A role for fruit structure in seed survival and germination of Swartzia langsdorffii Raddi beyond dispersal

• Diaspore structure has been hypothesised to play a role in seed viability and/or germination of recalcitrant seeds, especially for Swartzia langsdorffii. Thus, this work aims to (i) investigate the in situ contribution of pericarp and aril on seed viability and germination, and (ii) identify morphoanatomical traits of S. langsdorffii diaspores that allow its desiccation‐sensitive seeds to remain viable.
• The role of the pericarp and aril in seed survival and germination was investigated by placing the whole fruit, whole seeds (arillate seed) and bare seeds (without aril) in soil in the forest understorey, assessing germination, emergence, dead, firm and predated seeds, and water content of pericarps, arils and seeds. Correlation analysis was performed between environmental variables and physiological parameters. Histochemical features of diaspores were also investigated.
• Pericarp water content fell after several months, while the aril maintained its water content. Seeds did not lose water even without the presence of the pericarp and aril. However, presence of the pericarp promoted seed water content, viability and germination long after dispersal. The embryo had a thickened outer periclinal cell wall.
• Pericarp and aril are not essential to prevent water loss in seeds, but do help to retain seed moisture, favouring viability maintenance and promoting germination during the rainy season. Morphoanatomical features of seeds are suggested as main factors that reduce water loss. Survival of these desiccation‐sensitive seeds upon dispersal during the dry season appears to be facilitated by multiple diaspore features that prevent viability loss.

     

Impacts of fire cues on germination of Brassica napus L. seeds with high and low secondary dormancy

• Agricultural burning is used in farm management operations; however, information about the impact of fire cues on the release and/or induction of secondary dormancy in crop seeds is scarce.
• Seeds from two oilseed rape cultivars were induced for high (HD) or low (LD) secondary dormancy using polyethyleneglycol (PEG) pre‐treatment, and their germination after exposure to various fire cues was compared to control PEG pre‐treated and non‐dormant seeds.
• Non‐dormant seed germination was unaffected by various fire cues. Low doses of aerosol smoke released secondary dormancy in HD seeds, while higher doses increased dormancy of LD seeds. Dilute smoke water also released HD seed secondary dormancy, but concentrated smke water enhanced dormancy in both LD and HD seeds. The concentrated aqueous extracts from charred oilseed rape straw only promoted germination of HD seeds, while dilution inhibited LD seed germination. Heat shock (80 °C, 5 min) released secondary dormancy in HD seeds; however, higher temperatures and/or increased exposure time was associated with seed death. GC‐MS analyses of smoke water revealed two butenolides and an array of monoaromatic hydroxybenzene compounds with potential germination inhibitor or promoter activity.
• The extent of secondary dormancy induction in seeds affects their subsequent responses to fire cues. Both aerosol smoke and smoke water have both germination promoter and inhibitor activity. Lacking any butenolides, aqueous extracts of charred straw contain a potential germination stimulating steroid, i.e. ergosterol. The significance of fire‐derived cues on behaviour of oilseed rape seeds in the soil seed bank is discussed.

     

The Role of Water Uptake in the Transition of Recalcitrant Seeds from Dormancy to Germination

In recalcitrant seeds of horse chestnut (Aesculus hippocastanum L.) maintaining a high water content during winter, dormancy is determined by the presence and influence of the seed coat, while the axial organs of the embryos excised from these seeds are not dormant. Such axial organs were capable for active water uptake and rapid fresh weight increase, so that their fresh weights exceeded those in intact seeds at the time of radicle protrusion. Fructose plays an essential role in the water uptake as a major osmotically active compound. ABA interferes with the water uptake by the axial organs and thus delays the commencement of their growth. The manifestation of seed response to ABA during the entire dormancy period indicates the presence of active ABA receptors and the pathways of its signal transduction. The content of endogenous ABA in the embryo axes doubled in the middle of dormancy period, which coincided with a partial suppression of water uptake by the axes. During seed dormancy release and imbibition before radicle protrusion, the level of endogenous ABA in axes declined gradually. Application of exogenous ABA can imitate dormancy by limiting water absorption by axial organs. Fusicoccin A (FC A) treatment neutralized completely this ABA effect. Endogenous FC-like ligands were detected in the seed axial organs during dormancy release and germination. Apparently, endogenous FC stimulates water uptake via the activation of plasmalemmal H⁺-ATPase, acidification of cell walls, their loosening, and turgor pressure reduction. FC can evidently counteract the ABA-induced suppression of water uptake by controlling the activity of H⁺-ATPase. It is likely that, in dormant intact recalcitrant seeds, axial organs, maintaining a high water content, are competent to elevate their water content and to start their preparation for germination under the influence of FC when coat-imposed dormancy becomes weaker.     

