Responses in the physiology and biochemistry of Korean pine (Pinus koraiensis) under supplementary UV-B radiation

The effect of supplementary UV-B radiation on Korean pine (Pinus koraiensis Sieb. et Zucc) was investigated. Compared with the control, the T1, T2, and T3 UV-B treatments increased by 1.40, 2.81, and 4.22 kJ m^?2 d^?1, respectively. Gas-exchange parameters, photosynthetic pigment concentrations, contents of secondary metabolites, epicuticular wax, free radical, malondialdehyde (MDA), and the activities of antioxidant enzymes were determined after 40 d of exposure. The concentrations of chlorophyll (Chl) a, Chl b, total Chl, carotenoid (Car), and the ratio Chl a/b in the pine needles were in the following order: T1 > T2 > T3. Compared with the control, the contents of flavonoids and epicuticular wax significantly decreased in all levels of supplementary UV-B radiations (p<0.05). Moreover, the contents of hydrogen peroxide (H₂O₂) and MDA significantly increased with the enhanced UV-B radiations (p<0.05). Korean pine can increase the catalase, ascorbate peroxidase, and superoxide dismutase activities to prevent oxidative stress by supplementary UV-B radiation. However, its defence mechanism is not efficient enough to prevent UV-Binduced damage.     

Lanthanum improves salt tolerance of maize seedlings

In this study, the effects of lanthanum were investigated on contents of pigments, chlorophyll (Chl) fluorescence, antioxidative enzymes, and biomass of maize seedlings under salt stress. The results showed that salt stress significantly decreased the contents of Chl and carotenoids, maximum photochemical efficiency of PSII (F_v/F_m), photochemical quenching (q_P), and quantum efficiency of PSII photochemistry (Φ_PSII), net photosynthetic rate (P_N), and biomass. Salt stress increased nonphotochemical quenching (q_N), the activities of ascorbate peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and the contents of malondialdehyde and hydrogen peroxide compared with control. Pretreatment with lanthanum prior to salt stress significantly enhanced the contents of Chl and carotenoids, F_v/F_m, q_P, q_N, Φ_PSII, P_N, biomass, and activities of the above antioxidant enzymes compared with the salt-stressed plants. Pretreatment with lanthanum also significantly reduced the contents of malondialdehyde and hydrogen peroxide induced by salt stress. Our results suggested that lanthanum can improve salt tolerance of maize seedlings by enhancing the function of photosynthetic apparatus and antioxidant capacity.     

Influence of foliar-applied triacontanol on growth, gas exchange characteristics, and chlorophyll fluorescence at different growth stages in wheat under saline conditions

A greenhouse experiment was conducted to examine the effect of foliar application of triacontanol (TRIA) on two cultivars (cv. S-24 and MH-97) of wheat (Triticum aestivum L.) at different growth stages. Plants were grown in full strength Hoagland’s nutrient solution under salt stress (150 mM NaCl) or control (0 mM NaCl) conditions. Three TRIA concentrations (0, 10, and 20 μM) were sprayed over leaves at three different growth stages, i.e. vegetative (V), boot (B), and vegetative + boot (VB) stages (two sprays on same plants, i.e., the first at 30-d-old plants and the second 78-d-old plants). Salt stress decreased significantly growth, net photosynthetic rate (P _N), transpiration rate (E), chlorophyll contents (Chl a and b), and electron transport rate (ETR), while membrane permeability increased in both wheat cultivars. Stomatal conductance (g _s) decreased only in salt-sensitive cv. MH-97 under saline conditions. Foliar application of TRIA at different growth stages enhanced significantly the growth, P _N, g _s, Chl a and b contents, and ETR, while membrane permeability was reduced in both cultivars under salt stress. Of various growth stages, foliar-applied TRIA was comparatively more effective when it was applied at V and VB stages. Overall, 10 μM TRIA concentration was the most efficient in reducing negative effects of salinity stress in both wheat cultivars. The cv. S-24 showed the better growth and ETR, while cv. MH-97 exhibited higher nonphotochemical quenching.     

