Influence Of Leaf Age Research Articles

Comparison of three sigmoidal functions describing the leaf growth of Camptotheca acuminata Decne

Leaf ontogeny and maturation are attended by a transition from importing to exporting photosynthates, which has important implications to plant growth and reproductive success. However, the influence of leaf age on leaf size has been seldom studied, although ontogenetic growth trajectories plotted against time typically exhibit sigmoidal curves, which can be approximated by corresponding sigmoidal functions. The three-parameter logistic equation (LE) is a classical sigmoidal function that assumes a symmetrical growth rate curve (i.e., the derivative of the LE) when plotted against time. LE has been verified as a general tool for describing ontogenetic growth such as seen in leaf maturation. However, there are other sigmoidal functions that assume that growth rate curves are skewed bell-shaped. Whether leaf ontogeny follows the LE, or some other sigmoidal functions is unknown. To explore the relationship between leaf area and leaf age, we recorded the leaf length and width of 61 leaves of Camptotheca acuminata Decne at 21 time-points during leaf expansion, and used three sigmoidal functions to fit leaf area (represented by 2/3 × leaf length × leaf width) when plotted against leaf age, i.e., the LE, the beta sigmoidal equation (BSE), and the Lobry-Rosso-Flandrois sigmoidal equation (LRFSE). LE had the best close-to-linear behavior and the lowest Akaike information criterion (AIC) among the three sigmoidal functions for the pooled data of 61 leaves. For 49 of the 61 leaves (80.3 %), the AICs of the LE were smaller than those of the BSE, and for 52 out of 61 leaves (85.2 %), the AICs of the LE were smaller than those of the LRFSE. In addition, the BSE provided incorrect predictions for the starting time of leaf growth. Thus, the data indicate that (1) the LE is the best sigmoidal function for describing ontogeny at the individual leaf level and for the combined data, and (2) the growth rate of C. acuminata leaves tends to be a symmetrical function rather than an asymmetrical function of leaf age. These findings provide insights into the ontogenetic importing-exporting transition attending leaf maturation.

Influence of Leaf Age on the Scaling Relationships of Lamina Mass vs. Area.

Leaf lamina mass and area are closely correlated with the photosynthetic capacity and competitive ability of plants, whereas leaf age has been demonstrated to affect physiological processes such as photosynthesis. However, it remains unknown whether the lamina mass vs. area scaling relationship is influenced by leaf age, which is important for understanding plant adaptive strategies and, more broadly, resource utilization and growth. We measured the leaf functional traits of five leaf-age groups of Photinia × fraseri for a total of 1,736 leaves. ANOVA followed by Tukey’s honestly significant difference test was used to compare the functional traits among the five leaf-age groups. Reduced major axis regression protocols were used to fit the scaling relationship between lamina mass and area, and the bootstrap percentile method was used to compare the lamina mass vs. area scaling relationships among the leaf-age groups. Lamina area, and the ratio of lamina dry mass to lamina fresh mass increased with increasing leaf age. Lamina fresh mass per unit area, and lamina dry mass per unit area both exhibited a parabolic-like trend as leaf age increased, i.e., at the leaf maturation stage, it showed a slight but significant decline. The phenomenon called diminishing returns were confirmed by each of the five leaf-age groups, i.e., all of the numerical values of the scaling exponents of lamina mass vs. area were significantly greater than 1. There were significant differences in the scaling exponents of lamina mass vs. area for the leaves across different sampling times. The scaling exponents were lower at the early rapid growth stage, indicating a lower cost for increasing leaf area compared to the leaf maturation stage. These data are consistent with leaves undergoing a transition from resource acquisition to resource conservation in the process of their development and growth.

Anthracnose Risk Establishment Based on Age-Related Susceptibility of Grape Leaves, Flowers, and Berries to Infection by Elsinoë ampelina.

