Effect of Cytokinins on Photosynthetic Pigments and Chlorophyllase Activity in in Vitro Cultures of Axillary Buds of Dianthus caryophyllus L.

The effect of benzyladenine (BA) and two phenylurea cytokinins, N-phenyl-N′-(2-chloro-4-pyridyl)urea (4-PU-30) and thidiazuron (TDZ), on the growth, photosynthetic pigment content, and activity of chlorophyllase (chlorophyll-chlorophylliodhydrolase, EC 3.1.1.14) of in vitro cultures of carnations was studied. All cytokinins caused a rise in the fresh weigth and a drop in the dry weight of leaf mass produced by the explanted buds. Both 4-PU-30 and TDZ increased the chlorophyll content and this correlated with changes in chlorophyllase activity. The effect of 4-PU-30 and TDZ was similar to that caused by BA but at 10-fold or 100-fold lower concentrations. The application of higher concentrations of the phenylurea cytokinins caused an increase in the chlorophyll a/chlorophyll b ratio. However, at equimolar concentrations, the purine and both phenylurea cytokinins had opposite effects, probably indirect and related to some malformations caused by phenylureas. 4-PU-30 increased, but TDZ decreased, photosynthetic membrane stability, which argues for a different molecular organization of the chloroplast membranes. Received February 26, 1996; accepted May 30, 1997     

Effects of silicon on Zea mays plants exposed to water and oxygen deficiency

Effects of shoot and root supplementation with silicon on the response of Zea mays L. plants to matric water potential (Ψ_m) and oxygen deficiency (waterlogging) stresses were studied. The soil water limitation (Ψ_m) and oxygen deprivation significantly reduced shoot dry weight, chlorophyll (Chl) content, ascorbic acid content, as well as leaf relative water content. Both soil drying and waterlogging caused a significant increase in the leaf membrane injury by heat (51°C) and dehydration (40% PEG) stresses. The levels of lipid peroxidation (POL) and hydrogen peroxide (H₂O₂) content were increased by excess soil drying and oxygen deficiency. Supplementary silicon at 1.0 mM significantly increased Chl content and improved water status. Concentrations of H₂O₂, MDA, and proline and leaf membrane injury were significantly reduced by Si application. The reverse helds true for ascorbic acid. The results of this study indicate that application of silicon might improve growth attributes, effectively mitigate the adverse effect of drought and waterlogging, and increase tolerance of maize plants. The silicon-induced improvement of drought and anoxia tolerance was associated with the increase in oxidative defense abilities.     

Phosphorus alleviates aluminum-induced inhibition of growth and photosynthesis in Citrus grandis seedlings

Limited data are available on the effects of phosphorus (P) and aluminum (Al) interactions on Citrus spp. growth and photosynthesis. Sour pummelo (Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 50, 100, 250 and 500 μM KH₂PO₄× 0 and 1.2 mM AlCl₃· 6H₂O. Thereafter, P and Al in roots, stems and leaves, and leaf chlorophyll (Chl), CO₂ assimilation, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and Chl a fluorescence (OJIP) transients were measured. Under Al stress, P increased root Al, but decreased stem and leaf Al. Shoot growth is more sensitive to Al than root growth, CO₂ assimilation and OJIP transients. Al decreased CO₂ assimilation, Rubisco activity and Chl content, whereas it increased or did not affect intercellular CO₂ concentration. Al affected CO₂ assimilation more than Rubisco and Chl under 250 and 500 μM P. Al decreased root, stem and leaf P, leaf maximum quantum yield of primary photochemistry (F_v/F_m) and total performance index (PI_tot,abs), but increased leaf minimum fluorescence (F_o), relative variable fluorescence at K‐ and I‐steps. P could alleviate Al‐induced increase or decrease for all these parameters. We conclude that P alleviated Al‐induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from photosystem II (PSII) donor side up to the reduction of end acceptors of photosystem I (PSI), thus preventing photosynthesis inhibition through increasing Al immobilization in roots and P level in roots and shoots. Al‐induced impairment of the whole photosynthetic electron transport chain may be associated with growth inhibition.     

