Changes In Dry Mass Research Articles

Lipid reserves, fasting capability and the evolution of nestling obesity in procellariiform seabirds

Several alternative explanations have been proposed to account for the evolution of nestling obesity in a variety of avian groups. These predict quite different patterns of fat accumulation, storage and use by chicks of different ages. Yet surprisingly few studies have measured changes in body composition during chick development. We tested the applicability of these hypotheses for fulmars, Fulmarus glacialis , by direct measurement of changes in water, lipid and lean dry mass in growing chicks. Lipid and lean dry mass increased until ca. 70% of the way through chick rearing, but then levelled off. Total body water also increased until the same stage, but gradually declined thereafter, and it was this change rather than fat metabolism that resulted in mass recession. The observed pattern of a continued increase in stored lipid, and most importantly, its maintenance all the way through the mass–recession phase until chicks reach fledging, is incompatible with many of the proposed hypotheses. We suggest that the most likely ultimate explanation for large fat deposits is to fuel chicks during the initial critical period away from the nest site while they learn to forage

A biophysical model of fruit growth: simulation of seasonal and diurnal dynamics of mass

A model of fruit growth was developed, based on a biophysical representation of water and dry material transport, which is coupled with cell wall extension stimulated by turgor pressure. The fluxes of materials connect the growing fruit with the parent plant (by phloem and xylem transport) and with the ambient atmosphere (by respiration and transpiration). The sugars are transported from the phloem to the fruit mesocarp by mass flow, passive diffusion and an active (and/or facilitated) mechanism. The stages after cell division has ceased and when fruit growth is due mainly to cell enlargement were modelled. This enabled us to consider the fruit as a cell community with a constant number of cells and to apply directly the equation describing the effect of hydrostatic pressure on the irreversible cell wall expansion elaborated originally for a single cell. The model was applied to the peach [Prunus persica (L.) Batsch] fruit. Seasonal and diurnal fruit growth, expressed in terms of dry and fresh mass changes, was calculated for conditions of water stress with various crop loads. Simulation of the diurnal patterns of fruit fresh mass variation revealed, in agreement with observations, intensive growth by night and midday fruit shrinkage, which depend on plant water status and on crop load.

Genotypic variation in the regrowth of Lolium perenne following clipping: effects of nutrients and endophytic fungi

1. The objective of this research was to determine the extent to which regrowth rate after clipping and the specific leaf area (SLA) of genotypes of Lolium perenne were influenced by soil nutrients and endophytic fungi. 2. Twelve infected genotypes were cloned into ramets. Half were treated with a systemic fungicide that greatly reduced endophyte levels; half were untreated and retained high endophyte levels. Ramets of each genotype were subjected to low, medium or high levels of nutrients in a glasshouse for 11 weeks. 3. Plants were clipped at soil level at 11 weeks, allowed to regrow for 14 weeks and clipped again. SLA was determined at 11 and 25 weeks. Regrowth rate was calculated based on changes in leaf area and leaf dry mass between 11 and 25 weeks. 4. As a main effect, endophytes had no influence on regrowth rates and mean endophyte levels, as measured by hyphal counts within the leaves of five genotypes at high and low nutrients, were not correlated with regrowth rates. However, after clipping, regrowth responses to soil nutrients and endophytes were genotype‐specific. Some genotypes in the high endophyte group showed an enhancement of regrowth, whilst others showed no response or a depressive effect of endophytes. 5. At the time of leaf clipping, SLA was significantly affected by genotype, nutrients and endophytes. At medium nutrients, the SLA of high endophyte plants was significantly lower than that of low endophyte plants. However, the SLA of the regrowth was affected by nutrients but not endophytes. Mean endophyte levels, as measured by hyphal counts within the leaves of five genotypes at high and low nutrients, were not correlated with SLA at 11 or 25 weeks. 6. For both high and low endophyte plants, regrowth rate was negatively correlated with SLA. 7. Perennial ryegrass possesses genotypic variation in the ability to regrow following defoliation and this ability is conditioned by abiotic (nutrients) and biotic (endophyte) factors.

