Interaction between a plant-derived smoke extract,light and phytohormones on the germination of light-sensitive lettuce seeds

Plant-derived smoke extracts mimics the effect of red light on germination in light-sensitive lettuce seeds and partially overcomes the inhibitory effect of far-red light. Interaction between a smoke extract and gibberellins, cytokinins, abscisic acid and ethephon was investigated. Smoke acted synergistically with GA₃ and increased the sensitivity of the lettuce seeds to ABA. It seems likely that smoke affects membrane permeability or receptor sensitivity rather than influencing the phytochrome system of these seeds.Abbreviations R red light - FR far-red light - SM smoke extract     

The effect of a plant-derived smoke extract on the germination of light-sensitive lettuce seed

A simple and rapid bioassay using seeds of Lactuca sativa L. Grand Rapids has been developed for the detection of germination-enhancing compound(s) in plant-derived smoke extracts. This light-sensitive species germinates within 24 h in the dark at 20 or 25°C and shows responsiveness to smoke-derived extracts over a wide concentration range. For some seed lots where the P _fr level is high and germination in the dark is unacceptably high, a brief (10 min) exposure to far-red light, one hour after the start of imbibition in the dark, is necessary to clearly demonstrate biological activity in the smoke extracts.     

Effect of a plant-derived smoke extract, N6-benzyladenine and gibberellic acid on the thermodormancy of lettuce seeds

The effects of a plant-derived smoke extract, BA and GA₃ on the thermodormancy of Grand Rapids lettuce seeds were studied. Thermodormant lettuce seeds treated either with BA, GA₃ or smoke extract alone did not germinate. Combinations of BA with smoke extract and BA with GA₃ were most effective in overcoming induced thermodormancy. GA₃ plus smoke did not break the induced thermodormancy. The effects of the different treatments on germination were concentration dependent. BA was most effective at 10^–5 to 10^–3 M in combination with smoke dilutions 1:5,000 to 1:1,000,000 in overcoming thermodormancy.Abbreviations BA N⁶-benzyladenine; - GA₃ gibberellic acid; - SM smoke extract     

Effects of long-term storage on phytochrome-mediated germination in lettuce seeds

The effects of long-term seed storage on the physiological properties of phytochrome-mediated germination including water uptake, the temperature and light flunnce dependencies of germination and dark germination were studied. The fluenceresponse relationships of the brief irradiation with monochromatic red (660 nm, 7.5 W m⁻²) and far-red (750 nm, 6.6 W m⁻²) light at various times after sowing were also studied. The samples used consisted of three lots of seeds ofLactuca sativa L. cv. MSU-16, which had been harvested in 1976, 1979 and 1985 and stored dry for 9, 6 and 0 years, respectively, in darkness at 23±2 C until the experiments were carried out in July–August, 1985. Seeds with the longer storage periods showed the higher ability to germinate in both continuous darkness and continuous white fluorescent light at 20–30 C. In the seeds stored for 6 or 9 years, red light irradiation for 20 sec given at 15 min or more after sowing at 25 C induced as high a percent germination (85–95%) as those under continuous white fluorescent light. In the freshly harvested seeds, however, germination under continuous white fluorescent light (46%) was considerably lower than the germination induced by the red pulse (97%). Germination of the seeds decreased when the intervals between sowing and a far-red irradiation for 20 sec increased up to 100 min (or 30 min in the freshly harvested seeds). The far-red pulse given later than 100 min (or 6 hr in the freshly harvested seeds) after sowing resulted in an increased germination up to the dark-germination levels with increasing intervals between sowing and the pulse irradiation. Before or at 3 min after sowing, the seeds stored for 6 or 9 years were responsive to the far-red pulse although they were not or hardly responsive to the red pulse, while the freshly harvested seeds were responsive to both the far-red and the red pulses. These data indicate that normal functions of phytochrome completely survived in the dry seeds during storage at 25 C for as long as 6 or 9 years and that these functions are restored into full operation by means of imbibition. The differences in the dependence of germination on the time and fluence of a single pulse of red or far-red light seems to be related to the smaller water content throughout the imbibition in the seeds with the longer storage periods. The greater ability to germinate in the dark indicates the greater amounts of P_FR or the greater responsivity to P_FR, in the seeds with the longer storage periods.     

