Water relations of cotton flower petals and fruit

Water needed for expansion is believed to enter plant tissue in response to a growth-induced water potential gradient that occurs as turgor is reduced during relaxation of cell walls or in response to increased solutes. Under water stress, the cotton flower petal continues to expand when all leaves on the plant are wilted and new leaf expansion has ceased in the shoot tips. This study was undertaken to determine if water for expansion entered the petal in response to a gradient or to increased solutes. Water potentials of cotton petal, leaf, bract and fruit were determined pre-dawn and midday in dryland and irrigated field plots. The mechanism by which petal expansion occurs appears not to be associated with a growth-induced water potential gradient or to increased solutes because the gradient is reversed from that needed to drive expansion. The water potential of the petal tissues was consistently higher than that of the subtending leaves and bracts both during and after anthesis, and under different water stress conditions. How this reversal in water potential gradient is established and maintained should provide insight into mechanisms involved in growth during water stress.     

Adventitious shoot regeneration from cultured petal explants of carnation

Adventitious shoot regeneration was compared among leaf, stem and petal explants of carnation (Dianthus caryophyllus L.) cv. Scania on MS medium containing different concentrations of 6-benzyladenine (BA) and -naphthaleneacetic acid (NAA). High frequency regeneration was obtained only from petal explants on the media containing 5 to 10 M BA with or without 5 M NAA. Among the cytokinins tested, N-2-chloro-4-pyridyl-N-phenylurea and N-1,2,3-thiadiazol-5-yl-N-N-phenylurea were more effective than BA, kinetin, N⁶-2-isopentenyl adenine and zeatin on regeneration from petal explants. Although, high frequency shoot regeneration was obtained from all petal explants harvested from various developmental stages of buds, a significant decrease in regeneration capacity was observed in the explants obtained from fully-opened flowers. High frequency shoot regeneration was also obtained from the petal explants of cvs. Coral. Lena, Nora and White Sim, and an interspecific cultivar Eolo using the method developed in this study.Abbreviations NAA -naphthaleneacetic acid - BA 6-benzyladenine - GA₃ gibberellic acid - 2iP N⁶-2-isopentenyl adenine - KT-30 N-2-chloro-4-pyridyl-N-phenylurea (also called 4PU) - TDZ N-1,2,3-thiadiazol-5-yl-N-phenylurea (also called thidiazuron)     

Preferences of pollinators and herbivores in gynodioecious Geranium sylvaticum

BACKGROUND AND AIMS: For the maintenance of gynodioecy (i.e. the coexistence of female and hermaphroditic plants), females need to compensate for the lack of pollen production through higher seed production or better progeny quality compared to hermaphrodites. In Geranium sylvaticum, females produce more seeds per flower than hermaphrodites. This difference in seed production might be modified by biological interactions with pollinators and herbivores that may favour one sex and thus affect the maintenance of gynodioecy. METHODS: Sexual dimorphism in flower size and flowering phenology, and in attractiveness to pollinators, pre-dispersal seed predators and floral herbivores were examined in natural populations of G. sylvaticum. KEY RESULTS: Pollinators preferred hermaphrodites 25 % more often than females in two of the three study populations, and floral herbivores attacked hermaphrodites 15 % more often than females in two of the six study populations. These preferences might be explained by the larger flower size of hermaphrodites. In contrast, seed predators did not prefer either sex. CONCLUSIONS: The data suggest that pollinator preference does not benefit females, whereas the higher floral herbivory of hermaphrodites might enhance the maintenance of females in G. sylvaticum. Thus, although the data support the view that ecological factors may contribute to the maintenance of gynodioecy, they also suggest that these contributions may vary across populations and that they may function in opposite directions.     

Immunocytochemical localization of tubulins in spermatids and spermatozoa of Euptoieta hegesia (Lepidoptera: Nymphalidae)

A comparative analysis of the distribution of tubulin types in apyrene and eupyrene sperm of Euptoieta hegesia butterflies was carried out, also verifying the presence of tubulin in lacinate appendages of the eupyrene sperm. Ultrathin sections of LR White embedded spermatids and spermatozoa were labeled for alpha, beta, gamma, alpha-acetylated and alpha-tyrosinated tubulins. Apyrene and eupyrene spermatids show the same antibody recognition pattern for tubulins. All tubulin types were detected in axonemal microtubules. Alpha and gamma tubulins were also detected on the cytoplasmic microtubules. However, for beta and tyrosinated tubulins only scattered labeling was detected on cytoplasmic microtubules and acetylated tubulin was not detected. In apyrene and eupyrene spermatozoa only the axoneme labeling was analyzed since cytoplasmic microtubules no longer exist in these cells. Alpha, beta and tyrosinated tubulins were easily detected on the apyrene and eupyrene axoneme; gamma tubulin was strongly marked on eupyrene axonemes but was scattered on the apyrene ones. Acetylated tubulin appeared with scattered labeling on the axoneme of both sperm types. Our results demonstrate significant differences in tubulin distribution in apyrene and eupyrene axonemal and cytoplasmic microtubules. Extracellular structures, especially the lacinate appendages, were not labeled by antibodies for any tubulin.     

