Structural and developmental variability in the female gametophyte of Griffithella hookeriana, Polypleurum stylosum, and Zeylanidium lichenoides and its bearing on the occurrence of single fertilization in Podostemaceae.

Angiosperms are characterized by the phenomenon of double fertilization with Podostemaceae as an exception that appears to extend to the entire family. Our earlier work demonstrated the cause of failure of double fertilization and ascertained the occurrence of single fertilization in Dalzellia zeylanica (Tristichoideae, Podostemaceae). In continuation with this work, three more members, i.e., Griffithella hookeriana (Tul.) Warming, Polypleurum stylosum (Wight) Hall, and Zeylanidium lichenoides (Kurz) Engl. (Podostemoideae), have been investigated in the present work. We studied the ontogenetic development of female gametophyte and tracked the path of the two sperm cells from the time of their formation in the pollen tube through their entry into the synergid and gamete fusion. We report the occurrence of a remarkably reduced 3-nucleate, 3-celled mature female gametophyte consisting of an egg cell and two synergids in all the three genera. Interestingly, the central cell is formed during female gametophyte development, but exhibits a species-specific, limited life span, and eventually degenerates prior to the entry of the pollen tube into the synergid, resulting in a failure of double fertilization. Sperm dimorphism on the basis of fluorochrome stainability has been recorded in Z. lichenoides. Further, morphogenetic constraints on the part of male (sperm selection, functional reductionism) and female gametophyte (structural reductionism, inaccessibility of central cell) presumably ensure the failure of double fertilization in these species. Thus, loss of double fertilization in this family is likely a derived condition.

Reproductive biology of Butea monosperma (Fabaceae).

The reproductive biology encompassing phenology, floral biology, pollination and breeding systems, of Butea monosperma, a beautiful tree of the Indian subcontinent, was investigated in a protected dry, deciduous forest located in New Delhi. Phenological studies indicated that although the species shows a regular flowering season, all trees do not flower every year. Flowers are typically papilionaceous; the stigma is wet papillate and the style is hollow. The flowers show characteristics of bird pollination being large and bright orange-red in colour with copious amounts of nectar, and exhibiting diurnal anthesis. Although the flowers are frequented by as many as seven species of birds belonging to six families, only one species, the purple sunbird (Nectarinia asiatica), is the effective pollinator. The flowers are also pollinated by the three-striped squirrel (Funambulus tristiatus). Unlike other flower visitors, these two pollinators forage the nectar from the open side of the keel (legitimate path) during which pollen grains are deposited on their body parts. After the first visit of a sunbird or a squirrel, virgin flowers showed pollen load on the stigma and developed into fruits. B. monosperma shows a weak form of self-incompatibility. Fruit set following manual self-pollination (5.25 %) was comparable with open-pollination (approx. 5 %) but was significantly lower than manual cross-pollination (22.51 %). This indicates that there is a high degree of geitonogamous pollination in this species, which may lead to a weakening of self-incompatibility as a means of reproductive assurance. The results are analysed in the light of prevailing discussions on specialized vs. generalized pollination systems.

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

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.

Induction of division and differentiation of somatic embryos in the leaf epidermis of Gaillardia picta.

Somatic embroys and subsequent plant regeneration were obtained from isolated leaf epidermis of Gaillardia picta. Abaxial and adaxial epidermal peels (monolayer) from 45 days old aseptic seedlings were isolated and segments measuring 5 mm x 3 mm were cultured on B5 basal medium supplemented with various growth regulators such as naphthaleneacetic acid or indolebutyric acid and benzylaminopurine or kinetin. Within 12 h of culture the epidermal cells showed receding of cytoplasm from the walls. After 48 h of incubation 3 or 4 localized zones, each consisting of 3-8 cells that accumulated cytoplasm and stained densely, were observed. Mitotic divisions occurred in these zones on day 3 of culture and localized masses of callus were observed in 95% of the cultures after 10 days. In another 5 days, the callus differentiated somatic embryos or roots, depending on the growth regulators and their concentration in the medium.

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

Apical application of silver nitrate (AgNO3; 50 and 100 µg per plant) and silver thiosulphate anionic complex (Ag(S2O3) 2 (3-) ; 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 Nitsch's 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.

Induction of male flowers in a pistillate line ofRicinus communis L. by silver and cobalt ions.

Aqueous solutions of silver nitrate (10-100 µg/plant) and cobalt chloride (125-500 µg/plant), injected into the main stem of plants of the pistillate cv. 240 ofRicinus communis when the vegetative shoot apex was beginning to become reproductive, induced the formation of staminate (male) flowers with viable pollen in the normally strictly pistillate (female) terminal inflorescence, their number increasing with the dose of Ag(+) and Co(2+). No formation of bisexual flowers was noted. Female flowers pollinated with pollen from the induced male ones produced fruits and viable seeds.

Inhibition of gamete formation by cycloheximide in pollen tubes of Impatients balsamina.

Cycloheximide (CH) inhibited the division of generative cell in pollen cultures of Impatiens balsamina in concentrations of 1-200 µg/ml without affecting pollen germination or pollen tube growth. This inhibition was reversible up to 3 h in hanging drop cultures and up to 6 h in test tube cultures by replacement of the medium with a CH-free one.

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

Gibberellins (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.

Shortening the juvenile phase for flowering in Kalanchoe pinnata Pers.

Plants of Kalanchoe pinnata flower normally at the end of 2 years. Flowering in the juvenile phase (3- and 9-month-old plants) has been induced by application of gibberellin (GA) either to the shoot tip and the youngest pair of leaves, or to the third leaf. Three-month-old plants required more exogenous GA (50 µg/plant) than 9-month-old plants (5 µg/plant). The simultaneous application of the growth retardant (2-chloroethyl)trimethylammonium chloride=CCC via the roots did not interfere with GA-induced flowering but overcame the inhibitory effects produced by a high concentration of GA (150 µg/plant) when applied alone.