Endogenous Gibberellin Levels Research Articles

Effects of exogenous glycine betaine on growth and development of tomato seedlings under cold stress.

Low temperature is a type of abiotic stress affecting the tomato (Solanum lycopersicum) growth. Understanding the mechanisms and utilization of exogenous substances underlying plant tolerance to cold stress would lay the foundation for improving temperature resilience in this important crop. Our study is aiming to investigate the effect of exogenous glycine betaine (GB) on tomato seedlings to increase tolerance to low temperatures. By treating tomato seedlings with exogenous GB under low temperature stress, we found that 30 mmol/L exogenous GB can significantly improve the cold tolerance of tomato seedlings. Exogenous GB can influence the enzyme activity of antioxidant defense system and ROS levels in tomato leaves. The seedlings with GB treatment presented higher Fv/Fm value and photochemical activity under cold stress compared with the control. Moreover, analysis of high-throughput plant phenotyping of tomato seedlings also supported that exogenous GB can protect the photosynthetic system of tomato seedlings under cold stress. In addition, we proved that exogenous GB significantly increased the content of endogenous abscisic acid (ABA) and decreased endogenous gibberellin (GA) levels, which protected tomatoes from low temperatures. Meanwhile, transcriptional analysis showed that GB regulated the expression of genes involved in antioxidant capacity, calcium signaling, photosynthesis activity, energy metabolism-related and low temperature pathway-related genes in tomato plants. In conclusion, our findings indicated that exogenous GB, as a cryoprotectant, can enhance plant tolerance to low temperature by improving the antioxidant system, photosynthetic system, hormone signaling, and cold response pathway and so on.

Effect of Photoperiod and Gibberellin on the Bolting and Flowering of Non-Heading Chinese Cabbage

Non-heading Chinese cabbage (cabbage) is an essential green leafy vegetable, and bolting and flowering are necessary for reproduction. However, further research is needed to study the effect of photoperiod on the bolting and flowering of cabbage, particularly on the development of the stem. In this study, we performed phenotypic analysis and measured endogenous gibberellin levels in the cabbage. We carried out these experiments under four different photoperiodic treatments, 12 h (light)/12 h (dark), 14 h (light)/10 h (dark), 16 h (light)/8 h (dark), and 18 h (light)/6 h (dark). The results showed that the time of bolting and flowering gradually decreased with increasing light duration. The development of stems was optimal under the 16 h (light)/8 h (dark) photoperiod treatment, and the same result was obtained via cytological observation. In addition, the changes in the endogenous gibberellin3 (GA3) content under different photoperiodic treatments were consistent with the development of stems and peaked at 16 h (light)/8 h (dark). At the same time, qRT-PCR analysis showed that the relative expression of the key gibberellin synthase genes, BcGA3ox2 and BcGA20ox2, exhibited upregulation. When treated with exogenous GA3 and its synthesis inhibitor, paclobutrazol (PAC), exogenous gibberellins significantly promoted bolting; conversely, gibberellin inhibitors suppressed the bolting, flowering, and stem elongation of cabbage. Therefore, the photoperiod may regulate cabbage bolting by regulating endogenous GA3.

Somatic Embryogenesis in Spinach—A Review

A spinach-supplemented diet exerts numerous health benefits, but high levels of oxalic acid and nitrate can cause medical problems, so their levels should be reduced, while the levels of vitamins and phytochemicals could be further increased by breeding. Conventional spinach breeding is limited by the very complex sex determination. However, these limitations could be circumvented in synergy with a biotechnological approach. Accordingly, tissue culture techniques allow rapid and efficient clonal propagation of selected valuable genotypes, and somatic embryogenesis has been recognized as a superior process for clonal propagation because somatic embryos resemble zygotic embryos and therefore can spontaneously develop into complete plants. Since spinach has been considered recalcitrant to in vitro regeneration for decades, a deeper insight into the mechanisms underlying somatic embryogenesis is important for a better understanding and further improvement of the efficiency of this process. In this review, a comprehensive overview of the major factors affecting somatic embryogenesis in spinach is presented and discussed, with particular emphasis on the synergistic effects of α-naphthaleneacetic acid, gibberellic acid, light, and the intrinsic predisposition of individual seedlings to somatic embryogenesis, as well as the expression of genes encoding key enzymes involved in the maintenance of gibberellin homeostasis and the levels of endogenous gibberellins.

