Gibberellin A3 Treatment Research Articles

Effect of gibberellic acid on photosynthesis and oxidative stress response in maize under weak light conditions.

Gibberellin (GA) is an important endogenous hormone involved in plant responses to abiotic stresses. Experiments were conducted at the Research and Education Center of Agronomy, Shenyang Agricultural University (Shenyang, China) in 2021.We used a pair of near-isogenic inbred maize lines comprising, SN98A (light-sensitive inbred line) and SN98B (light-insensitive inbred line) to study the effects of exogenous gibberellin A3 (GA3) application on different light-sensitive inbred lines under weak light conditions. The concentration of GA3 was selected as 20, 40 and 60 mg L-1. After shade treatment, the photosynthetic physiological indexes of SN98A were always lower than SN98B, and the net photosynthetic rate of SN98A was 10.12% lower than SN98B on the 20th day after shade treatment. GA3 treatments significantly reduced the barren stalk ratios in SN98A and improved its seed setting rates by increasing the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), photosynthetic pigment contents, photochemical efficiency of photosystem II (PS II) (Fv/Fm), photochemical quenching coefficient (qP), effective quantum yield of PSII photochemistry (ΦPSII), and antioxidant enzyme activities, where the most effective treatment was 60 mg L-1GA3. Compared with CK group, the seed setting rate increased by 33.87%. GA3 treatment also regulated the metabolism of reactive oxygen species (ROS) and reduced the superoxide anion ( ) production rate, H2O2 content, and malondialdehyde content. The superoxide anion ( ) production rate, H2O2 content and malondialdehyde content of SN98A sprayed with 60 mg L-1 GA3 decreased by 17.32%,10.44% and 50.33% compared with CK group, respectively. Compared with the control, GA3 treatment significantly (P < 0.05) increased the expression levels of APX and GR in SN98A, and APX, Fe-SOD, and GR in SN98B. Weak light stress decreased the expression of GA20ox2, which was related to gibberellin synthesis, and the endogenous gibberellin synthesis of SN98A. Weak light stress accelerated leaf senescence, and exogenous GA3 application inhibited the ROS levels in the leaves and maintained normal physiological functions in the leaves. These results indicate that exogenous GA3 enhances the adaptability of plants to low light stress by regulating photosynthesis, ROS metabolism and protection mechanisms, as well as the expression of key genes, which may be an economical and environmentally friendly method to solve the low light stress problem in maize production.

Genome-Wide Identification and Expression Analysis of Cytokinin Response Regulator (RR) Genes in the Woody Plant Jatropha curcas and Functional Analysis of JcRR12 in Arabidopsis.

The cytokinin (CK) response regulator (RR) gene family plays a pivotal role in regulating the developmental and environmental responses of plants. Axillary bud outgrowth in the perennial woody plant Jatropha curcas is regulated by the crosstalk between CK and gibberellins (GA). In this study, we first analyzed the effects of gibberellin A3 (GA3), lovastatin (a CK synthesis inhibitor), decapitation, and their interaction, on the outgrowth of axillary buds. The results indicate that lovastatin completely inhibited GA-promoted axillary bud outgrowth and partially weakened the decapitation-promoted axillary bud outgrowth. To further characterize and understand the role of CK signaling in promoting the development of female flowers and branches, we performed bioinformatics and expression analyses to characterize the CK RR gene (JcRR) family in J. curcas. A total of 14 members of the JcRR family were identified; these genes were distributed on 10 chromosomes. Phylogenetic analysis indicated that the corresponding RR proteins are evolutionarily conserved across different plant species, and the Myb-like DNA-binding domain divides the 14 members of the JcRR family into type-A and type-B proteins. Further analysis of cis-acting elements in the promoter regions of JcRRs suggests that JcRRs are expressed in response to phytohormones, light, and abiotic stress factors; thus, JcRRs may be involved in some plant development processes. Genomic sequence comparison revealed that segmental duplication may have played crucial roles in the expansion of the JcRR gene family, and five pairs of duplicated genes were all subjected to purifying selection. By analyzing RNA sequencing (RNA-seq) and quantitative reverse transcription-polymerase chain reaction (qRT–PCR) data, we characterized that the temporospatial expression patterns of JcRRs during the development of various tissues and the response of these genes to phytohormones and abiotic stress. The JcRRs were mainly expressed in the roots, while they also exhibited differential expression patterns in other tissues. The expression levels of all six type-A and one type-B JcRRs increased in response to 6-benzylaminopurine (6-BA), while the four type-B JcRRs levels decreased. The expression levels of two type-B JcRRs increased in response to exogenous GA3 treatment, while those of three type-A and three type-B JcRRs decreased. We found that type-A JcRRs may play a positive role in the continuous growth of axillary buds, while the role of type-B JcRRs might be the opposite. In response to abiotic stress, the expression levels of two type-A and three type-B JcRRs strongly increased. The overexpression of JcRR12 in Arabidopsis thaliana slightly increased the numbers of rosette branches after decapitation, but not under normal conditions. In conclusion, our results provide detailed knowledge of JcRRs for further analysis of CK signaling and JcRR functions in J. curcas.

