Periodicity in the development of the root system of young rubber trees (Hevea brasiliensis Müell. Arg.): relationship with shoot development

The growth pattern of the root system of young rubber trees (Hevea brasiliensis) was studied in relation to shoot development over a period of 3 months. Temporal and spatial variations in elongation and branching processes were examined for the different root types, by means of root observation boxes. Shoot growth was typically rhythmic. Root development was periodic and related to leaf expansion. Root elongation was depressed during leaf growth, whereas branching was enhanced. Consequently, highly branched areas with vigorous secondary roots alternated along the taproot with poorly branched areas with shorter roots. Root types were not affected to the same degree by shoot competition: during leaf expansion, taproot growth was just depressed but remained continuous, the emergence and elongation rates of secondary roots were significantly affected and the elongation rates of tertiary roots fell to zero. These results were consistent with the hypothesis that root growth is related to competition for assimilates and to the sink strength of the different root types, whereas root branching appeared to be promoted by leaf development.     

不同磷效率小麦品种对缺磷胁迫反应的比较

在营养液培养条件下,以根据相对产量为指标筛选出的6个不同磷效率的小麦(Triticum aestivum L.)品种为材料,对其苗期在缺磷条件下生长、根冠磷含量及其分配,以及叶片韧皮部汁液中磷浓度等进行了比较研究.结果表明,缺磷抑制植株地上部生长,但刺激根系生长,导致植株根/冠比增加.无论在供磷或缺磷条件下,磷高效品种的根冠生长速率都低于磷低效品种.缺磷导致植株体内的磷含量下降与根系相比,地上部磷含量的下降速率更快.但在缺磷条件下,不同磷效率的小麦品种根冠间的磷分配变化没有差异.研究发现,在正常供磷条件下,磷高效小麦品种的叶片韧皮部汁液中磷浓度较低,而磷低效品种的叶片韧皮部汁液中磷浓度较高.但开始缺磷后,磷高效品种的叶片韧皮部汁液中的磷浓度下降较慢,使其相对磷浓度较高.缺磷后1 0天,磷低效品种叶片韧皮部汁液中的磷浓度为供磷对照的35.9%,而磷高效品种叶片韧皮部汁液中的磷浓度为供磷对照的59%.     

不同磷效率小麦品种对缺磷胁迫反应的比较

在营养液培养条件下,以根据相对产量为指标筛选出的6个不同磷效率的小麦(Triticum aestivum L.)品种为材料,对其苗期在缺磷条件下生长、根冠磷含量及其分配,以及叶片韧皮部汁液中磷浓度等进行了比较研究。结果表明,缺磷抑制植株地上部生长,但刺激根系生长,导致植株根／冠比增加。无论在供磷或缺磷条件下,磷高效品种的根冠生长速率都低于磷低效品种。缺磷导致植株体内的磷含量下降与根系相比,地上部磷含量的下降速率更快。但在缺磷条件下,不同磷效率的小麦品种根冠间的磷分配变化没有差异。研究发现,在正常供磷条件下,磷高效小麦品种的叶片韧皮部汁液中磷浓度较低,而磷低效品种的叶片韧皮部汁液中磷浓度较高。但开始缺磷后,磷高效品种的叶片韧皮部汁液中的磷浓度下降较慢,使其相对磷浓度较高。缺磷后10天,磷低效品种叶片韧皮部汁液中的磷浓度为供磷对照的35．9％,而磷高效品种叶片韧皮部汁液中的磷浓度为供磷对照的59％。     

