稻茬麦根系构型的定向分型分析

为探索稻茬麦根构型的方向性,使用田间数字化仪实现稻茬麦根系的数值化,将根系数据导入Pro-E重构出根系的空间状态图,然后将根构型每隔10°进行各向投影,计算根系构型在18个维度的分形维数与分形丰度.结果表明:小麦苗期根构型在各维度的分形特征具有较强的规律性,表明根系在土体中的分布具有明显的方向性.在苗期到返青期,根构型在18个维度的分形指标波动性大,表明这一时期内根系生长处于持续的动态变化过程.在拔节期,根构型在各维度的分形再次呈现出一定的规律性,表明根系在土体中的分布重新表现出明显的方向性.该研究方法可以精准描述和分析植物根系在田间环境中的分布状况.     

Modelling the branching growth fractal pattern of the maize root system

Using the technique of L-systems, a growth model of the maize root system is developed. From the observation of the root systems developed under various soil density in eight root boxes, a spatial hierarchy of growth rules was extracted. The rules were divided into three categories: a meta-rule for describing features of an entire root system, a branching growth rule and a tip elongation rule. Some variations in the entire features of the root system, such as the outline and the root distribution, were confirmed by observation, and then the respective meta-rules were re-defined. The branching properties of first- and second-order lateral roots were statistically almost equal in the observations, and this lead us to set up a single stochastic branching growth rule. Tip elongation movement was not observed here; its rule had to be assumed by reference to data in the literature. A single set of branching growth and tip elongation rules were coupled with the respective meta-rules corresponding to the root samples observed, where a small scale rule was loosely governed by a large scale rule. Computer simulations offered optimized drawings of the observed root systems, and they also reproduced a typical anisotropic power distribution of roots similar to those observed.     

Ethylene-induced root coiling in tomato seedlings

Roots of tomato seedlings can be induced to coil by treatment with ethylene. The extent of coiling is dependent on the level of ethylene to which the seedlings are exposed and can be prevented by the incorporation of Ag ions into the growing medium. In contrast to all other tomato mutants examined, roots of the mutant diageotropica do not reorientate their growth in response to ethylene. The results of an agar penetration test indicate that roots of this mutant are agravitropic. The relationship between gravitropism and root coiling, and the origin of the ethylene modified growth pattern is discussed.     

脱落酸被土壤“掩盖”了的功能:调节根系构型形态建成

植物根系发育是一个重要的农艺性状。由于根系具有结构和生长模式简单、信号感受灵敏等,有可能成为研究植物发育可塑性的良好材料。通过分析脱落酸在主根、侧根和根毛的发生和生长中及根构型形成中的可能信号转导过程中的作用,提出未来研究应关注的科学问题。对ABA调控根系发育分子机制的探讨不仅有利于阐明如何调控根发育可塑性这一复杂和困难的生物学问题,而且对农业生产也极为重要。     

Root growth as a function of ammonium and nitrate in the root zone

We examined the effect of soil NH₄⁺ and NO₃^? content upon the root systems of field-grown tomatoes, and the influence of constant, low concentrations of NH₄⁺ or NO₃^? upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH₄⁺ or NO₃^?; they increased to a maximum in zones having 2μg-N NO₃^? g^?1 soil and 6 μg-N NO₃⁼ g^?1 soil, but decreased in zones having higher NH₄⁺ or NO₃^? levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH₄⁺ or NO₃^?, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO₃^?. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH₄⁺ and NO₃^?.     

Patterns of variability in the diameter of lateral roots in the banana root system

The relative importance of root system structure, plant carbon status and soil environment in the determination of lateral root diameter remains unclear, and was investigated in this study. Banana (Musa acuminata) plants were grown at various moderate levels of soil compaction in two distinct experiments, in a field experiment (FE) and in a glasshouse experiment (GE). Radiant flux density was 5 times lower in GE. The distribution of root diameter was measured for several root branching orders. Root diameters ranged between 0.09 and 0.52 mm for secondary roots and between 0.06 and 0.27 mm for tertiary roots. A relationship was found between the diameter of the parent bearing root and the median diameter of its laterals, which appears to be valid for a wide range of species. Mean lateral root diameter increased with distance to the base of the root and decreased with branching density [number of lateral roots per unit length of bearing root (cm(-1))]. Typical symptoms of low light availability were observed in GE. In this case, lateral root diameter variability was reduced. Although primary root growth was affected by soil compaction, no effects on lateral root diameter were observed.     