Vegetative propagation of Cordia alliodora (Ruiz & Pavon) Oken: the effects of IBA concentration, propagation medium and cutting origin

The effects of different concentrations of IBA, rooting media and cutting origins on the rooting of leafy stem cuttings of Cordia alliodora (Ruiz & Pavon) Oken were investigated in three experiments using non-mist propagators. During the rooting period, changes in dry mass, photosynthetic rate, stomatal conductance and relative water content (RWC) of the cuttings were assessed. In Experiment 1, cuttings treated with 1.6% IBA achieved 70% rooting after 9 weeks. Bud growth in cuttings was inhibited by increasing concentrations of IBA, which were associated with higher final rooting percentages. No significant treatment differences in RWC or dry mass were found between IBA concentrations, although the dry mass of cuttings in all treatments tended to increase during the rooting period. In Experiment 2, higher rooting percentages were recorded in gravel (89%) and sand (88%) than in sawdust (76%). Although the water content of sawdust was relatively high, cuttings in this treatment displayed significantly lower stomatal conductances ( g s), which may be attributed to death of stem tissue resulting from anoxia. In Experiment 3, highly significant differences ( P < 0.01) were recorded between node positions with respect to rooting percentage, values ranging from 21.3% for Node 2 to 46.3% for Node 5 (basal). Cuttings actively photosynthesized during the rooting period, with photosynthetic rates ( P n) of 0.68–6.70 μmol CO 2 m −2 s −1 recorded. However, no clear relationship between P n and rooting ability was apparent. Contrary to previous studies with this species, it was concuded that C. alliodora cuttings may be rooted relatively easily using the propagation system described. However, the close relationships recorded between P n, irradiance and leaf-air vapour pressure deficit (VPD) suggest that propagator microclimate should be carefully managed if optimal rooting percentages are to be achieved.

The Importance of Neighbors, Soil pH, Phosphorus, and Nitrogen for the Growth of Two C4Grasses

In the coastal prairies of Texas, C4 grasses dominate. However, reasons for spatial differences in composition of these prairies are uncertain, and the reasons for codominance of Schizachyrium scoparium and Paspalum plicatulum are unexplained. We completed a greenhouse experiment that examined the effects of neighbors, soil pH, added P, and N on the growth of P. plicatulum and S. scoparium, two C4 grasses. Intraspecific competition was essentially equal to interspecific competition, and soil factors seem to control dry mass of these two species. For P. plicatulum, addition of P to native soil increased above- and belowground dry mass 1.8-2.5 times, while P and N together increased dry mass 2.9-6.5 times. The response was pH dependent, with the greatest dry mass at low pH. Root: shoot ratios changed from 0.3 to ca. 1.0 as the pH decreased in native soil regardless of the P level. When N was added, ratios were ca. 0.3 across all pH and P treatments. For S. scoparium in native soil, there was little change in aboveground dry mass when P was added; however, belowground dry mass was augmented 1.5-1.9 times, with the greatest dry mass at pH 7.0. Additions of P and N increased aboveground dry mass 2.2-2.7 times, with the greatest dry mass at pH 7.0. N additions caused reductions of 79%-89% in belowground dry mass compared with that of native soil, at all levels of P and pH. Root: shoot ratios were 5-10 times higher in the native soil compared with N addition treatments and increased to 1.0 as pH decreased. Ratios were about 15% higher with P added to native soil and remained constant at ca. 0.1 in all the N addition treatments. These two C4 grasses seem to be competitively equal. Their growth was not determined by the presence of neighbors but by levels of soil resources and soil pH.

Interaction between Nitrogen Deficit of a Plant and Nitrogen Content in the Old Leaves

We examined changes in nitrogen content of the first leaves in relation to growth and nitrogen status of sunflower (Helianthus annuus L.) plants that were raised hydroponically at two irradiance levels (high and low light, HL and LL) and at two nitrogen concentrations (high and low nitrogen, HN and LN). Initial increases in total dry mass and total nitrogen of the whole plant were faster in HL-plants than in LL-plants irrespective of nitrogen supply, but in LN-plants the increase in total nitrogen was soon blunted. When plants grown under the same irradiance were compared, nitrogen content of the first leaves (leaf N) decreased faster in LN-plants than in HN-plants, while for the plants grown at the same nitrogen concentrations, it decreased faster in HL-plants than in LL-plants. Since these changes in leaf N were not explained solely by the changes in plant dry mass or plant nitrogen, we introduced an index, ‘nitrogen deficit (ND*)’, to quantify nitrogen deficit of the whole plant. ND* was expressed as ND*(t)=[Nmax–N(t)]×DM(t), where Nmax and N(t) were nitrogen contents in the young, expanding leaves that had just unfolded to expand, at the initial stage with sufficient nitrogen and at time t, respectively, and DM(t), plant dry mass at t. The decrease in leaf N was expressed as a liner function of ND* irrespective of the growth conditions, which indicates validity of this index. Limitation of the use of ND*, and mechanisms by which leaves sense nitrogen demand are also discussed.

