Clonal plant production from self- and cross-pollinated seed families of <Emphasis Type="Italic">Pinus sylvestris</Emphasis> (L.) through somatic embryogenesis

Several factors affecting somatic embryogenesis (SE) in Pinus sylvestris from self- and cross-pollinated seed families were studied with the aim of producing large quantities of clonal plants. Somatic embryogenesis initiation from zygotic embryos was improved on a medium with lower than standard concentrations of 2,4-dichlorophenoxyacetic acid (2.2 vs. 9.5 μM) and 6-benzyladenine (2.2 vs. 4.5 μM). On this medium, initiation rates of four controlled crosses, including one self-cross, varied from 3% to 25%. Among the maturation factors tested, the concentration of abscisic acid (ABA 80, 120 μM) had no significant effect on the production of mature somatic embryos when the medium contained 0.1 M sucrose. When sucrose concentration was 0.2 M, however, 1.4 times more mature somatic embryos were produced on medium with 80 μM compared with 120 μM ABA. Under our best maturation conditions, mature somatic embryos accumulated amounts of storage proteins that were similar to the amounts in mature zygotic embryos. Activated charcoal exerted a beneficial effect on mature somatic embryo production of 24-week-old cultures; there was no evidence of such an effect in 8-week-old cultures. Thirty-seven embryogenic lines from a self-cross and an out-cross were chosen for clonal plant production. Highly embryogenic lines produced mature somatic embryos that were more likely to convert to plants than those from less embryogenic lines. After 4 months of growth in a shade house, plantlet survival rates exceeded 70% for 31 lines out of 35. This report describes an improved method for accelerated production of large quantities of Scots pine for clonal tests.     

Improved plantlet regeneration from open-pollinated families of <Emphasis Type="Italic">Abies alba</Emphasis> trees of Dobroč primeval forest and adjoing managed stand via somatic embryogenesis

Possibility to improve plantlet regeneration from Abies alba Mill. open-pollinated families of 4 trees in Dobroč primeval and 3 trees in managed forest was studied. Immature zygotic embryos were cultured in order to obtain initiation of embryogenic tissue. Totally, three from the families of the managed forest (57%) and two from the primeval families (50%) responded to initiation condition. Initiation frequencies among families ranged in managed forest: 4.5–56.2%, primeval: 5.4–16.8%. Maturation ability was shown by 77.3% of the primeval cell lines, 36.4% cell lines produced cotyledonary somatic embryos. In managed forest, in 62.5% of the cell lines embryo maturation was observed. Cotyledonary embryos developed only in 15% of cell lines. Regenerants were obtained from 9 cell lines of primeval and from 6 cell lines of managed forest. Biochemically, the mature somatic embryos were characterized by the variation in soluble and protein profiles. The corresponding profiles of insoluble proteins exhibited uniform pattern. The variation was characteristic for somatic embryos of individual cell lines rather than for the primeval and managed stands. Enzymatically, no indications were obtained supporting higher metabolic potential of somatic embryos derived from zygotic embryos of silver fir primeval stand than in somatic embryos originating from the trees of managed stand.     

Simplified and improved somatic embryogenesis for clonal propagation of Pinus pinaster (Ait.)

In this study, several improvements and simplifications of SE protocols in Pinus pinaster (Ait.), a species of economic importance in the regions of Western Europe, are described. These improvements pertained to all stages of SE including high initiation frequencies in eight control pollinated seed families, relatively high somatic embryo maturation yield when cells were coated with particles of activated charcoal and a rapid production of plants directly in a shade house. The SE initiation frequency from isolated zygotic embryos was high (up to 100%) and plants were produced from 11 embryogenic lines representing all crosses. Based on these results, the estimated number of somatic embryos required to produce 1,000 plants varied from slightly more than the required number of plants to more than double this number depending on the line. Such an estimate is critical in developing plant production strategy when a number of embryogenic lines are considered for production of clonal plants.     

