Onset of sheath extension and duration of lamina extension are major determinants of the response of maize lamina length to plant density

BACKGROUND AND AIMS: Plants regulate their architecture strongly in response to density, and there is evidence that this involves changes in the duration of leaf extension. This questions the approximation, central in crop models, that development follows a fixed thermal time schedule. The aim of this research is to investigate, using maize as a model, how the kinetics of extension of grass leaves change with density, and to propose directions for inclusion of this regulation in plant models. METHODS: Periodic dissection of plants allowed the establishment of the kinetics of lamina and sheath extension for two contrasting sowing densities. The temperature of the growing zone was measured with thermocouples. Two-phase (exponential plus linear) models were fitted to the data, allowing analysis of the timing of the phase changes of extension, and the extension rate of sheaths and blades during both phases. KEY RESULTS: The duration of lamina extension dictated the variation in lamina length between treatments. The lower phytomers were longer at high density, with delayed onset of sheath extension allowing more time for the lamina to extend. In the upper phytomers--which were shorter at high density--the laminae had a lower relative extension rate (RER) in the exponential phase and delayed onset of linear extension, and less time available for extension since early sheath extension was not delayed. CONCLUSIONS: The relative timing of the onset of fast extension of the lamina with that of sheath development is the main determinant of the response of lamina length to density. Evidence is presented that the contrasting behaviour of lower and upper phytomers is related to differing regulation of sheath ontogeny before and after panicle initiation. A conceptual model is proposed to explain how the observed asynchrony between lamina and sheath development is regulated.     

Maximum likelihood inference and bootstrap methods for plant organ growth via multi-phase kinetic models and their application to maize

* BACKGROUND AND AIMS: Fitting the parameters of models of plant organ growth is a means to investigate how environmental conditions affect plant architecture. The aim of this article is to evaluate some non-linear methods for fitting the parameters of multi-phase models of the kinetics of extension of plant organs such as laminae, sheaths and internodes. * METHODS: A set of computational procedures was developed allowing parameter-fitting of multi-phase models, using the maximum likelihood criterion, in which phases are identified with reference to ontogenic processes. Two bootstrap methods were compared to assess the precision of the estimates of fitted parameters, and of functions of these parameters such as the final leaf length, and the duration and rate of the rapid extension phase. Methods were applied to an experimental dataset, representing the kinetics of laminae, sheaths and internodes along the maize shoot, for two contrasting densities. * KEY RESULTS: A set of multi-phase models was proposed to describe the extension of laminae, sheaths and internodes along the shoot. The distinguishable phases differed between laminae, sheaths and internodes. For sheaths and laminae, but not for internodes, the same model could be fitted to all phytomers along the shoot. The variation of parameters along the shoot and between density treatments, as well as derived functions such as the durations of the phases of extension, are presented for laminae. It was the duration of the fast extension period, rather than its rate, which determined the difference in final length between treatments. * CONCLUSIONS: Such methods permit a large degree of objectivity and facilitate the analysis of such rather complicated but co-ordinated datasets. The work also illustrates some natural limitations of maximum likelihood methods, and viable ways of overcoming them by including a priori knowledge in the model fitting method are discussed.     

The physical resistance of grass patches to invasion

One of the important factors determining success in plant competition is the ability of a plant to extend laminae in order to capture resources.To do this in mixed swards the laminae of one plant must first grow into the volume that contains laminae of another. The ability of laminae to overcome the resistance presented by a neighbour, and the ability to resist this ingress, was examined for the grasses Agrostis capillaris, Festuca rubra, Holcus lanatus, Lolium perenne and Poa trivialis that were subject to 3 cm and 6 cm cutting treatments. These abilities were inferred from the behaviour of ‘indicator ’ leaves as they were pushed into monoculture target patches of each species. The 3 cm treatment resisted ingress significantly more than the 6 cm. Species patches differed significantly both in their ability to resist the ingress by the indicator species and in the ability of different indicator species to penetrate the target swards. These effects were still present when differences in leaf density (leaves cm^–2) had been taken into account. The results suggest that grasses can vary in the physical resistance that they present to the leaves of an invading neighbour.     

