Influence of ionic interactions on essential oil and phenolic diterpene composition of Dalmatian sage (Salvia officinalis L.)

The potential of four essential cations (K⁺, Ca²⁺, Mg²⁺ and Fe²⁺) to alleviate salt toxicity was studied in sage (Salvia officinalis L.) plants grown in pots. Two concentrations of the following chloride salts: KCl, CaCl₂, MgCl₂ and FeCl_3, were used together with 100 mM NaCl to study the effects of these nutrients on plant growth, leaf essential oils (EOs) and phenolic diterpenes composition. The sage plants accumulated Na⁺ in their leaves (includers); this has affected secondary metabolites’ biosynthesis. Treatment with 100 mM NaCl slightly decreased borneol and viridiflorol, while increased manool concentrations. Addition of KCl, CaCl₂ and MgCl₂ increased considerably in a dose-dependent manner the oxygen-containing monoterpenes (1.8-cineole, camphor, β-thujone and borneol) in 100 mM NaCl-treated sage. Whereas, the contents of viridiflorol decreased further with the addition of KCl in 100 mM NaCl-treated sage. Our results suggest that the changes in EOs composition were more related to K⁺ and Ca²⁺ availability than to Na⁺ toxicity. Furthermore, treatment with NaCl decreased by 50% carnosic acid (CA), a potent antioxidant, content in the leaves. K⁺ and Ca²⁺ promoted the accumulation of CA and its methoxylated form (MCA) in the leaves. The concentration of CA was positively correlated with leaf K⁺ (r = 0.56, P = 0.01) and Ca²⁺ (r = 0.44, P = 0.05) contents. It appears that different salt applications in combination with NaCl treatments had a profound effect on EOs and phenolic diterpene composition in sage. Therefore, ionic interactions may be carefully considered in the cultivation of this species to get the desired concentrations of these secondary metabolites in leaf extracts.     

Source and sink leaf metabolism in relation to Phloem translocation: carbon partitioning and enzymology

The import-export transition in sugar beet leaves (Beta vulgaris) occurred at 40 to 50% leaf expansion and was characterized by loss in assimilate import and increase in photosynthesis. The metabolism and partitioning of assimilated and translocated C were determined during leaf development and related to the translocation status of the leaf. The import stage was characterized by C derived from either ¹⁴C-translocate or ¹⁴C-photosynthate being incorporated into protein and structural carbohydrates. Marked changes in the C partitioning were temporally correlated with the import-export conversion. Exporting leaves did not hydrolyze accumulated sucrose and the C derived from CO₂ fixation was preferentially incorporated into sucrose. Both source and sink leaves contained similar levels of acid invertase and sucrose synthetase activities (sucrose hydrolysis) while sucrose phosphate synthetase (sucrose synthesis) was detected only in exporting leaves. The results are discussed in terms of intracellular compartmentation of sucrose and sucrose-metabolizing enzymes in source and sink leaves.     

Effects of leaf position and nitrogen supply on the expansion of leaves of field grown sunflower (Helianthus annuus L.)

Leaf growth responses to N supply and leaf position were studied using widely-spaced sunflower plants growing under field conditions. Both N supply (range 0.25 to 11.25 g added N per plant) and leaf position significantly (p=0.001) affected maximum leaf area (LA_max) of target leaves through variations in leaf expansion rate (LER); effects on duration of expansion were small. Specific leaf nitrogen (SLN, g N m^-2) fell quite rapidly during the initial leaf expansion phase (LA < 35% LA_max) but leveled off during the final 65% increase of leaf area. This pattern held across leaf positions and N supply levels. Leaf nitrogen accumulation after 35% LA_max continued up to achievement of LA_max; reductions in the higher SLN characteristic of the initial phase were insufficient to cover the nitrogen requirements for expansion during the final phase. LER in the quasi-linear expansion phase (35 to 100% of LA_max) was strongly associated with SLN above a threshold that varied with leaf position (mean 1.79±0.225 g N m^-2). This contrasts with the response of photosynthesis at high irradiance to SLN, which has previously been shown to have a threshold of 0.3 g N m^-2; in the present work saturation of photosynthetic rate was evident when SLN reached 1.97 g N m^-2. Thus, once the area of a leaf exceeds 35% of LA_max, expansion proceeds provided SLN values are close to the levels required for maximum photosynthesis. However, growth of leaves during the initial expansion phase ensures a minimum production of leaf area even at low N supply levels.     

