Decline In Chlorophyll Content Research Articles

Effect of divalent cations on ion fluxes and leaf photochemistry in salinized barley leaves

Photosynthetic characteristics, leaf ionic content, and net fluxes of Na(+), K(+), and Cl(-) were studied in barley (Hordeum vulgare L) plants grown hydroponically at various Na/Ca ratios. Five weeks of moderate (50 mM) or high (100 mM) NaCl stress caused a significant decline in chlorophyll content, chlorophyll fluorescence characteristics, and stomatal conductance (g(s)) in plant leaves grown at low calcium level. Supplemental Ca(2+) enabled normal photochemical efficiency of PSII (F(v)/F(m) around 0.83), restored chlorophyll content to 80-90% of control, but had a much smaller (50% of control) effect on g(s). In experiments on excised leaves, not only Ca(2+), but also other divalent cations (in particular, Ba(2+) and Mg(2+)), significantly ameliorated the otherwise toxic effect of NaCl on leaf photochemistry, thus attributing potential targets for such amelioration to leaf tissues. To study the underlying ionic mechanisms of this process, the MIFE technique was used to measure the kinetics of net Na(+), K(+), and Cl(-) fluxes from salinized barley leaf mesophyll in response to physiological concentrations of Ca(2+), Ba(2+), Mg(2+), and Zn(2+). Addition of 20 mM Na(+) as NaCl or Na(2)SO(4) to the bath caused significant uptake of Na(+) and efflux of K(+). These effects were reversed by adding 1 mM divalent cations to the bath solution, with the relative efficiency Ba(2+)>Zn(2+)=Ca(2+)>Mg(2+). Effect of divalent cations on Na(+) efflux was transient, while their application caused a prolonged shift towards K(+) uptake. This suggests that, in addition to their known ability to block non-selective cation channels (NSCC) responsible for Na(+) entry, divalent cations also control the activity or gating properties of K(+) transporters at the mesophyll cell plasma membrane, thereby assisting in maintaining the high K/Na ratio required for optimal leaf photosynthesis.

Spatial patterning of pigmentation in evergreen leaves in response to freezing stress

Evergreen leaves of temperate climate plants are often subject to frosts. Changes in carbon gain patterns arise from freezing-related tissue damage, and from interactions between light and temperature stress. We examined relationships between spatial patterns in freezing and concentrations of chlorophyll. Spatial patterns in pigmentation in leaves that had or had not been exposed to naturally occurring frosts were determined by conventional extraction techniques combined with high-resolution hyperspectral imaging of reflectance from intact leaves. Predictive indices were developed to relate reflectance to chlorophyll content and chlorophyll a/b ratios within intact leaves. Leaves exposed to frosts had lower chlorophyll contents and more variable a/b ratios than protected leaves. In frost-affected leaves, chlorophyll content was highest near leaf centres and decreased toward leaf tips and margins. Decline in chlorophyll content was associated with shifts in chlorophyll a/b ratios and increases in red pigmentation due to anthocyanin, with effects being greater on leaf sides exposed directly to the sun. These altered pigmentation patterns were consistent with patterns in freezing. The present results illustrate the fine scale of spatial variation in leaf response to freezing, and raise important questions about impacts of freezing on photosynthetic function in over-wintering evergreens.

Effects of simulated acid rain on germination, foliar damage, chlorophyll contents and seedling growth of five hardwood species growing in China

Seeds and seedlings of five hardwood species were subjected to a simulated acid rain adjusted to pH values of 2.0, 3.5, 5.0, 6.0, and to distilled water (the control). Seed germination was remarkably inhibited by pH 2.0 treatment for three species. Significant foliar damage, decline in chlorophyll contents, and retardation of growth for the seedlings of all the species, were observed at pH 2.0; while seedling growth was stimulated at pH levels between 3.5 and 5.0. The pH 2.0 treatment seemed to be a threshold level for inhibition of seed germination and seedling growth for all the treated species.

