Nonstructural carbohydrate metabolism during leaf ageing in tobacco (Nicotiana tabacum)

Nonstructural carbohydrate status and activities of ADP-glucose pyrophosphorylase (EC 2.7.7.27, ADPG pyrophosphorylase) and sucrose phosphate synthase (EC 2.4.1.14, SPS) were determined during ageing of tobacco ( Nicotiana tabacum L., cvs KY 14 and Speight G28) leaves sampled from control plants and from plants that had the apical meristem and subsequent axillary growth removed (detopped plants). Over the 30-day period shoot growth increased much more for control compared to detopped plants, but the increase in root growth was similar for both treatments. Dry matter and leaf area of the individual leaf used for enzyme and metabolite analysis were constant over time for controls but increased 5-fold for detopped plants. Ageing of control leaves was indicated by a progressive loss of chlorophyll and ribulose 1, 5-bisphosphate carboxylase (EC 4.1.1.39, Rubisco) activity; loss of these components was diminished for detopped plants. In contrast to chlorophyll and Rubisco activity, activities of ADPG pyrophosphorylase and SPS remained relatively constant over time for controls. Thus, under normal ageing conditions, changes in activities of ADPG pyrophosphorylase and SPS were not closely associated with changes in the standard senescence indicators chlorophyll and Rubisco activity. The activities of ADPG pyrophosphorylase and SPS were enhanced, relative to controls, within 6 days after applying the detopping treatment and activities remained high for the duration of the 30-day period. Detopping also led to increased concentrations of starch and sucrose, but the increases were not well correlated with changes in enzyme activities. The data indicated that the leaves of detopped plants functioned as both source leaves, with enhanced ability to synthesize carbohydrate, and sink leaves, with enhanced growth. Therefore, activities of ADPG pyrophosphorylase and SPS were more responsive to changes within an individual leaf than to changes in whole plant growth.     

Physiology of maize II: Identification of physiological markers representative of the nitrogen status of maize (Zea mays) leaves during grain filling

To illustrate the development of the source-to-sink transition in maize leaves during the grain-filling period, an integrated physiological-agronomic approach is presented in this study. The evolution of physiological markers such as total leaf nitrogen (N), chlorophyll, soluble protein, amino acid and ammonium contents was monitored from silking to a period close to maturity in different leaf stages of three maize genotypes grown at high and low levels of N fertilization. In addition, the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH), two enzymes known to play a direct or an indirect role during leaf N remobilization, were measured. In the three genotypes examined, we found that a general decrease of most metabolic and enzyme markers occurred during leaf ageing and that this decrease was enhanced when plants were N starved. In contrast, such variations were not observed between different sections of a single leaf even at an advanced stage of leaf senescence. We found that there is a strong correlation between total N, chlorophyll, soluble protein and GS activity, which is not dependent upon the N fertilization level, which indicates the N status of the plant, either in a single leaf or during ageing. In contrast, ammonium, amino acids and GDH activity were not subject to such variations, thus suggesting that they are indicators of the metabolic activity of the whole plant in response to the level of N fertilization. The use of these markers to predict the N status of maize as a function of both plant development and N availability is discussed.     

Sequence of morphological and physiological events during natural ageing and senescence of a castor bean leaf: sieve tube occlusion and carbohydrate back-up precede chlorophyll degradation

