Dormancy inDioscorea: Different temperature adaptation of seeds,bulbils and subterranean organs in relation to north-south distribution

Temperature dependencies of sprouting and germination were compared for subterranean perennating organs and seeds of ten closely related species of the genusDioscorea (Dioscoreaceae), a group of monocotyledonous summer perennials which are distributed from the tropics to the subarctic. The species used wereD. nipponica Makino,D. tokoro Makino,D. japonica Thunb.,D. tenuipes Franch. et Savat.,D. septemloba Thunb.,D. quinqueloba Thunb.,D. izuensis Akahori,D. bulbifera L. f.spontanea (Makino) Makino et Nemoto,D. pentaphylla. L. andD. alata L.; they are distributed from cold northern areas to warmer southern areas approximately in this order in and around Japan. Bulbil sprouting was also studied in those forming bulbils. Subterranean organs of the tropical species sprouted faster without any prior temperature treatment, whereas those of species from the more northern areas sprouted after prechilling. Northern species required longer, periods of prechilling for sprouting. On the other hand, with seeds or bulbils, the southern species required longer periods of prior temperature treatment for dormancy breaking. This difference in the length of dormant periods between seeds or bulbils and subterranean organs among the ten species may be related to their size and position of shedding; seeds or bulbils are small and are shed on the ground surface, whereas subterranean organs are large and are located below the surface. It is important to determine in other perennials whether the above relation between dormant features of seeds or bulbils and subterranean organs are common properties or not.     

Biochemical changes accompanying the long-term starvation of Micrococcus luteus cells in spent growth medium

Changes in the biochemical properties of Micrococcus luteus cells were studied during the transition to a dormant state after incubation in an extended stationary phase. The overall DNA content after 150 days of starvation was similar to its initial level, while the RNA content decreased by 50%. Total lipids and protein, phospholipids and membrane proteins declined rapidly within the first 1–10 days of starvation. After 180 days of starvation, cells contained 43% of the protein and 35% of the lipid initially present. Starvation for 120 days resulted in the loss of phosphatidylglycerol and, to some extent, of phosphatidylinositol, giving a membrane whose phospholipids consisted mainly of cardiolipin. The membrane fluidity declined during starvation, as judged by diphenyl hexatriene fluorescence anisotropy measurements. Oxidase activities declined to zero within the first 20–30 days of starvation, while the dehydrogenases and cytochromes were more stable. The activities of some cytoplasmic enzymes were lost very rapidly, while NADPH-linked isocitrate dehydrogenase had 30% of its initial activity after 120 days of starvation. For all parameters tested there were significant fluctuations during the first 10–20 days of starvation, which may reflect cryptic growth in the culture.Abbreviations MPN Most probable number - DPH Diphenyl hexatriene     

Pentose phosphate metabolism during dormancy breakage in Corylus avellana L.

Commercially obtained fruits of Corylus avellana exhibit the characteristic loss of dormancy of this seed following chilling under moist conditions. The activities of cytosolic and organellar enzymes of pentose phosphate pathway in cotyledonary tissue were assayed throughout stratification and over a similar period in damp vermiculite at 20° C. Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconic acid dehydrogenase (6PGDH) were both found in cytosolic extracts in all treatments; only 6PGDH was present in the organellar fraction.The enzyme activities monitored in seeds at 20° C remained relatively constant over the course of the investigation except in the case of cytosolic 6PGDH where it is suggested an inhibitor of the enzyme accumulated. This inhibitor was removed by the partial purification procedure. Increases in the activities of the enzymes occurred during stratification, the major increase coinciding exactly with dormancy breakage but prior to the initiation of germination. The marked increase in G6PDH and 6PGDH concurrent with the change in germination potential of the chilled seed may have considerable biochemical significance in breaking down the dormant state.Abbreviations G6P glucose-6-phosphate - G6PDH glucose-6 phosphate dehydrogenase - NADP nicotinamide adenine dinucleotide phosphate - 6 PGDH 6-phosphogluconic acid dehydrogenase - PPP pentose phosphate pathway     

The growth physics and water relations of red-light-induced germination in lettuce seeds