Effects of nitric oxide and Fe supply on recovery of Fe deficiency induced chlorosis in peanut plants

The effects of nitric oxide (NO) and/or iron (Fe) supplied to Fe deficient plants have been investigated in peanut (Arachis hypogaea L.) grown in Hoagland nutrient solution with or without Fe. Two weeks after Fe deprivation, recovery was induced by addition of 250 μM sodium nitroprusside (SNP, a NO donor) and/or 50 μM Fe (Fe-EDTA) to the Fe deprived (-Fe) nutrient solution. Activities of antioxidant enzymes, leaf chlorophyll (Chl), and active Fe content decreased, whereas activities of H⁺-ATPase, ferric-chelate reductase (FCR), nitrate reductase, and nitric oxide synthase and NO production increased in Fe deficient plants, consequently an Fe chlorosis symptom appeared obviously. In contrast, these symptoms disappeared gradually after two weeks with NO and/or Fe supply, which caused an increases in leaf Chl and active Fe content, especially following by co-treatment with NO and Fe to values found in Fe sufficient plants. Increased activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and decreased accumulation of reactive oxygen species (H₂O₂, O ₂ ^?? ) and malondialdehyde enhanced the ability of resistance to oxidative stress. Supplied NO alone had the obvious effect on increased NO production and on activity of H⁺-ATPase and FCR, whereas root length and root/shoot ratio were most effectively increased by Fe supplied alone. Co-treatment with NO and Fe did the best effects on recovery peanut chlorosis symptoms by significantly increased Chl and available Fe content and adjusted distribution of Fe and other mineral elements (Ca, Mg, and Zn) in both leaves and roots.     

Photoprotective function of betacyanin in leaves of <Emphasis Type="Italic">Amaranthus cruentus</Emphasis> L. under water stress

The photoprotective function of leaf betacyanin in water-stressed Amaranthus cruentus plants was examined by comparing leaves of two strains which differ significantly in the amount of betacyanin. At 0, 1, and 2 days after the imposed water stress, leaves were subjected to high-light (HL) treatment to assess their photosynthetic capacity and photoinhibition susceptibility. The water stress equally reduced leaf relative water content (RWC), gas-exchange rate and chlorophyll (Chl) contents in both leaves, indicating that the severity of water stress was comparable between the strains. Consequently, the extent of photoinhibition after the HL treatment increased in both strains as water stress developed; however, it was significantly greater in acyanic leaves than in betacyanic leaves, suggesting lower photoinhibition susceptibility in the betacyanic strain. The betacyanic leaves also exhibited approximately 30% higher values for photochemical quenching coefficient (q_P) during the period of water stress despite the nonphotochemical quenching coefficient (q_N) did not differ significantly between the strains. These results may be partially explained by the increased amount of leaf betacyanin under water stress. Moreover, a decrease in Chl content in betacyanic leaves might have enhanced light screening effect of betacyanin by increasing relative abundance of betacyanin to Chl molecule. In addition, reduced Chl content increased light penetrability of leaves. As a result, the extent of photoinhibition at the deeper tissue was exacerbated and the Chl fluorescence emitted from these tissues was more readily detected, facilitating assessment of photoinhibition at deeper tissues where the effect of betacyanic light screening is considered to be most apparent. Our results demonstrated that leaf betacyanin contributes to total photoprotective capacity of A. cruentus leaves by lowering excitation pressure on photosystem II (PSII) via attenuation of potentially harmful excess incident light under water stress.     

根茎萌发与幼苗期的虉草水分生态幅

为揭示虉草根茎萌发和幼苗期的水分生态幅,该研究通过盆栽控制试验,设置8个水分梯度：(2±0.5)％、(10±0.5)％、(15±0.5)％、(20±0.5)％、(25±0.5)％、(30±0.5)％、(40±0.5)％(水分饱和)和淹水(2 cm),通过萌发率、各形态指标和生理指标对虉草水分生态幅进行了探讨。结果表明：(1)土壤水分含量过低和过高都会降低虉草根茎萌发率。(2)随土壤水分含量的增加,虉草幼苗株高和地上生物量都呈现先上升后下降的趋势,两者并呈指数函数关系y ＝0.2038e0.0486x(R2＝0.803)。(3)虉草通过调整自身结构特点,降低个体大小、减少叶片数量和叶面积来适应胁迫环境,土壤水分含量为10％~30％时虉草含水率能保持相对稳定的水平。虉草的光和色素( Chl a、Chl b、Car)和相对叶绿素( SPAD)含量均随土壤水分含量的增加呈现出先上升后下降的趋势,Chl a/b则相反,呈先下降后上升趋势。(4) Chl/Car各组之间差异不显著。综合上述研究,利用高斯模型分析得出虉草的水分生态幅为7.48％~52.20％,最适水分生态幅为18.99％~40.60％。     

Limiting Factors in Photosynthesis: IV. Iron Stress-Mediated Changes in Light-Harvesting and Electron Transport Capacity and its Effects on Photosynthesis in Vivo

Using iron stress to reduce the total amount of light-harvesting and electron transport components per unit leaf area, the influence of light-harvesting and electron transport capacity on photosynthesis in sugar beet (Beta vulgaris L. cv F58-554H1) leaves was explored by monitoring net CO₂ exchange rate (P) in relation to changes in the content of Chl.

