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; )     

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.     

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.     

Uptake and distribution of potassium in tomato plants

Summary The uptake and distribution of potassium was examined in tomato plants, cv. Amberley Cross and Moneymaker, grown in peat/loam and given a nutrient feed either adequate or deficient in potassium.Detailed studies were also made of the distribution of potassium in various parts of tomato plants, cv. Amberley Cross, grown in sand and supplied with nutrient feeds containing four and seven concentrations of potassium. In these plants the concentration of potassium in stem, petiole and laminar tissue increased from the base to the apex of plants, irrespective of the potassium concentration in the nutrient feed. There was also a gradient of decreasing potassium concentration along leaves, from proximal to distal laminae. The concentration of potassium in all plant parts increased with increasing nutrient supply of potassium, petioles showing a greater response to nutrient potassium than laminar tissue.Marginal chlorosis and/or necrosis were observed when the potassium concentration in fully expanded leaves fell below 1.2 per cent of the dry weight for cv. Amberley Cross or 1.5 per cent for cv. Moneymaker. A 50 per cent incidence of chlorosis and/or necrosis occurred in leaf laminae containing 0.74 per cent potassium.Leaves rarely showed deficiency symptoms when the concentration of potassium in the petioles was higher than that in adjacent laminar tissue. However, chlorosis and/or necrosis occurred when the potassium concentration in petioles fell below that in laminae. In the diagnosis of the potassium status of tomato plants, the most suitable tissue for sampling for potassium analysis is considered to be the petioles of young fully expanded leaves.     

Role of carotenoids in the phototropic response of corn seedlings

The herbicide, 4 chloro-5-(methylamino)-2-(α,α,α,-trifluoro-m-tolyl)-3 (2H)-pyridazinone (SAN 9789), which blocks the synthesis in higher plants of colored carotenoids but not of flavins, was used to examine the involvement of carotenoids in corn seedling phototropism. It was concluded that “bulk” carotenoids are not the photoreceptor pigment based on the results that increasing concentrations of SAN 9789 (up to 100 micromolar) did not alter the phototropic sensitivity to 380 nanometers light (using geotropism as a control) and did not increase the threshold intensities of fluence response curves for both 380 and 450 nanometers light even though carotenoid content was reduced to 1 to 2% of normal. SAN 9789 treatment, however, did reduce seedling sensitivity toward 450 nanometers light indicating that carotenoids are involved in phototropism. Carotenoids, which are located mainly in the primary leaves, may act in phototropism as an internal screen, enhancing the light intensity gradient across the seedling and thus contributing to the ability of the seedling to perceive light direction. These results indicate that the action spectra for phototropic responses can be significantly affected by the absorbance of screening pigments in vivo thus altering its shape from the in vitro absorption spectrum of the photoreceptor pigment.     

Variations in sodium uptake along primary roots of corn seedlings

Entry of Na⁺ into segments of the apical 8-centimeter portion of corn (Zea mays) roots was investigated and analyzed for each centimeter segment separately. Influence of temperature in the 0 C to 30 C range was well described by the Arrhenius equation [U = A exp (-Ea/RT)]. Values of A and Ea differed for each segment, tending to lessen with increasing distance from root apex. Time course of Na⁺ entry was followed up to 70 minutes. Time relations of the process fit well the expression U = m [1 - exp (-nt)]. Calculated maximal uptake capacity (m) diminished with increasing distance from the apex. The data presented indicate that sodium uptake mechanisms vary qualitatively and quantitatively along corn roots. Thus, the use of entire roots for characterization of uptake mechanisms should be reassessed.     

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.     

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.     

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.     

Transport of potassium inChara australis: I. A symport with sodium

Summary Voltage-clamp and tracer techniques, applied simultaneously or separately to individual cells, have been used to show that K⁺-starved internodal cells ofChara australis can develop an electrogenic transport system, which requires and transports K⁺ with high affinity (K _1/2 about 30 m) and Na⁺ with lower affinity (K _1/2 about 500 m). The most likely mechanism is symport of K⁺ with Na⁺, with a stoichiometric ratio of 11. In simultaneous measurements of quantities of charge and of ions entering individual cells, the quantity of K⁺ was consistently half the quantity of electric charge, while that of Na⁺ was consistently somewhat lower than that. Possible reasons for this discrepancy are discussed. The electrogenic symport of K⁺ with Na⁺ has not previously been reported for any cell. Its functional significance inChara is apparently the active uptake of K⁺ at the expense of the electrochemical potential difference for Na⁺. This new symport reveals the unexpected presence inChara of a Na⁺-linked chemiosmotic circuit alongside the known H⁺-linked circuit.     

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.     

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 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.     

Metabolic factors influencing the sodium and potassium distribution in Ulva lactuca

1. Methods for the use of the marine green alga, Ulva lactuca, in studies on electrolyte metabolism are described. 2. The effect of illumination and iodoacetate on the potassium and sodium content, as well as the influence of light and running sea water on the iodoacetate effect was investigated. The rate of exchange of cellular potassium ion for K(42) under conditions of light and dark at 20 and 30 degrees C. was studied. 3. Ulva maintained in the dark for long periods loses some potassium and gains sodium, both effects being reversed upon illumination. The presence of 0.001 M iodoacetate in the dark causes a marked progressive loss of potassium and gain of sodium, phenomena which do not occur when the alga is illuminated. Evidence for the penetration of the inhibitor into the cell in the presence of light is presented. The iodoacetate effect on potassium and sodium content, once established, can be "washed out" of the alga when the plant is placed in light and running sea water without the inhibitor. Illumination and increased temperature each favor a more rapid exchange of tissue for environmental potassium ion. 4. In the interpretation of these findings it is emphasized that metabolic work, perhaps in the form of ion transports, must be done by the cell to compensate for the continual flow of potassium ion and sodium ion with their respective concentration gradients and thus maintain homeostasis within the cell. Evidence is presented which indicates separate mechanisms for the distribution of sodium and potassium in this organism. It is further suggested that the degradation of phosphoglyceric acid, an important glycolytic and photosynthetic intermediate, or one of the products of its metabolism supplied the energy for these ion transports(s). The role of permeability per se is considered.     

On the mechanism of the “photo-geo” response in the mesocotyl of oat seedlings

Summary The photo-geo response comes about through the differential inhibition of cell growth on the two curved sides of the mesocotyl.