Developmental basis for flower sex determination and effects of cytokinin on sex determination in Plukenetia volubilis (Euphorbiaceae).

KEY MESSAGE: Cytokinin might be an important factor to regulate floral sex at the very early stage of flower development in sacha inchi. Sacha inchi (Plukenetia volubilis, Euphorbiaceae) is characterized by having female and male flowers in a thyrse with particular differences. The mechanisms involved in the development of unisexual flowers are very poorly understood. In this study, the inflorescence and flower development of P. volubilis were investigated using light microscopy and scanning electron microscopy. We also investigated the effects of cytokinin on flower sex determination by exogenous application of 6-benzyladenine (BA) in P. volubilis. The floral development of P. volubilis was divided into eight stages, and the first morphological divergence between the male and female flowers was found to occur at stage 3. Both female and male flowers can be structurally distinguished by differences in the shape and size of the flower apex after sepal primordia initiation. There are no traces of gynoecia in male flowers or of androecia in female flowers. Exogenous application of BA effectively induced gynoecium primordia initiation and female flower development, especially at the early flower developmental stages. We propose that flower sex is determined earlier and probably occurs before flower initiation, either prior to or at inflorescence development due to the difference in the position of the female and male primordia in the inflorescence and in the time of the female and male primordia being initiated. The influence of cytokinin on female primordia during flower development in P. volubilis strongly suggests a feminization role for cytokinin in sex determination. These results indicate that cytokinin could modify the fate of the apical meristem of male flower and promote the formation of carpel primordia in P. volubilis.

Evaluación fitoquímica de hojas de Excoecaria lucida Sw. (Aité) (Euphorbiaceae) y Aislamiento e Identificación de un hemiterpenoide / Fitochemistry evaluation of leaves of Excoecaria lucida Sw. (Aité) (Euphorbiaceae) and isolation e identification of a hemiterpenoid

INTRODUCCIÓN: excoecaria lucida Sw. (Aité), es una especie que crece en Cuba y en la región del Caribe. La misma ha sido poco estudiada por científicos a pesar de que la población la utiliza con fines medicinales, en lo principal como antiasmático, antimicrobiano y para el dolor dental. OBJETIVOS: determinar la composición química de las hojas, así como aislar e identificar estructuralmente metabolitos secundarios. MÉTODOS: las hojas secas y molidas, se maceraron 72 horas con etanol al 95 % y se repitió el procedimiento en 4 ocasiones. Al extracto total se le determinó su composición química cualitativa y posterior se fraccionó con solventes. La fase de mayor rendimiento fue estudiada por Cromatografía Líquida de Alta Resolución y aislada la sustancia mayoritaria, la cual fue caracterizada por espectroscopía infrarroja y de Resonancia Magnética Nuclear 1H y 13C a 500 MHz (HMQC, HMBC, COSY y NOESY). RESULTADOS: se determinó la presencia cualitativa de alcaloides, triterpenos y esteroides, quinonas, flavonoides, cumarinas, lactonas sesquiterpénicas, fenoles y taninos. De la fase de mayor rendimiento (butanólica= 23,48 g) se logró aislar e identificar el compuesto mayoritario perteneciente a un hemiterpenoide. CONCLUSIONES: los metabolitos secundarios detectados coinciden con los reportes para otras especies del género. Se informa por primera vez para el género y la especie el aislamiento e identificación del hemiterpenoide (2E)-2-metil-2-buten-1,4-diol-1-O-ß-D-glucopiranósido.

INTRODUCTION: excoecaria lucida Sw. (Aité), it is a species that grow in Cuba and at the Caribbean region. It has been scientifically quite a little studied, in spite of the fact that the population utilizes it due to their medicinal properties as antiasthmatic, antimicrobial, and for the toothache treatment. OBJECTIVES: to determine the chemical composition of leaves, as well as the isolation and identification of their secondary metabolites. METHODS: dried and milled leaves were macerated 72 hours with ethanol 95 %, repeating the procedure in 4 occasions. Total extract was determined in his chemical qualitative composition and afterwards it was fragmented with solvents. The phase with greater yield was studied by High Performance Liquid Chromatography and isolated the main substance, which was characterized by infrared and Nuclear Magnetic Resonance spectroscopy: uni-dimensional 1H and 13C at 500 MHz and bi-dimensional HMQC, HMBC, COSY and NOESY. RESULTS: the identification of Alkaloids, triterpenes and steroids, quinone, flavonoids, coumarins, sesqiterpenic lactones, tannins and phenols were accomplished. From the greater yield phase (butanol= 23.48 g) was isolated and identified the main compound, a hemiterpenoid. CONCLUSIONS: the identified secondary metabolites are in coincidence with other reports related to the genera. For first time the hemiterpene (2E)-2-methyl-2- buten-1,4-di-hydroxyl-1-O-ß-D-glucopyranoside is informed in this genera and specie.

