Abscisic acid and gibberellin-like substances in roots and root nodules ofGlycine max

Summary The content of endogenous gibberellin (GA)-like substances of roots and root nodules of SOya, and GA production byRhizobium japonicum cultures, were investigated by a combined thin layer chromatographic (TLC)-dwarf pea epicotyl bioassay technique. GAs were more concentrated in root nodules than in the roots, totalling 1.34 and 0.16 nM GA₃ equivalents g⁻¹ dry wt. respectively. GA production byR. japonicum cultures was demonstrated (1.00 nM GA₃ equivalentsl ⁻¹) and comparison of the GA components of plant and bacterial culture medium extracts, suggested that rhizobial GA production may contribute to the nodule GA content. Cis-trans abscisic acid (ABA) was identified in root and nodule extracts by TLC-gas liquid chromatography (GLC), and amounted to 0.18 and 2.21 nM g⁻¹ dry wt. respectively, whereas 0.30 and 4.63 nM ABA equivalents g⁻¹ dry wt. were detected by a TLC-wheat embryo bioassay technique. ABA was not detected in extracts of bacterial cultures.     

A microcomputer based method for the rapid and detailed measurement of seedling root systems

Summary A simple method for making detailed measurements of seedling root systems is described. Photocopies of root systems are traced over by an operator using a digitizing system attached to a microcomputer. The computer calculates and prints the lengths of axis, laterals and sublaterals for each root system. Accurate measurements can be achieved with a degree of speed and detail unobtainable by other methods.     

Dynamics of extractable carbohydrates in Pisum sativum. III. The effect of IAA and temperature on content and translocation of carbohydrates in pea cuttings during rooting

The number of roots formed in cuttings of pea ( Pisum sativum L. cv. Alaska) was regulated both by the temperature and by IAA, whereas the time to the appearance of the first roots was regulated only by the temperature. Cuttings treated with 10^-3 M IAA had a smaller content of extractable carbohydrates than the control ones irrespective of the temperature. In the bases of cuttings rooted at 25°C the content of extractable carbohydrates was lower than in those rooted at 15°C. Cuttings treated with IAA showed up to elevenfold increase of extractable carbohydrates in the bases at day 3. This increase of soluble sugars was not correlated with the number of roots formed or the speed of rooting. It is concluded that IAA affects the accumulation of carbohydrates, and this is not connected with the rooting ability of the cuttings.     

Physical conditions of propagation media and their influence on the rooting of cuttings

Summary The air content in three types of propagation media, Jiffy-7 and Jiffy-9 which are Sphagnum peat and Grodan which is rockwool, were investigated when they were held at moisture tensions of 0,6 and 12 cm measured from the base of the media. At 0 cm tension the air content (vol. %) was highest in Jiffy-9 and lowest in Jiffy-7. At 12 cm tension the air content was higher in Grodan than in Jiffy-9 and Jiffy-7. Oxygen diffusion coefficients (ODC) and oxygen diffusion rates (ODR) were measured at the different air contents. At air contents below 20 vol. % ODC was about the same for Jiffy-9 and Grodan but at air contents above 20 vol.% it was larger for Jiffy-9 than for Grodan. The oxygen diffusion rate was measured at 0, 4 and 8 cm moisture tension. At all tensions it was approximately 20% higher in Jiffy-9 than in Grodan and Jiffy-7. The ODR in Jiffy-7 and Grodan were affected equally at the same tension, although Grodan contained more air. Report no 253     

Hormones are no causal links in phytochrome-mediated adventitious root formation in mustard seedlings (Sinapis alba L.)

The question of whether or not hormones are causal links in the realization of phytochrome control during photomorphogenesis was investigated using the phytochrome-dependent formation of adventitious roots in hypocotyl cuttings excised from mustard seedlings as a test system. Histological examination of regenerating rest seedlings revealed that phytochrome (operationally, continuous far-red light) mediates the de novo formation of root primordia in the pericycle region of the hypocotyl near the cutting surface withing 12–24 h after excision.Auxin (IAA), gibberellin (GA₃), Cytokinin (kinetin), abscisic acid (ABA), and ethylene had no promotive effect on primordium formation in dark-grown or far-red irradiated rest seedlings. Depending on concentration, the application of these hormones was either ineffective or inhibitory in the rooting response. It is concluded that phytochrome does not operate through changes of hormone (auxin, gibberellin, cytokinin, ABA, ethylene) levels.While externally applied ethylene had no specific effect on primordium formation, the number of primordia produced in darkness could be increased to the far-red light level by removing the endogenously formed ethylene. Since the stimulatory effect of light could not be related to a lower ethylene level, it is concluded that ethylene interferes with primordium formation by modulating the susceptibility of this process to phytochrome control. This ethylene effect takes place in a concentration range below the range that can be manipulated by external application of the hormone.Abbreviations ABA abscisic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - P_r P_fr red and far-red absorbing forms of phytochrome     

The regulation of K+ influx in excised barley roots

The electrochemical potential differences for potassium, between excised barley (Hordeum vulgare L.) roots and external media containing 0.05 mM KCl+0.5 mM CaSO₄, were determined over a 4-h period during which initially low-K⁺ roots accumulated K⁺ by pretreatment in 50 mM KCl plus 0.5 mM CaCl₂. This pretreatment resulted in increased internal [K⁺], decreased K⁺ influx (as measured from 0.05 mM KCl+0.5 mM CaSO₄) and decreased values of . These observations indicate that the decline of K⁺ influx associated with increased internal K⁺ concentration cannot be accounted for by passive adjustment to the electrochemical gradient for this ion.     

