Appearance of bulges on maize roots as affected by 6-benzylaminopurine and α-naphthylacetic acid

The thickening that appeared on maize roots under the influence of 6-benzylaminopurine and α-naphthylacetic acid (concentration 10⁻⁵, 10⁻⁶, 10⁻⁷ and 10⁻⁸ M) were analysed. The changes in length and width of maize roots at the edge of elongation zone after 24,48 and 72 h of treatment were studied. The growth in length of cells at the edge of elongation zone stopped abruptly but the growth in width slowly continued. So, the growth of cells in length and width under the influence of growth regulators was not simultaneous. They had distinct time limits.     

常绿阔叶林外生和丛枝菌根树种细根形态和构型性状对氮添加的可塑性响应

以中亚热带常绿阔叶林外生菌根树种罗浮栲和丛枝菌根树种木荷为研究对象,采用根袋法进行野外原位氮添加试验,研究了细根形态性状(比根长、比表面积、组织密度、平均根直径)和构型性状(分枝数、分枝比、根长增长速率、根尖密度、分枝密度),分析不同菌根树种细根形态和构型性状对氮沉降的响应.结果表明:随序级增加,外生和丛枝菌根树种细根...     

Architecture and development of the oil-palm (Elaeis guineensis Jacq.) root system

The growth dynamics and architecture of the oil-palm root system are described. Following a transitional juvenile phase, eight different morphological types of roots have been distinguished according to their development pattern and state of differentiation: primary vertical and horizontal roots, secondary horizontal roots, upward growing secondary vertical roots and downward growing secondary vertical roots, superficial and deep tertiary roots and quaternary roots. The relative position of these types of roots determines a morphological and functional unit of the root system called 'root architectural unit' of the oil palm. This root polymorphism enabled us to define a morphogenetic gradient, which reflected the oil-palm root-system ontogenesis.     

The interface between the cell cycle and plant growth regulators: a mini review

The aim was to review knowledge about the interface betweenplant growth regulators and molecular checkpoints of the cell cycle. Atwhat level of biochemical regulation of the cell cycle do plant growthregulators interface? Are there different levels of interfacingdependent on the plant growth regulator involved? As a preamble totackling these questions, we overview the eukaryotic cell cycle withparticular emphasis on checkpoints that regulate the transition fromG0-G1-S-phase and G2-M. Cytokinins feature strongly as activators ofcell division in plants both in vivo and in vitro.Recent research has shown that zeatin treatment led to the up-regulationof CycD3 in Arabidopsis. This is a D-type cyclin showing stronghomology with vertebrate D cyclins which themselves are up-regulated byextracellular growth factors. Benzyladenine treatment can also shortenthe duration of S-phase through recruitment of latent origins of DNAreplication. Kinetin is involved in the phosphoregulation of the G2-Mcheckpoint; the major cyclin-dependent kinase (Cdk) at this checkpointhas recently been shown to be dephosphorylated as a result of cytokinintreatment, an effect which can also be mimicked by the fission yeastCdc25 phosphatase. Hence, a picture emerges of a cytokinin-inducedcontinuum of cell cycle activation through the up-regulation of a plantD-type cyclin at the G1 checkpoint and the phosphoregulation of the Cdkat the G2/M checkpoint. During S-phase, we argue for a link betweencytokinins and the proteins associated with replication origins.Gibberellic acid (GA) treatment induces internode elongation. Indeepwater rice, this response is mediated, at least partly, by aGA-induced up-regulation of a cyclin-Cdk at the G2-M checkpoint. Recentevidence has also linked abscisic acid to a cyclin-dependent kinaseinhibitor. These, so-called CKIs are negative regulators of Cdks whichfits with ABA's general role in growth inhibition; we await news ofethylene interactions. We highlight two instances of plant growthregulator-cell cycle interfacing during development, arguing for aninvolvement in microtubule orientation as a prerequisite to leafinitiation, and suggest a link between IAA and the activation of celldivisions in the pericycle required for lateral root initiation. A newD-type cyclin, recently discovered in Arabidopsis, may have akey role in this process. Finally, a model is presented which features ageneralised cyclin-Cdk checkpoint exhibiting various interfaces with theplant growth regulators.     

Terpenoid lactones as plant growth regulators

Plant growth regulating activity of dehydrocostus lactone possessing an α-methylene-γ-lactone moiety has been compared with its two derived C-16 lactones, in which a trisubstituted double bond and a cyclopropane ring are conjugated with the lactone carbonyl. The results show that the two latter compounds are slightly more active than dehydrocostus lactone.     

