Structure of floral nectaries and comparison of reproductive and vestigial organs in the staminate and pistillate flowers of dioecious Silene latifolia (Caryophyllaceae)

Silene latifolia Poiret of Eurasia has established in North America, prompting this structural study of its mature unisexual buds and flowers. Floral nectaries, anther and stigma changes, and vestigial reproductive structures were studied using light and scanning electron microscopy. In staminate flowers, anthers dehisced before anthesis and > 90% of their pollen was liberated within 36 h. Accumulated in the tubular calyx, nectar descended an anthophore from the stomatal-bearing nectary at the stamen bases. Nectary tissue surrounded the pistillode, a central filamentous organ lacking ovules but tipped by hairs resembling stigmatic papillae. In pistillate flowers, nectar flowed into an inflated calyx. The annular nectary had 10 regularly-spaced, stomatal-lined craters and was continuous with the adaxial surfaces of the infertile antisepalous and epipetalous staminodes. Key elements of entomophilous pollination leading to successful sexual reproduction of this invasive species include secondary nectar presentation from disparate floral nectaries which, for pistillate flowers, also incorporate the staminodes; rapid pollen release from anthers; and elongation of papillae by tip growth that enhances each stigmaâ s receptive surface. Context is also provided for future studies of floral nectary development in this model dioecious species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Image-Based Rapid Estimation of Frost Damage in Canola (Brassica napus L.)

Traditional methods of estimating frost damage to crops are labor-intensive and time-consuming. Remote sensing imagery and vegetation indices can be used for condition assessment, however, the utility of using vegetative indices in assessing frost damage specifically is not known. The objective of this study was to estimate the freezing injury using a vegetative index developed from hyperspectral imagery. Three replicates of six 6-leaf stage canola plants were subjected to a temperature of −10 °C for 6hr. The resulting frozen plants were imaged at 6 different thawing times using an imaging spectrophotometer (400-1000 nm). Normalized difference vegetation index (NDVI) and triangular vegetation index (TVI) were calculated. Contrary to expectations, NDVI values from frozen plants increased in the initial thawing treatments (1, 2 and 4hr) and then decreased at 8hr. Whereas, TVI values decreased gradually with increased duration of thawing. Furthermore, when compared to NDVI, TVI clearly differentiated frozen from control plants and within the freezing treatments. The differential modes of response of the indices to post-freezing reflectance changes is the possible reason. These results suggest that with recent advancements in low altitude remote sensing in the areas of spectral, spatial and temporal resolution, early estimation of frost damage is possible