Germination behaviour of Conyza bonariensis to constant and alternating temperatures across different populations

Conyza bonariensis is one of the most problematic weed species throughout the world. It is considered highly noxious due to its interference with human activities, and especially the competition it poses with economically important crops. This research investigated the temperature requirements for seed germination of four populations of C. bonariensis with distinct origin and the influence of daily alternating temperatures. For this, a set of germination tests were performed in growth chambers to explore the effect of constant and alternating temperatures. Seeds of the four populations (from Lleida, Badajoz and Seville, Spain and Bahía Blanca, Argentina) were maintained at constant temperatures ranging from 5 to 35°C. The final germination and cardinal temperatures (base, optimum and maximum) of each population were obtained. We also tested the influence of daily alternating temperatures on final germination. To do so, seeds were exposed to two temperature regimes: 5/15, 10/20, 15/25, 20/30 and 25/35°C night/day temperature (intervals increasing 5°C, with constant oscillation of 10°C) and to 18/22, 16/24, 14/26, 12/28 and 10/30°C night/day temperature (intervals with average of 20°C, but increasing the oscillation in 4°C between intervals). In general, all populations behaved similarly, with the highest germination percentages occurring in the optimum temperature range (between 21.7°C and 22.3°C) for both constant and alternating temperatures. In general, climatic origin affected germination response, where seeds obtained from the coldest origin exhibited the highest germination percentage at the lowest temperature assayed. In addition, we observed that the alternating temperatures can positively affect total germination, especially in oscillations that were further from the average optimum temperature (20°C), with high germination percentage for the oscillations of 15/25, 20/30, 18/22, 16/24, 14/26, 12/28 and 10/30°C in all populations. The cardinal temperatures obtained were significantly different across the populations. These results provide information that will facilitate a better understanding of the behaviour of Conyza and improve current field emergence models.     

Low night temperatures have a differential effect on the diurnal cycling of gene expression in cold–sensitive and tolerant tomatoes*

Abstract. Comparisons were made between the changes in mRNA levels induced by low night temperatures in the cold–sensitive tomato and two altitudinal ecotypes of the wild species L. hirsutum. Changes in mRNA levels were detected by resolving in vitro translation products of poly(A)⁺ RNA by 2-D PAGE. The treatment was applied by first growing plants in a thermoperiod of 25/18°C and then switching to 25/6°C. All tomatoes displayed a diurnal cycling in which a set of mRNAs accumulated at the end of the 18°C nights, whereas another accumulated at the end of the 25°C days. The accumulation of night specific mRNAs was inhibited by 6°C nights in the cold sensitive tomatoes while that of the tolerant one was only marginally affected. All tomatoes showed a similar reduction in the apparent turnover rate of the day specific mRNAs during the 6°C nights. Finally, low night temperatures induced the accumulation of six to eight mRNAs in all genotypes. This number increased by 15 in L. esculentum after the seventh night and are likely involved in stress response rather than acclimation/tolerance. The tomato is proposed as a genetic model to discriminate genes involved in acclimation/tolerance from those involved in stress response.     

Viability and virulence of blastospores of Metarhizium anisopliae (Metch.) Sorokin after storage in various liquids at different temperatures

Blastospores of three strains of Metarhizium anisopliae were stored in 18 liquids at 4°C, 20°C and 35°C for 18 weeks, 12 weeks or 9 days respectively. Viability was quantified by determination of their germination. In bioassays the virulence of stored blastospores was studied using adults and third instars of Locusta migratoria migratorioides (R. & F.) and compared to those of freshly produced blastospores and conidia. Generally, there was great variability in the viability of blastospores, depending on the fungal strain and the liquids used. Blastospores survived best at 4°C in 10% hydroxyethyl starch; for example, germination of M. anisopliae strain 97 still amounted to more than 80% after storage for 18 weeks. Other suitable liquids were deionized water, 25% Ringer's solution and 1% sodium alginate. The viability of blastospores stored at 20°C was considerably shorter than at 4°C. During storage for 12 weeks at 20°C the best protective liquids for M. anisopliae strain 97 were 25% Ringer's solution (43% germination), deionized water (23%) and 10% hydroxyethyl starch (23%). At 35°C, 45% of M. anisopliae strain 97 blastospores still germinated after storage for 7 days in 25% glycerol. The bioassays revealed that the virulence of blastospores after storage was comparable to that of fresh ones and even better than that of fresh conidia. In general, the LT₅₀ was about 4–6 days at an alternating day/night temperature of 28/20°C.     