The mechanism of exogenous gibberellin A3 protecting sorghum shoots from S-metolachlor Phytotoxicity.

S-metolachlor (MET) was used to prevent weed infestation in sorghum fields, but inappropriate application could result in phytotoxicity on sorghum. Exogenous gibberellin A3 (GA3 ) has been applied for alleviating the phytotoxicity of MET. However, its detoxification mechanism is still not well known. Leaf deformity of sorghum caused by 200 mg/L MET was alleviated by treating sorghum shoots with 800 mg/L GA3 , and the injury recovery rate of growth index was over 73%. More importantly, GA3 could not accelerate the metabolic rate of MET in sorghum. The result of phytohormone metabolomics showed that endogenous GA3 content in sorghum decreased by 78.10% with MET treatment, while abscisic acid (ABA) content increased by 120.2%, resulting in 10.3-fold increase of ABA/GA3 ratio. Content of ABA and GA3 increased by 11.9- and 21.1-fold with MET and GA3 treatment, respectively, leading to ABA/GA3 ratio restoration. Moreover, MET inhibited the expression of genes encoding key enzymes related to GA synthesis including CPS1, KO2, KAO, GA20ox1D and ABA8ox gene related to ABA metabolism. The transcription levels of GA metabolism-related genes CYP714D1 and GA2ox were up-regulated by 11.2- and 7.2-fold, while ABA synthesis-related genes NCED and ZEP were up-regulated by 8.0- and 3.0-fold, respectively, with MET and GA3 treatment. In this study, exogenous GA3 protecting sorghum shoots from MET phytotoxicity was due to supplement the MET-induced GA3 deficiency by absorbing exogenous GA3 , and restore homeostasis of ABA and GA3 by promoting ABA synthesis, which provides novel insights for mechanism of GA3 alleviating MET phytotoxicity. © 2022 Society of Chemical Industry.

Identification of BcARR Genes and CTK Effects on Stalk Development of Flowering Chinese Cabbage.

Flowering Chinese cabbage (Brassica campestris L. ssp. Chinensis var. utilis Tsen et Lee) is an important and extensively cultivated vegetable in south China, whose major food product is the stalk. In the process of stalk formation, its initiation and development are regulated by a series of hormonal signals, such as cytokinin and gibberellin. In this study, we analyzed the effects of zeatin (ZT) and gibberellin A3 (GA3), and their interaction, on the bolting of flowering Chinese cabbage. The results indicated that the three-true-leaf spraying of ZT and GA synthesis inhibitor (PAC) inhibited plant height but increased stem diameter. Cytokinin (CTK) synthesis inhibitor (YZJ) and GA3 treatment increased plant height and decreased stem diameter. In addition, ZT and GA3 co-treated plants displayed antagonistic effect. Further, 19 type-B authentic response regulators (ARR-Bs), the positive regulators of cytokinin signal transduction were identified from flowering Chinese cabbage. Comprehensive analysis of phylogeny showed BcARR-Bs clustered into three subfamilies with 10 conserved motifs. Analysis of their expression patterns in different tissues and at various growth stage, and their response to hormone treatment suggest that ARR1-b localized in the nucleus displayed unique highest expression patterns in stem tips, are responsive both to ZT and GA, suggesting a significant role in mediating the crosstalk of ZT and GA in the bolting of flowering Chinese cabbage.

