Reproductive biology of Azadirachta indica (Meliaceae), a medicinal tree species from arid zones

Neem or the Margosa tree, Azadirachta indica (Meliaceae), is a versatile tree species common in arid zones. We investigated the reproductive biology of Neem, including phenology, floral biology, pollination ecology and the breeding system, in three natural populations in northern India. Phenological observations established that trees within a population flowered synchronously, but populations varied in the time of onset of flowering; a few trees flowered twice a year. An inflorescence bears ～ 91 bisexual, white and sweet‐scented flowers. The stigma consists of a non‐receptive apical region and a subjacent rim of receptive surface; papillae on the two regions differ in their morphology and function. The occurrence of natural pollination both by wind and insects indicates ambophily. Insect pollinators were predominantly represented by Hymenoptera and Lepidoptera; Apis spp. were the most effective pollinators. Although the occurrence of incomplete dichogamy and a pollen : ovule ratio of ～ 627 indicates the possibility of autogamy, supplemental pollinations clearly established that the trees were 100% self‐incompatible and incompatibility is regulated at the gametophytic level. Natural fruit set was low (～ 5%) and hand cross‐pollinations increased the fruit set to ～ 19%. Our study demonstrated that natural fruit set in Neem is possibly limited by insufficient amounts of xenogamous pollination and resources.     

Effect of sucrose, auxins and gibberellic acid on rooting of stem segments of Populus nigra under varying light conditions

This paper deals with the effects of sucrose, IAA, IBA and GA₃on rooting stem segments of Populus in a sterile culture whenexposed to varying periods of continuous dark. The results demonstrate that segments shorter than 3.5 cm inlength, root only when exposed to 3 or more days of darkness,the number of roots increasing with the number of days in dark.The dark requirement for rooting can be substituted both byIAA and IBA, as rooting occurred with auxins even under continuouslight. The failure of control segments to root under continuouslight is ascribed to low auxin content due either to inadequatesynthesis or its inactivation by light. This deficiency canbe met either by exogenous application of auxins or by increasingthe size of the segments. GA₃inhibits rooting under favourablelight conditions although it stimulates sprouting of buds andsubsequent elongation. Sucrose increases the effectiveness ofauxins. (Received July 15, 1968; )     

In vivo stimulation of ovarian development in the red swamp crayfish,Procambarus clarkii (Girard), by 5-hydroxytryptamine

Summary

The possibility that biogenic amines affect ovarian development in the red swamp crayfish, Procambarus clarkii, was investigated. Females were administered 15 μg/g body weight (bw) of norepinephrine, dopamine, 5-hydroxytryptamine (5-HT) or octopamine on days 1, 5 and 10 and were sacrificed on day 15. Crayfish given 5-HT showed significant increases in ovarian index (30.5%) and oocyte size (34.0%) over the concurrent controls, while norepinephrine, dopamine and octopamine did not significantly affect either the ovarian index or oocyte size. Significantly more labeling by ¹⁴C-leucine of ovarian proteins was found in ovaries of crayfish that were injected with 5-HT in vivo, but when ovarian lobes from crayfish that had not been injected with 5-HT were incubated in vitro with 5-HT added to the incubation medium, no significant change in the level of incorporation of ¹⁴C-leucine into ovarian proteins occurred.

The 5-HT receptor blocker LY53857 (25 μg/g bw) retarded ovarian development. The 5-HT releaser fenfluramine and the 5-HT potentiator fluoxetine (both 15 μg/g bw) were also used. Crayfish given fenfluramine, fluoxetine, fenfluramine plus 5-HT or fluoxetine plus 5-HT showed significant increases of ovarian index (24.0–102.8%), oocyte size (20.0–87.4%) and in vitro ¹⁴C-leucine labeling of ovarian proteins (30.6–123.6%) over the concurrent controls. The ovaries of crayfish that received the 5-hydroxytryptaminergic neurotoxin 5,6-dihydroxytryptamme (10 μg/g bw) did not show any significant change as compared with the initial control. These findings are consistent with the hypothesis that 5-HT, which is present in the central nervous system of Procambarus clarkii, exerts its stimulatory effect on the ovary of this crayfish indirectly by triggering release of the ovary-stimulating hormone.     

A substitution mutation in OsCCD7 cosegregates with dwarf and increased tillering phenotype in rice

Dwarf plant height and tillering ability are two of the most important agronomic traits that determine the plant architecture, and have profound influence on grain yield in rice. To understand the molecular mechanism controlling these two traits, an EMS-induced recessive dwarf and increased tillering1 (dit1) mutant was characterized. The mutant showed proportionate reduction in each internode as compared to wild type revealing that it belonged to the category of dn-type of dwarf mutants. Besides, exogenous application of GA3 and 24-epibrassinolide, did not have any effect on the phenotype of the mutant. The gene was mapped on the long arm of chromosome 4, identified through positional candidate approach and verified by cosegregation analysis. It was found to encode carotenoid cleavage dioxygenase7 (CCD7) and identified as an allele of htd1. The mutant carried substitution of two nucleotides CC to AA in the sixth exon of the gene that resulted in substitution of serine by a stop codon in the mutant, and thus formation of a truncated protein, unlike amino acid substitution event in htd1. The new allele will facilitate further functional characterization of this gene, which may lead to unfolding of newer signalling pathways involving plant development and architecture.     

Morphological and molecular characterization ofAquaticheirospora and phylogenetics of Massarinaceae (Pleosporales)

A morphologically interesting hyphomycete was collected from submerged wood in a stream in Doi Suthep-Pui National Park, Thailand. It is described as Aquaticheirospora lignicola gen. and sp. nov., and is characterized by euseptate conidia with divergent arms, which are vertically inserted in different planes to a basal cell. The genus differs from other chirosporous genera in having synnematous conidioma and conidia that are produced on conidiogenous cells borne at the apices of synnemata. The morphological characterization of this new fungus is reported and compared with similar chirosporous genera. To investigate the teleomorphic and phylogenetic relationships of this new taxon, three different regions of the ribosomal gene [18S rDNA, 28S rDNA, and internal transcribed spacer (ITS) including 5.8S] were sequenced and analysed. The results of phylogenetic analyses based on 18S, 28S, and partial ITS including 5.8S rDNA, employing different tree-making methods, indicate that Aquaticheirospora lignicola is closely related to the ascomycetes family Massarinaceae (Order: Pleosporales). The Massarinaceae as currently circumscribed is monophyletic. Massarina australiensis and M. bipolaris , however, appear to belong to the Lophiostomataceae.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 283–296.