High Temperatures and Net CO2 Uptake, Growth, and Stem Damage for the Hemiepiphytic Cactus Hylocereus undatus1

Hylocereus undatus, which is native to tropical forests experiencing moderate temperatures, would not be expected to tolerate the extremely high temperatures that can be tolerated by cacti native to deserts. Nevertheless, total daily net CO₂ uptake by this hemiepiphytic cactus, which is widely cultivated for its fruits, was optimal at day/night air temperatures of 30/20°C, temperatures that are higher than those optimal for daily net CO₂ uptake by cacti native to arid and semiarid areas. Exposure to 35/25°C for 30 weeks led to lower net CO₂ uptake than at 10 weeks; exposure to 40/30°C led to considerable necrosis visible on the stems at 6 weeks and nearly complete browning of the stems by 19 weeks. Dry mass gain over 31 weeks was greatest for plants at 30/20°C, with root growth being especially noteworthy and root dry mass gain representing an increasing percentage of plant dry mass gain as day/night air temperatures were increased. Viability of chlorenchyma cells, assayed by the uptake of the vital stain neutral red into the central vacuoles, was decreased 50 percent by a one‐hour treatment at 55°C compared with an average of 64°C for 18 species of cacti native to deserts. The lower high‐temperature tolerance for H. undatus reflected its low high‐temperature acclimation of only 1.4°C as growth temperatures were raised by 10°C compared with an average acclimation of 5.3°C for the other 18 species of cacti. Thus, this tropical hemiepiphytic cactus is not adapted to day/night air temperatures above ca 40/30°C, although its net CO₂ uptake is optimal at the relatively high day/night air temperatures of 30/20°C.     

Reproduction and population parameters of the Nearctic predator Geocoris punctipes at constant and varying temperature regimes

The heteropteran predator Geocoris punctipes (Say) has been used in augmentative biological control since 2000 to control Lepidoptera. However, surprisingly, few data are available about the influence of temperature on its population development, which is of key importance to plan the number and moment of releases to obtain sufficient pest reduction. The objective of this study was to evaluate daily and total fecundity, longevity and life table parameters (m_x, l_x, r_m, R, λ, T and TD) of G. punctipes at constant (16.8°C, 21.5°C, 24.5°C and 28.3°C) and corresponding varying (day/night) (21/11°C, 24/18°C, 27/21°C and 30/26°C) temperatures. Pairs of adult predators aged 24 h and originating from nymphs exposed to the same temperature regimes were kept at the above‐mentioned temperature regimes in Petri dishes containing Anagasta kuehniella (Zeller) eggs and an oviposition substrate. Tests were conducted in climatic chambers at the different temperature regimes and a RH 70 ± 10% and a 14L: 10D photoperiod. Reproduction, longevity and life table parameters were significantly affected by temperature, with clear differences between treatments at low (16.8°C, 21/11°C, 21.5°C, 24/18°C) or a high (24.5°C, 27/21°C, 28.3°C, 30/26°C) temperature regimes. Highest reproduction and fastest population growth of G. punctipes took place at average temperatures ranging from 24.5°C to 30°C, and neither reproduction nor population growth was negatively influenced by varying temperatures at any of the temperature regimes.     

