Development Of New Roots Research Articles

Physiological Characteristics of Root Regeneration in Rice Seedlings

The rapid development of new roots in transplanted rice (Oryza sativa L.) is crucial for shortening the returning green time of seedlings and accelerating tillering. Root regeneration plays an important role in enabling seedlings to resume normal growth and produce effective spikes after root injury. This study aimed to investigate the dynamic changes in new root production and the growth of seedlings of different varieties after root cutting in addition to the key physiological factors. We utilized hydroponics to set up four different time treatments to observe the occurrence of root systems in various rice seedling varieties after root cutting; we also measured related physiological indexes to further analyze the results. This study found that changes in aboveground nutrient, energy, and hormone levels in seedlings are critical for the growth of new roots after cutting. A morphological analysis showed that the root germination force of Zhongzao 39 (ZZ39) was stronger than Jiazao 311 (JZ311) before shearing and weaker after shearing. Physiological and biochemical analyses revealed that both ZZ39 and JZ311 experienced a decrease in their aboveground nitrogen and phosphorus content after root cutting. Soluble sugar content and starch content were found to decrease to their lowest levels after two days of root shearing. Furthermore, both varieties showed a significant increase in aboveground indole-3-acetic acid (IAA) content after two days of root shearing, and the IAA content in new roots was also higher. The results indicate that higher levels of hormones in seedlings with cut roots can enhance the transportation of nutrients and carbohydrates from the stems and leaves to the roots, leading to improved growth and the production of new roots. Additionally, the accumulation of IAA in damaged roots can also positively impact this process. This study found significant differences in the regeneration of rice seedling roots after cutting depending on the variety. We identified key physiological characteristics that affect new root generation, which provides a scientific basis for identifying strong root regeneration varieties and developing cultivation measures to promote new root growth in rice.

Genome expression profile analysis of two types of new roots in apple rootstock via Solexa sequencing

Currently, the molecular regulation mechanisms involved in the early development of new roots are poorly known in apple. To gain insight into the transcriptome dynamics that are associated with its development, genome-wide gene expression profiling was conducted by Solexa sequencing. More than five million tags were generated from two type new roots, long root and short root, including 5,913,044 and 6,236,711 clean tags in the two libraries, respectively. Of these, 44,513 (26.61%) and 43,117 (20.02%) tags were matched to the reference genes. The most differentially expressed tags with FDR≤0.001 and |log2Ratio|≥1 were analyzed further, representing 815 up-regulated and 831 down-regulated genes, except for unknown transcripts. These genes participated in biosynthesis of secondary metabolites, plant-pathogen interaction, plant hormone signal transduction, phenylpropanoid biosynthesis, ribosomes and flavonoid biosynthesis. Most genes were identified in the cell part function (82.7%), catalytic activity (71.1%), ion binding (59.2%) and membrane transcription (24.5%), etc. Next, the expression patterns of 20 genes were assessed by quantitative real-time PCR, and the results obtained showed general agreement with the Solexa analysis. Moreover, a visual database was constructed in order to browse and query the results, and the website is http://www.applegene.org/deg/. In conclusion, we first reveal the complex changes in the transcriptome during the early development of apple new root and provide a comprehensive set of data that are essential for understanding its molecular regulation.

Changes in chemical composition and structure of root cell wall of citrus rootstock seedlings in response to boron deficiency by FTIR spectroscopy

ABSTRACTBoron (B) is an essential microelement for higher plants, and plays a role in cell wall formation. Citrange seedlings with different amounts of B were studied through Fourier-transform infrared spectroscopy (FTIR) analyses. The results showed that the growth and development of new roots were evidently inhibited by B deficiency. Boron-deficiency significantly increased cell wall biomass (CWB) as a percentage of root fresh weight and the ratio of B concentration in cell wall to the total B in roots. The findings from CWB FTIR spectra showed the band at 3429 cm−1 under control condition was shifted to 3442 cm−1 after being B deprived, suggesting that the mode of hydrogen bonding was changed by B deficiency. Boron deficiency clearly decreased the peak height of carboxylic ester band around 1741 cm−1, but increased that of COO− stretching band around 1400 cm−1, suggesting that the relative amount and degree of esterification of carboxylic groups was decreased and pectin content and structure was altered. These results demonstrate that changes in amount, structure, and assembly of root cell wall polymers may be either specific or adaptive responses of citrange seedlings to B deficiency and FTIR can be an appropriate method to study changes in cell wall under B deficiency.