Somatic Embryogenesis from 20 Open-Pollinated Families of Portuguese Plus Trees of Maritime Pine

Immature zygotic embryos from 20 open-pollinated (OP) families of maritime pine (Pinus pinaster) plus trees were screened for their somatic embryogenic capacity. The best time for zygotic embryo collection was between 30th June and 16th July 1999 when most embryos were at a pre-cotyledonary stage of development. The somatic embryogenesis (SE) initiation frequency was highest on DCR basal medium with 13.6 µM 2,4-dichlorophenoxyacetic acid (2,4-D) and 4.4 µM 6-benzylaminopurine (BAP) supplemented with L-glutamine and casein hydrolysate. On this medium, initiation frequencies among OP families ranged from 4.6 to 49.1%. Initiation of embryogenic cell lines from all 20 OP families was possible only on DCR based medium, but the addition of L-glutamine and casein hydrolysate significantly increased the number of zygotic embryos producing SE. Most families showed a similar behaviour on different initiation media; however, a few exceptions were observed. Further development of somatic embryos on maturation medium, consisting of DCR with 120 µM abscisic acid (ABA), 100 g l^–1 polyethylene glycol (PEG) and 10 g l^–1 gellan gum, occurred in 29% of 896 embryogenic lines representing all 20 OP families. However, development into cotyledonary somatic embryos was observed in only 11% of the cell lines, but this still represented 18 OP families.     

Optimized somatic embryogenesis in Pinus strobus L.

Summary Somatic embryogenesis (SE) initiation in Pinus strobus was optimized by the manipulation of plant growth regulator (PGR) concentrations in the culture medium. Modified Litvay medium (MLV) of Litvay et al. (1985) supplemented with lower than routinely used PGR concentration increased initiation of established embryogenic cultures from approximately 20 to 53%. The original developmental stage of zygotic embryos had a pronounced effect on the SE response. The optimum stage was the pre- to shortly post-cleavage stage. A substantial genetic influence on initiation of SE was indicated by a significant variance component due to families. Genotype X collection date and genotype X media interactions had large effects on initiation of SE. The PGR levels in the culture medium prior to maturation had a significant effect on subsequent production of mature somatic embryos. Embryogenic tissue initiated and proliferated on medium with a low level of PGR consistently produced a high number of somatic embryos, indicating that optimized initiation protocol also enhanced somatic embryo production. Somatic embryos of 93 embryogenic lines (representing five families) that were initiated on media with different PGR concentrations were converted to plants at an overall frequency of 76%, and grown in the greenhouse. With these improved protocols, application of P. strobus SE in commercial clonal forestry is feasible as an alternative to traditional breeding and reforestation.     

Plant regeneration in Stone pine (<Emphasis Type="Italic">Pinus pinea</Emphasis> L.) by somatic embryogenesis

Regeneration of plants by somatic embryogenesis (SE) was achieved in Stone pine (Pinus pinea), one of the most characteristic tree species of the Mediterranean ecosystem. The initial explants were megagametophytes containing zygotic embryos from five selected half-sib families collected at different dates over 2 consecutive years. Rates of extrusion and initiation of SE differed in both years. However, qualitative patterns were very similar: for most families, the responsive developmental window was from late cleavage polyembryony to early cotyledonary stage. The highest overall mean frequencies of extrusion and SE initiation (7 and 0.9%, respectively, for the five families and the eight 2006 collections) were obtained on a modified Litvay’s medium with 9 μM 2,4-D and 4.5 μM BAP, supplemented with L-glutamine and casein hydrolysate. Families showed large differences in frequencies of SE initiation from year to year. Only seven embryogenic lines were induced in 2005, representing three of the five families tested, whereas 34 lines from all the families were obtained in 2006. Proliferation of embryonal masses (EM) was significantly improved when they were subcultured after dispersing in liquid medium and collected on filter paper disks, instead of being subcultured as small clumps. This effect showed a significant interaction with genotype. Several preconditioning treatments and culture media combinations were tested for embryo development and maturation. The high proliferation rate of EM hampered somatic embryo development. However, up to 42 mature embryos from different lines of three of the five families were obtained, 23 of them germinated and seven converted into somatic seedlings.     

