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1

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Abscisic acid involvement in the induction of summer-dormancy in Poa bulbosa, a grass geophyte (1998)

Ofir, Micha ; Kigel, Jaime

Copenhagen : Munksgaard International Publishers

Physiologia plantarum 102 (1998), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Summer-dormancy occurs in geophytes that inhabit regions with a Mediterranean climate (mild, rainy winters and hot, dry summers). The environmental control of summer-dormancy and the involvement of phytohormones in its induction have been little studied. Poa bulbosa L. is a perennial grass geophyte in which summer-dormancy is induced by long days and by high temperature. Prolonged treatment with ABA (0.1-1.0 mM) under non-inductive 8-h short days (SD) resulted in cessation of leaf and tiller production and in the development of typical features of dormancy: bulbing at the base of the tillers and leaf senescence. Short-term applications of ABA had similar effects but dormancy was transient, i.e. after a short while, leaf growth from the formed bulbs was resumed. ABA treatment of plants growing under an inductive 16-h photoperiod (LD) enhanced the onset of dormancy. Endogenous levels of ABA in leaf blades and at the tiller base (where the bulb develops) increased markedly after the plants were transferred from SD to LD. This increase was greater in the tiller base, and concomitant with bulb maturation. High temperature (27/22 vs 22/17°C) accelerated both bulb development and ABA accumulation in leaf blades.These results suggest that ABA plays a key role in the photoperiodic induction and development of summer-dormancy in P. bulbosa.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1020202.x

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2

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Photothermal control of the imposition of summer dormancy in Poabulbosa, a perennial grass geophyte (1999)

Ofir, Micha ; Kigel, Jaime

Copenhagen : Munksgaard International Publishers

Physiologia plantarum 105 (1999), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Poa bulbosa L., like many other Mediterranean geophytes, grows in the winter and enters a phase of summer dormancy in the spring. Summer dormancy enables these plants to survive the hot and dry summer. Long days are the main environmental factor active in the induction of summer dormancy in P. bulbosa and elevated temperatures accelerate dormancy development. P. bulbosa becomes dormant earlier than most other species that grow actively in the winter. Previous studies suggested that pre-exposure of P. bulbosa to short days and low temperatures during the autumn and early winter increased its sensitivity to photoperiodic induction in late winter, and thus enabled the early imposition of dormancy. To study this hypothesis, experiments were carried out under controlled photothermal conditions in the phytotron, under natural daylight extended with artificial lighting. The critical photoperiod for induction of summer dormancy at an optimal temperature (22/17°C day/night) was between 11 and 12 h. Photoperiods shorter than 12 h were noninductive, while 14- and 16-h days were fully inductive. A night break of 1 h of light given at the middle of the dark period of an 8-h photoperiod also resulted in full induction of dormancy. Pre-exposure to either low temperature (chilling at 5°C) or to short days of 8 h (SD) enhanced the inductive effect of subsequent 16-h long days (LD). The enhancing effect of chilling and SD increased with longer duration, i.e. fewer LDs were required to impose dormancy. However, the day-length during the low-temperature pretreatment had no effect on the level of induction at the following LD. Chilling followed by SD did not induce dormancy. The relevance of these responses to the development and survival of P. bulbosa in its natural habitat is discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1034/j.1399-3054.1999.105406.x

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Seed coat structure and oxygen availability control lowtemperature germination of melon (Cucumis melo) seeds (1995)

Edelstein, Menahem ; Corbineau, Francoise ; Kigel, Jaime ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 93 (1995), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The involvement of the seed coat in low-temperature germination of melon seeds was examined in two accessions differing in their ability to germinate at 14°C: Noy Yizre'el (a cold-sensitive cultivar) and Persia 202 (a cold-tolerant breeding line). Decoating resulted in full germination of Noy Yizre'el at 14°C, but splitting the coat increased germination only partially. Thus, the inhibition of Noy Yizre'el germination at 14°C is not due to physical constraint on radicle protrusion. At 25°C, seeds of both accessions submerged in water or agar germinated fully as long as the hilum aperture remained uncovered. Submerging the whole seed, or covering the hilum with lanolin, strongly depressed germination of Noy Yizre'el but not of Persia 202. Accessions differed in germination response to decreasing O2 concentration, with Noy Yizre'el showing higher sensitivity to hypoxia. These differences were correlated with differences in seed coat structure as well as in embryo sensitivity to hypoxia. Intercellular spaces in the outer layer of the seed coat were evident in the more tolerant Persia 202, while in the sensitive Noy Yizre'el this layer was completely sealed. Sensitivity to hypoxia increased at 15°C as compared with 25°C, the increase being greater in Noy Yizre'el. It is proposed that the seed coat-imposed dormancy at low temperature in Noy Yizre'el is the combined result of more restricted oxygen diffusion through the seed coat and a greater embryo sensitivity to hypoxia, rather than to physical constraints of radicle break-through or impairment of imbibition.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb06842.x

