Are wildfires an adapted ecological cue breaking physical dormancy in the Mediterranean basin?

2015 ◽  
Vol 25 (2) ◽  
pp. 120-126 ◽  
Author(s):  
Ganesh K. Jaganathan
Keyword(s):  
Mediterranean Ecosystems ◽  
Seasonal Temperature ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Anatomical Structures ◽  
Temperature Changes ◽  
Seed Mortality ◽  
Fire Environment ◽  
Impermeable Seed Coat

AbstractMany studies have claimed that fire acts as the chief ecological factor cueing dormancy break in seeds with a water-impermeable seed coat, i.e. physical dormancy (PY), in Mediterranean ecosystems. However, a proposal is made that seasonal temperature changes must be viewed as more meaningful dormancy-breaking cues because: (1) fire is erratic and may break PY in seasons during which seedlings cannot complete their life cycle; (2) fire may not occur for long periods, thereby only providing an opportunity for dormancy break and germination once in every several years; and (3) if fire opens the specialized anatomical structures called ‘water gaps’, in seconds, their evolutionary role of detecting environmental conditions becomes irrational. Although fire breaks dormancy in a proportion of seeds, given the risk of seed mortality and the post-fire environment providing cues for dormancy break, it is suggested that fire might possibly be an exaptation.

Sensitivity cycling and its ecological role in seeds with physical dormancy

2009 ◽  
Vol 19 (1) ◽  
pp. 3-13 ◽  
Author(s):  
K.M.G. Gehan Jayasuriya ◽  
Jerry M. Baskin ◽  
Carol C. Baskin
Keyword(s):  
Life Cycle ◽  
Environmental Conditions ◽  
Common Phenomenon ◽  
Ecological Role ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Physiological Dormancy ◽  
Seed Coats

AbstractCycling of physically dormant (PY) seeds between states insensitive and sensitive to dormancy-breaking factors in the environment has recently been demonstrated inFabaceaeandConvolvulaceae, and it may be a common phenomenon in seeds with water-impermeable seed coats. In contrast to seeds of many species with physiological dormancy (PD), those with PY cannot cycle between dormancy and non-dormancy (ND). In this paper, we evaluate the role of sensitivity cycling in controlling the timing of germination of seeds with PY in nature, and show that sensitivity cycling in seeds with PY serves the same ecological role as dormancy cycling in seeds with PD. Thus, sensitivity cycling in seeds with PY ensures that germination in nature occurs only at (a) time(s) of the year when environmental conditions for growth are, and are likely to remain, suitable long enough for the plant to complete its life cycle or to form a perennating structure. Further, we describe the experimental procedures necessary to determine whether sensitivity cycling is occurring, and discuss briefly the possible relevance of sensitivity cycling to dormancy classification.

Physical dormancy in Senna multijuga (Fabaceae: Caesalpinioideae) seeds: the role of seed structures in water uptake

2014 ◽  
Vol 24 (2) ◽  
pp. 147-157 ◽  
Author(s):  
Ailton G. Rodrigues-Junior ◽  
José M.R. Faria ◽  
Tatiana A.A. Vaz ◽  
Adriana T. Nakamura ◽  
Anderson C. José
Keyword(s):  
Water Uptake ◽  
Seed Coat ◽  
Parenchyma Cell ◽  
Hot Water ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Short Term Exposure ◽  
Hilar Region ◽  
Senna Multijuga

AbstractStructural studies in seeds with physical dormancy (PY) are important to better understand its causes and release when subjected to treatments for dormancy breaking. The aims of this study were to (1) characterize the PY break; (2) examine the role of different seed structures in water uptake; and (3) identify the water gap in Senna multijuga seeds. Imbibition patterns of dormant and non-dormant (subjected to dormancy breaking treatments) seeds and the morphological changes during dormancy breaking and germination were evaluated. To identify the water gap, the micropyle and lens were blocked separately, and the water absorption by seed parts was determined. Structural characteristics of the seed coat were also examined. Immersion in water at 80°C was efficient in breaking seed dormancy and imbibition occurred first at the hilar region, through the lens. Water was not absorbed through the micropyle or the extra-hilar region. S. multijuga seeds have a testa with a linearly aligned micropyle, hilum and lens. The seed coat consisted of a cuticle, macrosclereids, one (hilar region) or two (extra-hilar region) layer(s) of osteosclereids and parenchyma cell layers. The lens has typical parenchyma cells underneath it and two fragile regions comprised of shorter macrosclereids. Heat treatment stimulated the lens region, resulting in the opening of fragile regions at the lens, allowing water to enter the seeds. It is concluded that short-term exposure to a hot water treatment is sufficient for the formation of a water gap in S. multijuga seeds, and only the lens acts in the imbibition process.

