A probabilistic model for tropical tree seed desiccation tolerance and storage classification

Knowledge of seed desiccation tolerance is fundamental for conservation and use of forest species. The protocol used for classification of seed desiccation tolerance and storage is time consuming and many times limited by the lack of information about optimum conditions for seed germination and treatments to overcome seed dormancy. This study evaluated 66 Brazilian tree species aiming to correlate seed characteristics with desiccation tolerance. For this purpose, a model was established to explain the relationship of tegument/seed mass ratio (SCR), seed mass, and water content of embryo + endosperm with desiccation tolerance. The principal component analysis showed the establishment of two groups, indicating the interaction between desiccation tolerance and seed characteristics. Recalcitrant seeds are more often associated with the water content of embryo + endosperm and water content of tegument + endocarp, while orthodox seeds are more associated with SCR and number of seeds per kilogram. The classification found using the model proposed was significantly correlated with desiccation tolerance and storage, with 92% confidence for the analyzed species. Seeds morphological characteristics can be used for prediction of desiccation tolerance and storage behavior; however, the use of a model that combines more variables increases the chance of accurate classification.     

Germination of Eucalyptus sieberi L. Johnson seeds. II. Internal water relations

At 15-20 degrees C, seeds of Eucalyptus sieberi L. Johnson need to maintain a water content equal to 30% or more of dry weight for approximately 60 h in order to germinate. Several shorter periods of imbibition at 30% water content separated by between 6 and 120 h desiccation were as effective as an unintenupted imbibition in bringing seeds to the point of germination. Even after 8 months' desiccation an earlier imbibition shortened the time required for the completion of germination, although it did not hasten the onset of germination. The water potential of seeds sufficiently hydrated to germinate was about -0.6 MPa, whereas that of the embryo was only about -4.5 MPa. The difference was caused by the inhibition of water uptake by the inner integument of the seed coat. During germination, reserve protein in a small group of cells above the collet was hydrolyzed. Subsequent expansion of these cells caused rupture of the inner integument thereby allowing further water uptake by the embryo. The balance of water absorption and evaporative loss by the outer integument was such that most seeds on a moist substrate but exposed to dry air (6.5-8 x 10(-4) MPa) did not maintain the 30% water content necessary for germination. Thus although able to germinate on seedbeds subject to intermittent drying, E. sieberi seeds have the capacity to avoid germination except under humid conditions.     

Effect of Seed Maturity and Pretreatment on Dormancy and Germination of Sorbus mougeotii Seeds

The effect of harvest time on seed germination, desiccation tolerance and level of dormancy is not known in Sorbus mougeotii (Soyer-Will. & Godron). Dry weight (DW), moisture content (MC) and leakage conductivity (LC) were tested on seeds from six harvest times. Chilling requirement and germinability were tested on seeds without drying and after drying and rehydration. The effect of postharvest ripening of seeds with or without drying was also tested. The DW was stable during the last 6 weeks of maturation, whereas MC initially decreased but later increased simultaneously with an increase in LC. Seeds were desiccation tolerant, deeply dormant and after a chilling treatment germinated to a high percentage at all harvest times. The chilling requirement decreased significantly with later harvest, suggesting a decrease in level of dormancy. Drying and postharvest ripening reduced and synchronized the chilling requirement.     