Effects of Gibberellin and Abscisic Acid on Fruit Quality and Aromatic Compound Formation during Fruit Development in ‘Kyoho’ Grapes (&lt;i&gt;Vitis vinifera&lt;/i&gt; L.×&lt;i&gt;Vitis labrusca&lt;/i&gt; L.)

To understand the effects of plant growth regulators (PGRs) on the aromatic compounds of ‘Kyoho’ grapes, changes in fruit quality and aroma compound content at different growth and developmental stages were investigated after treatment with gibberellin A3 (GA3) at the flowering stage and with abscisic acid (ABA) at veraison. Thirty compounds were identified in peels and pulps, with 3-hexenal, (E)-2-hexenal, ethyl acetate, ethyl butyrate, and limonene being the main compounds. GA3 treatment inhibited ester synthesis, including ethyl acetate, ethyl butyrate, and terpenes, as well as limonene, while promoting the synthesis of C6 compounds, including 3-hexenal and (E)-2-hexenal in peels compered to no treatment. ABA treatment could promote the synthesis of most aroma compounds, especially esters, terpenes, and alcohols in peels and pulps at the ripening stage. Previously, it has been suggested that ABA reduce the negative influence of GA3 on aroma compound synthesis. The combination of GA3 and ABA can obtain high quality berries in ‘Kyoho.’ These results provide a reference for further studies on the effects of plant regulators on aroma compounds synthesis in grapes.

Comparative gene expression analysis reveals that multiple mechanisms regulate the weeping trait in Prunus mume

Prunus mume (also known as Mei) is an important ornamental plant that is popular with Asians. The weeping trait in P. mume has attracted the attention of researchers for its high ornamental value. However, the formation of the weeping trait of woody plants is a complex process and the molecular basis of weeping stem development is unclear. Here, the morphological and histochemical characteristics and transcriptome profiles of upright and weeping stems from P. mume were studied. Significant alterations in the histochemical characteristics of upright and weeping stems were observed, and the absence of phloem fibres and less xylem in weeping stems might be responsible for their inability to resist gravity and to grow downward. Transcriptome analysis showed that differentially expressed genes (DEGs) were enriched in phenylpropanoid biosynthesis and phytohormone signal transduction pathways. To investigate the differential responses to hormones, upright and weeping stems were treated with IAA (auxin) and GA3 (gibberellin A3), respectively, and the results revealed that weeping stems had a weaker IAA response ability and reduced upward bending angles than upright stems. On the contrary, weeping stems had increased upward bending angles than upright stems with GA3 treatment. Compared to upright stems, interestingly, DEGs associated with diterpenoid biosynthesis and phenylpropanoid biosynthesis were significantly enriched after being treated with IAA, and expression levels of genes associated with phenylpropanoid biosynthesis, ABC transporters, glycosylphosphatidylinositol (GPI)—anchor biosynthesis were altered after being treated with GA3 in weeping stems. Those results reveal that multiple molecular mechanisms regulate the formation of weeping trait in P. mume, which lays a theoretical foundation for the cultivation of new varieties.

