epesh N. De

Role of microtubules in secondary thickening of differentiating xylem element

The ontogeny of the xylem vessel from procambial cell was studied with the aid of electron microscope. The ultrastructure of procambial cells is made of highly dense cytoplasm with abundance of endoplasmic reticulum and Golgi apparatus with numerous vesicles. Moreover, dark-staining free ribosomes completely fill the cytoplasm. Microtubules can be detected along the cell wall. At a later stage of development, they appear to be localized. At this stage secondary wall thickening appears in the form of small electron transparent hemispherical humps in longitudinal sections of the procambial cells, and the microtubules are localized only in this region. In tangential sections it has been found that some Golgi vesicles lie in close proximity to microtubules, and sometimes the vesicles are completely surrounded by microtubules. From a series of electron micrographs of the primary xylem cell, at various stages of development, it has been concluded that the microtubules are instrumental for localized thickening of the tracheids.

Direct somatic embryogenesis and plantlet regeneration from seedling leaves of winged bean,Psophocarpus tetragonolobus (L.) DC

Excised seedling leaf segments of winged bean [Psophocarpus tetragonolobus (L.) DC.] underwent direct somatic embryogenesis under appropriate incubation conditions. Initiation and development of the somatic embryos occurred using a two-step culture method. The culture procedure involved incubation for 28 days on MS basal medium supplemented with 0.1–0.5 mg/l NAA and 1.0–2.0 mg/l BA (induction medium) before transfer to MS medium supplemented with 0.1 mg/l IAA and 2.0 mg/l BA (embryo development medium). The initial exposure to low levels of NAA coincident with high levels of BA in the induction medium was essential for embryogenic induction. Maximum embryogenesis (43.3%) was obtained with 0.2 mg/l NAA and 2.0 mg/l BA, and at least 14 days on induction medium were required prior to transfer to the embryo development medium. The conversion frequency of cotyledonary embryos was 53.3% upon culture on MS medium containing 0.1 mg/l ABA for 7 days followed by transfer to MS medium supplemented with 0.1 mg/l IBA and 0.2 mg/l BA. Following conversion, the regenerated plantlets were transferred to soil and showed normal morphological characteristics.

Tissue culture and plant regeneration from immature embryo explants of Calotropis gigantea (Linn.) R. Br.

Callus cultures were established from immature embryos of Calotropis gigantea (Linn.) R. Br. on a modified basal medium of Murashige & Skoog supplemented with 1 mgl-1 2,4-D. In addition to 0.1 mgl-1 of NAA the optimal BAP concentration for promoting shoot bud formation and growth was 2 mgl-1. Rooting was induced when shoots were transferred to auxin-supplemented Bonners solution or half-strength MS basal salt solutions.

Somatic embryogenesis and plant regeneration from leaf derived callus of winged bean [Psophocarpus tetragonolobus (L.) DC.]

Somatic embryos were obtained from callus cultures derived from leaf explants of the winged bean, Psophocarpus tetragonolobus (L.) DC. Initiation and development of the somatic embryos occurred with a two-step culture method. Callus cultures initiated on MS medium with NAA and BAP, upon transfer to a new medium with IAA and BAP, produced somatic embryos. Maximum embryogenesis of 60% was obtained on induction medium with 0.5 mg/l NAA plus 1.0 mg/l BAP followed by transfer to a secondary medium with 0.1 mg/l IAA and 2.0 mg/l BAP. Optimal embryo germination and plantlet development was achieved on MS medium with 0.2 mg/l BAP plus 0.1 mg/l IBA. The regenerated plants were successfully transferred to glasshouse conditions.

Cytological studies of the hybrid,Phaseolus aureus×P. mungo

The two closely related species,Phaseolus aureus andP. mungo were crossed successfully using the former as the female parent. A detailed cytological study of the hybrid, which showed morphological characters of both the parents, was carried out.At the pachytene stage, the pairing behaviour of 9 out of the 11 chromosomes belonging to the haploid complement of the two parents was investigated. The remaining two chromosomes are represented by morphologically distinct bivalents. The two species differ by a translocation, a deletion and a duplication. A consideration of the data from comparative morphology, geographical distribution, protein characters and genetical studies in the F2 and back cross generations, indicates a very close relationship between the two diploid species. Chromosome differentiation seems to constitute the major difference. The karyological evidences seem to indicate thatmungo is derived fromaureus.