In most light/CO₂ environments, and especially those with high light (≥1000 microeinsteins photosynthetically active radiation per square meter per second) and high CO₂ (≥300 microliters CO₂ per liter air), P per area was positively correlated with changes in Chl (a + b) content (used here as an index of the total amount of light-harvesting and electron transport components). This positive correlation of P per area with Chl per area was obtained not only with Fe-deficient plants, but also over the normal range of variation in Chl contents found in healthy, Fe-sufficient plants. For example, light-saturated P per area at an ambient CO₂ concentration close to normal atmospheric levels (300 microliters CO₂ per liter air) increased by 36% with increase in Chl over the normal range, i.e. from 40 to 65 micrograms Chl per square centimeter. Iron deficiency-mediated changes in Chl content did not affect dark respiration rate or the CO₂ compensation point. The results suggest that P per area of sugar beet may be colimited by light-harvesting and electron transport capacity (per leaf area) even when CO₂ is limiting photosynthesis as occurs under field conditions.

     

Inhibition of root respiration induces leaf senescence in <Emphasis Type="Italic">Alhagi sparsifolia</Emphasis>

Leaf senescence can be induced by numerous factors. In order to explore the relationship between root respiration and leaf senescence, we utilized different types of phloem girdling to control the root respiration of Alhagi sparsifolia and its physiological response. Our results showed that both girdling and inhibition of root respiration led to a decline of stomatal conductance, photosynthesis, transpiration rate, chlorophyll (Chl) a, Chl b, carotenoid (Car) content, Chl a/b, Chl/Car, water potential, and Chl a fluorescence, as well as to an increase of abscisic acid (ABA), proline, and malondialdehyde content in leaves and to upregulation of senescence-associated gene expression. Our present work implied that both inhibition of root respiration and girdling can induce leaf senescence. In comparison with phloem girdling, the leaf senescence caused by inhibition of root respiration was less significant. The reason for girdling-induced senescence was ABA and carbohydrate accumulation. Senescence induced by inhibition of root respiration occurred due to leaf water stress resulting from inhibition of water absorption.     

Relationship between specific leaf area,leaf thickness,leaf water content and <Emphasis Type="Italic">SPAD-502</Emphasis> readings in six Amazonian tree species

The aim of this work was to assess the effect of leaf thickness, leaf succulence (L_S), specific leaf area (SLA), specific leaf mass (W_s) and leaf water content (LWC) on chlorophyll (Chl) meter values in six Amazonian tree species (Carapa guianensis, Ceiba pentandra, Cynometra spruceana, Pithecolobium inaequale, Scleronema micranthum and Swietenia macrophylla). We also tested the accuracy of a general calibration equation to convert Minolta Chl meter (SPAD-502) readings into absolute Chl content. On average, SPAD values (x) increased with fresh leaf thickness (FLT [μm] = 153.9 + 0.98 x, r ² = 0.06**), dry leaf thickness (DLT [μm] = 49.50 + 1.28 x, r ² = 0.16**), specific leaf mass (W_s [g (DM) m⁻²] = 6.73 + 1.31 x, r ² = 0.43**), and leaf succulence (L_S [g(FM)] m⁻² = 94.2 + 1.58 x, r ² = 0.19**). However, a negative relationship was found between SPAD values and either specific leaf area [SLA (m² kg⁻¹) = 35.1 − 0.37 x, r ² = 0.38**] or the leaf water content (LWC [%]= 80.0 − 0.42 x, r ² = 0.58**). Leaf Chl contents predicted by the general calibration equation significantly differed (p<0.01) from those estimated by species-specific calibration equations. We conclude that to improve the accuracy of the SPAD-502 leaf thickness and LWC should be taken into account when calibration equations are to be obtained to convert SPAD values into absolute Chl content.     