Dormancy-breaking and germination requirements for seeds of Acacia papyrocarpa, Acacia oswaldii and Senna artemisioides ssp.×coriacea, three Australian arid-zone Fabaceae species

2014 ◽  
Vol 62 (7) ◽  
pp. 546 ◽  
Author(s):  
Leanne M. Pound ◽  
Phillip J. Ainsley ◽  
José M. Facelli
Keyword(s):  
Arid Zone ◽  
South Australia ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Dry Heat ◽  
Seed Mortality ◽  
Wet Heat ◽  
Pre Treatment ◽  
Unpredictable Environment ◽  
Germination Requirements

Physical dormancy is common in seeds of arid-land legumes. Improved understanding of germination requirements of hard-seeded species will further our understanding of arid lands and aid restoration projects. We studied the germination responses of Acacia papyrocarpa (Benth.), A. oswaldii (F.Muell) and Senna artemisioides (Gaudich. ex DC.) Randell ssp. × coriacea (Benth.) Randell from a chenopod shrubland in South Australia. Imbibition testing indicated that all three species had physical dormancy, but the proportion of dormant seeds was lower in A. oswaldii. This corresponded to a thinner testa in this species. Mechanisms tested to scarify seeds included mechanical scarification and different durations of wet or dry heat. Mechanically scarified seeds germinated readily, reaching maximum numbers in 10–15 days, independently of incubation temperatures, with the exception of S. artemisioides seeds, which germinated at a slower rate in cooler temperatures. Overall, wet heat was more effective than dry heat to alleviate physical dormancy, whereas dry heat in some cases resulted in seed mortality. On the basis of these results, it is recommended that seeds of A. papyrocarpa and S. artemisoides be pretreated with wet heat in future restoration programs. No pre-treatment is required for dormancy loss in A. oswaldii seeds. The different responses of seeds of these species suggest that their populations have varying strategies for persistence in this unpredictable environment.

Role of the lens in physical dormancy in seeds of Sophora alopecuroides L. (Fabaceae) from north-west China

2008 ◽  
Vol 59 (6) ◽  
pp. 491 ◽  
Author(s):  
X. W. Hu ◽  
Y. R. Wang ◽  
Y. P. Wu ◽  
Z. B. Nan ◽  
C. C. Baskin
Keyword(s):  
Sulfuric Acid ◽  
Water Entry ◽  
Primary Site ◽  
Hot Water ◽  
Field Conditions ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Field Exposure ◽  
Sophora Alopecuroides

Abstract Although many studies have been done on seeds with physical dormancy, i.e. water-impermeable seed or fruit coat, the primary site of water entry into seeds after dormancy-breaking treatments is still controversial. In this work, the role of the lens in physical dormancy breaking was examined. The present study investigated the primary site of water entry and changes in seed-surface features for seeds of Sophora alopecuroides L. following various periods of scarification with sulfuric acid, hot-water treatments, and exposure to field conditions. Most seed coats first cracked in the hilum when pre-treated with sulfuric acid and after field exposure, but they cracked in both the hilum and extrahilar regions when treated with hot water. After pre-treatment, seeds first became slowly permeable in the hilum or extrahilar region and not in the lens. Acid scarification for 35 or 50 min caused the lens to crack, thus causing seeds to enter a fast imbibition stage. Seeds exposed to field conditions had further damage to the hilum, causing them to enter a fast imbibition stage. Imbibition time is a key point that determines the primary site of water entry into seed, and at least in part explains various results and interpretations about the role of the lens in physical dormancy in previous research.

