Distribution and redistribution of extension growth along vertical and horizontal gravireacting maize roots

Horizontal primary roots of Zea mays L. were photographed during the course of their gravireaction and during a preceding growth period in the vertical orientation. The displacement, by root elongation, of marker particles on the root surface was recorded. The particle-displacement rates were used to estimate the distribution of elemental elongation rates along opposite sides of the growing root apex. In the temperature range 21–25°C there was a stimulation of local elongation rates along the upper side of a gravireacting root and a reduction (and sometimes a cessation) of elongation along the lower side. Elemental elongation rates have been related to the development of root curvature, and the magnitude of the differential growth between upper and lower sides required for a particular rate of bending has also been estimated. The results complement, and are compatible with, findings relating to the distribution of certain endogenous growth regulators believed to participate in the gravireaction.Abbreviation RELEL relative elemental rate of elongation     

Zeta potential of protoplasts from gravireacting maize roots

Protoplasts were isolated from cortical cells of the elongating zone of maize (Zea mays L. cv. LG 11) roots and submitted to microelectrophoresis. Significant and transient differences in zeta potential between protoplasts from upper and lower root sides were compared with the gravireaction and the differential elongation of these roots. The maximum difference in the zeta potential was obtained between protoplasts from the upper and lower cortical cells after 90 min, exactly the time of gravipresentation for which the maximum rate of gravireaction was observed. In addition, this almost corresponded to the time for which the difference between the elongation rates of upper and lower sides of the extending zone began to increase. Consequently, the changes in the charges of the plasmalemma of the cortical cells from the growing part of roots could be more or less directly related to the root graviresponse.     

Differential growth and hormone redistribution in gravireacting maize roots

When growing roots are placed in a horizontal position gravity induces a positive curvature. It is classically considered to be the consequence of a faster elongation rate by the upper side compared to the lower side. A critical examination indicates that the gravireaction is caused by differential cell extension depending on several processes. Some of the endogenous regulators which may control the growth and gravitropism of elongating roots are briefly presented. The growth inhibitors produced or released from the root cap move preferentially in a basipetal direction and accumulate in the lower side of the elongation zone of horizontally maintained roots. The identity of these compounds is far from clear, but one of these inhibitors could be abscisic acid (ABA). However, indol-3y1 acetic acid (IAA) is also important for root growth and gravitropism. ABA may interact with IAA. Two other aspects of root cell extension have also to be carefully considered. An elongation gradient measured from the tip to the base of the root was found to be important for the growth of both vertical and horizontal gravireactive roots. It was changed significantly during the gravipresentation and can be considered as the origin of the differential elongation. Sephadex beads have been used as both growth markers and as monitors of surface pH changes when they contain some pH indicator. This technique has shown that the distribution of cell extension along the main root axis is related to a pH gradient, the proton efflux being larger for faster growing parts of roots. A lateral movement of calcium is obtained when Ca2+ is applied across the tips of horizontally placed roots with a preferential transport towards the lower side. Endogenous calcium, which may accumulate inside the endoplasmic reticulum of some cap cells, may also act in the gravireception. These observations and several others strongly suggest that calcium may play an essential role in controlling root growth and several steps of the root gravireaction.     

Elongation and gravireaction of intact and segmented roots: light effects

Using a macrophotographic technique, kinetic studies were performed on growth and gravireaction, both measured on maize (cv. LG 11) roots. When using intact roots, it was found that the growth rate decreased two hours after the beginning of the gravistimulus, the rate of root curvature being optimal at that time. These two processes are greater in light than in the dark. Subsequently, the curvature rate decreased rapidly to zero in the dark but, in light, it continued for at least a further three hours. There was then a recovery of elongation in darkness whereas in light growth rate remained low. A comparative analysis between root segments and intact roots suggests that the correlation between the growth and the gravireaction rates differs according to the system studied and that light has a greater effect on growth rate when the roots are subject to gravitational stimuli. Present data are discussed in terms of hormone balance between several endogenous regulators.     