Plant Growth Regulators Affect Germination and Main Carbon-Nitrogen Metabolites of Potato Tubers

Assessing the effects of different growth regulators on sprout growth and tuber carbon-nitrogen metabolism during the storage of potato tubers is helpful to understand the physiological changes of dormancy in potatoes. In this study, a major potato cultivar ‘Chuanyu-117’ of Southwestern China was used as the experimental material. The tubers were immersed in sprouting inhibitors chlorpropham (CIPC), abscisic acid (ABA), and gibberellin A3 (GA3) to study sprout growth and changes in the carbon-nitrogen metabolism during tuber storage. The results showed that GA3 treatment shortened the dormancy intensity and amplitude by 17 days and 11 days, respectively, and that the sprouts grew faster after germination. Compared to the control treatment, ABA prolonged dormancy and increased its intensity by 6 days but shortened the amplitude by 11 days. After dormancy, the sprouts grew rapidly and uniformly. The CIPC treatment had a more significant dormancy prolonging effect. The stems germinated 70 days post treatment, and the germination period was extended by at least 40 days compared with the control. Tubers treated with different growth regulators showed similar carbon-nitrogen metabolism during the storage period. However, the rate of variation was significantly different. After 12 weeks, the starch content of tubers treated with GA3, ABA, and CIPC decreased by 13.36%, 11.30%, and 5.93%, respectively, while soluble sugar content decreased by 48.3%, 58.9%, and 56.1%, respectively. Soluble protein and crude protein content in the treated tubers first increased and then decreased. Soluble protein content in the tubers treated with GA3, ABA, and CIPC increased during storage but decreased in the later period. Crude protein content also increased the first time, and then decreased in the later period. Changes in the carbon-nitrogen ratio of tubers in different treatments during storage were also different. The carbon-nitrogen ratio of tubers treated with sprouting promotors was high, while that of the tubers treated with sprouting inhibitors was low and showed a gradual decreasing trend.

Genome-scale analysis of the cotton KCS gene family revealed a binary mode of action for gibberellin A regulated fiber growth.

Production of β‐ketoacyl‐CoA, which is catalyzed by 3‐ketoacyl‐CoA synthase (KCS), is the first step in very long chain fatty acid (VLCFA) biosynthesis. Here we identified 58 KCS genes from Gossypium hirsutum, 31 from G. arboreum and 33 from G. raimondii by searching the assembled cotton genomes. The gene family was divided into the plant‐specific FAE1‐type and the more general ELO‐type. KCS transcripts were widely expressed and 32 of them showed distinct subgenome‐specific expressions in one or more cotton tissues/organs studied. Six GhKCS genes rescued the lethality of elo2Δelo3Δ yeast double mutant, indicating that this gene family possesses diversified functions. Most KCS genes with GA‐responsive elements (GAREs) in the promoters were significantly upregulated by gibberellin A3 (GA). Exogenous GA3 not only promoted fiber length, but also increased the thickness of cell walls significantly. GAREs present also in the promoters of several cellulose synthase (CesA) genes required for cell wall biosynthesis and they were all induced significantly by GA3. Because GA treatment resulted in longer cotton fibers with thicker cell walls and higher dry weight per unit cell length, we suggest that it may regulate fiber elongation upstream of the VLCFA‐ethylene pathway and also in the downstream steps towards cell wall synthesis.

Gibberellin A3 Treatment of Seeds, Container Volume, Substrate pH, and Nitrogen Source and Rate Influence Growth of Containerized Seabeach Amaranth (Amaranthus pumilus)

