Mepiquat chloride seed treatment and germination temperature effects on cotton growth, nutrient partitioning, and water use efficiency

Cotton seed (Gossypium hirsutum L. cv. Stoneville 825), treated with 0, 0.2, 1.0, and 2.0 g active ingredient (a.i.) mepiquat chloride (MC) kg^–1, was evaluated for the effect of MC on early plant growth. Emergence rate and total emergence of MC-treated seed and control were similar regardless of germination temperature. However, the number of leaves and squares and the dry weight of leaves, stems, and roots for hydroponically grown cotton plants were significantly lower at lower germination temperatures (15°C for 3 day/30°C for 1 day and 15°C for 4 days) than at higher germination temperatures (30°C for 4 days and 30°C for 3 days/15°C for 1 day). All MC treatments significantly decreased the number of nodes, leaves, and squares, as well as dry weight of leaves, stems, and roots, as compared to control plants at 28 days after emergence. MC seed treatments also significantly reduced plant height and total leaf area compared to controls. Water-use efficiency (WUE) was significantly lower for the 1.0 g a.i. MC treatment than for control plants. In general, the highest rate of MC seed treatment resulted in greater concentrations of calcium, phosphorus, and nitrogen in plant leaves and stems and also in greater concentrations of magnesium, phosphorus, and nitrogen in roots than in controls.     

Maize seed cryo-storage modifies chlorophyll,carotenoid, protein,aldehyde and phenolics levels during early stages of germination

We recorded the crypreservation effects (direct immersion) on various parameters of early germination stages of maize seeds (0, 7 and 14 days). Percentages of germination; fresh mass of different seedling parts; levels of chlorophyll pigments (a, b); carotenoids; malondialdehyde; other aldehydes; phenolics (cell wall-linked, free) and proteins were determined. Various statistically significant effects of seed exposure to liquid nitrogen (LN) were recorded. Maize seeds did not seem to be affected by LN exposure either visually or regarding fresh weight or germination rate. However, delayed growth was observed in seedlings recovered from cryopreserved seeds. This trend indicated an increase in the effect of seed cryopreservation on growing plants. The most significant effects of LN exposure were recorded in the combined fresh weight of stems and leaves at day 7 of germination and in fresh weights of roots, stems and leaves at day 14. At the biochemical level, numerous indicators varied following LN exposure, but the most significant effects were recorded in carotenoids, malondialdehyde and other aldehyde contents. LN exposure modified 50.0% of indicators in cotyledons, 48.1% in stems and leaves, 38.8% in roots and 11.1% in seeds. LN storage modified 11.1% of the variables measured at day 0 of germination, 37.0% at day 7, and 52.7% at day 14. Field performance of cryostored seed-derived plants should be evaluated to measure the durability of the changes observed.     

Effect of mepiquat chloride and nitrogen levels on yield,growth characteristics,and elemental composition of cotton

A 3-year study was conducted to determine the effects of mepiquat chloride and N levels on yield and quality of cotton (Gossypium hirsutum L.). Mepiquat chloride (MC) treatments did not significantlyaffect yields; however, cotton lint yields (1980) were 688, 949, 1,011, and 1,045 kg/ha for N rates of 0, 45, 90, and 135 kg/ha, respectively. Nitrogen by MC interactions on yield were not significant for any of the 3 years. MC treatments reduced plant height for all N levels. Plant height averages over all N levels were reduced 15–33% by the addition of MC. The MC treatments significantly increased the percent of Ca and Mg in the cotton leaves on a dry-weight basis. Nitrogen concentrations of the leaves were not affected by MC treatments. Leaf N levels were not significantly affected by N fertilization in 1979, but leaf N levels in 1980 were significantly increased at the 90 kg N/ha rate when compared with the check treatment.     

