A re-investigation of the path of carbon in photosynthesis utilizing GC/MS methodology. Unequivocal verification of the participation of octulose phosphates in the pathway

A GC/EIMS/SIM methodology has been developed to re-examine the path of carbon in photosynthesis. Exposing isolated spinach chloroplasts to (13)CO(2 )on a solid support for a defined period followed by quenching and work-up provided a mixture of labelled sugar phosphates. After enzymatic dephosphorylation and derivatization, the Mox-TMS sugars were analysed using the above method. The purpose of the study was to try to calculate the atom% enrichment of (13)C in as many of the individual carbons in each of the derivatized sugars as was practical using diagnostic fragment ions. In the event, only one 45 s experiment provided sufficient data to enable a range of enrichment values to be calculated. This confirmed that D-glycero-D-altro-octulose phosphate was present in the chloroplasts and was heavily labelled in the C4, C5 and C6 positions, in keeping with the hypothesis that it had an inclusive role and a labelling pattern consistent with a new modified pathway of carbon in photosynthesis

Fluorescence-based versus reflectance proximal sensing of nitrogen content in Paspalum vaginatum and Zoysia matrella turfgrasses

Newly developed non-destructive fluorescence-based indices were used to evaluate nitrogen (N) fertilization rates and leaf nitrogen content in Paspalum vaginatum and Zoysia matrella turfgrasses. They were defined by combinations of the red (RF) and far-red (FRF) chlorophyll fluorescence signals excited under ultraviolet (UV), green (G) or red (R) radiation, as follow: Flavonol index, FLAV = log(FRFR/FRFUV); Chlorophyll indices, CHL = FRFR/RFR and CHL1 = FRFG/FRFR; Nitrogen Balance Indices, NBI = FRFUV/RFR and . Measurements were performed in situ by using a portable optical sensor able to scan 1 m2 plots, with a 0.2 m resolution, under 6 different nitrogen rates, from 0 to 250 kg ha−1, with four replicates each. From the same plots, reflectance spectra were recorded and several reflectance-based indices calculated. Most of them, as well as the fluorescence-based indices of chlorophyll, CHL and CHL1, had a quadratic response to N rate with a flattening above 150 kg ha−1 and 100 kg ha−1 for P. vaginatum and Z. matrella, respectively. The fluorescence-based NBI1 index was the only one able to discriminate all the 6 N levels applied to both P. vaginatum and Z. matrella plots. This result is due to the character of NBI1 as a ratio between an index of chlorophyll and an index of flavonols that present opposite responses to N rates. The spatial heterogeneity within and between plots treated with different levels of N was well represented by the map of the NBI indices. When the NBI1 and NBI were regressed against leaf N content linear fits were obtained with high regression coefficients in both P. vaginatum (R2 = 0.85–0.87, RMSE = 0.23–0.24% N) and Z. matrella (R2 = 0.75–0.78, RMSE = 0.20–0.22% N). The best relationships between leaf N content and reflectance-based indices, found for R730/R1000 (R2 = 0.71, RMSE = 0.43% N) and MCARI (R2 = 0.80, RMSE = 0.22% N) for P. vaginatum and Z. matrella, respectively, were curvilinear and, therefore, less effective than NBI indices in the estimation of N. Nevertheless, a reflectance vegetation index suitable as proxy of leaf N common to both turf species was not found. Our results indicate the high potential of the fluorescence-based method and sensors for the in situ proximal sensing of N status in the management of N fertilization in turfgrass

Dynamics of flavonol accumulation in leaf tissues under different UV-B regimes in Centella asiatica (Apiaceae)

A cumulative effect of UV-B doses on epidermal flavonol accumulation was observed during the first week of a time course study in Centella asiatica (Apiaceae). However, once flavonol levels had peaked, additional accumulation was possible only if higher daily UV-B irradiances were applied. We aimed to understand the dynamics of flavonol accumulation in leaf tissues using non-destructive spectroscopy and HPLC-mass spectrometry. When leaves that had grown without UV-B were given brief daily exposures to low-irradiance UV-B, they accumulated flavonols, predominantly kaempferol-3-O-β-D-glucuronopyranoside and quercetin-3-O-β-D-glucuronopyranoside, in their exposed epidermis, reaching a plateau after 7 days. More prolonged UV-B exposures or higher doses eventually augmented flavonol concentrations even in non-exposed tissues. If UV-B irradiance was subsequently reduced, leaves appeared to lose their ability to accumulate further flavonols in their epidermis even if the duration of daily exposure was increased. A higher irradiance level was then necessary to further increase flavonol accumulation. When subsequently acclimated to higher UV-B irradiances, mature leaves accumulated less flavonols than did developing ones. Our study suggests that levels of epidermal flavonols in leaves are governed primarily by UV-B irradiance rather than by duration of exposure.</p