Effects of desiccation on the physiology and biochemistry of Quercus alba acorns

Seeds that lose viability when dried to a water content of less than 12% are said to be recalcitrant. We subjected acorns of Quercus alba L., a species with recalcitrant seeds, to desiccation to determine the effects of drying on lipids, proteins and carbohydrates of the embryonic axis and cotyledon tissues. Samples of fresh seed and seed dried for selected intervals were analyzed for water content and germination, and for lipids, proteins and carbohydrates by Fourier transform-infrared (FT-IR) spectroscopy. Carbohydrates were further analyzed by gas chromatography (GC). The FT-IR analysis revealed that membrane lipid structure initially exhibited reversible shifts between gel and liquid crystalline phases in response to drying and rehydration; however, reversibility declined as viability was lost. Changes in carbohydrate concentration were observed based on peak height comparisons; sucrose concentration in the embryonic axis increased dramatically after 5 days of drying. The most sensitive indicator of desiccation damage was the irreversible change in protein secondary structure in embryonic axes and cotyledon tissue. These changes were illustrated by shifts in amide absorbance near 1650 cm(-1). Gas chromatography indicated an abundance of sucrose in both the embryonic axes and the cotyledon tissue. Although sucrose concentrations in these tissues were initially similar, sucrose concentration in the embryonic axes became significantly greater than in the cotyledons as the acorns dried. We hypothesize that, in drying acorns, increased concentration of sucrose does not prevent loss of viability, but acts as a glycoprotectant against cell collapse and cell wall membrane damage as water stress increases.     

Effects of presowing treatments, desiccation and storage conditions on germination of Strychnos nux-vomica seeds, a valuable medicinal plant

Seeds of Strychnos nux-vomica have slow and erratic germination; thus different presowing treatments were applied to enhance the germination of its seeds collected from Tamaraikulam, Tamil Nadu, India. In addition, the effects of desiccation and different storage conditions on the germination of S. nux-vomica seeds were investigated. The results show that soaking in 500 ppm gibberellic acid (GA₃) for 24 h, incubation of seeds at 40 °C for 3 days and alternate water soaking (16 h) and drying (8 h) for 14 days significantly increased the percentage germination compared to the control. Desiccation of seeds down to 10% moisture content resulted in better germination. Germination of S. nux-vomica seeds differed significantly between different storage periods, moisture contents of the seed and for first and second order interactions (p<0.001). The highest germination (92%) was achieved when seeds with 10% moisture content were stored at ambient temperature for 30 weeks. Evidence from the present study indicates that S. nux-vomica seeds possess physiological dormancy that can be broken effectively by after-ripening. As seeds of S. nux-vomica are found to be desiccation tolerant, dry seed (10% moisture content) can be hermitically stored at ambient temperature for 30 weeks without losing their viability.     

Morphological and biochemical changes of Aesculus chinensis seeds in the process of maturation

Morphological and biochemical changes of Chinese horse chestnut (Aesculus chinensis Bge.) seeds were studied during the process of maturation. Fruit and seed diameter increased linearly from DPA (Days Post Anthesis) 60 to DPA 150 and were stable thereafter. The weight of fruit and seed increased sigmoidally between DPA 100 and DPA 160. The water contents of whole seeds, axes and cotyledons had a sharp reduction from DPA 110 to DPA 130 but changed little after DPA 130. The water contents of whole seeds, axes and cotyledons were 1.42, 1.93 and 1.30?g?g^?1DW, respectively at the end of maturation. The starch content of cotyledons from mature seeds was high on a dry weight basis (31.4%) while the total soluble sugar content varied between 12 and 20%. In both axes and cotyledons, the total soluble sugar content decreased during the process of maturation, as did all five soluble sugar components measured (glucose, sucrose, trehalose, raffinose and stachyose). Sucrose and stachyose contents remained relatively high at the time of seed maturation, followed by glucose and a trace level of trehalose. The oligosaccharide/disaccharide (O/D) ratio in the axes was 3.1 at DPA 140. The high level of sucrose and stachyose might contribute to the greater desiccation tolerance of Aesculus chinensis seeds relative to typical recalcitrant tropical seeds. High levels of ABA content in seed coats and a low GA₃/ABA ratio in both seed coats and axes might also influence the desiccation tolerance and shallow dormancy of mature Aesculus chinensis seeds.     

