H. Y. Mohan Ram

IN VITRO STUDIES ON DEVELOPMENTAL MORPHOLOGY OF INDIAN PODOSTEMACEAE

Abstract The early developmental biology of seven species of Indian podostemads based on in vitro growth of plants from seeds is discussed. Unpublished observations on seed germination, destiny of the radicular pole of the embryo, origin of the ‘primary axis’, location of the site of initiation of the thallus, and variations in seedling morphology in three thalloid members of the subfamily Podostemoideae (Zeylanidium lichenoides (S. Kurz) Engler, Hydrobryopsis sessilis (Willis) Engl., Willisia selaginoides (Bedd.) Warming ex Willis) are communicated. Additional observations are added to previously published accounts of the seedling biology of the thalloid Cladopus hookerianus (Tul.) C. Cusset and Polypleurum stylosum (Wight) Hall (Podostemoideae) and one thalloid Tristichoideae (Dalzellia ceylanica (Gardn.) Wight). Special attention is focused on the sequence of developmental events from seed to flowering in Indotristicha ramosissima (Wight) Van Royen (Tristichoideae), the only Indian species that seems to correspond to the Classical Root Shoot (CRS) model. In I. ramosissima exogenous root primordia arise from the flattened radicle, of which only three develop into main roots with asymmetric root caps. Although the mature seed lacks a plumule, a ‘primary axis’ of limited growth is formed at the apex. The plant body, with its numerous long branches, develops from the main roots. Flowering has been stimulated by subjecting vegetative plants to water and nutrient stress. Comparisons are made of early seedling developmental patterns among the seven investigated species. Special attention is focused on determining at what stage in ontogeny the root-shoot versus thalloid growth forms diverge. A model of seedling development is presented that depicts interspecific variability among species examined. The homology of the thallus in Podostemaceae remains unclear.

Induction of female flowers on male plants of Cannabis sativa L. by 2-chloroethanephos-phonic acid.

Ethrel induziert auf männlichen Hanfpflanzen (Cannabis sativa L.) weibliche Blüten, welche nach der Bestäubung Früchte ausbilden.

Induction of male flowers on female plants of Cannabis sativa by gibberellins and its inhibition by abscisic acid

SummaryGibberellins (GA3, GA4+7, GA7 and GA9) induce male flowers on female plants of Cannabis sativa. This is, depending on concentration, partially or fully inhibited by abscisic acid (ABA). The ABA effect can in turn be partially overcome by increasing the concentration of GA3.

In vitro germination, growth, morphogenesis and flowering of an aquatic angiosperm, Polypleurum stylosum (Podostemacee)

Podostemads grow attached to rocks in fast-flowing streams. Their plant body is highly reduced with no clear distinction between shoot and root. The present paper deals with the in vitro developmental biology of Polypleurum stylosum (Wight) Hall, a plant occurring in south India. Murashige and Skoogs liquid medium of 1/20 strength with 2% sucrose promoted optimum percentage seed germination and sustained growth of the plants. The regenerative propensity of the plant has been described. Incorporation of kinetin and abscisic acid at different concentrations in the basal medium did not promote growth. Four-month-old, continuously growing cultures were induced to flower by transferring them from liquid medium to semi-solid medium gelled with 0.8% agar. This is the first report of in vitro flowering in Podostemaceae. Water is suggested to play a key role in the control of flowering in vitro. The high degree of structural reduction and the adaptive strategy for survival of this haptophyte have been discussed. Polypleurum stylosum is highly specialised and deviates widely from the classical root-shoot model typical of most angiosperms.

In vitro germination and origin of thallus in Griffithella hookeriana (Podostemaceae)

Abstract Griffithella hookeriana (Tul.) Warm. (Podostemaceae) is a thalloid plant with no true leaves, stem or root. The seeds are extremely small (1000 seeds weigh 0.809 mg) and can be germinated on moist filter paper, but the resulting seedlings fail to survive beyond 5–6 days. A technique of germinating seeds in vitro on thermocole cubes floated in Murashige and Skoogs liquid medium (MS 1/5 strength with 0.5% sucrose) in continuous light (500–1000 lux) at 27±2°C has been developed. During germination, the radicular pole emerges from the seed coat and elongation of the two cotyledons follows. Rhizoids arise from the radicular pole and secrete a sticky substance that helps the seedling to adhere firmly to the substratum. The plumular apex ceases to funciton after producing 2 or 3 pairs of leaf-like outgrowths. A lateral protuberance is formed from the primary axis below the level of cotyledons and develops into a flat, green and oval, round or tubular (branched or unbranched) thallus (up to 0.5–0.8 cm in diameter) within 65–70 days. There is a high mortality of seedlings and plants at various stages of development: about 20% senesce before the initiation of the plumule, 15–20% after the formation of the leaf-like structures and 2–4% during the thallus stage. Seeds retain 83% viability for more than a year when stored dry at 10–15°C.

