Wheat leaf photosynthesis loss due to leaf rust, with respect to lesion development and leaf nitrogen status

In wheat (Triticum aestivum cv. Soissons) plants grown under three different fertilisation treatments, we quantified the effect of leaf rust (Puccinia triticina) on flag leaf photosynthesis during the whole sporulation period. Bastiaans' model: Y = (1 - x)beta was used to characterize the relationship between relative leaf photosynthesis (Y) and disease severity (x). The evolution of the different types of symptoms induced by the pathogen (sporulating, chlorotic and necrosed tissues) was evaluated using image analysis. The beta-values varied from 2 to 11, 1.4-2, and 0.8-1 during the sporulation period, when considering the proportion of sporulating, sporulating + necrotic, and total diseased area, respectively. Leaf nitrogen (N) content did not change the effect of the disease on host photosynthesis. We concluded that leaf rust has no global effect on the photosynthesis of the symptomless parts of the leaves and that the large range in the quantification of leaf rust effect on the host, which is found in the literature, can be accounted for by considering the different symptom types. We discuss how our results could improve disease assessments and damage prediction in a wheat crop.     

Photosynthesis of Eucalyptus globulus with Mycosphaerella leaf disease

Mycosphaerella leaf disease (MLD) is a major cause of foliage damage in Eucalyptus globulus plantations. Our study is the first to describe the physiological effects of MLD on E. globulus leaves. It involved measurements on both field and potted plants. Changes in photosynthetic parameters in response to MLD were quantified in a study using gas exchange techniques. There was a negative linear relationship between light-saturated photosynthesis (A(max)) and leaf-level damage from MLD. Reductions in A(max) were proportionally greater than might be expected from the reduction in green leaf area as a result of the disease, indicating that asymptomatic tissue also was affected by MLD. The reductions in A(max) were not related to increases in stomatal resistance, but were a result of reduced activity of ribulose bisphosphate carboxylase (Rubisco) and changes in the capacity for ribulose bisphosphate (RuBP) regeneration. Changes in mesophyll resistance to CO2 were also implicated. The effect of MLD was similar at different sites and irrespective of tree-level infection, suggesting a general leaf-level response of E. globulus to MLD.     

Patterns of leaf size and morphology in relation to shoot length in Tsuga canadensis

Summary Pattern of change in leaf character was assessed along the length and around the circumference of Tsuga canadensis (L.) Carr. shoots of different length classes. Leaf size decreased, and number of leaves per unit length of shoot increased, with decrease in shoot length. Acropetally along the shoots, lamina length and width decreased, relative petiole length increased, apices became more pointed, and leaf margins bore more teeth. Around the shoot, from upper to side, and to lower surfaces, leaf size and number of marginal teeth in the proximal halves of leaves increased. These patterns were related both to production of preformed versus neoformed leaves, though their separation was indistinct, and to secondary orientation of leaves by twisting in their petiolar regions into two major bi-lateral ranks. An additional minor rank occurred along the upper surfaces of the shoots where secondary orientation of the leaves was minimal. Surface features of leaves did not differ in any obvious manner. Leaves on sylleptic shoots, which by definition were all neoformed, exhibited similar patterns, but were generally smaller than those on their parent shoots.     

Sensitivity of leaf size and shape to climate within Acer rubrum and Quercus kelloggii

* Variation in the size and shape (physiognomy) of leaves has long been correlated to climate, and paleobotanists have used these correlations to reconstruct paleo-climate. Most studies focus on site-level means of largely nonoverlapping species sets. The sensitivity of leaf shape to climate within species is poorly known, which limits our general understanding of leaf-climate relationships and the value of intraspecific patterns for paleoclimate reconstructions. * The leaf physiognomy of two species whose native North American ranges span large climatic gradients (Acer rubrum and Quercus kelloggii) was quantified and correlated to mean annual temperature (MAT). Quercus kelloggii was sampled across a wide elevation range, but A. rubrum was sampled in strictly lowland areas. * Within A. rubrum, leaf shape correlates with MAT in a manner that is largely consistent with previous site-level studies; leaves from cold climates are toothier and more highly dissected. By contrast, Q. kelloggii is largely insensitive to MAT; instead, windy conditions with ample plant-available water may explain the preponderance of small teeth at high elevation sites, independent of MAT. * This study highlights the strong correspondence between leaf form and climate within some species, and demonstrates that intraspecific patterns may contribute useful information towards reconstructing paleoclimate.     