Somatic embryogenesis from different tissues of Spanish populations of maritime pine

The somatic embryogenesis (SE) capacity of megagametophytes belonging to Continental and Mediterranean Spanish provenances of maritime pine (Pinus pinaster Aiton) was studied, noting factors (megagametophyte developmental stage and culture medium) that enhanced the induction and establishment of SE lines. In both provenances, initiation and establishment of embryogenic calli was higher on megagametophytes in which the dominant zygotic embryo had begun to develop. In the Mediterranean provenance, however, SE lines were also established from megagametophytes enclosing zygotic embryos with well-developed cotyledons. A modified Litvay medium (mLV) containing 9.9???M 2,4-dichlorophenoxyacetic acid (2,4-D) and 4.4???M 6-benzyladenine (BA) was superior to DCR medium containing 13.6???M 2,4-D and 4.4???M BA for SE induction, but there were no differences between media in terms of the number of SE lines established after 4?months in culture (153 vs. 155 established SE lines, for mLV and DCR media respectively). Of the 26 embryogenic lines tested for maturation, 15 (58?%) produced cotyledonary somatic embryos and 75?% of these gave rise to plants on germination medium. SE-like cultures from adult maritime pine trees were also initiated, but embryogenic lines could not be established. This is the first report on the production of SE in maritime pine of Continental and Mediterranean origin. The micropropagation protocols presented here provide an important tool for the vegetative multiplication of selected families and breeding programs for maritime pines from Spain.     

SOMATIC EMBRYOGENESIS AND PLANT REGENERATION FROM IMMATURE ZYGOTIC EMBRYOS OF MUSCADINE GRAPE (VITIS ROTUNDIFOLIA) CULTIVARS

Embryogenic cell lines of Vitis rotundifolia were produced from immature zygotic embryo explants obtained by culturing ovules, harvested at 20 d postanthesis, for 8 wk and then dissecting embryos from them. Ovules cultured on Nitsch and Nitsch medium with naphthoxyacetic acid and benzyladenine (BA) produced a brown exudate, necessitating three transfers to fresh medium at 2-wk intervals during the 8-wk culture cycle. Zygotic embryos that were subsequently isolated from cultured ovules and placed on the same medium produced a heterogenous callus from which eventually emerged embryogenic cell lines. A higher percentage of ovules from cultivars ‘Dixie’, ‘Fry’, ‘Nesbitt’, and ‘Welder’ produced zygotic embryos (31%–39%) than did those from ‘Carlos’ (3%). A higher percentage of ‘Fry’ ovules produced embryogenic lines from cultured zygotic embryos (6.3%) than did those of the other four cultivars (1%–1.6%). Embryogenic cell lines were white and composed of variably sized cell clusters, somatic embryos, and embryonic tissue embedded in a watery matrix. These lines were maintained for over 1 yr on modified Murashige and Skoog (MS) medium lacking growth regulators by transfer of selected cell clusters every 6 wk. White, opaque somatic embryos grew directly from cell clusters and passed through recognizable developmental stages. Germination was induced by transfer of somatic embryos to MS medium with BA. Although 80%–100% of embryos germinated, plant recovery was low due to poor shoot development.     

Embryogeny of gymnosperms: advances in synthetic seed technology of conifers

Synthetic seed technology requires the inexpensive production of large numbers of high-quality somatic embryos. Proliferating embryogenic cultures from conifers consist of immature embryos, which undergo synchronous maturation in the presence of abscisic acid and elevated osmoticum. Improvements in conifer somatic embryo quality have been achieved by identifying the conditions in vitro that resemble the conditions during in ovulo development of zygotic embryos. One normal aspect of zygotic embryo development for conifers is maturation drying, which allows seeds to be stored and promotes normal germination. Conditions of culture are described that yield mature conifer somatic embryos that possess normal storage proteins and fatty acids and which survive either partial drying, or full drying to moisture contents similar to those achieved by mature dehydrated zygotic embryos. Large numbers of quiescent somatic embryos can be produced throughout the year and stored for germination in the spring, which simplifies production and provides plants of uniform size. This review focuses on recent advances in conifer somatic embryogenesis and synthetic seed technology, particularly in areas of embryo development, maturation drying, encapsulation and germination. Comparisons of conifer embryogeny are made with other gymnosperms and angiosperms.Abbreviations ABA abscisic acid - LEA late embryogenesis abundant - PEG polyethylene glycol - PGR plant growth regulator - RH relative humidity - TAG triacylglycerol     

Plant regeneration through somatic embryogenesis from immature and mature zygotic embryos of Musa acuminata ssp. burmannica