Investigating seed dormancy in cotton (Gossypium hirsutum L.): understanding the physiological changes in embryo during after‐ripening and germination

• The dormancy of seeds of upland cotton can be broken during dry after‐ripening, but the mechanism of its dormancy release remains unclear.
• Freshly harvested cotton seeds were subjected to after‐ripening for 180 days. Cotton seeds from different days of after‐ripening (DAR) were sampled for dynamic physiological determination and germination tests. The intact seeds and isolated embryos were germinated to assess effects of the seed coat on embryo germination. Content of H₂O₂ and phytohormones and activities of antioxidant enzymes and glucose‐6‐phosphate dehydrogenase were measured during after‐ripening and germination.
• Germination of intact seeds increased from 7% upon harvest to 96% at 30 DAR, while embryo germination improved from an initial rate of 82% to 100% after 14 DAR. Based on T₅₀ (time when 50% of seeds germinate) and germination index, the intact seed and isolated embryo needed 30 and 21 DAR, respectively, to acquire relatively stable germination. The content of H₂O₂ increased during after‐ripening and continued to increase within the first few hours of imbibition, along with a decrease in abscisic acid (ABA) content. A noticeable increase was observed in gibberellic acid content during germination when ABA content decreased to a lower level. Coat removal treatment accelerated embryo absorption of water, which further improved the accumulation of H₂O₂ and changed peroxidase content during germination.
• For cotton seed, the alleviation of coat‐imposed dormancy required 30 days of after‐ripening, accompanied by rapid dormancy release (within 21 DAR) in naked embryos. H₂O₂ acted as a core link between the response to environmental changes and induction of other physiological changes for breaking seed dormancy.

     

朱唇种子吸水特性及其在干旱胁迫下萌发特性

种子粘液质是植物在长期适应环境过程中形成的,该物质对于种子的扩散、定居、生存力的改善、萌发、幼苗生存乃至抵御有毒化学物质毒害等都具有重要的生态学意义。朱唇为唇形科鼠尾草属多年生草本植物,原产美洲热带地区,现已广泛栽植于世界各地。为了理解朱唇种子表面的粘液物质吸水特性和种子在干旱胁迫下的萌发特性,该研究以朱唇种子为材料,运用光学显微镜和扫描电子显微镜观察以及种子萌发试验的方法,对种子和粘液层的形态结构、粘液质对种子萌发的影响进行了研究。结果表明:朱唇种子为卵形,表面为负网状结构,千粒重为(1.611±0.0084)g,无粘液种子吸水倍数为3,粘液种子吸水倍数为25,粘液层吸水倍数为122。粘液和无粘液种子及粘液层的重量都随吸水时间的延长而增长,但脱水过程要远长于吸水过程。朱唇种子吸水2 h达到饱和,经过36 h可干燥失水恢复原重。不同浓度PEG对朱唇种子的萌发均有影响,发芽势随PEG浓度升高而显著降低。朱唇种子在5%PEG胁迫下发芽率最高达(90.00±8.66)%,20%PEG胁迫下发芽率最低为(76.67±10.41)%,低浓度PEG对朱唇种子萌发有一定促进作用。这说明朱唇种子为速萌型种子,其粘液质在种子吸水过程中起到举足轻重的作用,能保证短时间内有充足的水分供其萌发。     

