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.     

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.     

14CO2 Assimilation and 14C-photosynthate Translocation in Different Leaves of Sunflower

Chlorophyll and nitrogen contents were highest in leaves of middle position, similarly as photosynthetic efficiency represented by ¹⁴C fixation (maxima in leaf 5 from the top). All the leaves lost ¹⁴C after 2 weeks of ¹⁴CO₂ exposure. However, the reduction in radioactivity was less in young upper leaves than in the mature lower leaves. Leaves exported ¹⁴C-photosynthates to stem both above and below the exposed leaf. Very little radioactivity was recovered from the seeds of plants in which only first or second leaves were exposed to ¹⁴CO₂ implying thereby that the carbon contribution of first two leaves to seed filling was negligible. The contribution of leaves to seed filling increased with the leaf position up to the sixth leaf from the top and after the seventh leaf their contribution to seed filling declined gradually.     

Developmental regulation of photosynthate distribution in leaves of rice

mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N_0.5, N_3.0). The relative gene expression patterns were similar in all leaves except for 9^th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS V_max, SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS V_max was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5^th and 7^th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9^th and flag leaves). PEPC activity and SPS V_max decreased with declining leaf N content. After using ¹⁴CO₂ the ¹⁴C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more ¹⁴C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more ¹⁴C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the N- or C-pool, respectively, regardless of the leaf N status.     

Photosynthesis in leaves of <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> L. infected with tobacco mosaic virus

In tobacco leaves inoculated with tobacco mosaic virus (TMV), changes in chlorophyll (Chl) and carotenoid contents, parameters of slow Chl fluorescence kinetics, i.e. the maximum quantum yield of photosystem (PS2) photochemistry F_v/F_m, the effective quantum yield of photochemical energy conversion in PS2 Φ₂, ratio of quantum yields of photochemical and concurrent non-photochemical processes in PS2 F_v/F₀, non-photochemical quenching (NPQ), and photochemical activities of isolated chloroplasts from systemically infected tobacco leaves were investigated. We compared two successive stages of infection, the first in the stage of vein clearing at 9^th day post inoculation (dpi) and the second at 22^nd dpi when two different regions, i.e. light- (LGI) or dark-green (DGI) islands in the infected leaf were apparent and symptoms were fully developed. These two different regions were measured separately. The Chl and carotenoid contents in infected leaves decreased with a progression of infection and were lowest in LGI in the second stage. Also the ratio of Chl a/b declined in similar manner. The maximum quantum yield of PS2 photochemistry F_v/F_m, was decreased in the following order: first stage, DGI, and LGI. The same is true for the ratio F_v/F₀. The decrease of Φ₂ in infected leaves declined as compared to their controls. On the contrary, NPQ increased in infected leaves, the highest value was found in the first infection stage. Photochemical activities of the whole electron transport chain in isolated chloroplasts dramatically declined with the progression of symptoms, the lowest value was in LGI. Similarly, but to a lesser extent, the activity of PS2 in isolated chloroplasts decreased in infected leaves. Generally, the most marked impairment of the photosynthetic apparatus was manifested in the LGI of infected leaves.     

Protective effects of complementary Ca2+ on low-light-induced oxidative damage in tall fescue

Low-light (LL) intensity is a primary abiotic stressor that negatively influences turf grass quality. In the present experiment, we studied the effect of exogenous Ca²⁺ (0, 10, 50, 100, and 200 mM) on the antioxidant system, the accumulation of MDA and proline, the content of photosynthetic pigments in plant leaves in order to investigate whether exogenous Ca²⁺ treatment improves LL tolerance in tall fescue (Festuca arundinacea Schreb.). We have found that LL significantly reduced a number of growth parameters (plant height, leaf width, leaf fresh weight, root fresh weight, leaf dry weight, and root dry weight), chlorophyll (Chl) a and Chl b contents, and carotenoid (Car) levels, while considerably enhancing electrolyte leakage (EL), MDA accumulation, calcium (Ca²⁺) concentration, and generation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide radical (O ₂ ^·? ). Moreover, LL significantly induced the activities of antioxidant enzymes, such as peroxidase (POD) and catalase (CAT), and slightly increased the activity of superoxide dismutase (SOD) in tall fescue leaves. In contrast, POD and SOD activities declined considerably while CAT activity significantly increased in plant roots under LL stress. The application of 50 mM Ca²⁺ significantly improved the aforementioned growth parameters, the content of photosynthetic pigments, and further enhanced the activities of POD, SOD, and CAT, but decreased electrolyte leakage and MDA and H₂O₂ levels in the leaves and roots of tall fescue under LL stress. These results suggest that Ca²⁺ is likely involved in a resistance to LL by regulating antioxidant enzyme action in tall fescue leaves and roots.     

