It is well known that glutathione is a ubiquitous and multifunctional compound which is important in maintaining cellular redox homeostasis. The balance between the reduced (GSH) and oxidized (GSSG) forms of this tripeptide plays a fundamental role in basic physiological and metabolic processes in plants. Recently, a remarkable amount of evidence has suggested that the role of glutathione within the plant system extends beyond the basic metabolic functions and that it may ultimately act as a modulator of plant development and morphogenesis. Therefore, it is not surprising that research has begun to focus on using the glutathione redox pair system for improving regeneration of cultured cells. One of the major themes that has emerged from in vitro studies is that GSH promotes cell proliferation, while GSSG promotes organized development. Thus, in vitro manipulation of this redox compound within the culture medium could lead to an enhancement of plant regeneration.

Genetic engineering techniques have so far had limited impact in the field of ornamental horticulture. As outlined in this review, transformation systems and potential genes of interest are available. As the development of new, novel varieties is an important driving force in the industry, there are, therefore, good prospects for the development of genetically modified ornamental varieties. The few products in the market to date may simply be a reflection of the relatively small scale of the industry compared to the major food crops, and the wide diversity of species within it. Commercial issues attendant to the use of gene technology in ornamental plants need careful consideration. These include careful choice of crop and background variety, the international regulatory process and freedom to operate.

Due to the commercial importance of some conifer species, advances in conifer biotechnology often appear to overshadow equally significant advances in the biotechnology of angiosperm forest trees. However, progress with some hardwood forest trees has been just as promising as that made with conifers, and in some areas, has surpassed conifer biotechnology, particularly in the past few years. Until relatively recently, progress with in vitro propagation and gene transfer in hardwood forest trees was confined primarily to the genus Populus. Similarly, compared to other hardwood species, the greatest progress has been made both in the areas of genomics and modification of wood quality traits in this genus. However, the advances in in vitro propagation, in general, and somatic embryogenesis, in particular, have brought mass clonal propagation of other top commercial hardwood trees, in particular Eucalyptus, closer to reality and gene transfer systems have been reported for a number of them. While by far the most extensive application of genomic tools, including genomic sequencing, expressed sequence tags, transcript profiling and molecular markers, has also been made with Populus, these tools are now being applied to wider range of hardwood species. Just as with conifers, potential biotechnology applications for hardwood forest species include development of trees with faster growth, altered wood quality, and insect and disease resistance. In addition, some hardwood species are being manipulated for such non-traditional uses as phytoremediation. Given these advances and the worldwide importance of the products derived from them, it is likely that in vitro propagated and transgenic hardwood forest trees will have just as great an impact on commercial forestry and our environment as the top coniferous species.

Although seeds have been the subject of extensive studies for many years, their seed coats are just beginning to be examined from the perspective of molecular genetics and control of development. The seed coat plays a vital role in the life cycle of plants by controlling the development of the embryo and determining seed dormancy and germination. Within the seed coat are a number of unique tissues that undergo differentiation to serve specific functions in the seed. A large number of genes are known to be specifically expressed within the seed coat tissues; however, very few of them are understood functionally. The seed coat synthesizes a wide range of novel compounds that may serve the plant in diverse ways, including defense and control of development. Many of the compounds are sources of industrial products and are components of food and feeds. The use of seed coat biotechnology to enhance seed quality and yield, or to generate novel components has not been exploited, largely because of lack of knowledge of the genetic systems that govern seed coat development and composition. In this review, we will examine the recent advances in seed coat biology from the perspective of structure, composition and molecular genetics. We will consider the diverse avenues that are possible for seed coat biotechnology in the future. This review will focus principally on the seed coats of the Brassicaceae and Fabaceae as they allow us to merge the areas of molecular biology, physiology and structure to gain a perspective on the possibilities for seed coat modifications in the future.

