Senescence of rice leaves IV. Influence of benzyladenine on chlorophyll degradation

Why benzyladenine (BA) retards chlorophyll degradation of riceleaf segments, but does not prevent it was investigated. WhenBA solutions bathing segments of rice leaves were replaced daily,the effect of BA was not enhanced. Solutions of BA kept at 27°Cin the dark for 4 days were as active as fresh solutions. Itseems unlikely, therefore, that the decrease in the chlorophyllcontent with increased incubation time in BA-treated leaf segmentsis caused by inactivation of BA either in the leaves or in solution.Of 25 L-amino acids at 50 mM added singly with BA, 19 were antagonisticto the effect of BA on chlorophyll content, but four, L-arginine,L-histidine, L-lysine and L-methionine, significantly enhancedthe effect of BA. The effects of amino acids decreased witha decrease in the amino acid concentration or an increase inBA concentration. When concentrations were decreased to 5 mM,only L-lysine slightly increased the chlorophyll content inBA-treated leaf segments. L-Proline and L-tryptophan did notmodify the effect of BA on chlorophyll content. Effects of aminoacids on chlorophyll content in leaf segments without BA treatmentare similar to those with BA. Furthermore, cycloheximide (50µg/ml), which decreased the soluble amino acid content,increased the chlorophyll content in BA-treated leaf segments. Since an accumulation of soluble amino acids precedes the degradationof chlorphyll in BA-treated leaf segments, probably antagonismscaused by the amino acids accumulated in the tissue, preventthe added BA from being fully effective in stopping chlorophyllloss. (Received June 2, 1980; )     

Effects of Benzyladenine on Photosynthesis, Growth and Senescence of the Bean Plant

The net photosynthetic rate of attached primary bean leaves treated with benzyladenine (BA) decreased from 35 nano-grams carbon dioxide per square centimetre and second (ng cm^?2 s^?1) at week 2 to 17 ng cm^?2 s^?1 at week 4, and thereafter increased to 24 at week 6. By contrast the net photo-synthetic rate of the water-treated leaves decreased to 4–5 ng cm^?2 s^?1 at weeks 5 and 6. The stomatal resistance was not markedly affected by BA treatment. The BA-treated primary leaves had higher dry and specific weights, and the chlorophyll and carotenoid contents were greater than for the water controls. The pigment content of the BA-treated leaves steadily increased from week 2 to 6, whereas in the water controls it remained constant till week 4 and thereafter decreased. It is concluded that retardation of leaf senescence by BA is assoclatcd with a mnintenance of photosynthetic activity.     

Influence of Benzyladenine, Leaf Darkening, and Ringing on Movement of C-labeled Assimilates Into Expanded Leaves of Vitis vinifera L

Leaves of Vitis vinifera L., nearly fully expanded, imported only trace amounts of ¹⁴C following assimilation of ¹⁴CO₂ by a lower leaf on the same shoot, but benzyladenine (BA) application at 4.4 × 10⁻³m caused a marked increase in the movement of ¹⁴C into these leaves. Older leaves near the shoot base were less responsive; BA treatment alone had little effect on import of labeled assimilates from adjacent leaves but when the BA-treated leaves were darkened there was an increased import of labeled materials. When these 2 treatments were combined and applied to leaves on shoots with ringed bases, relatively high levels of radioactivity were detected in the BA-treated leaves but under these conditions darkening, without the application of BA, also resulted in an increased import of ¹⁴C. Accumulation of imported ¹⁴C was found to be restricted to the area of the leaf blade treated with BA. Separation of labeled compounds in ethanol extracts of treated leaves showed a lower percentage of radioactivity present in the sugar fraction from BA-treated leaves and an increased percentage present in the amino acid fraction.     

Salicylic acid-induced adaptive response to copper stress in sunflower (Helianthus annuus L.)