Ecophysiological adaptation of <Emphasis Type="Italic">Calligonum roborovskii</Emphasis> to decreasing soil water content along an altitudinal gradient in the Kunlun Mountains,central Asia

To understand the ecophysiological adaptation mechanisms of Calligonum roborovskii to altitude variation, this study analyzed chlorophyll a (Chl a), chlorophyll b (Chl b), Chl (a + b), carotenoid (Car), malondialdehyde (MDA), ascorbate (AsA), proline (Pro), membrane permeability (MP), reactive oxygen species (ROS), specific leaf area (SLA), leaf mass per area (LMA), leaf nitrogen content based on mass (N_mass), and the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) in leaves of plants inhabiting different altitudes (A1: 2100 m, A2: 2350 m, A3: 2600 m) on the northern slope of the Kunlun Mountains. The results showed that Chl a, Chl b, Chl (a + b), SLA, N_mass, and the activity of CAT increased with increasing altitude. LMA, MP, MDA, Car, Pro, AsA, O₂⁻, H₂O₂ and the activities of SOD, POD, and APX decreased with increasing altitude. The test results also showed that, changes in venvironmental factors along an altitudinal gradient are not obvious. Soil water content is the main ecological factor. With increasing altitude, soil water content increased significantly. More non-enzymatic and enzymatic antioxidants played an important role in eliminating intracellular ROS. They kept the cell membrane in a stable state and ensured the normal growth of C. roborovskii.     

Spectral reflectance indices and pigment functions during leaf ontogenesis in six subtropical landscape plants

Pigment combinations are regulated during leaf ontogenesis. To better understand pigment function, alterations in chlorophyll, carotenoid and anthocyanin concentrations were investigated during different leaf development stages in six subtropical landscape plants, namely Ixora chinensis Lam, Camellia japonica Linn, Eugenia oleina Wight, Mangifera indica L., Osmanthus fragrans Lowr and Saraca dives Pierre. High concentrations of anthocyanin were associated with reduced chlorophyll in juvenile leaves. As leaves developed, the photosynthetic pigments (chlorophyll and carotenoid) of all six species increased while anthocyanin concentration declined. Chlorophyll fluorescence imaging of Φ_PSII (effective quantum yield of PSII) and of NPQ (non-photochemical fluorescence quenching) and determination of electron transport rate-rapid light curve (RLC) showed that maximum ETR (leaf electron transport rate), Φ_PSII and the saturation point in RLC increased during leaf development but declined as they aged. Juvenile leaves displayed higher values of NPQ and Car/Chl ratios than leaves at other developmental stages. Leaf reflectance spectra (400–800 nm) were measured to provide an in vivo non-destructive assessment of pigments in leaves during ontogenesis. Four reflectance indices, related to pigment characters, were compared with data obtained quantitatively from biochemical analysis. The results showed that the ARI (anthocyanin reflectance index) was linearly correlated to anthocyanin concentration in juvenile leaves, while a positive correlation of Chl NDI (chlorophyll normalized difference vegetation index) to chlorophyll a concentration was species dependent. Photosynthetic reflectance index was not closely related to Car/Chl ratio, while a structural-independent pigment index was not greatly altered by leaf development or species. Accordingly, it is suggested that the high concentration of anthocyanin, higher NPQ and Car/Chl ratio in juvenile leaves are important functional responses to cope with high radiation when the photosynthetic apparatus is not fully developed. Another two leaf reflectance indices, ARI and Chl NDI, are valuable for in vivo pigment evaluation during leaf development.     