Anthracnose is an important disease of grapevines caused by the fungus Elsinoë ampelina. In recent years, there have been regular outbreaks in humid grape-growing regions around the world. Young leaves and berries are reported to be highly susceptible to E. ampelina, but detailed and seasonal development of age-related susceptibility remains unclear. Experiments were conducted under greenhouse and vineyard conditions by inoculating 1- to 19-day-old leaves, flowers, and berries at different phenological stages of three grapevine cultivars (Vandal-Cliche, Marquette, and Vidal). Leaf susceptibility was highest when inoculated at 1 to 2 days old, and inoculated leaves were moderately susceptible at 3 to 6 days old and almost resistant when older than 6 days. The influence of leaf age on anthracnose relative severity was adequately described by an exponential decay model. The susceptibility of the inflorescences was high when inoculated from their initiation to the full flowering (50% fall of the caps), and the inflorescences/flowers were moderately susceptible until veraison, after which the berries were practically resistant. The flower/berry susceptibility as a function of degree-days accumulated since 1 April was modeled using a sigmoid model. Based on this model, 50% disease incidence is reached when 656, 543, and 550 degree days are accumulated for the cultivars Vandal-Cliche, Marquette, and Vidal, respectively. These results suggest that the risk of anthracnose development is high from bud-break to fruit set, and on newly emerged leaves either early in the season or following pruning. More knowledge on anthracnose epidemiology is needed, but these results could be used to improve timing of fungicide applications and pruning activities.

Characterization of Alternaria Species Associated with Leaf Spot Disease of Armoracia rusticana in Serbia.

Leaf spot diseases caused by Alternaria species have been reported worldwide in plants in the Brassicaceae family. However, there is little information on Alternaria species causing diseases in horseradish. In the present study, 89 Alternaria spp. isolates from Armoracia rusticana, sampled from nine districts in Serbia, were characterized based on their morphology, physiology, and molecular markers. Morphological characterization and molecular analyses based on ITS, GAPDH, Alt a 1, and PM-ATP sequences identified three distinct species associated with the disease: Alternaria brassicae, A. brassicicola, and A. alternata. For all species, growth and sporulation rates at 0, 5, 10, 15, 20, 25, 30, 35, and 40°C showed a quadratic response, with A. alternata having the widest temperature optimum (20 to 30°C) while A. brassicicola had higher optimum temperatures (20 to 25°C) than A. brassicae (15 to 20°C). To gain a better understanding of the pathogenicity of these species, the influence of leaf age, host susceptibility, and ability to infect artificially wounded and nonwounded leaves were tested. The pathogenicity test identified A. brassicicola and A. brassicae as the main causal agents of horseradish leaf spot disease. Results indicated that young and intact leaves of horseradish and cabbage were less susceptible to infection and also suggested the potential for cross-infection between these two hosts. Haplotype networks showed haplotype uniformity for A. brassicae, two haplotype groups of A. brassicicola, and eight haplotype groups of A. alternata in Serbia and suggest the possible association of some haplotypes with the geographic area. This study is the first to investigate Alternaria leaf spot disease on A. rusticana in Serbia and is the first record of A. brassicicola on horseradish in this country.

The Influence of Leaf Age, Oxidizing Pre-Treatment and Serving Temperature on Sensory Characteristics of Ampelgading Robusta Coffee Leaves Tea

The cultivation of coffee plants produces leaf-waste which is only currently used for feed and fertilizer. Traditionally coffee leaves tea could be processed as “kopi kawa”, a popular tea-like beverage in West Sumatera, Indonesia. This research was aimed at characterizing the sensory profile of beverage made from Ampelgading Robusta coffee leaves by considering different leaves age, processing method, and serving temperature applying the Rate-All-That-Apply (RATA) method involving 111 consumer respondents. It was observed that the coffee leaves tea were sensorially dominated by green aroma and flavor, bitter taste, and astringent mouth-feel. The leaves age significantly affected 6 sensory attributes, i.e. sweet taste, sour taste, bitter taste, sweet flavor, earthy flavor, and woody flavor. Meanwhile the processing method (oxidized and non-oxidized pre-treatment) as well as serving temperature had no significant effect on the sensory perception of consumer although significant influences were recorded on the changing of total phenolic content, caffeine content, pH, and color parameters. As conclusion, sensory characteristic of Ampelgading robusta coffee leave tea was strongly affected by the age of leaf, regardless the pre-treatment process and serving temperature.