Pendimethalin Influence on Azalea Shoot and Root Growth

Abstract Preemergence herbicides, especially members of the dinitroaniline class, are commonly applied to container-grown nursery stock. Dinitroaniline herbicides inhibit the development of new roots in susceptible plants, and can injure nursery crops. The effect of pendimethalin on root and shoot growth of ‘Tradition’ azalea was evaluated at 4 and 8 weeks after treatment. Pendimethalin was applied to azalea tops (shoot exposure), the growing medium (root exposure), or to the tops plus growing medium. Initial plant heights and root volumes were used to calculate percent increase in growth as affected by application method. Four weeks after treatment, plant height of shoot-only and shoot plus root treatments increased by 17 and 25%, respectively, while height in root-only and untreated control plots increased by 34%. Eight weeks after treatment (WAT), plant height of shoot-only and shoot plus root treatment increased by 61 and 63%, respectively, compared to root-only and untreated control plots, which increased by 105 and 108%, respectively. Greatest reductions in root growth were found in the shoot plus root and root-only treatments at 4 and 8 WAT, likely due to pendimethalin movement into the upper 3 cm of the growing mix. Pendimethalin can directly affect azalea shoot growth following exposure to only the foliage, and directly reduce root development following application to the growing medium. Any stunting of growth following over-the-top application of a sprayable pendimethalin formulation likely results from impacts on both the root and shoot systems.

Flooding effects in seedlings of Cytharexyllum myrianthum Cham. and Genipa americana L.: responses of two neotropical lowland tree species

Six-month-old seedlings of Cytharexyllum myrianthum and Genipa americana, two common tree species in different flood-prone areas in Brazil, were flooded for up to 90 days to compare their survival and growth responses under these conditions. Seedlings of both species were found to be relatively tolerant to flooding but growth responses changed according to treatment and plant species. Growth of G. americana was reduced by flooding, showing a decrease in root and leaf dry mass, root/shoot ratio and height, without showing any adaptive morphological changes. On the other hand, growth of C. myrianthum seedlings was stimulated under flooding conditions, showing an increase in root dry mass, root/shoot ratio, height, stem diameter and some morphological changes in roots and stems, i.e., development of new roots and stem base hypertrophy. These results could be regarded as an experimental corroboration of the field observations, showing that these species could be indicated for restoration programs of some Neotropical wetlands.

Carry-over effects of ozone on root growth and carbohydrate concentrations of ponderosa pine seedlings.

Ozone exposure decreases belowground carbon allocation and root growth of plants; however, the extent to which these effects persist and the cumulative impact of ozone stress on plant growth are poorly understood. To evaluate the potential for plant compensation, we followed the progression of ozone effects, with particular emphasis on the development of new roots. Ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings were exposed to ozone for 2 years. Following removal of the seedlings from ozone, root growth was assessed to characterize the carry-over effects on new root production, and carbohydrate concentrations were measured to determine if allocation strategies differed among ozone treatments. Four months after removal from ozone, dormant seedlings had significantly lower starch concentrations in stems, coarse roots and fine roots than control seedlings. Following root flushing, starch concentrations in all seedlings decreased, with ozone-treated seedlings containing significantly less starch, sucrose, fructose, glucose and total monosaccharides than control seedlings. There was some evidence that stem starch was mobilized to compensate partially for the lower concentrations of root starch in ozone-treated seedlings; however, there was significantly less new root production in seedlings previously exposed to ozone for 2 years than in control seedlings. Early senescence of older needle age classes, perhaps resulting in inadequate available photosynthate, may be responsible for the reduction in new root production during the year following exposure to ozone. Stored carbohydrate reserves, which were depleted in seedlings previously exposed to ozone, were insufficient to compensate for the ozone-induced reduction in canopy photosynthate. We conclude that there are carry-over effects of ozone exposure on ponderosa pine seedlings, including an enhanced potential for seedling susceptibility to other stresses even in respite years when ozone concentrations are low.

A large ephemeral release of nitrogen upon wetting of dry soil and corresponding root responses in the field

To assess changes in soil nutrients, root growth and mycrorrhizal infection in response to rain events, a water pulse was applied to a very dry soil. Wetting of a dry soil in the Great Basin of the Western United States led to a striking pulse of available soil nitrate in a field plot, but available phosphate was not affected. This is the first field demonstration of this phenomenon in the Great Basin as far as we are aware. This pulse was only apparent for a few days, probably due to microbial immobilization of the nitrogen. Root ammonium uptake capacity increased within one day of the water pulse, but new root growth was not apparent until 3 days after the water pulse. Thus, to capture this ephemeral release of nitrogen, enhanced uptake capacity of existing roots was probably more important than development of new roots. Mycorrhizal infection was not affected by the water pulse treatments. However, since the water pulse only affected nitrogen availability and mycorrhizae are generally most effective in facilitating acquisition of less mobile nutrients such as phosphate, mycorrhizae likely do not play an important role in taking advantage of this opportunity provided by the pulse of water.