Response of in vitro pollen germination and pollen tube growth of groundnut (Arachis hypogaea L.) genotypes to temperature

Air temperatures of greater than 35 °C are frequently encountered in groundnut‐growing regions, especially in the semi‐arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly‐tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures (T_min, T_opt and T_max) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55‐437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and T_max for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The T_min and T_opt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance‐based on pollen response were poorly related (R² = 0·334, P = 0·006) to relative injury as determined by membrane thermostability.     

Effects of low temperature on growth and non-structural carbohydrates of the imperial bromeliad <Emphasis Type="Italic">Alcantarea imperialis</Emphasis> cultured in vitro

The imperial bromeliad Alcantarea imperialis grows naturally on rocky outcrops (‘inselbergs’) in regions where daily temperatures vary from 5 to 40°C. As carbohydrate metabolism is altered in response to cold, it could lead to reprogramming of the metabolic machinery including the increase in levels of metabolites that function as osmolytes, compatible solutes, or energy sources in order to maintain plant homeostasis. The aim of this study was to evaluate the effects of different temperatures on plant growth and non-structural carbohydrates in plants of A. imperialis adapted to low temperature. Seedlings of A. imperialis were grown in vitro under a 12-h photoperiod with four different day/night temperature cycles: 5/5°C, 15/15°C, 15/30°C (dark/light) and 30/30°C. Plants were also cultivated at 26°C in ex vitro conditions for comparison. The results showed an inverse relationship between temperature and germination time and no differences in the percentage of germination. Plants maintained for 9 months at 15°C presented a reduced number of leaves and roots, and a dry mass four times lower than plants grown at 30°C. Sugar content was higher in plants grown at 15°C than at 30°C. However, the highest amount of total sugar was found in plants growing under warm day/cold night conditions. Myo-inositol, glucose, fructose and sucrose were found predominantly under high temperatures, while under low temperatures, sucrose was apparently replaced by trehalose, raffinose and stachyose. Starch content was highest in plants grown under high temperatures. The lowest starch content was detected under low temperatures, suggesting its conversion into soluble carbohydrates to protect the plants against cold. These results indicated that low temperature retarded growth of A. imperialis and increased sugar levels, mainly trehalose, thus suggesting that these sugar compounds could be involved in cold tolerance.     

Embryo rescue inVicia faba andVicia narbonensis

Embryo rescue in twoVicia faba L. cultivars (‘Polycarpe’ and ‘A-107’) and oneV. narbonensis L. population (A-202) was studied under a 22 ± 2°C/ 16 ± 1° day/night temperature regime. Very young ovules (1.0–1.8 mm long) cultured, in-ovule, on five liquid media remained green for a longer period of time on modified B5, modified Murashige and Skoog and modified Beasley and Ting media than on modified Phillips and Collins and modified Bourgin and Nitsch media. However, no embryo growth or embryo germination was observed. In-ovule culture of older ovules, 6 and 8 days forV. narbonensis and 10 and 14 days forV. faba, on modified B5 liquid medium allowed 6-day-oldV. narbonensis and 14-day-oldV. faba embryos to be rescued. Finally, culture of whole pods of the two species resulted in the rescue of even younger embryos. Thus, plantlets were obtained from as young as 4-day-oldV. narbonensis pods and 11-day-oldV. faba pods.     

Effect of Temperatures on Dormancy and Germination in Three Species in the Lamiaceae Occurring in Northern Wetlands

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9 °C in Mentha and 12 °C in Lycopus and Stachys, and a maximum temperature of 33 °C for Lycopus and 36 °C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8 °C in Mentha, 10 °C in Stachys and 14 °C in Lycopus (mean temperature 22 °C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3 °C and 18 °C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures (≤12 °C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12 °C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12 °C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8 °C) were effective. At high test temperatures (25 °C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.     