Ecological Energetics of the Desert Tortoise (Gopherus Agassizii): Effects of Rainfall and Drought

To elucidate ecological effects of variation in the temporal distribution of a limiting resource (water in the Mojave Desert), energetics of two free—living populations of desert tortoises (Gopherus [Xerobates] agassizii) were studied concurrently over 18 mo with use of doubly—labeled water. Field metabolic rates (FMR) and feeding rates (estimated from rates of water influx and rates of change in dry mass) were highly variable. This variability was manifested at several levels, including seasonal changes within populations, year—to—year differences within populations, and differences between populations. Underlying observed patterns and contrasts was considerable variation among individuals. Much of the variation in energetic variables was associated with a single climatic variable, rainfall. Seasonal, annual, and interpopulation differences in FMR and foraging rates corresponded to differences in availability of free—standing water from rainstorms. At least some of the differences among individuals were apparently due to differences in proclivity or ability to drink. Tortoises had very low FMRs relative to other reptiles, which allowed them to tolerate long periods of chronic energy shortage during a drought. Calculations suggested that tortoises experienced a net loss of energy on their spring diet of succulent annual plants. If so, tortoises require drier forage to accrue an energy profit, which emphasizes their reliance on drinking rainwater (which can be stored in the bladder and resorbed later to hydrate dry forage). Further, it suggests that growth (as protein deposition) and net acquisition of energy may be temporally decoupled in desert tortoises, which has potential consequences for geographic variation in life history traits. Energy acquisition and expenditure in desert tortoises are thus strongly constrained by the contingencies of rainfall, both indirectly through effects on availability and quality of food, and directly through reliance on free—standing water for drinking, which is apparently necessary for achieving a net annual energy profit.

Lichen Pendants for Transplant and Growth Experiments

Lichens were cultured by attaching a thallus fragment to a nylon monofilament loop with silicone sealer. Two effective methods for adjusting lichen mass to a standard moisture content were developed (the ‘reference-sample’ and ‘sacrificial’ methods). These corrections for moisture content allow detection of very small changes in dry mass without having to oven dry (and kill) all transplants. Average annual biomass growth rates for non-fragmenting species were typically between 5 and 30%. Annual biomass growth rates of healthy, vigorous individuals, as indicated by the 75th percentile, were mostly between 10 and 40%. Alectoria sarmentosa was prone to fragmentation despite the maintenance of healthy thalli. The other species can be ranked by biomass growth rates as follows: Evernia prunastri&gt; Lobaria pulmonaria=Usnea longissima&gt; Pseudocyphellaria rainierensis=Lobaria oregano.

LICHEN PENDANTS FOR TRANSPLANT AND GROWTH EXPERIMENTS

Lichens were cultured by attaching a thallus fragment to a nylon monofilament loop with silicone sealer. Two effective methods for adjusting lichen mass to a standard moisture content were developed (the ‘reference-sample’ and ‘sacrificial’ methods). These corrections for moisture content allow detection of very small changes in dry mass without having to oven dry (and kill) all transplants. Average annual biomass growth rates for non-fragmenting species were typically between 5 and 30%. Annual biomass growth rates of healthy, vigorous individuals, as indicated by the 75th percentile, were mostly between 10 and 40%. Alectoria sarmentosawas prone to fragmentation despite the maintenance of healthy thalli. The other species can be ranked by biomass growth rates as follows: Evernia prunastri> Lobaria pulmonaria= Usnea longissima> Pseudocyphellaria rainierensis= Lobaria oregana. 1996 The British Lichen Society

Changes in Soluble Sugars and Proteins during Development of Rye Coleoptiles

Summary An analysis was made of the changes in dry mass, soluble sugars and protein complement in coleoptiles of rye seedlings ( Secale cereale L.) that were either grown in darkness or irradiated with white light. Dry mass and the concentration of soluble sugars (glucose, fructose) increased during growth of the juvenile organ. After emergence of the primary leaf (cessation of coleoptile elongation) dry mass and sugar content decreased. Cytoplasmic proteins have been extracted from growing and non-growing (mature) coleoptiles and separated by gel electrophoresis. Examination of the silver stained profiles of polypeptides revealed only minor chnages, i.e. no loss of protein was detected. Because protein breakdown is a main characteristic of senescence, we conclude that the pierced coleoptile is a mature, metabolically active organ that provides carbohydrates for the growing parts of the developing seedling.