Effects of flooding on leaf dynamics and other seedling responses in flood-tolerant Alnus japonica and flood-intolerant Betula platyphylla var. japonica.

Two-year-old seedlings of Alnus japonica Steud. and Betula platyphylla var. japonica Hara were flooded from mid-June to early November, to study the effects of flooding on seedling survival and growth, morphological changes in stems and roots, leaf emergence, leaf fall, and leaf longevity. In A. japonica, growth was not affected by flooding, except for a slight decrease in height growth, but some morphological changes of stems and roots were observed, i.e., stem base hypertrophy, hypertrophied lenticels, formation of adventitious roots and development of new roots. In B. platyphylla var. japonica, growth was severely reduced by flooding and all seedlings died by the 20th week of flooding, without showing any adaptive morphological changes in stems or roots. Flooding induced rapid depression of leaf emergence, promoted leaf abscission, and reduced leaf longevity in B. platyphylla var. japonica. In contrast, in A. japonica, basal leaf senescence was delayed in flooded seedlings, thereby extending leaf longevity compared with unflooded seedlings.

Responses to salinity of grapevine plants with split root systems.

Grape yield, shoot and root vigour and water use by grapevine plants with split root systems were investigated. Some plants had both root parts continuously irrigated either with fresh or with saline water. Some plants got a dual treatment; one portion got fresh water and the other saline water. The irrigation water of a third group was changed during the experiment from fresh to saline water or vice versa. Fruit yield and root and shoot viability were positively correlated with the actual water use. Water ascent along the stem of the grapevines was found to be sectorial. Most of the water was supplied by the freshwater roots. Only small quantities of water were supplied by salt-affected roots to their respective twigs. Changes in the water quality of the root medium induced a dual effect: (a) a fast response, caused by the direct change in the ambient w7 ater potential; and (b) a long-term response that developed over several weeks. The latter response was induced by the development of new roots, or by death of others, upon a change in the quality of the irrigation water. The commonly used grapevine plants of the Arava valley are negatively affected by NaCl already at concentrations below 100 mM. Under such conditions, shoot growth and fruit yield were seriously inhibited, even when one part only of the root system was exposed to saline water.

Variations in the rates of nitrification and denitrification during the growth of potatoes (Solanum tuberosum L.) in soil with different carbon inputs and the effect of these inputs on soil nitrogen and plant yield

A potato crop (Solanum tuberosum L. cv. Maris piper) was grown in a soil to which N was added, as NH4NO3, with or without added C, as sucrose or straw. Shortly after amendment the soil, in all treatments, contained only relatively low levels of mineral N. However, these levels increased later. The increase, which was greatest in the absence of added C and least with added sucrose, occurred before the emergence of the plant canopy. The addition of C to the soil had no effect on plant yield, measured either as dry matter or total N content. The potential nitrification rate was high early in the season, and decreased significantly as the plants developed. The potential denitrification rate showed two significant peaks in activity, possibly related to plant development, the first to the development of new roots and the second to root senescence. It seems probable that the amount of C released by the potato plants was only about one-quarter of that required for the maximum microbial activity.

Importance of current photosynthate to new root growth in planted conifer seedlings

A series of experiments were conducted to examine the importance of current photosynthate for development of new roots in planted conifer seedlings and to assess the possible importance of carbohydrate reserves. Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and Sitka spruce (Piceasitchensis (Bong.) Carr.) seedlings, labelled with 14CO2 in October, contained 14C in old roots but little in new roots when placed into growing conditions in January. New roots of seedlings labelled after 12 days growth in January were highly radioactive, indicating that current photosynthate was the primary carbon source for new roots. These results agreed with an experiment in which the amount of new root growth of 1 + 1 Douglas-fir transplants was proportional to light intensity. Net photosynthesis (Pn) of similar Douglas-fir nursery stock was inadequate to supply carbon for respiration and new root growth at 200 μE•m−2•s−1, although new root growth occurred. The ability to achieve gas exchange from the moment of planting in moist soil was evident from photosynthesis measurements and transpiration weighings, but although preconditioning affected new root growth in lodgepole pine (Pinuscontorta Loud.), no relationship between new root growth and Pn was observed.