Seeds of seabeach amaranth (Amaranthus pumilus Raf.), a species federally listed as ‘threatened,’ were stratified (moist-chilled) for 90 days at 4C (39F) or treated with a solution of the potassium (K) salt (K-salt) of gibberellin A3 (K-GA3) at 1000 mg·liter−1 (ppm) for 24 hr. After treatment, both groups of seeds were sown in containers of two volumes, 139 or 635 cm3 (9 or 39 in3) with a substrate of peat:pine bark (1:1, v/v) amended with one of two rates of pulverized dolomitic lime [2.24 or 4.48 kg·m−3 (3.8 or 7.6 lb·yd−3)]. Containers were maintained in a greenhouse. After seedling emergence, seedlings were fertilized with a 20N-4.4P-16.6K (20N-10P205-20K20) acidic, water soluble fertilizer or a 15N-2.2P-12.5K (15N-5P205-15K20) basic, water soluble fertilizer applied thrice weekly at nitrogen (N) application rates (NARs) of 75, 150, 225, or 300 mg·liter−1. The study was terminated 8 weeks after seeds were sown and data recorded. Regardless of fertilizer, acidic or basic, top dry weight and leaf area of seabeach amaranth increased linearly with increasing NAR. Maximum top dry weight and leaf area occurred with N at 300 mg·liter−1, whereas root dry weight was unaffected by NAR. Both fertilizers increased electrical conductivity (EC) linearly with increasing NAR, and EC values of 1.15 to 1.18 dS·m−1 were adequate for maximum top growth or leaf area. Substrate pH decreased linearly with increasing NAR 21, 43, and 57 days after initiation. Top and root dry weights and leaf area were greatest for seedlings derived from seeds treated with K-GA3. Large containers yielded top and root dry weights and leaf area 61, 33, and 57% greater, respectively, than smaller containers. Top N concentration increased linearly with increasing NAR for acidic and basic fertilizers with N concentrations of 58.4 and 50.4 mg·g−1, respectively, at maximum top dry weight. Although top nutrient content of N increased linearly with NAR, top N content was unaffected by either rate of lime or type of fertilizer.

Effects of Plant Growth Regulators on Fruit Set and Fruit Shape of Parthenocarpic Apple Fruits

We applied auxin, cytokinin, gibberellins, and gibberellin synthetic inhibitor to flowers of ‘Ohrin’, which is parthenocarpic, and ‘Fuji’, which is non-parthenocarpic, to elucidate the relationship between plant growth regulators and parthenocarpy in apple. The percentage of fruit set in gibberellin A3 (GA3) was about 60% in ‘Ohrin’ and about 7% in ‘Fuji’. Forchlorfenuron (CPPU) combined with GA3 treatment increased the fruit retention rate more than 14 days after treatment (DAT) than GA3 alone. Dichlorprop (2,4-DP) combined with GA3 slightly enhanced the gibberellin effect of inducing parthenocarpy. In ‘Ohrin’, GA3 and gibberellin A4 + 7 (GA4 + 7) showed a higher fruit retention rate before flowering than after. Parthenocarpic fruits were induced even when uniconazole (UCZ) was sprayed after flowering, but not before flowering. The calyx end was large in GA4 + 7, and in GA3 and CPPU singly, and GA3 and CPPU combined treatments, which increased the percentage of fruit set. These results suggest that gibberellins before flowering trigger parthenocarpic apple fruits. Subsequent fruit growth requires cytokinins and auxin.

Seed Germination of Seabeach Amaranth (Amaranthus pumilus) in Response to Temperature, Light, and Gibberellin A3 Treatments

Abstract Seeds of seabeach amaranth (Amaranthus pumilus Raf.) stored at 4C (39F) for approximately 1 year (harvested September 2003) and freshly harvested seeds (October 2004) were soaked in November 2004 in solutions of the potassium (K) salt (K-salt) of gibberellin A3 (K-GA3) at 0, 100, 500, or 1000 mg/liter (ppm) for 24 hr in darkness. After treatment, seeds were germinated at 25C (77F) or at an 8/16-hr thermoperiod of 30/20C (86/68F) with daily photoperiods at each temperature of 0 (total darkness) or 16 hr. Germination was recorded every 3 days for 30 days. Stored and fresh seeds responded similarly. However, the 2003 seeds had greater viability (percent germination) and vigor (germinated faster) and these data are presented. Regardless of germination temperature and photoperiod, nontreated seeds [0 mg/liter (ppm) K-GA3] did not germinate. When germinated at 25C (77F) the response of seeds to K-GA3 treatment was linear for both photoperiods with significantly greater total (30-day) germination occurring in the dark for seeds treated with 100, 500, or 1000 mg/liter (ppm) K-GA3. At 25C (77F), the greatest total germination (84%) was observed for seeds treated with 1000 mg/liter (ppm) K-GA3 and maintained in darkness, whereas for seeds exposed to a 16-hr photoperiod, maximum germination was 72%. At 30/20C (86/68F) the response to K-GA3 was quadratic with maximum germination at predicted rates of 882 and 875 mg/liter (ppm) KGA3 (88 and 92%, respectively) for photoperiods of 0 and 16 hr, respectively. Treatment of nonstratified seeds of seabeach amaranth with K-GA3 removed physiological (embryo) dormancy and eliminates the need for stratification (moist-prechilling). Treatment also reduced sensitivity of the seeds to light, and appeared to broaden the range of temperatures for germination.