Effect of environmental factors on seed germination and emergence of Lepidium vesicarium

Lepidium vesicarium is a weed species with a wide distribution in the rangelands and dry‐land farming in East Azarbaijan, Iran. The experiments were undertaken to assay the effects of light, temperature, pH, osmotic potential, NaCl concentration and burial depth on seed germination and emergence of L. vesicarium. Germination was maintained at high levels (> 80%) over a wide day/night temperature range (10/5 to 30/20°C), but a severe reduction in the germination rate of L. vesicarium was found below 20/10°C. Germination of L. vesicarium was influenced by different light/dark regimes, as the germination rate was highest at 16 h light for the all treatments (0, 8, 12, 16 and 24 h light). Germination was 92–95% over a wide range of pH (2‐10). Germination was >50% at a water potential of ?0.7 MPa and salinity of 21 dS/m, indicating that drought and salt conditions have a minimal impact on seed germination. With increasing burial depth from 0 to 2 cm, the number of days required for 50% emergence increased and no germination was observed at burial depths deeper than 3 cm. This suggests that L. vesicarium would become troublesome in the rangelands and for growers in reduced‐tillage cropping systems. The ability to emerge from shallow depths, coupled with tolerance of a wide pH range, drought and salinity at germination, should be taken into account when managing this weed species.     

Expression of a gene encoding β‐ureidopropionase is critical for pollen germination in tomatoes

Global warming has seriously decreased world crop yield. High temperatures affect development, growth and, particularly, reproductive tissues in plants. A gene encoding β‐ureidopropionase (SlUPB1, EC 3.5.1.6) was isolated from the stamens of a heat‐tolerant tomato (CL5915) using suppression subtractive hybridization. SlUPB1 catalyzes the production of β‐alanine, the only β‐form amino acid in nature. In the anthesis stage, SlUPB1 expression in CL5915 stamens, growing at 35/30°C (day/night), was 2.16 and 2.93 times greater than that in a heat‐sensitive tomato (L4783) cultivated at 30/25°C or 25/20°C, respectively. Transgenic tomatoes, upregulating SlUPB1 in L4783 and downregulating SlUPB1 in CL5915, were constructed, and the amount of β‐alanine measured by liquid chromatography‐electrospray ionization‐mass spectrometry in the transgenic overexpression of SlUPB1 was higher than that of L4783. However, the β‐alanine in the transgenics downregulating SlUPB1 was significantly lower than the β‐alanine of CL5915. Pollen germination rates of these transgenics were analyzed under different developmental and germinating temperatures. The results indicated that germination rates of transgenics overexpressing SlUPB1 were higher than germination rates of the background tomato L4783. Germination rates of transgenics downregulating SlUPB1 were significantly lower than germination rates of background tomato CL5915, indicating the necessity of functional SlUPB1 for pollen germination. Pollen germinating in the buffer with the addition of β‐alanine further indicated that β‐alanine effectively enhanced pollen germination in tomatoes with low SlUPB1 expression. Together, these results showed that the expression of SlUPB1 is important for pollen germination, and β‐alanine may play a role in pollen germination under both optimal and high temperatures.     

Effect of photoperiod and temperature on apical growth cessation in two ecotypes of Salix and Betula

Apical growth cessation as affected by photoperiod and temperature has been studied in seedlings of two latitudinal ecotypes of Salix and Betula. The critical photoperiod for apical growth cessation at constant temperatures of 15 and 21°C was about 22 h for a northern (69°C39′N) and about 15–16 h for a southern (59°C40′N) ecotype of Salix pentandra. Fluctuating day/night temperatures (21°C/9°C, 15°C/6°C) induced apical growth cessation in northern ecotypes even at 24–h photoperiod. Disagreements in critical photoperiods found in various studies are discussed.     