Linum usitatissimum FUSCA3–1 regulates plant architecture and seed storage reserve accumulation in Arabidopsis thaliana

Flax ( Linum usitatissimum L.) as a self-pollinated annual diploid crop is grown worldwide primarily for its seed storage reserves of oil and storage proteins. The B3 domain transcription factor AtFUSCA3 (AtFUS3) has been identified as a master regulator of seed storage reserve accumulation in Arabidopsis thaliana . However, the function of LuFUS3 from L. usitatissimum has not yet been assessed. Here, we found that there were two LuFUS3 homologs, LuFUS3–1 and LuFUS3–2, in the L. usitatissimum genome. The subcellular localization and yeast transcriptional activation assays indicated that LuFUS3–1 functions as a transcription factor. Heterogeneous expression of LuFUS3–1 in the A. thaliana wild type background changed the plant architecture, including moderately dwarf stature, wrinkled leaves, increased branch number, altered floral morphology, and shorter and wider siliques, which was at least partially caused by the significantly decreased level of endogenous gibberellins. On the other hand, we demonstrated that LuFUS3–1 enhances the accumulation of seed storage reserves inclusive of oil and storage proteins in A. thaliana seeds. Consistently, LuFUS3–1 promotes the expression of many genes involved in the biosynthesis of seed oil and storage proteins during seed development. These findings provide new insights into the FUS3 function in plant architecture and seed storage reserve accumulation, and also represent a promising target for genetic modification of L. usitatissimum . • LuFUS3-1 functions as a B3 domain transcription factor. • LuFUS3-1 regulates plant architecture at least dependent on gibberellin biosynthesis. • LuFUS3-1 promotes the accumulation of seed oil and storage proteins. • LuFUS3 boosts the expression of genes involved in seed oil and storage protein biosynthesis.

Functional Analysis of the Gibberellin 2-oxidase Gene Family in Peach.

Peach (Prunus persica L. Batsch) trees grow vigorously and are subject to intense pruning during orchard cultivation. Reducing the levels of endogenous gibberellins (GAs) represents an effective method for controlling branch growth. Gibberellin 2-oxidases (GA2oxs) deactivate bioactive GAs, but little is known about the GA2ox gene family in peach. In this study, we identified seven PpGA2ox genes in the peach genome, which were clustered into three subgroups: C19-GA2ox-I, C19-GA2ox-II, and C20-GA2ox-I. Overexpressing representative genes from the three subgroups, PpGA2ox-1, PpGA2ox-5, and PpGA2ox-2, in tobacco resulted in dwarf plants with shorter stems and smaller leaves than the wild type. An analysis of the GA metabolic profiles of the transgenic plants showed that PpGA2ox-5 (a member of subgroup C19-GA2ox-II) is simultaneously active against both C19-GAs and C20-GAs,which implied that C19-GA2ox-II enzymes represent intermediates of C19-GA2oxs and C20-GA2oxs. Exogenous GA3 treatment of shoot tips activated the expression of all seven PpGA2ox genes, with different response times: the C19-GA2ox genes were transcriptionally activated more rapidly than the C20-GA2ox genes. GA metabolic profile analysis suggested that C20-GA2ox depletes GA levels more broadly than C19-GA2ox. These results suggest that the PpGA2ox gene family is responsible for fine-tuning endogenous GA levels in peach. Our findings provide a theoretical basis for appropriately controlling the vigorous growth of peach trees.