Bud composition, branching patterns and leaf phenology in cerrado woody species

BACKGROUND AND AIMS: Plants have complex mechanisms of aerial biomass exposition, which depend on bud composition, the period of the year in which shoot extension occurs, branching pattern, foliage persistence, herbivory and environmental conditions. METHODS: The influence of water availability and temperature on shoot growth, the bud composition, the leaf phenology, and the relationship between partial leaf fall and branching were evaluated over 3 years in Cerrado woody species Bauhinia rufa (BR), Leandra lacunosa (LL) and Miconia albicans (MA). KEY RESULTS: Deciduous BR preformed organs in buds and leaves flush synchronously at the transition from the dry to the wet season. The expansion time of leaves is <1 month. Main shoots (first-order axis, A1 shoots) extended over 30 d and they did not branch. BR budding and foliage unfolds were brought about independently of inter-annual rainfall variations. By contrast, in LL and MA evergreen species, the shoot extension rate and the neoformation of aerial organs depended on rainfall. Leaf emergence was continuous for 2-6 months and lamina expansion took place over 1-4 months. The leaf life span was 5-20 months and the main A1 shoot extension happened over 122-177 d. Both evergreen species allocated biomass to shoots, leaves or flowers continuously during the year, branching in the middle of the wet season to form second-order (A2 shoots) and third-order (A3 shoots) axis in LL and A2 shoots in MA. Partial shed of A1 shoot leaves would facilitate a higher branching intensity A2 shoot production in LL than in MA. MA presented a longer leaf life span, produced a lower percentage of A2 shoots but had a higher meristem persistence on A1 and A2 shoots than LL. CONCLUSIONS: It was possible to identify different patterns of aerial growth in Cerrado woody species defined by shoot-linked traits such as branching pattern, bud composition, meristem persistence and leaf phenology. These related traits must be considered over and above leaf deciduousness for searching functional guilds in a Cerrado woody community. For the first time a relationship between bud composition, shoot growth and leaf production pattern is found in savanna woody plants.     

Effects of simulated root herbivory and fertilizer application on growth and biomass allocation in the clonal perennialSolidago canadensis

Summary Compensatory growth in response to simulated belowground herbivory was studied in the old-field clonal perennialSolidago canadensis. We grew rootpruned plants and plants with intact root systems in soil with or without fertilizer. For individual current shoots (aerial shoot with rhizome and roots) and for whole clones the following predictions were tested: a) root removal is compensated by increased root growth, b) fertilizer application leads to increased allocation to aboveground plant organs and increased leaf turnover, c) effects of fertilizer application are reduced in rootpruned plants. When most roots (90%) were removed current shoots quickly restored equilibrium between above-and belowground parts by compensatory belowground growth whereas the whole clone responded with reduced aboveground growth. This suggests that parts of a clone which are shared by actively growing shoots act as a buffer that can be used as source of material for compensatory growth in response to herbivory. Current shoots increased aboveground mass and whole clones reduced belowground mass in response to fertilizer application, both leading to increased allocation to aboverground parts. Also with fertilizer application both root-pruned and not root-pruned plants increased leaf and shoot turnover. Unfertilized plants, whether rootpruned or not, showed practically no aboveground growth and very little leaf and shoot turnover. Effects of root removal were as severe or more severe under conditions of high as under conditions of low nutrients, suggesting that negative effects of belowground herbivory are not ameliorated by abundant nutrients. Root removal may negate some effects of fertilizer application on the growth of current shoots and whole clones.     

Number,position, diameter and initial direction of growth of primary roots in Musa

To understand soil colonization by a root system, information is needed on the architecture of the root system. In monocotyledons, soil exploration is mainly due to the growth of adventitious primary roots. Primary root emergence in banana was quantified in relation to shoot and corm development. Root emergence kinetics were closely related to the development of aerial organs. Root position at emergence on the corm followed an asymptotic function of corm dry weight, so that the age of each root at a given time could be deduced from its position. Root diameter at emergence was related to the position of the roots on the corm, with younger roots being thicker than older ones. However, root diameters were not constant along a given root, but instead decreased with the distance to the base; roots appear to be conical in their basal and apical parts. Root growth directions at emergence were variable, but a high proportion of the primary roots emerged with a low angle to the horizontal. Further research is needed to evaluate whether these initial trajectories are conserved during root development. Results presented in this study are in good agreement with those reported for other monocotyledons such as maize and rice. They give quantitative information that will facilitate the development of models of root system architecture in banana.     

Root and shoot growth of semi-dwarf and taller winter wheats

Investigations are reported of root and shoot growth in semi-dwarf and taller winter wheat varieties grown in contrasting soils over three years. Comparisons were made of the distribution with depth of roots, estimated by injecting rubidium-86 into stem bases and counting the content in soil cores. The relative ability to absorb phosphate from different zones was measured from the recovery in aerial parts of ³²P injected into the soil at different depths. The distribution of dry matter in roots and aerial parts, and total root length, was measured using soil cores and samples of aerial parts taken during the growth of the crop. Relative growth rates of the aerial parts followed a sigmoid curve, but those of the roots showed little change between germination and anthesis. There was little evidence of varietal differences in root growth, though there was some indication that at depth the roots of the semi-dwarf varieties were more extensive and absorbed more phosphate than those of the taller varieties.     