Effects of simulated acid rain on seedling emergence and growth of five broad-leaved species

Seeds and seedlings of five broad-leaved species were separately exposed to simulated acid rain at pH values of 2.0, 3.5, 5.0, and 6.0, or to distilled water (the control). The results showed that seed germination was remarkably inhibited by pH 2.0 treatment for three species. Significant foliar damage, decline in chlorophyll contents, and retardation of the seedlings growth of all the species, were observed at pH 2.0 treatment. The pH 2.0 treatment seemed to be a threshold level for inhibition of seed germination and seedling growth for all the treated species, while seedling was stimulated at pH value between 3.5 and 5.0.

Chlorophyll content of spring wheat flag leaves grown under elevated CO 2 concentrations and other environmental stresses within the ‘ESPACE-wheat’ project

Spring wheat cv. Minaret was grown in open-top chambers at four sites across Europe. The effect of different treatments (CO 2 enrichment, O 3 fumigation, drought stress and temperature) on the chlorophyll content of the flag leaf was investigated using the MINOLTA SPAD-502 meter. Under optimum growth conditions the maximum chlorophyll content, which was reached at anthesis, was consistent among the sites ranging from 460 to 500 mg chlorophyll m −2. No significant effect of elevated CO 2 or O 3 was observed at anthesis. Leaf senescence, indicated by the chlorophyll breakdown after anthesis, was relatively constant in the control chambers. Under control conditions, thermal time until 50% chlorophyll loss was reached was 600°C day. Elevated CO 2 caused a faster decline in chlorophyll content (thermal time until 50% chlorophyll loss was reduced to 500–580°C day) indicating a faster rate of plant development at two experimental sites. The effect of ozone on chlorophyll content depended on the time and dose of O 3 exposure. During grain filling, high O 3 concentrations induced premature senescence of the flag leaves (up to −130°C day). This deleterious effect was mitigated by elevated CO 2. Drought stress led to faster chlorophyll breakdown irrespective of CO 2 treatment.

Response of antioxidant systems and leaf water relations to NaCl stress in pea plants.

A pea (Pisum sativum cv. Puget) cultivar was grown on a medium containing different NaCl concentrations (0-160 mol m-3 ) in order to study the effects of salt stress on leaf water relations and on the activity of antioxidant enzymes. NaCl stress caused a rapid decline in chlorophyll content. Both leaf water (ψl ) and osmotic potentials (ψs ) decreased progressively with the severity of the stress (from 90-160 mol m-3 NaCl) whereas leaf turgor pressure (ψp ) increased in treated plants. Pea leaves contained an iron-containing superoxide dismutase (Fe-SOD) isozyme in chloroplasts alongside a copper-zinc-containing (CuZn-SOD) form (CuZn-SOD II). The lowest NaCl concentration (70 mol m-3 ) had no effect on the activity of these antioxidant enzymes while higher concentrations (110-130 mol m-3 ) enhanced the activity of cytosolic CuZn-SOD I and chloroplastic CuZn-SOD II as well as that of mitochondrial and/or peroxisomal manganese-containing superoxide dismutase (Mn-SOD). These inductions were matched by increases in the activity of ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR). The increased activities coincided with decreased stomatal conductance and were unaffected by the severity of stress except in the case of CuZn-SOD II which fell to control values under the highest stress conditions (140-160 mol m-3 NaCl), when a concomitant increase in chloroplastic Fe-SOD activity was observed. Glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities were only induced under severe NaCl stress (130-160 mol m-3 ) and were accompanied by losses in the ascorbate and glutathione pools, lower ASC/DHA and GSH/GSSG ratios and increases in GSSG. Electron microscopy showed that the thylakoidal structure of the chloroplasts became disorganized and their starch content decreased in plants treated with 160 mol m-3 NaCl. Overall, the results suggest that salt stress is accompanied by oxidative stress, perhaps at the cell compartment level. The capacity of Puget cultivar to ensure cell turgor and to enhance the activity of enzymes involved in the defence against oxidative stress seems to be important in determining adaptation to moderate NaCl stress conditions. In plants exposed to severe NaCl stress (130-160 mol m-3 ) it seems that such resistance to oxidative stress is overcome, which might contribute to the deleterious effects of salt and significant growth reduction in these conditions.