Influence of Ethrel on sex expression in cucurbitaceous vegetables

Crops belonging to family Cucurbitaceae are generally known as ‘Cucurbits’. It consists of a wide range of vegetables either used for salad purpose. Majority of cucurbits are monoecious and sex ratio (male: female) ranges from 25-30:1 to 15:1. Sex ratio is influenced by environmental factors. High N content in the soil, long days and high temperature favour maleness. Besides environmental factors, endogenous levels of auxins, gibberellins, ethylene and abscisic acid also determine sex ratio and sequence of flowering. High ethylene level induces female sex and is suggested to increase female flowers in cucumber, musk melon, summer squash and pumpkin. This review enumerates the detailed information on the effect of ethrel, a ripening hormone, on sex expression in cucurbitaceous vegetables.

Increased endogenous gibberellin level inhibits root growth of Pinus massoniana Lamb. plantlets during long-term subculture

In this study, we investigated the roles of the plant hormones indole-3-acetic acid (IAA) and gibberellin (GA) in regulating Pinus massoniana Lamb. plantlet regeneration during long-term in vitro subculture. Six generations (1st, 5th, 10th, 20th, 30th and 40th with 40 days for each transfer cycle) of subcultured shoots derived from mature and juvenile explants were characterised for their different rooting capacities. In the present experiment, shoots were subcultured on rooting medium containing indole-3-acetic acid (IAA), naphthaleneacetic acid (NAA) or gibberellin (GA) inhibitor (paclobutrazol, PBZ). In addition, high-performance liquid chromatography (HPLC) was used to analyse endogenous hormone levels in shoots developed on medium with low concentrations of NAA. The concentration of endogenous IAA was highest in the 20th generation shoots, which also exhibited the strongest rooting ability. However, the highest GA concentration was observed in the 40th generation shoots, which exhibited a poor rooting capacity. For shoots subcultured for 40 generations, incubation on rooting medium containing IAA caused an enhanced root number, shoot length and survival rate. This suggested that the effects of IAA on shoot and root formation were positive. PBZ promoted plantlet regeneration from in vitro cultures but impaired shoot elongation at high levels. Furthermore, PBZ improved performance of in vitro cultures after long-term (3 to 4 y) subculture. These results suggest the inhibitory role of a high endogenous GA level in plant regeneration and the use of appropriate levels of PBZ for plant regeneration of P. massoniana.

TDIF overexpression in poplars retards internodal elongation and enhances leaf venation through interaction with other phytohormones.

As a member of the CLAVATA3 (CLV3)/EMBRYO SURROUNDING REGION-related (CLE) peptide family, tracheary element differentiation inhibitory factor (TDIF) plays crucial roles in vascular meristem maintenance by promoting cell proliferation and inhibiting xylem cell differentiation. In Populus trichocarpa, six TDIF-encoding genes are all expressed in vascular tissues, and in Arabidopsis PtTDIFpro:GUS lines, the expression driven by PtTDIF promoters were predominantly detected in stem vascular bundles, initiating leaves and leaf veins. Although exogenous application of two poplar TDIF peptides did not evidently affect the shoot growth in vitro, overexpression of PtTDIF genes in hybrid poplar severely retarded the internodal elongation by upregulating the expression of GA2ox and GA20ox genes and thus decreasing the level of endogenous gibberellins (GAs), which phenotypic defect could be rescued by exogenously applied GA3. In addition, TDIF overexpression unexpectedly induced a more complex venation pattern in poplar leaves, which was underpinned by the elevated expression of WOX4 and WOX13 genes. Upon TDIF treatment, the DR5:GUS poplar leaves revealed a higher GUS activity and in TDIF-overexpressing leaves, the transcript abundances of several PIN-FORMED (PIN) genes, especially that of PIN1, were increased, which implied an integration of TDIF and auxin in mediating this process. Collectively, data of this work presented novel activities of TDIF involved in internode elongation and leaf vein formation, thus revealing the divergent functions of TDIF in perennial tree species from those in annual herbaceous Arabidopsis.

Development of dwarfish and yield-effective GM maize through passivation of bioactive gibberellin.