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。     

The Lipoxygenase Isozymes in Soybean [Glycine max (L.) Merr.] Leaves (Changes during Leaf Development,after Wounding,and following Reproductive Sink Removal)

The levels of individual lipoxygenase isozymes in soybean [Glycine max (L.) Merr.] leaves were assessed during leaf development, after mechanical wounding, and in response to reproductive sink removal. Native isoelectric focusing followed by immunoblotting was employed to examine individual lipoxygenase isozymes. In leaves of all ages, two distinct classes of lipoxygenase isozymes were detected. One class of lipoxygenase isozymes had nearly neutral isoelectric points (pls) ranging from pH 6.8 to 7.2. The other class of lipoxygenase isozymes had acidic pls ranging from pH 4.7 to 5.6. During leaf development, all of the neutral lipoxygenase isozymes and most of the acidic isozymes were present in greatest abundance in the youngest leaves examined and declined in amount as leaf age increased. However, four acidic lipoxygenase isozymes (pl = 4.70, 4.80, 4.90, 4.95) were more abundant in intermediateage leaves than in either the youngest or oldest leaves examined. Following mechanical wounding of leaves, these same four acidic isozymes also increased in abundance both locally and systemically in leaves from wounded plants. Unlike the specific effects of wounding on the lipoxygenase isozymes in leaves, reproductive sink removal stimulated a general increase in most of the acidic lipoxygenase isozymes in leaves.     

Developmental changes of plant affecting primary photosynthate distribution in rice leaves

Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the ¹⁴CO₂ tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5^th leaf than in the 6^th one. Correspondingly, the V_max of PEPC was significantly higher in the 5^th than in the 6^th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the V_max of SPS and PEPC was lower in the 5^th than in the 6^th leaf. As the 5^th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6^th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6^th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of ¹⁴C was transiently changed in the 5^th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage.     

The Heterogeneity of Structural and Functional Photosynthetic Characteristics of Mesophyll Chloroplasts in Various Parts of Mature or Senescing Leaf Blade of Two Maize (Zea Mays L.) Genotypes

Differences in ultrastructural parameters of mesophyll cell (MC) chloroplasts, contents of photosynthetic pigments, and photochemical activities of isolated MC chloroplasts were studied in the basal, middle, and apical part of mature or senescing leaf blade of two maize genotypes. A distinct heterogeneity of leaf blade was observed both for structural and functional characteristics of chloroplasts. In both mature and senescing leaves the shape of MC chloroplasts changed from flat one in basal part of leaf to nearly spherical one in leaf apex. The volume density of granal thylakoids decreased from leaf base to apex in both types of leaves examined, while the amount of intergranal thylakoids increased in mature leaves but decreased in senescing leaves. The most striking heterogeneity was found for the quantity of plastoglobuli, which strongly increased with the increasing distance from leaf base. The differences in chloroplast ultrastructure were accompanied by differences in other photosynthetic characteristics. The Hill reaction activity and activity of photosystem 1 of isolated MC chloroplasts decreased from leaf base to apex in mature leaves. Apical part of senescing leaf blade was characterised by low contents of chlorophyll (Chl) a and Chl b, whereas in mature leaves, the content of Chls as well as the content of total carotenoids (Car) slightly increased from basal to apical leaf part. This was reflected also in the ratio Chl (a+b)/total Car; the ratio of Chl a/b did not significantly differ between individual parts of leaf blade. Both genotypes examined differed in the character of developmental gradient observed along whole length of leaf blade.     

The effect of elevated CO2 concentration on leaf chlorophyll and nitrogen contents in rice during post-flowering phases

The effect of elevated CO₂ concentration (CE) on leaf chlorophyll (Chl) and nitrogen (N) contents and photosynthetic rate (P_N) was evaluated during the post-flowering stages of rice grown at CE (570 ± 50 μmol mol⁻¹) in open top chamber (OTC), at ambient CO₂ concentration (∼ 365 μmol mol⁻¹) in OTC and at open field. Thirty-five day old seedlings were transplanted in OTCs or in field and allowed to grow till maturity. Chl and N contents were highest at the time of flowering and thereafter it started to decline. The rate of decline in Chl and N contents was faster in plants grown under CE mostly in later part of growth. Irrespective of treatment difference, flag leaf contained the highest amount of Chl and N than penultimate and third leaf. The higher P_N was observed in leaves under CE than in the leaves in other two growing conditions. Considering growth stage, P_N was the highest at flowering which reduced at the later part of growth due to degradation of Chl and N content of the leaf. Under CE it was 40.02 μmol m⁻² s⁻¹ at flowering and it reduced to only 14.77 μmol m⁻² s⁻¹ at maturity stage. The beneficial effect of CE in increasing leaf P_N may be maintained by applying extra dose of nitrogen at the later stages of plant growth.     

