Role Of Gibberellins Research Articles

Free and Bound Gibberellin Activities and Ent‐kaurene Synthesis during Induction of Cold Hardiness in Black Locust Seedlings

AbstractThe role of gibberellin in the development of cold hardiness in black locust (Robinia pseudoacacia L.) seedlings was investigated. Free and bound gibberellin activities were followed during induction of cold hardiness using ethyl acetate partitioning and pH variation, with subsequent paper chromatographic fractionation and gibberellin bioassay. While total gibberellin activity decreased during the induction of cold hardiness in black locust seedlings, no convincing evidence was found to support conversion of free gibberellin to a bound form. However, bound gibberellin activity did appear to be more stable than did free gibberellin activity during the final stages of cold hardening at freezing temperatures. Gibberellin synthesis was followed using 14C‐mevalonate conversion to ent‐kaurene in a cell‐free extract of the tissue. Ent‐kaurene synthesis decreased during cold hardening with no detectable synthesis in fully hardened seedlings. However, since growth cessation precedes development of cold hardiness, decreased gibberellin synthesis and corresponding trends in free and bound fractions might have been expected, and a cause and effect relationship is difficult to establish. Even so, a decline in one step in gibberellin synthesis and a greater stability of bound than free gibberelin activity are associated with induction of cold hardiness in black locust seedlings.

The Role of Gibberellin, Abscisic Acid, and Auxin in the Regulation of Developing Wheat Grains

The Role of Gibberellin, Abscisic Acid, and Auxin in the Regulation of Developing Wheat Grains

Involvement of Endogenous Gibberellins in the Chilling Requirements of Strawberry (Fragaria×ananassa Duch.)

Plants of Fragaria ananassa Duch. cvs Tioga and Fresno were chilled in a cold store at -1 °C for 2-8 months, after which they were transferred to short-day (SD) and long-day (LD) growth chambers. Chilling promoted subsequent vegetative development, as expressed through leaf area, petiole length and stolon production, but inhibited the formation of inflorescences. Leaf area and petiole length responses appeared to be almost saturated by 2 months' chilling. The increase in stolon production and the reduction in inflorescence formation came into full expression with longer periods of chilling. Application of gibberellin A3 (GA3) to plants pre-chilled for 2 months had little effect on leaf area or petiole length but promoted stolon production and retarded the formation of inflorescences. AMO-1618 applied to plants pre-chilled for 4 months antagonized the chilling responses. The level of diffusible gibberellin-like substances from crown apices remained low during most of the chilling period but increased markedly after 6-8 months of chilling, when plants approached spontaneous sprouting in the cold store. Plants pre-chilled for 2 months had low levels of gibberellin-like substances which increased several fold upon transfer to the growth chambers. This increase was somewhat delayed in plants treated with AMO-1618. The role of gibberellins in the responses of strawberry plants to chilling is discussed.

Primary, preventive and permissive roles of hormones in plant systems

The discovery that cytokinins oppose the actions of seed germination inhibitors provided a powerful conceptual tool in designing new hypotheses and in interpreting old ones. By using highly specific gibberellin-mediated seed processes, it was shown that gibberellins, inhibitors and cytokinins have primary, preventive and permissive roles respectively in the control of seed germination. We can now explain for the first time that seed dormancy can occur not only in presence of inhibitors as was generally believed but in many cases in absence or presence of promotors such as gibberellins or cytokinins. Thus, the uniqueness of the hormonal model presented lies in the effective use of the concept of designated functions of hormones in the control of seed germination. Cytokinin-inhibitor antagonism is not limited to seed systems but occurs in other systems, as well, including lateral bud growth and growth of tissues in culture. Evidence presented supports the hypothesis that auxin is the primary stimulus in the control of bud growth and growth of tissues in culture while the roles of gibberellins, cytokinins and inhibitors are secondary. Gibberellin appears to act after auxin has initiated growth in these systems. The highly selective roles of hormones in plant systems explains such anomalous situations as continued rapid growth in presence of high levels of inhibitors and lack of growth in spite of the presence of large amounts of cytokinins, gibberellins or auxins. Cytokinin-inhibitor antagonism and selective actions of hormones have also been shown at the level of nucleic acid and enzyme synthesis suggesting that both transcriptional and translational mechanisms might be involved.