During the Green Revolution in the 1960s, breeding dwarf cultivars turned out to be a landmark, leading to a significant increase in the global production of wheat and rice. The most direct and effective strategy for breeding dwarf crops, among others, would be to control endogenous gibberellin (GA) levels of the crops. GA 2-oxidases are a group of 2-oxoglutarate-dependent dioxygenases that catalyze the deactivation of bioactive GAs. The ArabidopsisAtGA2ox1 gene was transformed into maize with the aim of obtaining a height-reduced GM maize. The characterization of the GM maize revealed that the highest plant height reduction was accomplished by a 74% decline in GA1 level, and by approximately twofold increases in both chlorophyll content and root/shoot ratio over the wild-type (WT). Interestingly, the stem cells of the GM maize were condensed, and the typical vascular bundle structure was found to be deformed. Based on a 2-season field trial, the GM maize exhibited a higher harvest index (9-17%) and grain yield (10-14%) than the WT. The current results suggest that a modulation of the endogenous GA level would be a sensible approach for improving the crop architecture and grain yield in maize.

Hormonal interactions during early physiological partenocarpic fruitlet abscission in persimmon (Diospyros Kaki Thunb.) ‘Triumph’ and ‘Shinshu’ cultivars

Fruitlet abscission is typical to many fruit trees, including persimmon, (Diopyros kaki Thunb.), and often results in unstable fruit production and yield. We documented massive parthenocarpic fruitlet abscission in the persimmon cultivars 'Triumph' and 'Shinshu', which initiated soon after anthesis and peaked at 45 days post anthesis. In contrast, abscission of mature fruitlets 45–65 days after anthesis was minor. The early parthenocarpic fruitlet abscission in 'Shinshu' and 'Triumph' took place in the abscission zone located at the calyx-pedicel junction. Differentiation of the abscission layer occurred during flower development and preceded fruitlet abscission. Endogenous analysis of gibberellins, cytokinins and auxin levels in the abscission zone of 'Triumph' and 'Shinshu' during the developmental stages preceding abscission revealed a reduction in cytokinin endogenous levels in both cultivars. In addition, a decline in GA3 and IAA levels was found in 'Triumph' and 'Shinsu' respectively during flower development. Gibberellin, auxin and cytokinin application to inhibit early fruitlet abscission were analyzed and gibberellin treatment exhibited the highest and most consistent inhibition effect in 'Triumph' and 'Shinshu'. An increase in endogenous levels of gibberellins, cytokinins and auxin in the flower abscission zone was found following GA application in both cultivars. Our results suggest that gibberellin application inhibits early fruitlet abscission by elevating cytokinins, and auxin levels and that a reduction in gibberellins, cytokinins and auxin levels may induce abscission during parthenocarpic fruitlet development in 'Shinshu' and 'Triumph' cultivars.

Effects of gibberellic acid on photosynthesis and endogenous hormones of Camellia oleifera Abel. in 1st and 6th leaves

ABSTRACTTo investigate the effects of gibberellic acid (GA) on photosynthesis, nutrient partitioning and endogenous hormones at different leaf locations (1 and 6), Camellia oleifera was treated with four levels of GA (0, 100, 200 and 300 mg L−1) during the flower bud physiological differentiation stage. GA increased the net photosynthetic rate (Pn), chlorophyll content and chlorophyll fluorescence parameters of 1st and 6th leaves. The 100 mg L−1 dose was most effective for increasing the total chlorophyll content and Pn, which increased by 100.00% and 59.55%, respectively, in the 1st leaf, and 110.18% and 44.90%, respectively, in the 6th leaf compared with the control. The 100 and 200 mg L−1 GA solutions decreased the starch and soluble sugar levels in both 1st and 6th leaves, but increased those of the 1st and 6th buds which suggested that exogenous GA promotes the transportation of photosynthetic products from leaves to buds with the regulation of a sink–source relationship. Endogenous levels of gibberellin and auxin increased, but abscisic acid decreased in the 1st and 6th leaves after GA applications. The Pn was positively correlated with the total chlorophyll content (0.922 for 1st leaf and 0.944 for 6th leaf) and fluorescence parameters, but negatively correlated with soluble sugar and starch contents in 1st (−0.940 and −0.875, respectively) and 6th (−0.866 and −0.854, respectively) leaves. The difference in responses of leaves at different positions to exogenous GA due to the physiological differences of the leaves themselves.