Distribution of growth regulators in relation to the light-induced geotropic responsiveness in Zea roots

Growth regulators were measured in extracts from the upper and lower halves of 7-mm apical segments of horizontally oriented, red-light-irradiated and non-irradiated roots of Zea mays L. cv. Golden Cross Bantam 70 which exhibit a georesponse only after an exposure to light. Abscisic acid (ABA) was measured by gas-liquid chromatography, auxin (indole-3-acetic acid, IAA) by the Avena straight-growth assay, and an unidentified growth inhibitor by a Zea root-growth assay. The ratio of ABA in the upper and lower halves was 1.6 in the irradiated roots and 1.0 in the non-irradiated ones. The total amount of ABA after irradiation was increased by a factor of ca. 1.8. The ratio of IAA in the upper and lower halves of irradiated and non-irradiated roots was 1:3.4 and 1:2.9, respectively. The content (or activity) of an unidentified growth inhibitor was highest in the lower halves of horizontally oriented roots which had been irradiated with red light. The unidentified growth inhibitor, rather than IAA or ABA, may be the major factor in the light-induced geotropic responsiveness in Zea roots.     

Enzymes of asparagine synthesis in maize roots

An asparagine synthetase which is active with either glutamine or NH ₄ ⁺ has been found in maize (Zea mays L.) roots. Unlike the enzyme obtained from legume cotyledons, the maize-root enzyme is only slightly more efficient with glutamine (Km, 1.0 mM) than with NH ₄ ⁺ (Km, 2.0–3.0 mM). The activity of this enzyme is higher in the mature root than in the root-tip region, i.e. root cells develop a capacity to make asparagine from glutamine or NH ₄ ⁺ as they mature. -Cyanoalanine synthetase is also present in maize roots. The apparent Km for cysteine is 2.6 mM and for cyanide is 0.57 mM. The enzyme is more active in the root tip than in mature root tissue. Thus, if asparagine were made in the root tip, the cyanide pathway could represent the mechanism of synthesis. It is our contention, however, that this potential is not realized under normal conditions because ¹⁴C-experiments performed previously have indicated a limited availability of both CN and cysteine in the maize root.     

Isolation and metabolism of Vigna unguiculata root nodule protoplasts

Axenic cultures of bacteroid-containing protoplasts were isolated from root nodules of Vigna unguiculata L. Walp. Dimensions of the protoplasts were 35 to 135 m long x 35 to 95 m wide. Yields were about 30 to 50 mg dry weight per gram fresh weight of nodules. About 5x10⁸ protoplasts packed into 1 ml of basal medium under the influence of gravity. When incubated in hypertonic, nitrogen-free media, freshly isolated protoplasts began to reduce acetylene to ethylene after a lag period of 24 to 48 h. Various additions to the basal medium showed that the system possessed functional glycolytic and tricarboxylic acid pathways. Endogenous application of various intermediary metabolites stimulated both acetylene reduction and respiration, though not often equally. As acetylene reduction, but not respiration, was inhibitable by both asparagine and glutamine, the system appears suitable for the study of mechanisms controlling symbiotic nitrogen fixation.Abbreviations BSA bovine serum albumine - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - PEP phospho(enol)pyruvate - UMKL 76 University of Malaga, Kuala Lumpur, Rhizobium, No. 76 - TCAC tricarboxylic acid cycle     

Cytokinin biosynthesis in roots of corn

Removal of the quiescent center (QC) from the root apex of maize (Zea mays L., cv. Kelvedon 33) initiates a set of events which culiminate in the regeneration of an intact apex with a newly formed QC. Concomitant with the formation of a new QC is a marked reduction in extractable cytokinins in the tissue of the proximal meristem. Replacing the excised QC with a Dowex (acidic cation-exchange resin) bead affects both root growth and QC regeneration. Root growth is inhibited by plain Dowex beads and Dowex beads treated with zeatin; this inhibition is reversed if the beads have been treated with CaCl₂ (±zeatin). Dowex beads treated with zeatin delay the formation of a new QC; this effect is the same whether or not the beads also contain CaCl₂. The results of this investigation support the notions that cytokinin biosynthesis in roots is a result of activities of both the QC and the proximal meristem, and that cytokinins, at least if supplied exogenously, can play a role in root morphogenesis by delaying the regeneration of the QC.Abbreviations used throughout the text PM proximal meristem - QC quiescent center - RC root cap