玉兰肉质外种皮挥发性成分与功能的初步研究

以玉兰(Magnolia denudata Desr.)发育成熟的种子为材料,采用水蒸气蒸馏法和GC-MS技术对其肉质外种皮化学成分的种类和含量进行了分析研究,并就玉兰肉质外种皮对其种子吸水和失水的影响以及化感作用进行比较研究,以探讨其相应的生态学和生物学功能。结果表明:(1)玉兰肉质外种皮占整个完整种子重量的48.25%,有无肉质外种皮对其种子自身吸水没有明显影响,但在失水过程中有肉质外种皮的种子失水较慢,具有一定的保水作用。(2)玉兰种子肉质外种皮中萜烯类和醇类的种类较多,分别有12种和11种;但酮类和酯类的相对含量较高,分别为32.84%和18.03%,其中含量较多的成分依次是甲基庚烯酮(31.95%)、乙酸丁酯(17.69%)、对伞花烃(13.64%)和芳樟醇(6.61%)。(3)玉兰肉质外种皮浸提液对豌豆、白菜种子萌发具有明显的抑制作用,且随着浸提液浓度增加,豌豆种子发芽率由86.7%下降为6.0%,白菜种子发芽率由28.0%下降为0。研究推测,玉兰种子的肉质外种皮在功能上可能是一种类似肉质果果肉的结构,具有丰富的化学成分,不仅可以吸引鸟类传播其种子,也具有一定的化感作用。     

Anatomy of two mechanisms of breaking physical dormancy by experimental treatments in seeds of two North American Rhus species (Anacardiaceae)

Anatomy of the endocarp was studied in relation to the physical dormancy-breaking mechanisms in experimentally treated Rhus aromatica var. aromatica and R. glabra germination units, which include seed plus endocarp (hereafter seeds). The endocarp has three distinct layers, with brachysclereids on the outside, osteosclereids in the middle, and macrosclereids on the inside. Brachysclereids in the carpellary micropyle region (i.e., region immediately adjacent to the integumentary micropyle) are shorter than those in other parts of the endocarp, and the macrosclereids in this region are not elongated. Thus, a weak point is formed in the endocarp. Concentrated sulfuric acid broke seed dormancy in R. aromatica by eroding the brachysclereids and osteosclereids in the carpellary micropyle region, whereas boiling water broke dormancy in seeds of R. glabra by inducing a blister adjacent to the carpellary micropyle.     

Effects of mucilage on seed germination of the desert ephemeral plant Plantago minuta Pall. under osmotic stress and cycles of wet and dry conditions

To test the role of the seed mucilage of Plantago minuta Pall. in regulating germination under osmotic stress and cycles of hydration and dehydration, two experiments were carried out using seeds with intact mucilage and mucilage‐free seeds. In Experiment 1 seeds were immersed in a range of iso‐osmotic polyethylene glycol solutions (?1.15 to 0 MPa) for 14 days; any ungerminated seeds were transferred to deionized water to investigate the recovery germination. In Experiment 2 seeds were immersed in deionized water for 24 h, and were then incubated on filter paper for an additional 13 days to ensure complete desiccation before reimbibition to test the germination recovery percentage. Under mild osmotic stress (?0.73 to 0 MPa), the intact seeds with mucilage were shown to have higher germination rates than the mucilage‐free seeds, indicating that the mucilage led to a “fast sprouting” germination strategy under mild osmotic stress. However, when seeds were exposed to high osmotic stress (?1.15 MPa), the mucilage apparently slowed the germination rate, resulting in a “risk‐balancing” germination strategy. Extreme drought induced by polyethylene glycol solution and the desiccation pretreatment accelerated germination rates compared to non‐pretreated seeds; both germination potential and recovery percentage of the mucilage seeds were significantly higher than that of the mucilage‐free seeds. Our results revealed that the seed mucilage of P. minuta plays a crucial role in regulating seed germination rates and the germination strategies adopted by controlling seed water absorption when the seeds experience different osmotic stresses or alternating wet and dry conditions.     