Studies on pachytene and somatic chromosomes ofPhaseolus mungo L.

The pachytene and somatic chromosomes ofPhaseolus mungo L. (2n=22), were identified and classified on the basis of their relative length, arm ratio, chromomere pattern and nucleolar association. A comparison of the karyotypes during the somatic and pachytene stages, revealed that some chromosomes are of different relative lengths during the two phases. Thus, the two nucleolar organizer chromosomes are the 2nd and 3rd longest at somatic metaphase, but only 7th and 9th longest during pachytene. The pachytene chromosomes belong to the differentiated group.

Tissue culture propagation of tree legume Albizia lebbek (L.) Benth

Abstract Callus cultures were established on modified Murashige and Skoog medium from hypocotyl, leaf and stem tissues of the tree legume Albizia lebbek (L.) Benth. A high frequency of multiple buds and shoots was obtained on callus derived from diverse somatic explants on a medium with α-naphthalene acetic acid (NAA) and benzyladenine/kinetin combinations. Rooting of the shoots was induced in Bonners salt solution with indole-3-butyric acid (IBA). Thirty to forty plantlets were regenerated in an 8-week period from each explant. Some plants have been established in soil. Regenerated plantlets showed no morphological abnormalities and cytological investigations revealed no change in chromosomal complement.

Haploid plants from in vitro anther culture of the leguminous tree, Peltophorum pterocarpum (DC) K. Hayne (Copper pod)

The development of haploid callus, embryos and plantlets from cultured anthers and the various factors affecting androgenesis in Peltophorum pterocarpum (Copper pod), a tropical legume tree is reported. A pretreatment of flower buds at moderate temperature of 14°C for 8 days was most effective for callus production. The colour of the anther was found to be a reliable and efficient indicator for identification of suitable stage of anther for culture. The frequency of anthers which produced callus and shoots was highest when anthers were cultured at mid or late-uninucleate stage. A high sucrose concentration of 10% is a specific media requirement for androgenesis. The haploid nature of the embryos, callus and regenerated plants (n=14) were confirmed by chromosome count.

Protein constitution of the chromosome axis

Abstract. Diverse studies indicate that certain nonhistone proteins may be responsible for maintaining the integrity of the eukaryotic chromosomes. In view of their dispersal during nuclear division and their acknowledged role in gene expression, none of the nuclear matrix proteins can be regarded as integral proteins of the chromosome. Topoisomerase II, structural maintenance of chromosome (SMC) proteins and high-mobility-group (HMG) proteins exhibit characteristic enzymatic and mechanochemical roles as well as transitory association with chromosomes. Hence they may be regarded as accessory chromosome proteins. In contrast, certain high molecular weight synaptonemal complex proteins (SCPs) exhibit chemical and physical properties that suggest a structural role as the chromosome axis. It is proposed in an experimentally testable model that, in the minimal structure of a eukaryotic chromosome, the terminals of the loops of DNA-histone solenoids are constitutively affixed to chromosome axis proteins that have elastic properties.

Cell suspension culture and plant regeneration in the latex-producing plant, Calotropis gigantea (Linn.) R. Br.

A procedure is outlined for the establishment of a proliferating cell suspension culture and subsequent plant regeneration of the latex-producing plant,Calotropis gigantea (Linn.) R. Br. Friable calluses were obtained by culturing hypocotyl explants on modified Murashige and Skoog medium with 2.69 μM α-naphthaleneacetic acid and 4.44 μM 6-benzyl-aminopurine. Friable calluses were transferred to modified Murashige and Skoog liquid medium containing 500 mg l−1 casein hydrolysate, 5% (v/v) coconut water and 5% (w/v) sucrose to initiate suspension cultures. Suspensions were subcultured every 10–12 days and supplemented with 13.56 μM 2,4-dichlorophenoxyacetic acid (2,4-D). After 3–4 subcultures, suspensions consisted of small, highly cytoplasmic cell clumps and large vacuolate cells. Plating the suspension clumps on medium containing 4.52 μM 2,4-dichlorophenoxyacetic acid and culturing in darkness produced macroscopic calluses, which subsequently produced a high number of shoots when placed in light and supplemented with 2.22 μM 6-benzyl-aminopurine and 0.45 μM 2,4-dichlorophenoxyacetic acid. Shoots were rooted using Bonners solution containing 0.49 μM indole-3-butyric acid, and the plants successfully transferred to soil.