Effect of light and temperature on the germination of lettuce seeds

A short period (15–30 min) at 30° C promotes germination of seeds of Lactuca sativa L. cv. Repolhuda in darkness. Far-red light reverses this stimulation, and the escape curves for phytochrome and high-temperature action are quite similar, indicating that the two factors act at a common point in the chain of events leading to germination. It is suggested that high temperature acts by decreasing the threshold of the active, far-red absorbing, form of phytochrome (Pfr) needed to promote germination.Abbreviations FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light     

Identification in lettuce seedlings of a catecholamine active in synergistically enhancing the gibberellin effect on lettuce hypocotyl elongation

The occurrence of catecholamines in lettuce seedlings was examined by bioassay and gas chromatography-mass spectrometry (GC-MS), since synthetic catecholamines can synergistically enhance the stimulating effect of gibberellic acid (GA₃) on hypocotyl elongation of decotylized lettuce seedlings. The catecholamine fraction on TLC obtained from lettuce seedlings synergistically enhanced the GA₃ effect on hypocotyl elongation. The analysis of the catecholamine fraction from lettuce seedlings by GC-MS demonstrated the occurrence of dopamine.     

Dormancy break of celery (Apium graveolens L.) seeds by plant derived smoke extract

Seed dormancy of a highly-dormant cultivar of celery (Apium graveolens L.) was broken by combinations of plant-derived smoke extract or N⁶-benzyladenine (BA) and gibberellins A_4/7 (GA_4/7) in the dark at temperatures between 18 and 26°C. A less dormant cultivar which responded to GA_4/7 alone showed no additional response to smoke extract or BA. Neither smoke extract nor BA affected either cultivar in the dark in the absence of GA_4/7. The partial dormancy-breaking effect of short exposures to red-light was also enhanced by smoke extracts in this highly-dormant cultivar. The results suggest that smoke extracts act in a similar way to cytokinins, by enhancing gibberellin activity in the celery seed system.Abbreviations BA N⁶-benzyladenine - GA_4/7 A₄ and A₇ gibberellin mixture     

The effect of ethrel and temperature on the germination of Manihot glaziovii Muell. Arg. seeds

Dormancy in seeds of Manihot glaziovii is overcome at 25°C by application of ethrel at effective ethylene concentrations equal to and greater than 10 ll^–1. Imbibition of seeds in ethrel broadens the temperature optimum for germination but does not prevent the development of secondary dormancy at temperatures of 35°C and greater and 15°C and lower. Secondary dormancy must be due to factors other than reduced ethylene production.     

The growth physics and water relations of red-light-induced germination in lettuce seeds

Using lettuce (Lactuca sativa L., cv. Grand Rapids) embryos in osmotica, we have demonstrated that when the growth rates of the embryonic axes of seeds treated with red (R) or far-red (FR) light are equalized, the axes of R-treated seeds develop a 3.4-bar decrease in water potential (paper No. III).As axial growth begins, reserve protein and phytin decrease rapidly, concomitant with increases in reducing sugars, -amino nitrogen, and inorganic and esterified soluble phosphates. However, no differences between the axes of R-and FR-treated seeds are found with respect to the changes in these compounds, indicating that these changes arise as a result of growth and are not under immediate phytochrome control. Little change in the total lipid content is found in either treatment. The axes of FR-treated seeds hydrolyze endogenous sucrose at a greater rate thant those of R-treated seeds. Axes of R-treated seeds accumulate K⁺ and Na⁺ to a greater extent than those of FR-treated seeds. When potassium salts are added to the incubation medium, R induces increased K⁺ uptake by the axis and greater medium acidification by the axis. Malate and other organic acids and acidic amino acids increase at equal rates in both treatments, indicating that inorganic anions may also be taken up to balance the ionic charges. The results are compatible with the assumption that changes in the osmotic and pressure potentials of the embryonic axes of R-treated seeds are the result of a phytochrome-stimulated proton pump which, in whole dormant seeds, would initiate water-potential changes allowing the embryos to overcome the mechanical restraint of the surrounding seed layers, resulting in germination.Abbreviations FR far-red light - PEG polyethylene glyeol 4000 - Pfr far-red-absorbing form of phytochrome - R red light III=Carpita et al. 1979     