Influence of post-flowering temperature on seed development, and subsequent performance of crisp lettuce

Crisp lettuce plants cv. Saladin were grown from the time they started flowering, at 20/10°C (16 h day, 8 h night), 25/15°C and 30/20°C in glasshouses on two occasions in 1985. Yields of seed increased from, on average, 15 g to 27 g and then fell to 20 g per plant with progressive increases in temperature. The number of mature florets per plant increased with temperature but the number of seeds per mature floret was lower at 20/10°C and 30/20°C than at 25/15°C. An increase in temperature reduced mean seed weight by up to 45%, seed volume by 15%, cell numerical volume density (N_v) by 27% and the number of cells per seed by 39%. Percentage seed germination reached a maximum early in seed development at the stage when the pappus appeared through the involucral bracts. Differences in percentage germination and vigour of seeds (slope test) from different temperatures were accounted for largely by the effects on mean seed weight. However, when germinated at 30°C seeds produced at 30/20°C germinated more readily than those produced at 25/15°C or 20/10°C. Seed vigour gradually increased with an increase in the length of storage after harvest, reaching a maximum after 260 days. In general, seeds produced at 25/15°C exhibited a greater variation in numbers of seeds per floret, N_v, seed weight, times of seedling emergence, seedling and mature head weight than seeds produced at lower or higher temperatures.     

Daily Temperature Amplitude Affects the Vegetative Growth and Carbon Metabolism of Orange Trees in a Rootstock-Dependent Manner

Both instantaneous and average growth temperatures affect plant metabolism, and the physiological importance of daily variations in temperature is frequently underestimated. To improve our understanding of the environmental regulation of citrus trees, we hypothesized that vegetative growth would be stimulated in orange plants subjected to large daily temperature variations, even without changes in the average daily air temperature or the amount of energy given by degree-days. This hypothesis was tested with orange plants grafted onto Rangpur lime or Swingle citrumelo rootstocks and grown for 20?days under thermal regimes (day/night) of 25/25°C or 32.5/17.5°C. Such regimes imposed growth conditions with daily temperature variations of 0 and 15°C. Plant growth, photosynthesis, respiration, and carbohydrate availability in leaves, stems, and roots were measured under both thermal conditions. The daily temperature variation affected the carbon metabolism of young citrus trees; plants grown under daily variation of 15°C used more of the carbon stored in mature leaves and roots and the energy generated by respiration for the biosynthesis of vegetative structures, such as leaves and branches. Thus, there was a significant increase in the leaf area of plants subjected to high daily temperature variation. Current photosynthesis was similar in the two thermal regimes; however, the photosynthetic rates increased under the 15°C variation when measurements were normalized to 25°C. In addition to the stimulatory effect of the source?Csink relationship on photosynthesis, we suggest a probable involvement of hormonal regulation of plant growth through gibberellin metabolism. The rootstock affected the response of the canopy to daily temperature amplitude, with the Rangpur lime improving plant growth through higher carbohydrate availability in roots. This is the first report that highlights the importance of daily temperature variations for citrus growth and physiology under nonlimiting conditions.     

九里香种子脱水耐性和萌发生理的研究

九里香种子自花后 42～ 77d,含水量和电导率逐渐降低 ,种子干重、发芽率、发芽指数和活力指数逐渐增加。硅胶脱水 1～ 6d后 ,种子含水量下降 1 0 %～ 3 5 % ,发芽率、发芽指数和活力指数均有不同程度的降低 ,不同发育时期九里香种子的脱水耐性有别 ,花后 42～ 70d不断增强 ,77d有所减弱。花后 70d的种子含水量降至 1 0 % ,种子发芽率无明显降低 ;含水量为 9%的种子在 4°C和 2 0°C的低温条件贮存 3 0d和 42d ,多数种子仍能萌发 ,这表明九里香种子是一种正常型种子。光照能促进种子的萌发 ;在 2 0～ 3 0°C、室温和 2 0 /3 0°C变温条件下种子萌发较好 ;光照和温度对种子萌发有单独影响 ,但又相互作用 ,同时光照对萌发的影响还与种子含水量有关。     

Effects of seed moisture content,warm, chilling,and exogenous hormone treatments and germination temperature on the germination of blackthorn seeds