The influence of leaf age and drying temperature on antioxidant capacity of Cassia alata

Antioxidants play an important role in inhibiting and scavenging free radicals, thus providing protection to human against infections and degenerative diseases. Current research is now directed towards natural antioxidants originated from plants due to safe therapeutics. Cassia alata plant has been commonly used as medicinal herbs for treating fungal infection such as ringworm and eczema. Nevertheless, there are only few studies focused on C. alata. This work aims to provide information about the antioxidant capacity of C. alata leaves at different stages of maturity and drying temperatures. The leaf maturity (young, medium and old) were determined by using chlorophyll meter. The leaves were dried at different temperatures (30, 40, 60 and 80 °C) using a laboratory oven. The leaves were then analysed for its antioxidant capacity. The extract of C. alata exhibited strong scavenging effect on 2, 2-diphenyl-2-picryl hydrazyl (DPPH) free radical.The antioxidant capacity in the examined extracts ranged from 85.81 to 89.71%. The results exhibited that the antioxidant capacity of C. alata extracts increased when the maturity of the leaves increased. Besides that, drying temperature was also found to increase the antioxidant capacity of C. alata leaves.

Influence of leaf age on infection of <i>Actinidia</i> species by <i>Pseudomonas syringae</i> pv <i>actinidiae</i>

The influence of leaf age on infection of Actinidia species by Pseudomonas syringae pv actinidiae (Psa) was investigated using two approaches (a) inoculation of potted Hayward and Hort16A kiwifruit plants and (b) inoculation of whole leaves in a detached leaf assay Whole plants and detached leaves were spray inoculated with Psa biovar 3 (haplotype NZV; PsaV) and maintained in a saturated environment Flecking was evident on some of the leaves 8 days after inoculation Many of the flecks later became necrotic spots with halos similar to the Psa leaf infections that have been observed in the field With both methods a higher percentage of leaves that were 13 weeks of age at inoculation had flecking and spotting than did leaves of other ages Leaves that were 7 weeks or older did not show any symptoms of infection by Psa Overall leaves of Hort16A showed slightly more flecking and spotting than Hayward

Influence of leaf age on induced resistance in grapevine against Plasmopara viticola

Sulfated laminarin (PS3) has previously been shown to induce resistance of grapevine leaves against the oomycete Plasmopara viticola, the causal agent of grape downy mildew. Here, we observed that the level of PS3-induced resistance (PS3-IR) was higher in the adult leaf (in position P3) than in the younger, not fully expanded leaf (in position P1, located above P3). By investigating grapevine defense reactions upon PS3 treatment and inoculation, we found that the production of H2O2, of phytoalexins, and the deposition of phenolics were more abundant in P3 than in P1 leaves. In addition, PS3 significantly reduced stomatal colonization by zoospores only in P3 leaves. Thus, the capacity of an adult leaf to express a higher level of defense reactions during PS3-IR may partly explain why it exhibits a more elevated resistance when compared to a young leaf, still in growth. These findings have likely practical consequences in induced resistance application.

Screening faba bean for chocolate spot resistance: evaluation methods and effects of age of host tissue and temperature

Chocolate spot is an important disease of faba bean (Vicia faba) caused by the necrotrophic fungus Botrytis fabae. The aims of this work were: i) to compare different methods of screening for resistance; ii) to assess the influence of the age of host tissue and temperature on this pathosystem. To this effect, a collection of 42 faba bean accessions was evaluated in mature plant stage in the field in Cordoba (Southern Spain) and in detached leaflet and whole plant tests under controlled conditions. Field results correlated better with those of the whole plant test than with those of the detached leaflet assay. Integration of results from the field and whole plant experiments resulted in the selection of six accessions of interest as sources of resistance. Influence of leaf age on disease development was found to be genotype dependent. Older leaves were more susceptible than younger ones in 23 accessions, while no difference between leaf ages was detected in the remaining accessions. The effects of plant age and temperature were assessed by a whole plant test on seven accessions at two plant ages (4 and 7 weeks) and three temperatures (13, 20, and 25°C). Results showed that the differential genotypic responses to B. fabae were not significantly influenced by either plant age or temperature, although there was a tendency towards lower susceptibility to chocolate spot in faba bean plants as they become older. Further, a partial high-temperature, young-plant resistance was detected.

Bacterial populations on the phyllosphere of Mediterranean plants: influence of leaf age and leaf surface

In the present study, we estimated the size of phyllosphere bacterial populations in young and mature leaves from the same plants and also assessed the population abundance on adaxial and abaxial leaf surfaces. We examined eight perennial species naturally occurring in the same area, in Halkidiki (northern Greece). They are Arbutus unedo, Quercus coccifera, Pistacia lentiscus, and Myrtus communis (evergreen sclerophyllous species), Lavandula stoechas and Cistus incanus (drought semideciduous species), and Calamintha nepeta and Melissa officinalis (nonwoody perennial species). Young and mature leaves were examined from the four sclerophyllous evergreen species for their epiphytic bacterial colonization, and it was found that mature leaves were highly populated compared to the younger ones except in M. communis. As regards the bacterial colonization of the two leaf surfaces, no differences were found in most species except for the drought semideciduous type where the two leaf surfaces behaved differently.