The development of castor bean ( Ricinus communis L. var. sanguineus) leaves from bud break to abscission was studied to determine whether senescence of phloem precedes or follows chlorophyll degradation in the course of natural ageing of leaves. The castor bean leaf blade took 20 days for full expansion and its average life span was 60 days. From the day of full expansion on it suffered a substantial loss in N, a small loss in C, K and P and a gain in Ca, Mg and S. The content of soluble sugars increased with time, paralleled by a decrease of photosynthetic activity. Starch accumulated shortly before chlorophyll breakdown. The amino acid level in the leaves decreased steadily together with nitrate reductase and glutamine synthetase activity. Reactive oxygen species increased and oxidation-protecting compounds decreased during the life span of the leaves. Shortly after full leaf expansion an increasing number of sieve plates showed strong callose depositions when visualized by aniline blue method. At day 40 only half of the sieve tubes appeared functional. Chlorophyll breakdown followed these processes with a time lag of approximately 10 days. The sieve tube sap of ageing leaves had the same sucrose concentrations as young leaves, whereas amino acid concentrations decreased. High levels of reduced ascorbic acid and glutathione together with increasing levels of glutaredoxin indicated oxidative strain during senescence. We speculate that the gradual increase of reactive oxygen species during ageing together with the import of calcium ions lead to the stimulation of callose synthesis in plasmodesmata and sieve plates with the consequence of inhibition of phloem transport leading to carbohydrate back-up in the leaf blade. The latter may finally induce chlorophyll breakdown and, at the end, leaf abscission at the petiole base. Thus phloem blockage would precede and may be causal for chlorophyll degradation in leaf senescence.     

Decline of photosynthetic capacity with leaf age in relation to leaf longevities for five tropical canopy tree species

The effect of leaf aging on photosynthetic capacities was examined for upper canopy leaves of five tropical tree species in a seasonally dry forest in Panama. These species varied in mean leaf longevity between 174 and 315 d, and in maximum leaf life span between 304 and 679 d. The light-saturated CO2 exchange rates of leaves produced during the primary annual leaf flush measured at 7-8 mo of age were 33-65% of the rates measured at 1-2 mo of age for species with leaf life span of < 1 yr. The negative regression slopes of photosynthetic capacity against leaf age were steeper for species with shorter maximum leaf longevity. In all species, regression slopes were less steep than the slopes predicted by assuming a linear decline toward the maximum leaf age (20-80% of the predicted decline rate). Maximum oxygen evolution rates and leaf nitrogen content declined faster with age for species with shorter leaf life spans. Statistical significance of regression slopes of oxygen evolution rates against leaf age was strongest on a leaf mass basis (r = 0.49-0.87), followed by leaf nitrogen basis (r = 0.48-0.77), and weakest on a leaf area basis (r = 0.35-0.70).     

Metabolic Activity of Isolated Leaf Cells of Phaseolus vulgaris in Relation to Leaf Development

Mesophyll cells were isolated from primary leaves of 5- to 21-day Phaseolus vulgaris plants. The rate of photosynthesis and respiration, and RNA, protein, and lipid synthesis was determined for these cells. Appropriate ¹⁴C substrates and product purification procedures were used for each process prior to liquid scintillation counting. The size of the leaves increased about 5-fold between days 5 and 11, and then remained relatively constant. The greatest increase in size occurred between days 5 and 6. The age of the leaf from which the cells were isolated had a pronounced effect on the rate of all of these processes. The largest changes occurred during the period of leaf expansion (days 5-11). Initially the rate of RNA, protein, and lipid synthesis increased rapidly, maintained a maximum rate for only 1 day (day 6 or day 7), and then declined. The rate of photosynthesis increased more slowly reaching a maximum at day 9, remained relatively constant until day 15, and then declined. The rate of respiration decreased during the first 4 days to low level which was maintained throughout the experiment. The time course patterns of these biochemical processes in isolated cells were similar to those which have been reported for intact leaves. It seems that isolation of leaf cells does not modify their metabolic activity.     