The role of gibberellin in hypocotyl extension of dark-growing Lupinus albus seedlings

Six authentic gibberellins marginally promoted hypocotyl lengthening of etiolated lupin seedlings whereas extracted lupin "gibberellin-like" compounds were ineffective. However, dwarfing by AMO-1618 [2'-isopropyl-4'-(trimethyl-ammonium chloride)-5'-methylphenyl piperidine carboxylate] was totally counteracted by co-application with GA3 and partially overcome by extracted lupin "gibberellins". Meaningful quantities of free extractable and diffusible gibberellins were detected; "bound" gibberellin activity was not found. The time-course of the decline in extractable gibberellin levels during the process of dwarfing showed a significant difference from 6 h after applying AMO-1618. It is suggested that axis growth is dependent on gibberellin in a system normally close to saturation for endogenous growth.

The Role of Gibberellins in Early Growth and Development of Sugar Beet

Two gibberellin(GA)-like compounds were found in both roots and shoots of sugar beet plants using the barley endosperm bioassay. One had chromatographic properties similar to GA3 and GA1; the other was highly non-polar, relatively inactive in the endosperm assay, and may be a new gibberellin. Presence of the GA3/1-like compound was confirmed with the dwarf rice bio-assay. The quantity of this GA was relatively high in the root compared with the shoot at the 3–4 leaf stage when the first supernumerary cambia are being formed in the root. As plants developed through the 8–9 leaf stage and the 15–16 leaf stage the quantity of GA per unit fresh weight of material decreased. Application of gibberellic acid (GA3) to the roots of young sugar beet plants caused a significant increase in root dry weight shortly after treatment and the rate at which supernumerary cambia were produced was increased. Application of GA3 to a single petiole caused a significant increase in both root and shoot dry weight. GA3 applied to either root or shoot caused a reduction in the rate of leaf formation although total leaf area per plant and shoot dry weight were unaffected. The probable role of GA-like substances in controlling the growth and development of young sugar beet plants is discussed.

Endogenous Gibberellins in Marchantia polymorpha and Their Possible Physiological Role in Thallus Elongation and Orthogeotropic Growth

Gibberellin activity was detected in vegetative Marchantia polymorpha. Increasing the photoperiod from 12 to 18 hours elicited quantitative differences in the activity of these gibberellins. Such changes were associated with increased thallus elongation and orthogeotropic growth in the 18-hour tissue. Gibberellin antagonists reduced the endogenous gibberellin levels and retarded both thallus elongation and erect growth. The physiological implications of this response and the role of gibberellins in thallus elongation are considered. The role of auxins in mediating geotropic curvature is widely recognized. Halevy et al. (1969), however, reported that gibberellin treatment caused certain varieties of peanut plants that possessed normally diageotropic branches to become orthogeotropic. The branch angle increased from a range of 0-25 degrees to one of 50-60 degrees. Such angles were similar to those normally found in peanut varieties that exhibited an erect growth habit. Furthermore, 2-(chloroethyl)-trimethyl-ammonium chloride (CCC) and 2-isopropyl-4-dimethylamino-5-methylphenyl-l-piperdine carboxylate methyl chloride (Amo 1618) inhibited this negative geotropic response. An analysis of the gibberellin content of the two different growth forms indicated that both quantitative and qualitative variations occurred. Recent experiments with sunflower (Phillips, 1972a) and corn (Phillips, 1972b) demonstrated that variations in endogenous gibberellin concentrations were associated with geotropism. In both species, the level of gibberellin transport was ten times greater in the ventral half of a horizontal shoot. Significant concentration differences were also associated with strong phototropic stimuli. Gibberellin levels were eight times higher on the shaded side of the shoot than on the lighted side. Fredricq and DeGreef (1968) observed that under short day conditions (12 hours light) thalli grew prostrate, but that when the light period was extended to 18 hours, the habit became erect. The physiological nature of this response was not apparent from their experimental data. There is some evidence that exogenous gibberellins can influence growth in bryophytes. Asprey et al. (1958) demonstrated that seta elongation in the sporophyte of Pellia epiphylla could be induced under short day conditions if the plant was treated with auxins or gibberellins. In fact treatment with either hormone, or with the two hormones simultaneously, elicited different responses. This suggests that gibberellin may promote auxin-mediated elongation, possibly through the 1Department of Biology, Lawrence University, Appleton, Wisconsin 54911. This content downloaded from 157.55.39.197 on Sun, 11 Dec 2016 04:34:27 UTC All use subject to http://about.jstor.org/terms 34 THE BRYOLOGIST [Volume 77