The Influence of Leaf Age on C(4) Photosynthesis and the Accumulation of Inorganic Carbon in Flaveria trinervia, a C(4) Dicot

Characteristics of C₄ photosynthesis were examined in young, mid-age, and mature leaves of Flaveria trinervia (an NADP-malic enzyme-type C₄ dicot). The turnover of [4-¹⁴C] (malate plus aspartate) following a pulse with ¹⁴CO₂ was similar in leaves of different ages (apparent half-time of 18-25 seconds). However, the rate of ¹⁴CO₂ incorporation in mid-age leaves was about 1.5-fold higher than in young leaves, and about 2.5-fold higher than in mature leaves. The rate of ¹⁴CO₂ fixation was proportional to the total active pool of malate plus aspartate but was not correlated with the total photosynthetically derived inorganic carbon pool. The leaf's ability to concentrate inorganic carbon photosynthetically declined during leaf expansion, from 29 down to 7 nanomoles per milligram chlorophyll. Similarly, the active aspartate pool also declined during leaf expansion, from about 123 down to 20 nanomoles per milligram chlorophyll. Enhanced metabolism of aspartate to CO₂ and pyruvate in young leaves is suggested to facilitate the maintenance of high CO₂ levels in bundle sheath cells which are thought to have a higher conductance to CO₂.     

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.     

Effect of drought stress on net CO2 uptake by Zea leaves

The net CO₂ assimilation by leaves of maize (Zea mays L. cv. Adonis) plants subjected to slow or rapid dehydration decreased without changes in the total extractable activities of phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and malic enzyme (ME). The phosphorylation state of PEPC extracted from leaves after 2–3 h of exposure to light was not affected by water deficit, either. Moreover, when plants which had been slowly dehydrated to a leaf relative water content of about 60% were rehydrated, the net CO₂ assimilation by leaves increased very rapidly without any changes in the activities of MDH, ME and PEPC or phosphorylation state of PEPC. The net CO₂-dependent O₂ evolution of a non-wilted leaf measured with an oxygen electrode decreased as CO₂ concentration increased and was totally inhibited when the CO₂ concentration was about 10%. Nevertheless, high CO₂ concentrations (5–10%) counteracted most of the inhibitory effect of water deficit that developed during a slow dehydration but only counteracted a little of the inhibitory effect that developed during a rapid dehydration. In contrast to what could be observed during a rapidly developing water deficit, inhibition of leaf photosynthesis by cis-abscisic acid could be alleviated by high CO₂ concentrations. These results indicate that the inhibition of leaf net CO₂ uptake brought about by water deficit is mainly due to stomatal closure when a maize plant is dehydrated slowly while it is mainly due to inhibition of non-stomatal processes when a plant is rapidly dehydrated. The photosynthetic apparatus of maize leaves appears to be as resistant to drought as that of C₃ plants. The non-stomatal inhibition observed in rapidly dehydrated leaves might be the result of either a down-regulation of the photosynthetic enzymes by changes in metabolite pool sizes or restricted plasmodesmatal transport between mesophyll and bundle-sheath cells.     