Differential distribution of ampullary and tuberous processing in the torus semicircularis of Eigenmannia

Summary Gymnotiform electric fish sense low-and high frequency electric signals with ampullary and tuberous electroreceptors, respectively. We employed intracellular recording and labeling methods to investigate ampullary and tuberous information processing in laminae 1–5 of the dorsal torus semicircularis of Eigenmannia. Ampullary afferents arborized extensively in laminae 1–3 and, in some cases, lamina 7. Unlike tuberous afferents to the torus, ampullary afferents had numerous varicosities along their finest-diameter branches. Neurons that were primarily ampullary were found in lamina 3. Neurons primarily excited by tuberous stimuli were found in lamina 5 and, more rarely, in lamina 4. Cells that had dendrites in lamina 1–3 and 5 could be recruited by both ampullary and tuberous stimuli. These bimodal cells were found in lamina 4. During courtship, Eigenmannia produces interruptions of its electric organ discharges. These interruptions stimulate ampullary and tuberous receptors. The integration of ampullary and tuberous information may be important in the processing of these communication signals.Abbreviations JAR jamming avoidance response - EOD electric organ discharge - S1 sinusoidal signal mimicking fish's EOD - S2 jamming signal - Df frequency difference (S2-S1) or between a neighbor's EODs and fish's own EODs - CNS central nervous system     

Root proliferation and seed yield in response to spatial heterogeneity of below-ground competition

Here, we tested the predictions of a 'tragedy of the commons' model of below-ground plant competition in annual plants that experience spatial heterogeneity in their competitive environment. Under interplant competition, the model predicts that a plant should over-proliferate roots relative to what would maximize the collective yield of the plants. We predict that a plant will tailor its root proliferation to local patch conditions, restraining root production when alone and over-proliferating in the presence of other plants. A series of experiments were conducted using pairs of pea (Pisum sativum) plants occupying two or three pots in which the presence or absence of interplant root competition was varied while nutrient availability per plant was held constant. In two-pot experiments, competing plants produced more root mass and less pod mass per individual than plants grown in isolation. In three-pot experiments, peas modulated this response to conditions at the scale of individual pots. Root proliferation in the shared pot was higher compared with the exclusively occupied pot. Plants appear to display sophisticated nutrient foraging with outcomes that permit insights into interplant competition.     

Computing competition for light in the GREENLAB model of plant growth: a contribution to the study of the effects of density on resource acquisition and architectural development

BACKGROUND AND AIMS: The dynamical system of plant growth GREENLAB was originally developed for individual plants, without explicitly taking into account interplant competition for light. Inspired by the competition models developed in the context of forest science for mono-specific stands, we propose to adapt the method of crown projection onto the x-y plane to GREENLAB, in order to study the effects of density on resource acquisition and on architectural development. METHODS: The empirical production equation of GREENLAB is extrapolated to stands by computing the exposed photosynthetic foliage area of each plant. The computation is based on the combination of Poisson models of leaf distribution for all the neighbouring plants whose crown projection surfaces overlap. To study the effects of density on architectural development, we link the proposed competition model to the model of interaction between functional growth and structural development introduced by Mathieu (2006, PhD Thesis, Ecole Centrale de Paris, France). KEY RESULTS AND CONCLUSIONS: The model is applied to mono-specific field crops and forest stands. For high-density crops at full cover, the model is shown to be equivalent to the classical equation of field crop production (Howell and Musick, 1985, in Les besoins en eau des cultures; Paris: INRA Editions). However, our method is more accurate at the early stages of growth (before cover) or in the case of intermediate densities. It may potentially account for local effects, such as uneven spacing, variation in the time of plant emergence or variation in seed biomass. The application of the model to trees illustrates the expression of plant plasticity in response to competition for light. Density strongly impacts on tree architectural development through interactions with the source-sink balances during growth. The effects of density on tree height and radial growth that are commonly observed in real stands appear as emerging properties of the model.     

