Water balance of plants during root application of high concentrations of growth substances

Using hydroponic cultures, the effect of high concentrations (10^?3 m) of 2-methyl-4-chlorophenoxyacetic acid (MCPA) in the root medium on the water balance of 8–9 week old plants ofPisum sativum L. and of 9–10 week-old plants ofSinapis alba L. was studied. The water balance was determined in the light and in the dark gravimetrically by measuring the intensity of water uptake and transpiration in plants cultivated by the method of root bridges according to Werner. MCPA present in the root medium in illuminated plants decreased rapidly the intensity of both the uptake and the loss components of the water balance. In permanent darkness, MCPA brought about an increase in the intensity of uptake of water and of transpiration. Simultaneous determination of water uptake and transpiration showed that the intensity of transpiration remained higher than the intensity of water uptake. This indicates that in the presence of MCPA in the root medium the relationship between the uptake and the loss components of water balance is not quantitatively equal, enboth in the light and in the dark. The existing disproportion results in the formation of a passive water balance of plants.     

The effect of high concentrations of growth substances on water uptake

Changes in water uptake immediately following the application of high concentrations of 2-methyl-4-chlorophenoxyacetic acid (MCPA) into the root medium of whole plants ofPisum sativum andVicia faba were investigated potometrically under controlled conditions. It was found that concentrations between 10^?2 and 10^?5 m bring about a sudden, pronounced and lasting inhibition of water uptake. Its rate depends directly on MCPA concentration. At 10^?2 m, sudden inhibition of water uptake becomes apparent as early as 10 min after application. With decreasing concentrations the appearance of inhibition is retarded but the inhibition is still sudden and well-pronounced. The inhibition of water uptake observed after MCPA application to the root medium of whole plants agrees with the sudden striking reduction in transpiration intensity observed byAllerup (1964) after the application of similar concentrations of 2,4-dichlorophenoxyacetic acid. The presence of MCPA in the nutrient medium causes inhibition of water uptake even in cut plants. Its rate again depends on the concentration of the growth substance. The inhibition does not appear here as quickly and is not as sudden and pronounced. High concentrations of MCPA during application to over-ground plant organs do not bring about immediate inhibition of water uptake by the root.     

Morphological and physiological characteristics of a root-hairless mutant in rice (Oryza sativa L.)

This paper reports morphological and physiological characteristics of a first root-hairless mutant (RH2) of rice (Oryza sativa L.), which can be useful in advancing knowledge on the role of root hairs in water and nutrient uptake, and genetics of root hairs. The mutant was selected among NaN₃ mutagenized progeny of the rice cultivar Oochikara. Microscopic observations showed absence of root hairs in RH2. At the seedling stage, RH2 showed shorter seedling height and shorter roots compared to the wild type variety Oochikara. Because of the differences in seedling growth, all comparisons between Oochikara and RH2 in uptake-related characters were made on the basis of values adjusted by the dry weight of either the shoot or the root. When grown at low water potential in soil, Oochikara and RH2 were similar in shoot water content and transpiration per unit shoot dry weight, and similarly, at low water potential in solution culture, there was no significant difference between Oochikara and RH2 in transpiration per unit shoot dry weight. These results suggest that at the seedling stage, root hairs do not significantly contribute to uptake of water. In solution culture, Oochikara and RH2 did not significantly differ in phosphate uptake per unit root dry weight. This result supports the previous work that root hairs do not contribute to phosphate uptake in solution culture. Regarding to response to plant hormones, RH2 showed a higher level of resistance to two synthetic auxins, 2,4-dichlorophenoxyacetic acid (2,4-D) and 1-naphthaleneacetic acid (NAA) than Oochikara. NAA treatment induced very short root hairs in RH2, suggesting that the absence of root hairs in RH2 may be due to a shortage of endogenous auxin. Genetic analysis showed that the root hairless character in RH2 is inherited as a single recessive gene.     