The role of gibberellins in the growth of floral organs of <italic>Pharbitis nil</italic>

Evidence that the synthesis of GA3 is involved in the growth of floral orga'ns of Pharbitis nil is presented. GAs in floral organs at different developmental stages were surveyed using TLC followed by the bioassay with two dwarf rice seedlings, ‘Tanginbozu’ and ‘Waito-C’. The amount of GAs in the petal and stamen increased rapidly after the petal emerged from calyx, reached a maximum 12 hr before anthesis, then declined markedly thereafter. The GA content in the calyx remained unchanged before and after anthesis, and that in the pistil increased after anthesis. Pharbitis flowers contained at least two active GAs, one of which was probably GA3, the other appeared to be GA19. GA3 was detected in relatively large amounts in both the petal and stamen during their rapid elongation. In the calyx, which showed little increase in fresh weight during rapid flower growth, GA9 was the dominant GA. Exogenously supplied GA3 promoted elongation of sections in excised young filaments. Sucrose was necessary for definite growth promotion by GA3. GA19 had little effect on filament elongation, and IAA was rather inhibitive.

Role of Gibberellins in Stem Elongation and Flowering in Radish

The relationship among gibberellins, CCC, vernalization, and photoperiod in the flowering response of radish, Raphanus sativus L., cv. Miyashige-sofuto, was studied. The optimal condition for flowering was vernalization and a 16-hour photoperiod; GA(3) had no additional effect. Gibberellin A(3) (60 mug total) was not able to induce flowering in nonvernalized plants grown on 8-hour days, but it did increase the percentage of nonvernalized plants that flowered under long days from 60 to 100.Gibberellin content of vernalized seedlings increased within the first 24 hours after seedlings were transferred to the greenhouse. Content reached a peak in the first 4 days after transfer and thereafter remained constant. Essentially no gibberellin was found in 2 day-old non-vernalized (control) seedlings of comparable size to the vernalized ones. Gibberellin content in the controls reached a peak on the fourth day of growth in the greenhouse; thereafter, it decreased steadily.Bolting was inhibited slightly by CCC when applied during vernalization; it was almost completely inhibited when CCC was applied after seed vernalization. Extraction experiments revealed that CCC actually reduced the gibberellin content when applied during or after vernalization. The dwarfing agent, however, had essentially no effect on flowering. We concluded that gibberellins likely play a direct role in bolting of ;Miyashige-sofuto' radish, but probably are not directly functional in initiating flowering.

Expansion growth of isolated leaf blades of Todea barbara

Etiolation of Todea barbara sporophytes and the subsequent deetiolation of excised leaf blades have been studied. In etiolated plants leaf blade growth is arrested, petiole and stem growth is enhanced, and root growth is decreased. De-etiolation permits the resumption of leaf blade growth and differentiation, and the resulting de-etiolated blade appears comparable to its light-grown counterpart in every respect but cell number. Only two factors are required to attain maximum surface area growth in cultured leaf blades; these are light and sucrose. The addition of plant growth substances does not increase the final area attained. However, the inhibition of leaf blade growth with growth retardants and its partial reversal by exogenously supplied gibberellic acid demonstrates a role for gibberellins in leaf expansion in Todea.

THE EFFECTS OF GIBBERELLIC ACID AND CYCOCEL ON THE GROWTH OF CULTURED LEAF TISSUE

Meristematic sections of Pteris cretica var. wimsetti leaves were cultured in various nutrient media. Gibberellic acid (GA), in the presence of sucrose, brought about a significant increase in area compared with controls over a 4-week period. GA also prolonged meristematic activity for up to 8 months, the tissue increasing many times in area and dry weight during this interval. GA significantly increased total cell number, while having no effect on the size of individual epidermal cells. Cycocel ((2-chloroethyl) trimethylammonium chloride) strongly inhibited the growth of leaf sections, but this inhibition was completely reversed by GA. The possible role of gibberellins in leaf morphogenesis is discussed.