Comparison of GAD65 and 67 Immunoreactivity in the Lumbar Spinal Cord Between Young Adult and Aged Dogs

We investigated distribution and age-related changes in two isoforms of GABA synthesizing enzymes, glutamic acid decarboxylase (GAD) 65 and 67, in the lumbar levels (L(5)-L(6)) of the dog spinal cord. Male German shepherds were used at 1-2 years (young adult dogs) and 10-12 years (aged dogs) of age. GAD65 immunoreaction was observed in neuropil, not in cell bodies, in all laminae of the adult lumbar spinal cord: Many punctate GAD65-immunoreactive structures were shown in all laminae. The density of GAD65 immunoreactive structures was highest in laminae I-III, and lowest in lamina VII. In the aged dog, the distribution pattern of GAD65 immunoreactivity was similar to that in the adult dog; however the density of GAD65-immunoreactive structures and its protein levels were significantly increased in the aged lumbar spinal cord. GAD67 immunoreaction in the adult dog was also distributed in all laminae of the lumbar spinal cord like GAD65; however, we found that small GAD67-immunoreactive cell bodies were observed in laminae II, III and VIII. In the aged dogs, GAD67 immunoreactivity and its protein levels were also increased compared to those in the adult group. In conclusion, our results indicate that the distribution of GAD65-immunoreactive structures is different from GAD67-immunoreactive structures and that their immunoreactivity in the aged dogs is much higher than the adult dogs.     

Ultrastructure of the basal lamina of bovine ovarian follicles and its relationship to the membrana granulosa

Different morphological phenotypes of follicular basal lamina and of membrana granulosa have been observed. Ten preantral follicles (< 0. 1 mm), and 17 healthy and six atretic antral follicles (0.5-12 mm in diameter) were processed for light and electron microscopy to investigate the relationship the between follicular basal lamina and membrana granulosa. Within each antral follicle, the shape of the basal cells of the membrana granulosa was uniform, and either rounded or columnar. There were equal proportions of follicles 相似文献   

The calcium binding proteins calbindin,parvalbumin, and calretinin have specific patterns of expression in the gray matter of cat spinal cord

Calcium binding proteins (CBPs) regulate intracellular levels of calcium (Ca²⁺) ions. CBPs are particularly interesting from a morphological standpoint, because they are differentially expressed in certain sub-populations of cells in the nervous system of various species of vertebrate animals. However, knowledge on the cellular regulation governing such cell-specific CBP expression is still incomplete. In this work on the L7 segment of the cat spinal cord, we analyzed the localization and morphology of neurons expressing the CBPs calbindin-28 KD (CB), parvalbumin (PV), and calretinin (CR), and co-expressing CB and PV, CB and CR, and PV and CR. Single CBP-positive (⁺) neurons showed specific distributions: (1) CB was present in small neurons localized in laminae I, II, III and X, in small to medium size neurons in laminae III–VI, and in medium to large neurons in laminae VI–VIII; (2) PV was present in small size neurons in laminae III and IV and in medial portions of laminae V and VI, medium neurons and in lamina X at the border with lamina VII, in medium to large neurons in laminae VII and VIII; (3) CR labeling was detected in small size neurons in laminae I, II, III and VIII, in medium to large size neurons in laminae I and III–VII, and in small to medium size neurons in lamina X. Double labeled neurons were a small minority of the CBP⁺ cells. Co-expression of CB and PV was seen in 1 to 2% of the CBP⁺ cells, and they were detected in the ventral and intermediate portions of lamina VII and in lamina X. Co-localization of CB and CR was present in 0.3% of the cells and these cells were localized in lamina II. Double labeling for PV and CR occurred in 6% of the cells, and the cells were localized in ventral part of lamina VII and in lamina VIII. Overall, these results revealed distinct and reproducible patterns of localization of the neurons expressing single CBPs and co-expressing two of them. Distinct differences of CBP expression between cat and other species are discussed. Possible relations between the cat L7 neurons expressing different CBPs with the neurons previously analyzed in cat and other animals are suggested.     