Blackthorn (Prunus spinosa L.) germination is often low, so new methods need to be developed with a view to improving nursery yields and to inform decision-making on natural regeneration. To this end, the effects of seed moisture content (MC) levels in combination with warm and chilling treatments on blackthorn seed dormancy release were investigated. In another experiment, the effect on seed germination of warm and chilling treatments in combination with exogenous hormones was investigated. Following treatment, the seeds were allowed to germinate at a constant 15°C with 8 h lighting per day or 20 (dark)/30°C (light). Seed lot effects were evident, but were consistent across treatments. Seeds adjusted to the lower target MC level (TMC) maintained high germination potential over a longer period of treatment than in those held in the fully imbibed (FI) state. The highest germination was achieved in the TMC seeds that were given six weeks warm treatment followed by 32 weeks chilling. Hormone treatments significantly reduced the amount of chilling needed to release dormancy in TMC seeds, but not in the FI seeds. Overall, germination response was better at 15°C test temperature than at 20/30°C.     

Germination studies ofMolucella laevis

Seed of Molucella laevis (L.) was gathered in the years 1963-66 and germinated soon after harvest and at various intervals subsequently. All seeds showed dormancy on gathering. There was a noticeable fluctuation in the percentage of seeds germinating during storage. Dormancy persisted throughout the years of the experiment. It appears that a number of factors are operative in the inhibition of germination of M. laevis seeds. One factor is an inhibitor which may be adsorbed by active charcoal or heavy loam, involving some process which requires fluctuating temperature. Rupture of the seed-coat also improved the germination of dormant seed, and a subsequent water rinse for 24 hrs. further increased the percent of germinating seed. Immersion of the seed for 48 hrs. in gibberellic acid (G.A.), 400 ppm, greatly improved germination, but it did not completely overcome dormancy. The maximum effect (93% germinating seed) was obtained when seed pre-treated with G.A. was germinated on top of active charcoal. The optimal germination temperature was found to be a daily alternating one of 16 hrs. at 15°C and 8 hrs. at 30°C with light supplied at the latter temperature. Treated seed was sown in the screen house and found to develop normal plants and seed. The dormancy-breaking effect of G.A. lasts for at least 180 days. The fluctuations in germination of seed pre-treated with gibberellin were similar to those of the untreated ones. The effect of dormancy-breaking factors differed with year of gathering and date of application. Thus, M. laevis seeds display much heterogeneity in their germination potential.     

Interactions between seed priming treatments and nine seed lots of carrot, celery and onion. I. Laboratory germination

Samples of three seed lots of each of three cultivars of carrot, celery and onion were primed in polyethylene glycol solution for 2 weeks at 15 °C. Priming reduced the mean germination times (recorded at 15 °C) of all seed lots (compared to the untreated control) by 3–4 days in carrot, 6–10 days in celery and 3–5 days in onion. The largest reductions in mean germination time occurred in the slowest-germinating seed lots. There were highly significant interactions between priming and cultivars, and between priming and seed lots within cultivars for each species. Drying back the primed seeds at 15 °C increased the mean germination times (compared to primed seed which had not been dried) by 0·6 day in carrot and 1·4 days in celery, and there was no interaction with cultivars or seed lots. The corresponding increase for onion was either 1·0 or 1·8 days, according to the cultivar, but this variation was largely attributable to differences in time taken for the dried seeds to re-imbibe. Seeds dried back at 30 °C germinated 0·2·0·7 day (depending on the species) later than those dried at 15 °C. Percentage germination was not affected by either priming or drying back. Priming reduced the spread of germination times in all cultivars. For primed and dried-back seed, the spread of germination times was larger than that of primed seed in certain cultivars, but was always smaller than that of untreated seeds.     

Sunflower seed deterioration as related to moisture content during ageing, energy metabolism and active oxygen species scavenging