Partial Restoration of the High Rate of Plastid Pigment Development and the Ultrastructure of Plastids in Detached Water-stressed Wheat Leaves

Detached etiolated wheat (Triticum aestivum L. cv. Chris) leaves accumulated plastid pigments at a high rate, developed chloroplasts with stacked thylakoids, and stored plastid starch when wetted on filter paper in light. A moderate water deficit of — 10 bars markedly reduced the accumulation of chlorophyll and carotenoids in the 8-day-old detached leaves during greening. δ-Aminolevulinic acid treatment of stressed leaf segments resulted in slightly increased pigment accumulations but benzyladenine application restored plastid pigment formation in stressed tissue to within 15% of the pigment content of the nonstressed detached leaves. The addition of δ-aminolevulinic acid to benzyladenine-treated stressed leaf segments improved both chlorophyll and carotenoid formation to nearly the amounts found in nonstressed leaf tissue. Stressed leaf sections developed plastids that were small, lacked starch, contained few thylakoids per granum, and possessed dilated thylakoids. Benzyladenine application to the stressed leaf segments did not restore normal plastid stacking but benzyladenine induced the formation of extended intergranal lamellae and stimulated pigment accumulations in both stressed and nonstressed detached leaves. Starch was absent in plastids of benzyladeninetreated leaf sections.     

Photosynthesis and Chlorophyll Fluorescence Characteristics in Relationship to Changes in Pigment and Element Composition of Leaves of Platanus occidentalis L. during Autumnal Leaf Senescence

The loss of chlorophyll and total leaf nitrogen during autumnal senescence of leaves from the deciduous tree Platanus occidentalis L. was accompanied by a marked decline in the photosynthetic capacity of O₂ evolution on a leaf area basis. When expressed on a chlorophyll basis, however, the capacity for light-and CO₂-saturated O₂ evolution did not decline, but rather increased as leaf chlorophyll content decreased. The photon yield of O₂ evolution in white light (400-700 nanometers) declined markedly with decreases in leaf chlorophyll content below 150 milligrams of chlorophyll per square meter on both an incident and an absorbed basis, due largely to the absorption of light by nonphotosynthetic pigments which were not degraded as rapidly as the chlorophylls. Photon yields measured in, and corrected for the absorptance of, red light (630-700 nanometers) exhibited little change with the loss of chlorophyll. Furthermore, PSII photochemical efficiency, as determined from chlorophyll fluorescence, remained high, and the chlorophyll a/b ratio exhibited no decline except in leaves with extremely low chlorophyll contents. These data indicate that the efficiency for photochemical energy conversion of the remaining functional components was maintained at a high level during the natural course of autumnal senescence, and are consistent with previous studies which have characterized leaf senescence as being a controlled process. The loss of chlorophyll during senescence was also accompanied by a decline in fluorescence emanating from PSI, whereas there was little change in PSII fluorescence (measured at 77 Kelvin), presumably due to decreased reabsorption of PSII fluorescence by chlorophyll. Nitrogen was the only element examined to exhibit a decline with senescence on a dry weight basis. However, on a leaf area basis, all elements (C, Ca, K, Mg, N, P, S) declined in senescent leaves, although the contents of sulfur and calcium, which are not easily retranslocated, decreased to the smallest extent.     

Effect of transient accumulation of anthocyanin on leaf development and photoprotection of Fagopyrum dibotrys mutant

Changes in pigments contents, leaf area, leaf dry mass per unit area (LMA), photosynthetic rate and chlorophyll a fluorescence were investigated in developing leaves of Fagopyrum dibotrys Hara. mutant. Anthocyanins transiently accumulate below the upper epidermis during leaf ontogeny of this mutant. Red leaves possessed lower Chl content, LMA, photosynthetic rate and apparent carboxylation efficiency than green leaves. However, content of anthocyanins declined and above mentioned parameters increased during further leaf development. In both red and green leaves, chronic photoinhibition did not take place according to variable to maximum chlorophyll fluorescence ratio (F_v/F_m). Red leaves had higher non-photochemical quenching (NPQ) and higher PS 2 efficiency.     