Microbial Decomposition of Elm and Oak Leaves in a Karst Aquifer

Dry Chinquapin oak (Quercus macrocarpa) and American elm (Ulmus americana) leaves were placed in four microcosms fed by groundwater springs to monitor changes in dry mass, ash-free dry mass, and microbial activity over a 35-day period. Oxygen microelectrodes were used to measure microbial activity and to estimate millimeter-scale heterogeneity in that activity. Oak leaves lost mass more slowly than elm leaves. Generally, there was a decrease in total dry weight over the first 14 days, after which total dry weight began to increase. However, there were consistent decreases in ash-free dry mass over the entire incubation period, suggesting that the material remaining after initial leaf decomposition trapped inorganic particles. Microbial activity was higher on elm leaves than on oak leaves, with peak activity occurring at 6 and 27 days, respectively. The level of oxygen saturation on the bottom surface of an elm leaf ranged between 0 and 75% within a 30-mm area. This spatial heterogeneity in O(2) saturation disappeared when the water velocity increased from 0 to 6 cm s. Our results suggest that as leaves enter the groundwater, they decompose and provide substrate for microorganisms. The rate of decomposition depends on leaf type, small-scale variations in microbial activity, water velocity, and the length of submersion time. During the initial stages of decomposition, anoxic microzones are formed that could potentially be important to the biogeochemistry of the otherwise oxic aquifer.

Effects of Simulated Herbivory and Intraspecific Competition on the Compensatory Ability of Birches

To improve our knowledge regarding plant responses to herbivory we subjected juvenile birches (Betula pubescens) to different types of simulated herbivory, i.e., removal of the top (1 cm) of the main stem or defoliaiton (including removal of main stem top), and to different levels of intraspecific competition (i.e., three stand densities). Treatments were also repeated during the following year. Birch responses to these treatments were measured as changes in plant height and dry mass. Defoliated plants showed reduced growth irrespective of the level of intraspecific competition. Topped plants in the low—density plots showed enhanced growth, i.e., over—compensation, whereas topped plants growth in the high— and medium—density plots were unaffected by the treatments. Our results indicate that we should expect a continuum of plant responses to herbivory. Thus, there is little value in asking whether herbivory has a positive or negative effect on plant growth. Instead, emphasis should be placed on identifying conditions under which we would expect different responses. Further, we suggest that overcompensation should not generally be considered as an adaptive response that has evolved as a consequence of natural selection due to herbivory, but rather as an indirect consequence of selection for competitive ability. Because apical dominance (assumed to be an adaptation to competition) restricts growth, the growth rate will increase if apical dominance is removed.

Lipid accumulation by migrating monarch butterflies (Danaus plexippus L.)

The migration of Danaus plexippus during the late summer in southern Ontario in 1986 lasted for about 8 weeks and consisted of three phases, an early phase characterized by increasing abundance, a middle phase of peak abundance, and a late phase characterized by declining abundance. As the season progressed, systematic changes were observed in wet mass, dry mass, lean dry mass, lipid mass, and forewing length. Wet mass, lean dry mass, and forewing length were similar for early- and middle-phase individuals, but declined in late-phase migrants. Lipid mass peaked in the middle phase of the migration and then declined abruptly in the late phase. Dry mass also peaked in the middle phase, reflecting changes in lipid mass and lean dry mass. We hypothesize that the observed changes in lipid mass and lean dry mass over the 8 weeks resulted from changes in population structure as well as seasonal changes in the weather, and in availability of nectar. Opposing conclusions reached in previous studies of lipid accumulation in D. plexippus are probably the result of failure to control for phase of migration.

Electron probe X‐ray microanalysis of intracellular element concentrations in cryosections in the presence of changes in cell volume

The interpretation of element concentration data for X-ray microanalyses of biological tissues, which are subjected to some experimental treatment, can be complicated by changes in cell volume and total cell dry matter induced by the treatment. We have examined the manner in which such changes would affect the values measured in frozen-dried cryosections of soft tissues, and how they may be taken into account in the interpretation of the results. The element content (mass per unit dry weight) measured by the peak-to-continuum or Hall method is independent of changes in cell volume, but is sensitive to a change in the local dry mass. Conversely, intracellular concentrations in terms of mass per unit volume, as determined by the peripheral or internal standard technique, are dependent on volume changes but independent of dry mass. The estimated dry weight fraction is affected by changes in both volume and dry mass. The results obtained from both quantification methods can therefore provide information on the combination of changes in cellular element levels, volume and total dry mass that may occur following the experimental treatment. In a study of the late effect of the drug cisplatin on electrolyte concentrations in kidney proximal tubules, both quantification methods have been used to obtain wet weight and dry weight concentrations. By applying the above considerations, the analytical results have been interpreted as a combination of changes in element levels and a shrinkage of the tubule cells. Cell shrinkage was confirmed by morphometric analysis of tubular cross-sections.