Role of the lens in controlling water uptake in seeds of twoFabaceae(Papilionoideae) species treated with sulphuric acid and hot water

2009 ◽  
Vol 19 (2) ◽  
pp. 73-80 ◽  
Author(s):  
Xiao Wen Hu ◽  
Yan Rong Wang ◽  
Yan Pei Wu ◽  
Carol C. Baskin
Keyword(s):  
Sulphuric Acid ◽  
Water Uptake ◽  
Water Entry ◽  
Primary Site ◽  
Hot Water ◽  
Sesbania Sesban ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Water Treatments

AbstractAlthough many studies have been conducted on seeds with a water-impermeable seed or fruit coat (physical dormancy), the primary site of water entry into these seeds after dormancy-breaking treatments is still controversial. Thus, the role of lens, hilum, micropyle and extrahilar regions in water uptake of seeds treated to break physical dormancy was examined inVigna oblongifoliaandSesbania sesban(Fabaceae) following pretreatment with sulphuric acid and hot water. Morphology of seed surfaces in treated versus non-treated seeds of both species was examined with scanning electron microscopy. Most seeds ofV. oblongifoliafirst cracked in the hilum when pretreated with sulphuric acid, but they cracked in both the hilum and extrahilar regions when pretreated with hot water. However, inS. sesbanseeds, a crack formed only in the lens following either acid scarification or hot-water treatments, and the seeds imbibed water only through the lens. These results indicate that the primary site of water entry into seeds following physical dormancy break can vary with species and treatments. Slow, early imbibitionviathe hilum, and subsequent rapid imbibitionviathe lens, may not be detected unless seeds are monitored for several days. Time allowed for imbibition studies may, at least in part, explain various interpretations about the role of the lens in physical dormancy reported in the literature.

Role of temperature and light in the germination ecology of buried seeds of weedy species of disturbed forests. II. Erechtites hieracifolia

1996 ◽  
Vol 74 (12) ◽  
pp. 2002-2005 ◽  
Author(s):  
Carol C. Baskin ◽  
Jerry M. Baskin
Keyword(s):  
Seed Bank ◽  
Full Range ◽  
Soil Disturbance ◽  
Seasonal Temperature ◽  
Temperature Changes ◽  
Test Conditions ◽  
Buried Seeds ◽  
Weedy Species ◽  
Dormancy Cycles

At maturity in September, about half the seeds (achenes) of Erechtites hieracifolia (Asteraceae) collected in Kentucky were dormant (did not germinate at any test condition), whereas the others were conditionally dormant (germinated only at a narrow range of test conditions). Seeds sown on top of soil in an unheated greenhouse in September failed to germinate in autumn because temperatures were below those required for germination; however, they germinated at comparable temperatures the following spring. Seeds buried in soil in September 1987 and exposed to natural seasonal temperature changes were nondormant (germinated over full range of test conditions) by April 1988, but they entered conditional dormancy by October 1988. Each October through 1995, exhumed seeds exhibited conditional dormancy. Since 89% of the seeds were viable after 8 years of burial, it appears that although seeds of this species are wind dispersed, they also have the potential to form a long-lived seed bank. Thus, soil disturbance at any time from May to September could result in establishment of plants from seeds in the seed bank. Keywords: seed dormancy, Asteraceae, dormancy cycles, buried seeds, light.

Water absorption and dormancy-breaking requirements of physically dormant seeds of Schizolobium parahyba (Fabaceae – Caesalpinioideae)

2012 ◽  
Vol 22 (3) ◽  
pp. 169-176 ◽  
Author(s):  
Thaysi Ventura de Souza ◽  
Caroline Heinig Voltolini ◽  
Marisa Santos ◽  
Maria Terezinha Silveira Paulilo
Keyword(s):  
Water Absorption ◽  
Atlantic Forest ◽  
High Temperatures ◽  
Hot Water ◽  
Dormancy Breaking ◽  
Physical Dormancy ◽  
Maximum Percentage ◽  
Schizolobium Parahyba ◽  
Inhibited Water