Gas exchange and water use efficiency of trees and maize in agroforestry systems in semi-arid Kenya

Improved understanding of the impact of leafing phenology and soil water supplies on the gas exchange and water use efficiency ( WUE) of trees in agroforestry systems in the semi-arid tropics is essential to optimise tree/crop interactions and the use of scarce natural resources, particularly in view of recent initiatives to use carbon credits to reward subsistence farmers who plant and manage trees effectively. Understanding of the relationships between photosynthetic and transpiration rates and chlorophyll content may help to explain variation in growth rate, productivity and WUE between species and growth environments. Such information is lacking for the species examined here, the evergreen Grevillea robusta (A. Cunn), semi-deciduous Alnus acuminata (HBK) and deciduous Paulownia fortunei (Hemsl.). Although differences in leafing phenology influence the extent of competition or complementarity between trees and crops in agroforestry systems, and hence crop yield, farmers may deliberately plant fast-growing, competitive tree species if they provide attractive economic returns or carbon credit subsidies. The objectives were to characterise: (1) the extent of variation in foliar gas exchange and instantaneous water use efficiency ( WUE i ) between trees with contrasting leafing phenologies; (2) the influence of leaf age and available soil moisture on gas exchange and WUE i of trees; and (3) chlorophyll and foliar nitrogen (N) concentrations and gas exchange parameters for maize in agroforestry and sole crop systems. Foliar chlorophyll and N concentrations, assimilation ( A) and transpiration rate ( E) were much greater in P. fortunei than in A. acuminata or G. robusta. A, E and WUE i were greatest in young mature leaves of all three species but declined as they senesced. WUE i increased as soil moisture content declined and was similar in all species, suggesting their differing leafing phenologies were responsible for observed differences in long-term water use and growth. A and WUE i were greater in maize than in tree species, consistent with its C4 photosynthetic pathway. The implications for tree and crop growth, yield and acceptability to subsistence farmers in the semi-arid tropics are discussed.

Age-dependent variations of local and systemic defence responses in Arabidopsis leaves towards an avirulent strain of Pseudomonas syringae

Despite the identification of several key mechanisms underlying disease resistance, comparatively little is known about the way developmental factors affect the capability of plants to defend themselves against microbial pathogens. Here, the influence of leaf age on inducible local and systemic defence responses in the incompatible interaction between Arabidopsis thaliana and Pseudomonas syringae pv. maculicola ( avrRPM1) is investigated. Comparison of the local defence behaviour of rosette leaves differing in age revealed that younger leaves generally had to invest in more pronounced inducible defences than older (non-senescent) leaves to achieve a similar degree of resistance. For instance, younger leaves exhibited a more distinctive oxidative burst and a stronger hypersensitive cell death response than older ones. The pathogen-induced expression of the defence related genes phenylalanine ammonia lyase ( PAL) and glutathione- S-transferase ( GST) proved to be higher and faster in younger leaves, respectively, whereas gene induction of PR-1 (pathogenesis-related protein 1) was largely independent of leaf age. Similarly, upon bacterial inoculation, the defence signal salicylic acid (SA) and the phytoalexin camalexin accumulated to higher amounts in younger than in older leaves. Despite these differences in inducible defences, bacterial growth as a measure of disease resistance proved to be similar in inoculated younger and older leaves. In tissue distant from the inoculation site, systemic acquired resistance (SAR) developed most effectively in younger leaves, and this response was associated with strong accumulation of SA and PR-1 transcripts. However, older leaves still exhibited SAR to a certain degree, and this resistance developed essentially without systemic SA or PR-1 accumulation. These results suggest that mechanisms independent of SA signalling in systemic leaves contribute to realise SAR.