High photosynthetic efficiency of a rice (Oryza sativa L.) xantha mutant

Comparative analysis revealed that a xantha rice mutant (cv. Huangyu B) had higher ratios of chlorophyll (Chl) a/b and carotenoids/Chl, and higher photosynthetic efficiency than its wild type parent (cv. II32 B). Unexpectedly, the mutant had higher net photosynthetic rate (P _N) than II32 B. This might have resulted from its lower non-photochemical quenching (q_N) but higher maximal photochemical efficiency (F_V/F_M), higher excitation energy capture efficiency of photosystem 2 (PS2) reaction centres (F_V′/F_M′), higher photochemical quenching (q_P), higher effective PS2 quantum yield (Φ_PS2), and higher non-cyclic electron transport rate (ETR). This is the first report of a chlorophyll mutant that has higher photosynthetic efficiency and main Chl fluorescence parameters than its wild type. This mutant could become a unique material both for the basic research on photosynthesis and for the development of high yielding rice cultivars.     

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.     

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.     

Nitrogen deposition limits photosynthetic response to elevated CO2 differentially in a dioecious species

Sexual dimorphisms of dioecious plants are important in controlling and maintaining sex ratios under changing climate environments. Yet, little is known about sex-specific responses to elevated CO₂ with soil nitrogen (N) deposition. To investigate sex-related physiological and biochemical responses to elevated CO₂ with N deposition, Populus cathayana Rehd. was employed as a model species. The cuttings were subjected to two CO₂ regimes (350 and 700???mol?mol^?1) with two N levels (0 and 5?g?N?m^?2?year^?1). Our results showed that elevated CO₂ and N deposition separately increased the total number of leaves, leaf area (LA), leaf mass, net photosynthetic rate (P _n), light saturated photosynthetic rate (P _max), chlorophyll a (Chl a), and chlorophyll a to chlorophyll b ratio (Chl a/b) in both males and females of P. cathayana. However, the effects on LA, leaf mass, P _n, P _max, Chl a and Chl a/b were weakened under the combined treatment of elevated CO₂ and N deposition. Males had higher leaf mass, P _n, P _max, apparent quantum yield (??), carboxylation efficiency (CE), Chl a, Chl a/b, leaf N, and root carbon to N ratio (C/N) than did females under elevated CO₂ with N deposition. In contrast to males, females had significantly higher levels of soluble sugars in leaves and greater starch accumulation in roots and stems under the same condition. The results of the present work imply that P. cathayana females are more responsive and suffer from greater negative effects on growth and photosynthetic capacity than do males when grown under elevated CO₂ with soil N deposition.     

Effect of transient accumulation of anthocyanin on leaf development and photoprotection of Fagopyrum dibotrys mutant

Changes in pigments contents, leaf area, leaf dry mass per unit area (LMA), photosynthetic rate and chlorophyll a fluorescence were investigated in developing leaves of Fagopyrum dibotrys Hara. mutant. Anthocyanins transiently accumulate below the upper epidermis during leaf ontogeny of this mutant. Red leaves possessed lower Chl content, LMA, photosynthetic rate and apparent carboxylation efficiency than green leaves. However, content of anthocyanins declined and above mentioned parameters increased during further leaf development. In both red and green leaves, chronic photoinhibition did not take place according to variable to maximum chlorophyll fluorescence ratio (F_v/F_m). Red leaves had higher non-photochemical quenching (NPQ) and higher PS 2 efficiency.     

Leaf chloroplast ultrastructure and photosynthetic properties of a chlorophyll-deficient mutant of rice

Leaf chloroplast ultrastructure and photosynthetic properties of a natural, yellow-green leaf mutant (ygl1) of rice were characterized. Our results showed that chloroplast development was significantly delayed in the mutant leaves compared with the wild-type rice (WT). As leaves matured, more grana stacks formed concurrently with increasing leaf chlorophyll (Chl) content. Except for the lower intercellular CO₂ concentration, the ygl1 plants had a higher leaf net photosynthetic rate, stomatal conductance, and transpiration rate than those of the WT plants. Under equal amounts of Chl, the excitation energy of PSI and PSII was much stronger in the mutant than that in the WT. The ygl1 plants showed higher nonphotochemical quenching and lower photochemical quenching. They also exhibited higher actual photochemical efficiency of PSII with a higher electron transport rate. Under the light of 200 μmol(photon) m^?2 s^?1, the ygl1 mutant showed lesser deepoxidation of violaxanthin in the xanthophyll cycle than WT, but it increased substantially under strong light conditions. In conclusion, the photosynthetic machinery of the ygl1 remained stable during leaf development. The plants were less sensitive to photoinhibition compared with WT due to the active xanthophyll cycle. The ygl1 plants were efficient in both light harvesting and conversion of solar energy.     