Metabolism of Monoterpenes : Metabolic Fate of (+)-Camphor in Sage (Salvia officinalis)

The bicyclic monoterpene ketone (+)-camphor undergoes lactonization to 1,2-campholide in mature sage (Salvia officinalis L.) leaves followed by conversion to the β-d-glucoside-6-O-glucose ester of the corresponding hydroxy acid (1-carboxymethyl-3-hydroxy-2,2,3-trimethyl cyclopentane). Analysis of the disposition of (+)-[G-³H]camphor applied to midstem leaves of intact flowering plants allowed the kinetics of synthesis of the bis-glucose derivative and its transport from leaf to root to be determined, and gave strong indication that the transport derivative was subsequently metabolized in the root. Root extracts were shown to possess β-glucosidase and acyl glucose esterase activities, and studies with (+)-1,2[U-¹⁴C]campholide as substrate, using excised root segments, revealed that the terpenoid was converted to lipid materials. Localization studies confirmed the radiolabeled lipids to reside in the membranous fractions of root extracts, and analysis of this material indicated the presence of labeled phytosterols and labeled fatty acids (C₁₄ to C₂₀) of acyl lipids. Although it was not possible to detail the metabolic steps between 1,2-campholide and the acyl lipids and phytosterols derived therefrom because of the lack of readily detectable intermediates, it seemed likely that the monoterpene lactone was degraded to acetyl CoA which was reincorporated into root membrane components via standard acyl lipid and isoprenoid biosynthetic pathways. Monoterpene catabolism thus appears to represent a salvage mechanism for recycling mobile carbon from senescing oil glands on the leaves to the roots.     

Seasonal variation in ammonia compensation point and nitrogen pools in beech leaves (Fagus sylvatica)

Ammonia (NH₃) fluxes between beech leaves (Fagus sylvatica) and the atmosphere were investigated in a 90-year-old forest canopy and related to leaf nitrogen (N) pools and glutamine synthetase (GS) activities. The stomatal ammonia compensation point, ?? _NH3, was measured by both a twig cuvette and bioassay techniques involving measurements of pH and ammonium (NH ₄ ⁺ ) concentration in the leaf apoplastic solution. The ?? _NH3 determined on the basis of the gas exchange measurements followed a seasonal variation with early-season peaks during leaf expansion (9.6 nmol NH₃ mol^?1 air) and late-season peaks during leaf senescence (7.3 nmol NH₃ mol^?1 air). In the mid-season, the ?? _NH3 of mature green leaves was much lower (around 3 nmol NH₃ mol^?1 air) and dropped below the NH₃ concentration in the ambient atmosphere. For comparison, ?? _NH3 obtained by the apoplastic bioassay were 7.0, 3.7 and 6.4 nmol NH₃ mol^?1 air in early-, mid-, and late -season, thus agreeing reasonably well with ?? _NH3 values derived from the gas exchange measurements. Potential NH₃ emission fluxes during early and late season were 1.31 and 0.51 nmol m^?2 leaf surface area s^?1, respectively, while leaves were a sink for NH₃ during mid-season. During leaf establishment and senescence, both apoplastic and bulk tissue NH ₄ ⁺ concentrations were relatively high coinciding with low activities of glutamine synthetase, which is a key enzyme in leaf N metabolism. In conclusion, the exchange of NH₃ between beech leaves and the atmosphere followed a seasonal variation with NH₃ emission peaks being related to N mobilization during early leaf establishment and remobilization during late leaf senescence.     

Catabolism of camphor in tissue cultures and leaf disks of common sage (Salvia officinalis).

(+)-Camphor constitutes nearly 30% of the monoterpenes accumulated in the leaves of common sage (Salvia officinalis), and as the plant approaches maturity the content of this monoterpene ketone decreases by roughly half. Although the ability to catabolize camphor has been demonstrated previously in sage leaf disks, tissue cultures proved to be a more suitable system for examining the responsible degradative pathway. Cell suspension cultures were shown to convert (+)-[3-3H2]camphor, in sequence, to 6-hydroxycamphor, 6-oxocamphor, alpha-campholonic acid, and 2-hydroxy-alpha-campholonic acid, and each intermediate of the pathway was identified by chromatographic and spectroscopic means. This oxidative ring opening sequence resembles the pathway for camphor degradation by the soil diphtheroid, Mycobacterium rhodochrous, that ultimately leads to isoketocamphoric as the last defined metabolite that contains all 10 carbons of the original bicyclic nucleus. Studies with both cell cultures and leaf disks also demonstrated that the catabolism of camphor via 1,2-campholide, a metabolite in sage leaves previously described, was a minor degradative pathway. The first step in the metabolism of camphor was demonstrated in cell-free extracts of the cultured sage cells, and several lines of evidence indicated that this microsomal (+)-camphor-6-exo-hydroxylase is a cytochrome P-450-dependent monooxygenase.     