Effects of heavy metals on water hyacinths ( Eichhornia crassipes (Mart.) Solms)

Water hyacinths ( Eichhornia crassipes (Mart.) Solms) were exposed for 6 wk to solutions containing 0–5 mg/1 Ph, Cd or Cu. The metal concentrations and metal accumulations within plant tissues increased linearly with solution concentration in the order leaves < stems < roots. The order of increasing mobility at solution concentrations ≥ 1.0 mg/l was Pb < Cu < Cd. There was no apparent effect of Pb on plant growth, but both Cd and Cu were toxic and caused substantial reductions in growth. The threshold toxicity of Cd was approximately 0.5 mg/l, whereas that for Cu was between 1.0 and 2.0 mg/l. Concentrations of Cd and Cu beyond the threshold toxicity produced chlorosis, suppressed development of new roots, and reduced relative growth rates to about ten percent of those of either the controls or plants exposed to Pb. These studies indicate that caution should be exercised when using results of short-term laboratory studies in combination with data on biomass production under optimum field conditions to predict the ability of plants to absorb toxic substances from waste water.

Factors Influencing the Survival of Propagules of Tall Fescue (Festuca arundinacea Schreb.)

SUMMARYPropagules of five tall fescue genotypes, planted monthly, from April to December, made the greatest growth in April and September and the least in December. Despite the diverse geographic origin of the genotypes, there was no indication of interaction between genotypes and daylength. Propagules grew more vigorously when cut just above the basal leaf sheath then when cut to two or three inches in length. The complete removal of roots, which would facilitate planting, did not reduce growth and appeared to enhance the development of new roots. Propagules consisting of two or three culms grew more vigorously than those consisting of a single culm. Accordingly, if propagules were fragile or if survival was poor, two-culm propagules would become established more readily. Genotypes differed in growth rate even when planting weights were kept uniform. Results of this study could be used to reduce the time and cost of vegetative propagation of tall fescue.

Errata: Corynephorus Canescens (L.) P. Beauv. as a Model for the Ammophila Problem

Corynephorus canescens, a tufted perennial, 10-30 cm high, is a widespread plant of European coastal and inland sand dunes where it often forms a major component of the vegetation. In Britain it is much rarer, being present in abundance only on the coastal dunes of East Anglia (Marshall 1964). The experimental study to be described was concentrated on the populations of Corynephorus on the National Nature Reserve north of Winterton, Norfolk, a description of which appears in Steers & Jensen (1953), but was supplemented by comparisons with populations from other dune systems. C. canescens and Ammophila arenaria behave somewhat similarly in relation to sand accretion. In areas where there is accretion up to 40 cm per annum for Ammophila and up to 10 cm per annum for Corynephorus, they grow vigorously. The plants are large, green and fresh in appearance, there is an abundance of new root production and flowering occurs freely. On areas of stable dune, however, both grasses show a marked decline in vigour, they are smaller, there is litter accumulation, the development of new roots is rare and there is sometimes a decline in flowering. Ammophila exhibits a tussock growth form in comparison with the more uniform shoot distribution in unstable areas (GreigSmith 1961). This decline in vigour of Ammophila has been commented on in the literature for over 100 years (early literature cited in Marshall 1963) and many authors have suggested reasons to account for it though these are rarely based on an experimental study (Table 1). It is noteworthy that the reasons listed in Table 1 take relatively little account of factors associated with the morphology of this highly specialized species and its pattern of growth in a changing environment. Further discussion of the reasons presented in Table 1 is deferred to Section IV (ii); the reasons are considered in relation to Corynephorus in Section II (ii). The intractability of Ammophila as an experimental plant, due to its size, was obviated in the present study by using Corynephorus as a model for the problem because it responds similarly to stable dune conditions.

Studies on the Physiological Function of the Crop Roots. : (II) Nitrogen metabolism and growth responses in the rice plant in which RNA synthesis of the roots was inhibited by soaking the roots in ribonuclease solution.