毛竹各器官和根际土浸提液对杉木种子萌发的化感作用

随着毛竹杉木混交林面积的不断扩大,它们之间既会产生促进作用,又会产生抑制作用。本研究对比分析了不同浓度毛竹各器官(鲜叶、干叶、枝条、竹杆、竹鞭和鞭根)的浸提液及枯落物、根际土浸提液对杉木种子发芽率的影响,探讨了毛竹各器官浸提液及枯落物、根际土浸提液对杉木种子萌发的化感作用。结果表明:(1)处理前期,毛竹各器官浸提液对杉木种子萌发具有抑制作用,且当浸提液浓度为1∶25和1∶50的高浓度时,相对于低浓度浸提液对杉木种子萌发的抑制作用更为持久;(2)处理后期,低浓度的毛竹各器官浸提液对杉木种子萌发促进作用较快,而高浓度的浸提液仍呈现抑制作用,促进作用出现较为缓慢;(3)枯落叶浸提液总体上对杉木种子萌发具有抑制作用,在整个实验过程中低于对照组的发芽率,仅在1∶50浓度时略高对照组实验;而根际土浸提液对杉木种子萌发自始至终都具有促进作用,其中低浓度的促进作用十分显著。故在实际的毛竹杉木混交林生产营林过程中可选用毛竹根际土制备浸提液,促进杉木种子萌发,为毛竹杉木混交林的生产经营提供参考。     

Effect of hypobaric conditions on ethylene evolution and growth of lettuce and wheat

Elevated levels of ethylene occur in enclosed crop production systems and in spaceflight environments, leading to adverse plant growth and sterility. There are engineering advantages in growing plants at hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on growth and ethylene evolution of lettuce (Lactuca sativa) and wheat (Triticum aestivum). Plants were grown under variable total gas pressures [from 30 to 101 kPa (ambient)]. In one study, lettuce and wheat were direct seeded, germinated and grown in the same chambers for 28 d at 50 or 101 kPa. Hypobaria increased plant growth and did not alter germination rate. During a 10-day study, 28-day-old lettuce and 40-day-old wheat seedlings were transplanted together in the same low and ambient pressure chambers; ethylene accumulated in the chambers, but the rate of production by both lettuce and wheat was reduced more than 65% under 30 kPa compared with ambient pressure (101 kPa). Low O2 concentrations [partial pressure of O2 (pO2) = 6.2 kPa] inhibited ethylene production by lettuce under both low (30 kPa) and ambient pressure, whereas ethylene production by wheat was inhibited at low pressure but not low O2 concentration. There was a negative linear correlation between increasing ethylene concentration and decreasing chlorophyll content of lettuce and wheat. Lettuce had higher production of ethylene and showed greater sensitivity to ethylene than wheat. The hypobaric effect on reduced ethylene production was greater than that of just hypoxia (low oxygen).     

Stage-specific crosstalk between light, auxin, and ethylene during low-pH-induced root hair formation in lettuce (Lactuca sativa L.) seedlings

In the light, transfer of lettuce seedlings precultured on liquid medium at pH 6.0 to fresh medium at pH 4.0 induces root hair formation. However, no root hairs form in the dark. Here, we investigated how light induces root hair formation. Randomization of the transverse cortical microtubule (CMT) arrays which occurs in root epidermal cells in the light prior to root hair initiation was not observed in the dark. However, addition of indole-3-acetic acid (IAA) or 1-aminocyclopropane-1-carboxylic acid (ACC) induced CMT randomization and root hair formation. In these cases, CMT randomization occurred in almost the same time-dependent manner as under light. However, root hair initiation was delayed for several hours in the dark. These results suggest that light promotes CMT randomization and root hair initiation via auxin and ethylene signaling but light additionally influences root hair initiation independently of these signaling mechanisms. Furthermore, addition of a microtubule-depolymerizing drug in the dark disrupted the transverse CMT arrays and initiated root hair formation; however, root hair elongation was still suppressed. Root hairs elongated when IAA or ACC was applied with the drug. These results suggest that light also promotes root hair elongation via auxin and ethylene signaling.     

