Effect of high temperature pre-treatment on elongation of the mesocotyl of rice seedlings I. Cell multiplication in the mesocotyl

Mesocotyl elongation in paddy rice seedlings of the japonicatype was markedly stimulated by high temperature pre-treatmentof seeds. Examination of the number of parenchyma cells perone cell layer in longitudinal sections of mesocotyl revealedthat stimulation may be mainly caused by cell multiplication. (Received February 24, 1970; )     

Translocation of potassium and sodium in intact maize seedlings

Summary The distribution of K and Na between root and shoot of intact maize seedlings after absorption periods of increasing length up to 24 hours was determined in three series of experiments. In two additional series the redistribution between root and shoot of K and Na absorbed previously during a period of 12 hours was followed up during the next 12 hours. Concentrations were such that either the specific or both the specific and non-specific mechanism of K-absorption present in this tissue were operative.A high degree of specificity in the transfer to the shoot became apparent, the amount of Na transported to the shoot within 24 hours being negligible in comparison to the amount of K transferred within the same period. For the most part this specificity appeared to be due to the fact that the specific mechanism of K-absorption is especially involved in the supply of K for transfer to the shoot. However, non-specifically absorbed K is also liable to transport to the aerial parts at a much higher rate than Na and, in contrast to Na, the translocation of K continues after the plants have been transferred to K- and Na-free media.A scheme is proposed to explain the phenomena described.     

Nickel in plants: I. Uptake kinetics using intact soybean seedlings

The absorption of Ni²⁺ by 21-day-old soybean plants (Glycine max cv. Williams) was investigated with respect to its concentration dependence, transport kinetics, and interactions with various nutrient cations. Nickel absorption, measured as a function of concentration (0.02 to 100 μm), demonstrated the presence of multiple absorption isotherms. Each of the three isotherms conforms to Michaelis-Menten kinetics; kinetic constants are reported for uptake by the intact plant and for transfer from root to shoot tissues. The absorption of Ni²⁺ by the intact plant and its transfer from root to shoot were inhibited by the presence of Cu²⁺, Zn²⁺, Fe²⁺, and Co²⁺. Competition kinetic studies showed Cu²⁺ and Zn²⁺ to inhibit Ni²⁺ absorption competitively, suggesting that Ni²⁺, Cu²⁺, and Zn²⁺ are absorbed using the same carrier site. Calculated K_m and K_i constants for Ni²⁺ in the presence and absence of Cu²⁺ were 6.1 and 9.2 μm, respectively, whereas K_m and K_i constants were calculated to be 6.7 and 24.4 μm, respectively, for Ni²⁺ in the presence and absence of Zn²⁺. The mechanism of inhibition of Ni²⁺ in the presence of Fe²⁺ and Co²⁺ was not resolved by classical kinetic relationships.     

Uptake and distribution of trace metal elements in wheat seedlings

The uptake and distribution of eight metallic elements were examined in wheat seedlings for a period of 12 d with a radioactive multitracer technique. The radioactive nuclides of the seedlings were simultaneously determined by γ-ray spectrometry. All of the elements studied were taken up by the wheat seedlings and mainly accumulated in the roots. Only some elements were transported to shoots and leaves of the seedlings or bound to leaf proteins, and two elements were transported into the chloroplast. Uptake of most elements reached a maximum on the fifth or the eighth day and then gradually decreased afterward. In the cases of ^95mTc and ⁷²Se, the uptake increased continuously within 12 d without the peak uptake. The change of elemental concentrations was dependent on uptake and excretion rates. The dynamics of metal elements taken up by the wheat seedlings and their distribution in roots, shoots, and leaves were different for each element, suggesting that it may depend on the characteristics of the elements.     

Role of potassium and malate in nitrate uptake and translocation by wheat seedlings

Wheat seedlings (Triticum vulgare) treated with 1 mm KNO₃ or NaNO₃, in the presence of 0.2 mm CaSO₄, were compared during a 48-hour period with respect to nitrate uptake, translocation, accumulation and reduction; cation uptake and accumulation; and malate accumulation. Seedlings treated with KNO₃ absorbed and accumulated more nitrate, had higher nitrate reductase levels in leaves but less in roots, accumulated 17 times more malate in leaves, and accumulated more of the accompanying cation than seedlings treated with NaNO₃. Within seedlings of each treatment, changes in nitrate reductase activity and malate accumulation were parallel in leaves and in roots. Despite the great difference in malate accumulation, leaves of the KNO₃-treated seedlings had only slightly greater levels of phosphoenolpyruvate carboxylase than leaves of NaNO₃-treated seedlings. NADP-malic enzyme levels increased only slightly in leaves and roots of both KNO₃- and NaNO₃-treated seedlings. The effects of K⁺ and Na⁺ on all of these parameters can best be explained by their effects on nitrate translocation, which in turn affects the other parameters. In a separate experiment, we confirmed that phosphoenolpyruvate carboxylase activity increased about 2-fold during 36 hours of KNO₃ treatment, and increased only slightly in the KCl control.     