We report a protocol for somatic embryogenesis and plantlet regeneration of Buchanania lanzan Spreng (Family – Anacardiaceae), which is a tropical fruit tree widely distributed in the dry forests of India. Calluses were initiated from immature zygotic embryos cultured on Murashige and Skoog (MS) medium supplemented with various combinations of 2,4-dichlorophenoxyacetic acid (2,4-D), 6-benzyladenine (BA) and/or 1-naphthaleneacetic acid (NAA). The highest frequency (60%) of somatic embryo induction was obtained in cultures grown on MS medium fortified with 4.53 μM 2,4-D, 5.32 μM NAA and 4.48 μM BA. The medium supplemented with 15 μM abscisic acid (ABA) was most effective for maturation and germination of somatic embryos. This is the first report on somatic embryogenesis in B. lanzan, which may be helpful for in vitro propagation, ex situ conservation and genetic manipulation of this species.

This study reports a protocol for successful micropropagation of Decalepis arayalpathra (Joseph and Chandras) Venter. (Janakia arayalpathra Joseph and Chandrasekhran; Periplocaceae), a critically endangered and endemic ethnomedicinal plant in the southern forests of the Western Ghats which is overexploited for its tuberous medicinal roots by the local Kani tribes. Natural regeneration is rare and conventional propagation is difficult. Conservation of the species through micropropagation was attempted. The nodal explants of greenhouse-raised plants, were more desirable than cotyledonary nodal explants of aseptic seedlings. The basal nodes (73%) of 12–16-wk-old greenhouse-grown plants cultured in Murashige and Skoog (MS) medium containing 12.96 μM 6-benzyladenine (BA), 2.48 μM 2-isopentenyladenine (2-ip) and 2.68 μM α-naphthaleneacetic acid (NAA) formed 16–17 cm long unbranched robust solitary shoots in 8 wk. Cotyledonary nodal explants cultured in the same medium showed multiple shoot formation and axillary branching. But the shoots were thin, fragile and not suitable for mass propagation. Single nodes of a solitary shoot subcultured on MS medium containing 2.22 μM BA and 0.24 μM 2-ip together produced 9.8 ± 0.3 nodes from 18.0 ± 0.6 cm long shoots within 5–6 wk. The basal nodes of the shoots so formed were repeatedly subcultured to increase the stock of propagules while the 2.5–3.0 cm terminal cuttings were used for rooting. The best root induction (68%) and survival (86%) was achieved on half-strength MS medium supplemented with 1.07 μM NAA. Field-established plants showed uniform growth and phenotypic similarity to parental stock.

A protocol was developed for high frequency somatic embryogenesis and plant regeneration from cotyledon and hypocotyl explants of Eruca sativa. Explants grown on Murashige and Skoog (MS) medium supplemented with 4.52 μM 2,4-D formed embryogenic callus after 4 wk of culture. Secondary somatic embryos were also produced from primary somatic embryos on MS medium containing 0.56 μM 2,4-D. Somatic embryos developed into mature embryos on MS medium in the presence of 45 g l⁻¹ polyethylene glycol. After desiccation, somatic embryos developed into plantlets by culturing the mature somatic embryos on 1/2×MS medium containing 0.24 μM indole-3-butyric acid.

An efficient and reproducible protocol for mass propagation of Eclipta alba (L.) Hassk, an important medicinal plant, was standardized by culturing shoot tips and nodal segments taken from in vitro raised plants. Maximum shoot proliferation occurred when the explants were cultured on Murashige and Skoog (MS) medium supplemented with 1 mg l⁻¹ benzylaminopurine (BAP). The shoot buds formed were further multiplied and maintained on medium containing BAP (0.5 mg l⁻¹) and gibberellic acid (0.5 mg l⁻¹). Rooting was best achieved on MS medium supplemented with 1 mg⁻¹ indole-3-butyric acid. Rooted plantlets attained maturity and flowered normally in the field.