The ameliorative effect of salicylic acid (SA: 0.5 mM) on sunflower (Helianthus annuus L.) under Cu stress (5 mg l⁻¹) was studied. Excess Cu reduced the fresh and dry weights of different organs (roots, stems and leaves) and photosynthetic pigments (chlorophyll a, b and carotenoids) in four-week-old plants. There was a considerable increase in Chl a/b ratio and lipid peroxidation in both the roots and leaves of plants under excess Cu. Soluble sugars and free amino acids in the roots also decreased under Cu stress. However, soluble sugars in the leaves, free amino acids in the stems and leaves, and proline content in all plant organs increased in response to Cu toxicity. Salicylic acid (SA) significantly reduced the Chl a/b ratio and the level of lipid peroxidation in Cu-stressed plants. Under excess Cu, a higher accumulation of soluble sugars, soluble proteins and free amino acids including proline occurred in plants treated with 0.5 mM SA. Exogenous application of SA appeared to induce an adaptive response to Cu toxicity including the accumulation of organic solutes leading to protective reactions to the photosynthetic pigments and a reduction in membrane damage in sunflower.     

Benzyladenine-induced increase in DNA content per chloroplast in intact bean leaves

Benzyladenine (BA) treatment was found to induce chloroplast DNA (ctDNA) synthesis after it had stopped in primary leaves of light-grown intact bean plants (Phaseolus vulgaris L.). The leaves were treated with BA from 7 days after sowing. Chloroplasts were isolated and the ctDNA content per chloroplast was determined. Chloroplast division occurred until 13 days after sowing in untreated leaves. BA stimulated the division keeping the level of ctDNA content per chloroplast the same as that in the untreated controls. After the division period, the ctDNA content per chloroplast increased in BA-treated leaves, but not in controls. Consequently, ctDNA per leaf (or per cell) increased immediately after the beginning of BA treatment, but remained constant in the control leaves.     

Benzyladenine-Enhanced Growth of Attached Young Bean Leaves. Studies with Inhibitors of Nucleic Acid and Protein Synthesis

Benzyladenine (BA) stimulated division but not expansion ofmesophyll cells and repressed chlorophyll accumulation in attachedyoung bean leaves. Even in the presence of fluorodeoxyuridine(FUdR) or mitomycin C which causes complete suppression of BA-inducedincrease in DNA content, BA increased RNA and protein contentsand fresh weight, but decreased chlorophyll accumulation. Moreover,BA n the presence of FUdR induced marked cell expansion. Inthe presence of a-amanitin (AM), BA did not produce any changein DNA content, fresh weight or cell size. All of the BA effectswere observed even in the presence of fluorouracil (FU) plusthymidine (TdR). AM and cycloheximide added 0–12 h effectively inhibitedBA-stimulated cell division but showed no effect if added at18 h. FU plus TdR added 0–18 h had almostno effect onthe cell number at 24 h. These results indicate that BA stimulates the mRNA synthesisnecessary for induction of cell division, and that the synthesisof cytoplasmic rRNA is not always necessary for BA-stimulatedcell division, and moreover, that BA stimulates expansion growthof cells in which DNA synthesis is suppressed. (Received August 16, 1982; Accepted March 31, 1983)     

Changes occurring during aging and senescence in a submerged aquatic angiosperm (Potamogeton pectinatus)

Changes occurring during aging and senescence of leaves of a submerged aquatic angiosperm ( Potamogeton pectinatus L.) were studied. Total chlorophyll and chlorophylls a and b were maximal in mature, and minimal in old leaves. The chlorophyll a to b ratio was highest in mature leaves. During senescence, the chlorophyll content and the ratio of chlorophyll a to b decreased. The content of DNA, RNA, protein and dry weight, and the activity of alkaline pyrophosphatase decreased while free amino acids, the activity of protease, RNase and acid pyrophosphatase, and the ratio of acid to alkaline pyrophosphatase activity increased during aging and senescence. Kinetin (0.23 m M ) deferred leaf senescence by delaying the loss of chlorophyll, protein, nucleic acids and dry weight, and reducing the rise in free amino acids, the activity of protease, RNase and acid pyrophosphatase and the ratio of acid to alkaline pyrophosphatase activity; while both 0.69 m M ethrel and 0.075 m M ABA hastened senescence. Kinetin pretreatment for an optimum period (12 h) followed by ethrel or ABA treatment partially erased the senescence-promoting effect of the latter. But treatments in a reverse order markedly reduced the delaying effect of kinetin on senescence.     