Using lettuce (Lactuca sativa L., cv. Grand Rapids) embryos in osmotica, we have demonstrated that when the growth rates of the embryonic axes of seeds treated with red (R) or far-red (FR) light are equalized, the axes of R-treated seeds develop a 3.4-bar decrease in water potential (paper No. III).As axial growth begins, reserve protein and phytin decrease rapidly, concomitant with increases in reducing sugars, -amino nitrogen, and inorganic and esterified soluble phosphates. However, no differences between the axes of R-and FR-treated seeds are found with respect to the changes in these compounds, indicating that these changes arise as a result of growth and are not under immediate phytochrome control. Little change in the total lipid content is found in either treatment. The axes of FR-treated seeds hydrolyze endogenous sucrose at a greater rate thant those of R-treated seeds. Axes of R-treated seeds accumulate K⁺ and Na⁺ to a greater extent than those of FR-treated seeds. When potassium salts are added to the incubation medium, R induces increased K⁺ uptake by the axis and greater medium acidification by the axis. Malate and other organic acids and acidic amino acids increase at equal rates in both treatments, indicating that inorganic anions may also be taken up to balance the ionic charges. The results are compatible with the assumption that changes in the osmotic and pressure potentials of the embryonic axes of R-treated seeds are the result of a phytochrome-stimulated proton pump which, in whole dormant seeds, would initiate water-potential changes allowing the embryos to overcome the mechanical restraint of the surrounding seed layers, resulting in germination.Abbreviations FR far-red light - PEG polyethylene glyeol 4000 - Pfr far-red-absorbing form of phytochrome - R red light III=Carpita et al. 1979     

The influence of plant growth regulators on the growth of the embryonic axes of red- and far-red-treated lettuce seeds

The influence of several plant growth regulators on the growth of the embryonic axes from red- and far-red-(R- and FR-)treated lettuce (Lactuca sativa L., cv. Grand Rapids) seeds was examined; as shown previously, the water potential of the axes from R-treated seeds has been lowered by 3.5–5.6 bars compared to that in axes from FR-treated ones. Kinetin and abscisic acid (ABA), when included in the incubation medium, reduced the elongation of the axes whereas fusicoccin stimulated it; however, these effects were the same in axes of both R- and FR-treated seeds. In contrast, elongation of axes from FR-treated seeds was stimulated by gibberellic acid (GA₃, but elongation of axes from R-treated ones was not affected by this hormone. This latter result indicates that gibberellins may be involved in the phytochrome-mediated growth responses in lettuce axes.When the root caps of the embryos were removed prior to light treatment, R was still able to induce a water-potential decrease in the embryonic axes, indicating that at least a portion of the active Pfr resides in the axis and not the root cap.Abbreviations ABA abscisic acid - FR far red light - GA₃ gibberellic acid - PEG polyethylene glycol - Pfr far-red-absorbing form of phytochrome - R red light     

Germination inhibitors in the pine seed coat

Inhibitors from (Pinus pinea L.) seed coats were separated using paper chromatography, thin layer chromatography, and a Sephadex G-10 column. The inhibitory activity was resolved into several fractions. One of these behaved similarly to abscisic acid. It has exhibed the same properties as ABA in thin-layer chromatography, paper chromatography, and Sephadex G-10 chromatography and in UV absorption and fluorescence spectra. These germination inhibitors, present in the seed coats, are involved in the regulation of P. pinea seed germination.Abbreviations ABA abscisic acid - TLC thin-layer chromatography     

Membrene turnover in imbibed and dormant embryos of the wild oat (Avena fatua L.)