Aggregation of the Light‐Harvesting Complex in Intact Leaves of Tobacco Plants Stressed by CO2Deficit

ABSTRACTPronounced aggregation of the photosystem II light‐harvesting complex (LHC II) was observed in low‐lightgrown tobacco plants stressed with a strong CO2deficit for 2–3 days. The LHC II aggregates showed a typical band at 697–700 nm (F699) in low‐temperature emission spectra. Its excitation spectrum corresponded to that of detergent‐solubilized LHC II. Formation of F699in stressed plants was not reversed in the dark and leaves did not contain any zeaxanthin showing that neither a light‐induced transthylakoid pH gradient nor zeaxanthin was required for LHC II aggregation. The CO2‐stressed plants showed clear signs of photodamage: depression of the potential yield of photosystem II photochemistry (F,/FM) by 50–70% and a decline in chlorophyll content by 10–15%. Therefore, we propose that the photodamage to the photosynthetic apparatus is the cause of the LHC II aggregation in plants. The F699exhibited a reversible decrease of its intensity upon irradiation of leaves with intensive light. There was no or only slight decrease around 700 nm in unstressed plants. The nonphotochemical quenching of chlorophyll fluorescence showed the opposite relation, being higher before than after the strong CO2deficit. This discrepancy was likely related to the different LHC II aggregation state in control and stressed plants.

Protection mechanisms against excess light in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa

Mechanisms of avoidance and protection against light damage were studied in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa. In C. wilmsii, a combination of both physical and chemical changes appeared to afford protection against free radical damage. During dehydration leaves curled inwards, and the abaxial surface became exposed to light. The tissue became purple/brown in colour, this coinciding with a three-fold increase in anthocyanin content and a 30% decline in chlorophyll content. Thus light-chlorophyll interactions are progressively reduced as chlorophyll became masked by anthocyanins in abaxial layers and shaded in the adaxial layers. Ascorbate peroxidase (AP) activity increased during this process but declined when the leaf was desiccated (5% RWC). During rehydration leaves uncurled and the potential for normal light-chlorophyll interaction was possible before full hydration had occurred. Superoxide dismutase (SOD) and glutathione reductase (GR) activities increased markedly during this stage, possibly affording free radical protection until full hydration and metabolic recovery had occurred. In contrast, the leaves of X. viscosa did not curl, but light-chlorophyll interactions were minimised by the loss of chlorophyll and dismantling of thylakoid membranes. During dehydration, free radical protection was afforded by a four-fold increase in anthocyanin content and increased activities of AP, GR and SOD. These declined during rehydration. It is suggested that potential free radical damage may be avoided by the persistence of anthocyanins during the period of thylakoid membrane re-assembly and full chlorophyll restitution which only occurred once the leaves were fully rehydrated.

Differences in Chlorophyll Loss at 13 degrees C for Two Broccoli (Brassica oleracea L.) Cultivars Associated with Antioxidant Enzyme Activities.

Two broccoli cultivars which have been previously found to have large differences in yellowing susceptibility were studied to determine if there was a relationship between antioxidant capability and chlorophyll loss at a simulated retail display temperature. Greenbelt cultivar retained a stable chlorophyll content over 4 days at 13 degrees C, while Emperor cultivar showed a constant decline in chlorophyll content. These differences were not related to differences in water loss. Superoxide dismutase (SOD) and peroxidase (POD) activities were approximately 30% higher in Greenbelt than in Emperor. The ratio of superoxide dismutase to peroxidase activity was also lower in Greenbelt. The susceptibility of Emperor to oxygen radical damage and lipid peroxidation is expected to be higher since an excessive SOD activity, with respect to POD activity, can potentially lead to enhanced hydroxyl radical formation. Catalase (CAT) activity was higher in Emperor, suggesting that catalase is not important in providing resistance to chlorophyll loss in broccoli. Water soluble, nonenzymatic antioxidant activity was similar for both cultivars. These results support the hypothesis that antioxidant protection offered by superoxide dismutase and peroxidase is important to retention of green color in broccoli.