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.     

Growth and gibberellin relations of the extreme dwarf dx tomato mutant

The extreme dwarf d ^x tomato ( Lycopersicon esculentum Mill.) mutant has very short internodes which were found to contain shorter and fewer epidermal cells. The leaves are highly abnormal. The mutant showed a substantial stem growth response to GA₃, without approaching normal stature or morphology. The active gibberellin GA₁ and its precursors GA₁₉ and GA₂₀ were identified by coupled gas chromatography-mass spectrometry (GC/MS) in d ^x shoots. Quantitative GC/MS revealed that GA₂₀ accumulated to far higher levels than normal in stems and leaves of the mutant.     

Water deficit, root demography, and the causes of internal blackening in field-grown tomatoes:(Lycopersicon esculentum Mill.)

An internal blackening disorder may cause substantial losses in the value of tomatoes grown for processing. The disorder resembles an internal form of blossom-end rot and appears to be more common in dry seasons. In an experiment to test whether the internal blackening is caused by water deficit and whether it is indeed blossom-end rot, plots of cv. Cannery Row were irrigated to keep the soil moisture deficit <50 mm and others were sheltered from rain and not irrigated from early flowering onwards. Shoot growth (total and fruit dry mass) was measured destructively at intervals, and root growth and death nondestructively using minirhizotrons. There was a greater incidence of internal blackening and blossom-end rot, and lower Ca concentrations, in the fruit of non-irrigated plants. Root growth and root death were accelerated in these plants around the time that internally-blackened fruit were set. Although the internal blackening syndrome shared some features with blossom-end rot some differences were apparent in this experiment. It is suggested that internal blackening could have resulted from increased root competition for photosynthate, leading to abnormal seed development. Root turnover was appreciable (30–40% of the roots survived 28 days). This suggests there may be substantial errors in contemporary models of dry matter partitioning in tomato crops.     

Estimation of tree root lengths using fractal branching rules: a comparison with soil coring for Grevillea robusta

Previous theoretical research has suggested that lengths of tree roots can be estimated on the basis of their branching characteristics, if branching has a fractal pattern that is independent of root diameter. This theory and its underlying assumptions was tested for Grevillea robusta trees at a site in Kenya by comparing estimates of root length from conventional soil coring and the output of a fractal branching algorithm. The trees were in a 4-year-old stand established on a 3 × 4 m planting grid. Root lengths (L _r) in four units of the planting grid were estimated by soil coring. Branching characteristics determined by examination of 32 excavated roots from 16 trees were: The number of branches at each branching point; the length of links between branching points (L _l); the diameter of root tips; and parameters which describe the change in diameter at each branching point. Each was found to be independent of root size. These data were used to parameterise a branching algorithm, which was then used to estimate numbers of root links in the four grid units (n _l) from root diameters at the bases of the four trees at the corners of each unit. Root lengths, from L _r = n₁ L₁, severely underestimated L _r. This discrepancy probably resulted from inaccuracy in the parameterisation of the branching algorithm, as output from the algorithm was very sensitive to small changes in parameter values. Use of fractal branching rules alone to estimate roots length does not appear possible unless the algorithm is calibrated to adjust for errors in parameter estimation. Calibration can be achieved by calculation of an 'effective link length', L ^eff ₁, from L _r/n _l, where L _r is measured by a reference method such as soil coring.     

Fractal geometry of bean root systems: correlations between spatial and fractal dimension

An obstacle to the study of root architecture is the difficulty of measuring and quantifying the three-dimensional configuration of roots in soil. The objective of this work was to determine if fractal geometry might be useful in estimating the three-dimensional complexity of root architecture from more accessible measurements. A set of results called projection theorems predict that the fractal dimension (FD) of a projection of a root system should be identical to the FD of roots in three-dimensional space (three-dimensional FD). To test this prediction we employed SimRoot, an explicit geometric simulation model of root growth derived from empirical measurements of common bean (Phaseolus vulgaris L.). We computed the three-dimensional FD, FD of horizontal plane intercepts (planar FD), FD of vertical line intercepts (linear FD), and FD of orthogonal projections onto planes (projected FD). Three-dimensional FD was found to differ from corresponding projected FD, suggesting that the analysis of roots grown in a narrow space or excavated and flattened prior to analysis is problematic. A log-linear relationship was found between FD of roots and spatial dimension. This log-linear relationship suggests that the three-dimensional FD of root systems may be accurately estimated from excavations and tracing of root intersections on exposed planes.     