The influence of leaf age on the oviposition preference of Chrysophtharta bimaculata (Olivier) and the establishment of neonates

Summary1 The degree of discrimination shown by a herbivore when selecting oviposition sites has been suggested as a key factor to understanding herbivore population dynamics. Chrysophtharta bimaculata (Coleoptera: Chrysomelidae) is a primary pest of Tasmanian eucalypt forests and can cause severe defoliation. Previous work suggests that females show discrimination when selecting oviposition sites. Our aim was to test the degree of oviposition discrimination exhibited by C. bimaculata with regards to leaf toughness, a character that is critical to neonate survival.2 We conducted an experiment examining the leaf toughness critical for neonate survival and found that significant larval mortality occurs above a toughness of 46.9 g. We also determined that the maximum toughness of leaves upon which larvae established in the field was 48.2 g, supporting the laboratory result.3 Field surveys showed that although the majority of eggs were laid on leaves suitable for larval establishment, many eggs were laid on unsuitable, tougher leaves. However, all eggs were normally placed within 20 cm of suitable leaves and glasshouse trials demonstrated the neonates could move this distance without mortality occurring.4 We conclude that egg batch distribution and larval performance of C. bimaculata will influence the population dynamics of C. bimaculata in two ways. Firstly, the availability of expanding/newly expanding leaves of eucalypt hosts will determine larval carrying capacity. Secondly, at a more localized level, the deposition of large numbers of egg batches on both suitable and unsuitable leaves followed by successful neonate migration increases the risk of resource depletion and poor larval development.

Adaptation of tobacco plants to elevated CO2: influence of leaf age on changes in physiology, redox states and NADP-malate dehydrogenase activity

Transgenic tobacco plants (Nicotiana tabacum L. cv. Xanthi) with altered chloroplast NADP-malate dehydrogenase (NADP-MDH) content were grown under ambient or under doubled atmospheric CO2 in order to analyse the effect of elevated CO2 on the redox state of the chloroplasts. Since large differences exist between the individual leaves of tobacco plants, gas exchange characteristics, enzyme capacities and metabolite contents were measured separately for each leaf of the plants. Large variations between leaves of different age were found in nearly every parameter analysed, and the differences between younger and older leaves were, in most cases, larger than the differences between comparable leaves at ambient or elevated CO2. For all parameters (chlorophyll fluorescence, P700 reduction, NADP-MDH activation) that are indicative for the redox situation in the electron transport chains and in the chloroplast stroma, more oxidized values were determined under elevated CO2. The increased redox state of ferredoxin, observed at ambient conditions in the NADP-MDH-under-expressing plants, disappeared under elevated CO2. It was concluded that the reduced rate of photorespiration under elevated CO2 decreases the amount of excess electrons. Interestingly, this lowered not only the activation state of NADP-MDH, but also the expression of the enzyme in the wild-type plants. The results are discussed with respect to a possible interaction between stromal reduction state and gene expression.

Adaptation of tobacco plants to elevated CO2: influence of leaf age on changes in physiology, redox states and NADP-malate dehydrogenase activity

Adaptation of tobacco plants to elevated CO2: influence of leaf age on changes in physiology, redox states and NADP-malate dehydrogenase activity

Seletividade alimentar e influência da idade da folha de Eucalyptus SPP. para Thyrinteina Arnobia (Lepidoptera: Geometridae)

Thyrinteina arnobia (Stoll, 1782) (Lepidoptera: Geometridae) é considerada uma das mais sérias pragas do eucalipto no Brasil. Este trabalho foi realizado com o objetivo de estudar a preferência alimentar de T. arnobia em seis espécies de eucalipto e a influência da idade foliar sobre a seleção hospedeira, utilizando-se folhas jovens e velhas de Eucalyptus grandis, Eucalyptus camaldulensis, Eucalyptus saligna, Eucalyptus citriodora, Eucalyptus robusta e Eucalyptus cloeziana. Lagartas de T. arnobia alimentadas na geração anterior com folhas de E. grandis preferiram folhas jovens de E. grandis e E.cloeziana, enquanto as alimentadas com E. saligna, na geração anterior, preferiram folhas velhas de E. grandis. A espécie preferida por lagartas de T. arnobia foi E. grandis, observando-se, também maior preferência por folhas jovens que por folhas velhas nas espécies utilizadas nos testes.

Influence of leaf age on responsiveness of Potamogeton nodosus to ABA-induced heterophylly

The heterophyllous aquatic angiosperm, Potamogeton nodosus, produces morphologically distinct leaves above and beneath the surface of the water. Application of abscisic acid induced entirely submerged plants to produce leaves normally formed at the water surface. A 1 µM application of abscisic acid for 4 h was effective in inducing these developmental changes. There was a “window of responsiveness” to ABA in that changes in leaf morphology were evident within 2 to 3 days after the treatment and continued for only 4 to 5 days. In addition, only leaves that emerged subsequent to the ABA application developed stomata. This pattern was repeated consistently in plants of different age indicating that leaf age and not plant age was the determining factor in this response to ABA.