The objectives of the present work were to investigate whether loss of sunflower (Helianthus annuus L.) seed viability was affected by the embryo moisture content (MC) during seed pretreatment at 35°C, and was related to changes in energy metabolism and in the antioxidant defence system. Non‐dormant seeds were equilibrated at MC of the embryonic axis ranging from 0.037 to 0.605 g H₂O g^?1 dry matter (DM) for 1 day at 15°C, and they were then placed at 35°C for various durations up to 14 days before the germination assays at 15°C. As expected, the higher the MC, the faster was seed deterioration. There existed a negative linear relationship between the time taken for germination to drop to 50% (P₅₀) and the embryonic axis MC ranging from 0.108 and 0.438 g H₂O g^?1 DM. In dry seeds, adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate represented 6.3, 14.8 and 70.9% of the adenylate pool, respectively, and the energy charge (EC) was very low (0.14). ATP and ADP levels and EC increased sharply during the first day of equilibrium of seeds at a MC above 0.158 g H₂O g^?1 DM. Subsequent controlled deterioration at 35°C resulted in a decrease in the adenylate pool, and consequently in ATP level. The higher the energy metabolism during ageing, the lower was seed viability. Loss of seed viability was associated with an accumulation of H₂O₂, and then of malondialdehyde (MDA) suggesting that lipid peroxidation was not the only cause of seed deterioration. When there was a sublinear relationship between H₂O₂ content in the embryonic axis and seed viability, MDA accumulation only occurred when 50% of the seed population died within 7 days, i.e. when MC was higher than 0.248 g H₂O g^?1 DM. Ageing was associated with a decrease in the activity of superoxide dismutase, catalase and glutathione reductase, the main enzymes involved in cell detoxification. The involvement of seed MC, as key factor of ageing is discussed with regards to energy metabolism and the regulation of active oxygen species accumulation.     

Low temperature acclimation of root fatty acid composition, leaf water potential, gas exchange and growth of soybean seedlings

Abstract Root fatty acid composition, photosynthesis, leaf water potentials, stomatal resistances, leaf specific weights, and root: shoot ratios of soybean were measured in two temperature regimes. Groups of soybean plants were grown in controlled chambers of the Duke University Phytotron under two thermoperiods. One group of the plants was grown from seed for 3 weeks in either 29/23°C or 17/11°C thermoperiods, and another group was grown for 2 weeks in 29/23°C and then transferred to the 17/11°C thermoperiod where it remained for 8 days. Broccoli was also grown in either 29/23°C or 17/11°C thermoperiods. Soybean roots contained more unsaturated fatty acids than broccoli roots, although broccoli roots showed a larger increase in unsaturation than soybean roots with decreased temperature. The fatty acid unsaturation in the roots of soybean began to increase rapidly after the temperature regime was changed. The increase was in the new roots produced in the cold regime rather than in the pre-existing roots. The soybean leaf water and osmotic potentials decreased about 0.4 MPa, beginning one day after the transfer from 29/23°C to 17/11°C, but recovered significantly after 8 d. Plants grown at 17/11 °C had lower rates of photosynthesis and adaxial stomatal resistances, but higher root: shoot ratios and specific leaf weights compared to plants grown at 29/23°C. Plants grown and maintained at 29/23°C showed a steady increase in photosynthetic rates over the 8-d experimental period, whether rates were measured in 1 mol m^?3 or 9 mol m^?3 oxygen. Plants transferred to 17/11°C however maintained constant rates of photosynthesis at 1 mol m^?3 O₂, whereas at 9 mol m^?3 rates declined for 2 d then were constant for the remaining 6 d of the experimental period. These results suggest that changes in membrane fatty acid unsaturation is an important aspect of plant acclimation to chilling temperatures in terms of maintaining root permeability and water uptake. However, the degree of unsaturation is not a good indicator of differences in chilling tolerance among species. The apparent acclimation of photorespiration to a constant percentage of photosynthesis suggests a role of photorespiration in the plant.     

Acetylcholine in plants: Presence,metabolism and mechanism of action

Acetylcholine (ACh) has been detected in representatives of many taxonomic groups throughout the plant kingdom. The site of its synthesis in plants is probably young leaves. In some plant species choline acetyltransferase (ChAT) activity has been found. This enzyme showing properties similar to animal ChAT, probably participates in ACh synthesis from its precursors, choline and acetyl-Coenzyme A. Acetylcholinesterase (AChE) activity has also been found in many plant tissues. This enzyme decomposes ACh and exhibits properties similar to animal AChE. The presence of both ChAT and AChE in plant tissues suggests that ACh undergoes similar metabolism in plants as it does in animals. Exogenous ACh affects phytochrome-controlled plant growth and development. Mimicking red light (R), ACh stimulates adhesion of root tips to a glass surface and influences leaf movement and membrane permeability to ions. It also affects seed germination and plant growth. Moreover, ACh can modify some enzyme activity and the course of some metabolic processes in plants. Acetylcholine in the presence of calcium ions (Ca²⁺), like R stimulates swelling of protoplast isolated from etiolated wheat leaves. It is proposed that the primary mechanism of action of ACh in plant cells is via the regulation of membrane permeability to protons (H⁺), potassium ions (K⁺), sodium ions (Na⁺) and Ca²⁺.     