The restriction of Cladosporium fulvum and Botrytis cinerea, attacking glasshouse tomatoes, by automatic humidity control

Decreasing periods of atmospheric humidity in excess of 90 and 75 % r.h. by automatic control decreased the incidence of C. fulvum and B. cinerea and sometimes increased tomato yields. The desired value of humidity was not always achieved but nevertheless environments which were both physically and biologically different were obtained with humidistats set at 90 and 75 % r.h. in glasshouses maintaining two temperature régimes–20 °C day and night, or 20 °C by day and 13 °C at night. Less B. cinerea and C. fulvum occurred on tomatoes grown constantly at 20 °C than on those grown in conditions with lower night temperatures. In the latter regime the end-of-season incidence of C.fulvumvas decreased from 25.0% where humidity was not controlled to 2.8% and 0.0% where humidistats were set at 90 and 75 % r.h. In the same conditions the proportion of blemished fruit damaged by B. cinerea decreased from 2.6% to 1.6% and 0.2%.     

A new method to determine the energy saving night temperature for vegetative growth of Phalaenopsis

Knowledge of the energy saving night temperature (i.e. a relatively cool night temperature without affecting photosynthetic activity and physiology) and a better understanding of low night temperature effects on the photosynthetic physiology of Phalaenopsis would improve their production in terms of greenhouse temperature control and energy use. Therefore, Phalaenopsis‘Hercules’ was subjected to day temperatures of 27.5°C and night temperatures of 27.0°C, 24.2°C, 21.2°C, 18.3°C, 15.3°C or 12.3°C in a growth chamber. A new tool for the determination of the energy saving night temperature range was developed based on temperature response curves of leaf net CO₂ exchange, chlorophyll fluorescence, organic acid content and carbohydrate concentrations. The newly developed method was validated during a complete vegetative cultivation in a greenhouse environment with eight Phalaenopsis hybrids (i.e. ‘Boston’, ‘Bristol’, ‘Chalk Dust', ‘Fire Fly’, ‘Lennestadt’, ‘Liverpool’, ‘Precious’, ‘Vivaldi’) and day/night temperature set points of 28/28°C, 29/23°C and 29/17°C. Temperature response curves revealed an overall energy saving night temperature range for nocturnal CO₂ uptake, carbohydrate metabolism, organic acid accumulation and photosystem II (PSII) photochemistry of 17.1°C to 19.9°C for Phalaenopsis‘Hercules’. At the lower end of this energy saving night temperature range, a high malate‐to‐citrate ratio switched towards a low ratio and this transition seemed to alleviate effects of night chilling induced photoinhibition. At night temperatures of 24°C or higher, the degradation of starch, glucose and fructose indicated an increased respiratory CO₂ production. During the greenhouse validation experiment, the differences between the eight Phalaenopsis hybrids with regard to their response to the warm day/cool night temperature regimes were remarkably large. In general, the day/night temperature of 29/17°C led to a significantly lower biomass accumulation and less leaves which were in addition shorter, narrower and smaller in size as compared to the day/night temperature regimes of 28/28°C and 29/23°C. During week 25 of the cultivation period, plants matured and flower initiation steeply increased for all hybrids and in each day/night temperature regime. Before week 25, early spiking was only sufficiently suppressed in the 29/23°C and 29/17°C temperature regimes for three hybrids (‘Boston’, ‘Bristol’ and ‘Lennestadt’) but not in the other five hybrids. Although a considerable biochemical flexibility was demonstrated for Phalaenopsis‘Hercules’, inhibition of flowering after exposure to a combination of warm days and cool nights appeared to be largely hybrid dependent.     

Effect of Gibberellic Acid on Dark and Light Germination at Different Temperatures of Calluna, Ledum andRhododendron Seeds

The aim of the experiments was to study the effects of gibberellic acid (GAs) on the germination of Calluna vulgaris L., Ledum palustre L. and Rhododendron lapponicum (L.) Wahlenb. seeds under different environmental conditions. Under continuous light from white fluorescense tubes (3000 lux), untreated seeds of Calluna were partly dormant at all temperatures studied (9, 15, 21, 27, 27/9, 8/16 hours). Percentage of dormant seeds increased, however, with decreasing temperature, and it varied also from seed lot to seed lot. Untreated seeds of Ledum were dormant in light at 9° and 15°C but not at higher temperatures. Untreated seeds of Rhododendron were completely dormant in light at temperatures from 13° to 24°C. Seeds of all species were completely dormant in darkness both at 15° and 27°C. GA₃ stimulated greatly the germination of all species under all studied environmental conditions. The used concentrations (0.2–3.2 mM) gave nearly 100% germination in most cases. At 9°C the dormancy in some seed lots of Calluna and Ledum was only partly broken by the used concentrations of GA₃.     