Physiology of flower bud growth and opening

Flower growth and opening are commonplace events, but physiologically intricate and inadequately explained. In this review, we have brought together and evaluated information on this subject to focus attention on the dynamic facets of flower development. In particular, the physiological basis of flower bud dormancy, nature of cleistogamy, mechanism of flower bud growth and turgor maintenance and role of stamens in corolla growth have been examined. The regulation of flower movements and opening by temperature and light, and circadian rhythms in flower opening have been discussed, along with a consideration of the role of the petal epidermis in light perception.It is emphasized that studies on flower physiology need to be intensified in view of the lacunae in our basic knowledge as well as to provide a sound basis for improving yields of both agricultural and horticultural crops.

Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex.

SummaryApical application of silver nitrate (AgNO3; 50 and 100 μg per plant) and silver thiosulphate anionic complex (Ag(S2O3)23−; STS; 25, 50 and 100 μg per plant) to female plants of Cannabis sativa induced the formation of reduced male, intersexual and fully altered male flowers on the newly formed primary lateral branches (PLBs); 10 μg per plant of AgNO3 was ineffective and 150 μg treatment proved inhibitory. A maximum number of fully altered male flowers were formed in response to 100 μg STS. The induced male flowers produced pollen grains that germinated on stigmas and effected seed set. Silver ion applied as STS was more effective than AgNO3 in inducing flowers of altered sex. The induction of male flowers on female plants demonstrated in this work is useful for producing seeds that give rise to only female plants. This technique is also useful for maintaining gynoecious lines.

In-vitro induction of aerial leaves and of precocious flowering in submerged shoots ofLimnophila indica by abscisic acid

Nodal explants of submerged shoots ofLimnophila indica (L.) Druce were cultured in Nitschs liquid medium containing abscisic acid (ABA, 10-9-10-6 M). At 10-7 and 10-6 M, ABA induced typical aerial leaves (entire, ovate, opposite-decussately arranged) even under submerged conditions and completely suppressed the development of water leaves (pinnately dissected and whorled). Flowers that invariably arise from aerial shoots were induced precociously by ABA even on submerged nodes.

Floral sexuality and breeding system in gum karaya tree, Sterculia urens

Abstract.Comprehensive studies were carried out on phenology, floral sexuality, pollination biology, pollen-pistil interaction, breeding system and fruit and seed set on three populations of gum karaya tree (Sterculia urens). The species is andromonoecious and produces a large number of male and a limited number of “bisexual” (functionally female) flowers. The numbers of male and “bisexual” flowers varies not only between trees but also during the flowering period within a tree. Each male flower produces about 5000 fertile pollen grains. Neither in morphology nor in number, is there any difference between pollen grains in the “bisexual” and male flowers. However, pollen grains of “bisexual” flowers are completely sterile and incapable of siring any seeds. Their anthers, however, serve to attract pollinators; the emasculated “bisexual” flowers fail to do so. Thus S. urens is apparently andromonoecious but exhibits cryptic monoecy. That the species is self-incompatible was confirmed by controlled pollinations. The self-incompatibility is of the late-acting type and manifests after the entry of the pollen tube into the ovule. Apis indica is the only pollinator recorded by us and wind plays no role in pollination. The efficacy of pollination is low as only 56% of flowers were estimated to be pollinated. The pollen load on one-third the number of pollinated stigmas was lower than the number of ovules present. Fruit set under open pollination is poor and is highly variable from tree to tree (0.7−3.2%). Apart from pollination constraint, limited resource availability may also contribute to low fruit set.

Micropropagation of gum karaya (Sterculia urens) by adventitious shoot formation and somatic embryogenesis

Abstract Nodal explants from selected trees of gum karaya (Sterculia urens Roxb.) in the adult growth phase cultured on Murashige and Skoog (MS) medium supplemented with 6.62 μm N6-benzylaminopurine (BAP) produced an average of six adventitious shoots in 30 days. Shoots were rooted in vitro on 1/4-strength MS medium containing 9.82 μm indole-3-butyric acid. Nodulated callus was produced from hypocotyl explants cultured on MS medium supplemented with 4.52 μm 2,4-dichlorophenoxyacetic acid and 8.90 μm BAP. Somatic embryos developed when the nodulated callus was transferred to MS medium containing 0.45 μm thidiazuron (TDZ). TDZ treatment for 2 days gave the optimum response. Over 30% of the somatic embryos developed into plantlets when transferred to 1/4-strength MS basal medium without any growth regulators. Plantlets produced from adventitious shoots and somatic embryos were acclimatized to ex vitro conditions and established in the field.