Effect of Low Temperature upon Lipid and Fatty Acid Composition of Roots and Leaves of Winter Rape Plants

When winter rape plants were transferred from favourable temperature conditions (25/20°C day/night temperature) to 5°C, the frost resistance of the leaves was increased whereas the frost tolerance of the roots remained unaffected. This permitted an analysis of the changes in lipid and fatty acid composition both as related to functioning of the plant at low temperature alone (roots) and as related to adaptation to freezing and functioning at low temperature (leaves). — Transfer of the plants to 5°C lead to an increase in the level of linolenic acid in roots and leaves. This increase was most evident in the phosphatidyl choline and ethanolamine fractions of the leaves, and in the neutral lipids and in an unidentified phospholipid from the roots. It was concluded that upon transfer of the plants to 5°C a general and non-specific increase in linolenic acid level contributed to functioning of the rape plants at low temperature; and that parallel but minor increases in linolenic acid level of digalactosyl diglyceride, phosphatidyl inositol and the unknown phospholipid in roots and leaves could only contribute to low-temperature functioning in specific membrane enzyme locations. Combined adaptation of the leaves to freezing tolerance and low-temperature functioning was correlated with a higher level of phosphatidyl choline and ethanolamine, predominantly esterified with linolenic acid.     

Successful expression of a novel bacterial gene for pinoresinol reductase and its effect on lignan biosynthesis in transgenic Arabidopsis thaliana

Pinoresinol reductase and pinoresinol/lariciresinol reductase play important roles in an early step of lignan biosynthesis in plants. The activities of both enzymes have also been detected in bacteria. In this study, pinZ, which was first isolated as a gene for bacterial pinoresinol reductase, was constitutively expressed in Arabidopsis thaliana under the control of the cauliflower mosaic virus 35S promoter. Higher reductive activity toward pinoresinol was detected in the resultant transgenic plants but not in wild-type plant. Principal component analysis of data from untargeted metabolome analyses of stem, root, and leaf extracts of the wild-type and two independent transgenic lines indicate that pinZ expression caused dynamic metabolic changes in stems, but not in roots and leaves. The metabolome data also suggest that expression of pinZ influenced the metabolisms of lignan and glucosinolates but not so much of neolignans such as guaiacylglycerol-8-O-4′-feruloyl ethers. In-depth quantitative analysis by liquid chromatography–tandem mass spectrometry (LC-MS/MS) indicated that amounts of pinoresinol and its glucoside form were markedly reduced in the transgenic plant, whereas the amounts of glucoside form of secoisolariciresinol in transgenic roots, leaves, and stems increased. The detected levels of lariciresinol in the transgenic plant following β-glucosidase treatment also tended to be higher than those in the wild-type plant. Our findings indicate that overexpression of pinZ induces change in lignan compositions and has a major effect not only on lignan biosynthesis but also on biosynthesis of other primary and secondary metabolites.     

Germination and Dormancy of Reed Canary-Grass Seeds (Phalaris arundinacea)

Effects of various chemical and physical factors on the germination of several seed lots of reed canary-grass (Phalaris arundinacea L.) have been studied. Germination at the optimum constant temperatures of 24 to 27°C was significantly stimulated by the following treatments: moist chilling in light, red light given during the first 3 days of imbibition, three 2-h periods at 12°C given during the second day of imbibition, ethylene, increased oxygen tension and soaking in aerated water for 4 days. Dry storage at 20–30°C had no effect on the germination ability of the seeds. No significant quantities of germination inhibitors were found either in water or methanol extracts of seed dispersal units. By comparing three cultivars with various degrees of seed dormancy, respiration measurements showed that there was a significant positive correlation between oxygen uptake prior to visible germination and germination capacity. Similarly, germination-stimulating treatment significantly enhanced oxygen uptake prior to visible germination.     