Salicylic acid increased aldose reductase activity and sorbitol accumulation in tomato plants under salt stress

Increased aldose reductase (ALR) activities were detected in the leaf tissues of tomato plants grown for 3 weeks in culture medium containing 10^?7 or 10^?4 M salicylic acid (SA), and in the roots after the 10^?4 M SA pretreatment. The ALR activity changed in parallel with the sorbitol content in the leaves of the SA-treated plants. Salt stress elicited by 100 mM NaCl enhanced the accumulation of sorbitol in the leaves of control plants and as compared with the untreated control the sorbitol content in the SA-pretreated leaves remained elevated under salt stress. DEAE cellulose anionexchange column purification of the protein precipitated with 80 % (NH₄)₂SO₄ revealed two enzyme fractions with ALR activity in both the leaf and the root tissues. The fraction of the leaf extract that was not bound to the column reacted with glucose and glucose-6-P as substrates, whereas glucose was not a substrate for the bound fraction or for root isoenzymes. The root enzyme was less sensitive to salt treatment: 50 mM NaCl caused 30 % inhibition in the leaf extract, whereas the enzyme activity of the root extract was not affected. It is suggested that increased ALR activity and sorbitol synthesis in the leaves of SA-treated tomato plants may result in an improved salt stress tolerance.     

Photosynthetic activity of poikilochlorophyllous desiccation tolerant plant <Emphasis Type="Italic">Reaumuria soongorica</Emphasis> during dehydration and re-hydration

Diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem 2 (PS2) as well as Chl content were analyzed in Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub during dehydration and rehydration. The net photosynthetic rate (P _N), maximum photochemical efficiency of PS2 (variable to maximum fluorescence ratio, F_v/F_m), quantum efficiency of non-cyclic electron transport of PS2, and Chl content decreased, but non-photochemical quenching of fluorescence and carotenoid content increased in stems with the increasing of drought stress. 6 d after re-hydration, new leaves budded from stems. In the re-watered plants, the chloroplast function was restored and Chl a fluorescence returned to a similar level as in the control plants. This improved hydraulic adjustment in plant triggered a positive effect on ion flow in the tissues and increased shoot electrical admittance. Thus R. soongorica plants are able to sustain drought stress through leaf abscission and keep part of Chl content in stems.     

Zirconium induced physiological alterations in wheat seedlings

The effects of zirconium ascorbate (Zr-ASC), a water-soluble complex of Zr, were examined on wheat seedlings (Triticum aestivum L. cv. MV. 20). Hydroponically grown plants were exposed to 10, 33, 55, 100 and 550 µM Zr-ASC (Zr₁₀, Zr₃₃ etc.). After 9 d of treatment inhibition of germination, retarded root and shoot growth, and increased activities of antioxidant enzymes (guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase) showed that Zr-ASC was only harmful at and over a concentration limit of 100 µM. Chlorophyll (Chl) content of plants was only decreased by Zr₅₅₀. Zr-ASC at lower concentrations was beneficial for plant development: Zr₁₀ and Zr₃₃ enhanced root elongation, Zr₅₅ induced about 30 % increase in the total Chl content, while the activity of antioxidant enzymes was not elevated indicating that no oxidative stress was generated by the intracellularly accumulated Zr⁴⁺ ions.This research was supported by the Hungarian National Scientific Research Fund (OTKA T043063).     

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.     

Influence of GA3 and 4-PU-30 on Leaf Protein Composition, Photosynthetic Activity, and Growth of Maize Seedlings

The effects of gibberellic acid (GA3) and N1-(2-chloro-4-pyridyl)-N2 phenylurea (4-PU-30) on maize seedling growth, photosynthetic parameters, and leaf protein composition were investigated. The agents used alone or in combination increased leaf growth and photosynthetic rate of the seedlings. Chlorophyll and total nitrogen contents in leaves as well as the quantity of individual protein fractions increased simultaneously. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble proteins (albumins and globulins) revealed quantitative differences between 4-PU-30-treated plants and the other experimental variants. They differed in polypeptide composition associated with changes in soluble proteins and amino acids. However, GA3 did not induce similar changes in polypeptide composition of soluble proteins. This revised version was published online in July 2006 with corrections to the Cover Date.     

Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO₂ concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F_v/F_m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.     