Root morphological responses to population density vary with soil conditions and growth stages: The complexity of density effects

AimHow plants cope with increases in population density via root plasticity is not well documented, although abiotic environments and plant ontogeny may have important roles in determining root response to density. To investigate how plant root plasticity in response to density varies with soil conditions and growth stages, we conducted a field experiment with an annual herbaceous species (Abutilon theophrasti).MethodsPlants were grown at low, medium, and high densities (13.4, 36.0, and 121.0 plants m⁻², respectively), under fertile and infertile soil conditions, and a series of root traits were measured after 30, 50, and 70 days.ResultsRoot allocation increased, decreased, or canalized in response to density, depending on soil conditions and stages of plant growth, indicating the complex effects of population density, including both competitive and facilitative effects.Main conclusionsRoot allocation was promoted by neighbor roots at early stages and in abundant resource availability, due to low‐to‐moderate belowground interactions among smaller plants, leading to facilitation. As plants grew, competition intensified and infertile soil aggravated belowground competition, leading to decreased root allocation in response to density. Root growth may be more likely restricted horizontally rather than vertically by the presence of neighbor, suggesting a spatial orientation effect in their responses to density. We emphasized the importance of considering effects of abiotic conditions and plant growth stages in elucidating the complexity of density effects on root traits.     

The interaction between lodging and plant population in combining peas

The effects of preventing lodging in three varieties of combining peas with contrasting standing ability were studied over a range of plant populations and in two growing seasons. Maximal yield losses resulted when lodging occurred prior to the end of the flowering period. The likelihood of this event occurring was increased by high populations and was maximised when such populations were used in conjunction with conditions suitable for vigorous plant growth. In such seasons, optimum plant populations (30 plants m^-2) were seen to be very much below those currently recommended. When conditions were less favourable to plant growth, lodging tended to occur after flowering had ceased. Little yield loss due to population effects were then recorded. Under such conditions, yields were maximised by high plant populations. Under all growing conditions, little yield loss due to interplant competition was noted with increasing plant populations. It was concluded from these results that if combining pea production is to be successfully expanded out of traditional production areas, plant population recommendations should be lowered to compensate for increased plant vigour.     

Characterization of the effects of inter-tree competition on source–sink balance in Chinese pine trees with the GreenLab model

We investigate the characteristics of individual tree response to competition on source–sink balance through the functional–structural plant model GreenLab. Four Chinese pine (Pinus tabulaeformis Carr.) trees were destructively sampled and were divided into two groups: high-density group and low-density group. First, the effects of density on organ dimensions and on organ relative mass were analysed based on experimental measurements. These were primary indicators of the plant response to competition. Second, the hidden parameters of the GreenLab model, as well as a tree-specific characteristic surface, were estimated using the data of total tree biomass for needle and wood compartments, for each of the four trees in parallel. The quality of the fitting is finally validated using data of individual organ mass at shoot level for the sampled branches. The Mann–Whitney Student’s t test showed that there were significant differences between the shoot attributes of the two groups for shoot diameter, shoot biomass and needle biomass. No significant difference was found for current year shoot lengths of the two groups. The parametric identification of the model allowed estimating and comparing the amount of biomass that was allocated to primary growth and to secondary growth in the two density conditions. It showed that biomass allocated to secondary growth (ring compartment) was the most strongly affected by density, and that the organ demand satisfaction ratio profiles of each of these trees were a relevant, integrated indicator of the tree state.     

Shoot development in grapevine (Vitis vinifera) is affected by the modular branching pattern of the stem and intra- and inter-shoot trophic competition

BACKGROUND AND AIMS: Shoot architecture variability in grapevine (Vitis vinifera) was analysed using a generic modelling approach based on thermal time developed for annual herbaceous species. The analysis of shoot architecture was based on various levels of shoot organization, including pre-existing and newly formed parts of the stem, and on the modular structure of the stem, which consists of a repeated succession of three phytomers (P0-P1-P2). METHODS: Four experiments were carried out using the cultivar 'Grenache N': two on potted vines (one of which was carried out in a glasshouse) and two on mature vines in a vineyard. These experiments resulted in a broad diversity of environmental conditions, but none of the plants experienced soil water deficit. KEY RESULTS: Development of the main axis was highly dependent on air temperature, being linearly related to thermal time for all stages of leaf development from budbreak to veraison. The stable progression of developmental stages along the main stem resulted in a thermal-time based programme of leaf development. Leaf expansion rate varied with trophic competition (shoot and cluster loads) and environmental conditions (solar radiation, VPD), accounting for differences in final leaf area. Branching pattern was highly variable. Classification of the branches according to ternary modular structure increased the accuracy of the quantitative analysis of branch development. The rate and duration of leaf production were higher for branches derived from P0 phytomers than for branches derived from P1 or P2 phytomers. Rates of leaf production, expressed as a -function of thermal time, were not stable and depended on trophic competition and environmental conditions such as solar radiation or VPD. CONCLUSIONS: The application to grapevine of a generic model developed in annual plants made it possible to identify constants in main stem development and to determine the hierarchical structure of branches with respect to the modular structure of the stem in response to intra- and inter-shoot trophic competition.     