Effects of 6N-Benzyladenine on Primary Leaves of Intact Bean Plants and on their Sodium Absorption Capacity

The application of ⁶N-benzyladenine (BA) to primary bean-leaves attached to the intact plant resulted in increased leaf area. This was due to an extension of the duration of the period of leaf expansion. The dry-weight percentage of untreated leaves decreased continuously from emergence to abscission. In BA treated leaves this decrease stopped with the cessation of leaf expansion. Net chlorophyll synthesis occurs in untreated leaves as long as they continue to expand, shortly afterwards net chlorophyll decomposition starts. Benzyladenine treatments diminished the rate of chlorophyll synthesis immediately after its first application, but prevented the loss of chlorophyll afterwards. The abscission of primary leaves was also delayed by BA. During the period of rapid leaf expansion in slices cut from BA treated leaves, sodium absorption rates were lower than in those from untreated leaves. From the age of 14 days after sowing, till abscission time of untreated primary leaves, the BA treatment did not significantly affect sodium absorption rates by leaf slices.     

Benzyladenine effects on the development of the photosynthetic apparatus in Zea mays: Studies on photosynthetic activity, enzymes and (etio)chloroplast ultrastructure

Primary leaf segments from 8-day-old dark-grown, and from 4- and 8-day-old light-grown seedlings of Zea mays L. cv. Fronica, were treated with 10^-bM benzyladenine (BA) in the dark for 14 h. The segments were then studied after an exposure to light for 14 h. Photosynthetic activity (O₂ evolution and CO₂ fixation) and chlorophyll accumulation were stimulated by BA in dark-grown leaf segments with etioplastids in the earliest stage of development. In these segments BA stimulated the activities of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39), phosphoenolpyruvate carboxylase (EC 4.1.1.31), NADP⁺-malic enzyme (EC 1.1.1.40) and pyruvate, orthophosphate dikinase (EC 2.7.9.1). In segments taken from 4- and 8-day light-grown seedlings, BA did not enhance the photosynthetic activity nor the chlorophyll accumulation. The activity of the enzymes mentioned above, was significantly enhanced by the BA-treatment. BA mainly affected grana stacking in mesophyll cell chloroplasts in primary leaf segments taken from 3- to 5-day light-grown seedlings. Stroma thylakoid development was stimulated only in leaf segments from 3-day-old plants. At the same time BA accelerated grana loss in chloroplasts of bundle sheath cells, a typical phenomenon of development in such chloroplasts. Stroma thylakoid length in these chloroplasts increased by a BA treatment in segments from 3- and 4-day light-grown plants. A significantly higher number of chloroplasts was only observed with segments taken from 8-day light-grown seedlings and treated with BA. The etiochloroplast number in segments taken from 8-day etiolated plants was significantly higher in BA-treated segments after 26 h illumination. In etiochloroplasts from both mesophyll and bundle sheath cells, BA enhanced grana stacking after illumination for 4 h or more, whereas stroma membrane length was significantly higher only after 26 h light. It is concluded that the effects of BA depend on the developmental stage. BA accelerates the development of mesophyll and bundle sheath cell (etio)chloroplasts, but does not affect the ultrastructure of mature chloroplasts.     