Root growth and gravireaction: Influence of the shoot

The kinetics of root gravicurvature of intact maize ( Zea mays L., cv. LG 11) seedlings can be separated into two steps. From 0 to 2 h, a rapid downward bending, enhanced by light, occurred. During the next 4 h (2 to 6 h) no further curvature appeared in the dark, whereas it continued in light. The final root gravicurvature was greater for light-than dark-treated seedlings. Growth was particulary inhibited during the first 2 h.
When intact seedlings were placed horizontally and returned to the dark after a 4 h light pretreatment in a vertical position, only the second step (2 to 6 h) was changed. A negative gravitropism, associated with a stimulation of growth, appeared. Thus, when gravireaction took place in darkness, the final root gravicurvature was similar for the light-pretreated intact seedlings and the dark control. Using apical root segments, this phase of negative gravicurvature was not observed although the stimulation of gravicurvature of light-pretreated roots remained. Similar experiments were performed with seedlings having coleoptile or endosperm removed, after intact seedlings had been exposed to a light pretreatment, and gravireaction took place in the dark. Results indicated that these two organs could play an essential role in the development of gravicurvature and in the regulation of the light effects, respectively.     

Effect of triazinone on root growth and gravireaction

The effects of a synthetic growth promoter, 4-ethoxy-l-( p -tolyl)-S-triazine-2,6 (1H, 3H)-dione [TA], on growth and gravireaction of Zea mays L. (cv. LG 11) roots were investigated. In horizontal, intact roots, pretreatment with TA at 4 × 10⁻⁴ M inhibited the gravireaction. If the pretreated roots were rinsed with a buffer solution before incubation, the TA effect was reduced, indicating that a continuous presence of TA was necessary for its maximal activity. On the other hand, the TA pretreatment (1×10⁻⁵, 1×10⁻⁴ and 4 × 10⁻⁴ M ) promoted the elongation of these roots. The TA effect was stronger for illuminated roots than for those kept in darkness. TA also decreased the lateral curvature of half-decapitated roots maintained vertically in light. This indicates that the action of TA could be associated with some growth inhibiting substances produced or released in cap cells.     

Effect on Root Growth of Endogenous and Applied IAA and ABA: A Critical Reexamination

Applications of indole-3yl-acetic acid (IAA) and abscisic acid (ABA) were done on two-day-old intact maize (cv LG 11) roots. The effect of the treatment on the root growth depends on their initial elongation rate. The slow growing roots were all inhibited by exogenous IAA and ABA at any concentrations used whereas for the fast growing roots their elongation was promoted by these two hormones at low concentrations. Quantitative analyses of endogenous IAA and ABA were performed using the gas chromatography-mass spectrometry technique. Detection and quantification of endogenous IAA and ABA were done on the zone of the root implicated in elongation. These techniques were achieved by electron impact on the IAA-Me-heptafluorobutyryl derivative and by negative ion chemical ionization with NH₃ on the ABA-Me ester derivative. A negative correlation between the growth and the endogenous content of these two hormones was obtained. ABA presented a larger range of endogenous level than IAA on the whole population of roots tested. When using applied IAA and ABA at different concentrations the same differentiating effect on the growth was observed. This allowed us to conclude that for identical concentrations, IAA has a more powerful effect on root elongation than ABA. Present results are discussed in relation to previous data related to the role of IAA and ABA in the growth and gravireaction of maize roots.     

Concentration dependencies of some effects of ethylene on etiolated pea, peanut, bean, and cotton seedlings

The effects of a series of concentrations of ethylene (10, 20, 40, to 10,240 nl/l) on elongation, diameter, and geotropism of the stems and roots of etiolated seedlings of Pisum sativum L., Arachis hypogea L., Phaseolus vulgaris L., and Gossypium hirsutum L. were measured or observed. Of the 24 possible responses, 4 were unaffected at the concentrations used, 5 were affected slightly, and the remaining responses exhibited a 14-fold range of apparent half-maximum concentration dependencies (i.e. 95 nl/l for the effect on pea epicotyl geotropism to 1350 nl/l for the promotion of cotton hypocotyl diameter). Six or possibly eight of these responses appear to have the same concentration dependencies while the others fell in pairs or as individual responses. The data, if interpreted in a manner analogous to enzyme kinetics, are indicative of more than one primary mechanism for ethylene action in plants.     