Role of proteinaceous amino acids released in root exudates in nutrient acquisition from the rhizosphere

The role of proteinaceous amino acids in rhizosphere nutrient mobilization was assessed both experimentally and theoretically. The degree of adsorption onto the soil's solid phase was dependent on both the amino acid species and on soil properties. On addition of amino acids to both soil and freshly precipitated Fe(OH)₃, no detectable mobilization of nutrients (K, Na, Ca, Mg, Cu, Mn, Zn, Fe, S, P, Si and Al) was observed, indicating a very low complexation ability of the acidic, neutral and basic amino acids. This was supported by results from a solution equilibria computer model which also predicted low levels of amino acid complexation with solutes present in the soil solution. On comparison with the Fe(OH)₃ and equilibria data obtained for the organic acid, citrate, it was concluded that amino acids released into the rhizosphere have a limited role in the direct acquisition of nutrients by plants. The effectiveness of root exudates such as amino acids, phytosiderophores and organic acids in nutrient mobilization from the rhizosphere is discussed with reference to rhizosphere diffusion distances, microbial degradation, rate of complexation and the root's capacity to recapture exudate-metal complexes from the soil.     

Upscaling from Rhizosphere to Whole Root System: Modelling the Effects of Phospholipid Surfactants on Water and Nutrient Uptake

While the rhizosphere presents a different chemical, physical and biological environment to bulk soil, most experimental and modelling investigations of plant growth and productivity are based on bulk soil parameters. In this study, water and nutrient acquisition by wheat (Triticum aestivum L.) roots was investigated using rhizosphere- and root-system-scale modelling. The physical and chemical properties of rhizosphere soil could be influenced by phospholipid surfactants in the root mucilage. Two models were compared: a 2-dimensional (2D) Finite Element Method rhizosphere model, and a 3-dimensional (3D) root architecture model, ROOTMAP. ROOTMAP was parameterised to reproduce the results of the detailed 2D model, and was modified to include a rhizosphere soil volume. Lecithin (a phospholipid surfactant) could be exuded into the rhizosphere soil volume, decreasing soil water content and hydraulic conductivity at any given soil water potential, and decreasing phosphate adsorption to soil particles. The rhizosphere-scale modelling (5 × 5 mm² soil area, 10 mm root length, uptake over 12 h) predicted a reduction in water uptake (up to 16% at 30 kPa) and an increase in phosphate uptake (up to 4%) with lecithin exudation into the rhizosphere, but little effect on nitrate uptake, with only a small reduction in dry soil (1.6% at 200 kPa). The 3D root model reproduced the water (y = 1.013x, R² = 0.996), nitrate (y = 1x, R² = 1) and phosphate (y = 0.978x, R² = 0.998) uptake predictions of the rhizosphere model, providing confidence that a whole root system model could reproduce the dynamics simulated by a Finite Element Method rhizosphere model. The 3D root architecture model was then used to scale-up the rhizosphere dynamics, simulating the effect of lecithin exudation on water, nitrate and phosphate acquisition by a wheat root system, growing over 41 d. When applied to growing and responsive roots, lecithin exudation increased P acquisition by up to 13% in nutrient-rich, and 49% in relatively nutrient-poor soil. A comparison of wheat (Triticum aestivum L.) and lupin (Lupinus angustifolius L.) root architectures, suggested an interaction between the P acquisition benefit of rhizosphere lecithin and root architecture, with the more highly-branched wheat root structure acquiring relatively more P in the presence of lecithin than the sparsely-branched lupin root system.     

Effect of sub-optimal root zone temperatures at varied nutrient supply and shoot meristem temperature on growth and nutrient concentrations in maize seedlings (Zea mays L.)

Maize seedlings were grown for 10 to 20 days in either nutrient solution or in soils with or without fertilizer supply. Air temperature was kept uniform for all treatments, while root zone temperature (RZT) was varied between 12 and 24°C. In some treatments the basal part of the shoot (with apical shoot meristem and zone of leaf elongation) was lifted up to separate the indirect effects of root zone temperature on shoot growth from the direct effects of temperature on the shoot meristem.Shoot and root growth were decreased by low RZT to a similar extent irrespective of the growth medium (i.e. nutrient solution, fertilized or unfertilized soil). In all culture media Ca concentration was similar or even higher in plants grown at 12 as compared to 24°. At lower RZT concentrations of N, P and K in the shoot dry matter decreased in unfertilized soil, whereas in nutrient solution and fertilized soil only the K concentration decreased.When direct temperature effects on the shoot meristem were reduced by lifting the basal part of the shoot above the temperature-controlled root zone, shoot growth at low RZT was significantly increased in nutrient solution and fertilized soil, but not in unfertilized soil. In fertilized soil and nutrient solution at low RZT the uptake of K increased to a similar extent as plant growth, and thus shoot K concentration was not reduced by increasing shoot growth rates. In contrast, uptake of N and P was not increased, resulting in significantly decreased shoot concentrations.It is concluded that shoot growth at suboptimal RZT was limited both by a direct temperature effect on shoot activity and by a reduced nutrient supply through the roots. Nutrient concentrations in the shoot tissue at low RZT were not only influenced by availability in the substrate and dilution by growth, but also by the internal demand for growth.