Development of Nitrate Reductase Activity in Expanding Leaves of Nicotiana tabacum in Relation to the Concentration of Nitrate and Potassium

Up to 80% of the total nitrate reductase activity (NRA) determined in vivo in different parts of vegetative tobacco plant (Nicotiana tabacum) was located in the leaves. The NRA reached a peak when a leaf had expanded to 27% of its final weight and 33% of its final area. Thereafter, with advancing expansion and age of the leaf, the activity declined. This pattern of development of NRA during the ontogenesis of leaves was not influenced by raising the supply of NO₃⁻ from 3 to 6 milliequivalent per cubic decimeter in the substrate solution. The concentration of NO₃⁻ in leaves, stem and root was inversely related to NRA at both NO₃⁻ levels. Raising the supply of K⁺ from 1 to 6 milliequivalent per cubic decimeter at either concentration of NO₃⁻ slowed down the development of NRA in the initial stages of expansion, but promoted it subsequently. The peak of the activity which developed in a leaf of 62% of its final area was higher at the higher supply of K⁺. The higher activity was maintained thereafter in the expanding and in matured and older leaves. It was concluded that NRA and the pattern of its development in expanding leaves is related to the availability of metabolites and their incorporation into enzyme proteins. Both these processes are influenced by: (a) the vertical profile of concentration of K⁺ in the shoot and (b) the concentration of K⁺ in a leaf, which depend upon its supply.     

Seasonal changes in nitrate use by three woody species: the importance of the leaf-expansion period

Seasonal changes in plant NO₃ ⁻-N use were investigated by measuring leaf nitrate reductase activity (NRA), leaf N concentration, and leaf expansion in one evergreen woody species (Quercus glauca Thunb.) and two deciduous woody species [Acer palmatum Thunb. and Zelkova serrata (Thunb.) Makino]. Leaf N concentration was highest at the beginning of leaf expansion and decreased during the expansion process to a steady state at the point of full leaf expansion in all species. The leaf NRA of all species was very low at the beginning of leaf expansion, followed by a rapid increase and subsequent decrease. The highest leaf NRA was observed in the middle of the leaf-expansion period, and the lowest leaf NRA occurred in summer for all species. Significant positive correlations were detected between leaf NRA and leaf expansion rates, while leaf N concentrations were negatively correlated with leaf area. In the evergreen Q. glauca, the N concentration in current buds increased before leaves opened; concurrently, the N concentration in 1-year-old leaves decreased by 25%. Our results show that the leaf-expansion period is the most important period for NO₃ ⁻-N assimilation by broadleaf tree species, and that decreases in leaf N concentration through the leaf-expansion period are at least partly compensated for by newly assimilated NO₃ ⁻-N in current leaves.     

Leaf expansion and carbon assimilation in cotton leaves grown at two photosynthetic photon flux densities

Increasing photosynthetic photon flux density (PPFD) received during development from 5.5 to 31.2 mol m^-2 d^-1 resulted in greater leaf and mesophyll cell surface areas in cotton (Gossypium hirsutum L.). The relationships between the amounts of these surface areas and potential CO₂ assimilation by these leaves were evaluated. Leaf area (epidermal surface area of one side of a leaf), mesophyll cell surface area, and net rate of CO₂ uptake (P_n) were measured from the time leaves first unfolded until P., was substantially reduced. At the higher PPFD, leaf and mesophyll surface areas increased more rapidly during expansion, and P_n per unit leaf area was greater than at the lower PPFD. Although leaves at the higher PPFD reached the maximum P., per unit mesophyll cell surface area 4 to 5 days earlier than leaves at the lower PPFD, the maxima for these P., were similar. Leaves grown at the higher PPFD had the potential to assimilate 2.2, 3.5, or 5.8 times the amount of CO₂ as leaves from the lower PPFD when P., was expressed per unit mesophyll surface, per unit leaf surface, or per whole leaf, respectively. Greater and earlier development of both P., and mesophyll cell surface area at higher PPFD apparently had a compounding effect on the potential for carbon assimilation by a leaf.     