Seed dormancy of Cardiospermum halicacabum (Sapindaceae) from three precipitation zones in Sri Lanka

• This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species.
• We compared mass, moisture content (MC), dormancy and dormancy‐breaking treatments and imbibition and germination of scarified and non‐scarified seeds of C. halicacabum from a low‐elevation dry zone (DZ), low‐elevation wet zone (WZ1) and mid‐elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water‐impermeable seed coats (physical dormancy, PY) decreases with increased precipitation.
• Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non‐scarified DZ and WZ1 seeds imbibed water, but only a few non‐scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA₃ promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds.
• At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low‐cost method to produce C. halicacabum plants for medicinal and ornamental purposes.

     

Imbibition phases and germination response of Mimosa bimucronata (Fabaceae: Mimosoideae) to water submersion

Mimosa bimucronata is a pioneering tree that occurs predominantly in moist lowlands, floodplains and on margins of rivers and lakes in Latin America. The effect of submergence on seed germination in M. bimucronata was firstly studied. Patterns of water absorption by M. bimucronata seeds were investigated thereafter to assess the imbibition phases of scarified and unscarified seeds. The germination percentage was significantly higher in scarified than in unscarified seeds, and the velocity of seed germination also increased considerably in scarified seeds. Submergence duration did not significantly affect germination percentages of scarified and unscarified seeds. Therefore, seed viability after submersion suggests that M. bimucronata may display hydrochorous dispersal and also that seeds are able to germinate successfully in areas with frequent seasonal flooding. With respect to imbibition phases, phase II was very short or even absent for scarified and unscarified seeds; therefore, a plateau, where water absorption by seeds is established, was not observed. Finally, we verified that the passage from phase I to III was very tenuous and took a long time in seeds without scarification.     

Osmoconditioning prevents the onset of microtubular cytoskeleton and activation of cell cycle and is detrimental for germination of Jatropha curcas L. seeds

• Jatropha curcas is an oilseed crop renowned for its tolerance to a diverse range of environmental stresses. In Brazil, this species is grown in semiarid regions where crop establishment requires a better understanding of the mechanisms underlying appropriate seed, seedling and plant behaviour under water restriction conditions. In this context, the objective of this study was to investigate the physiological and cytological profiles of J. curcas seeds in response to imbibition in water (control) and in polyethylene glycol solution (osmoticum).
• Seed germinability and reactivation of cell cycle events were assessed by means of different germination parameters and immunohistochemical detection of tubulin and microtubules, i.e. tubulin accumulation and microtubular cytoskeleton configurations in water imbibed seeds (control) and in seeds imbibed in the osmoticum.
• Immunohistochemical analysis revealed increasing accumulation of tubulin and appearance of microtubular cytoskeleton in seed embryo radicles imbibed in water from 48 h onwards. Mitotic microtubules were only visible in seeds imbibed in water, after radicle protrusion, as an indication of cell cycle reactivation and cell proliferation, with subsequent root development. Imbibition in osmoticum prevented accumulation of microtubules, i.e. activation of cell cycle, therefore germination could not be resumed.
• Osmoconditioned seeds were able to survive re‐drying and could resume germination after re‐imbibition in water, however, with lower germination performance, possibly due to acquisition of secondary dormancy. This study provides important insights into understanding of the physiological aspects of J. curcas seed germination in response to water restriction conditions.