Changes in photosynthetic apparatus during dark incubation of detached leaves from control and ultraviolet-B treatedVigna seedlings

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.     

Chlorophyll meter and leaf colour chart to estimate chlorophyll content, leaf colour, and yield of cassava

A field experiment was conducted with two cassava cultivars and eight levels of nitrogen to examine the relationship between extractable chlorophyll (Chl) content of cassava leaves and both the Chl meter value (SPAD) and leaf colour chart (LCC) score. The SPAD, LCC, and Chl a+b content were influenced by leaf position, growth stage, cultivar (cv.), and N fertilization. The cvs. and N fertilization had significant effect on SPAD, LCC, and Chl a+b content of youngest fully expanded leaf (leaf 1) blade in most cases. An F-test indicated that common equations pooled across cvs., N fertilization, and growth stages could be used to describe the relationships between Chl a+b content and LCC and between SPAD and LCC, but not between SPAD and Chl a+b content. Relationships between tuber yield and SPAD, LCC, and Chl a+b content were significant (p<0.05) and positive at 30 and 60 d after planting. Thus LCC and SPAD can be used to estimate leaf Chl content which is an indicator of leaf N status.     

Nitrogen accumulation and redistribution in soybean genotypes with variation in seed protein concentration

Breeding for high seed protein concentration in soybean [Glycine max (L.) Merrill] often results in lower yield, but the basis for this negative relationship is not well understood. To address this question, we evaluated the N acquisition characteristics of three high protein and three normal soybean genotypes in the field for 3 years. Plants were grown in 0.76 m rows following conventional cultural practices and water stress was minimized with sprinkler irrigation. We determined the mass and N concentration of leaves, petioles and stems at the beginning of seed filling (growth stage R5) and of stems at maturity. The N concentration of abscised leaves and petioles was also determined. There was significant variation among genotypes in total seed N (g m⁻²) at maturity (range from 14.7 to 24.4 g N m⁻²) as a result of variation in seed N concentration and yield. There was no evidence that the larger amounts of mature seed N were associated with a larger vegetative N reservoir at growth stage R5 as determined by vegetative mass at R5 or the concentration of N in vegetative tissues. Increasing seed N at maturity did not lower the N concentration in abscised leaves and petioles, or in the stems at maturity. The rate and timing of leaf senescence (loss of chlorophyll) was essentially the same for all genotypes. With no increase in the contribution from redistributed N, increases in N uptake or fixation during seed filling must have been responsible for the higher levels of seed N at maturity in high-protein genotypes. These data suggest that increasing total seed N at maturity by selecting for higher seed protein concentration or higher yield in soybean does not require, as some models suggest, a larger vegetative N reservoir at the beginning of seed filling or more rapid senescence.     

Enhanced antioxidant protection at the early stages of leaf expansion in ginkgo under natural environmental conditions

Photosynthetic pigments, gas exchange, chlorophyll (Chl) a fluorescence kinetics, antioxidant enzymes and chloroplast ultrastructure were investigated in ginkgo (Ginkgo biloba L.) leaves from emergence to full size. Under natural conditions, the net photosynthetic rate (P_N), contents of Chl a, Chl b and total soluble proteins and fresh and dry leaf mass gradually increased during leaf expansion. The maximum photochemical efficiency of photosystem (PS) 2 (variable to maximum fluorescence ratio, F_v/F_m) was considerably higher at the early stages of leaf development than in fully expanded leaves. During daily course, only reversible decrease in F_v/F_m was distinguished at various stages, implying that no photo-damage occurred. Absorption flux per cross section (CS) and trapped energy flux per CS were significantly lower in newly expanding leaves compared with fully expanded ones, however, dissipated energy flux per CS was only slightly lower in expanding leaves. The ratio of carotenoids (Car)/Chl decreased gradually during leaf expansion due to increasing Chl content. Moreover, activities of the antioxidant enzymes, such as superoxide dismutase, ascorbate peroxidase, catalase and peroxidase, increased at the early stages of leaf expansion. The appearance of osmiophilic granules in fully expanded leaves further proves that photo-protection is significantly strengthened at the early stages of leaf expansion.     