Potassium influx and efflux of 2,4-D- and MCPA-treated rice plants

Summary A study was made of the effects of the herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (4-chloro-2-methyl-phenoxyacetic acid) on ion uptake, leakage and growth of rice seedlings. Using isotopically-labelled solutions containing different concentrations of 2,4-D or MCPA, it was established that 10^–4 M 2,4-D or MCPA effectively inhibited potassium ion uptake, while K-ion leakage from the roots occurred only at 10^–3 M. The growth of the rice seedlings was markedly retarded even at low (10^–6 M) concentrations, and the roots and shoots showed different tolerances to the herbicide. At 10^–8 M herbicide, the effects were not injurious, but rather favourable. Reduction in root length by herbicides was not in accordance with dry-matter production.     

Translocation of nitrogen in osmotically stressed wheat seedlings

Wheat (Triticum aestivum L., cv. Drabant) seedlings were grown in a ‘split root’ system where either the whole root system or one root half was subjected to osmotic stress for 24 h, using 200 g polyethylene glycol (PEG, molecular weight 4000) dm^?3 nutrient solution. ¹⁵N-Labelled nitrate was fed to one of the root compartments and total N and ¹⁵N-labelling were measured in plant material and xylem sap. Untreated plants translocated 87% of the N taken up to the shoot, and 10% of this was then retranslocated back to the root. Recalculated on a root nitrogen basis, 36% of the label recovered in the root after 24 h had passed through the shoot. Significant labelling of xylem sap collected from non-labelled roots indicated cycling of organic N through the roots. PEG-treatment of the whole root system caused significant water loss in both roots and shoots. Uptake of nitrate and retranslocation of N to roots were inhibited, whereas cycling of organic nitrogen through the root was still measurable. Treatment of half the root system with PEG had minor effects on shoot water content, but reduced the water content of the treated root part. The total uptake of nitrate by the root system was unaffected, and the effect on the treated root half was comparatively small. Nitrate reductase activity (NRA) declined in PEG-treated roots even if high nitrate uptake rates were maintained. Shoot NRA was unaffected by osmotic stress. The data indicate that the reduction in water content of the root per se has only small effects on nitrate uptake. Major inhibition of nitrate uptake was observed only after treatment of a sufficiently large portion of the root system to given an effect on shoot water content.     

Anatomy and photosystem II activity of <Emphasis Type="Italic">in vitro</Emphasis> grown <Emphasis Type="Italic">Aechmea blanchetiana</Emphasis> as affected by 1-naphthaleneacetic acid

Auxins are one of the main regulators of in vitro plant growth and development. However, the mechanisms, by which auxins, such as 1-naphthaleneacetic acid (NAA), affect in vitro root and leaf anatomy and photosystem function, remain unclear. Accordingly, the aim of the present study was to analyze the effect of different NAA concentrations on the anatomy and photosynthetic performance of in vitro-propagated Aechmea blanchetiana and to determine whether such a treatment affects micropropagated plants after acclimatization. In vitro-established A. blanchetiana plants were transferred to culture media that contained 0, 2, 4, or 6 μM NAA, and after 50 d, they were transplanted into plastic seedling trays with a commercial substrate and cultivated for 60 d in a greenhouse. The plants were evaluated after a 50-d in vitro NAA exposure (growth traits, chlorophyll α fluorescence, and root and leaf anatomy) and after 60 d of acclimatization in the greenhouse (root and leaf growth). Changes induced by NAA in root anatomy might improve uptake of minerals and sugars from the medium, thereby increasing the in vitro growth. In the leaves, the lowest chlorenchyma thickness and sclerenchyma area were observed in plants grown without NAA, and NAA exposure also improved photosystem II activity. The highest ex vitro growth rate was observed for plants that were propagated with 4 μM NAA. Therefore, the use of NAA during in vitro propagation can improve the anatomical and physiological quality of A. blanchetiana plants, as well as to improve ex vitro transfer.     

Influence of humus substances on the toxic effect of 2-methyl-4-chlorphenoxyacetic acid

Effect of humus fractions on the toxicity of 2-methyl-4-chlorphenoxyacetic acid (MCPA) was examined in water cultures. Humus fractions and different MCPA quantities were added to Richter's nutrient solution used for maize (Zea mays L., cv. Ko?ovská raná) cultivation. The results show that MCPA and humus substances in the applied concentrations intensively influence the maize root system, especially the rhizodermis and apical meristem cells. MCPA reduces ion absorption, induces phosphorus excretion from root, reduces tissue hydratation and relatively quickly kills these cells, at the end stage and/or in the highest concentration. Humus fractions have an unambiguously positive effect on these processes, they increase the cell vitality. When humus substances are applied, the MCPA effect does not appear in potassium and nitrogen absorption, the inhibitory effect is maintained in phosphorus absorption and in tissue hydratation even with the most effective fraction—with fulvo acids. But all fractions increased the cell vitality of sorption tissue and meristems in the presence of MCPA.     