Seed storage behavior of <Emphasis Type="Italic">Knema attenuata</Emphasis>, an endemic species of Western Ghats,India

We performed desiccation and storage trials to better under- stand storage behavior of Knema attenuata seeds. Mature seeds with moisture content (MC) of 31% exhibited 73% germination. During the period of desiccation (open lab condition) seeds with MC 23% showed 40% germination. After further drying to MC 21% germination was reduced to 16%. Complete loss in viability resulted when seed moisture was reduced to 18%. The seeds stored at -10°C, 0°C, 10°C and 28±2°C (open lab condition) lost their viability within 10 days. Seeds stored in sealed polythene bags and moist sand retained viability for more days than did seeds stored under all other storage conditions. Sensitivity of seeds to lower temperature and desiccation suggest that the storage be- havior of K. attenuata seeds is recalcitrant. Seeds stored in moist condi- tions can, at best, be stored for a period of two months.     

Induction of tolerance to desiccation and cryopreservation in silver maple (Acer saccharinum) embryonic axes

Twenty percent of of the world's flowering plants produce recalcitrant seeds (i.e., seeds that cannot withstand drying or freezing). We investigated whether the embryonic axis from the normally recalcitrant seeds of silver maple (Acer saccharinum L.) can be made tolerant to desiccation (10% water content) and low temperature (-196 degrees C, cryopreservation) by pretreatment with ABA or the compound tetcyclacis, which enhances endogenous ABA concentrations. Pretreatment of axes with both ABA and tetcyclacis increased germination after desiccation and freezing to 55% from a control value of zero. Pretreatment of axes with ABA and tetcyclacis increased the ABA content of the axes, as measured by enzyme-linked immunoassay, and stimulated the synthesis of storage and dehydrin-like proteins, believed to have a role in the desiccation tolerance of orthodox seeds.     

自然脱水过程中七叶树种子生理特性的变化

于 2003 年研究了自然脱水过程中七叶树种子生理特性的变化。结果表明:七叶树种子对脱水高度敏感,为顽拗性种子。种子成熟采收时含水量高达 60.3%,种子在室温下自然干燥 30 天后,含水量下降到 30.2%,此时种子生活力完全丧失。在脱水初期,种子发芽率有所上升,但随后种子发芽率迅速降低。随着含水量的下降,种子浸出液相对电导率上升,但当含水量在 53.7% 到 50.9%之间时,种子浸出液相对电导率出现异常升高。同时种子超氧化物歧化酶(SOD)的活性随脱水时间的延长而下降,只有种子含水量在 53.7% 到 50.9%之间时出现例外。丙二醛(MDA)含量在脱水初期缓慢上升,在含水量下降到低于 50.9%时,丙二醛(MDA)含量快速上升。可溶性糖含量随脱水时间的延长缓慢上升。当种子含水量为 47%–60%时,种子发芽率较高,说明这一含水量区间有利于种子生活力的保持。图 6 参 13。     

野生欧洲李种子萌发特性

为了掌握野生欧洲李种子萌发特性,探讨野生欧洲李实生繁殖规律,以新疆野生欧洲李为研究对象,观察种子形态,测定种子千粒质量、种皮透水性、种子含水量、种子活力,测定种子浸提液对白菜种子发芽和胚根生长抑制活性的影响。结果表明:新疆野生欧洲李种子的种皮透水性比较差;种子含水量为30.57%;TTC法检测种子活力为81.67%;4℃低温沙藏层积的野生欧洲李种子,在处理后90 d种子出现萌发,持续层积200 d后总萌发率为47%;种子各部分浸提液对白菜种子发芽率作用不明显,但对胚根生长有明显的抑制作用,随着浸提液浓度增长,对白菜种子发芽抑制活性越强,其胚根长度越短;随着野生欧洲李层积天数的增加,浸提液处理的白菜种子胚根长度增加;野生欧洲李种子各部分浸提物对白菜种子发芽抑制活性顺序为:种胚最强,种皮次之,种壳最弱。     

Adaptations to intermittent drying in germinating Eucalyptus sieberi L. Johnson seeds and young seedlings