花生叶片衰老过程中氮素代谢指标变化

以鲁花11和辐8707两个花生（Arachis hypogea L.)品种为材料,对大田条件下花生叶片衰老过程中N素代谢指标变化进行了研究,结果表明,花生叶叶片展开至衰老过程中,蛋白酶活性逐渐升高,叶中N含量逐渐降低;硝酸还原酶（NR）活性、叶绿素、游离氨基酸和可溶性蛋白质含量呈抛物线型变化,最先开始降低的是NR活性,其次是叶绿素含量,最后是游离氨基酸和可溶性蛋白质含量。     

Photosynthetic Electron Transport in Plastids in Detached Cucumber Cotyledons Treated with 6-Benzylaminopurine and Potassium

Etiolated cotyledons of cucumber (Cucumis sativus L.) were excisedand incubated for 16 days on agar in the absence or in the presenceof 6-benzylaminopurine (BA) (3 µM) or KCl (10 mM) undercontinuous light. Treatment with BA or KCl increased growthand greening of cotyledons, KCl being particularly active duringthe last few days of the incubation. The rate of photosynthetic electron transport reached a maximumafter 3 days, as did the chlorophyll content, and then it declinedby approximately 95%. An uncoupling from phosphorylation wasobserved in older cotyledons. BA and KCl increased the rateof electron flow per cotyledon, and KCl delayed the onset ofthe decline in this rate. PS I and PS II activities per chlorophyllunit were lower in BA-treated cotyledons, but KCl-treated cotyledonsbehaved like the controls. Fluorescence analysis indicated that the level of active chlorophyllsinvolved in the transfer of energy in PS II decreased between3 and 7 days under all conditions tested. In BA-treated cotyledons,the proportion of active chlorophylls was consistently lowerthan that in the control. Thus, it appears that, in the absenceof exogenous K⁺, cytokinin has only a low antisenescence effecton photosynthetic activity, and that K⁺ may enhance the photosyntheticelectron flow between plastoquinone and plastocyanin via thecytochrome b₆-f complex. (Received August 2, 1989; Accepted January 23, 1990)     

BA对花生叶片腺苷酸含量和能荷的影响

去顶去根花生幼苗库叶（上位叶）经１０＾－５ｍｏｌ／Ｌ ＢＡ涂抹处理１２ｈ和４８ｈ时,库叶ＡＴＰ含量增加,分别高于对照１９．４％和３３．１％。ＡＤＰ含量在处理后１２－３６ｈ,不断增加,以后逐渐降低,接近对照水平,ＢＡ处理库叶减少ＡＭＰ含理。ＢＡ促进库叶能荷值增加,调节总腺苷酸含量的动态变化。ＢＡ处理库叶１２ｈ,叶片组织和线粒体呼吸速率增加,加强了线粒体氧化磷酸化和能量传递的过程。     

Effect of phosphorus and nitrogen on growth,chlorophyll, amino nitrogen,soluble sugar contents and algal heterocysts of water fernAzolla pinnata

The P uptake inAzolla pinnata in mineral medium increased linearly with increasing phosphate doses and optimum growth and chlorophyll content of fern were recorded at 1.2 mM of K₂HPO₄. The higher doses of phosphate reduced growth and chlorophyll, but an increase in soluble sugar and amino nitrogen was noticed. Addition of combined nitrogen sources decreased the fern growth, soluble sugar, chlorophyll and heterocyst frequency but amino nitrogen was comparatively higher. The growth and chlorophyll content were always high when the fern was grown in the absence of added nitrogen sources; this supports the thesis about the specific importance of symbiosis for the nutrition of fern with nitrogen which cannot be replaced by mineral compounds.     

Reduction of paraquat toxicity in maize leaves by benzyladenine

The protective effect of a cytokinin benzyladenine (BA), against toxicity of paraquat (PQ), a widely used herbicide and a well-known oxidative stress inducer, was investigated in the leaves of maize. Maize leaves have been pretreated with BA at concentrations of 1, 10 and 100 microM and afterwards treated with PQ. At all concentrations tested, BA retarded PQ-induced decreases in chlorophyll, carotenoid and ascorbic acid contents. Pretreatment with 10 and 100 microM of BA significantly increased superoxide dismutase (SOD) activity after 8 h of PQ treatment but there was no significant change in SOD activity in the leaves pretreated with BA at 12 and 24 h. However, peroxidase activity significantly increased in 100 microM of BA pretreated leaves. Results indicate that pretreatment with BA reduce PQ toxicity and BA-treated plants might become more tolerant against oxidative stress.     