     

Does seed ingestion by bats enhance germination? A new meta‐analysis 15 years later

相似文献   

Sensitivity of seed germination to water stress in high-altitude populations of a threatened palm species

• Divergence in seed germination patterns among populations of the same species is important for understanding plant responses to environmental gradients and potential plant sensitivity to climate change. In order to test responses to flooding and decreasing water potentials, over 3 years we germinated and grew seeds from three habitats of Euterpe edulis Mart. occurring along an altitudinal gradient.
• Seed germination and root growth were evaluated under different water availability treatments: control, flood, −0.4 MPa, −0.8 MPa, in the years 2012, 2013 and 2014, and in the final year of the experiment (2014) at −1.0 MPa and −1.5 MPa.
• Seeds from the montane habitat did not germinate in the flooding treatment. Seed germination of all three habitats decreased in the −1.5 MPa treatment and the montane habitat had lowest germination in this treatment. Time required for half of the seeds to germinate increased up to −0.8 MPa. Seeds from montane habitats germinated more slowly in all treatments. The only difference in seed germination synchrony was an increase in the submontane population under the flooding treatment. However, synchrony decreased at the lowest water potentials. Roots of the montane population were more vigorous in most treatments, except at −0.8 MPa.
• The unusual ability of these seeds to germinate at low water potentials might be related to early seed germination at the onset of the rainy season, which potentially decreases seed predation pressure. Seeds of the montane population were more sensitive to both types of water stress. A predicted increase in the frequency and intensity of extreme high rainfall or drought events may predispose early stages of this population to adverse factors that might negatively affect population viability with elevational in future climate change scenarios.

     

Germination requirements and seed banks of some nymphaeid macrophytes: Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze

SUMMARY.

• 1 Germination experiments demonstrated that the innate dormancy of the seeds of Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze could be overcome by a cold treatment. Light stimulated the germination of the three species. Hypoxic conditions stimulated the germination of Nymphaea alba and Nuphar lutea seeds but the seeds of Nymphoides peltata did not germinate under these conditions.
• 2 Experimental seed banks of Nymphaea alba, Nuphar lutea and Nymphoides peltata were laid out in three water bodies, varying in pH and alkalinity. Germination patterns indicated that Nymphaea alba and Nuphar lutea produce transient seed banks, but that Nymphoides peliata produces a persistent seed bank. Sampling of natural seed banks and subsequent germination tests were in concordance with the results of the seed bank experiment.
• 3 The experimental above-ground seed banks of Nymphaea alba, Nuphar lutea and Nymphoides peltata showed similar germination patterns in the three selected water bodies, despite the differences in pH and alkalinity between them. However, the distribution of Nymphoides peliata is restricted to well-buffered waters, so that its absence from soft and acid water bodies must be due to post-germination mechanisms and/or processes.
• 4 In aquatic systems where Nymphoides peltata co-exists with the other nymphaeid species studied, it is largely restricted to a bell between the helophytes and the vegetation at deeper sites. The deeper sites were dominated by Nuphar lutea and Nymphaea alba. Germination requirements and seedling emergence from buried seeds of Nymphaea alba, Nuphar lutea and Nymphoides peliata play an important role in the establishment of the zonation pattern of these nymphaeid macrophytes.

     

Enzymatic scarification of Anacamptis morio (Orchidaceae) seed facilitates lignin degradation,water uptake and germination

• The seed coat of many species contains hydrophobic lignins, and in soil the action of microbial ligninases may contribute to release from dormancy. Laboratory use of ligninases to stimulate germination is promising because of the specific action on the seed coat, whereas chemical scarification agents may also corrode the embryo. We hypothesised that exposure of Anacamptis morio (Orchidaceae) seeds to fungal laccase would stimulate germination, and that the mechanism involves lignin degradation and increased imbibition.
• Germination capacity in vitro was quantified with 1 U filter‐sterilised laccase added to agar medium following autoclaving, compared to a 10% bleach solution (standard bleach surface sterilisation/scarification method used in orchid seed sowing). Lignin degradation was quantified using an optical method (phloroglucinol‐HCl staining) combined with image analysis, following experimental pre‐treatments involving immersion in laccase solution, distilled water (negative control) or bleach (positive control). Water uptake after experimental treatments was quantified as the proportion of seeds exhibiting visible uptake of an aqueous fluorochrome under UV excitation.
• Laccase stimulated a doubling of germination in vitro with respect to bleach surface sterilisation/scarification alone, from 23.7 to 49.8% (P = 0.007). Laccase and bleach methods both significantly decreased the optical signal of phloroglucinol (for laccase, to 79.9 ± 1.3% of controls; anova : F = 10.333, P = 0.002). Laccase resulted in a modest but highly significant (P < 0.0001) increase in water uptake with respect to the control (11.7%; cf 99.4% for bleach).
• Laccase scarification can stimulate germination of A. morio through a mechanism of targeted seed coat degradation. The results demonstrate the potential of this relatively non‐invasive enzymatic scarification technique.