Inhibition of germination and early growth of rape seed (Brassica napus L.) by MCPA in anionic and ester form

MCPA (4-chloro-2-methylphenoxy) acetic acid is a common synthetic auxin used as a herbicide. The purpose of this study was to determine the effects of four new forms of MCPA being the herbicidal ionic liquids (HILs) with MCPA as an anion and two previously known formulations (potassium–sodium salt and 2-ethylhexyl ester) on seed germination and seedling development of winter oilseed rape (Brassica napus). Rape plants are susceptible to MCPA and volunteers can be a big problem in crop rotation. Seedling fresh weight and root length were quantified, mitotic activity, as well as lipid, starch, hydrogen peroxide and polyphenol contents were assessed by light and fluorescence microscopy and the computer-aided cytophotometer. In primary roots mitotic activity was almost completely inhibited under the influence of herbicides, cell elongation zones and root hair zones were significantly reduced, and a characteristic bolded root segment formed just above a meristem. In contrast to the traditional salt formulation the new HILs were weak inducers of hydrogen peroxide synthesis, but were potent stimulators of the synthesis of phenolic compounds and storage as well as emergency substances such as lipids and starch. All tested forms of MCPA caused strong phytotoxic effect on winter rape seedlings, but the tested HILs were more effective.     

Correlative Studies on Plant Growth and Metabolism. III. Metabolic Changes Accompanying Inhibition of the Longitudinal Growth of Stem and Root by Kinetin

Kinetin-induced expansion of lettuce (Lactuca sativa) cotyledons and inhibition of root are accompanied by parallel changes in protein nitrogen. However, during its inhibition of the longitudinal growth and water uptake of hypocotyl and pea (Pisum sativum) epicotyl sections kinetin markedly stimulates protein synthesis. Kinetin seems to separate auxin induced effects on protein synthesis and water uptake and indicates that water uptake and protein synthesis may not necessarily be correlated.

In contrast to gibberellic acid, kinetin restricts in lettuce seedlings, the mobilization of nitrogen reserves from the cotyledons, and kinetin induced growth is accompanied by a high protein nitrogen/soluble-nitrogen ratio which is characteristic of growth in light. Growth in light may be under the dominant control of kinins.

     

Lateral root development and saponin accumulation as affected by IBA or NAA in adventitious root cultures of <Emphasis Type="Italic">Panax ginseng</Emphasis> C.A. Meyer

Summary The effect of indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA) on lateral root formation was investigated in adventitious root culture of Panax ginseng. Lateral root formation was affected by IBA (24.6 μM) or NAA (9.8 μM). Lateral root primordia emerged from the explant root pericycle after about 7 d of culture when the roots were cultured on Schenk and Hildebrandt (SH) medium supplemented with 24.6 μM IBA or 9.8 μM NAA. However, no changes were observed in the explant root pericycle on auxin-free medium. The IBA treatment was more effective for lateral root induction and root growth compared to NAA. In morphological and histological aspects, the lateral roots formed under IBA treatment developed normally, while NAA-treated roots exhibited abnormal growth. The accumulation of total saponin was greater in roots treated with IBA than with NAA.     

Endogenous indole-3-acetic acid during adventitious root formation inPopulus £canadensis Moench.

Indole-3-butyric acid (IBA), phenylacetic acid (PAA) and naphthaleneacetic acid (NAA) were applied at a concentration of 10^-4 mol dm^-3 to stem cutting bases ofPopulus x canadensis Moench. During adventitious root formation, the content of indole-3-acetic acid (IAA) in cutting bases was estimated using the fluorimetric method. In the control variant, a rapid increase in endogenous IAA appeared after 24-h cultivation followed by gradual decrease during the following days. In contrast, the variants treated with IBA, PAA, and especially NAA exhibited firstly a decrease in endogenous IAA content and only afterwards an increase, reaching a maximum 48 h after excision. As root regeneration proceeded gradually, a decrease in the level of endogenous IAA occurred in all treatments. The first adventitious roots appeared in all treatments after 216-h cultivation.     