Appearance and accumulation of c(4) carbon pathway enzymes in developing maize leaves and differentiating maize a188 callus

Regenerating maize A188 tissue cultures were examined for the presence of enzymes involved in C₄ photosynthesis, for cell morphology, and for ¹⁴C labeling kinetics to study the implementation of this pathway during plant development. For comparison, sections of maize seedling leaves were examined. Protein blot analysis using antibodies to leaf enzymes showed a different profile of these enzymes during the early stages of shoot regeneration from callus from the closely-coordinated profile observed in seedling leaves. Pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) and phosphoenolpyruvate carboxylase (PEPC) (EC 4.1.1.31) were found in nonchlorophyllous callus while ribulose 1,5-bisphosphate carboxylase (RuBPC, EC 4.1.1.39) and malic enzyme, NADP-specific (ME-NADP) (EC 1.3.1.37) were not detectable until later.

Enzyme activity assays showed the presence of ME-NADP as well as PEPC and PPDK in nonchlorophyllous callus. However, the activities of ME-NADP and PEPC had properties similar to those of the enzymes from C₃ leaves and from etiolated C₄ leaf tissues, but differing from the corresponding enzymes in the mature leaf.

Immunoprecipitation of in vitro translation products of poly(A)RNA extracted from embryoid-forming callus showed both the 110 kilodalton precursor to chloroplast PPDK and the 94 kilodalton polypeptide. Therefore, the chloroplast tye of PPDK mRNA is present prior to the appearance of leaf morphology.

Analysis of the labeled products of ¹⁴CO₂ fixation by nonchlorophyllous calli indicated β-carboxylation to give acids of the tricarboxylic acid cycle, but no incorporation into phosphoglycerate. With greening of the callus, some incorporation into phosphoglycerate and sugar phosphates occurred, and this increased in shoots as they developed, although with older shoots the increase in β-carboxylation products was even greater. Analysis of enzyme levels in young leaf sections by protein blot and of ¹⁴C-labeling patterns in the present study are in general agreement with enzyme activity determinations of previous studies, providing additional information about PPDK levels, and supporting the model proposed for developing young leaves.

These results suggest that maize leaves begin to express C₄ enzymes during ontogeny through several stages from greening and cell differentiation as seen in the callus and then shoot formation, and finally acquire capacity for full C₄ photosynthesis during leaf development concomitant with the development of Kranz anatomy and accumulation of large amounts of enzymes involved in carbon metabolism.

     

Regulation of Carbon Partitioning in Source and Sink Leaf Parts in Sweet Pepper (Capsicum annuum L.) Plants : Role of Fructose 2,6-Bisphosphate

Area expansion rate, partitioning of photosynthetically fixed carbon, and levels of fructose 2,6-bisphosphate (fru-2,6-P₂) were determined in individual parts of developing leaves of sweet pepper (Capsicum annuum L.). The base was rapidly expanding and allocated less carbon to sucrose synthesis in comparison to the leaf tip, where expansion had almost stopped. The change in leaf expansion rate and carbon partitioning happened gradually. During day time levels of fru-2,6-P₂ were consistently higher in the leaf base than in the leaf tip. Leaf expansion rate and carbon partitioning were closely related to day time levels of fru-2,6-P₂, suggesting that fru-2,6-P₂ is an important factor in adjustment of metabolism during sink-to-source transition of leaf tissue. The levels of fru-2,6-P₂ changed markedly after a dark-to-light transition in the leaf base, but not in the leaf tip, suggesting that regulatory systems based on fru-2,6-P₂ are different in sink and source leaf tissue. During the period upon dark-to-light transition the variations in level of fru-2,6-P₂ did not show a close correlation to changes in the carbon partitioning, until the metabolism had reached a steady state.     