Plant population and weeds influence stalk insects, soil moisture, and yield in rainfed sunflowers

Insect infestation, soil moisture, and yield were examined in populations of≈33 140 plants/ha （low） and ≈ 40 340 plants/ha （high） of an oilseed sunflower, Helianthus annuus L, cv. ＇ Triumph 660CL＇ with two levels of weediness. Less weedy plots resulted from the application of herbicide combination of S-metolachlor and sulfentrazone, whereas more weedy plots resulted from application of sulfentrazone alone. Among the 12 weed species recorded, neither plant numbers nor biomass differed between crop plant densities. Larvae of the stalk-boring insects Cylindrocopturus adspersus （Coleoptera： Curculionidae） and Mordellistena sp. （Coleoptera： Mordellidae） were less abundant in high density sunflowers, ostensibly due to reduced plant size. However, the same effect was not observed for Dectes texanus （Coleoptera： Cerambycidae） or Pelochrista womanana （Lepidoptera： Tortricidae）, two other stalk-boring insects. Soil moisture was highest in low density and lowest in the high density sunflowers that were less weedy. Stalk circumference, head diameter, and seed weight were reduced for sunflower plants with short interplant distances （mean = 20 cm apart） compared to plants with long interplant distances （mean = 46 cm apart）. These three variables were greater in less weedy plots compared with more weedy plot〉 and positively correlated with interplant distance. Yields on a per-hectare basis paralleled those on a per-plant basis but were not different among treatments. The agronomic implications of planting density are discussed in the context of weed and insect management.     

Modelling the structural response of cotton plants to mepiquat chloride and population density

Background and Aims

Cotton (Gossypium hirsutum) has indeterminate growth. The growth regulator mepiquat chloride (MC) is used worldwide to restrict vegetative growth and promote boll formation and yield. The effects of MC are modulated by complex interactions with growing conditions (nutrients, weather) and plant population density, and as a result the effects on plant form are not fully understood and are difficult to predict. The use of MC is thus hard to optimize.

Methods

To explore crop responses to plant density and MC, a functional–structural plant model (FSPM) for cotton (named CottonXL) was designed. The model was calibrated using 1 year''s field data, and validated by using two additional years of detailed experimental data on the effects of MC and plant density in stands of pure cotton and in intercrops of cotton with wheat. CottonXL simulates development of leaf and fruits (square, flower and boll), plant height and branching. Crop development is driven by thermal time, population density, MC application, and topping of the main stem and branches.

Key Results

Validation of the model showed good correspondence between simulated and observed values for leaf area index with an overall root-mean-square error of 0·50 m² m⁻², and with an overall prediction error of less than 10 % for number of bolls, plant height, number of fruit branches and number of phytomers. Canopy structure became more compact with the decrease of leaf area index and internode length due to the application of MC. Moreover, MC did not have a substantial effect on boll density but increased lint yield at higher densities.

Conclusions

The model satisfactorily represents the effects of agronomic measures on cotton plant structure. It can be used to identify optimal agronomic management of cotton to achieve optimal plant structure for maximum yield under varying environmental conditions.     

Metal complexes increase uptake of Zn and Cu by plants: implications for uptake and deficiency studies in chelator-buffered solutions

The allocation of resources among roots and shoots represents the largest flux of resources within a plant and therefore should have been selected to maximize benefits to plants. Yet, it is unclear why some species like temperate grasses have such high root length density (RLD). Either the slow rate of diffusion of inorganic N in soils or interplant competition could explain the high RLD of temperate grasses. Using a fine-scale model of nutrient dynamics in the soil and plant growth, a cost–benefit approach was used to assess optimal allocation rates for plants that accounted for value of both carbon and nitrogen. In the absence of interplant competition, resource benefits are maximized with very little root length except in extremely dry soils for ammonium. In the presence of a competitor, optimal allocation of N to roots is much greater and increases as ability of competitors to produce root length increase. Competition for inorganic nitrogen generates a classic aspect of the tragedy of the commons, the “race for fish”, where plants must allocate more resources to acquisition of the limiting resource than is optimal for plants in the absence of competition. As such, nutrient competition needs to be directly addressed when understanding plant- and ecosystem-level resource fluxes as well as the evolution of root systems.     