Studies on mechanism of germination of photoblastic lettuce seeds : Regulation of endogenous levels of gibberellins and abscisic acid(The JSCRP Award for the Encouragement of Young Scientists)

Studies on mechanism of germination of photoblastic lettuce seeds : Regulation of endogenous levels of gibberellins and abscisic acid(The JSCRP Award for the Encouragement of Young Scientists)

Effect of exogenous Brassinolide (BR) application on the morphology, hormone status, and gene expression of developing lateral roots in Malus hupehensis

Malus hupehensis seedlings were treated with exogenous applications of 0.5 mg L−1 brassinolide (BR) in order to investigate the mechanism by which BR promotes and effects lateral root development. Root morphology, plant height, plant crown diameter, and endogenous levels of Brassinolide (BR), Auxin (IAA), Abscisic acid (ABA), and Gibberellin (GA3) in lateral roots were evaluated. Additionally, differential gene expression of genes related to root development were examined in treated and untreated roots by RT-qPCR during lateral root development. Results indicated that BR treatment promoted both root and shoot growth and auxin levels increased, while ABA and GA3 declined. Additionally, there was also a significant upregulation in the expression of MdBAK1, MdBRI1, and MdBZR1 in response to the BR treatment. Transcript levels of key auxin synthesis and transport genes, such as MdYUCCA6, MdYUCCA10, MdPIN1, MdPIN2, MdPIN3, which corresponded with higher auxin levels in the BR-treated samples. MdIAA23 were induced, but the expression of MdIAA5, a negative regulator of MdARF7 and MdARF19, was downregulated in BR-treated apple seedlings, leading to an elevated expression of MdARRO1; which in turn increased lateral root development. On the other hand, MdBRI1 induced MdWOX5 expression, resulting in enhanced expression of the cell cycle related genes: MdCYCD1;1, MdCYCD3;1, and MdCYCD3;2; leading to upregulated expression of MdLBD29. Collectively, the changes in gene expression and hormone levels resulted in an increased number of lateral roots, and other growth characteristics in BR-treated plants.

Natural Variation of Molecular and Morphological Gibberellin Responses.

Although phytohormones such as gibberellins are essential for many conserved aspects of plant physiology and development, plants vary greatly in their responses to these regulatory compounds. Here, we use genetic perturbation of endogenous gibberellin levels to probe the extent of intraspecific variation in gibberellin responses in natural accessions of Arabidopsis (Arabidopsis thaliana). We find that these accessions vary greatly in their ability to buffer the effects of overexpression of GA20ox1, encoding a rate-limiting enzyme for gibberellin biosynthesis, with substantial differences in bioactive gibberellin concentrations as well as transcriptomes and growth trajectories. These findings demonstrate a surprising level of flexibility in the wiring of regulatory networks underlying hormone metabolism and signaling.

Regulatory Networks in Pollen Development under Cold Stress.

Cold stress modifies anthers’ metabolic pathways to induce pollen sterility. Cold-tolerant plants, unlike the susceptible ones, produce high proportion of viable pollen. Anthers in susceptible plants, when exposed to cold stress, increase abscisic acid (ABA) metabolism and reduce ABA catabolism. Increased ABA negatively regulates expression of tapetum cell wall bound invertase and monosaccharide transport genes resulting in distorted carbohydrate pool in anther. Cold-stress also reduces endogenous levels of the bioactive gibberellins (GAs), GA4 and GA7, in susceptible anthers by repression of the GA biosynthesis genes. Here, we discuss recent findings on mechanisms of cold susceptibility in anthers which determine pollen sterility. We also discuss differences in regulatory pathways between cold-stressed anthers of susceptible and tolerant plants that decide pollen sterility or viability.