A comparison between 3,5-diiodo-4-hydroxybenzoic acid and 2,3,5-triiodobenzoic acid. I. Effects on growth and gravireaction of maize roots

A comparison between the effects of DIHB and TIBA on growth and gravireaction of 15 mm primary maize ( Zea mays L. cv. LG 11) roots is presented. Intact roots were pretreated in the dark for 1 h with buffered solutions (pH 5.0 or 6.0) containing DIHB (10, 50, 100 μ M ). The plantlets were then maintained either vertically or horizontally in the dark or the light, and growth and gravireaction were recorded using a macrophotographic technique. Pretreatment with DIHB slightly inhibited growth and delayed gravireaction. These effects were most marked with DIHB at 100 μ M and were enhanced when DIHB was applied at pH 5.0. Similar effects were observed in roots pretreated with TIBA, but at a lower concentration (1 μ M ). The similarities between DIHB and TIBA as regards both chemical structure and the inhibition of gravireaction and growth, lead us to suggest that a major mode of action of DIHB, like TIBA, is the inhibition of indol-3yl-acetic acid transport.     

4,4,4-trifluoro-3-(indole-3-)butyric acid promotes root elongation in Lactuca sativa independent of ethylene synthesis and pH

We studied the mode of action of 4,4,4-trifluoro-3- (indole-3-) butyric acid (TFIBA), a recently described root growth stimulator, on primary root growth of Lactuca sativa L. seedlings. TFIBA (100 µ M ) promoted elongation of primary roots by 40% in 72 h but inhibited hypocotyl growth by 35%. TFIBA induced root growth was independent of pH. TFIBA did not affect ethylene production, but reduced the inhibitory effect of ethylene on root elongation. TFIBA promoted root growth even in the presence of the ethylene biosynthesis inhibitor l - α -(2-aminoethoxyvinyl)glycine. TFIBA and the ethylene-binding inhibitor silver thiosulphate (STS) had a similar effect on root elongation. The results indicate that TFIBA-stimulated root elongation was neither pH-dependent nor related to inhibition of ethylene synthesis, but was possibly related to ethylene action.     

Factors affecting induction and development of in vitro rooting in apple rootstocks

Shoots of apple rootstocks raised in vitro were transferred to various rooting media to study the effect of different factors on root initiation and development. Various concentrations of indole-3-butyric acid (IBA) initiated rooting but maximum rooting percentage was found with 2.0 and 2.5 mg l(-1) of IBA in M7 and with 1.0 mg l(-1) of IBA in MM106. The drawback was that the roots were thick, short and with profuse callus. The presence of activated charcoal (AC) in the rooting medium improved the rooting quality but reduced the rooting percentage in both the rootstocks. In high auxin dip of 70, 80 and 90 mg l(-1) IBA for 2, 2 and 1 hr showed 75-85 per cent rooting in M7, but lacked reproducibility of the results. Whereas in MM106, 66 - 70 % rooting was achieved with 70 mg l(-1) of IBA dip for 3 h. Root induction in shoots in IBA containing liquid medium (LM) in dark for few days and root elongation in IBA--free medium in light proved most effective. On the other hand, continuous light treatment showed reduced rooting. Reduction of MS salts and sucrose in root elongation medium showed decreased rooting. Plantlets from two--stage rooting procedure showed more rapid growth and satisfactory survival during hardening of plants and on transfer to field.     

The influence of ionic concentration on population parameters,development time,activity, and respiration rate of Arctodiaptomus spinosus (Daday) (Calanoida,Copepoda)

Summary For A. spinosus, significant correlations were found between population parameters and the ecological parameters of alkalinity and temperature. For the birth rate, 43.33% of variance is explained by alkalinity and 56.33% by alkalinity and temperature. Alkalinity, and alkalinity and temperature combined account for 48.22% and 70.23% respectively of the observed variances in nauplii hatching. It was demonstrated that, provided sufficient time for adaptation is allowed, the activity of individuals is not affected by differences in the alkalinity of the medium within the normal range of concentration. Embryonic development does not appear to be influenced by the ionic concentration, but significant increases in time of development of the nauplii (at alkalinity 100 meq/l: 8.8 days/20°C) and of the copepodites (at alkalinity 100 meq/l: 12.6 days/20°C) were recorded at both low and high ionic concentrations. The lowest respiration rates (3.7 nl O₂·h^-1·g dw^-1/20°C) occurred at an alkalinity of 100 meq/l. Rates increased at lower (10 meq/l: 5.7 nl) and at higher (400 meq/l: 11.9 nl) alkalinities.     

Root elongation rate is correlated with the length of the bare root apex of maize and lupin roots despite contrasting responses of root growth to compact and dry soils

Background

We investigated interacting effects of matric potential and soil strength on root elongation of maize and lupin, and relations between root elongation rates and the length of bare (hairless) root apex.