Impact of elevated atmospheric CO2and O3on gas exchange and chlorophyll content in spring wheat (Triticum aestivumL.)

Stands of spring wheat grown in open-top chambers (OTCs) were used to assess the individual and interactive effects of season-long exposure to elevated atmospheric carbon dioxide (CO 2 ) and ozone (O 3 ) on the photosynthetic and gas exchange properties of leaves of differing age and position within the canopy. The observed effects were related to estimated ozone fluxes to individual leaves. Foliar chlorophyll content was unaffected by elevated CO 2 , but photosynthesis under saturating irradiances was increased by up to 100% at 680 μmol mol -1 CO 2 relative to the ambient CO 2 control; instantaneous water use efficiency was improved by a combination of increased photosynthesis and reduced transpiration. Exposure to a seasonal mean O 3 concentration (7 h d -1 ) of 84 nmol mol - - 1 under ambient CO 2 accelerated leaf senescence following full expansion, at which time chlorophyll content was unaffected. Stomatal regulation of pollutant uptake was limited since estimated O 3 fluxes to individual leaves were not reduced by elevated atmospheric CO 2 . A common feature of 03-treated leaves under ambient CO 2 was an initial stimulation of photosynthesis and stomatal conductance for up to 4 d and 10 d, respectively, after full leaf expansion, but thereafter both variables declined rapidly. The 03-induced decline in chlorophyll content was less rapid under elevated CO 2 and photosynthesis was increased relative to the ambient CO 2 treatment. A/C i analyses suggested that an increase in the amount of in vivo active RuBisCO may be involved in mitigating O 3 -induced damage to leaves. The results obtained suggest that elevated atmospheric CO 2 has an important role in restricting the damaging effects of O 3 on photosynthetic activity during the vegetative growth of spring wheat, and that additional direct effects on reproductive development were responsible for the substantial reductions in grain yield obtained at final harvest, against which elevated CO 2 provided little or no protection.

Effect of light and gibberellic acid on photosynthesis during leaf senescence of alstroemeria cut flowers.

The functioning of the photosynthetic apparatus during leaf senescence was investigated in alstroemeria cut flowers by a combination of gas‐exchange measurements and analysis of in vivo chlorophyll fluorescence. Chlorophyll loss in leaves of alstroemeria cut flowers is delayed by light and by a treatment of the cut flowers with gibberellic acid (GA3). The maximal photosynthesis of the leaves was approximately 6 μmol CO2 m−2 s−1 at I 350 μmol m−2 s−1 (PAR) which is relatively low for intact C3 leaves. Qualitatively the gas‐exchange rates followed the decline in chlorophyll content for the various treatments, i.e. light and GA3‐treatment delayed the decline in photosynthetic rates. However, when chlorophyll loss could not yet be observed in the leaves, photosynthetic rates were already strongly decreased. In vivo fluorescence measurements revealed that the decrease in CO2 uptake is (partly) due to a decreased electron flow through photosystem II. Furthermore, analysis of the fluorescence data showed a high nonphotochemical quenching under all experimental conditions, indicating that the consumption of reducing power in the Calvin cycle is very low. The chlorophyll, remaining after 9 days incubation of leaves with GA3 in the dark should be considered as a ‘cosmetic’ pigment without any function in the supply of assimilates to the flowers.

Mechanisms of Starvation Tolerance in Pearl Millet

The response of pearl millet (Pennisetum glaucum [L.]) seedlings to prolonged starvation was investigated at the biochemical and ultrastructural level. After 2 days of darkness the bulk of the seedling carbohydrate reserves were depleted. After 8 days in the dark the respiratory rate had declined to less than 50% of its initial value and the plants had lost half of their total protein content. Unlike the situation with carbohydrate depletion, protein loss was restricted to specific organs. The secondary leaf and stem (including the apical meristem) showed little or no protein loss during this period. In the primary leaf, seed, and roots, protein loss was substantial. In spite of the high rate of protein degradation in the primary leaf and roots, these organs showed no ultrastructural changes suggestive of tissue, cellular, or subcellular degradation. In addition, ribulose bisphosphate carboxylase was not preferentially degraded during starvation and only a small decline in chlorophyll content was observed after 8 days in the dark. During the period from 8 to 14 days, cell death started at the tip of the primary leaf and gradually spread downward. Both shoot and root meristems remained alive up to 14 days. Consequently, the eventual death of the plant was due to the loss of the carbohydrate-producing regions rather than the meristems. We suggest that these results provide an explanation for the high degree of starvation tolerance exhibited by pearl millet.