Seasonal changes in photosynthesis and nitrogen allocation in leaves of different ages in evergreen understory shrub <Emphasis Type="Italic">Daphniphyllum humile</Emphasis>

Seasonal changes in photosynthetic capacity, leaf nitrogen (N) content, leaf chlorophyll (Chl) content and leaf N allocation patterns in leaves of different ages in the evergreen understory shrub, Daphniphyllum humile Maxim, growing at a forest border and an understory site were studied. In current-year leaves at the understory site, the N and Rubisco contents increased from spring to autumn although their light-saturated photosynthetic rate at 22°C (P _max²²) remained stable, indicating that their mesophyll conductance rates declined as they completed their development and/or that they invested increasing amounts of their resources in photosynthetic enzymes during this period. In contrast, seasonal changes in P _max²² in current-year leaves at the forest border site were correlated with changes in Rubisco content. In 1-year old leaves at the understory site, P _max²² and contents of Chl, leaf N, and Rubisco remained stable from spring to autumn, while these parameters decreased in 1-year-old forest border leaves, indicating that N may have been remobilized from shaded 1-year-old leaves to sunlit current-year leaves. When leaves senesced at the forest border site the Rubisco content decreased more rapidly than that of light-harvesting proteins such as LHCII, suggesting that N remobilization from Rubisco may be more efficient, possibly because Rubisco has greater N costs and is soluble, whereas the light-harvesting proteins are membrane components.     

Plant leaf area expansion and assimilate production in wheat (Triticum aestivum L.) growing under low phosphorus conditions

Under phosphorus deficiency reductions in plant leaf area have been attributed to both direct effects of P on the individual leaf expansion rate and to a reduced availability of assimilates for leaf growth. In this work we use experimental and simulation techniques to identify and quantify these processes in wheat plants growing under P-deficient conditions. In a glasshouse experiment we studied the effects of soil P addition (0–138 kg P₂O₅ ha^-1) on tillering, leaf emergence, leaf expansion, plant growth, and leaf photosynthesis of wheat plants (cv. INTA Oasis) that were not water stressed. Plants were grown in pots containing a P-deficient (3 mg P g^-1 soil) sandy soil. Sowing and pots were arranged to simulate a crop stand of 173 plants m^-2. Experimental results were integrated in a simulation model to study the relative importance of each process in determining the plant leaf area during vegetative stages of wheat. Phosphorus deficiency significantly reduced plant leaf area and dry weight production. Under P-deficient conditions the phyllochron (PHY) was increased up to a 32%, compared to that of high-P plants. In low-P plants the rate of individual leaf area expansion during the quasi-linear phase of leaf expansion (LER) was significantly reduced. The effect of P deficiency on LER was the main determinant of the final size of the individual leaves. In recently expanded leaves phosphorus deficiency reduced the photosynthesis rate per unit leaf area at high radiation (AMAX), up to 57%. Relative values of AMAX showed an hyperbolic relationship with leaf P% saturating at 0.27%. Relative values of the tillering rate showed an hyperbolic relationship with the shoot P% saturating at values above 0.38%. The value of LER was not related to the concentration of P in leaves or shoots. A morphogenetic model of leaf area development and growth was developed to quantify the effect of assimilate supply at canopy level on total leaf area expansion, and to study the sensitivity of different model variables to changes in model parameters. Simulation results indicated that under mild P stress conditions up to 80% of the observed reduction in plant leaf area was due to the effects of P deficiency on leaf emergence and tillering. Under extreme P-deficient conditions the simulation model failed to explain the experimental results indicating that other factors not taken into account by the model, i.e. direct effects of P on leaf expansion, must have been active. Possible mechanisms of action of the direct effects of P on individual leaf expansion are discussed in this work.     