Selenium Modifies the Effect of Short-Term Chilling Stress on Cucumber Plants

The objective of this study was to investigate the effect of selenium (Se) supply (0, control; 2.5, 5, 10, or 20 μM) on cucumber (Cucumis sativus L.) cv. Polan F1 plants grown under short-term low temperature stress. About 14–16 day-old seedlings, grown at an optimal temperature (25/20°C; day/night), were exposed to short-term chilling stress with a day/night temperature of 10°C/5°C for 24 h, for a further 24 h at 20°C/15°C, and then transferred to 25/20°C (re-warming) for 7 days. Se did not affect the fresh weight (FW) of plants at a concentration of 2.5–10 μM, but in the presence of 20 μM Se, the biomass of shoots significantly decreased. The contents of chlorophylls and carotenoids witnessed no significant change after Se supplementation. Compared with the control, the Se-treated plants showed an increase of proline content in leaves, once after chilling and again after 7 days of re-warming. However, proline levels were much higher immediately after chilling than after re-warming. The malondialdehyde (MDA) content in the root of plants treated with 2.5–10 μM Se decreased directly after stress. This was in comparison with the plants grown without Se, whereas it increased in roots and leaves of plants exposed to 20 μM Se. Seven days later, the MDA level in the root of plants grown in the presence of Se was still lower than those of plants not treated with Se and generally witnessed no significant change in leaves. Although Se at concentrations of 2.5–10 μM modified the physiological response of cucumber to short-term chilling stress, causing an increase in proline content in leaves and diminishing lipid peroxidation in roots, the resistance of plants to low temperature was not clearly enhanced, as concluded on the basis of FW and photosynthetic pigments accumulation.     

Effect ofAgrobacterium radiobacter and its polysaccharide on emergence and damping-off of tomato plants

Agrobacterium radiobacter B6 and agrobacteran (an exopolysaccharide of the succinoglycan group) stimulated seed germination and tomato plant emergence. The germination was most stimulated by dipping the seeds in 0.1 % agrobacteran for 30 min whereas plant emergence in garden soil was best with 0.4 % agrobacteran at 10–20°C. Treatment of the plants withA.radiobacter cells and agrobacteran solution at 30–35°C. had a lower effect.A.radiobacter cells applied on seed surface protected the plants against damping off in garden soil artificially inoculated with the fungiRhizoctonia solani andPythium ultimum; in soils contaminated withFusarium solani 0.1 to 0.2% agrobacteran had a higher protective effect than the bacterization. The difference can be attributed to the varying density ofA.radiobacter population in plant rhizosphere in the presence of different plantpathogenic fungi, different interactions of microorganisms in the rhizosphere and different mode of penetration of the pathogens into plant roots.     

Some properties of pea cholinesterase and its activity in plant parts at different growth stages

Cholinesterase activity was studied in 2 to 10-week-old pea plants cultivated under artificial illumination. Free and membrane-bound forms of the enzyme were separated by extracting the enzyme from pea shoots with buffers differing in ionic strength. The ratio of the free cholinesterase to the membrane-bound one fluctuated between 1 : 1 and 1 : 2.5. The free cholinesterase was inhibited by neostigmine (0.1mmoll^-1) by 50%, the membrane-bound enzyme by 90%. The pH optimum of cholinesterase activity was 8.5, the temperature optimum 37 °C. The enzyme activity was increased by some cations in this order: Mg²⁺ < < K⁺. The K^m value for the substrate S-acetylthiocholine iodide was 250 μmoll^-1, the enzyme activity being inhibited by concentrations higher than 3 mmoll^-1 of this substrate. The activity of the membrane-bound enzyme was demonstrated in the roots, leaves, stems, fruits, seeds and carpels, but could not be reliably detected in the blossoms. The highest activity expressed per fresh matter was found in older leaves and in the fruits, the lowest in the roots and stems. Cholinesterase activity in plant parts markedly varied during the investigated growth period.     

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.