Effects of 6-methoxy-2-benzoxazolinone on the germination and α-amylase activity in lettuce seeds

Germination of lettuce seeds was inhibited by 6-methoxy-2-benzoxazolinone (MBOA) at concentrations greater than 0.03 mmol/L. MBOA also inhibited the induction of α-amylase activity in the lettuce seeds at concentrations greater than 0.03 mmol/L. These two concentration–response curves for the germination and α-amylase indicate that the percentage of the germination was positively correlated with the activity of α-amylase in the seeds. Lettuce seeds germinated around 18 h after incubation and inhibition of α-amylase by MBOA occurred within 6 h after seed incubation. These results show that MBOA may inhibit the germination of lettuce seeds by inhibiting the induction of α-amylase activity.     

Salicylic acid inhibits the biosynthesis of ethylene in detached rice leaves

The effects of salicylic acid (SA) on ethylene biosynthesis in detached rice leaves were investigated. SA at pH 3.5 effectively inhibited ethylene production within 2 h of its application. It inhibited the conversion of ACC to ethylene, but did not affect the levels of ACC and conjugated ACC. Thus, the inhibitory effect of SA resulted from the inhibition of both synthesis of ACC and the conversion of ACC to ethylene.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - SA salicylic acid     

The influence of abscisic acid on different polysomal populations in embryonal tissue during pea seeds germination

The influence of abscisic acid (ABA) on the processes of formation of different polysomal populations, their structures and stability in embryonal tissue during pea seeds germination was studied. The contents of total ribosomal fraction increased in all samples up to 72 h of germination and then decreased. The contents of polysomal population (FP, MBP, CBP and CMBP) extracted from the embryonal tissue after 72 hrs of germination of pea seeds were then quantified. It turned out that in examined tissue of control sample, fraction of free polysomes (FP) was the most abounded. This population of polysomes in sprouts decreased after ABA treatment. FP content decreased even more when the higher ABA concentration was applied during germination. Similar changes were observed in the fraction of membrane-bound polysomes (MBP). Quite different tendencies were found, however, in forming population of the cytoskeleton-membrane-bound polysomes (CMBP). The CMBP population content in embryonal tissue increased in a dosage dependent manner with increasing concentration of ABA applied during seed germination. This indicates the important role of CMBP fraction in synthesis of specific proteins in embryos in the time when processes of seeds germination are retarded by ABA. In the final part we examined the stability of polysomes isolated from sprouts of germinating seeds in water and sprouts isolated from seeds treated with ABA (100 μM) during germination. Total polysomes isolated from embryonal tissue of germinating seeds treated with ABA showed much higher resistance to exogenous ribonuclease digestion than total polysomes of control sample. The obtained results suggest that ABA influence on different polysomal population formation also controls their stability.     

ACC conversion to ethylene by sunflower seeds in relation to maturation,germination and thermodormancy

Conversion of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene was studied in sunflower (Helianthus annuus L., cv. Mirasol) seeds in relation to germinability. Ethylene production from ACC decreased during seed maturation, and non-dormant mature seeds were practically unable to synthesize ethylene until germination and growth occurred, indicating that ethylene forming enzyme (EFE) activity developed during tissue imbibition and growth. ACC conversion to ethylene was reduced by the presence of pericarp, and in young seedlings it was less in cotyledons than in growing axes.ACC conversion to ethylene by cotyledons from young seedlings was optimal at c. 30°C, and was strongly inhibited at 45°C. Pretreatment of imbibed seeds at high temperature (45°C) induced a thermodormancy and a progressive decrease in EFE activity.Abscisic acid and methyl-jasmonate, two growth regulators which inhibit seed germination and seedling growth, and cycloheximide were also shown to inhibit ACC conversion to ethylene by cotyledons of 3-day-old seedlings and by inbibed seeds.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - CH cycloheximide - EFE ethylene forming enzyme - IAA indole-3-acetic acid - Me-Ja methyl-jasmonate     