A simple and effective procedure has been developed for plantlet regeneration from cotyledon-derived callus of the medicinally important herb and ornamental species, Incarvillea sinensis. An average of 18.4 adventitious shoots per explant were obtained from 100% cotyledon explants cultured on half-strength Murashige and Skoog (MS) medium containing 1.0 mg l⁻¹ 6-benzylaminopurine for 3 wk, followed by another 4 wk on hormone-free 1/2×MS medium. The cotyledon explants continued to expand and regenerate new shoots upon repeated subculturing onto fresh medium. Most regenerated shoots (66.9%) were rooted on 1/4×MS medium containing 1.0 mg l⁻¹ indole-3-acetic acid, with an average of about 3.8 roots per shoot. Regenerated plants with well developed shoots and roots were successfully acclimatized in soil and were normal phenotypically.

Dendrobium candidum Wall. Ex Lindl. is an important species used in the formulation of Shih-hu, a Chinese traditional medicine. An efficient protocol for in vitro propagation of D. candidum using the axenic nodal segments of the shoots, originated from the in vitro germinated seedlings, was developed. The seeds from 120-d-old capsules after pollination were first germinated on half-strength Murashige and Skoog (MS) basal medium supplemented with 30 g l⁻¹ sucrose. After 4 mo., the seedlings were subcultured on a similar medium supplemented with 1 ml l⁻¹ HYPONeX, 80 g l⁻¹ potato homogenate and 2 g l⁻¹ activated charcoal for further growth. Axenic nodal segments excised from 9-mo.-old seedlings were cultured on the medium in the presence of 2 mg l⁻¹ benzyladenine (BA) and 0.1 mg l⁻¹ naphthaleneacetic acid (NAA). After 75 d, 73.2% of the explants gave rise to buds/shoots. The elongated shoots were rooted on the medium containing 0.2 mg l⁻¹ NAA and the plantlets were successfully acclimatized in soil.

An efficient system to regenerate shoots on excised sepals (calyx) of greenhouse-grown ‘Bounty’ strawberry (Fragaria × ananassa Duch.) was developed in vitro. Sepal cultures produced multiple buds and shoots without an intermediary callus phase on 2–4 μM 1-phenyl-3-(1,2,3-thiadiazol-5-yl) urea (thidiazuron, TDZ)-containing shoot induction medium within 4–5 wk of culture initiation. Young expanding sepals with the adaxial side touching the culture medium and maintained for 14 d in darkness produced the best results. In a second experiment, sepals proved more effective than the leaf discs and petiole segments for regenerating shoots. A third experiment compared the effects of six concentrations of two cytokinins (TDZ at 0, 0.5, 2, and 4 μM and zeatin at 2 and 4 μM) for elongation of sepal-derived adventitious shoots. The media containing TDZ generally promoted more callus formation and suppressed shoot elongation. TDZ-initiated cultures transferred into the medium containing 2–4 μM zeatin, produced usable shoots after one additional subculture. Shoots were rooted in vitro in the same medium used for shoot regeneration, but without any growth regulators. When transferred to potting medium, 85–90% of in vitro plantlets survived.

An efficient in vitro propagation system was developed for Arnebia euchroma, an important Chinese traditional medicinal plant. The present study utilized thidiazuron (TDZ) for the induction of shoot organogenesis on cotyledon and hypocotyl explants. The maximal number of shoots was obtained on the modified Linsmaier and Skoog (LS) medium supplemented with 1.0 mg l⁻¹ (4.5 μM) TDZ for 12 d on cotyledon explants (8.6 shoots per cotyledon explant). Other cytokinins (kinetin and 6-benzyladenine) and auxin (α-naphthaleneacetic acid) were not efficient in inducing regeneration on cotyledon explants. Browning of the basal portion of the subcultured shoots could be significantly reduced when they were cultured on the modified LS medium supplemented with 100 mg l⁻¹ (33.3 μM) polyvinylpyrrolidone. Well-developed shoots formed roots on the same medium containing 1.0 mg l⁻¹ (4.9 μM) indole-3-butyric acid. The efficient regeneration protocol reported here provides an important means of micropropagation of this plant. Furthermore, this protocol is essential to future genetic improvement of plants via transformation protocols.