Effects of Proline and Glycinebetaine on Vicia Faba Responses to Salt Stress

Plants of bean (Vicia faba L. cv. Calvor 103) were salt-stressed with NaCl and CaCl₂ in concentrations inducing soil osmotic potentials (ψ_soil) from 0 to -1.2 MPa and were sprayed with proline (8.7 μM) and glycinebetaine (8.5 μM) solutions. Bean plants respond to increasing soil salinity by decreased leaf relative water content and osmotic potential. Salinity decreased the contents of dry mass, chlorophyll, soluble and hydrolysable sugars, soluble proteins and enhanced content of total free amino acids, Na⁺, Ca²⁺ and Cl^-. The ratio of K⁺/Na⁺ was decreased on salinization. The membranes of leaf discs from salt-stressed plants appeared to be less stable under heat stress (51 °C) than that of unstressed plants. The reverse was true for discs placed under dehydration stress (40 % polyethylene glycol 6000). Proline and glycinebetaine application reduced membrane injury, improved K⁺ uptake and growth. Also both solutes increased chlorophyll contents. This revised version was published online in July 2006 with corrections to the Cover Date.     

Changes in Mulberry Leaf Metabolism in Response to Water Stress

A series of experiments were conducted to characterize the water stress-induced changes in the activities of RuBP carboxylase (RuBPCO) and sucrose phosphate synthase (SPS), photosystem 2 activity, and contents of chlorophylls, carotenoids, starch, sucrose, amino acids, free proline, proteins and nucleic acids in mulberry (Morus alba L. cv. K-2) leaves. Water stress progressively reduced the activities of RuBPCO and SPS in the leaf extracts, the chlorophyll content, and PS2 activity in isolated chloroplasts. Plants exposed to drought showed lower content of starch and sucrose but higher total sugar content than control plants. While the soluble protein content decreased under water stress, the amino acid content increased. Proline accumulation (2.5-fold) was noticed in stressed leaves. A reduction in the contents of DNA and RNA was observed. Reduced nitrogen content was associated with the reduction in nitrate reductase activity. SDS-PAGE protein profile showed few additional proteins (78 and 92 kDa) in the water stressed plants compared to control plants.     

万寿菊属不同品种初花期抗旱特性分析

以万寿菊属(Tagetes)9个品种为试验材料,研究了自然持续干旱胁迫对它们初花期的花最大直径、叶色、旱害指数等形态指标以及叶绿素含量(Chl a+b,Ch a/b)、叶片相对含水量(RWC)、叶片保水力(WHC)、叶片和花的脯氨酸、可溶性糖和可溶性蛋白含量等生理指标的影响,以揭示其抗旱特性及其生理机制.结果显示:(1)持续6d干旱胁迫条件下,万寿菊9个品种花的最大直径显著降低,叶绿素含量和相对含水量均呈明显下降趋势.(2)万寿菊叶片的脯氨酸、可溶性蛋白和可溶性糖含量均呈上升趋势;而花的脯氨酸含量持续上升,可溶性蛋白含量呈下降趋势,但可溶性糖含量变化趋势复杂.(3)万寿菊旱害指数与其叶片相对含水量、叶绿素总含量、叶片和花的脯氨酸含量、叶片可溶性蛋白含量呈极显著相关.研究表明,抗旱性强的品种可以通过调节自身的渗透调节物质含量减轻干旱伤害;9个品种初花期抗旱性强弱依次为:珍妮>金门>鸿运>拳王>巨人>发现>小英雄>大英雄>迪阿哥.     