Production of therapeutically relevant indolizidine alkaloids in Securinega suffruticosa in vitro shoots maintained in liquid culture systems.

Microshoot cultures of the Chinese medicinal plant Securinega suffruticosa (Pall.) Rehd. were established and evaluated for the presence of therapeutically relevant indolizidine alkaloids securinine (S) and allosecurinine (AS). The cultures were maintained in shake flasks (SFs) and a bubble column bioreactor (BCB) using the modified Murashige's shoot multiplication medium supplemented with 1.0 mg l(-1) benzyladenine (BA), 3.0 mg l(-1) 2-isopentenyladenine (2iP), and 0.3 mg l(-1) 1-naphthaleneacetic acid (NAA). The influence of light and medium supplementation strategies with biosynthesis precursor (lysine (LY)) and nutrient formulations (casein hydrolysate (CH) and coconut water (CW)) on biomass growth and alkaloid production were investigated. SF cultures grown in the presence of light yielded up to 6.02 mg g(-1) dry weight (DW) S and 3.70 mg g(-1) DW AS, corresponding to the respective productivities of 98.39 and 60.21 mg l(-1). Among feeding experiments, CW supplementation proved most effective for SF-grown shoots, increasing biomass yield and AS productivity by 52 and 44 %, respectively. Maximum concentrations of securinine (3.25 mg g(-1) DW) and allosecurinine (3.41 mg g(-1) DW) in BCB cultures were achieved in the case of 1.0 g l(-1) LY supplementation. These values corresponded to the productivities of 42.64 and 44.47 mg per bioreactor, respectively.

Effect of different concentrations of benzyladenine and frequency of watering on growth and quality of Dracaena sanderiana and Codiaeum variegatum.

The effect of benzyladenine concentration and watering frequency on the growth and quality of Dracaena sanderiana and Codiaeum variegatum was evaluated. Plants were treated with different benzyladenine concentrations of (0, 75, 150, 225 or 300 mg l(-1)) and watering frequencies, daily, every 4, 7 or 10 days interval. Benzyladenine concentration and watering frequency interacted significantly for plant grade on both species. This interaction resulted in the highest grade at 225 mg l(-1) benzyladenine and daily watering for D. sanderiana and 150 mgl(-1) benzyladenine and daily watering for C. variegatum. No significant interactions between benzyladenine concentration and watering frequency were observed for photosynthesis rate, stomatal conductance, specific leaf area and fresh weight of either species. For D. sanderiana, the highest photosynthesis rate (5.70 mmolm(-2)s(-1)) occurred at 225 mg l(-1) and decreased with increasing watering frequency. For C. variegatum, the highest photosynthesis rate (4.49 mmolm(-2)s(-1)) was recorded with benzyladenine concentration of 150 mg l(-1), and photosynthesis rate was found independent of watering frequency. For both species, stomatal conductance was recorded highest at 225 mg l(-1), but watering frequency failed to influence stomatal conductance. For better quality, D. sanderiana should be sprayed with benzyladenine at 225 mg l(-1), and C. variegatum with benzyladenine at 150 mg l(-1) in combinations with watering at 4 days interval.

Testing the Janzen-Connell mechanism: pathogens cause overcompensating density dependence in a tropical tree.

The Janzen-Connell hypothesis is a leading explanation for plant-species diversity in tropical forests. It suggests that specialized natural enemies decrease offspring survival at high densities beneath parents, giving locally rarer species an advantage. This mechanism, in its original form, assumes that density dependence is overcompensating: mortality must be disproportionately high at the highest densities, with few offspring recruiting below their parents. We tested this assumption using parallel shadehouse and field density-series experiments on seedlings of a tropical tree, Pleradenophora longicuspis. We found strong, overcompensating mortality driven by fungal pathogens, causing 90% (shadehouse) or 100% (field) mortality within 4 weeks of germination, and generating a negative relationship between initial and final seedling densities. Fungicide treatment led to much lower, density-independent, mortality. Overcompensating mortality was extremely rapid, and could be missed without detailed monitoring. Such dynamics may prevent dead trees from being replaced by conspecifics, promoting coexistence as envisioned by the Janzen-Connell hypothesis.