Field investigations in Welwitschia mirabilis during a severe drought.: II. Influence of leaf age, leaf temperature and irradiance on photosynthesis and photoinhibition

Summary During drought Welwitschia mirabilis , a desert plant indigenous to the west coast deserts of southern Africa exhibited a two-peaked pattern of diurnal CO 2 exchange, with carbon losses for most time of the light period over all age classes of the approximately 5 years old leaf. Leaf conductances for water vapour and water potentials were high only during the cooler, humid morning and declined thereafter with increasing temperatures, water vapour deficits of the air and irradiation. Although there was no gradient in water deficit over the whole leaf, leaf conductances were lower and carbon losses higher in 4 to 5 years old leaf sections. The latter also showed substantially reduced CO 2 uptake capacity and quantum yield, In those leaf parts photoinhibition, estimated from the diurnal reduction in the ratio of dark adapted variable (F v ) to maximum fluorescence (F M ), was about 55% larger than in the young (≈ 1 year old) tissue. The mature mid-leaf tissue behaved intermediate. Inhibition of F V /F M was due to the reduction of F M , the dark adapted initial fluorescence (F 0 ) increased only slightly. q 1 , the slowly relaxing component of non-photochemical quenching, was only 26% higher in the older leaf parts. F 0 -quenching (q 0 ) was low and constant in the young tissue but increased when q 1 was very high in the old one. The sum of ql and qo was linearily correlated with the diurnal inhibition of F V /F M , Except in the morning hours carbon exchange followed any changes in leaf temperature, while variations in F V /F M and q 1 were due to the synergism of temperature and radiation.

Influence of Leaf Age, Soil Moisture, VPD and Time of Day on Leaf Conductance of Various Musa Genotypes in a Humid Forest-Moist Savanna Transition Site

Leaf age effects on the leaf conductance to water vapour diffusion of the adaxial and abaxial leaf surfaces were measured in the morning and in the afternoon on 17 different plantain and banana (Musa spp.) genotypes. The irradiance levels increased three-fold while leaf to air vapour pressure deficit levels increased two- to four-fold from morning to afternoon during the sampling period in a field site located in the humid forest-moist savanna transition zone of Nigeria. Conductance values were reduced in older, and senescing leaves relative to the young and mature leaves both in the morning and in the afternoon. Conductances were higher for the abaxial leaf surfaces than the adaxial surface and higher in the afternoon than in the morning, with some genotypic differences. Lower values of leaf conductance to water vapour in the afternoon under a short dry spell was sufficiently variable (P ⩾ 0·05) among the test genotypes to indicate potential adaptation to transient dry conditions. Differential and relative leaf conductance adjustments were noted among genotypes experiencing a short dry spell versus non-limiting soil moisture conditions. Significant genotypic differences were observed for leaf conductance among the 17 genotypes during the afternoon on the lower leaf surface of younger leaves. ABB cooking banana cultivars 'Fougamou' and 'Bluggoe' might be potentially promising cultivars for transient dry conditions while AAB plantain 'Bobby Tannap' and one of its hybrids TMPx 582-4 could be very sensitive to short dry spells according to this evaluation.

Senescence and protein degradation in leaf segments of young winter wheat: influence of leaf age

Leaf senescence in intact wheat plants can be strongly influenced by altered source/sink relations. Interactions with other plant parts are no longer possible in detached leaves and therefore differences in their senescence behaviour reflect the physiological status of the leaf before cutting. The net degradation of chlorophylls and of selected enzyme proteins (detected by SDS-PAGE and immunoblotting) was delayed in detached young leaves as compared to senescing or mature leaves excised from the same field-grown wheat plants. The physiological leaf age was therefore decisive for the velocity of artificial senescence. Net degradation rates of the enzymes investigated varied in detached leaves. The protein quantities of plastidial glutamine synthetase, phosphoribulokinase and phosphoglycolate phosphatase decreased more rapidly than those of ferredoxin-dependent glutamate synthase and nitrite reductase. Differences were also detected between two enzymes involved in the same metabolic pathway (photorespiratory carbon cycle) but located in different subcellular compartments: the plastidial enzyme phosphoglycolate phosphatase was lost more rapidly than glycolate oxidase (peroxisomal enzyme).