In the case of root injuried, it was observed that protein breakdown occurred with rapid decrease of RNA in the shoots of rice plant (from the previous report). Accordingly, author considers that RNA metabolism of the roots played an inportant role im nitrogen metabolism of the shoots. In this experiment, RNA synthesis in the root was inhibited by soaking the root in ribonuclease solution. Results obtained are as follow: (1) The content of protein-nitrogen decreased with the increase of soluble-nitrogen and this tendency attained maximum at the concentration of 500 ppm RNase. (2) The ratio of protein-N/soluble-N fell with the lapse of time, and soluble-nitrogen attained maximum at the 8th day after treatments and then decreased. (3) The rate of growth in the term of fresh weight was greatly retarded by RNase-treatment during the 8 days. After that, this tendency was disappeared and the growth of the shoot recovered. (4) As regards the relationship between roots and shoots, it was observed that elongation of the newly developing leaf was largely affected by the treatments of rots, and with the cessation of the treatments, new roots developed so quickly that new leaf began to appear. This fact suggests that there is close relationship between development of new roots and formation of new leaves.

Studies on the reduction of the transplanting injury in Japanese persimmon trees. II

Japanese persimmon trees make poor growth very often in the first growing season after they are transplanted into the field. It is said that one of the causes of this trouble is due to the delayed and poor growth of new roots from the transplants. In this study, application of potassium α-naphthaleneacetate, a growth regulator, was made in an, effort to overcome this trouble by promoting the new root development of the transplants. Oneyear-old persimmon seedlings were dug up and all their fine roots were trimmed off. Some of the seedlings were treated by soaking their roots in the growth regulator solution of 0.001 to 0.05% for 24 hours (dipping method). Others were treated by applying the solution of 0.005 to 0.01% into the soil once or twice after they were planted in the soil (soil application method). The check plants were dipped in tap water for 24 hours. All the plants were grown in an unheated glass house for protecting them from frost. In June, their roots were washed out for the observation of new root development. The growth regulator treatments accelerated neither the opening of buds nor the unfolding of leaves. The treatments, however, promoted the elongation of new shoots and increased the size of leaves (Fig.1). These effects were significant from an early stage of growth. The treatments induced earlier development of new roots, and markedly increased the number and weight of new roots (Fig. 2). The dipping method was more effective than the soil application method. The higher the concentration of the growth regulator solution, the greater was the effect, up to 0.05%, the highest concentration used in this study.

Studies on Rape Culture by means of Provisional Transplanting in the Nursery Bed

Investigation has been carried out on the effect of provisional transplanting of rape seedlings in the nursery bed since 1949. Their results may be summerized as follows. (1) The growth of the provisionally transplanted seedlings in the nursery bed was discouraging and that of its seedlings also was small in size. Accordingly the fresh weight of the aerial part of the seedlings was low. The growth of the aerial portion of the plants after transplanting in the main field was also not satisfactory. Flower bud differentiation and both flowering and maturing were delayed and the yield was also relatively low. (2) Most of the roots had been damaged by provisional transplanting in the nursery bed. Though the rest roots grew up rapidly and vigorously, the growth of the tap-root stopped and it remained short. So that the roots then developed shallow root system which had fine roots around the short tap-root. The stele of root was remarkably lignified, and fine roots were apt to get damaged when seedlings were pulled up from the nursery bed. The increase of roots weve lower in comparison to control seedlings, because of the poor development of new roots. (3) The provisionally transplanted seedlings could take roots quickly after setting in the main field. But the absolute number of leaves were fewer, as a result of which sound leaves were less in number. (4) At any kinds of spacing in the nursery bed, the provisionally transplanted seedlings could not become large, but the growth of the seedlings was uniform. On the contrary, the controlled seedlings were able to get large, but their growth was not uniform. (5) Close correlation could be found between the fresh weight of seedlings and the yield, but on the other hand there was less correlation between the ratio of pith length to the width and the yield.

Fusarium Wilt and Corm Rot of Freesias

1. Fusarium wilt and corm rot of freesias is prevalent in California, Florida, and Indiana, and has become destructive in Texas with the introduction of extensive freesia growing. Four species of Fusarium, F. bulbigenum, F. martii-minus, F. moniliforme, and F. solani, were isolated from infected freesia corms, and reproduced the disease in inoculation experiments. F. conglutinans from cabbage plants and F. lycopersici from tomato plants also induced typical symptoms on inoculated freesias; and five other Fusarium species were found able to cause somewhat less severe injury. It is probable that other species of Fusarium may at times cause wilt and corm rot of freesias. The disease is carried by infected corms, by old remnants of infected plants, and by the soil. 2. Fusarium solani and F. martii-minus caused decay of inoculated onion bulbs, but the other two Fusarium spp. isolated from freesia corms did not attack onions. Normal gladiolus corms planted in soil inoculated with the four species of Fusarium from freesias were attacked by a decay of the plates, which also prevented development of new roots.