AbstractPhysical dormancy refers to seeds that are water impermeable. Within the Fabaceae, the structure associated with the breaking of dormancy is usually the lens. This study verified the role of the lens in physical dormancy of seeds of Schizolobium parahyba, a gap species of Fabaceae from the Atlantic Forest of Brazil. The lens in S. parahyba seeds appeared as a subtle depression near the hilum and opposite the micropyle. After treatment of the seeds with hot water, the lens detached from the coat. Blocking water from contacting the lens inhibited water absorption in hot-water-treated seeds. High constant (30°C) and alternating (20/30°C) temperatures promoted the breaking of physical dormancy and germination in non-scarified seeds. Maximum percentage of germination occurred earlier for seeds incubated at 20/30°C than for those incubated at 30°C. Seeds with a blocked lens did not germinate at alternating or high temperatures. This study suggests that alternating temperatures are probably the cause of physical dormancy break of seeds of S. parahyba in gaps in the forest.

A parametrized model of seasonal temperature changes in lakes

1990 ◽  
Vol 5 (1) ◽  
pp. 12-25 ◽  
Author(s):  
S.S. Zilitinkevich ◽  
V.A. Rumyantzev
Keyword(s):  
Seasonal Temperature ◽  
Temperature Changes

Putative antihyperpyretic factor induced by LPS in spleen of guinea pigs

2005 ◽  
Vol 289 (3) ◽  
pp. R680-R687 ◽  
Author(s):  
Carlos Feleder ◽  
Vit Perlik ◽  
Ying Tang ◽  
Clark M. Blatteis
Keyword(s):  
Kupffer Cells ◽  
Guinea Pigs ◽  
Collateral Circulation ◽  
Splenic Vein ◽  
Inhibitory Factor ◽  
Febrile Response ◽  
Temperature Changes ◽  
The Core ◽  
Temporally Correlated

We reported previously that the onset of LPS-induced fever, irrespective of its route of administration, is temporally correlated with the appearance of LPS in the liver and that splenectomy significantly increases both the febrile response to LPS and the uptake of LPS by Kupffer cells (KC). To further evaluate the role of the spleen in LPS fever production, we ligated the splenic vein and, 7 and 30 days later, monitored the core temperature changes over 6 h after intraperitoneal (ip) injection of LPS (2 μg/kg). Both the febrile response and the uptake of LPS by KC were significantly augmented. Like splenectomy, splenic vein ligation (SVL) increased the febrile response and LPS uptake by KC until the collateral circulation developed, suggesting that the spleen may normally contribute an inhibitory factor that limits KC uptake of LPS and thus affects the febrile response. Subsequently, to verify the presence of this factor, we prepared splenic extracts from guinea pigs pretreated with LPS (8 μg/kg ip) or pyrogen-free saline, homogenized and ultrafiltered them, and injected them intravenously into splenectomized (Splex) guinea pigs pretreated with LPS (8 μg/kg ip). The results confirmed our presumption that the splenic extract from LPS-treated guinea pigs inhibits the exaggerated febrile response and the LPS uptake by the liver of Splex guinea pigs, indicating the presence of a putative splenic inhibitory factor, confirming the participation of the spleen in LPS-induced fever, and suggesting the existence of a novel antihyperpyretic mechanism. Preliminary data indicate that this factor is a lipid.

Role of ion transfer processes in acid-base regulation with temperature changes in fish

1984 ◽  
Vol 246 (4) ◽  
pp. R441-R451 ◽  
Author(s):  
N. Heisler
Keyword(s):  
Ion Transfer ◽  
Bicarbonate Concentration ◽  
Acid Base ◽  
Fish Tissues ◽  
Model Calculations ◽  
Temperature Changes ◽  
Transfer Processes ◽  
Transfer Mechanisms

The contributions of transmembrane and transepithelial ion transfer processes and of nonbicarbonate buffering to the in vivo acid-base regulation have been evaluated. Model calculations were performed utilizing experimental data on transepithelial transfer of ions relevant for the acid-base regulation, the intracellular buffering properties of fish tissues, and the behavior of intracellular and extracellular pH and bicarbonate concentration with changes of temperature. The results of these studies indicate that the changes in the pK values of physiological nonbicarbonate buffers with changes in temperature support the adjustment of pH to lower values with rising temperature; however, transmembrane and transepithelial ion transfer mechanisms determine the acid-base regulation of intracellular and extracellular compartments.

Sign in / Sign up

Export Citation Format

Share Document