Microcutting leaf area,weight and position on the stock shoot influence root vigour,shoot growth and incidence of shoot tip necrosis in grape plantlets in vitro

The physiological parameters of microcuttings, namely leaf area, weight (wt) and position on the stock shoot, had significant effects on root vigour, microshoot growth and incidence of shoot tip necrosis (STN) in cultures of grape (Vitis vinifera L.) ‘Arka Neelamani’. Single-node leafy cuttings cultured in MS medium containing 1 μM IAA and 0.1 μM GA₃ generally rooted first and subsequently sprouted into a single shoot. Small leafed cuttings exhibited slow root emergence, poor quality roots, early sprouting and weak shoot growth. Large leafed cuttings on the other hand, showed early rooting, vigorous roots, delayed sprouting and healthier shoots. Significant correlations were observed between fresh root wt per plantlet at 1 month in culture and wt of lamina, total wt and leaf area of the cuttings in that order. A significant correlation also existed between wt of roots and height or wt of the sprout that developed. The study suggests that the weight or area of the leaf governed the root growth in a microcutting. STN was observed in some plantlets particularly those derived from large leafed cuttings. Such cuttings showed vigorous roots and delayed but fast sprout growth that ended in STN. Plantlets showing STN had less Ca⁺⁺ and Mg⁺⁺ in the shoot tissue than in the shoots of normal plantlets while the roots showed similar Ca⁺⁺ or higher Mg⁺⁺ contents. Both had comparable amounts of cytokinins in shoot and root tissues. This revised version was published online in June 2006 with corrections to the Cover Date.     

Differences in root and shoot development of tomato (Lycopersicon esculentum L.) varieties across contrasting soil environments

Summary The root and shoot growth of three tomato (Lycopersicon esculentum L.) varieties, VF-10, VF-1908 and Paste 56 were compared in either a river-washed sand or an alluvial silty loam, with or without added nutrients, to determine factors influencing root growth and development. VF-10 had consistently higher shoot weights than the other two varieties, particularly by 45 days from germination. Although the root-to-shoot ratio varied with soil treatment, no significant differences in this ratio occurred among varieties. The roots were characterised by a taproot, thickened in the uppermost 3 to 5 cm, with 86 to 190 secondary roots when harvested 30 days after germination. The variety VF-1908 had a higher proportion of fine roots than the other two varieties over all treatments. On the basis of root weight and length, VF-1908 was also more stable across the imposed environmental gradient than the varieties VF-10 or Paste 56. This arose from less variability across soil treatments in secondary branching in VF-1908; over the four soil treatments the number of secondary roots varied from 104 to 131 in VF-1908 compared to 86 to 139 in VF-10 and 95 to 190 in Paste 56. VF-1908 and Paste 56 also had less variation in tertiary branching than VF-10, which had a consistently greater number of major tertiary roots than the other two varieties over all soil treatments. With the exception of Paste 56 in the fertilized silt, shoot growth was correlated with root length.     

Root cooling strongly affects diel leaf growth dynamics,water and carbohydrate relations in Ricinus communis

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root‐zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant – especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root‐zone temperature and its heterogeneity inside pots.     

The effect of spraying with DNOC (4,6-dinitro-o-cresol) on the growth of the roots and shoots of winter rye plants

Summary Spraying young winter rye plants with 4,6-dinitro-o-cresol (DNOC), as a contact herbicide, initially depressed the growth rate of the plants although this subsequently increased until ultimately the yield of plant material was greater than achieved by the control plants, also apart from the herbicidal effect of the treatment.It was observed that the growth rate of the roots of the treated plants recovered sooner than did the growth rate of the aerial parts. Ultimately a greater root dry weight was produced by the treated plants than by the control plants. This was achieved before the dry weights of the aerial parts of the treated plants equalled those of the untreated plants. The shoot/root ratio of the treated plants was lower than that of the control plants and the roots of the treated plants survived longer in the deeper layers of the soil than did those of the control plants.It is suggested that the subsequent increase in shoot growth in the treated plants may be a consequence of increased uptake of nutrients from the soil by a more vigorous root system. It is concluded that the increase in root growth which follows the initial depression, after treatment of the plants with DNOC, may be due to factors within rather than outside the roots.     