Lead distribution in corn seedlings (Zea mays L.) and its effect on growth and the concentrations of potassium and calcium

It was observed that dry weight yield is not a sensitive parameter withwhich to assess lead toxicity to plants. Elongation growth of corn seedlingroots was more sensitive to lead than shoot growth and was inhibited by allconcentrations tested (10^–5, 10^–4, and 10^–3 M).It was positively correlated with potassium concentration and negativelycorrelated with lead concentration in the roots. Negative correlation also wasobserved between lead concentration and potassium concentration in roots. It ispostulated that inhibition of corn root growth is connected with potassiumleakage from root cells. The toxic action of lead on corn seedling mesocotylandcoleoptile growth was not correlated with potassium concentration in planttissue and correlation between growth and lead concentration was low. Inseedlings treated with 10^–4 and 10^–3 M lead the growthof mesocotyl and coleoptile was affected similarly, although the concentrationof lead was threefold higher in mesocotyl tissue than in coleoptile tissue. It isproposed that depression of corn seedlings shoot growth is not an effect ofpotassium leakage or lead accumulation but of an unknown signal induced inroots, as a response to exposure to lead, which is transmitted to shoots. Thepositive correlation between lead and calcium concentrations found in seedlingroots might be connected with high constitutional tolerance of corn to lead.Since the first 8 mm of an apical root accounts for 50% of thelead accumulated by the whole root, it is postulated that rhizofiltration oflead contaminated waters should be more efficient when plant species withhighly branched root systems are used.     

Effect of replacing nutrient potassium by sodium on uptake and distribution of sodium in tomato plants

Summary Tomato plants (Lycopersicon esculentum cv. Amberley Cross) were grown in a series of nutrient solutions in which 0, 60, 90, 95, 98 and 99 per cent of the K was replaced by Na. The plants selectively absorbed K relative to Na from the nutrient solutions and transported K to the shoots in preference to Na. In the nutrient solution having the highest K/Na ration most of the Na taken up by the plants accumulated in the roots, but as the K was progressively replaced by Na an increasing proportion of the total Na absorbed was transported to the leaves. Sodium was present at up to 2.4 per cent of the dry wt of whole, fully-expanded leaves without there being any apparent visual signs of damage or reduction in the rate of growth of the plants. On closer examination it was found that most of the Na transported to the leaves was excluded from the laminar tissue and accumulated in the adjacent petioles. The ability of the roots and petioles to retain large amounts of Na depended on an adequate supply of K to the plants.     

Uptake and distribution of sodium selenite in rat brain tumor

Eighteen weanling male Wistar rats with brain gliomas were divided into three groups, which received 0., 2.0, 5.0 ppm selenium (Se) in their drinking water. The accumulation and retention of selenium in the brain bearing tumor was investigated. Significantly higher concentrations of Se were observed in tumor tissue than normal brain tissue after exposure to sodium selenite. Tumors were observed in the 2.0 Μg/g selenium group. The difference in selenium concentration between the tumor tissue and contralateral normal brain tissue was not influenced by the weight of brain or body, and water consumption. We observed that selenium accumulated in tumor tissue more than in normal brain tissue.     

Rb86 as tracer for potassium: I. Uptake of Rb and K by rice plant in nutrient solution

Summary The successful use of Rb⁸⁶ as a tracer for potassium in rice nutrition studies is related to the relative uptake of these two nutrient elements and the estimation of potassium by Rb⁸⁶ analysis. Results obtained under nutrient culture condition showed that the ratio of rubidium: potassium in the substrate was similar to that in the plant and the amount of potassium determined by conventional method was comparable to that of radiochemical analysis of Rb⁸⁶.     

Role of sodium and potassium in aldosterone binding of kidney receptors in the rat.

An increase of the sodium concentration produced a diminished binding of labeled aldosterone to kidney receptors in both in vivo and in vitro conditions. The elevation of potassium level did not change the binding capacity of kidney nuclear receptors for aldosterone. Hypernatraemia-induced decrease of aldosterone uptake was significant in the nuclear fraction of both medullary and cortical region of the kidney but did not show remarkable changes in the uptake of cytosol fraction. The transfer of aldosterone from cytosol into the nuclear compartment seems to be changed by the alteration of extracellular sodium concentration.     

Uptake and translocation of griseofulvin by wheat seedlings

Summary 1. A roughly quantitative technique for studying uptake and translocation of the antibiotic griseofulvin by wheat plants has been devised. Wheat plants were grown in nutrient solutions containing griseofulvin and translocation measured by bioassay of the griseofulvin appearing in the guttation drops induced by transfer to a humid atmosphere.2. Griseofulvin was phytotoxic at concentrations of 5 µg/ml and above, the first symptoms observed being stunting and swelling of the roots.3. The concentration of griseofulvin in the guttation drops was directly related to the concentration in the nutrient solution; there was evidence of griseofulvin accumulation in the leaves, the concentration in the guttation drops being frequently higher than that in the nutrient solution.4. Atmospheric conditions favouring transpiration increased uptake and translocation of griseofulvin.5. Uptake and translocation of griseofulvin was inhibited by inclusion of respiratory enzyme inhibitors in the nutrient solution.     

