** Nutritional supplements seller's shares MTEX.O rise
13.3 pct to $20.50
** Company says it will begin repurchase of $500,000 worth
of shares, pursuant to existing buyback plan
** Stock among top advancers on the Nasdaq, in mid-day trade
** Mannatech to buy the shares from time to time in open
market
** As of July 31, company had 2.4 mln outstanding shares
** Mid-May company announced plan to buy back shares worth
about a third of its market cap urn:newsml:reuters.com:*:nL3N1SP4X6
** Stock up 37 pct this year, including session gains
(Reporting by Medha Singh in Bengaluru)
((medha.singh@thomsonreuters.com))