The consequence of peroxidase overexpression in transgenic plants on root growth and development

Transgenic tobacco plants that overproduce the tobacco anionic peroxidase wilt upon reaching maturity, although having functional stomata and normal vascular anatomy and physiology. These plants were examined further to determine the cause for wilting, and thus better understand how the anionic peroxidase functions in plant growth and development. Shoots from young peroxidase overproducing plants were grafted onto wild-type tobacco root stock to determine if the roots could absorb and transmit sufficient water to maintain leaf turgidity. These grafted plants never wilted when grown in the greenhouse though shoot peroxidase activity remained ten-fold greater than in control plants, thus indicating that wilting is a consequence of peroxidase expression in the roots. Close examination of root systems revealed considerably less root mass in the transformed plant, primarily exhibited through a decrease in branching. At flowering, root growth rate and total root mass in transformed plants were less than 50% of control plants although shoot mass and growth rate were unchanged. This is in contrast to root growth in young seedlings where transformed plants performed equivalently to controls. Root hydraulic conductivity was measured to evaluate the effect of elevated peroxidase expression on water absorption and transport; however, no significant change in hydraulic conductivity was found in transformed plants. The consequence of anionic peroxidase overexpression on indoleacetic acid (IAA) metabolism was also examined. No significant difference in IAA levels was observed; however, root elongation in plants overexpressing peroxidase was insensitive to exogenous IAA. It can be concluded that the overexpression of the tobacco anionic peroxidase in transformed plants results in diminished root mass from fewer root branches, which contributes to the wilting phenomenon seen in these plants. Further, this developmental change in transformed plants may be a consequence of the metabolism of IAA by the anionic peroxidase.     

Zeatin-induced one-step in vitro cloning affects the vegetative growth of cranberry (<Emphasis Type="Italic">Vaccinium macrocarpon</Emphasis> Ait.) micropropagules over stem cuttings

Shoot proliferation and rooting of three cranberry (Vaccinium macrocarpon Ait.) cultivars Bergman, Pilgrim, and Stevens were obtained in vitro on a modified nutrient medium containing zeatin following a one-step procedure. Bergman and Stevens differed in terms of shoot height, leaf number per shoot, rooting frequency, root number per explant, and root length; this was manifested with various concentrations of zeatin. Shoots proliferated and roots developed best when nodal segments were cultured in the medium supplemented with very low concentration of zeatin (2–4 μM). Such zeatin-induced tissue culture (TC) shoots of Bergman, Pilgrim, and Stevens were rooted ex vitro and compared with those propagated by conventional softwood cuttings (SC) for growth and morphology over four growth seasons. Significant interactions for leaf number per upright were observed among the treatments. The cultivars differed in terms of runner number per plant, upright length, number of leaves per upright, and shoot vigor. The propagation method had an effect on morphology of cranberry plants. The TC plants produced more runners and uprights with more leaves per upright than the conventional cuttings. This increase in vegetative growth of in vitro-derived plants over stem cuttings varied among genotypes. In vitro culture on zeatin-containing nutrient medium apparently induces the juvenile branching characteristics that favored enhanced vegetative growth with more shoots and leaf production.     

Abscisic acid accumulation in the roots of nutrient-limited plants: its impact on the differential growth of roots and shoots

We describe the involvement of abscisic acid (ABA) in the control of differential growth of roots and shoots of nutrient limited durum wheat plants. A ten-fold dilution of the optimal concentration of nutrient solution inhibited shoot growth, while root growth remained unchanged, resulting in a decreased shoot/root ratio. Addition of fluridone (inhibitor of ABA synthesis) prevented growth allocation in favour of the roots. This suggests the involvement of ABA in the redirecting of growth in favour of roots under limited nutrient supply. The ABA content was greater in shoots and growing apical root parts of starved plants than in nutrient sufficient plants. Accumulation of ABA in shoots of nutrient deficient plants was linked to a decrease in leaf turgor. Increased flow of ABA in the phloem apparently contributed to the accumulation of ABA in the apical part of the roots. Thus, partitioning of growth between roots and shoots of wheat plants limited in mineral nutrients appears to be modulated by accumulation of ABA in roots. This ABA may originate in the shoots, where its synthesis is stimulated by the loss of leaf turgor.     

