) and carotenoids (Car) of leaves grown under high irradiance, HI (30 and 45 W m^–2) was faster than at moderate irradiance, MI (15 W m^–2). However, the senescence phase started earlier in the samples and proceeded at a faster rate. Chl a/b and Chl (a+b)/Car values showed faster loss of Chl a (compared to Chl b) and Chl (a+b) (compared to Car) in HI leaves. Protein accumulation and loss were also similar to that of Chl (a+b) content. Increase in Chl fluorescence during the development phase may suggest a gradual change in thylakoid organisation, however, the temporal kinetics were different in HI and MI samples. Increase in fluorescence polarisation during senescence of HI leaves compared to the control (MI) suggests conversion of thylakoid membranes to gel phase. Chloroplasts prepared from HI seedlings showed higher rate of photochemical activities, however, the activity declined earlier and at faster rate compared to the control.