Interaction between Effects of Photoperiod and Plant Growth Regulators on the Development of Tubers and Inflorescences in Japanese Yams (Dioscorea japonica)

The interaction between 8- and 24-hr photoperiods and plant growth regulators (PGR) (gibberellin A3 (GA3) and uniconazole-P (Uni)) on the development of the main shoots, aerial tubers (bulbils) and new tubers (below ground), and inflorescences (spikes) in Japanese yam (Dioscorea japonica Thunb.) plants was examined. Within the same PGR treatment, the main shoots of plants grown under the 24-hr photoperiod (constant light, LD) were longer than those grown under the 8-hr photoperiod (SD) in all season; under LD and SD, the main shoots of the GA3-treated plants were the same size as shoots sprayed with water (control), whereas the main shoots of the Uni-treated plants were significantly shorter. Under LD, whereas the control and PGR-treated plants produced a negligible amount of aerial tubers, under SD, their development was severely inhibited by GA3 treatment. During the early growing period, the fresh weight of new tubers and that of the combined fresh weight of aerial and new tubers in plants grown under SD were heavier than those grown under LD. From the middle to the end of the growing period, the development of aerial and new tubers in plants grown under LD accelerated so that the difference between the final fresh weights of the combined fresh weight of aerial and new tubers in plants grown under SD and those grown under LD at harvest became small. Although, there was not such LD promoting effect of those growth as would be observed in D.opposita cv. Ichoimo and Nagaimo. Under SD, the new tubers development were significantly promoted by GA3 treatment because the inhibition of aerial tubers development by GA3 treatment promotes the diversion of photosynthates stored in shoots to growth of new tubers. Under SD, plants grown developed one flush of inflorescences in June, whereas those grown under LD developed a flush in June and again in August through October. We conclude that the GA3 and Uni had no significant effects on the ratio of plants that initiated flowers, the nodal position of the first and final spikes, and the total number of spikes per plant in both season of spikes development in the main shoots were not clear.

Gibberellin A3 stimulates adventitious rooting of cuttings from cherry (Prunus avium)

We have examined the effect of exogenous gibberellin A3(GA3) on adventitious rooting of Prunus avium(cherry) cultivars Stella, F12/1 and Charger. We show that GA3pre-treatment of P. avium stock plants causes an increasein shoot growth rate and also improves the rooting of cuttings subsequentlytaken from the treated plants. Approximately 37% of cuttings from controlshootsrooted, whereas the percentage rooting could be increased to 80% or more withGA3 pre-treatment. The number of roots per rooted cutting was alsoincreased by GA3 pre-treatment. The stimulation of adventitiousrooting could be partially explained by the increase in shoot growth rate.Cultivar Charger responded better than the other cultivars to the lowest levelof GA3 treatment. In vitro cultures of cultivarCharger were also treated with GA3. However, the stimulation ofadventitious rooting was less marked than in the GA3-treated stockplants: percentage rooting increased from 70% to 85%. The results are discussedin the context of 'rejuvenation' effects of GA3.

