UK stock markets opened tentatively on Tuesday morning with concerns over the US economy back in the spotlight following yesterday's disappointing manufacturing data and increasing worries about the 'fiscal cliff'.The FTSE 100 finished broadly flat yesterday after the US Institute for Supply Management (ISM) purchasing managers' index fell from 51.7 to 49.5 in November, well below the 51.4 forecast."Not only did the US ISM manufacturing fall below the important 50 mark but also reignited worries similar as mentioned also in the Beige Book a few days ago that the current uncertainty concerning the Fiscal Cliff might already is having a bigger negative impact on the economy than previously thought," said Markus Huber, the head of German HNW trading at ETX Capital.In a letter to President Barack Obama, House Speaker John Boehner presented a deficit-reduction proposal that included $1.4tn in spending cuts and $800bn in new revenue. However, the plan was rejected by the Obama administration as it didn't include higher tax rates for top earners.FTSE 100: Wolseley declines after first-quarter resultsLike-for-like (LFL) revenue growth at plumbing merchant Wolseley continues to be polarised across its geographic regions, with growth in the US and Central Europe accelerating and declines in France and the Nordic markets worsening. Shares fell early on.Mining giant Rio Tinto gained after Credit Suisse increased its target price from 3,500p to 3,700p and reiterated its 'outperform' rating on the shares, adding the stock to its 'European Focus list'.Engineering and project management group AMEC was wanted after winning a contract worth over half a billion dollars to build a new oil refinery in Kuwait, expected to be the largest in the Middle East. British Gas owner Centrica rose after partner EDF Energy announced that it has extended the life of two UK power stations by seven years.FTSE 250: Greene King cheers with solid interimsPub operator Greene King was higher after delivering solid interim results driven by a good performance from its retail division, although it warned that trading conditions are likely to remain challenging for the rest of the year.Package tour operator TUI Travel gained after saying that the winter 2012/13 season has got off to a "very encouraging" start, though trading in France remains challenging.Conference and exhibition organiser ITE Group rose after full-year revenue rose 11% to £172m.FTSE 100 - RisersSchroders (SDR) 1,643.00p +1.36%Royal Bank of Scotland Group (RBS) 295.50p +0.99%Aviva (AV.) 354.00p +0.91%Lloyds Banking Group (LLOY) 46.13p +0.86%Centrica (CNA) 331.30p +0.85%Barclays (BARC) 246.25p +0.76%Hargreaves Lansdown (HL.) 742.00p +0.75%BG Group (BG.) 1,078.50p +0.75%Prudential (PRU) 904.00p +0.72%Shire Plc (SHP) 1,824.00p +0.72%FTSE 100 - FallersFresnillo (FRES) 1,953.00p -1.81%Randgold Resources Ltd. (RRS) 6,570.00p -1.43%Wolseley (WOS) 2,829.00p -1.22%ARM Holdings (ARM) 762.50p -1.04%Vodafone Group (VOD) 159.45p -0.90%Xstrata (XTA) 1,026.50p -0.68%Tate & Lyle (TATE) 765.00p -0.65%Carnival (CCL) 2,506.00p -0.63%Kingfisher (KGF) 273.80p -0.54%Aggreko (AGK) 2,238.00p -0.53%FTSE 250 - RisersITE Group (ITE) 202.90p +2.89%Talvivaara Mining Company (TALV) 96.75p +2.49%TUI Travel (TT.) 275.20p +2.30%TR Property Inv Trust Sigma Shares (TRYS) 83.55p +2.01%Jupiter Fund Management (JUP) 280.90p +1.74%Rank Group (RNK) 141.40p +1.73%Kentz Corporation Ltd. (KENZ) 378.00p +1.64%KCOM Group (KCOM) 69.30p +1.54%Cable & Wireless Communications (CWC) 35.63p +1.51%Soco International (SIA) 363.10p +1.45%FTSE 250 - FallersCentamin (DI) (CEY) 55.30p -2.98%African Barrick Gold (ABG) 403.00p -2.18%Kenmare Resources (KMR) 30.35p -2.10%Diploma (DPLM) 478.30p -1.42%JPMorgan Indian Inv Trust (JII) 366.90p -1.40%Micro Focus International (MCRO) 577.00p -1.28%FirstGroup (FGP) 181.60p -1.25%Imagination Technologies Group (IMG) 406.70p -1.17%AZ Electronic Materials SA (DI) (AZEM) 366.20p -1.03%Homeserve (HSV) 241.80p -0.94%BC