A comparative study of protein synthesis has been carried out with embryos excised from dormant (D) and non-dormant (ND) caryopses of the wild oat. Although D embryos imbibed in water or ND embryos imbibed in abscisic acid do not germinate, they incorporate [¹⁴C]leucine into TCA-insoluble material for the first 48 h as readily as embryos that do germinate (ND embryos imbibed in water, or D embryos imbibed in gibberellic acid). Pulsechase experiments with [¹⁴]leucine show that in both D and ND embryos the proteins associated with the membranes undergo turnover. The rates of decay of incorporated radioactivity are similar in both dormant and germinating embryos up to 98 h following embryo excision. Fractionation of the membrane proteins in SDS-polyacrylamide gels indicates that the different polypeptides have different rates of turnover. It is concluded that membrane proteins in imbibed D embryos are in a state of constant turnover, and that this is a part of the replacement processes necessary to maintain the integrity of hydrated cells. The continuation of such synthetic events could account for long term survival of dormant Avena fatua in the imbibed state.Abbreviations CCRSE cytochrome relative stain equivalents - D dormant - ND nondormant - ABA abscisic acid - GA gibberellic acid GA₃     

Cell cycle inHelianthus tuberosus tuber tissue in relation to dormancy

Summary Observations are presented on the patterns of DNA synthesis and mitotic activity in medullary parenchyma cells excised from tubers ofHelianthus tuberosus in four different periods of dormancy. Dormancy break (activation) was induced byin vitro culture on media added with 2,4-dichlorophenoxyacetic acid. The cell cycle responsein vitro to different combinations of growth substances has also been investigated.The results show that remarkable changes in the timing of the first and second cell cycles and their phases occur with the progression of dormancy. With increasing time after tuber harvest, the following behaviours are observed: (i) a lengthening of the first cell cycle, chiefly due to a lengthening of the G₂ phase (G₂ is absent at the beginning of dormancy) and an increase in the time interval between the start of thein vitro culture and the onset of the first mitotic wave; (ii) an increased duration of the S phase; (iii) a remarkable reduction in the cell synchrony.These behaviours, as indicated also by their comparison with thein vitro response of the cell cycle to different hormonal treatments, seem to depend on the physiological status of the tubers at the time of explant. It is concluded that the analysis of the cell cycle is an useful tool for understanding some aspects of such a complex physiological situation as dormancy.Istituto di Mutagenesi e Differenziamento del C.N.R., Pisa, Italy, publication no. 321.     

The isolation of abscisic acid (ABA) deficient mutants by selection of induced revertants in non-germinating gibberellin sensitive lines of Arabidopsis thaliana (L.) heynh.

Summary By selecting for germinating seeds in the progeny of mutagen-treated non-germinating gibberellin responsive dwarf mutants of the ga–1 locus in Arabidopsis thaliana, germinating lines (revertants) could be isolated. About half of the revertants were homozygous recessive for a gene (aba), which probably regulates the presence of abscisic acid (ABA). Arguments for the function of this gene were obtained from lines homozygous recessive for this locus only, obtained by selection from the F₂ progeny of revertant X wild-type crosses. These lines are characterized by a reduced seed dormancy, symptoms of withering, increased transpiration and a lowered ABA content in developing and ripe seeds and leaves.Abbreviations ABA Abscisic acid - GA₄₊₇ Mixture of gibberellin A₄ and A₇ - EMS Ethylmethanesulfonate - NG Non-germinating - G Germinating     

Ultrastructural changes in the endoplasmic reticulum during dormancy release of apple embryos (Pyrus malus L.)

Apple embryos were treated by cold (0°C) within the fruits, to break their dormancy; the controls were treated at 12°C or at 20°C. Ultrastructural features of meristematic cells in the embryonic axis were compared for each treatment. The organization of the cells of dormant embryos was described: Endoplasmic reticulum consisted in some short rough cisternae; lipid droplets regularly arranged near the plasmalemma constituted a kind of shell; mitochondria had a few cristae; and dictyosomes were rarely observed. All these features are typical of dry seeds. After cold treatments, the only evolution observed was in the endoplasmic reticulum, where highly organized stacks appeared progressively as a function of time at 0°C. An intermediate temperature (12°C) induced similar formations in the reticulum but they were rarely observed and their degree of organization was lower than that obtained at 0°C. At 20°C, endoplasmic reticulum resembled that of the dormant embryo cells. The relation between the appearance of these structures in the reticulum and the disappearance of dormancy induced by cold is discussed.Abbreviations ER endoplasmic reticulum - RER rough endoplasmic reticulum