2-methylisoborneol and geosmin, the main sources of soil odor, inhibit the germination of brassicaceae seeds

The effects of 2-methylisoborneol (MIB) and geosmin, the main sources of soil odor produced by microorganisms, on plant seed germination were examined for 15 kinds of Brassicaceae seeds including radish (Raphanus sativus var. radicula). Authentic MIB or geosmin was used at the concentration of 100 mg L-1 in the assay, the effects were quantitatively indexed based on four parameters of cumulative seed germination: the final germination percentage, germination onset, weighted mean rate, germination index. MIB and geosmin inhibited germination of all kinds of seeds tested for these parameters. Radish variety “Comet” was the most affected of all of the tested plant seeds. The estimated 50% inhibitory concentration values on germination of “Comet” were 70.5 and 7.5 mg L-1 for MIB and geosmin, respectively. We also conducted the primary characterization of the inhibition by MIB and geosmin on “Comet” seeds. Our findings were as follows: (1) onset of seed imbibition was not affected; (2) germination of seeds pre-imbibed in the control solution until approx. 2 h before germination onset was inhibited by subsequent MIB or geosmin treatment; (3) growth of seedlings was not significantly affected; (4) the germination was restored by stratification, gibberellin A3 treatment, or seed coat removal; and (5) light irradiation affected the degree of inhibition. These results suggest that inhibition by MIB and geosmin is restricted to the germination process, at least in the early stage of growth, that they act as growth -regulating substances.

Postharvest Gibberellin and Heat Treatment Effects on Polyamines, Abscisic Acid and Firmness in Lemons

ABSTRACTLemons at two ripening stages were vacuum‐infiltrated with 100 ppm of gibberellin A3 (GA3) or heat‐treated at 45°C, and then stored at 15°C for 3 wk. Both treatments increased fruit firmness either in stage 1 or in stage 2. Also, the levels of free putrescine and spermidine in the skin were higher in treated lemons than in controls but spermine concentration did not show significant differences, in fruits of either stage. GA3 treatment was the most effective in retarding the color change during storage, especially in stage 1 fruits, which was related to the lowest levels of abscisic acid found.

Roles of Soluble Sugars in Protecting Phytochrome- and Gibberellin A3-Mediated Germination Control in Skotodormant Lettuce Seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A3 (GA3). Soluble sugars in the imbibition solutions influenced the depth of skotodormancy. Ten-day DS seeds, imbibed in 50–500 mm sucrose or 100–500 mm glucose and given terminal GA3 germinated completely and germinated about 80% when imbibed in 100 mm galactose, mannose, lactose, or maltose. In contrast, terminal R applied to 10-day DS seeds caused only 20–50% germination. If given R at day 0 and imbibed for 10 days in darkness in 500 mm sucrose or glucose, seeds washed free of exogenous glucose or sucrose then germinated about 50% in darkness in water. These seeds responded to terminal R or GA3 with complete germination. When seeds were given FR at day 0, germination responses following terminal R or GA3 were significantly lower when the duration of DS was increased from 7–10 day DS to 15 days. In 10-day DS seeds given initial FR and imbibed in either solutions of 50 or 100 mm sucrose and KNO3, either terminal R or GA3 treatment gave complete or near complete germination. It is concluded that seed exposure to certain soluble sugars and/or nitrate during a 10-day DS protected certain substrates and thereby extended the sensitivity of the seeds to terminal R or GA3 treatment. The study provides substantial evidence for nonhormonal factors associated with light and GA action in the control of seed skotodormancy.

The roles of inorganic nitrogen salts in maintaining phytochrome- and gibberellin A3-mediated germination control in skotodormant lettuce seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A3 (GA3). Inorganic nitrogen salts in the imbibition solutions reduced seed skotodormancy. Ten-day DS seeds, imbibed in 25 mm salt solutions followed by terminal R, germinated 99% if imbibed in NH4NO3, 70% if imbibed in KNO3 or NH4Cl, and 55% if imbibed in NaNO3. Seeds imbibed in higher salt concentrations germinated fully upon terminal R treatment. Seeds imbibed in 25 mm NH4Cl or in 50 mm NH4NO3 germinated completely upon GA3 treatment. Osmotic effects of imbibition media accounted for only part of the effect, since seeds imbibed in 50 mm CaCl2 or NaCl germinated poorly following R or GA3 treatment. Seeds imbibed in 500 mm polyethylene glycol (PEG) 1000 or mannitol solutions for 10 days still exhibited skotodormancy. Treatments of R or GA3 did not stimulate germination in seeds imbibed in mannitol, but germination was complete if seeds were given 1-h acid immersion plus a water rinse before the terminal R or GA3 treatment. Seeds imbibed in 50–500 mm PEG during 10-day DS germinated significantly better in response to terminal R. Terminal GA3 significantly improved germination only in seeds imbibed at 500 mm PEG. Pfr appeared to function in mannitol-imbibed seed only after an acid treatment. Seed exposure to inorganic nitrogen salts during the 10-day DS maintained seed sensitivity to terminal R or GA3 treatment. The depth of seed skotodormancy was related to the availability of inorganic nitrogen and also involved the levels of Pfr or endogenous GA3.