Limiting Factors in Photosynthesis: I. USE OF IRON STRESS TO CONTROL PHOTOCHEMICAL CAPACITY IN VIVO

The possibility of using Fe stress as an experimental tool in the study of limiting factors was explored. Results show that Fe stress decreased the chlorophyll (Chl) a, Chl b, carotene, and xanthophyll content of leaves of sugar beets (Beta vulgaris L.) and that the maximum rate of photosynthetic CO₂ uptake (P_max) per unit area was linearly related to Chl (a + b) per unit area. Measurements of noncyclic ATP formation by isolated chloroplasts at light saturation indicate that photosynthetic electron transport capacity decreased concomitantly with pigment content under Fe stress.     

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.     

Effect of gamma radiation on mutant induction of <Emphasis Type="Italic">Fagopyrum dibotrys</Emphasis> Hara

Agronomic traits, photosynthetic pigments, gas exchange, and chlorophyll (Chl) fluorescence parameters of red stem buckwheat (Fagopyrum dibotrys Hara) mutants induced by γ-radiation were compared with green control at seedling stage. Plant height, number of first-class branches, and rhizome biomass were inhibited significantly (p<0.01). Chl a, Chl b, and Chl a+b contents decreased with elevated dose of γ-rays, while increasing carotenoid content indicated that buckwheat was capable of adjusting to the radiation damage. Decrease in net photosynthetic rate was the result of both stomatal and non-stomatal limitations. Fluorescence parameters, such as F₀, F_m, F_v/F_m, F_v/F₀, Φ_PS2, electron transport rate, and photochemical quenching declined significantly (p<0.01) as compared with control due to photoinhibition, while non-photochemical quenching increased to enhance thermal dissipation. Lower parameters implied that leaf tissue was damaged significantly by high dose of γ-radiation and therefore leaf senescence was accelerated.     

Gas exchange and water relations of three <Emphasis Type="Italic">Vitis vinifera</Emphasis> L. cultivars growing under Mediterranean climate

Optical characteristics, contents of photosynthetic pigments, total soluble sugars, and starch, rates of gas exchange, chlorophyll (Chl) a fluorescence, and leaf water relations were analysed in three Vitis vinifera L. cultivars, Tinto Cão (TC), Touriga Nacional (TN), and Tinta Roriz (TR), grown in Mediterranean climate. Chl content was significantly lower in TC than in TN and TR leaves, while the Chl a/b ratio was higher. TR had the lowest net photosynthetic rate, stomatal conductance, and contents of soluble sugars and starch than TN and TC. In spite of low Chl content, TC showed the lowest photon absorbance and the highest photochemical efficiency of photosystem 2. TC had the lowest predawn and midday leaf water potential. The capability for osmotic adjustment was similar among cultivars and the calculated modulus of elasticity was higher in TC leaves. The typical lighter green leaves of TC seemed to be an adaptive strategy to high irradiance and air temperature associated to water stress.     

Responses of Acacia Mangium Seedlings to Different Irradiances

The photosynthetic and growth responses of A. mangium to different photosynthetic photon flux density (PPFD) during early seedling establishment (36 d after sowing) were investigated. Shade-grown A. mangium seedlings exhibited lower chlorophyll (Chl) a/b ratio, higher Chl and carotenoid (Car) contents, and higher total Chl/Car ratio than sun-grown seedlings. Sun-grown seedlings showed significantly higher photosynthetic capacity and total plant dry mass. High PPFD was crucial for the successful early establishment and robust growth of A. mangium seedlings.     

Variations in light energy dissipation in <Emphasis Type="Italic">Woodfordia fruticosa</Emphasis> leaves during expansion

Young leaves of tropical trees frequently appear red in color, with the redness disappearing as the leaves mature. During leaf expansion, plants may employ photoprotective mechanisms to cope with high light intensities; however, the variations in anthocyanin contents, nonphotochemical quenching (NPQ), and photorespiration during leaf expansion are poorly understood. Here, we investigated pigment contents, gas exchange, and chlorophyll (Chl) fluorescence in Woodfordia fruticosa leaves during their expansion. Young red leaves had significantly lower Chl content than that of expanding or mature leaves, but they accumulated significantly higher anthocyanins and dissipated more excited light energy through NPQ. As the leaves matured, net photosynthetic rate, total electron flow through PSII, and electron flow for ribulose-1,5-bisphosphate oxygenation gradually increased. Our results provided evidence that photorespiration is of fundamental importance in regulating the photosynthetic electron flow and CO₂ assimilation during leaf expansion.     