Roles of the fructans from leaf sheaths and from the elongating leaf bases in the regrowth following defoliation of Lolium perenne L

The study of carbohydrate metabolism in perennial ryegrass (Lolium perenne L. cv. Bravo) during the first 48 h of regrowth showed that fructans from elongating leaf bases were hydrolysed first whereas fructans in mature leaf sheaths were degraded only after a lag of 1.5 h. In elongating leaf bases, the decline in fructan content occurred not only in the differentiation zone (30–60 mm from the leaf base), but also in the growth zone. Unlike other soluble carbohydrates, the net deposition rate of fructose remained positive and even rose during the first day following defoliation. The activity of fructan exohydrolase (FEH; EC 3.2.1.80) was maximal in the differentiation zone before defoliation and increased in all segments, but peaked in the growth zone after defoliation. These data strongly indicate that fructans stored in the leaf growth zone were hydrolysed and recycled in that zone to sustain the refoliation immediately after defoliation. Despite the depletion of carbohydrates, leaves of defoliated plants elongated at a significantly higher rate than those of undefoliated plants, during the first 10 h of regrowth. This can be partly attributed to the transient increase in water and nitrate deposition rate. The results are discussed in relation to defoliation tolerance. Received: 16 June 2000 / Accepted: 17 October 2000     

玉米SSR连锁图谱构建及叶面积的QTL定位

叶片是玉米进行光合作用的主要器官,叶面积的大小(尤其是穗三叶面积)对于玉米干物质的积累及产量形成起着至关重要的作用。研究玉米叶面积的遗传基础对于指导玉米高产育种具有理论意义。文章以两个叶面积差异显著的亲本478×武312为基础材料所构建的218个F8代的重组自交系为作图群体,构建了一张包含184个SSR标记的遗传连锁图谱,图谱总长度为2084.1cM,平均图距为11.3cM。通过两年的田间试验对玉米叶面积(穗三叶)进行了QTL定位分析。两年共定位到7个和叶面积相关的QTL位点,2006年定位到4个QTL位点;2007年定位到3个QTL位点。在第2染色体umc1542-umc1518标记区间发现一个主效QTL位点,该位点可以在两年同时检测到,两年分别解释12.5%和17.3%的表型变异。该位点能稳定地检测到且具有较大的贡献率,可能会在玉米叶面积分子标记辅助选择上有所应用。     

Uptake,accumulation and metabolism of auxins in tobacco leaf protoplasts

Uptake and metabolism of exogenous naphthalene-1-acetic acid (NAA) and indole-3-acetic acid (IAA) have been studied in tobacco (Nicotiana tabacum L. cv. Xanthi) mesophyll protoplasts. Both auxins entered protoplasts by diffusion under the action of the transmembrane pH gradient without any detectable participation of an influx carrier. Molecules were accumulated by an anion-trapping mechanism and most of them were metabolized within hours, essentially as glucose-ester and amino-acid conjugates. Protoplasts were equipped with a functional auxin-efflux carrier as evidenced by the inhibitory effect of naphthylphtalamic acid on IAA efflux. Basically, similar mechanisms of NAA and IAA uptake occurred in protoplasts. However, the two auxins differed in their levels of accumulation, due to different membrane-transport characteristics, and the nature of the metabolites produced. This shows the need to estimate the accumulation and the metabolism of auxins when analyzing their effects in a given cell system. The internal auxin concentration could be modulated by changing the transmembrane pH gradient, giving an interesting perspective for discriminating between the effects of intra- and extracellular auxin on physiological processes.Abbreviations BA benzoic acid - C_i/C_e accumulation ratio of auxin - IAAasp N-[3-indolylacetyl]-dl-aspartic acid - NAA naphthalene-1-acetic acid - NAAasp N-[1-naphthylacetyl]-l-aspartic acid - NPA N-1-naphthylphthalamic acid The authors thank Dr. M. Caboche (I.N.R.A, Versailles, France) for his generous gifts of some amide derivatives of 1-NAA, Mr. P. Varennes and Dr. B. Das (I.C.S.N., C.N.R.S., Gif-sur-Yvette, France) for recording and interpreting the mass spectra of NAA glucose ester, and Prof. P. Manigault (Institut des Sciences Végétales, Gif-sur-Yvette) for microscopy measurements of protoplast dimensions. This work was supported by funds from the C.N.R.S, I.N.R.A, and E.E.C.     

