Epidermal transmittance of leaves of Vicia faba for UV radiation as determined by two different methods.

Leaves of Vicia faba were collected from the field and the greenhouse and transmittance of epidermal peels from adaxial and abaxial sides was determined in the wavelength range from 250 to 800 nm using a spectrophotometer equipped for the measurement of turbid samples. From the same leaves, epidermal transmittance was estimated by a recently developed fluorometric method. Both methods gave highly correlated results with a slope of the regression line between both methods close to 1 and an intercept close to 0. Transmittances at around 310 nm as low as 3% were detected in the adaxial epidermis of field-grown leaves, while transmittance could be as high as 70% in the abaxial epidermis of greenhouse-grown leaves. There was a strong correlation between UV-A (ca. 366 nm) and UV-B (ca. 310 nm) transmittance detected by both methods which could be explained by the pigment composition in methanolic extracts where flavonols accounted for 90% of the absorption at 310 nm in the extract, while hydroxycinnamic acid derivatives which absorb only at the shorter wavelength constituted about 5%. It is concluded that the fluorescence method which allows rapid measurements on intact leaves can provide a quantitative estimate of epidermal transmittance for UV-B (280-320 nm) and UV-A (320-400 nm) radiation.

Are variations in cuticular hydrocarbons of queens and workers a reliable signal of fertility in the ant Harpegnathos saltator?

One of the key features of insect societies is the division of labor in reproduction between one or a few fertile individuals and many sterile nestmates that function as helpers. The behavioral and physiological mechanisms regulating reproduction in ant societies are still not very well understood, especially in species in which all colony members are reproductively totipotent. In the ponerine ant Harpegnathos saltator, queen-worker dimorphism is very limited, and a few mated workers reproduce ("gamergates") once the founding queen becomes senescent. Worker oviposition is regulated by highly directed aggressive interactions among nestmates, who can recognize different levels of ovarian activity. We show that variations in cuticular hydrocarbons (CHC) correlate with oogenesis, both for queens and workers. 13,23-Dimethylheptatriacontane is present in egg-layers, but not in infertile workers and queens. Proportions of other CHCs vary as well, resulting in clear separation of the ants in a multivariate analysis. Egg-layers are characterized by an elongation of the chain length of CHCs. We used solid-phase microextraction to measure CHCs in live ants that were experimentally induced to start producing eggs. Over a period of 118 days, CHC profiles of infertile workers changed completely to that of reproductives. The effect of age can be excluded in this modification. This striking correlation of ovarian activity with CHC variation and its correspondence with the observed recognition behavior exhibited by the workers toward egg-laying nestmates suggests that CHCs serve as a fertility signal in the ant H. saltator, a reliable basis for regulating reproduction.

Cutin monomers and surface wax constituents elicit H2O2 in conditioned cucumber hypocotyl segments and enhance the activity of other H2O2 elicitors

Hypocotyls from etiolated cucumber (Cucumis sativus L.) seedlings were gently abraded at their epidermal surface and cut segments were conditioned to develop competence for H2O2 elicitation. Alkaline hydrolysates of cutin from cucumber, tomato, and apple elicited H2O2 in such conditioned segments. The most active constituent of cucumber cutin was identified as dodecan-1-ol, a novel cutin monomer capable of forming hydrophobic terminal chains. Additionally, the cutin hydrolysates enhanced the activity of a fungal H2O2 elicitor, similar to cucumber surface wax, which contained newly identified alkan-1,3-diols. The specificity of elicitor and enhancement activity was further elaborated using some pure model compounds. Certain saturated hydroxy fatty acids were potent H2O2 elicitors as well as enhancers. Some unsaturated epoxy and hydroxy fatty acids were also excellent H2O2 elicitors but inhibited the fungal elicitor activity. Short-chain alkanols exhibited good elicitor and enhancer activity, whereas longer-chain alkan-1-ols were barely active. The enhancement effect was also observed for H2O2 elicitation by ergosterol and chitosan. The physiological significance of these observations might be that once the cuticle is degraded by fungal cutinase, the cutin monomers may act as H2O2 elicitors. Corrosion of cutin may also bring surface wax constituents in contact with protoplasts and enhance elicitation.