(ShareCast News) - The FTSE 250 plunged on Thursday, down 289.81 points (1.87%) to 15,222.73 by mid-afternoon.Al Noor was technically the biggest faller, after it went ex-dividend with a special dividend of 328p per share.However, the company's share price had risen 2p when taking the dividend into account at 1543 GMT.The UAE-based healthcare provider's proposed merger with South Africa's Mediclinic was been approved unconditionally by South Africa's Competition Tribunal last month.The merger, which the company said would create one of the world's largest acute hospital operators outside the US, was announced in October and approved by Al Noor shareholders in December.Under the terms of the deal, Al Noor will acquire Mediclinic, with shareholders receiving 0.625 new shares for each Mediclinic share held.Tate & Lyle shares were also down due to lower margins and continuing difficulties in the ethanol market during its third quarter.In the three months to 31 December, the agribusiness described trading in its Specialty Food Ingredients division as steady, with volumes ahead of the same period a year earlier."Strong volume growth in Europe and Asia Pacific more than offset softer demand in North America and Latin America," the company confirmed.In the Food Systems division, Tate & Lyle's board said volume continued to grow in the quarter, benefiting from the acquisition of Gemacom in December 2014.Margins in that business declined, however, as a result of a sharp increase in the cost of some ingredients. "Splenda sucralose volume was ahead of the comparative period although, as expected, pricing was lower year-on-year," the board added.A more cautious outlook statement from Henderson Group sent shares in the company lower despite annual earnings beating consensus forecasts.Final results from the funds group saw assets under management (AuM) of £92.0bn, up 13% over the year and ahead of consensus forecasts of just over £89bn thanks to record net inflows for the year of £8.5bn.Net revenue was slightly below expectations at £602m though performance fees up 19% to £99m were ahead.However, chief executive Andrew Formica said: "The first few weeks of 2016 have been challenging for investors and our clients, with a wide range of economic and geo-political risks weighing on markets."We will review our short term plans if difficult market conditions persist, but remain focused on our long term goals to grow and globalise our business."Meanwhile Informa shares were up after it revealed some good numbers as a result of the company's renewed focus and restructuring over the 12 months to 31 December.The business intelligence, exhibitions, events and academic publishing group described the year as one delivering improved revenue, profits, earnings and free cash flow.Revenue was up 6.6% to £1.21bn, with adjusted operating profit increasing by 9.5% to £365.6m.Informa's statutory profit before tax was £219.7m, up from the prior year's statutory loss of £31.2m.Adjusted earnings per share were up 4.6% to 42.9p."Informa made significant progress in 2015," said group chief executive Stephen Carter, referring to the numbers."Our results reflect the benefits of the Growth Acceleration Plan, our cost discipline and the effective integration and operation of recently acquired businesses."FTSE 250 - RisersAcacia Mining (ACA) 245.80p 5.27%Centamin (DI) (CEY) 79.40p 5.17%Informa (INF) 617.50p 4.66%Man Group (EMG) 151.60p 3.69%Entertainment One Limited (ETO) 135.20p 3.60%Zoopla Property Group (WI) (ZPLA) 219.90p 2.85%Enterprise Inns (ETI) 74.75p 2.75%Northgate (NTG) 336.40p 2.56%Aldermore Group (ALD) 182.50p 2.53%Cairn Energy (CNE) 139.90p 2.42%FTSE 250 - FallersAL Noor Hospitals Group (ANH) 836.00p -28.42%Interserve (IRV) 365.10p -14.09%Clarkson (CKN) 1,736.00p -7.61%Tate & Lyle (TATE) 540.50p -7.05%Atkins (WS) (ATK) 1,201.00p -6.75%Amec Foster Wheeler (AMFW) 339.30p -6.73%Telecom Plus (TEP) 810.00p -6.36%DFS Furniture (DFS) 286.50p -5.91%Henderson Group (HGG) 232.90p -5.52%Vectura Group (VEC) 163.10p -5.34%