Light differentially regulates lateral and longitudinal auxin transport in the mesocotyl of etiolated maize seedlings

The uptake of IAA into excised mesocotyls of non-irradiated maize seedlings was linear up to a concentration of about 4×M and in this range there was a tight coupling between the IAA in the stele and the cortex. Prior irradiation with white light of intact seedlings unbalanced this coupling. Lateral and longitudinal transport were affected differently. In the stele, the effect of prior irradiation on longitudinal transport was multiphasic, with an initial stimulatory effect followed by a negative effect at longer prior irradiation times. The lateral transport from the stele to the cortex showed no stimulatory effect and appeared to be inhibited within at least 15 min. The effect of the prior irradiation on longitudinal transport in the stele appeared to be a high intensity effect. In contrast, the effect of the prior irradiation on the lateral transport from the stele to the cortex was saturated at much lower intensities. The data suggest that the light induced change in the lateral transport of IAA between the two tissues may be due to changes either in the number of open lateral transport channels/carriers or in the conductivity of these channels/carriers.     

Effect of high sodium chloride concentrations on the pigment content and free-radical processes in corn seedlings leaves

The effect of sodium chloride on general morphometrical parameters of seedlings, and biochemical parameters in the leaves of corn seedlings was studied. Exposure to 100 and 200 mM NaCl slowed down the growth of stem and roots, whereas 100 and 200 mM NaCl during 24 h enhanced the concentration of chlorophylls, carotenoids, anthocyans, and thiobarbituric acid reactive substances. The decrease in protein carbonyl groups was found at 24-hour exposure to 200 mM salt. The treatment during 24, 48 and 72 h to 200 mM salt increased the level of total and high molecular mass thiols, whereas low molecular mass thiol content was by 20-25% higher at 48 h exposure to all used salt concentrations. The activity of guaiacol peroxidase was higher only at 24 h exposure to 100 and 200 mM salt, and catalase--at 50 mM during 48 h. At 72-hour exposure, catalase activity was by 27 and 41% higher in seedlings, exposed to 50 and 200 mM NaCl, respectively. Therefore, it is concluded the plant exposure to 50-200 mM salt initially developed oxidative stress, inducing adaptive response--an increase in antioxidant potential and efficiency of systems of energy production. That results in plant adaptation to unfavourable conditions.     

Uptake and distribution of calcium, magnesium and potassium in cucumber of different age

Uptake and distribution of Ca⁺, Mg²⁺ and K²⁺ were investigated in plants of cucumber ( Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 m M Ca²⁺, 2.0 m M Mg²⁺ and 2.0 m M K⁺. The ⁺ concentration was about the same in roots and shoots, while the Ca²⁺ and Mg²⁺ concentrations were low in roots compared to shoots. The K⁺ concentration decreased with increasing leaf age, while the Ca²⁺ and Mg²⁺ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21-day-old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca²⁺ (⁴⁵Ca) uptake. Transport of Ca²⁺ increased to leaves above and below the excision point and total Ca²⁺ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca²⁺ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites.     

Cellular re-distribution of flavin-containing polyamine oxidase in differentiating root and mesocotyl of <Emphasis Type="Italic">Zea mays</Emphasis> L. seedlings

Plant polyamine oxidases (PAOs; EC 1.5.3.11) are hydrogen peroxide-producing enzymes supposedly involved in cell-wall differentiation processes and defence responses. Maize (Zea mays L.) PAO (MPAO) is a 53 kDa secretory glycoprotein, abundant in primary and secondary cell walls of several tissues. Using biochemical, histochemical, ultrastructural and immunocytochemical techniques, the distribution and sub-cellular compartmentalisation of MPAO in the primary root and mesocotyl of seedlings at different maturation stages or after growth under varying light conditions were analysed. In apical root tissues, MPAO immunoreactivity was mainly detected in the cytoplasmic compartment, while a lower immunoreactivity was observed in the cell walls. In the more mature, basal part of the root, intense immunogold labelling was found in the primary and secondary walls of protoxylem precursors and vessels, while endodermal cells and living metaxylem precursors were immunopositive both in their walls and in their thin cytoplasmic compartments. A re-distribution of MPAO protein from the cytoplasm toward the primary and secondary walls was also recognised when immunoreactivity of basal root tissues from 3-day-old seedlings was compared with that detected in 11-day-old tissues. Accordingly, biochemical analyses revealed MPAO entrapment in the extracellular matrix of mature tissues. In the mesocotyl, an enrichment of MPAO immunolabelling in the cell wall of protoxylem, metaxylem and epidermal tissues, as a function of light exposure, was observed. Taken together, these data support the hypothesised role of PAOs in cell-wall maturation. Moreover, the relevant intraprotoplasmic MPAO localisation observed mainly in differentiating root tissues suggests an additional role in intracellular production of hydrogen peroxide.Alessandra Cona and Sandra Moreno have contributed equally to this paper.