Root growth responses to lead in young maize seedlings

This work was undertaken to follow the appearance and development of symptoms of lead toxicity in growing roots of seedlings. The effects of lead nitrate (10^-2–10⁵ M) were studied on the roots of maize (Zea mays) seedlings, cvs. Diamant and Sterling. The roots were grown on filter paper either on glass in trays or in large Petri dishes. The following characteristics of root growth were studied: seed germination, length of primary and seminal roots, number of seminal and lateral roots, length of branching zone, length of meristem and fully-elongated cells and the number of fully-elongated cells along the daily length increment. 10^-2 M lead nitrate exerted a clear toxic effect on root elongation just after radicle emergence; its influence on shoot growth was weak. However 10^-2 M Pb solution did not affect either radicle emergence itself or seminal root emergence, which can be explained by the impermeability of seed testa to lead salt. The inhibitory effect of 10^-3 M lead nitrate appeared a day later and was not as toxic: the growth of primary and seminal roots proceeded at lower rate due to a partial inhibition of cell division and cell elongation in them. 10^-3 M lead nitrate modified the root system morphology: it exerted no effect on the emergence of lateral roots and their number, but induced a more compact distribution of lateral roots along a shorter branching zone due to a reduced length of mature cells in the primary root. As a result of the more prominent inhibition of primary root growth, a shorter branching zone with more compactly located lateral roots occupied a position much closer to the root tip than in roots grown without the influence of lead.     

The role of roots and cotyledons as storage organs in early stages of establishment in Quercus crispula: a quantitative analysis of the nonstructural carbohydrate in cotyledons and roots

Quercus seedlings have hypogeal cotyledons and tap roots, both of which act as storage organs. The importance of the storage function in the two organs may change as the seedling develops. Therefore, changes in carbohydrate reserves in cotyledons and roots of Q. crispula grown under 40 % and 3 % of full light from shoot emergence to the completion of the first leaf flush were monitored. In addition, a shoot-clipping treatment was performed to examine the relative contribution of the cotyledons and tap roots to resprouting. Cotyledons maintained large amounts of nonstructural carbohydrates during shoot development, and carbohydrates were still present in the cotyledons during the final phase of leaf flush. In addition, a notable increase in the amount of carbohydrates was observed in tap roots before leaf flush at both light levels. Since root development occurred before leaf flush, even in plants grown under 3 % light, the carbohydrate found in them presumably originated from seed reserves and was translocated to roots as storage reserves. When shoots were clipped at the leaf flushing stage, the amount of carbohydrate decreased only in the cotyledons after resprouting, suggesting that cotyledons act as the main storage organs during shoot development stages. However, it could be advantageous as a 'risk avoidance strategy' for the seedlings to store reserves in both cotyledons and roots, since cotyledons may be removed by predators during shoot development.     

Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root:shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.     

Tomato (Lycopersicon esculentum Mill., cv. 'Better Bush') Plant Response to Root Restriction

Observations presented here describe changes in the growth ofLycopersicon esculentum Mill., cv. ‘Better Bush’,at the onset of root-restriction stress. Plants were grown ineither 1500 cm³ (control) or 25 cm³ (treated) containers ina flow-through hydroponic culture system (FTS). Seeds were imbibed,germinated, held for 13 d in sterile germination bags, thenplaced into the FTS and designated day zero plants. Plants grownin the FTS were harvested, every 7 d, from day 11 to day 46.Plant height, root and shoot weights, leaf areas, leaf lengths,branching and flowering were measured to illustrate morphologicalchanges that occurred in response to root-restriction stress.Plants restricted to a 25 cm³ root volume experienced a markedstress after 18 d in the FTS. A reduction in leaf elongationwas evident and preceded the time (prior to day 25) when maximumdry weights were attained by restricted root systems. Controlplants had greater leaf areas and plant dry weights than thoseof root-restricted plants after day 18. Treated plants showedno significant increase in dry weights from day 32 to the endof the experiment. Between day 18 and 25 the root: shoot ratiofor the treated plants dropped below that of the controls. Adventitiousrooting was evident in treated plants by day 25. Roots of thetreated plants showed an apparent waterlogging indicated bybrowning of roots by day 32. Root turnover followed as the primaryroot system was replaced by adventitious roots. The number ofbranches or flowers did not differ between control and treatedplants. The timing of the events described here can be usedto further the study of specific physiological responses oftomato plants to root-restriction stress.