Nuclear DNA content of the Solanum spp. in the series Etuberosa as determined by laser flow cytometry

Nuclear DNA content was determined in three accessions of Solanum brevidens, three accessions of S. etuberosum, and one accession of S. fernandezianum, which are diploid (2n = 2×= 24), closely related, non tuber-bearing wild potato species belonging to the series Etuberosa (Solanaceae). The plants were grown in vitro at 18°C or at 25°/22°C (day/night). S. brevidens was also grown in soil in the glasshouse at 25°/19°C (day/night), and in growth chambers at 18°C or 32°C. Leaf nuclei were isolated using a chopping method and stained with propidium iodide. Chicken red blood cells (CRBC; 2.33 pg) were added to the samples of nuclei as internal standards. The fluorescence of plant nuclei relative to CRBC was measured with an EPICS PROFILE flow cytometer. The 2C values of in vitro-grown S. brevidens and S. etuberosum were similar (1.48–1.54 pg, depending on the accession), but they were smaller than the 2C value of S. fernandezianum (1.63 pg). The 2C values of S. brevidens and S. etuberosum were generally smaller than those of the diploid species S. berthaultii (1.60–1.61 pg) and the diploid clones of S. tuberosum (1.60–1.72 pg). A similar relative difference of nuclear DNA content was found also between tetraploid S. brevidens and tetraploid S. tuberosum (2C = 3.15–3.16 pg and 3.50–3.62 pg, respectively). High (32°C) and low (18°C) growth temperatures caused abnormal changes in morphology and reduced fertility in S. brevidens in the growth chamber. The 2C values of S. brevidens grown at 25°/19°C (day/night) or at 32°C were similar, whereas the 2C values were c. 10% lower at 18°C.     

Environmental cues for germination of the invasive bunch grass <Emphasis Type="Italic">Pennisetum ciliare</Emphasis> (L.) Link

Responses of seed germination to air temperature, water potential, light, and smoke were studied in the laboratory for seeds of the invasive bunch grass Pennisetum ciliare (L.) Link (syn. Cenchrus ciliare L.; buffel grass). First introduced to North America during the mid-twentieth Century for establishing pastures, this African bunch grass has become an invasive species of concern. Across all the experiments conducted, a low germination was observed for P. ciliare fascicles that never exceeded 30 % at 21 days after sowing. Optimal day/night air temperatures for germination, controlled with an environmental chamber, were 25/15 and 30/20 °C, while extreme temperatures of 15/5 and 45/35 °C inhibited germination. By sowing seeds of P. ciliare under different water potentials, created with aqueous solutions of polyethylene glycol, an optimum of ?0.03 MPa led to the highest germination, while no germination was observed at ?1.0 MPa. Monochromatic optical filters were utilized to germinate seeds under various wavelengths, of which red (650 nm) and far red (730 nm) led to the highest germination. In addition, seeds that were incubated in the dark had higher germination than those incubated under white light. Incubation in smoke water, which can stimulate germination of pyrophytic species, resulted in a marginal inhibition of germination compared with imbibition with distilled water.     