Changes in Cellular Dry Mass during Macrophage Development

Measurements of dry mass were made on developing human macrophages in suspension culture using a scanning and integrating microinterferometer. The mean dry mass (+/- SEM) of day 0 monocytes of 19 healthy individuals was 53.6 +/- 2.4 pg. There was a significant increase in cellular dry mass over the period of culture, mean values at 2, 4 and 6 days being 61.1, 79.8 and 110.4 pg, respectively. A comparison of the results with those obtained previously by ultrastructural morphometry inferred that there is a disproportionate increase in the water content of macrophages during development. The technique may have potential for investigating changes in mononuclear phagocytes in clinical states.

Plasma ion balance of North American freshwater turtles during prolonged submergence in normoxic water

1. 1. Plasma ion (Na +, K +, Cl −, HCO − 3, lactate, Ca, and Mg) concentrations were measured during apneic submergence in aerated water at 10°C of 4 species of freshwater turtles: Chelydra serpentina serpentina (Chelydridae), Chrysemys picta bellii (Emydidae), Sternotherus odoratus (Kinosternidae), and Trionyx spiniferus asperus (Trionychidae). Measurements were made at intervals up to 21, 13, 100, and 100 days, respectively. In addition, final wet and dry masses were measured in Sternotherus and Trionyx and compared to control values to assess changes in body water and dry mass. 2. 2. In Chelydra and Chrysemys, which have a relatively poor aquatic O 2 uptake capacity, plasma ions changed as previously reported in animals submerged in anoxic water; [Na +] was unchanged, [K +], [Ca], and [Mg] were evaluated, and [Cl −1] and [HCO − 3] were depressed. This overall pattern is probably a regulated response and respresents a compensation for the severe acidosis exhibited by these animals. 3. 3. In Sternotherus and Trionyx, which have effective aquatic respiration and could remain submerged much longer, plasma ion concentrations, except [K +] and [lactate], fell due (largely in Sternolherus, less so in Trionyx to dilution by water uptake. Both species were slightly alkalotic after prolonged normoxic submergence, and we suggest that changes in ion concentrations can be considered as compensatory to this alkalosis. 4. 4. We conclude that these turtles fall into two distinct physiologic response types. In Chelydra and Chrysemys, normoxic submergence at 10°C is limited principally by acidosis, and observed plasma ionic changes act to counteract this effect; in Sternotherus, and to a much lesser degree, Trionyx, the limitation is largely osmoregulatory, due to a failure to exclude ambient water and to maintain ionic homeostatasis.

Electron probe X-ray microanalysis of Pseudomonas syringae pv. tabaci isolated from inoculated tobacco leaves

Cells of Pseudomonas syringae pv. tabaci were infiltrated into leaves of tobacco, recovered from leaf macerates at various time intervals during the development of wildfire disease, then investigated by electron probe X-ray microanalysis to determine changes in elemental composition and dry mass. Analysis of individual cells in air-dried preparations revealed the presence of the major elements P, S, K and Ca, as well as Fe and occasional peaks of Cl and Zn. Detectable levels of Cu and Ni were also demonstrated in chemically-processed cells. Elemental mass fractions in air-dried preparations varied considerably between cells within a particular sample and appeared to involve cation associations with both phosphate groups (e.g., in nucleic acids) and sulphur-containing proteins. Comparison of mean mass fractions in different samples suggested that although some elemental changes occurred during the infection sequence (in relation to the phases of bacterial multiplication and final senescence) the elemental composition of the phytopathogen remained relatively stable throughout the development of the disease in the region of inoculation. The relative dry mass of bacterial cells, determined from the X-ray continuum, showed a significant decrease during the period of multiplication (from 6 to 48 h).