Effect of day/night temperature difference on chlorophyll content,photosynthesis and fluorescence parameters of tomato at fruit stage

In order to investigate the effect of day/night temperature difference (DIF) on photosynthetic characteristics of tomato plants (Solanum lycopersicum, cv. Jinguan 5) at fruit stage, an experiment was carried out in climate chambers. Five day/night temperature regimes (16/34, 19/31, 25/25, 31/19, and 34/16°C) with respective DIFs of -18, -12, 0, +12, and +18 were used and measured at mean daily temperature of 25°C. The results showed that chlorophyll (Chl) a, Chl b, net photosynthetic rate (P_N), stomatal conductance (g_s), maximum quantum yield of PSII photochemistry (F_v/F_m), effective quantum yield of PSII photochemistry (?_PSII), and photochemical quenching (qp) significantly increased under positive DIF, while they decreased with negative DIF. In contrast, the Chl a/b ratio and nonphotochemical quenching (NPQ) decreased under positive DIF, while increased with negative DIF. Chl a, Chl b, P_N, g_s, F_v/F_m, ?_PSII, and qp were larger under +12 DIF than those at +18 DIF, while Chl a/b and NPQ showed an opposite trend.     

Photosynthetic apparatus organization and function in the wild type and a chlorophyll b-less mutant of Chlamydomonas reinhardtii. Dependence on carbon source

 The assembly, organization and function of the photosynthetic apparatus was investigated in the wild type and a chlorophyll (Chl) b-less mutant of the unicellular green alga Chlamydomonas reinhardtii, generated via DNA insertional mutagenesis. Comparative analyses were undertaken with cells grown photoheterotrophically (acetate), photomixotrophically (acetate and HCO⁻ ₃) or photoautotrophically (HCO⁻ ₃). It is shown that lack of Chl b diminished the photosystem-II (PSII) functional Chl antenna size from 320 Chl (a and b) to about 95 Chl a molecules. However, the functional Chl antenna size of PSI remained fairly constant at about 290 Chl molecules, independent of the presence of Chl b. Western blot and kinetic analyses suggested the presence of inner subunits of the Chl a-b light-harvesting complex of PSII (LHCII) and the entire complement of the Chl a-b light-harvesting complex of PSI (LHCI) in the mutant. It is concluded that Chl a can replace Chl b in the inner subunits of the LHCII and in the entire complement of the LHCI. Growth of cells on acetate as the sole carbon source imposes limitations in the photon-use efficiency and capacity of photosynthesis. These are manifested as a lower quantum yield and lower light-saturated rate of photosynthesis, and as lower variable to maximal (F_v/F_max) chlorophyll fluorescence yield ratios. This adverse effect probably originates because acetate shifts the oxidation-reduction state of the plastoquinone pool, and also because it causes a decrease in the amount and/or activity of Rubisco in the chloroplast. Such limitations are fully alleviated upon inclusion of an inorganic carbon source (e.g. bicarbonate) in the cell growth medium. Further, the work provides evidence to show that transformation of green algae can be used as a tool by which to generate mutants exhibiting a permanently truncated Chl antenna size and a higher (per Chl) photosynthetic productivity of the cells. Received: 10 November 1999 / Accepted: 22 December 1999     

Evidence that Isolated Developing Chloroplasts Are Capable of Synthesizing Chlorophyll b from 5-Aminolevulinic Acid

Developing chloroplasts isolated from cucumber (Cucumis sativus L. var Beit Alpha) cotyledons are capable of incorporating [¹⁴C]5-aminolevulinic acid into chlorophyll (Chl) b and Chl a when incubated under photosynthetic illumination. Thin layer chromatography and high pressure liquid chromatography were employed to analyze the pigments. The specific radioactivity in Chl a was over three times higher than that found in Chl b. Both Chl a and b synthesizing activities in organello decayed rapidly at approximately the same rate. We conclude that concomitant synthesis of Chl a/b-binding apoprotein is not required for Chl b synthesis.     

Specifity of Genetic Determination of Content of Photosynthetic Pigments in Triticale

Lines of winter hexaploid Triticale and their F₁ and F₂ hybrids differing in morphological structure, pigment contents, photosynthetic productivity, and grain crops were studied. F₁ hybrids received by crossing of Triticale lines contrasting in pigment contents showed in some cases a heterosis effect for chlorophyll (Chl) content per unit leaf area. Variation analysis demonstrated a polygenic control of Triticale pigment contents, and different rate of increase in F₂ generation. We found maternal type of heritability of Chl b content and Chl content in light-harvesting complex of photosystem 2.