Involvement of cytokinins in the germination of chick-pea seeds

Eight cytokinins detected in germinated chick-pea (Cicer arietinum L. var. Castellana) seeds were first present in the embryonic axes but appeared in the cotyledons after 12h of germination. The cytokinins detected in the cotyledons originate in the embryonic axes, but no passage of these substances from the cotyledons to the axes was detected, except when the seeds were treated with red light.It is concluded that the role played by the embryonic axis in mobilizating the main reserves of the cotyledons is mainly effected through these cytokinins. Both natural and synthetic cytokinins exert an important regulatory role in the hydrolysis of reserve proteins and calcium could be involved as an intermediate.Abbreviations BA benzyladenine - cot. cotyledon - (diH)Z dihydrozeatin - (diH)ZR dihydrozeatin riboside - GZR glycosyl zeatin riboside - 2iP 277-1 - iPA 277-2 riboside - Kin kinetin - Z zeatin - ZG zeatin glucoside - ZR zeatin riboside     

Crossing experiments of lettuce cultivars and species (Lactuca sect.Lactuca,Compositae)

The degree of relationships withinLactuca sativa and three wild relativesL. serriola, L. saligna, andL. virosa was studied by observing the performance, vigour and fertility of the F 1 hybrids obtained from crosses made in and between the four species. The crosses ofL. saligna ×L. virosa and the reciprocal crosses produced no hybrids.L. saligna andL. virosa are the least related of the four species.L. sativa ×L. serriola and the reciprocal crosses were successful and produced fertile hybrids These two species are genetically very closely related.L. saligna is known to produce, as a female parent, hybrids withL. sativa andL. serriola. Now the reciprocal cross was successful for the first time, so the unability to obtain hybrids in the past was based on the choice of accessions and not caused by unilateral incompatibility.L. virosa ×L. sativa and the reciprocal combination produced hybrids. The combinationL. serriola ×L. virosa produced hybrids with very limited fertility. In contrast to earlier reports (sterile hybrids) one combination of the reciprocal cross too produced hybrids with very limited fertility.—Some of theL. saligna ×L. sativa (and reciprocal) hybrids were found to look strikingly likeL. serriola. This adds evidence for the descent ofL. serriola andL. sativa:L. saligna also made part of the ancestral complex of the cultivated lettuce.     

Prior hydration of Brassica tournefortii seeds reduces the stimulatory effect of karrikinolide on germination and increases seed sensitivity to abscisic acid

Background and Aims

The smoke-derived compound karrikinolide (KAR₁) shows significant potential as a trigger for the synchronous germination of seeds in a variety of plant-management contexts, from weed seeds in paddocks, to native seeds when restoring degraded lands. Understanding how KAR₁ interacts with seed physiology is a necessary precursor to the development of the compound as an efficient and effective management tool. This study tested the ability of KAR₁ to stimulate germination of seeds of the global agronomic weed Brassica tournefortii, at different hydration states, to gain insight into how the timing of KAR₁ applications in the field should be managed relative to rain events.

Methods

Seeds of B. tournefortii were brought to five different hydration states [equilibrated at 15 % relative humidity (RH), 47 % RH, 96 % RH, fully imbibed, or re-dried to 15 % RH following maximum imbibition] then exposed to 1 nm or 1 µm KAR₁ for one of five durations (3 min, 1 h, 24 h, 14 d or no exposure).

Key Results

Dry seeds with no history of imbibition were the most sensitive to KAR₁; sensitivity was lower in seeds that were fully imbibed or fully imbibed then re-dried. In addition, reduced sensitivity to KAR₁ was associated with an increased sensitivity to exogenously applied abscisic acid (ABA).

Conclusions

Seed water content and history of imbibition were found to significantly influence whether seeds germinate in response to KAR₁. To optimize the germination response of seeds, KAR₁ should be applied to dry seeds, when sensitivity to ABA is minimized.