青藏高原不同海拔地区唐古特山莨菪叶片光合色素含量和抗氧化酶活性的比较研究

以青藏高原东北隅的西宁和海北(海拔分别为2 300 m和3 200 m)人工栽培唐古特山莨菪为材料,对两不同海拔地区间各叶层叶片光合色素含量和抗氧化酶活性等生理指标进行比较分析.结果显示:(1)生长在海北的唐古特山莨菪叶片厚度极显著高于西宁(P<0.01),且两地区植物的叶片厚度从第1层到第4层均呈显著增加趋势;海北唐古特山莨菪叶片的叶绿素a、叶绿素b、总叶绿素、类胡萝卜素含量以及紫外吸收物质的含量均显著高于西宁地区(P<0.05),从第1层到第4层,两地植株叶片的光合色素和紫外吸收物质的含量都呈降低的趋势,且两地区让差异显著;叶绿素a/b的层间差异显著(P<0.05),但两海拔地区间差异不显著;类胡萝卜素/叶绿素比值海北高于西宁,从第1层到第4层叶片呈降低趋势.(2)生长于海北的唐古特山良菪叶片组织中的SOD、CAT活性和MDA含量比西宁的高,POD、APX则相反;从第1层叶片到第4层,西宁和海北唐古特山莨菪叶片中的SOD活性显著增高(P<0.05),但两地区各层间的CAT、POD、APX活性和MDA含量无明显的变化.研究表明,不同海拔对唐占特山莨菪叶片的生理特性有影响,同一海拔不同叶层叶片之间差异也较为明显;生长在高海拔地区的植物尽管表现出诸多生理适应特征,但膜系统依然有一定受损.     

Relationship between photosynthetic pigments and chlorophyll fluorescence in soybean under varying phosphorus nutrition at ambient and elevated CO<Subscript>2</Subscript>

To assess the relationship between chlorophyll (Chl) fluorescence (CF) and photosynthetic pigments, soybean was grown under varying phosphorus (P) nutrition at ambient and elevated CO₂ (EC). The EC stimulated, but P deficiency decreased plant height, node numbers, and leaf area concomitantly with the rates of stem elongation, node addition, and leaf area expansion. Under P deficiency, CF parameters and pigments declined except that carotenoids (Car) were relatively stable indicating its role in photoprotection. The CF parameters were strongly related with Chl concentration but not with Chl a/b or Car. However, total Chl/Car showed the strongest association with CF parameters such as quantum efficiency and yield of photosystem II. This relationship was not affected by CO₂ treatment. The high correlation between CF and total Chl/Car underscores the significance of the quantification of both, Chl and Car concentrations, to understand the photochemistry and underlying processes of photoprotection and mechanisms of excess energy dissipation in a given environment.     

Stomatal and photosynthetic responses ofCichorium intybus leaves to sulfur dioxide treatment at different stages of plant development

Fifty-day-oldCichorium intybus Linn, plants were exposed to 1 ppm sulfur dioxide gas, 2 h per day for 7 consecutive days. Their leaves as well as those from the control plants were sampled at pre-flowering, flowering, and post-flowering stages to study their morphological, physiological, and biochemical responses to SO₂ stress. The number, dimensions, area, and biomass of leaves were less in the treated plants. Length and width of stomatal apertures on both epidermises were greater for leaves exposed to SO₂. The Stomata were longer on the adaxial epidermis, but shorter on the abaxial epidermis, except at the pre-flowering stage. Stomatal widths varied widely. Compared with the controls, the abaxial epidermis on treated leaves showed consistently lower stomatal densities as well as stomatal indices. This was also true for the adaxial epidermis during the post-flowering stage. The photosynthetic rate and stomatal conductance were reduced in the SO₂-exposed plants, but intercellular CO₂ concentrations increased at the pre-flowering stage and, subsequently, declined. Chlorophyll a, carotenoid, and total chlorophyll contents increased at the pre-flowering stage, and then decreased. The level of chlorophyllb was reduced throughout plant development compared with the untreated controls.