Before Eucalyptus sieberi L. Johnson seeds germinate, the protein reserves in a small group of cells in the collet are mobilized and the cells swell sufficiently to break the seed coat allowing further water uptake. If the seedling is desiccated at this stage, the embryo remains viable and when the seed is rewetted reserves are mobilized in the cells immediately behind those which expanded initially. Mobilization of reserves and subsequent cell elongation occur sequentially along the hypocotyl after successive dry periods until the reserves are exhausted. Early in the sequence, the distal end of the hypocotyl extends and is positively geotropic, whereas at the end of the sequence the proximal end of the hypocotyl extends and is negatively geotropic, raising the cotyledons rapidly. If the radicle is destroyed or unable to elongate, it is replaced by two adventitious roots, one below the petiole of each cotyledon. Indole acetic acid and sucrose can substitute for the cotyledons in the production of adventitious roots.     

色木槭和拧筋槭种子脱水耐性分析——基于含水量、发芽率和ABA含量变化的结果

通过采集不同发育阶段种子并对其进行自然干燥处理,以含水量、发芽率和ABA含量变化为指标,研究了色木槭和拧筋槭种子在自然发育和干燥过程中的脱水耐性变化.结果表明,色木槭和拧筋槭种子虽经历了成熟脱水,但种子仍不耐脱水;其发芽率和活力指数随发育进程而逐渐增加,但随自然脱水进程而逐渐降低;色木槭和拧筋槭种子最大脱水耐性分别出现在花后100 d和120 d;在整个发育过程中,两树种种子的ABA(脱落酸)含量均较低;拧筋槭种子中ABA含量在脱水过程中呈下降趋势,而色木槭种子中ABA含量在脱水过程中虽有升高但变化不显著.推测ABA含量低可能为色木槭和拧筋槭种子不耐脱水的主要原因之一.     

Seed Development, Maturation and Storage Behaviour of Mimusops elengi L.

Mass maturity (end of the seed-filling phase) occurred at about 72 days after flowering (DAF) in developing seeds of Mimusops elengi, at which time seed moisture content had declined to about 55%. The onset of ability to germinate was detected at 56 DAF and seeds showed 98% germination by 84 DAF. Tolerance of desiccation to 10% moisture content was first detected at 70 DAF and was maximal by 84 DAF. Delaying collection by a further 14 days to 98 DAF, when fruits began to be shed, reduced seed viability, particularly for seeds first dried to 10% moisture content. Hence the best time for seed collection appears to be about 14 days before fruits shed. In a separate investigation with six different seed lots, desiccation below about 8–12% moisture content reduced viability (considerably in some lots). The viability of dry seeds (below about 10% moisture content) stored hermetically was reduced at cool temperatures (5 °C and below), and none survived storage at sub-zero temperatures. The results suggest that Mimusops elengi shows intermediate seed storage behaviour and that the optimal hermetic seed storage environment is about 10% moisture content at 10 °C, while short-term, moist, aerated storage at high (40%) moisture content is also feasible.     

Consequences of dry-season seed dispersal on seedling establishment of dry forest trees: Should we store seeds until the rains?

We examined the following hypotheses: (i) seeds of dry forest trees have high pre- and post-germination mortality by desiccation due to the time between seed dispersal and germination and to irregular rains at the onset of the rainy season; (ii) seedlings from seeds dispersed in the dry season which survive the dry spells are larger at the end of the first rainy season than those dispersed in the rainy season because the former have more time to grow. We evaluated the possible trade-off between few large seedlings (resulting from natural dispersal) × many small seedlings (resulting from delayed dispersal) on seedling survival during the dry season. We sowed eight tree species in a greenhouse in September, simulating the natural dispersal timing (before the rains), and in November, when rains are more constant. Because shading can counteract the effects of desiccation, we applied three levels of shade (10%, 40% and 72% of PPFD). From September 2005 to December 2006, we provided the daily precipitation of a median year from a major patch of dry forest in Central Brazil. At the end of the rainy season, a subset of seedlings was collected for growth measurements (dry mass) and the remainder was left to follow the dry season survivorship. The lower germination expected for seeds dispersed in the dry season and in full sun was not confirmed for species that had some dormancy. The delayed dispersal was advantageous for the initial establishment of fast germinating species, but it was irrelevant or even disadvantageous for others. Also, the greenhouse weather was certainly milder than the natural environment, reducing the potential for mortality by desiccation. The growth of the four species of higher dormancy were not affected by timing of seed dispersal, while three out of four fast germinating species had higher root biomass when dispersed in the dry season. The growth during the rainy season did not affect seedling survival during the dry season. Keeping seeds to sow when rain is constant might be a good strategy to increase the establishment of fast-germinating tree species.     