FURTHER EXAMINATION OF GIBBERELLIN A, EFFECTS ON FLOWERING OF GLOBE ARTICHOKES (CYNARA SCOLYMUS L.) UNDER CONTROLLED ENVIRONMENT AND FIELD CONDITIONS

The effect of gibberellin A3(GA3) treatments on flowering of seed-grown globe artichoke (Cynara scolymus)was investigated under controlled environment and field conditions. GA3induced flower initiation in lines ‘060’ and ‘Talpiot’ under strictly noninductive, short-day-high-temperature conditions. In ‘Talpiot’, GA3induced microscopically detectable flower initiation but no stem elongation, suggesting involvement of gibberellins in the flower formation process. Under field conditions, GA3replaced the cold requirements of line ‘HU 271’, thereby enabling the start of flowering during autumn. The vegetative clone Bianca d'Espana flowered during autumn without GA3treatment, probably due to its minimum cold requirements. Definition of the response type and the role of gibberellins in the flowering of globe artichoke are discussed.

Geibberllin and temperature influence carbohydrate content and flowering in Phalaenopsis

When Phalaenopsis amabilis is grown under high temperature (30/25°C, day/night), flowering is blocked, and this can be reversed by gibberellin A3 (GA3) treatment. Associated with GA3 treatment under high temperature are increases in sucrose, glucose and fructose as compared with warm‐treated plants. Spraying with sucrose solution alone caused leaf epinasty in plants grown under high temperature. Epinasty was released by about 9 days of GA3 treatment. In GA3‐treated plants under high temperatures, sucrose application to the source leaves led to an increase in sugar content in both leaves and inflorescence. In contrast, although in warm‐treated plants sucrose application to the source leaves increased sugar content in the leaves, it did not increase sucrose content in the inflorescence. These results corroborate our hypothesis that in Phalaenopsis GA3 stimulates sink activity in the apical meristem and promotes the translocation of sucrose from source leaves to the apex of the inflorescence, where it accumulates. GA3 treatment led to an increase in sucrose synthase activity and had no effect on invertase activity.

Dormancy in peach (Prunus persica L.) flower buds

Peach buds (floral and vegetative) were periodically collected from midsummer until the spring flowering and sprouted under continuous light, 100% relative humidity and 20–25°C. Treatments with 200 ppm gibberellin A3 (GA3) or chilling (2–4°C for 30 days before planting) were applied. Vegetative buds showed well-defined phenological stages: pre-dormancy, “true dormancy”, and end of dormancy. Both GA3 and chilling treatments shortened the sprouting times of vegetative dormant buds close to those in predormancy. Isolated floral buds were irresponsive under all conditions and did not sprout even with the GA3 or chilling treatments. In a comparative study with buds immediately after collection anatomical analysis demonstrated that vegetative buds were almost completely developed by midsummer/early automn and remained in a resting state until the end of winter. Floral buds developed continuously over the same period. Both types of verticils began to differentiate in midsummer. Sepals and petals developed mainly in late summer, androecious floral parts developed throughout the resting period, while gynoecious floral parts showed differentiation in late winter. The flower was completely formed a few days prior to blossoming. Thus, in isolated peach buds fertile verticils are not sufficiently developed during the resting time to allow sprouting.