On-line monitoring of cell growth in plant tissue cultures by conductometry

Use of conductivity change in the medium for the on-line monitoring of cell mass growth was investigated in cultures of Coffea arabica, Nicotiana tabacum, Withania somnifera, and Catharanthus roseus. It was found that the effect of pH (4.5–7.0) and sugar concentration (0–1%) changes on medium conductivity can be neglected. Linear relationships between the dry cell mass and conductivity change were observed for all the four cell lines: ΔX = k ( Δκ), where the coefficient k = 3.6, 2.8, 3.2, and 4.1 g · cm · l −1 · ms −1 for C. arabica, N. tabacum, W. somnifera, and C. roseus, respectively. By this method it was possible to estimate the cell mass concentrations in situ during the growth phase for various plant cell cultures.

Quantitative Translocation of Photoassimilates from Nonsurviving Tillers in Barley

Many tillers produced in barley (Hordeum vulgure L.) crop communities senesce without bearing grain. To better understand the physiological and agronomic implications of this tiller mortality, partitioning of photoassimilate by nonsurviving tillers was monitored for field‐grown plants at St. Paul, MN on a Waukegan silt loam soil (fine‐silty over sandy or sandy‐skeletal, mixed Typic Hapludoll). Primary tillers formed in the axils of the first and second main shoot leaves (designated T1 and T2, respectively) were labeled with 14C02 on four occasions and the labeled plants sampled at 7‐ to 10‐day intervals. Some labeled tillers were immediately girdled using steam to restrict photoassimilate export and permit estimation of radioactivity losses due to tiller respiration. Knowing the respiratory losses as well as the quantity of radioactivity remaining in a labeled tiller following a given translocation period, the proportional 14C export from the tiller was calculated. These estimates were coupled with changes in tiller dry mass to calculate the photoassimilate dry matter transferred from a tiller between labeling dates, which were summed to give the cumulative dry matter translocated during the entire period of labeling. Nonsurviving T1 tillers translocated 45% of their photoassimilate to other plant parts, which equated to approximately 150 mg of dry matter. These tillers retained 17% and respired 38% of their fixed radioactivity. Nonsurviving T2 tillers exported 57% (approximately 40 mg), retained 20%, and respired 23%. Most photoassimilate exported from nonsurviving tillers was recovered in the main shoot stem, with lesser amounts in the main shoot spike and leaves. Nonsurviving primary tillers may contribute substantial amounts of dry matter for growth of other plant parts, particularly the main shoot. Thus, initiation of such tillers may not be inherently wasteful of plant photoassimilates.

Accumulation of Storage Materials, Precocious Germination and Development of Desiccation Tolerance During Seed Maturation in Mustard (Sinapis alba L.)

AbstractUnder defined environmental conditions (20°C, continuous light of 15 klx) development of mustard seeds from artificial pollination to maturity takes about 60 d. After surpassing the period of embryo cell division and histodifferentiation (12–14d after pollination = dap), the seed enters into a maturation period. The time courses of various physiological, biochemical, and structural changes of embryo and testa during seed maturation were analyzed in detail (dry and fresh mass changes, osmotic and water potential changes, respiration, DNA amplification by endomitosis, total ribosome and polysome formation, storage protein synthesis and accumulation, storage lipid accumulation). In addition to the final storage products protein and lipid, embryo and testa accumulate transiently large amounts of starch within the chloroplasts during early maturation. Concomitantly with the subsequent total breakdown of the starch, the plastids lose most of their internal structure and chlorophyll and shrink into proplastids, typical for the mature seed. At about 30 dap the seeds shift from a desiccation‐sensitive to a desiccation‐tolerant state and are able then to germinate rapidly upon drying and reimbibition. If isolated from the immature fruit and sown directly on water, the seeds demonstrate precocious germination from about 13 dap onwards. Young seeds (isolated ≦ 38 dap) germinate only after surpassing a lag‐phase of several days (after‐ripening) during which the embryo continues to accumulate storage protein and lipid at the expense of the surrounding seed tissues. We conclude from these results that the maturing seed represents a rather closed developmental system which is able to continue its development up to successful germination without any specific regulatory influence from the mother plant. Immature seeds are able to germinate without a preceding dehydration treatment, which means that partial or full desiccation does not serve as an environmental signal for reprogramming seed development from maturation to germination. Instead, it is argued that the water relations of the seed are a critical element in the control of maturation and germination: during maturation on the mother plant the embryo is subject to a considerable turgor pressure (of the order of 12 bar) accompanied by a low water potential (of the order of −12 bar). This turgor permits maturation growth but is subcritical for germination growth. However, upon imbibition in water, the low water potential provides a driving force for a burst of water uptake overcoming the critical turgor threshold and thereby inducing germination.