A mechanism is proposed by which secondary products of nitrate reduction in the shoot control the uptake of nitrate by the roots. KNO3 enters the roots and is translocated to the shoot where nitrate is reduced and, at the same time, malate is produced. The reduction of nitrate is stoichiometric to the synthesis of malate (1). Part of the K‐malate moves down to the root system in which malate is oxidized, yielding KHCO3 which exchanges for KNO3. Nitrate reduction in the shoot promotes the synthesis of malate which, after its translocation to the root, allows the preferential uptake of nitrate. Thus, plants reducing large amounts of nitrate may take up the anion without a superfluous accumulation of the cation. Furthermore, the utilization of nitrate by the shoot regulates its uptake by the root.
Carnation (Dianthus caryophyllus) flowers were exposed to 2^i/l ethylene and examined at intervals to determine the time course of wilting, decrease in water uptake, and increase in ionic leakage in response to ethylene. A rapid decrease in water uptake was observed about 4 hours after initiating treatment with ethylene. This was followed by wilting (in-rolling of petals) about 2 hours later. Carbon dioxide inhibited the decline in water uptake and wilting and this is typical of most ethylene-induced responses. Ethylene did not affect closure of stomates. Ethylene enhanced ionic leakage, as measured by efflux of 36CI from the vacuole. This was judged to coincide with the decrease in water uptake. Gassing flowers with propylene initiated autocatalytic ethylene production within 2.4 hours. Since the increase in ethylene production by carnations preceded the increase in ionic leakage and the decline in water uptake by several hours, it is apparent that the change in ionic leakage does not lead to the initial increase in ethylene production as reported (Hanson and Kende 1975 Plant Physiol 55:663-669) in morning glory but may explain the autocatalytic phase of ethylene production.The association of ethylene with senescence of flowers is widely recognized and carnation flowers have been thoroughly examined in this respect (13). As the cut flower approaches senescence, a dramatic rise in the rate of ethylene production occurs followed soon after by wilting of the petals. Senescence can be hastened by as little as 30 nl/l of ethylene (2, 15). The events taking place between the rise in ethylene production, or exposure to ethylene, and the development of visual symptoms remain obscure. Lieberman et al. (11) over-all length, and placed individually in 20-ml vials. Flowers were obtained from a local grower and experiments were begun on the day of harvest. Four flowers in a 10-liter desiccator with a CO2 scrubber (NaOH solution) comprised a treatment. Flowers were exposed to ethylene at 21AI/I for 0, 3, 6, 9, or 12 hr, after which they were ventilated with ethylene-free air at a rate of 100 ml/min for the remainder of the experiment. Flowers were observed at 1-hr intervals to determine the onset of wilting symptoms as judged by in-rolling of petals.Effect of Ethylene on Rate of Water Uptake. Cut flowers were fitted into a specially designed glass sphere in which the flower bud was maintained in the desired gas atmosphere while the stem was connected to a potometer (5) and water uptake was measured at 30-min intervals. The flowers were ventilated continuously with 2 ,ul/l ethylene in dry air or with ethylene-free at a flow rate of 40 ml/min.Effect of Ethylene on Stomatal Aperture of Carnation Sepals. Flowers were cut to 10 cm over-all length and treated with ethylenie in desiccators as described above. Flowers were removed at 3-hr intervals from each of four desiccators and the sepals were excised, frozen in liquid N2, and freeze-dried. Sections (4 x 4 mm) were sputter-coated with gold and the surface was observed ...
Sumnniary. The capacity of tobacco (Nicotiatna rutstica) leaf discs to incorporate L-leuicine "-C into proteins was measured. Leaf discs were obtained from plants which experienced soil water depletion, or which were exposed to a saline or osmotic stress in the root nmediuim. The stresses were brief of relatively short duration and water potential did not decrease below 4 bars in the root media. Leaf discs were sampled 2 hours a fter stress removal, achieved by reirrigation, or replacement of saline and osmotic solutions with normal nutrient solution. Plants were always tutrgid when leaves were sampled.All stressed tissues showed redutced capacity to incorporate L-leucine 14C into protein. The reduction was about 50 % and could not be attributed either to reduced uLptake into the discs, or to possible isotopic diluition. Incorporation decreased progressively with leaf age in control discs as well as in stressed leaf discs. At all ages tested, incorporation in stressed discs was lower than that of the control. Full recovery of incorporation capacity in stressed discs was obtained when discs were sampled 72 hours after stress removal but not earlier.Kinetin pretreatment prior to incuibation with labelled letucine partially restored incorporation in stressed discs. The differences in response to kinetin of stressed and control discs suggest a lower endogenouis level of cytokinins in the stressed discs. The results were qualitatively similar regardless of the kind of stress given to the plants dturing pretreatment and oni recovery of these rates in the presence of kinetin. Materials and MethodsSingle tobacco plants (Nicotiana rustica) were grown for about 10 weeks in a cooled greenhoulse (20°-30°) in pots containing either 3 kg of a soil-manutre mixture (3: 2 v/v)
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