Estimates of root system topology of five plant species grown at steady-state nutrition

Results from a controlled growth-analysis experiment were used to illustrate some methods for measuring and describing root system topology. The experiment was performed in a nutrient solution system with an exponential nutrient supply and steady-state growth, to achieve well-defined levels of whole-plant nutrient status. Five naturally coexisting grassland species were included: The slow-growing forbs Polygala vulgaris L. and Crepis praemorsa (L.) F. L. Walth., and the grass Danthonia decumbens (L.) DC. were compared with the more common, fast-growing grasses Agrostis capillaris L. and Dactylis glomerata L. The most marked difference in morphological indices was a much higher specific root length in the grasses than in the forbs, which implies thinner roots. In contrast to the conclusions of previous studies, an index of the topology for the grasses was very similar to that for the forbs. The specific root lenght and link length apparently vary more between species and nutrient levels than topology does, and may therefore be more ecologically important. The only clear plastic response to growth-limiting nitrogen supply was a markedly increased link length in P. vulgaris. There were also indications that nitrogen limitation led to more herringbone-like root systems in P. vulgaris and C. praemorsa. In general, there was a clear tendency for the estimates of topology to change with plant size, which may make many topological indices, especially those based on regression slopes, very difficult to interpret. Until interactions with plant size, other morphological parameters and among-plant competition can be properly understood, the relevance of root topology for plant performance remains unclear. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of ammonium ions on membrane potential and anion flux in roots of barley and tomato

The effects of ammonium (0–5 mol m^?3) on root hair membrane potential and on the influx of nitrate and phosphate were investigated in roots of intact barley and tomato plants. In both species, addition of ammonium to the medium bathing the roots caused an almost immediate depolarization of the membrane potential; the depolarization was greater at higher concentrations of ammonium. Influx of ¹³NC₃^? and ³²Pi was inhibited over the same time scale and concentration range. In tomato roots, there was little further depolarization of the membrane potential or inhibition of anion influx at ammonium concentrations above 0.4 mol m^?3. In barley roots, the inhibition of nitrate influx and the depolarization of the membrane potential did not saturate below 5 mol m^?3 ammonium.     

Phenalenone pigments of the root system of Lachnanthes tinctoria

The root system of Lachnanthes tinctoria (Haemodoraceae) contains lachnanthoside, a glycoside of trihydroxy-9-phenylphenalenone; lachnanthofluorone, a red-fluorescent compound having a novel naphthoxanthenone structure; and a naphthalide related to the phenalenones.     

Branching out in new directions: the control of root architecture by lateral root formation

Plant roots are required for the acquisition of water and nutrients, for responses to abiotic and biotic signals in the soil, and to anchor the plant in the ground. Controlling plant root architecture is a fundamental part of plant development and evolution, enabling a plant to respond to changing environmental conditions and allowing plants to survive in different ecological niches. Variations in the size, shape and surface area of plant root systems are brought about largely by variations in root branching. Much is known about how root branching is controlled both by intracellular signalling pathays and by environmental signals. Here, we will review this knowledge, with particular emphasis on recent advances in the field that open new and exciting areas of research.     

The chilling sensitivity of root ammonium influx in a cultivated and wild tomato

A chilling episode of a few hours damaged root ammonium absorption in a cultivated tomato ( Lycopersicon esculentum cv. T-5), but not in a wild congener from high altitudes ( Lycopersicon hirsutum LA1778). In the cultivar, ammonium influx was strongly temperature dependent and showed the residual effects of chilling, whereas ammonium efflux was nearly temperature invariant and showed no persistent effects. A 2 h exposure to 5 °C significantly depressed subsequent ammonium absorption at 20 °C, and about 12 h at 20 °C was required for recovery. For both the cultivated and wild species, rerooted cuttings were slightly less sensitive to chilling than seedlings. The relative inhibition (mean ± SE) of ammonium absorption before and after chilling was 58·4 ± 2·5% for the cultivated species and 29·0 ± 9·1% for the wild species. The F₁ hybrid between the species showed a relative inhibition of 52·4 ± 3·6%, suggesting that chilling sensitivity may be dominant. In a backcross of the hybrid to L. esculentum , the phenotypic distribution of the relative inhibition of ammonium absorption indicated that this trait is segregating.