The Roles of Gibberellin and Auxin in Cucumber Hypocotyl Growth

The Roles of Gibberellin and Auxin in Cucumber Hypocotyl Growth

The Chemical Regulation of the Dormancy Phases of Bud Development

literature pertaining to the development and regulation of dormancy in the buds of woody species is reviewed and interpreted as follows. Morphological observations, the effects of environmental factors, and other evidence support the concept that bud dormancy involves a cycle of 3 separate phases of development. Beginning at the developmental pattern of spring, the 3 phases are: (1) dormancy development leading to the dormant state; (2) release from dormancy leading to the non-dormant state; and (3) the initiation of spring burst leading again to spring development. The regulation of dormancy is, therefore, discussed in terms of the regulation of development of the apex within each phase and the regulation of transitions between phases. The principal existing theory of dormancy regulation implies that dormancy consists, in total, of merely the inhibition of spring development, and that regulation involves first the accumulation of an inhibitor then its disappearance. The conceptual basis of this inhibitor theory is argued to be inadequate as is the experimental evidence for the existence of a specific inhibitor and for a correlation between its concentration and dormancy induction or release. There is little direct evidence on the mechanism of the regulation of bud development within any developmental phase. Circumstantial evidence suggests the developmental patterns arise from chemical patterns resulting from the interactions of classes of growth regulator such as auxin, kinin, and gibberellin. Some evidence exists concerning the regulation of the transitions between the phases of dormancy. A substance has recently been detected which may be a hormone regulating the initiation of dormancy development. The production of this substance may be photoperiodically determined. A role for gibberellins in the regulation of dormancy release has been postulated.

THE CHEMICAL REGULATION OF THE DORMANCY PHASES OF BUD DEVELOPMENT

literature pertaining to the development and regulation of dormancy in the buds of woody species is reviewed and interpreted as follows. Morphological observations, the effects of environmental factors, and other evidence support the concept that bud dormancy involves a cycle of 3 separate phases of development. Beginning at the developmental pattern of spring, the 3 phases are: (1) dormancy development leading to the dormant state; (2) release from dormancy leading to the non‐dormant state; and (3) the initiation of spring burst leading again to spring development. The regulation of dormancy is, therefore, discussed in terms of the regulation of development of the apex within each phase and the regulation of transitions between phases. The principal existing theory of dormancy regulation implies that dormancy consists, in total, of merely the inhibition of spring development, and that regulation involves first the accumulation of an inhibitor then its disappearance. The conceptual basis of this inhibitor theory is argued to be inadequate as is the experimental evidence for the existence of a specific inhibitor and for a correlation between its concentration and dormancy induction or release. There is little direct evidence on the mechanism of the regulation of bud development within any developmental phase. Circumstantial evidence suggests the developmental patterns arise from chemical patterns resulting from the interactions of classes of growth regulator such as auxin, kinin, and gibberellin. Some evidence exists concerning the regulation of the transitions between the phases of dormancy. A substance has recently been detected which may be a hormone regulating the initiation of dormancy development. The production of this substance may be photoperiodically determined. A role for gibberellins in the regulation of dormancy release has been postulated.

The role of gibberellin in the Control of Pea growth by Temperature

a) Alaska peas were grown in greenhouses maintained at various temperatures, and the effects of periodic treatments with different levels of gibberellic acid on growth and on fresh and dry weight accumulation were measured. Early seedling growth was most rapid at higher temperatures. Gibberellic acid promoted seedling growth at all temperatures. b) Later vegetative growth was most rapid at the lower temperatures. At low temperatures gibberellic acid did not increase the growth rate during this stage, but it did increase growth at high temperatures to a rate approaching that attained at the lower temperatures. c) Gibberellic acid delayed but did not prevent the onset of maturity. d) In complete darkness seedling growth was not influenced by gibberellic acid at any temperature from 10° to 30°. e) Adenine had no significant effect on stem growth or on the onset of maturity at 30° under fluorescent light. f) Gibberellin controls pea seedling growth in response to light but not with respect to temperature. Gibberellin participates in the control of stem growth of older plants, limiting growth in light at high temperatures. It affects but does not control the onset of maturity in these plants.