Callus cultures of Adhatoda zeylanica Medicus were established from leaf and petiole explants. Accumulation of a bioactive pyrroloquinazoline alkaloid, vasicine, in callus cultures was detected and confirmed by thin layer chromatography, electron-ionization mass spectra, ¹³C NMR and high-pressure liquid chromatography analysis. The mass of vasicine obtained from leaf-derived callus cultures was found as 188 and this is comparable to that of the authentic sample. The retention time for leaf-derived extract was 10.065 and for the petiole-derived extract was 9.78 (authentic sample had 9.6 retention time) on high-performance liquid chromatography. The mass and NMR spectra were compared with the spectra obtained from the authentic sample of vasicine. Different growth regulators greatly influenced the growth of callus cultures. The accumulation of vasicine was more in leaf-derived callus grown on Murashige and Skoog (MS) medium fortified with 10.7 μM naphthaleneacetic acid (NAA) and 4.4 μM 6-benzyladenine than in petiolar callus grown on MS medium with 2.3 μM kinetin, and 4.5 μM 2,4-dichlorophenoxyacetic acid. This is the first report on in vitro production of a pharmacologically important compound vasicine and its characterization by mass spectrometry and ¹³C NMR studies from callus cultures of Adhatoda zeylanica.

Structure and ultrastructure changes that occurred during tissue culture of upper explants of hypocotyl (adjacent to cotyledons) of 10-d-old seedlings of Gentiana cruciata were studied. The explants were cultured on Murashige and Skoog induction medium supplemented with 1.0 mg l⁻¹ dicamba 0.1 mg l⁻¹ naphthaleneacetic acid 2.0 mg l⁻¹ benzyladenine 80.0 mg l⁻¹ adenine sulfate. The initial response of the explant and callus formation were ultrastructurally analyzed during the first 11 d of culture. After 6–8 wk, various methods were employed to collect evidence of indirect somatic embryogenesis. After 48 h of culture, the earliest cell response was cell division of epidermis and primary cortex. There were numerous disturbances of karyo- and cytokinesis, leading to formation of multinuclear cells. With time, the divisions ceased, and cortex cells underwent strong expansion, vacuolization and degradation. About the 6th day of culture, callus tissue proliferated and the initial divisions of vascular cylinder cells were observed. Their division appeared normal. Cells originating from that tissue were small, weakly vacuolated, with dense cytoplasm containing active-looking cell organelles. Numerous divisions occurred in the vascular cylinder, which led to its expansion and the formation of embryogenic callus tissue. During the 6–8th wk of culture, in the proximal end of the explant, masses of somatic embryos were formed from outer parts of intensively proliferating tissue.

The types of auxin in Murashige and Skoog (MS) medium containing N⁶-benzyladenine (BA) determined indirect morphogenesis, i.e. development to bipolar somatic embryos or monopolar shoots in Euphorbia nivulia Buch.-Ham. Indirect in vitro morphogenesis depended on growth regulators, explant excision period, and light. Calli induced from explants collected in March–April were superior in the induction of indirect morphogenesis to those collected in July–August. Light enforced in vitro morphogenesis, while darkness was inhibitory. The presence of kinetin in the medium also inhibited morphogenesis. Calli developed on explants collected in March–April grown on MS medium fortified with α-naphthaleneacetic acid (NAA) and BA facilitated indirect organogenesis, while those developed on medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) and BA underwent somatic embryogenesis. MS medium with 13.3 μM BA and 2.69 μM NAA was the best for induction of shoots from callus, which developed a mean of 15.7 shoots. Shoots were best rooted on half-strength MS medium enriched with 2.46 μM indole-3-butyric acid with a mean of 5.1 roots per shoot. MS medium supplemented with 2.26 μM 2,4-D and 4.44 μM BA induced the highest number (mean of 13.4) of somatic embryos. Of the embryos transferred on half-strength MS medium containing 2.89 μM gibberellic acid, 78% of embryos developed to the cotyledonary stage. Most cotyledonary embryos (80%) underwent conversion to plantlets upon being transferred to half‐strength MS basal medium in light. The survival rate of organogenesis and embryo-derived plants was 80 and 90%, respectively. Calli transformed with Agrobacterium tumefaciens showed expression of the gusA transgene and resistance to kanamycin, but did not undergo morphogenesis.