Quantifying Seasonal and Diurnal Cycles of Solar‐Induced Fluorescence With a Novel Hyperspectral Imager

Solar-induced fluorescence (SIF) is a proxy of ecosystem photosynthesis that often scales linearly with gross primary productivity (GPP) at the canopy scale. However, the mechanistic relationship between GPP and SIF is still uncertain, especially at smaller temporal and spatial scales. We deployed a ultra-hyperspectral imager over two grassland sites in California throughout a soil moisture dry down. The imager has high spatial resolution that limits mixed pixels, enabling differentiation between plants and leaves within one scene. We find that imager SIF correlates well with diurnal changes in leaf-level physiology and gross primary productivity under well-watered conditions. These relationships deteriorate throughout the dry down event. Our results demonstrate an advancement in SIF imaging with new possibilities in remotely sensing plant canopies from the leaf to the ecosystem. These data can be used to resolve outstanding questions regarding SIF's meaning and usefulness in terrestrial ecosystem monitoring

Effects of Exposure to a DNA Damaging Agent on the Hypoxia Inducible Factors in Organogenesis Stage Mouse Limbs

Hypoxia plays a critical role in coordinating cell survival, differentiation and death in normal embryogenesis; during limb pattern formation, hypoxia affects two key processes, chondrogenesis and cell death. Hypoxia promotes chondrocyte differentiation and cartilage matrix synthesis and suppresses terminal differentiation. Depending on the context, hypoxia may induce cell cycle arrest, pro- or anti-apoptotic genes, or autophagy. The response to hypoxia is controlled by hypoxia inducible transcription factors, specifically Hif1a, Hif2a and Hif3a. Under normoxia, the hypoxia-inducible factors respond to a variety of stimuli that include several well established teratogens, such as retinoic acid, heavy metals and hyperglycemia. We hypothesize that teratogenic exposures disrupt limb development by altering the hypoxia signalling pathway. To test this hypothesis, we assessed the effects of a DNA damaging alkylating agent, 4-hydroperoxycyclophosphamide, on the hypoxia inducible factor (HIF) transcription factors and on hypoxia in the murine limb bud culture system. 4-Hydroperoxycyclophosphamide exposure increased HIF1 DNA binding activity and HIF1A and HIF2A, but not HIF3A, protein concentrations. HIF1A and HIF2A immunoreactivities were detected in the apical ectodermal ridge and interdigital regions, where cell death sculpts the limb; 4-hydroperoxycyclophosphamide treatment enhanced their immunoreactivities, specifically in these regions. In contrast, hypoxia was localized to areas of chondrogenesis, the cartilaginous anlagen of the developing long bone and phalanges, and was not enhanced by drug exposure. Thus, the exposure of limb buds in vitro to a DNA damaging teratogen triggered a hypoxia signalling response that was associated with cell death. During limb development the HIFs have oxygen-independent functions

Immunolocalization of VEGF in control and 4-OOHCPA treated limbs.

<p>VEGF protein was detected in control limbs in the apical ectodermal ridge and interdigital regions (I.R.) with stronger staining observed at 24 h. Staining was increased in these areas in limbs exposed to either 1.0 or 3.0 µg/ml 4-HOOCPA for 24 h. Four separate replicates were done.</p

Western blot of HIF3A.

<p>HIF3A protein was detected in control limbs at all time points. A: Western blot analysis of HIF3A protein (118 KD) and actin (43 KD) in limbs at 30 min, 1, 3, 6, and 24 h after treatment with 4-OOHCPA at 0.3 µg/ml (L) 1.0 µg/ml (M) or 3.0 µg/ml (H). B: Densitometric quantification of HIF3A in drug treated groups compared to control groups. Hatched bar: 0.3 µg/ml (L), cross-hatched bar: 1.0 µg/ml (M) and gray bar: 3.0 µg/ml (H). HIF3A protein concentrations were not affected by drug treatment or time. Each bar (mean ± SEM) represents six to seven replicates.</p

4-OOHCPA exposure induced HIF2A.

<p>A: Western blot analysis of HIF2A protein (118KD) and actin (43KD) in limbs at 10 min, 1, 3, 6, and 24 h after treatment with 4-OOHCPA at 0.3 µg/ml (L) 1.0 µg/ml (M) or 3.0 µg/ml (H). P represents the positive control. B: Fold changes from the scan densitometry quantification of the HIF2A band in drug treated groups compared to control groups. Hatched bar: 0.3 µg/ml (L), cross-hatched bar: 1.0 µg/ml (M) and gray bar: 3.0 µg/ml (H). Each bar (mean ± SEM) represents six to seven replicates; bars with an asterisk are significantly different from control at the same time point (p ≤0.05).</p

Localization of HIF2A immunoreactivity in limbs.

<p>HIF-2A reactivity was detected in control limbs at 1 and 3 h in the apical ectodermal ridge, interdigital area (I.R.) and developing cartilaginous anlagen (Digits). 4-OOHCPA exposure increased HIF2A immunoreactivity in the apical ectodermal ridge and interdigital regions (I.R.) at 3 h. No differences were observed between control and drug-treated limbs after 6 h or 24 h of culture. Four separate replicates were done.</p