In Vitro Clonal Propagation Through Bud Culture of Hemidesmus indicus (L) R Br: An Important Medicinal Herb

The present study involves in vitro propagation of Hemidesmus indicus (L) R Br through bud multiplication and subsequent plant regeneration. The buds multiplied to produce numerous shoots at variable rates in presence of a-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (BAP) as well as NAA and kinetin. The best response in bud multiplication was obtained in Murashige and Skoog’s (MS) basal medium supplemented with 0.1 mg I^-1 NAA and 2.0 mg I^-1 BAP (7-8 shoots per explant) and the bud break time was only 4 days after inoculation. The multiplication rate was low when the buds were cultured in NAA and kinetin media and the shootlets regenerated were very thin, weak and elongated. The shoots regenerated were further cultured on MS and half strength MS basal media with variable levels of indole-3-butyric acid (IBA) for initiation of roots. Culture of shootlets for 34 weeks in one half strength of MS medium followed by culturing in the same medium with 1.5 mg 1-1 IBA induced highest production of roots (3-5 roots per shoot) within 2 weeks. Chromosome number stability with no detectable structural changes was observed in the regenerates. The rooted plants were successfully established in the soil with 85% survival rate.     

Tissue culture of forest trees: Clonal multiplication of Eucalyptus grandis L.

Axillary shoot proliferation was obtained using explants of Eucalyptus grandis L. juvenile and mature stages on a defined medium. Murashige and Skoog medium (MS) supplemented with benzyladenine (BA), naphthalene acetic acid (NAA) and additional thiamine. Excised shoots were induced to root on a sequence of three media: (1) White's medium containing indoleacetic acid (IAA), NAA and indole butyric acid; (IBA), (2) half-strength MS medium with charcoal and (3) half-strength MS liquid medium. The two types of explants differed in rooting response, with juvenile-derived shoots giving 60% rooting and adult-derived ones only 35%. Thus, the factors limiting cloning of selected trees in vitro are determined to be those controlling rooting of shoots in E. grandis.     

Effects of sucrose concentration and exogenous hormones on growth and periplocin accumulation in adventitious roots of Periploca sepium Bunge

Periploca sepium adventitious roots were cultured on 0.5 Murashige and Skoog solid media supplemented with exogenous hormones of different types and various concentrations, and with sucrose of different concentrations. Auxins (indole butyric acid (IBA) and naphthalene acetic acid (NAA)) and cytokinins (6-benzylaminopurine (BA) and kinetin (KT)) were selected as exogenous hormones for adventitious root proliferation. Compared with other hormones, IBA was the suitable auxin for adventitious root proliferation. Under this circumstance, every root explant generates 10?C15 adventitious roots (1- to 2-cm long) after 30?days. However, nothing but callus was induced on the root explants when NAA was added into the medium and the same result was achieved when auxins (IBA or NAA) were added into the media together with cytokinins (BA or KT). The suitable concentration of IBA for adventitious root proliferation was 1?C2?mg/l, when every root explant generated 10?C20 adventitious roots (1- to 2-cm long). The optimum concentration of IBA for periplocin accumulation was 1?mg/l, when the periplocin content reached 95.46???g/g. With regard to the investigation of sucrose concentration, 2?C3% (w/v) sucrose was favorable for adventitious root proliferation as every root explant in this concentration generated 10?C20 adventitious roots (1- to 2-cm long). The highest periplocin content (101.56???g/g) was achieved at 5% (w/v) sucrose, whereas the periplocin content at 5% (w/v) sucrose did not show significant difference from the periplocin content (95.38 and 98.47???g/g, respectively) at 3% (w/v) or 4% (w/v) sucrose.     

Patterns of adventitious root formation in English ivy

Adventitious root formation by debladed petiole cuttings of English ivy (Hedera helix L.) proceeds via a direct rooting pattern for the easy-to-root juvenile phase, while the difficult-to-root mature phase roots through an indirect rooting pattern. Juvenile petiole cuttings treated with α-naphthaleneacetic acid (NAA, 100 μM) plus the polyamine biosynthesis inhibitor, difluoromethylarginine (DFMA, 1 mM), formed an increased number of roots per cutting initiated by the indirect rooting pattern. The increased root formation and change in rooting pattern were reversed by the addition of putrescine (1 mM). Delaying auxin application to petiole cuttings for 15 days also induced juvenile petioles to root by the indirect pattern. This could be reversed by rewounding the base of the cutting prior to auxin application after day 15. The data support the use of the terms “competent root-forming cells” and “induced competent root-forming cells” to describe the target cells for the initial events of root formation for the direct and indirect rooting patterns, respectively.     