Mechanism of Senescence Induction by Silicone Oil

The physiological basis for senescence symptoms induced by spraying attached primary leaves of bean plant (Phaseolus vulgaris L. cv. Brittlewax) with silicone oil emulsions was investigated. It was found that chlorophyll levels declined significantly between 24 and 48 h after spraying, whereas neither protein levels nor respiration rates were affected over a 7-day period. Rates of photosynthesis and reducing sugar levels in silicone-sprayed leaves were however significantly reduced after 1 and 24 h respectively. These responses were obtained using plants grown under low stress controlled environment conditions. By contrast, leaves on greenhouse plants did not senesce in response to silicone sprays. A possible mechanism of silicone oil action based on selective leaf penetration and inhibition of photosynthesis is postulated.     

Development of Photochemical Activity and the Appearance of the High Potential Form of Cytochrome b-559 in Greening Barley Seedlings

The development of photochemical activity during the greening of dark-grown barley seedlings (Hordeum vulgare L. cv. Svalöfs Bonus) was studied in relation to the formation of the high potential form of cytochrome b-559 (cytochrome b-559_HP). Photosynthetic oxygen evolution from leaves was detected at 30 minutes of illumination. The rate of oxygen evolution per gram fresh weight of leaf was as high at 2 to 2.5 hours of greening as at 24 hours or in fully greened leaves. On a chlorophyll basis, the photosynthetic rate at 90 minutes of greening was 80-fold greater than the rate at 45 hours. It is concluded that the majority of photosynthetic units are functional at an early stage of greening, and that chlorophyll synthesis during greening serves to increase the size of the units.     

土壤pH值对烤烟叶片生理生化特性的影响

烟草生长初期,超氧化物歧化酶(SOD)活性及丙二醛(MDA)含量与pH增长呈正相关,而过氧化氢酶(CAT)和过氧化物酶(POD)活性则随着pH的增加而下降,pH值6.5和7.5时叶绿素含量和净光合速率(Pn)较高,旺长期达到高峰;生长后期,各处理的MDA含量和POD活性最高,SOD、CAT活性最低.各pH值处理的叶片中,叶绿素含量、Pn下降,比叶重达到高峰,但pH 8.5下的烟叶中叶绿素含量高,Pn大,比叶重较小.pH 6.5和7.5下的烟叶中蛋白质和可溶性糖总体含量高于其它pH的.烟碱含量在pH 5.5时最高,pH 8.5时最低.     

Enzymes of Ammonia Assimilation, Photosynthesis, and Respiration in Alfalfa Leaves of Different Ages

The activities of enzymes involved in ammonia metabolism ferredoxin-dependent glutamate synthase (Fd-GOGAT), glutamine synthetase (GS) and glutamate dehydrogenase (GDH), the rates of photosynthetic oxygen evolution, dark respiration, and the activity of RuBP carboxylase (RuBPC) were determined in alfalfa (Medicago sativa L.) leaves taken from the apex (apical leaves), from the second to the fourth internode (mature leaves) and from the bottom of the canopy (basal leaves). Photosynthetic rate and the activities of RuBPC, GS and Fd-GOGAT showed their maximum in the mature leaves. The respiration rate together with amino acid and ammonium contents decreased with leaf age, whereas the opposite was true for GDH activity. Basal leaves still maintained substantial levels of chlorophylls, GS and Fd-GOGAT activities and oxygen evolution rate, thus suggesting that photosynthesis has some role in the reassimilation of the nitrogen liberated during protein degradation. This revised version was published online in June 2006 with corrections to the Cover Date.     