A simple and efficient protocol has been developed for in vitro regeneration of M. acuminata ssp. burmannica (AA) plants. Somatic embryos were produced when immature and mature zygotic embryo explants were cultured on Murashige and Skoog medium supplemented with plant growth regulators 2,4-dichlorophenoxyacetic acid; (2,4-D), picloram or benzyl adenine and indole acetic acid. In general, immature embryos responded better than mature embryos. Callus proliferation was highest in medium supplemented with 2,4-D (4.5???M). Subsequent transfer of callus to fresh medium produced rapidly proliferating embryogenic calli. Embryogenic calli were maintained in complete darkness for 15?d followed by cycles of 8?h dark and 16?h light, under white fluorescent lamps with a light intensity of 3,000?lm/m² and at temperature of 28?±?2°C. Regeneration of embryogenic calli into plantlets was higher for immature embryos (76.6%) than for mature embryos (50.6%). This plant regeneration protocol using mature or immature zygotic embryos, via somatic embryogenesis, has significant potential to improve germination efficiencies of hybrid progenies used in conventional breeding strategies. Furthermore, tests on seed storage showed that seed viability rapidly decline after harvesting and was negligible after 9?mo of storage. This indicates using freshly harvested seeds as explant material is necessary for maximizing the tissue culture response.     

Progress towards initiation of somatic embryogenesis from differentiated tissues of radiata pine (Pinus radiata D. Don) using cotyledonary embryos

Green cones of radiata pine were collected from two open-pollinated, elite families in two successive years at weekly intervals, and initiation of embryogenic cultures was investigated as a function of sampling date, initiation medium, explant type, and developmental stage. A combination of dissected embryos and a modified Litvay medium, Glitz, was best. This combination gave the highest rate of initiation, and it was possible to initiate somatic embryogenesis (SE) from differentiated cells in the epicotyledonary region of post-cotyledonary zygotic embryos from the two tested families with an average initiation rate of approximately 24% and 7% from stage five and six embryos, respectively. This is different from established initiation protocols of embryogenic cultures in radiata pine, which has traditionally been based on embryo rescue and continued proliferation of immature zygotic embryos. A further implication of initiation of SE from excised post-cotyledonary embryos was that the period of initiation of embryogenic cultures was extended from 4 to 12 wk.     

Enhancing initiation and proliferation in radiata pine (<Emphasis Type="Italic">Pinus radiata</Emphasis> D. Don) somatic embryogenesis through seed family screening,zygotic embryo staging and media adjustments

In Pinus spp., initiation of somatic embryogenesis (SE) is influenced by the developmental stage of immature embryos, the genotype of the parent trees and the formulation of tissue culture medium. Optimizing all these factors can lead to improved initiation and proliferation response; however, few studies have focused on improving these stages. For this reason, the objectives of this research were to determine the best immature zygotic embryo developmental stage for initiation and to test the effect of different sources of organic nitrogen in the initiation and proliferation steps in Pinus radiata SE. We have determined and verified the optimum zygotic embryo developmental stages 2–4 for embryogenic tissue (ET) initiation and proliferation and identified the most responsive seed families in two consecutive years. Besides EDM (Walter et al. 1998), medium with high gellan gum content during ET proliferation maintained the embryogenic tissue in a better micro-morphological arrangement for a longer time.     

Effects of various partial pressures of oxygen and carbon dioxide on different stages of somatic embryogenesis in Picea abies

Effects of various partial pressures of oxygen (5, 20 and 45 kPa) and carbon dioxide (0.03 and 6 kPa) on initiation, proliferation and maturation of somatic embryos in Picea abies were studied. The pO₂ had a significant effect on the initiation of embryogenic tissue from mature zygotic embryos. However, the effect of pO₂ was dependent on the strength of the basal medium. Low pO₂ stimulated the formation of embryogenic tissue when the zygotic embryos were incubated on full strength medium, but was inhibitory when half-strength medium was used. Proliferation of embryogenic tissue was stimulated by higher partial pressures of both CO₂ and O₂. The effect of the gas phase on maturation of somatic embryos varied between different cell lines. However, there was a general tendency for 5 kPa O₂ and 6 kPa CO₂ to stimulate maturation.Abbreviations ABA abscisic acid - BA benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - ET embryogenic tissue     

Relation of the developmental stage of zygotic embryos of yellow-poplar to their somatic embryogenic potential