Nitrate Nutrition and Temperature Effects on Wheat: Enzyme Composition, Nitrate and Total Amino Acid Content of Leaves

Lawlor, D. W., Boyle, F. A., Kendall, A. C. and Keys, A. J.1987. Nitrate nutrition and temperature effects on wheat: Enzymecomposition, nitrate and total amino acid content of leaves.—J.exp. Bot. 38: 378–392. Wheat plants were grown in controlled environments in two temperatureregimes with two rates of nitrate fertilization. In some experimentstwo light intensities were combined with the nitrogen and temperaturetreatments. The composition of the third leaf was studied fromsoon after emergence until early senescence. The amounts ofchlorophyll, soluble protein, ribulose bisphosphate carboxylase-oxygenase(RuBPc-o) protein, nitrate, and total amino acids were measuredtogether with the activities of RuBPc-o, fructose- 1,6-bisphosphatase,glycolate oxidase, carbonic anhydrase, nitrate reductase, glutaminesynthetase and serine- and glutamate-glyoxylate aminotransferases.Additional nitrate supply increased the amounts, per unit leafarea, of chlorophyll, total soluble protein and RuBPc-o proteinand the activities of all the enzymes. The ratio of RuBP carboxylaseto RuBP oxygenase activity, when measured at constant CO²/O²ratio and temperature, was unaffected by growth conditions orleaf age. Leaves grown at the lower temperature, especiallywith more nitrate, contained much more soluble protein, nitratereductase, fructose bisphosphatase and free amino acids perunit area than the plants grown in the warmer conditions. However,young leaves grown in the warm contained more nitrate than thosegrown in the cool. Amounts of protein, amino acids and chlorophylland most enzyme activities reached maxima near full leaf expansionand decreased with age; additional nitrate slowed the decreaseand senescence was delayed. Nitrate content and nitrate reductaseactivities were highest in leaves before full expansion andthen fell rapidly after full expansion. Increased light intensityincreased the content of RuBPc-o protein at the higher rateof nitrate supply. Chloroplast components and, to a lesser extent,peroxisomal enzymes associated with photosynthetic nitrogenassimilation changed in proportion with different treatmentsbut nitrate reductase activity was not closely related to chloroplastenzymes. Control of tissue composition in relation to environmentalconditions is discussed. Key words: Nitrate nutrition, temperature, wheat, enzyme, amino acid, leaves, ribulose bisphosphate carboxylase oxygenase, nitrate reductase     

Leaf gas exchange,water relations,nutrient content and growth in citrus and olive seedlings under salinity

The effects of salinity on growth, leaf nutrient content, water relations, gas exchange parameters and chlorophyll fluorescence were studied in six-month-old seedlings of citrus (Citrus limonia Osbeck) and rooted cuttings of olive (Olea europaea L. cv. Arbequina). Citrus and olive were grown in a greenhouse and watered with half strength Hoagland’s solution plus 0 or 50 mM NaCl for citrus, or plus 0 or 100 mM NaCl for olive. Salinity increased Cl⁻ and Na⁺ content in leaves and roots in both species and reduced total plant dry mass, net photosynthetic rate and stomatal conductance. Decreased growth and gas exchange was apparently due to a toxic effect of Cl⁻ and/or Na⁺ and not due to osmotic stress since both species were able to osmotically adjust to maintain pressure potential higher than in non-salinized leaves. Internal CO₂ concentration in the mesophyll was not reduced in either species. Salinity decreased leaf chlorophyll a content only in citrus.     

Impacts of Boron Application on Maize Plants Growing under Flooded and Unflooded Conditions

Plants of maize (Zea mays L.) were waterlogged for 7 d and irrigated (root application) or sprayed (foliar application) with 0, 1, 3 and 6 mg dm-3 of boron. The stability of leaf membranes was assessed by determining leakage of electrolytes from leaf discs exposed to heat (51 °C) and dehydration (40 % PEG). Leaf membranes were more stable to heat than to dehydration. The membranes of waterlogged plants were more injured than those of control plants. Waterlogging reduced contents of dry mass, chlorophyll, soluble proteins, total free amino acids and soluble sugars and leaf relative water content (RWC). Application of boron increased the stability of leaf membranes, chlorophyll, soluble sugars, soluble proteins, amino acids contents, leaf RWC and dry mass accumulation. Foliar boron application was more effective. Application of boron alleviated the deleterious effect of waterlogging. This revised version was published online in July 2006 with corrections to the Cover Date.