The distribution of NADPH-protochlorophyllide oxidoreductase in relation to chlorophyll accumulation along the barley leaf gradient

The possible regulatory role of NADPH-protochlorophyllide oxidoreductase for chlorophyll accumulation has been investigated in barley plants. Within the primary leaf of etiolated plants the different maturation stages of etioplasts are found in a linear series with the youngest in cells near the base and the oldest in cells near the tip. This distribution of different plastid forms is paralleled by drastic differences in the NADPH-protochlorophyllide-oxidoreductase content of the plastids and their capacity to accumulate chlorophyll during illumination. The amount of enzyme and the rate of chlorophyll accumulation are highest in the mature etioplast in the tip of the leaf and both decline rapidly with decreasing age of the leaf tissue, being almost undetectable in the leaf base. The translatable mRNA coding for the enzyme shows a different distribution pattern within the leaf. The highest concentration is found in the middle part of the leaf while in the top part only traces of this mRNA are detectable. It is concluded that during leaf development the enzyme is synthesized rapidly only during a limited time period and that it is stored subsequently in the mature etioplast as a stable protein. The close correlation between the distribution of the enzyme within the barley leaf and that of the potential to accumulate chlorophyll during illumination would favour a control of chlorophyll accumulation by the amount of NADPH-protochlorophyllide oxidoreductase. Dark-grown plants which were exposed to far-red light were used to test this possibility. The far-red-absorbing form of phytochrome (P_fr) has an inverse effect on the kinetics of chlorophyll accumulation and the enzyme concentration. Our results indicate that the rate of chlorophyll accumulation in barley is not determined by the level of NADPH-protochlorophyllide oxidoreductase present in the leaves.     

Development of chlorophyll and hill activity

A sensitive luminometer is used to measure directly the low rates of oxygen evolution during greening of etiolated barley (Hordeum vulgare L. var. Wong) leaves. Oxygen evolution is measured in leaf segments infiltrated with p-benzoquinone. When illuminated, these leaves do not produce significant amounts of oxygen until the end of the lag phase of chlorophyll synthesis. Chlorophyll is increased by feeding δ-aminolevulinic acid to leaves in the lag phase, but this does not cause an earlier appearance of photosynthesis. Chloramphenicol, and to a lesser extent cycloheximide, when fed to leaves together with δ-aminolevulinic acid, strongly inhibit the development of oxygen evolution in the light while only slightly inhibiting chlorophyll synthesis. The ability to evolve oxygen develops to only a slight extent in darkness, even in the presence of high levels of chlorophyll.     

墨兰幼叶和成熟叶不同部位叶绿体超微结构和光合作用

墨兰试管苗植株成熟叶片叶绿体基粒较发达,类囊本膜垛叠较紧密。幼叶叶绿体中少有亲锇颗粒,成熟叶的叶绿体中往往既有亲锇颗粒又有淀粉粒。幼叶中基粒数目比成熟叶的少,叶绿体也比成熟叶的小。幼叶的光合放氧速率比成熟叶的低。幼叶中叶尖部叶绿体最大而叶基部最小,但叶尖部的光合放氧速率比叶基部小。成熟叶中叶绿体大小及光合放氧速率区别不明显。通过对各部位叶绿素含量的测定发现,叶绿素含量与光合放氧速率之间没有正相关性     