Phytochrome-mediated swelling of etiolated leaf protoplasts and its possible biological significance

Summary Red light, mediated by the photoreceptor phytochrome, induces maize leaf unrolling as well as leaf expansion. Protoplasts prepared from maize leaves still in the rolled condition swell in a red-far red photoreversible manner indicating that phytochrome mediates this phenomenon. To determine if protoplast swelling is related to leaf unrolling, leaf expansion, or both, we compared red-light induced swelling of protoplasts from rolled maize leaves to protoplasts prepared from tissues that are known to grow in response to light but do not unroll. We also compared the swelling response of protoplasts from rolled vs. unrolled leaves. In all cases, we found that swelling correlated with the unrolling response and not leaf expansion.     

Polygalacturonase expression during leaf abscission of normal and transgenic tomato plants

Polygalacturonase (PG, EC 3.2.1.15), an enzyme commonly found in ripening fruit, has also been shown to be associated with abscission. A zone-specific rise in PG activity accompanies the abscission of both leaves and flowers of tomato (Lycopersicon esculentum Mill.) plants. Studies of transgenic plants expressing an antisense RNA for fruit PG indicate that although the enzyme activity in transgenic fruit is < 1 % of that in untransformed fruit, the PG activity in the leaf abscission zone increases during separation to a similar value to that in untransformed plants. The timing and rate of leaf abscission in transgenic plants are unaffected by the introduction of the antisense gene. A polyclonal antibody raised against tomato fruit PG does not recognise the leaf abscission protein. Furthermore a complementary DNA (cDNA) clone (pTOM6), which has been demonstrated to code for fruit PG, does not hybridise to mRNA isolated from the abscission-zone region of tomato leaves. These results indicate that the PG protein in abscission zones of tomato is different from that in the fruit, and that the gene coding for this protein may also be different.Abbreviation PG polygalacturonase The authors of this paper are grateful to David Jackson of the John Innes Institute, Norwich, UK for his assistance with the in-situ hybridisation work. This research was supported by an Agricultural and Food Research Council Post-Doctoral award to J.E.T., and by a grant to D.G. from the Science and Engineering Research Council Biotechnology Directorate in association with ICI seeds. The work was carried out under Ministry of Agriculture, Food and Fisheries licences.     

Protein degradation and nitrogen remobilization during leaf senescence

Leaf senescence, a type of programmed cell death, is a complex and highly regulated process that involves the degradation of macromolecules, including proteins, nucleic acids, and lipids. Nutrients, especially nitrogen, are re-mobilized from senescing leaves to newly developing tissues or reserve organs. Our review focuses on three pathways for protein breakdown and the resorption of N during this process: the ubiquitin/proteosome system, the chloroplast degradation pathway, and the vacuolar and autophagic pathway. We propose that two relative biochemical cycles exist for amino acid recycling and N-export — the GS/GOGAT cycle and the PPDK-GS/GOGAT cycle.     

Enhancement of rice canopy carbon gain by elevated CO(2) is sensitive to growth stage and leaf nitrogen concentration

Increasing our understanding of the factors regulating seasonal changes in rice canopy carbon gain (C(gain): daily net photosynthesis -- night respiration) under elevated CO(2) concentrations ([CO(2)]) will reduce our uncertainty in predicting future rice yields and assist in the development of adaptation strategies. In this study we measured CO(2) exchange from rice (Oryza sativa) canopies grown at c. 360 and 690 micromol mol(-1)[CO(2)] in growth chambers continuously over three growing seasons. Stimulation of C(gain) by elevated [CO(2)] was 22-79% during vegetative growth, but decreased to between -12 and 5% after the grain-filling stage, resulting in a 7-22% net enhancement for the whole season. The decreased stimulation of C(gain) resulted mainly from decreased canopy net photosynthesis and partially from increased respiration. A decrease in canopy photosynthetic capacity was noted where leaf nitrogen (N) decreased. The effect of elevated [CO(2)] on leaf area was generally small, but most dramatic under ample N conditions; this increased the stimulation of whole-season C(gain). These results suggest that a decrease in C(gain) enhancement following elevated CO(2) levels is difficult to avoid, but that careful management of nitrogen levels can alter the whole-season C(gain) enhancement.     