Bud vigor, budburst lipid peroxidation, and hormonal changes during bud development in healthy and moribund beech (Fagus sylvatica L.) trees

Key message Despite meristem totipotency, epicormic branches from moribund trees produce buds with less vigor and increased lipid peroxidation compared to those of healthy trees. Abstract A better understanding of the factors governing bud vigor and development, and their underlying mecha- nisms is essential for management of broad-leaved stands, of which oaks and beeches are among the most important species. This study investigated possible differences in leaf bud vigor and development in healthy and moribund beech trees. Leaf buds on shaded branches found in the under- story of a natural beech stand in Catalonia (NE Spain) were used for comparison. The vigor, extent of lipid peroxida- tion, and hormonal profile of leaf buds of healthy and moribund beech trees were investigated. Results showed less bud vigor in moribund trees than in healthy ones. In the former, there was increased lipid peroxidation at bud- burst. Although endogenous levels of gibberellins, cytoki- nins, and auxin were significantly influenced by bud development in both tree types, buds of moribund trees showed markedly different dynamics in the endogenous concentrations of auxin, abscisic acid and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid. We conclude that moribund trees (a) are less efficient in pro- ducing new leaves, as indicated by less bud vigor and greater lipid peroxidation at budburst than healthy trees and (b) show a marked differential hormonal pattern during bud development compared to healthy trees.

Effect of plant growth regulators on calyx abscission, fruit quality, and auxin-repressed protein (ARP) gene expression in fruitlets of ‘Dangshansuli’ pear (Pyrus bretschneideri Rehd.)

SummarySepals of a pome fruit flower are collectively called the calyx. Calyxes may be shed to produce calyx-shed fruit (CSF), or remain to produce calyx-persistent fruit (CPF). To investigate the relationship between calyx shedding and phytohormone concentrations in fruitlets and fruit quality in ‘Dangshansuli’ pear (Pyrus bretschneideri Rehd.), endogenous levels of gibberellins, indole-3-acetic acid, abscisic acid, and zeatin riboside were measured in CSF and CPF at different stages of development. Manual excision of the calyx at an early stage of fruitlet development was also performed. The auxin-repressed protein gene (ARP) was cloned, and relative levels of ARP gene expression were determined in fruitlets on trees treated by spraying separately with water (control) or each of the plant growth regulators (PGRs) gibberellic acid (GA3), paclobutrazol (Pac), or 1-naphthaleneacetic acid (NAA) using real-time quantitative reverse transcription-PCR. The results indicated that manual calyx excision at an early stage of fruit development altered only the shape and appearance, but not the inner quality of the fruit. Higher endogenous levels of all gibberellins in fruitlets at 10 - 20 d after full bloom (DAFB) played an important role in calyx persistency on fruitlets. The ARP gene was cloned from fruitlets of ‘Dangshansuli’ pear and named PbARP. The full-length cDNA was 707 bp with a 5'-untranslated region (UTR) of 40 bp, a 3'-UTR of 316 bp, and a coding region of 351 bp, encoding a deduced polypeptide containing 116 amino acids.GA3 [100 mg l-1 of 90% (w/w)] inhibited expression of the PbARP gene and increased calyx persistency, whereas 100 mg l-1 of 15% (w/w) Pac enhanced PbARP gene expression and accelerated calyx shedding. Higher levels of PbARP gene expression in fruitlets of ‘Dangshansuli’ pear were associated with calyx shedding.The percentage of CSF increased by > 20% following treatment with 100 mg l-1 of 15% (w/w) Pac, 100 ml l-1 of an emulsifiable concentrate of 40% (w/v) flusilazole (Fls), a mixture of 100 mg l-1 of 15% (w/w) Pac plus 50 mg l-1 of 99% (w/w) benzylaminopurine (BA), or a mixture of 100 ml l-1 of 40% (w/v) Fls plus 50 mg l-1 of 99% (w/w) BA, with no significant difference in fruit set percentage or fruit quality. Persistence or shedding of the calyx in pear fruit is therefore an epigenetic trait that can be regulated by the application of PGRs.