A theoretical approach to the relationship between wettability and surface microstructures of epidermal cells and structured cuticles of flower petals

Background and Aims The epidermal surface of a flower petal is composed of convex cells covered with a structured cuticle, and the roughness of the surface is related to the wettability of the petal. If the surface remains wet for an excessive amount of time the attractiveness of the petal to floral visitors may be impaired, and adhesion of pathogens may be promoted. However, it remains unclear how the epidermal cells and structured cuticle contribute to surface wettability of a petal.Methods By considering the additive effects of the epidermal cells and structured cuticle on petal wettability, a thermodynamic model was developed to predict the wetting mode and contact angle of a water droplet at a minimum free energy. Quantitative relationships between petal wettability and the geometries of the epidermal cells and the structured cuticle were then estimated. Measurements of contact angles and anatomical traits of petals were made on seven herbaceous species commonly found in alpine habitats in eastern Nepal, and the measured wettability values were compared with those predicted by the model using the measured geometries of the epidermal cells and structured cuticles.Key Results The model indicated that surface wettability depends on the height and interval between cuticular steps, and on a height-to-width ratio for epidermal cells if a thick hydrophobic cuticle layer covers the surface. For a petal epidermis consisting of lenticular cells, a repellent surface results when the cuticular step height is greater than 0·85 µm and the height-to-width ratio of the epidermal cells is greater than 0·3. For an epidermis consisting of papillate cells, a height-to-width ratio of greater than 1·1 produces a repellent surface. In contrast, if the surface is covered with a thin cuticle layer, the petal is highly wettable (hydrophilic) irrespective of the roughness of the surface. These predictions were supported by the measurements of petal wettability made on flowers of alpine species.Conclusions The results indicate that surface roughness caused by epidermal cells and a structured cuticle produces a wide range of petal wettability, and that this can be successfully modelled using a thermodynamic approach.     

Comparative floral anatomy of Pontederiaceae

Floral anatomy is described in eight species (representing five genera) of Pontederiaceae, and floral ontogeny is described in Pontederia cordata. The results are assessed in the context of recent phylogenetic work on Pontederiaceae, which indicates that the unilocular ovary condition has been achieved by two different, non-homologous routes in Pontederiaceae: via loss of interlocular septa in Heteranthera and Hydrothrix , and via pseudomonomery in Pontederia , which has a single fertile carpel. Absence of septal nectaries has evolved more than once in Pontederiaceae, at least in Heterantha and Monochoria , probably due to a transfer of the insect reward from nectar to pollen in these taxa. The presence of an elliptical or linear unvascularized appendage on the abaxial outer stamen in Monochoria is also probably correlated with enantiostyly. In Pontederia , air spaces in the ovary wall are modified into canals, each with a ring of apparently secretory epithelial cells.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 395–408.     

Aerial manoeuvrability in wingless gliding ants (Cephalotes atratus)

In contrast to the patagial membranes of gliding vertebrates, the aerodynamic surfaces used by falling wingless ants to direct their aerial descent are unknown. We conducted ablation experiments to assess the relative contributions of the hindlegs, midlegs and gaster to gliding success in workers of the Neotropical arboreal ant Cephalotes atratus (Hymenoptera: Formicidae). Removal of hindlegs significantly reduced the success rate of directed aerial descent as well as the glide index for successful flights. Removal of the gaster alone did not significantly alter performance relative to controls. Equilibrium glide angles during successful targeting to vertical columns were statistically equivalent between control ants and ants with either the gaster or the hindlegs removed. High-speed video recordings suggested possible use of bilaterally asymmetric motions of the hindlegs to effect body rotations about the vertical axis during targeting manoeuvre. Overall, the control of gliding flight was remarkably robust to dramatic anatomical perturbations, suggesting effective control mechanisms in the face of adverse initial conditions (e.g. falling upside down), variable targeting decisions and turbulent wind gusts during flight.