Methods

Root elongation rates and the length of bare root apex were determined for maize and lupin seedlings in sandy loam soil of various matric potentials (?0.01 to ?1.6 MPa) and bulk densities (0.9 to 1.5 Mg m^?3).

Results

Root elongation rates slowed with both decreasing matric potential and increasing penetrometer resistance. Root elongation of maize slowed to 10 % of the unimpeded rate when penetrometer resistance increased to 2 MPa, whereas lupin elongated at about 40 % of the unimpeded rate. Maize root elongation rate was more sensitive to changes in matric potential in loosely packed soil (penetrometer resistances <1 MPa) than lupin. Despite these differing responses, root elongation rate of both species was linearly correlated with length of the bare root apex (r² 0.69 to 0.97).

Conclusion

Maize root elongation was more sensitive to changes in matric potential and mechanical impedance than lupin. Robust linear relationships between elongation rate and length of bare apex suggest good potential for estimating root elongation rates for excavated roots.     

Heat Shock Increases the Tolerance of Plants to UV-B Radiation: 2. Ethylene and Carbon Dioxide Evolution

The effects of heat shock (HS, 45°C) and UV-B radiation (280–320 nm, 18.3 kJ/(m²h)) and the consecutive action of the combination of these factors on ethylene production, gas exchange, and the growth of intact melon (Melo sativusSager.) seedlings were investigated. The changes in ethylene production and carbon dioxide exchange were described by a single-peaked curve. In the course of UV-B irradiation, the time of maximum ethylene and CO₂evolution coincided (the first 5 min) and comprised 0.36 nl/(seedling h) for ethylene and 146.2 l/(seedling h) for carbon dioxide. After HS, the maximum of ethylene production (0.37 nl/(seedling h)) was reached within 10 min, and that of carbon dioxide production (313 l/(seedling h)), within 45 min. The rate of ethylene production (0.22 nl/(seedling h)), carbon dioxide production (97.7 l/(seedling h)), and oxygen consumption (162.5 l/(seedling h)) in the control seedlings did not change in the course of experiment. Throughout the experiment, the respiratory quotient of seedlings was ca. 0.6 regardless on the nature and duration of the acting factor. Preliminary heating at 45°C for 1 h increased the tolerance of seedlings to the subsequent UV-B radiation for 1 h. The protective effect of HS manifests itself in alleviating the inhibiting action of UV-B radiation on seedling growth and development, and this effect was preceded by an increase in ethylene production and respiration. The possible mechanisms of cross-tolerance of plants to overheating and UV-B radiation are discussed.     

INFLUENCE OF THE TONIC EFFECT OF GRAVITATION AND AUXIN ON CELL ELONGATION AND POLARITY IN ROOTS

The influence of a longitudinal (tonic) gravitational force and of auxin on the pattern of growth and cell polarity has been studied on intact roots of wheat seedlings. A klinostat technique was used for controlling gravitation. Growth in length was evaluated as cell division activity, rate of cell elongation (μ/h) and duration of elongation (h). Exogenous auxin (1-NAA) increases the rate of cell elongation in all concentrations tested (10⁻⁸ — 3 × 10⁻⁷m ) and shortens the time of elongation with increasing concentration. It promotes rate of cell elongation in roots as it does in shoots. It also accentuates the polar insertion of root hairs and their growth. The tonic effect of gravitation resembles that of an increase in auxin both in light and darkness. The results are discussed in relation to plagiotropic growth of roots, root growth promotions by auxin, and the difference between root and shoot growth.     

2,4—D对水稻根尖微管排列的影响

通过共焦激光扫描显微镜对经过２,４－Ｄ处理水稻（Ｏｒｙｚａ ｓａｔｉｖａ Ｌ．）根尖的微管骨轲的排列进行了研究。结果表明,对照（未经２,４－Ｄ处理）根尖的不同生长区微管呈现不同的排列方式,生长区皮导呈管呈随机排列,伸长区微管呈横向排列,根毛区的呈斜向排列。经过２,４－Ｄ处理的根,不但皮层细胞微管表现重新定向,同时也伴随着生长受到强烈抑制。１ｍｇ／Ｌ２,４－Ｄ处理１ｈ,分生区细胞微管由随机排列变成横     

Spatial aluminium sensitivity of root apices of two common bean (Phaseolus vulgaris L.) genotypes with contrasting aluminium resistance