The influence of mycorrhizal inoculation and paclobutrazol on water and nutritional status of Arbutus unedo L.

The purpose of this study was to analyze morphological and physiological aspects of Arbutus unedo L. plants treated with paclobutrazol (PAC), compounds characterized by their double activity as plant growth regulators and fungicides, and the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch, which forms a special type of mycorrhizal colonization called arbutoid mycorrhiza. Native A. unedo L. seedlings were grown in a greenhouse and subjected to four treatments for 4 months: 0 or 60 mg of PAC and inoculated or not with P. tinctorius (Pers.). The arbutoid mycorrhizal inoculation increased in plants treated with PAC. Paclobutrazol reduced shoot and root biomass, plant height, internode length, stem diameter, leaf area, total root length and number of tips. P. tinctorius increased plant height and had a beneficial effect on the root system (increasing root diameter and the number of tips). PAC treatment led to an increase in ion levels in the leaf tissue, while mycorrhizal inoculation induced lower K and higher P contents in the roots. Leaf water potentials (at predawn and at midday) increased with the combined treatment. The absence of water deficit conditions meant there was no osmotic adjustment. Higher photosynthesis (P_n) values were associated with higher stomatal conductance (g_s) values in the mycorrhizal plants, which influenced water uptake from the roots. However, g_s decreased in the PAC-treated plants, reducing photosynthesis and, as a consequence, growth. The higher hydraulic conductivity (L_p) in the plants treated with PAC may have induced a better water energy status and good water transport. The combined treatment produced beneficial effects in the plants, improving their water and nutritional status.     

Induction mechanism of adventitious root from leaf explants of <Emphasis Type="Italic">Morinda citrifolia</Emphasis> as affected by auxin and light quality

An efficient protocol for adventitious root induction from leaf explants of Morinda citrifolia treated with different concentrations of indole-3-butyric acid (IBA) and α-naphthaleneacetic acid (NAA) was established in relation to physiological process changes during adventitious root induction under different light sources (fluorescent, red, blue, red + blue, and far-red). Among the different concentrations of IBA and NAA, 1.0 mg l⁻¹ IBA was proven as the best auxin source for adventitious root induction under fluorescent light. Higher concentrations of IBA and NAA trigger callus formation in both light and dark conditions. Maximum numbers of adventitious roots were induced under red light (26) followed by blue light (22) and the lowest under far-red light (6). In contrast, numerous callus formations were induced by red + blue followed by red and blue, while the highest root length (1.66 cm) with negligible callusing was observed under fluorescent light. Catalase and guaicacol peroxidase activities were highest under red light followed by fluorescent light and the lowest under red + blue light, but superoxide dismutase activity was not significantly influenced by different light sources. Ascorbate peroxidase played an important role in detoxification of the harmful effects of hydrogen peroxide (H₂O₂). Under fluorescent light, significantly lower accumulation of H₂O₂ was observed. Accumulation of H₂O₂ in the induced root under different light showed a positive correlation with peroxidation of lipids and was observed higher under far-red followed by red + blue and blue light.     

Evidence against the Regulation of Grain Set by Spikelet Abscisic Acid Levels in Water-Stressed Wheat

A possible role of abscisic acid (ABA) in the regulation of grain set in water-stressed wheat (Triticum aestivum L.) was investigated using a split root system to dry half the roots while the remainder were kept watered. Water uptake by the wet roots maintained the leaf water potential at the normal level, whereas the ABA produced in the dry roots was transported to the spike. This caused the spikelet ABA level to increase to the same extent as when the entire root system was stressed to permit a drop in the leaf water potential. In spite of this, the former treatment did not induce a reduction in grain set, whereas the latter did. Thus, contrary to previous reports, water stress-induced changes in spikelet ABA level alone do not appear to regulate grain set.