Effect of Putrescine, 4-PU-30, and Abscisic Acid on Maize Plants Grown under Normal, Drought, and Rewatering Conditions

The experiments were carried out with maize (Zea mays L.) seedlings, hybrid Kneja 530, grown hydroponically in a growth chamber. Twelve-day-old plants were foliar treated with putrescine, N¹-(2-chloro-4-pyridyl)-N²-phenylurea (4-PU-30), and abscisic acid (ABA) at concentrations of 10⁻⁵ m. Twenty-four hours later the plants were subjected to a water deficit program, induced by 15% polyethylene glycol (PEG; molecular weight, 6,000). Three days after drought stress half of the plants were transferred to nutrient solution for the next 3 days. The effects of the water shortage, rewatering, and plant growth regulator (PGR) treatment on the fresh and dry weights, leaf pigment content, proline level, relative water content (RWC), transpiration rate, activities of catalase and guaiacol peroxidase, hydrogen peroxide content, and level of the products of lipid peroxidation were studied. It was established that the application of PGRs alleviated to some extent the plant damage provoked by PEG stress. At the end of the water shortage program the plants treated with these PGRs possessed higher fresh weight than drought-subjected control seedlings. It was found also that putrescine increased the dry weight of plants. Under drought, the RWC and transpiration rate of seedlings declined, but PGR treatment reduced these effects. The accumulation of free proline, malondialdehyde, and hydrogen peroxide was prevented in PGR-treated plants compared with the water stress control. The results provided further information about the influence of putrescine, 4-PU-30, and ABA on maize plants grown under normal, drought, and rewatering conditions. Received September 25, 1997; accepted August 10, 1998     

Triadimefon enhances growth and net photosynthetic rate in NaCl stressed plants of Raphanus sativus L.

The effect of sodium chloride and triadimefon (TDM) on the chlorophyll (Chl) content, net photosynthetic rates (P_N), rate of transpiration (E), and intercellular CO₂ concentration (C_i) in Raphanus sativus was studied. The effect of NaCl salinity was partially ameliorated by TDM which caused increase in Chl content, P_N, and C_i. TDM also increased root dry matter production, decreased E, and increased the water use efficiency.     

Epidermal UV-shielding and photosystem II adjustment in wild type and chlorina f2 mutant of barley during exposure to increased PAR and UV radiation

The wild-type barley (WT; Hordeum vulgare L.) and its chlorophyll (Chl) b-less mutant chlorina f2 (clo f2) grown under shaded conditions in a greenhouse were transferred to outdoor conditions in early June with predominantly bright sunny days. During 6 days following transfer of plants we monitored the content of photosynthetic pigments, functional state of photosystem II (PSII) by means of Chl fluorescence induction kinetics and epidermal UV-shielding efficiency using Chl fluorescence imaging technique. Clo f2 mutant was more sensitive to exposure to an enhanced natural solar irradiance than WT barley. Nevertheless, clo f2 as well as WT were able to cope with stressful outdoor conditions, as was documented by the recovery of Chl a content and the maximal photochemical efficiency of PSII (F_V/F_M) after an initial decline. This was due to the immediate carotenoid-mediated photoprotection, reflected by strongly increased total carotenoids content and thermal energy dissipation localized within light-harvesting complexes of PSII (assessed by non-photochemical quenching of minimal fluorescence level). The positive acclimation response was further documented by an enhanced light-saturated electron transport rate through PSII (ETR). Based on the ratios of blue- to UV-excited Chl fluorescence we found that for both WT and clo f2 epidermal UV-shielding increased clearly after transfer to outdoor conditions and reached a saturation level after 3 days. In comparison with WT, clo f2 exhibited lower ability to induce UV-shielding. The kinetics of UV-shielding development during the outdoor treatment was different for the particular leaf regions. We suggest that this is related to the different age and developmental stage of the tissue along the leaf blade. The complementarity of carotenoid-mediated photoprotection and UV-shielding in acclimation of the assimilatory apparatus to increased visible and UV radiation is discussed.     

Inhibition of chlorophyll biosynthesis by lead in greeningPisum sativum leaf segments

Supply of 0.01 to 1.0 mM lead acetate to greening pea(Pisum sativum L.) leaf segments either in the absence or in the presence of inorganic nitrogen lowered total chlorophyll (Chl) content. During a time course study, there was not any appreciable effect of Pb²⁺ upto 4 h but thereafter Pb inhibited Chl synthesis. While supply of succinate, cysteine dithiothreitol, 5,5-dithio-bis-2-nitrobenzoic acid and NH₄C1 had no protective action against Pb²⁺ toxicity, and glycine, glutamate 2-oxoglutarate, MgCl₂, KH₂PO₄, CaCl₂, KC1 protected only partially, reduced glutathione (GSH) could completely overcome the inhibition of Chl biosynthesis by the metal. It is suggested that Pb²⁺ interferes with Chl biosynthesis through GSH availability