The initial response of plants to aluminium (Al) is an inhibition of root elongation. In the present study, short and medium-term effects of Al treatment (20 muM) on root growth and Al accumulation of two common bean (Phaseolus vulgaris L.) genotypes, VAX-1 (Al-sensitive) and Quimbaya (Al-resistant), were studied. Root elongation of both genotypes was severely inhibited during the first 3-4 h of Al treatment. Thereafter, both genotypes showed gradual recovery. However, this recovery continued in genotype Quimbaya until the root elongation rate reached the level of the control (without Al) while the genotype VAX-1 was increasingly damaged by Al after 12 h of Al treatment. Short-term Al treatment (90 microM Al) to different zones of the root apex using agarose blocks corroborated the importance of the transition zone (TZ, 1-2 mm) as a main target of Al. However, Al applied to the elongation zone (EZ) also contributed to the overall inhibition of root elongation. Enhanced inhibition of root elongation during the initial 4 h of Al treatment was related to high Al accumulation in root apices in both genotypes (Quimbaya>VAX-1). Recovery from Al stress was reflected by decreasing Al contents especially in the TZ, but also in the EZ. After 24 h of Al treatment the high Al resistance of Quimbaya was reflected by much lower Al contents in the entire root apex. The results confirmed that genotypic differences in Al resistance in common bean are built up during medium-term exposure of the roots to Al. For this acquisition of Al resistance, the activation and maintenance of an Al exclusion mechanism, especially in the TZ but also in the EZ, appears to be decisive.     

Responses of banana fruit to treatment with 1-methylcyclopropene

Experiments were conducted to determine levels of 1-methylcyclopropene (1-MCP) exposure needed to prevent ethylene-stimulated banana fruit ripening, characterise responses of ethylene-treated fruit to subsequent treatment with 1-MCP, and to test effects of subsequent ethylene treatment on 1-MCP-treated fruit softening. Fruit softening was measured at 20°C and 90% relative humidity. One hour exposure at 20°C to 1000 nl 1-MCP/l essentially eliminated ethylene-stimulated ripening effects. Exposure for 12 h at 20°C to just 50 nl 1-MCP/l was similarly effective. Fruit ripening initiated by ethylene treatment could also be delayed with subsequent 1-MCP treatment. However, 1-MCP treatment only slowed down ripening of ethylene-treated fruit when applied at 1 day after ethylene and was ineffective when applied 3 or 5 days after ethylene treatment. The ripening response of fruit treated with 1-MCP and subsequently treated with ethylene varied with interval time between 1-MCP and ethylene treatments. As time increased, the response of 1-MCP-treated fruit to ethylene was enhanced. Responses to 0.1, 1, 10 or 100 µl ethylene/l concentrations were similar. Enzyme kinetic analysis applied to 1-MCP effects on ethylene-induced softening of banana fruit suggested that 1-MCP inhibition is by noncompetitive antagonism of ethylene binding.     

Auxin, actin and growth of the Arabidopsis thaliana primary root

To understand how auxin regulates root growth, we quantified cell division and elemental elongation, and examined actin organization in the primary root of Arabidopsis thaliana. In treatments for 48 h that inhibited root elongation rate by 50%, we find that auxins and auxin-transport inhibitors can be divided into two classes based on their effects on cell division, elongation and actin organization. Indole acetic acid (IAA), 1-naphthalene acetic acid (NAA) and tri-iodobenzoic acid (TIBA) inhibit root growth primarily through reducing the length of the growth zone rather than the maximal rate of elemental elongation and they do not reduce cell production rate. These three compounds have little effect on the extent of filamentous actin, as imaged in living cells or by chemical fixation and immuno-cytochemistry, but tend to increase actin bundling. In contrast, 2,4-dichlorophenoxy-acetic acid (2,4-D) and naphthylphthalamic acid (NPA) inhibit root growth primarily by reducing cell production rate. These compounds remove actin and slow down cytoplasmic streaming, but do not lead to mislocalization of the auxin-efflux proteins, PIN1 or PIN2. The effects of 2,4-D and NPA were mimicked by the actin inhibitor, latrunculin B. The effects of these compounds on actin were also elicited by a 2 h treatment at higher concentration but were not seen in two mutants, eir1-1 and aux1-7, with deficient auxin transport. Our results show that IAA regulates the size of the root elongation zone whereas 2,4-D affects cell production and actin-dependent processes; and, further, that elemental elongation and localization of PINs are appreciably independent of actin.