     

Echinochloa crus‐galli seed physiological dormancy and germination responses to hypoxic floodwaters

• Hypoxic floodwaters can seriously damage seedlings. Seed dormancy could be an effective trait to avoid lethal underwater germination. This research aimed to discover novel adaptive dormancy responses to hypoxic floodwaters in seeds of Echinochloa crus‐galli, a noxious weed from rice fields and lowland croplands.
• Echinochloa crus‐galli dormant seeds were subjected to a series of sequential treatments. Seeds were: (i) submerged under hypoxic floodwater (simulated with hypoxic flasks) at different temperatures for 15 or 30 days, and germination tested under drained conditions while exposing seeds to dormancy‐breaking signals (alternating temperatures, nitrate (KNO₃), light); or (ii) exposed to dormancy‐breaking signals during hypoxic submergence, and germination monitored during incubation and after transfer to drained conditions.
• Echinochloa crus‐galli seed primary dormancy was attenuated under hypoxic submergence but to a lesser extent than under drained conditions. Hypoxic floodwater did not reinforced dormancy but hindered secondary dormancy induction in warm temperatures. Seeds did not germinate under hypoxic submergence even when subjected to dormancy‐breaking signals; however, these signals broke dormancy in seeds submerged under normoxic water. Seeds submerged in hypoxic water could sense light through phytochrome signals and germinated when normoxic conditions were regained.
• Hypoxic floodwaters interfere with E. crus‐galli seed seasonal dormancy changes. Dormancy‐breaking signals are overridden during hypoxic floods, drastically decreasing underwater germination. In addition, results indicate that a fraction of E. crus‐galli seeds perceive dormancy‐breaking signals under hypoxic water and germinate immediately after aerobic conditions are regained, a hazardous yet less competitive environment for establishment.

     

Evidence for physiological seed dormancy cycling in the woody shrub Asterolasia buxifolia and its ecological significance in fire‐prone systems

• Dormancy cycling is a key mechanism that contributes to the maintenance of long‐term persistent soil seed banks, but has not been recorded in long‐lived woody shrub species from fire‐prone environments. Such species rely on seed banks and dormancy break as important processes for post‐fire recruitment and recovery.
• We used germination experiments with smoke treatments on fresh seeds and those buried for 1 year (retrieved in spring) and 1.5 years (retrieved the following late autumn) to investigate whether Asterolasia buxifolia, a shrub from fire‐prone south‐eastern Australia with physiologically dormant seeds, exhibited dormancy cycling.
• All seeds had an obligation for winter seasonal temperatures and smoke to promote germination, even after ageing in the soil. A high proportion of germination was recorded from fresh seeds. but germination after the first retrieval was significantly lower, despite high seed viability. After the second retrieval, germination returned to the initial level. This indicates a pattern of annual dormancy cycling; one of the few observations, to our knowledge, for a perennial species. Additionally, A. buxifolia’s winter temperature and smoke requirements did not change over time, highlighting the potential for seeds to remain conditionally dormant (i.e. restricted to a narrow range of germination conditions) for long periods.
• For physiologically dormant species, such as A. buxifolia, we conclude that dormancy cycling is an important driver of successful regeneration, allowing seed bank persistence, sometimes for decades, during fire‐free periods unsuitable for successful recruitment, while ensuring that a large proportion of seeds are available for recruitment when a fire occurs.