Desiccation-tolerance ofFagus crenata blume seeds from localities of different snowfall regime in central Japan

In beech (Fagus crenata Blume) forests on the Pacific Ocean side in Central Japan, snowpack depth is little and xeric conditions may prevail in winter, in contrast to heavy snow in beech forests on the Japan Sea side. The effects of such conditions during winter on the viability of beech seeds were studied at a beech forest on the Pacific Ocean side. Thickness and weight ratio of pericarp of beech seeds were significantly greater in populations on the Pacific Ocean side compared to the Japan Sea side, this apparently being related to snowpack depth in winter. During the initial stage of seed drying, the drying rate of seeds from the Fuji population (the Pacific Ocean side) was less than that from the Sumon population (the Japan Sea side), possibly due to the thicker pericarp. Germination percentage of seeds which dried to a water content as low as 7% d.w. did not decrease for either population, indicating desiccation tolerance of beech seeds. In the beech forest (University Forest at Yamanaka) on the Pacific Ocean side, water content of seeds sown below litter from both populations remained sufficient for viability during winter. Germinating seeds from the populations on the Japan Sea side were more desiccation-sensitive in early spring, compared to those from the Fuji population, partially due possibly to differences in pericarp thickness.     

Freezing tolerance of conifer seeds and germinants

Survival after freezing was measured for seeds and germinants of four seedlots each of interior spruce (Picea glauca x engelmannii complex), lodgepole pine (Pinus contorta Dougl. ex Loud.), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata Donn ex D. Donn). Effects of eight seed treatments on post-freezing survival of seeds and germinants were tested: dry, imbibed and stratified seed, and seed placed in a growth chamber for 2, 5, 10, 15, 20 or 30 days in a 16-h photoperiod and a 22/17 degrees C thermoperiod. Survival was related to the water content of seeds and germinants, germination rate and seedlot origin. After freezing for 3 h at -196 degrees C, dry seed of most seedlots of interior spruce, Douglas-fir and western red cedar had 84-96% germination, whereas lodgepole pine seedlots had 53-82% germination. Freezing tolerance declined significantly after imbibition in lodgepole pine, Douglas-fir and interior spruce seed (western red cedar was not tested), and mean LT50 of imbibed seed of these species was -30, -24.5 and -20 degrees C, respectively. Freezing tolerance continued to decline to a minimum LT50 of -4 to -7 degrees C after 10 days in a growth chamber for interior spruce, Douglas-fir and lodgepole pine, or after 15 days for western red cedar. Minimum freezing tolerance was reached at the stage of rapid hypocotyl elongation. In all species, a slight increase in freezing tolerance of germinants was observed once cotyledons emerged from the seed coat. The decrease in freezing tolerance during the transition from dry to germinating seed correlated with increases in seed water content. Changes in freezing tolerance between 10 and 30 days in the growth chamber were not correlated with seedling water content. Within a species, seedlots differed significantly in freezing tolerance after 2 or 5 days in the growth chamber. Because all seedlots of interior spruce and lodgepole pine germinated quickly, there was no correlation between seedlot hardiness and rate of germination. Germination rate and freezing tolerance of Douglas-fir and western red cedar seedlots was negatively correlated. There was a significant correlation between LT50 after 10 days in the growth chamber and minimum spring temperature at the location of seedlot origin for interior spruce and three seedlots of western red cedar, but no relationship was apparent for lodgepole pine and Douglas-fir.     