Influence of repeated water stress on wheat

Fertility-induced performance alterations in wheat (cv Kalyansona) have been evaluated under two cycles of droughts at various developmental stages and also repeated droughts. The significant alleviation of growth and yield, despite the higher stress experienced by plants under improved soil fertility, seems to be related to larger root growth and greater post-drought nutrient uptake and not to favourable tissue water modulations. Limited wet-period interludes, under repeated stress, reduced these advantages. Stress-mediated increases in proline and free aminoacids and decline in chlorophyll content in leaves followed established trends. Their levels, however, were relatively higher under better soil fertility. The proline accumulation was reduced in the second cycle of drought, as compared to the first, indicating an absence of hardening effect.

The Role of Abscisic Acid (ABA) in Regulation of Some Photosynthetic Enzyme Activities in Apple Seedlings in Relation to Embryonal Dormancy

Changes in RuDPC and PEPC activities were investigated in non-dormant apple embryos grown in water as well as in solutions of abscisic acid (ABA) at various concentrations. At all concentrations applied ABA caused a decrease in ribulose-1.5-diphosphate carboxylase (RuDPC) activity and an increase in phosphoenolpyruvate carboxylase (PEPC) activity. These effects were correlated with a decrease in germinability as well as with a decrease in growth rate and a decline in chlorophyll content. The results reported suggest that endogenous ABA in dormant embryos regulates the carboxylating enzyme activities and chlorophyll content.

Nucleic acid and protein synthesis in discs cut from mature leaves of Nicotiana tabacum L. and cultured on nutrient agar with and without kinetin

The effect of kinetin on aspects of the metabolism of discs cut from mature leaves of Nicotiana tabacum and cultured in the light on agar containing mineral salts and sucrose was studied. In the first few days of culture there was a rapid decline in chlorophyll content. Discs treated with kinetin in the light began to resynthesise chlorophyll after 3-4 days and this was correlated with chloroplast replication. Kinetin promoted chloroplast replication but was not always essential. An increase in fresh weight also occurred, due mainly to cell expansion. Nitrate reductase activity increased rapidly during the first few hours after placing discs on the culture medium but kinetin had no effect on this reponse. Subsequently there were dramatic increases in RNA and protein content which were largely independent of kinetin. Gel electrophoresis showed that cytoplasmic and chloroplast ribosomal RNA and a large amount of soluble RNA were synthesised during culture of the discs. These results are discussed in relation to the role of kinetin in delaying leaf sensescence.

The effect of seawater on the metabolism of some seashore and inland mosses.

Photosynthesis and protein synthesis were determined, by measuring uptake and incorporation of radioactive bicarbonate and L-valine, in some seashore and inland mosses after treatment with artificial seawater. In the inland species there was a progressive decline in both processes with increasing seawater concentration. Photosynthesis in the seashore mosses Grimmia maritima and Tortella flavovirens was unaffected by increasing seawater concentration, and supralittoral Ulota phyllantha was less seriously affected than epiphytic material from a subcoastal location. There was a marked decline in chlorophyll content and cessation of photosynthesis in the inland moss G. pulvinata after 3 days' seawater treatment whereas material treated with deionised water showed increased photosynthesis and chlorophyll levels over the same period. In G. maritima both chlorophyll levels and photosynthesis remained relatively unaffected by treatment with seawater for 4 days. Treatment of G. pulvinata with seawater and NaCl led to increased leakage of photosynthetic products to the external solution but this was insufficient to explain the reduction in carbon retained by the plant. The seawater-induced disruption of metabolism in inland bryophytes is believed to be primarily due to the uncontrolled entry of toxic ions into the moss cells whereas seawater tolerance in the seashore species probably reflects the possession of an efficient intracellular cation control mechanism.