The goal of the study was to characterize the optimal developmental stage of zygotic embryo expiants of the hardwood forest tree species yellow-poplar (Liriodendron tulipifera L.) for the initiation of embryogenic cultures, using morphological measurements and polypeptide profiles of the embryos. Developing zygotic embryos from seeds of six full-sib families, collected every two weeks from 4 weeks postpollination until seed maturity (18 weeks postpollination) were divided into 2 subsamples for each collection date. One group was used to initiate tissue cultures. Embryos in the other group were measured (total length, cotyledon length and hypocotyl thickness) and soluble polypeptide profiles of the embryos were analyzed by SDS-polyacrylamide gel electrophoresis. Potential of an expiant to produce an embryogenic culture peaked during the eighth week following pollination, with an average of 28% of the expiants producing proembryogenic masses, and declined to near zero for mature zygotic embryos. The maximum embryogenic potential corresponded to the globular stage of embryo developmet. Soluble protein profiles of zygotic embryos from 5 sampling dates indicated that decline in embryogenic potential appeared to parallel an increase in the level of a polypeptide of approximately 55 kDa, possibly a storage protein.Abbreviations BA Benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - CH Casein hydrolysate - SDS-PAGE Sodium dodecylsulfate polyacrylamide gel electrophoresis - PEM Proembryogenic mass     

Plant Regeneration Through Somatic Embryogenesis in Taxus wallichiana

We describe an efficient process for regeneration of Taxus wallichiana (Zucc) plants from callus cultures derived from zygotic embryos. Zygotic embryos cultured on half strength Lloyd and McCown’s basal medium supplemented with SH vitamin (1/2 WPMSH), 0.5 mg I^?1 6-benzyladenine (BA) and 1.0–2.0 mg I^?1 á-Napthaleneacetic acid (NAA) produced compact yellow (CY) callus after 4 weeks of culture. The 8-week-old CY call! (lines CY-A and CY-B) were initially slow growing but proliferated on transfer to WPM basal medium supplemented with 8.0 mg I^?1 2,4-D, 0.1–0.9 mg^?1 NAA and 0.3–1.0 mg^?1 BA after 4 weeks. Four morphologically distinct calli lines were obtained, of which only two call! lines, CY-B-FW and CY-B-FY were embryogenic. The 12-week-old callus line CY-B-FW developed globular somatic embryos on transfer to secondary medium after 8 weeks and matured in maturation medium after 4 weeks. Only 10% of the mature somatic embryos regenerated into complete plantlets after 4 weeks on conversion medium. Although the frequency of conversion was low, complete regenerated plantlets via somatic embryogenesis were obtained after 7–8 months of initiation of culture. Taxane analysis showed that the paclitaxel accumulation was higher in embryogenic callus than in non-embryogenic callus.     

糜子离体体细胞胚胎发生的组织学研究

利用组织学连续石腊切片的研究方法,观察了糜子组织培养中植株再生的过程,从而证明了植株再生是通过体细胞胚胎发生途径的。结果表明:(1) 糜子成熟胚培养首先从下胚轴及胚根区愈伤组织化;(2) 体细胞胚起源于下胚轴及胚根维管束周围愈伤组织中单个离散的胚性细胞;(3) 糜子离体体细胞胚有与典型禾谷类作物合子胚大致相似的发育过程。     

Histology of somatic embryogenesis in <Emphasis Type="Italic">Coffea arabica</Emphasis> L.

The objective of this study was to characterize the histodifferentiation of somatic embryogenesis obtained from leaf explants of C. arabica. Therefore, we histologically analyzed the respective stages of the process: leaf segments at 0, 4, 7, 15 and 30 days of cultivation, Type 1 primary calli (primary calli with embryogenic competence) and 2 (primary calli with no embryogenic competence), embryogenic calli, globular, torpedo and cotyledonary embryos, and mature zygotic embryos. Callus formation occurred after seven days of culture, with successive divisions of procambium cell. In this cultivation phase, it was found that Type 1 primary calli are basically formed by parenchymal cells with reduced intercellular spacing, whereas Type 2 primary calli are predominantly composed of parenchymal cells with ample intercellular spaces and embryogenic calli composed entirely of meristematic cells. After 330 days, it was evident from the differentiation of somatic embryogenesis that there was formation of globular somatic embryos, consisting of a characteristic protoderm surrounding the fundamental meristem. With the maturation of these propagules after 360 days, torpedo-stage somatic embryos arose, in which tissue polarization and early differentiation of procambial strands were verified. After 390 days, cotyledonary somatic embryos were obtained, where the onset of vessel elements differentiation was verified, a characteristic also observed in mature zygotic embryos. We concluded that somatic embryogenesis obtained from C. arabica leaves initiates from procambium cell divisions that, in the course of cultivation, produce mature somatic embryos suitable for regenerating whole plants.     