Effects of tallowtree seed coat on seed germination

We measured physiological parameters including water uptake, in-vitro embryo germination ratio, and seed coat structure observed by scanning electron microscopy (SEM) to explore the influence of seed coat on the germination of seeds of tallow tree (Sapium sebiferum (Linn) Roxb.). Tallow tree seeds had good water permeability. We found that germination of cabbage seeds was inhibited when cabbage seeds were soaked in extracted solutions from tallow tree seed coat. Seed coat structure at the side of the radicle appeared to be a barrier to seed germination. We tested methods to break tallow tree seed dormancy. Dormancy of tallow tree seeds was overcome by soaking the seeds in 500 mg·L-1 or 1000 mg·L-1 GA3, followed by 100 days of cold stratification.     

Desiccation and storage behavior of bay laurel (Laurus nobilis L.) seeds

The effect of seed moisture content (m.c.) and seed storage conditions of bay laurel (Laurus nobilis L.) was investigated in relation to seed viability. In the first experiment, the effect of drying rate on seed moisture and seed germination was investigated. Fresh seeds, with their original moisture content displayed a germination percentage of 55.1%. When the seed moisture content was reduced by 2.0% in an oven, the germination percentage rose to 81.0%. When the seed moisture content was reduced even more by using the same method, the germination percentages decreased dramatically. Reducing the seed moisture content to 28.7 and 23.5% by drying the seeds in alternating room conditions resulted in an increase of seed germinability to 84.3 and 90.9%, respectively. The drying of the seeds for 45, 60 and 75 days reduced their seed germination to 66.8, 49.4 and 48.0%, respectively. Reducing seed moisture content below 15.0% resulted in practically nullifying seed germinability. The fact that bay laurel seeds cannot retain their germinability at lower moisture contents demonstrates that it is a species with recalcitrant seeds. In the second experiment, moist and dry storage conditions were tested under different temperatures and moisture contents. The storage experiment showed that the most effective way of conserving the bay laurel seeds is moist storage at 0 ± 1°C for 4 months without previous drying of the seeds.     

Calophyllum inophyllum: recalcitrant or intermediate seed?

We studied seed storage behaviour of a multipurpose tree Calophyllum inophyllum (Clusiaseae). Seeds were collected at Roslyn bay (23°7′60″ S, 150°43’60″ E) Central Queensland. Seed drying and desiccation tolerance tests were carried out according to International Seed Testing Association (ISTA) rules. We found C. inophyllum seeds to be recalcitrant and vulnerable to chilling injury, hence, unsuited for cold storage. C. inophyllum seeds maintained their viability for an appreciable period (> 8 months) if stored in warmer environments.     

Effects of logging, liana tangles and pasture on seed fate of dry forest tree species in Central Brazil

We assessed seed fate of six tree species in a seasonally deciduous forest of Central Brazil. Seed germination, predation, removal and death caused by pathogens or dessication were followed in an undisturbed forest site, a logged forest site, and an active pasture. In both forest types we sowed seeds under patches of liana tangles (Low Forest habitat) and under patches of mature forest (High Forest habitat). Seeds were monitored weekly for up to 8 months. Overall, small-seeded species (Astronium fraxinifolium and Tabebuia impetiginosa) had high germination, although germination was lower in the pasture due to insect predation. The hard-coated seeds of Erythrina sp. had higher germination rates in the pasture. The large-seeded Cavanillesia arborea and Swartzia multijuga had high seed removal (ca. 90%) in the pasture and under High Forest, but only 23–34% under Low Forest in the logged site. Lower removal of large seeds in Low Forest suggests that this habitat conceals the seeds and constrains the movement of large mammals. Both species were favored in Low Forest, suggesting that caution should be used when managing lianas. When protected from predation, seeds with a soft coat and high water content, such as the seeds of Eugenia dysenterica and S. multijuga, died from desiccation in the pasture. Restoration efforts must take into consideration high mortality caused by desiccation or insect predation in abandoned pastures of dry forests.