The effect of temperature on C(4)-type leaf photosynthesis parameters

C(4)-type photosynthesis is known to vary with growth and measurement temperatures. In an attempt to quantify its variability with measurement temperature, the photosynthetic parameters - the maximum catalytic rate of the enzyme ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) (V(cmax)), the maximum catalytic rate of the enzyme phosphoenolpyruvate carboxylase (PEPC) (V(pmax)) and the maximum electron transport rate (J(max)) - were examined. Maize plants were grown in climatic-controlled phytotrons, and the curves of net photosynthesis (A(n)) versus intercellular air space CO(2) concentrations (C(i)), and A(n) versus photosynthetic photon flux density (PPFD) were determined over a temperature range of 15-40 degrees C. Values of V(cmax), V(pmax) and J(max) were computed by inversion of the von Caemmerer & Furbank photosynthesis model. Values of V(pmax) and J(max) obtained at 25 degrees C conform to values found in the literature. Parameters for an Arrhenius equation that best fits the calculated values of V(cmax), V(pmax) and J(max) are then proposed. These parameters should be further tested with C(4) plants for validation. Other model key parameters such as the mesophyll cell conductance to CO(2) (g(i)), the bundle sheath cells conductance to CO(2) (g(bs)) and Michaelis-Menten constants for CO(2) and O(2) (K(c), K(p) and K(o)) also vary with temperature and should be better parameterized.     

Research progress on leaf mass per area

Leaf mass per area (LMA) is a composite structural parameter as well as a basic leaf functional trait in the leaf economics spectrum (LES). It is not only closely related to many physiological responses of plants, but also can measure the investment of dry mass per unit of light-intercepting leaf area. LMA is considered an important indicator of plant ecological strategies and has been studied widely in plant ecology, agronomy, forestry, and plant physiology. This paper elucidates the structural analysis and computational methods of LMA at the organizational scales of whole leaf, tissues and cells, examines the influence of LMA on photosynthesis, and discusses the inherent differences in LMA and the responses of LMA to environmental stresses (temperature, water and light), aiming for clarifying research frameworks and methods in studies of LMA and providing guidance on future research.     

The effect of gibberellic acid on the response of leaf extension to low temperature

The effect of cooling on leaf extension rate (LER) and on relative elemental growth rate (REGR) was measured in both gibberellic acid (GA)-responsive dwarf barley and in the same barley variety treated with GA. Seedlings were maintained at 20 degrees C while their leaf extension zone (LEZ) temperature was reduced either in steps to -6 degrees C in short-term cooling experiments, or to 10 degrees C for 48 h in long-term cooling experiments. Short-term cooling resulted in a biphasic response in LER, with a clear inflection point identified. Below this point, the activation energy for leaf extension becomes higher. The short-term response of LER to cooling was altered by the application of GA, which resulted in a lower base temperature (Tb), inflection point temperature and activation energy for leaf extension. Both GA-treated and untreated seedlings were less sensitive to cooling maintained for a prolonged period, with LER making a partial recover over the initial 5 h. Although long-term cooling reduced maximum REGR, it resulted in a longer LEZ and an increase in the length of mature interstomatal cells in GA-treated and untreated seedlings. These changes in overall physiology appear to enhance the ability of the leaves to continue expansion at suboptimal temperatures. In both GA-treated and cold-acclimated tissue, the occurrence of a longer LEZ was associated with a lower temperature sensitivity in LER.     

Identification of peptidases in Nicotiana tabacum leaf intercellular fluid

Peptidases in the extracellular space might affect the integrity of recombinant proteins expressed in, and secreted from, plant cells. To identify extracellular peptidases, we recovered the leaf intercellular fluid from Nicotiana tabacum plants by an infiltration-centrifugation method. The activity of various peptidases was detected by an in vitro assay in the presence of specific inhibitors, using BSA and human serum gamma-globulin as substrates. Peptidases were detected by 1- and 2-D zymography in a polyacrylamide gel containing gelatin as substrate. Proteolytic activity was observed over a wide range of molecular masses equal to, or higher than, 45 kDa. To identify the peptidases, the extracellular proteins were digested with trypsin and analyzed by LC and MS. Seventeen peptides showing identity or similarity to predicted plant aspartic, cysteine, and serine peptidases have been identified. The extracellular localization of a cysteine peptidase aleurain homolog was also shown.     

Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)

This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO₂ assimilation (A_l) and total nitrogen content (N_l) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO₂ partial pressure (p_a) at saturating photosynthetic photon flux density (I about 1000 μ mol m ^{? 2} s ^{? 1}) and (ii) to saturating CO₂ partial pressure (p_a about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20–38 °C). A biochemical model of leaf photosynthesis relating A_l to intercellular CO₂ partial pressure (p_i) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (V_lm) and the maximum rate of electron transport (J_m). The results indicated that rose leaves growing at the top of the canopy had higher values of J_m and V_lm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, N_l, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non‐photosynthetic nitrogen, N_b, varied from 76 mmol_N m ^{? 2}_leaf (layer 1) to 60 mmol_N m ^{? 2}_leaf (layer 4), representing a large fraction of N_l (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (N_p = N_l–N_b) and I profiles supports the hypothesis that rose leaves acclimate to the time‐integrated absorbed I. The relationships between I and N_p, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer.     

Spatio-temporal leaf growth patterns of Arabidopsis thaliana and evidence for sugar control of the diel leaf growth cycle

Leaf growth dynamics are driven by diel rhythms. The analysis of spatio-temporal leaf growth patterns in Arabidopsis thaliana wild type and mutants of interest is a promising approach to elucidate molecular mechanisms controlling growth. The diel availability of carbohydrates is thought to affect diel growth. A digital image sequence processing (DISP)-based noninvasive technique for visualizing and quantifying highly resolved spatio-temporal leaf growth was adapted for the model plant A. thaliana. Diel growth patterns were analysed for the wild type and for a mutant with altered diel carbohydrate metabolism. A. thaliana leaves showed highest relative growth rates (RGRs) at dawn and lowest RGRs at the beginning of the night. Along the lamina, a clear basipetal gradient of growth rate distribution was found, similar to that in many other dicotyledonous species. The starch-free 1 (stf1) mutant revealed changed temporal growth patterns with reduced nocturnal, and increased afternoon, growth activity. The established DISP technique is presented as a valuable tool to detect altered temporal growth patterns in A. thaliana mutants. Endogenous changes in the diel carbohydrate availability of the starch-free mutant clearly affected its diel growth rhythms.     

Ultrastructural analysis of leaf trichome plasmodesmata reveals major differences from mesophyll plasmodesmata

Functional studies on molecular transport through plasmodesmata in leaf mesophyll and trichome cells revealed significant differences in their basal size-exclusion limits and their response to microinjected tobacco mosaic virus movement protein (E. Waigmann et al., 1994, Proc. Natl. Acad. Sci. USA 91: 1433–1437; E. Waigmann and P. Zambryski, 1995, Plant Cell 7: 2069–2079). To address the basis for these functional differences, Nicotiana clevelandii trichome and mesophyll plasmodesmata were compared ultrastructurally. Trichome plasmodesmata increase in ultrastructural complexity from the tip to the base cell. Their neck regions, thought to control molecular traffic through plasmodesmata, are clearly distinct from necks of mesophyll plasmodesmata. In contrast to the electron-dense desmotubular area in mesophyll plasmodesmata, trichome plasmodesmata contain an electron-translucent circle in their center, surrounded by an electron-dense ring. This latter ring is connected to the inner leaflet of the plasma membrane by multiple spokes or filaments. Two monoclonal antibodies raised against a maize plasmodesmal protein preparation (A. Turner et al., 1994, J Cell Sci. 107: 3351–3361) interact with both trichome and mesophyll N. clevelandii plasmodesmata. Based on the localization pattern and the high degree of cross-reactivity, both antibodies likely recognize a conserved structural component of plasmodesmata, and may be useful to mark plasmodesma in a variety of plants and tissues. Received: 24 January 1997 / Accepted: 3 March 1997