Somatic embryogenesis and plantlet formation from a rare and endangered tree species,Oplopanax elatus

We tested the possibility of plantlet formation via somatic embryogenesis with leaf segments and mature zygotic embryos from a rare and endangered tree species,Oplopanax elatus. To induce calli, expiants were cultured under darkness in a solid MS medium containing 3% sucrose, 1g L^-1 glutamine, and 0.3% gelrite. Treatment supplements included 2,4-D alone or in combination with thidiazuron. Generally, callus induction and growth were good from leaf expiants, whereas embryogenic calli could be induced only from zygotic embryos. These embryogenic calli were white or pale yellow and very friable. ABA and activated charcoal appeared to be important factors when inducing somatic embryos, with optimum levels being 0.1 mg L^-1 and 0.02%, respectively. Many somatic embryos showed abnormalities during their development on the germination medium, but 35% could be converted if placed on a medium containing gibberellic acid (GA₃). The germinating embryos sometimes formed secondary embryos at the lower portion of the hypocotyls. Normal or converted plantlets were acclimatized in an artificial soil mixture; their survival was about 60% after two months. This culturing system provides a feasible approach for regenerating plants, via somatic embryogenesis, from mature zygotic embryos.     

Maturation and conversion ofLiriodendron tulipifera somatic embryos

Summary Embryogenic suspension cultures of the hardwood forest tree yellow-poplar (Liriodendron tulipifera) have the potential to produce millions of plantlets. However, low conversion frequencies limit the realization of this potential. Using 4 embryogenic yellow-poplar lines, we first tested the ability of somatic embryos, selected for their similarity to mature zygotic embryos, to convert to plantlets, then tested physical and chemical treatments for their effects on promoting maturation of somatic embryos and subsequent plantlet production. Embryos selected based on resemblance to mature zygotic embryos and transferred to a hormone-free basal medium without casein hydrolysate (CH) produced plantlets at a frequency of 63%. Populations of synchronized somatic embryos were obtained by repeated fractionation of liquid medium-cultured proembryogenic masses (PEMs) on stainless steel sieves. These fractionated embryos failed to mature properly when cultured in liquid basal medium, however. Development of embryos cultured in basal medium supplemented with 5×10⁻⁷ M abscisic acid (ABA) was slowed and embryos appeared to mature properly, with separated cotyledons and little precocious germination. However, ABA-treated embryos only rarely converted to plantlets, possibly due to residual effects of the ABA. PEMs fractionated on sieves, transferred to filter paper and placed on solidified basal medium gave a 60–70% synchronous population of mature embryos 10–12 days following plating. Mature embryos transferred to basal medium without CH converted at a frequency of 72%. The percentage of all embryos differentiating from PEMs on filter paper that formed plantlets was 32%. This material is based upon work supported by the U. S. Department of Agriculture Cooperative State Research Service under Agreement No. 85-FSTY-9-0117.     

Morphogenic and genetic stability in longterm embryogenic cultures and somatic embryos of Norway spruce (Picea abies {L.} Karst)

Embryogenic cultures were initiated from mature zygotic embryos of Picea abies. The somatic embryos in the embryogenic cultures were first stimulated to mature and then either to develop further into plantlets or to differentiate new embryogenic cultures. The procedure was repeated three times during two years. The ability to give rise to new embryogenic cultures or to develop into plantlets was similar for all somatic embryos irrespective of how long they had been cultured in vitro. The nuclear DNA content, measured in a flow cytometer, was estimated at 32 pg/G1 nuclei in seedings developed from zygotic embryos. Nuclei isolated from embryogenic cultures and from plantlets regenerated from somatic embryos had the same DNA content as those isolated from seedlings.Abbreviations N⁶-benzyladenine BA - 2,4-dichlorophenoxyacetic acid 2,4-D - abscisic acid ABA