Effects of 2-Chloroethylphosphonic Acid on Growth, Plastid Pigments, and Sucrose Translocation in Radish

2-Chloroethylphosphonic acid (CEPA) caused a significant decline in chlorophyll content of radish plant within 5 d of treatment. Such effects were greater when plants were treated at the two- than at the four-leaf stage. In early treated plants, concentration of CEPA increasing from 20 mg/1 progressively increased leaf weight, while decreasing root (radish) weight. A concentration of 10 mg/1, applied at the three-leaf stage, increased leaf and root weights by 27 and 30 per cent respectively in the cultivar ‘Cavalier’. Similar responses were obtained with the cultivar ‘Cherry Belle’. While Cavalier showed a discrete 10 mg/1 optimum, ‘Cherry Belle’ exhibited a range of concentrations (10-40 mg/1) optimal for growth. At relatively high concentrations, early application of CEPA caused inverse changes in sucrose-14C in the leaves and the root, so that decreased retention by leaves was accompanied by increased transport to roots. Low concentrations of CEPA appear promising for growth stimulation in root-crop plants.

Physiological Changes in Barley Induced by Greenbug Feeding Stress1,3

SummaryQuantitative amounts of greenbug (Schizaphis graminum Rondani) feeding stress on the first foliar leaf of barley (Hordeum vulgare L.) caused a severe detrimental decline in chlorophyll content and in the rate of photosynthesis. The stress produced an increase in the rate of respiration but no change in leaf area, fresh weight, or dry weight during 7 days of controlled infestation.

Symbiosis in sacoglossan opisthobranchs: functional capacity of symbiotic chloroplasts

It has been previously reported that many species of the order Sacoglossa (Mollusca: Opisthobranchia) contain algal chloroplasts within the cells of their digestive gland and maintain them in a symbiotic condition. In the present study, two species, Elysia hedgpethi Marcus and Placobranchus ianthobapsus Gould, were compared as to their abilities to retain functional chloroplasts in their tissues. Animals were starved for varying lengths of time, and the functional capacity of the plastids was ascertained at intervals. The chlorophyll content of whole animals, and the ability to incorporate 14CO2 were used as the assay for functional capacity. E. hedgpethi decreased in chlorophyll content during starvation until the tenth day, when no chlorophyll was detectable spectrophoto-metrically. Incorporation of 14CO2 paralleled the decline in chlorophyll, and was at control levels by the tenth day. P. ianthobapsus showed no decline in chlorophyll content over 27 days starvation, although the ability to incorporate 14CO2 showed a decrease.

Nonphotosynthetic Retardation of Chloroplast Senescence by Light

Excised apical portions of green wheat leaf sections were treated with aminotriazole to prevent formation of new chloroplasts. Illumination retarded the decline in chlorophyll content per leaf section, the disintegration of chloroplast ultrastructure, and the loss of capacity for photosynthetic carbon fixation. We interpret these 3 effects of illumination as facets of a single light effect in retarding chloroplast senescence. This light effect in retarding chloroplast senescence has features differing from characteristics of photosynthetic carbon fixation. For example, A) application of the photosynthetic inhibitor 3-(3,4-dichlorophenyl)-1, 1-dimethylurea did not decrease, and may have even slightly increased, the effectiveness of light; B) although the action spectrum contains peaks in the blue and red regions, it differs from the action spectrum for photosynthetic CO(2) assimilation in wheat; C) in nonphotosynthesizing tissue, application of sugars did not retard chloroplast senescence; D) light saturation was achieved by only a few hundred microwatts/cm(2). Considered together with the well-known light requirement for chloroplast formation, our results indicate that light has a dual, photomorphogenetic control in maintaining the green status of the plant by also exerting a second effect: retarding of senescence of chloroplasts already present.