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Role of endogenous gibberellins in germination of melon (Cucumis melo) seeds (1995)

Edelstein, Menahem ; Ben Tal, Yossi ; Wodner, Maria ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 95 (1995), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The effect of the plant growth retardants ancymidol. mefluidide and uniconazole on germination of two melon accessions differing in their ability to germinate at 14°C was examined. The accessions were the cold sensitive Noy Yizre'el and the cold tolerant Persia 202. The three growth retardants were able to delay the germination of intact Noy Yizre'el seeds, but did not affect that of intact Persia 202 seeds. On the other hand germination of decoated seeds of both accessions was unaffected by these inhibitors at normal oxygen concentration, but was inhibited at 5% oxygen. When gibberellin-like activity was measured by a dwarf rice biological assay following HPLC fractionation, it was found that seeds of Persia 202 contained much more gibberellin-like activity than Noy Yizre'el seeds. Among the extracted compounds several endogenous gibberellins were identified by combined gas chromatography-mass spectrometry (GC-MS). They included GA4, GA20, GA1 and GA3 in Noy Yizre'el and GA34, GA20, GA1 and GA8 in Persia 202. It is suggested that the better germination of intact Persia 202 seeds, compared to Noy Yizre'el seeds at low temperature and low oxygen concentration, is due to a higher endogenous level of GA and a better seed coat permeability to oxygen.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00816.x

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5

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The role of the leaves in the regulation of internode elongation in Phaseolus vulgaris (1980)

KIGEL, JAIME

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 49 (1980), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Time-course patterns of leaf and internode elongation were studied in bean plants. Each leaf started its main elongation period when the leaf below reached half of its final length. The onset of leaf unfolding was nearly synchronous with the initiation of the elongation of the subjacent internode. Excision of young leaves increased the rate of stem elongation as a result of an earlier unfolding of the next upper leaves and the concomitant advancement in the elongation of their subjacent internodes. IAA or NAA (1% in lanolin) suppressed the enhancement effects of leaf excision on leaf and internode elongation. The excision of a young leaf increased the final length of internodes located below it, and at the same time decreased the final length of the internodes located above the excised leaf. The reduction was greater the younger the internode. Differences in internode elongation after leaf excision were related to changes during internode ontogenesis in their relative response to the availability of assimilates on the one hand, and on the other hand to hormonal factors transported acropetally from the young leaves to the growing internodes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1980.tb02646.x

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Effects of Azospirillum brasilense on root morphology of common bean (Phaseolus vulgaris L.) under different water regimes (2000)

German, Marcelo A. ; Burdman, Saul ; Okon, Y. ; [et al.]

Springer

Biology and fertility of soils 32 (2000), S. 259-264

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ISSN: 1432-0789

Keywords: Key words Azospirillumbrasilense ; Phaseolus vulgaris ; Common bean ; Root morphology ; Water stress

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The effects of inoculation with Azospirillum brasilense Cd on root morphology and growth of common bean (Phaseolus vulgaris L.) were studied under different growth systems and water regimes. The root systems were evaluated by image analysis. In a PVC-tube growth system, inoculation with A. brasilense at 107 colony forming units (CFU) ml–1 increased root length, root projection area, specific root length (m g–1) and specific root area (cm2 g–1), as compared with non-inoculated controls, resulting in root systems with longer and thinner roots. Water stress induced similar root responses to those observed after inoculation with A. brasilense. No increase in plant biomass was observed in inoculated plants, suggesting that under the tested growth conditions, a relatively larger amount of resources is required for the maintenance of the thinner roots. In water-stressed potted plants, the effect of A. brasilense on tap root length was inoculum-concentration dependent. At 107 CFU ml–1 this effect was significant as compared to non-inoculated controls. In a pouch system without water stress, inoculation with A. brasilense at a concentration of 105–107 CFU ml–1 2 days after germination resulted initially (2 days after inoculation) in an increase in root length (95%) and root fresh weight (66%), but reduced root diameter (20%), compared to controls. At this early stage of growth the distribution of root length among the different root diameter classes changed: the thinner-root classes had the largest proportion of longer roots.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003740000245

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