Antioxidant capacity of sage grown on heavy metal-polluted soil

Oxidative stress response and essential oil composition of sage (Salvia officinalis L.), grown on industrially polluted soil were studied. Sage plants were grown on the soil polluted with Cd, Cu, Pb, Zn, and non-polluted control soil. One-year-old sage possessed a high potential for heavy metal accumulation mainly in the roots. Heavy metal pollution resulted in root and shoot dry biomass inhibition. The increased levels of hydrogen peroxide and MDA showed that the heavy metal uptake caused oxidative stress. The increase towards the control was observed in the levels of glutathione, ascorbate, dehydroascorbate, catalase, dehydroascorbate reductase, and glutathione peroxidase. Weak activities of the most enzymes of the ascorbate-glutathione cycle allowed to suppose that H₂O₂ neutralization is rather non-enzymatic than enzymatic process. Observed decline in α- and β-thujones and elevated camphor content in the sage leaves did not indicate a deterioration of the essential oil quality. Sage grown on heavy metal-polluted soil successfully accumulated cadmium, lead, and zinc, which is resulted in plant biomass inhibition, but essential oil yield and quality was not declined.     

Study of the senescence process in primary leaves of sunflower (Helianthus annuus L.) plants under two different light intensities

Different parameters that vary during leaf development may be affected by light intensity. To study the influence of different light intensities on primary leaf senescence, sunflower (Helianthus annuus L.) plants were grown for 50 days under two photon flux density (PFD) conditions, namely high irradiance (HI) at 350 μmol(photon) m^?2 s^?1 and low irradiance (LI) at 125 μmol(photon) m^?2 s^?1. Plants grown under HI exhibited greater specific leaf mass referred to dry mass, leaf area and soluble protein at the beginning of the leaf development. This might have resulted from the increased CO₂ fixation rate observed in HI plants, during early development of primary leaves. Chlorophyll a and b contents in HI plants were lower than in LI plants in young leaves. By contrast, the carotenoid content was significantly higher in HI plants. Glucose concentration increased with the leaf age in both treatments (HI and LI), while the starch content decreased sharply in HI plants, but only slightly in LI plants. Glucose contents were higher in HI plants than in LI plants; the differences were statistically significant (p<0.05) mainly at the beginning of the leaf senescence. On the other hand, starch contents were higher in HI plants than in LI plants, throughout the whole leaf development period. Nitrate reductase (NR) activity decreased with leaf ageing in both treatments. However, the NR activation state was higher during early leaf development and decreased more markedly in senescent leaves in plants grown under HI. GS activity also decreased during sunflower leaf ageing under both PFD conditions, but HI plants showed higher GS activities than LI plants. Aminating and deaminating activities of glutamate dehydrogenase (GDH) peaked at 50 days (senescent leaves). GDH deaminating activity increased 5-fold during the leaf development in HI plants, but only 2-fold in LI plants. The plants grown under HI exhibited considerable oxidative stress in vivo during the leaf senescence, as revealed by the substantial H₂O₂ accumulation and the sharply decrease in the antioxidant enzymes, catalase and ascorbate peroxidase, in comparison with LI plants. Probably, systemic signals triggered by a high PFD caused early senescence and diminished oxidative protection in primary leaves of sunflower plants as a result.     

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.     

Distribution of assimilate during the flush cycle of growth in Theobroma cacao L.

The growth of the shoot and roots of seedling plants of cocoa (Theobroma cacao L.) under constant glasshouse conditions showed a rhythmic cycle, with the maximum growth stages of each alternating in a regular sequence. When the growth cycle of the shoot was upset by removing all new leaves immediately after unfolding, the roots showed a high constant growth rate during this period, suggesting that normally the rapidly expanding leaves exert an inhibitory influence on the roots. Conversely removal of portions of the root delayed the production of new leaves in the shoot. The level of soluble and starch carbohydrate in the mature leaves, roots and stem declined during the period of expansion of the flush leaves, but accumulated again at the end of the leaf expansion stage. It is likely that this reserve carbohydrate was remobilised and translocated to the flush leaves during their period of expansion. A large proportion of newly formed photoassimilate, as shown by the distribution of ¹⁴C radioactivity from different source leaves, was also translocated to the young leaves during expansion. The large sink created by these leaves may cause photoassimilate and reserve carbohydrate to be diverted from the roots, thereby inhibiting root growth during the stage of leaf expansion. It is suggested that the rhythmic leaf production at the apex may control the growth cycle of the roots.