By Celine Aswad

DUBAI, April 20 (Reuters) - Profit-taking and weak first-quarter earnings weighed on Gulf stock markets on Thursday, with Saudi Arabia's index pulled lower by petrochemical shares after oil prices fell sharply, but Dubai's Union Properties and Abu Dhabi's TAQA bucked the trend.

Dubai's index .DFMGI lost 1.0 percent as financially troubled builder Arabtec ARTC.DU , which had jumped almost 11 percent on Wednesday after shareholders approved its capital restructuring plan, retreated 4.4 percent.

Union Properties UPRO.DU , however, leapt 5.8 percent to close at 1.03 dirhams in its heaviest trade since Jan. 23 and accounted for almost half of trading volume on the exchange. It ended off its intra-day high of 1.12 dirhams, failing to conclusively break chart resistance at the end-February peak of 1.07.

Fund managers and traders said the reason for the jump was not clear but it could be related to positive corporate news that had not yet been disclosed.

"Shares of UPP moved against the grain, and if it was just market participants taking a contrarian view on the stock, it would happen gradually. The volume spike in today's session suggests it's a company-specific event," one fund manager said.

Elsewhere, Abu Dhabi National Energy Co TAQA.AD surged 7.1 percent in very heavy trade after its chief operating officer told Reuters it might sell some oil and gas interests in North America to raise capital for core businesses.

Profit-taking in other shares, however, pulled the Abu Dhabi index .ADI down 0.2 percent. First Abu Dhabi Bank NBAD.AD fell 0.5 percent after trading as much as 1.4 percent higher earlier in the day.

The lender, which was formed on April 1 by the merger of National Bank of Abu Dhabi and First Gulf Bank, announced a 12.4 percent rise in combined "pro-forma" first quarter net profit to 2.93 billion dirhams ($798 million).

That was aided by a 145.5 percent jump in "other non-interest" income while loan impairment charges slipped 3.9 percent.

The Saudi index .TASI lost 0.7 percent as almost two-thirds of listed petrochemical shares fell, with heavyweight Saudi Basic Industries 2010.SE dropping 1.3 percent.

Most Saudi banking shares also fell, with Saudi Investment Bank 1030.SE the worst performer, down 1.6 percent. All Saudi banks have now reported first-quarter earnings; while results were mixed, most beat analysts' expectations.

The Saudi index was the worst performer in the Gulf for the week, down 2.5 percent.

In Doha, Gulf International Services GISS.QA dropped 5.0 percent after it reported an 81 percent slide in first-quarter profit to 15 million riyals ($4.1 million), far below QNB Financial's forecast of 452 million riyals and Alphamena's estimate of 378 million riyals.

The Qatari stock index .QSI fell 0.5 percent and was down 2.0 percent for the week.

In Egypt, the index .EGX30 edged up 0.1 percent in very low volume as Orascom Construction ORAS.CA jumped 5.1 percent on news a major U.S. nitrogen fertiliser plant which it built had started operations.

Declining shares, however, outnumbered advancing ones by 124 to 46.



THURSDAY'S HIGHLIGHTS



SAUDI ARABIA



* The index .TASI lost 0.7 percent to 6,899 points.



DUBAI



* The index .DFMGI fell 1.0 percent to 3,470 points.



ABU DHABI



* The index .ADI edged down 0.2 percent at 4,522 points.



QATAR



* The index .QSI lost 0.5 percent to 10,242 points.



EGYPT



* The index .EGX30 edged up 0.1 percent to 12,906 points.



KUWAIT



* The index .KWSE added 0.4 percent to 6,814 points.

OMAN



* The index .MSI slipped 0.7 percent to 5,474 points.



BAHRAIN



* The index .BAX was down 0.4 percent at 1,334 points. (Editing by Andrew Torchia and Mark Potter) ((celine.aswad@thomsonreuters.com)(+9715 6224 7653)(Reuters Messaging: celine.aswad.thomsonreuters.com@reuters.net))