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AMNON EREZ 《Physiologia plantarum》1977,39(4):285-289
Exposure of peach plants to the blue plus far-red (B/FR) portions of the sunlight spectrum caused a rapid rise in ethylene evolution from their apices. Two days were enough to produce a significant rise in ethylene evolution relative to blue without far-red or to neutral shade. Maximal level of ethylene evolution in the B/FR light, more than eight times that of the blue or the neutral shade, was reached after four days of exposure. A higher endogenous ethylene content was also found under B/FR relative to blue or to neutral shade conditions. The level of ethylene evolution from peach apices was correlated with their arrested growth as observed a few days later. Exposure of peach plants to dense leaf shade, under the canopy of a big avocado tree, enhanced ethylene evolution from their apices, relative to unfiltered sunlight and to neutral shade. It was suggested that the rise in ethylene evolution in both B/FR and leaf shade conditions resulted from a high far-red: red ratio. Ethylene was further suggested to act as a mediator of photomorphogenetic regulation of vegetative development in far-red-rich tree shade. 相似文献
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Boron (B) is known to accumulate in the leaf margins of different plant species, arguably a passive consequence of enhanced transpiration at the ends of the vascular system. However, transpiration rate is not the only factor affecting ion distribution. We examine an alternative hypothesis, suggesting the participation of the leaf bundle sheath in controlling radial water and solute transport from the xylem to the mesophyll in analogy to the root endodermis. In banana, excess B that remains confined to the vascular system is effectively disposed of via dissolution in the guttation fluid; therefore, impairing guttation should aggravate B damage to the leaf margins. Banana plants were subjected to increasing B concentrations. Guttation rates were manipulated by imposing a moderate osmotic stress. Guttation fluid was collected and analysed continuously. The distribution of ions across the lamina was determined. Impairing guttation indeed led to increased B damage to the leaf margins. The kinetics of ion concentration in guttation samples revealed major differences between ion species, corresponding to their distribution in the lamina dry matter. We provide evidence that the distribution pattern of B and other ions across banana leaves depends on active filtration of the transpiration stream and on guttation. 相似文献
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Thiourea (TU) promoted growth in cytokinin-requiring soybean,tobacco, and apple callus tissues, in the absence of kinetin.The increase in fresh and dry weight obtained was a result ofcell multiplication. Callus tissues grew well when repeatedlysubcultured in kinetin-free medium containing TU. The best growthwas obtained with 10–4-10–3 M TU. At these concentrationssynergism was demonstrated between TU and the cytokinins, kinetin,benzyladenine, and zeatin. TU caused greater growth than diphenylureaand phenylthiourea. The possibility that a breakdown productof TU is responsible for the enhanced growth was not excluded.The dormancy-breaking effect of TU was suggested to be relatedto its growth-enhancing effect. 相似文献
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Young peach plants (Prunus persica) were grown outdoors under different colored filters, to examine the effect of light quality on plant behavior. It was found that under blue light growth rate, leaf size and number, rate of spring bud opening and secondary branching were very similar to control plants grown under neutral shade. Blue + far-red light showed an overall strong inhibitory effect on all these characteristics. Red + far-red light produced the strongest growth activity with best results in growth rate and leaf size and number. The phytochrome pigment system was suggested to be the only pigment regulating growth under high light intensities. Blue and blue + far-red light acted antagonistically on apical dominance features of the tree. The former produced a wider tree with nearly horizontal shoots, while the latter produced a more erect narrow tree. 相似文献
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SHAWN R. THATCHER SHAUL BURD CHRISTOPHER WRIGHT AMNON LERS PAMELA J. GREEN 《Plant, cell & environment》2015,38(1):188-200
MicroRNAs (miRNAs) are a class of small RNAs, which typically function by guiding cleavage of target mRNAs. They are known to play roles in a variety of plant processes including development, responses to environmental stresses and senescence. To identify senescence regulation of miRNAs in Arabidopsis thaliana, eight small RNA libraries were constructed and sequenced at four different stages of development and senescence from both leaves and siliques, resulting in more than 200 million genome‐matched sequences. Parallel analysis of RNA ends libraries, which enable the large‐scale examination of miRNA‐guided cleavage products, were constructed and sequenced, resulting in over 750 million genome‐matched sequences. These large datasets led to the identification a new senescence‐inducible small RNA locus, as well as new regulation of known miRNAs and their target genes during senescence, many of which have established roles in nutrient responsiveness and cell structural integrity. In keeping with remobilization of nutrients thought to occur during senescence, many miRNAs and targets had opposite expression pattern changes between leaf and silique tissues during the progression of senescence. Taken together, these findings highlight the integral role that miRNAs may play in the remobilization of resources and alteration of cellular structure that is known to occur in senescence. 相似文献
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AMNON ROSENFELD 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1979,12(4):353-360
The carapaces of some living freshwater and brackish-water ostracode species have been studied by means of light microscope, scanning electron microscope. transmission electron microscope, electron probe analyzer and X-ray diffractometer, with emphasis placed on the 'pigment' granules. The granules were found to consist of calcite and apatitic calcium orthophosphate. They are located within the epidermis, as a layer which is attached to the internal side of the calcite layer. It is suggested that the main function of the granules is the construction of the new calcareous valve in the moulting process. The layer of granules probably recrystallizes to form the calcite crystals of the valves. 相似文献
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