Physiological responses of Opuntia ficus-indica to growth temperature

The influences of various day/night air temperatures on net CO₂ uptake and nocturnal acid accumulation were determined for Opuntia ficus-indica, complementing previous studies on the water relations and responses to photosynthetically active radiation (PAR) for this widely cultivated cactus. As for other Crassulacean acid metabolism (CAM) plants, net nocturnal CO₂ uptake had a relatively low optimal temperature, ranging from 11°C for plants grown at day/night air temperatures of 10°C/0°C to 23°C at 45°C/35°C. Stomatal opening, which occurred essentially only at night and was measured by changes in water vapor conductance, progressively decreased as the measurement temperature was raised. The CO₂ residual conductance, which describes chlorenchyma properties, had a temperature optimum a few degrees higher than the optimum for net CO₂ uptake at all growth temperatures. Nocturnal CO₂ uptake and acid accumulation summed over the whole night were maximal for growth temperatures near 25°C/15°C, CO₂ uptake decreasing more rapidly than acid accumulation as the growth temperature was raised. At day/night air temperatures that led to substantial nocturnal acid accumulation (25°C/15°C.). 90% saturation of acid accumulation required a higher total daily PAR than at non-optimal growth temperatures (10°C/0°C and 35°C/25°C). Also, the optimal temperature of net CO₂ uptake shifted downward when the plants were under drought conditions at all three growth temperatures tested, possibly reflecting an increased fractional importance of respiration at the higher temperatures during drought. Thus, water status, ambient PAR, and growth temperatures must all be considered when predicting the temperature response of gas exchange for O. ficus-indica and presumably for other CAM plants.     

The in vitro germination and storage characteristics of Keteleeria fortunei var. cyclolepis pollen provide a reference for cross breeding

Keteleeria fortunei var. cyclolepis is an ideal tree species for mountain afforestation, timber forests, and landscaping. Its pollination process can be affected by the rainy season, making it difficult to pollinate the massive female cones, which leads to a high abortion rate and low quality of seeds. Here, we observed the pollen morphology of K. f. cyclolepis using scanning electron and light microscopes, investigated the characteristics of its in vitro germination by the detached method, and explored the effect of different storage temperatures and times on the pollen germination rate and the activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Our results indicated that the pollen of K. f. cyclolepis is a five-cell pollen, comprising one noumenon and two air sacs, both of which were oval in polar view. The optimal condition for pollen germination of K. f. cyclolepis was 240 g/L sucrose + 70 mg/L CaCl₂ + 210 mg/L H₃BO₃ at 24 °C and pH 6.0, resulting in a germination rate of 45.0%. The effects of different storage temperature and time on pollen germination rate varied significantly. The best storage temperature was − 80 °C, at which the germination rate was 20.9% after 365 days of storage, and the activity of three protective enzymes remained relatively high, representing relatively strong antioxidation and antiaging activity. Stepwise regression analysis showed that SOD was the main factor affecting the pollen germination rate of K. f. cyclolepis. The function of the three protective enzymes differed under various temperatures, for example, SOD served as a sensitive protective enzyme at room temperature, − 20 °C and − 80 °C, whereas both SOD and CAT served as sensitive protective enzymes at 4 °C.

     

Effects of light, temperature and water stress on germination of Artemisia sphaerocephala

Artemisia sphaerocephala is widely used for vegetation rehabilitation, but its germination is very low after air seeding of achenes. We explored effects of light, temperature and water stress on germination. Results show that both final percent germination and germination rate were increased by temperature increment, with the highest values occurring at 15: 25°C (night: day) in dark and 20: 30°C under light. Light inhibited germination, especially at lower alternating temperatures (5: 15°C and 10: 20°C). The alternating temperature window for germination was slightly narrower under light than in dark, and germination was slower under light than in dark across the temperature range. Achenes incubated in the dark and at constant temperatures had over 80% germination at 10 to 25°C, with an optimum at 20°C. Under dark and 25μmol m^‐2 s^‐1 light flux density at 10: 20°C, final percent germination was over 94%, but if the light flux density was increased to 100 and 400 μmol m^‐2 s^‐1, final percent germination was significantly lower (64% and 38% respectively). However, achenes could keep their germination capacity for a long time (over 50 days) and germinate well after going back to the dark. Germination was also lower under water stress and few achenes germinated at ‐1.4 MPa. This was more pronounced at high and low temperatures. Given these findings and the prevailing climatic characteristics, the most suitable time for air seeding of achenes may be mid‐May.