Carbonic anhydrase in leaves during radish plant ontogeny and glucose effect

Radish (Raphanus sativus L.) plants were grown in a greenhouse in soil at natural illumination, temperature, and CO₂ concentration. A relationship between the activity of soluble carbonic anhydrase (sCA) and the content of soluble carbohydrates (sCH) was investigated depending on leaf position on the stem during plant development. Indices characterizing leaf ageing during the phase of vegetative growth (PVG) (in lower leaves as compared to upper ones) were a decrease in the rate of photosynthetic release of O₂, photosynthetic efficiency, quantum efficiency of photosystem II, and the content of chlorophylls a and b. During PVG and the phase of flower bud formation, the activity of sCA and the contents of sCH, soluble protein, and Glu were the greatest in young (topmost) leaves and declined in the leaves of middle and lower storeys. From the top to the middle leaves, a dependence of sCA activity on the content of Glu or other sCH (without Glu) was direct, whereas, from the middle and the lower leaves, it became inversed. During leaf ageing in vegetatively growing plants and in the phase of budding, the relation between sCA and a relative content of Glu (percent of the rest sCH) was similar to that described above and yielded broken lines, and, during flowering, an inverse relation was observed in the leaves of all three storeys with a low content content of Glu and a low sCA activity. In order to study a dependence of sCA activity on the levels of sCH and Glu during PVG, one half of the leaf was incubated in a thin layer of water at a light schedule: by 12 h of night/day/night + 3-h-long illumination (control material). Within the period of active growth of the hypocotyl up to the storage root formation, the sCA activity and the content of sCH in the leaves incubated in water (control) increased. During a later PVG, both characteristics declined with sCA activity reduced stronger. The rate of the photosynthetic O₂ release changed in accordance with the changes in sCA activity. Incubation of the other half of the same leaf in 20 mM Glu during early PVG brought about a considerable increase in sCA activity as compared with control material. During a later PVG and at a much greater Glu concentration (330 mM), its content in the leaves increased manifold; however, there were no significant changes in the activity of sCA, the content of protein or chlorophyll. It was concluded that the activity of sCA in the radish leaves during PVG was not regulated by the absolute content of sCH or Glu in the leaves but depended on endogenous factors associated with plant development.     

Leaf development in Lolium temulentum: plastid membrane polypeptides in relation to assembly of the photosynthetic apparatus and leaf growth

Cellular and compositional changes related to tissue growth and assembly of the photosynthetic apparatus were established with reference to the developmental gradient along the expanding fourth leaf of Lolium temulentum L. Ba 3081. The number of cells and the fresh weight per leaf segment fell with increasing cell age (distance from the leaf base). Components of the photosynthetic apparatus increased in concentration towards the more mature part of the leaf. Appreciable levels of chlorophyll and carotenoid could be detected in basal tissue enclosed in the sheaths of previous leaves prior to emergence into full light. The distributions of NADPH-protochlorophyllide oxidoreductase (PCR. EC 1.6.99.1) and cytochrome f along the age gradient were visualized by Western blotting. Leaf base tissue contained two forms of PCR, 41 and 39 kDa, the smaller of which diminished with increasing cell age and proximity to full light. Cytochrome f comprised a 52 kDa species, which also declined with distance from the base, and a group of polypeptides at around 30–33 kDa which greatly intensified with tissue maturity. The significance of multiple forms of plastid proteins and the role of the light gradient penetrating the leaf sheath in regulating growth and plastid assembly processes are discussed.     

The anti-photooxidation of anthocyanins-rich leaves of a purple rice cultivar

In the leaf of rice (Oryza sativa L.) cultivar Yunnan purple rice,the anthocyanins with an obvious absorption peak at 530nm were distributed in the cells of upper and lower epidermis,bulliform tissue and bristle. The maximal photosynthetic oxygen evolution rate and chlorophyll content in flag leaves were 28% and 23%,respectively,more than the common green leaf rice cultivar Chijiaoru-anzhan. Higher chlorophyll content is probably one of the physiological adaptations for enhancing light harvesting capacity of the antenna in photosystems in this cyanic leaves species. Upon the photooxidation of leaf segments mediated by methyl viologen in weak light for 3 days,the distinct bleaching of anthocyanins in purple rice was associated with the reduction of scavenging ability to DPPH· free radical ability and the increase in membrane leakage rate. But almost no changes in contents of flavonoids and total phenolics were observed. Chlorophyll fluorescence parameters Fv/Fo,qP and φPSⅡ decreased with the increase in NPQ and DES of xanthophylls cycle after photooxidation treatment. Green rice leaves showed more decrease in DPPH· scavenging rate and more increase in cell membrane leakage rate but showed a trace of anthocyanins during photooxidation. It is sug-gested that anthocyanin may be a beneficial and primary antioxidant in sun cyanic rice leaves against oxidative stress induced by environmental adversity. And photooxidation could induce different changing patterns of anthocyanins between the tested purple and green rice leaves.