Reduction of Gibberellin by Low Temperature Disrupts Pollen Development in Rice

Microsporogenesis in rice (Oryza sativa) plants is susceptible to moderate low temperature (LT; approximately 19°C) that disrupts pollen development and causes severe reductions in grain yields. Although considerable research has been invested in the study of cool-temperature injury, a full understanding of the molecular mechanism has not been achieved. Here, we show that endogenous levels of the bioactive gibberellins (GAs) GA4 and GA7, and expression levels of the GA biosynthesis genes GA20ox3 and GA3ox1, decrease in the developing anthers by exposure to LT. By contrast, the levels of precursor GA12 were higher in response to LT. In addition, the expression of the dehydration-responsive element-binding protein DREB2B and SLENDER RICE1 (SLR1)/DELLA was up-regulated in response to LT. Mutants involved in GA biosynthetic and response pathways were hypersensitive to LT stress, including the semidwarf mutants sd1 and d35, the gain-of-function mutant slr1-d, and gibberellin insensitive dwarf1. The reduction in the number of sporogenous cells and the abnormal enlargement of tapetal cells occurred most severely in the GA-insensitive mutant. Application of exogenous GA significantly reversed the male sterility caused by LT, and simultaneous application of exogenous GA with sucrose substantially improved the extent of normal pollen development. Modern rice varieties carrying the sd1 mutation are widely cultivated, and the sd1 mutation is considered one of the greatest achievements of the Green Revolution. The protective strategy achieved by our work may help sustain steady yields of rice under global climate change.

Studies on the role of gibberellins in the regulation of spermatogenesis in Chara vulgaris L.

Antheridia from isolated nodes of Chara vulgaris, developing in the presence of either AMO-1618 or GA<sub>3</sub>, were studied. AMO-1618 which lowers the level of endogenous gibberellins causes a significant, proportional to the concentration, reduction in: 1) the number of antheridial filaments formed in antheridia, 2) spermatid number within a filament, as a result of eliminating one mitotic division at the first stage of spermatogenesis. Exogenous GA<sub>3</sub> at the concentration 10<sup>-5</sup> M evokes opposite effect i.e. increase in the number of antheridial filaments and increase in the number of spermatids within filament. Total number of spermatids within an antheridium decreases under the influence of 10<sup>-4</sup>M AMO-1618 three times in comparison with the control, whereas it increases twice following 10<sup>-5</sup>M GA<sub>3</sub> treatment. It has been suggested that the normal course of spermatogenesis requires precisely determined level of endogenous gibberellins.

Effects of gibberellic acid and AMO-1618 on the development of vegetative systems in generatively matured thalli of Chara vulgaris L.

Effects of GA<sub>3</sub> (10<sup>-11</sup>-10<sup>-4</sup> M) and AMO-1618 (10<sup>-6</sup>-10<sup>-4</sup> M) on the development of generatively matured thalli of <em>Chara vulgaris</em> were investigated during 21-day culture of plants in axenic conditions. It has been found that in the main bud the divisions of apical cells of the thalli are not stimulated by GA<sub>3</sub>, whereas in the lateral buds the cell divisions are stimulated by higher GA<sub>3</sub> concentrations. Subsequent mitotic activity of the apical cells in the branches of the main axis is not stimulated by GA<sub>3</sub>, whereas the lateral buds of these branches are activated. The development of rhizoids in younger nodes is accelerated by high GA<sub>3</sub> concentrations. The elongation of the polynuclear, internodal cells of the main axis and that of pleuridia are inhibited proportionally to the GA<sub>3</sub> concentration. AMO-1618 stimulates the development of new nodes, elongation of internodes and delays the activation of lateral buds as well as the formation of rhizoids. These results suggest that the GA<sub>3</sub>-induced inhibition of elongation of the thalli and diminution of the apical domination is connected with a high level of endogenous gibberellins in the generatively matured thallus.