Photosynthetic activities of vegetative and fruiting tissues of tomato

Photosynthetic activities of different chlorophyll-containing parts of tomato plants (Lycopersicon esculentum Mill. cv. Saporo) were assessed using chlorophyll fluorescence techniques. Trusses selected for study contained near mature, green fruit and measurements were carried out on the truss peduncle, pedicels, calyces, and fruit. Activities of these tissues were compared with those of adjacent compound leaves considered to be the primary suppliers of photosynthetic assimilates to fruit. All tissues showed high intrinsic efficiencies of photosystem II, measured as FV/FM, in dark-adapted tissue (range 0.77-0.82). Maximal photosynthetic electron transfer activities varied from 110 to 330 mol m^-2 s^-1. With increasing photon flux density there was a gradation of tissue activity with actual photosynthetic yields, electron transport rates and photochemical quenching coefficients (qP) of tissues decreasing in the order: upper leaf lamina, lower leaf lamina, leaf petiole, truss peduncle, pedicel, calyx, and fruit. The reverse order was found for the rapidity at which absorbed photon energy was diverted to non-photochemical pathways as photon flux density was increased. The onset of FO quenching at high photon flux densities suggested that all tissues contained a regulated mechanism for dissipating excess energy as heat. It was concluded that the non-leaf green tissues of tomato are quite active photosynthetically and therefore potentially contribute significantly to plant growth. At a photon flux density of 185 mol m^-2 S^-1, 29% of photosynthetic electron transport activity on a surface area basis was located in tissues other than leaf laminae, with fruit accounting for 15%.     

Influence of intra-shoot trophic competition on shoot development in two grapevine cultivars (Vitis vinifera)

The effect of trophic competition between vegetative sources and reproductive sinks on grapevine ( Vitis vinifera L.) shoot development was analyzed. Two international cultivars (Grenache N and Syrah) grown in pots, which were well watered, were studied. A large range of trophic competition levels was obtained by modifying the cluster loads per plant. An analytical breakdown of the branching system was used to analyze the effects of trophic competition. Phytomer production on the primary axis and the probability and timing of axillary budburst were not affected by trophic competition. However, the duration of development and leaf production rate for secondary axes were both significantly affected. The impact of trophic competition differed within the P0–P1–P2 architectural module, locally within the shoot and between cultivars. Trophic competition reduced the organogenesis of secondary axes most strongly close to clusters, on P1–P2 phytomers and in Grenache N. Based on these results, a modeling approach simulating sink strength variation and the local effects of sink proximity would be more relevant than a model considering only development as a function of thermal time or the global distribution of available biomass.     

Response of plasmodesmata formation in leaves of C4 grasses to growth irradiance

Rapid metabolite diffusion across the mesophyll (M) and bundle sheath (BS) cell interface in C₄ leaves is a key requirement for C₄ photosynthesis and occurs via plasmodesmata (PD). Here, we investigated how growth irradiance affects PD density between M and BS cells and between M cells in two C₄ species using our PD quantification method, which combines three‐dimensional laser confocal fluorescence microscopy and scanning electron microscopy. The response of leaf anatomy and physiology of NADP‐ME species, Setaria viridis and Zea mays to growth under different irradiances, low light (100 μmol m^?2 s^?1), and high light (1,000 μmol m^?2 s^?1), was observed both at seedling and established growth stages. We found that the effect of growth irradiance on C₄ leaf PD density depended on plant age and species. The high light treatment resulted in two to four‐fold greater PD density per unit leaf area than at low light, due to greater area of PD clusters and greater PD size in high light plants. These results along with our finding that the effect of light on M‐BS PD density was not tightly linked to photosynthetic capacity suggest a complex mechanism underlying the dynamic response of C₄ leaf PD formation to growth irradiance.