     

Water Relations of Tomato Seeds During Imbibition and Osmotic Priming

Water uptake of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seeds during germination was obviously triphasic. The completion of the first phase of water uptake by whole seed could not be realized until 10~12 h later after sowing though varies in different parts of seed. The mechanical resistance of endosperm and seed coat restricted water uptake of the embryo envoleped by the endosperm. Water potential of the intact embryo was still 0. 6~0. 9 Mpa lower than the whole seed when the equilibrium between seed and imbibing solution was established. GA and ABA had no direct effects on the water uptake of tomato seeds. The water potential of embryo was positively correlated with its moisture content. The osmotic potential of tomato embryos decreased slowly during imbibition in water and osmotic solution as well.     

Drought tolerance of Periploca sepium during seed germination: antioxidant defense and compatible solutes accumulation

Periploca sepium Bunge is a native and widespread shrub on the Loess Plateau, an arid and semi-arid region in China. To understand the adaptability of its seed germination to dry environments, we investigated the germination rate, water relations, lipid peroxidation, antioxidant capacity and accumulation of major organic solutes during seed germination under water deficit conditions. Results showed that seeds pre-treated by hydration–dehydration or ?0.9 MPa PEG germinated faster than control seeds, indicating strong resistance of P. sepium to drought condition. The re-dried seeds showed higher proline, total free amino acids (TFAA) and soluble proteins (SP) contents than control dry seeds, indicating the maintenance of physiological advancement when dehydrated. Osmotic stress made seed germination stay on the plateau phase (phase II). However, germinating seeds moved into phase III immediately once transferred into distilled water. Large increases in SP and soluble sugars (SS) of both re-dried and osmotic stressed seeds help themselves to resist drought stress. The re-hydrated seeds showed significantly higher levels of proline, TFAA, SP and SS than control seeds. The largely accumulated SS during osmotic stress declined sharply when transferred into distilled water. Our data demonstrate that P. sepium’s tolerance to drought stresses during germination is associated with enhanced activity of antioxidant enzymes and accumulation of some compatible solutes. Seed physiological advancement progressed slowly under low water conditions and it was maintained when seeds were air dried. This strategy ensures high and more rapid seed germination of P. sepium under drying and wetting conditions in drought-prone regions.     

Biotypes of the seed beetle Callosobruchus maculatus have differing effects on the germination and growth of their legume hosts

• 1 Populations of the seed beetle Callosobruchus maculatus (F.) exhibit considerable differences in body size and larval behaviour. We examined whether such variation modifies the relationship between beetle infestation and host plant performance.
• 2 Larvae from African and Asian biotypes were reared in seeds of four hosts that represented an almost four‐fold variation in seed mass. We estimated mass lost to larval consumption, and compared germination rates and seedling growth between infested and control seeds.
• 3 In seeds bearing a single larva, the larger‐bodied, contest‐competing larvae of the Asian biotype caused a 38–47% greater reduction in seed mass compared with the smaller‐bodied, scramble‐competing larvae of the African biotype. The amount of seed mass lost per larva remained similar in seeds with one or two scramble‐competing larvae but decreased significantly in seeds bearing two contest‐competing Asian larvae.
• 4 Differences in larval consumption and behaviour produced striking differences in the frequency of germination. Germination of singly‐infested mung bean (i.e. the smallest host) was 71% for African‐infested seeds versus 11% for Asian‐infested seeds. In cowpea (i.e. the largest host), 76% of Asian‐infested seeds germinated, whereas the germination rate of African‐infested cowpeas (92%) was similar to that of uninfested seeds.
• 5 Effects of beetle origin persisted after germination. Seedlings derived from Asian‐infested seeds had greater cotyledon damage 7 days after germination, and displayed lower height and less biomass 15 days after germination. Cotyledon damage was a good predictor of seedling performance (i.e. better than seed mass consumed) 15 days after germination.
• 6 Previous studies have suggested that population differences in larval size and burrowing behaviour (‘centripetal tendency’) reflect adaptation to different‐sized seeds. The present study demonstrates that these differences in turn influence the impact of larval feeding on host viability. Strong biotypic variation makes it difficult to generalize about pest impacts at the level of pest species.