It doesn't seem like they will be buying many Bitcoins. The nasdaq press release says they will be working with chain.com
http://www.nasdaq.com/press-release/nasdaq-and-chain-to-partner-on-blockchain-technology-initiative-20150624-00446The chain.com blog at
http://blog.chain.com/ gives this link to their explanation of how they intend to use the blockchain
https://medium.com/investing-2-0/wall-street-meet-block-chain-b2747909eb90They say they will use the Bitcoin blockchain to move assets but that they will only pay pennies worth of Bitcoin for each transaction.
Bitcoin is the oil in the machine. When creating or transferring a digital asset, you use a standard bitcoin transaction as the mechanism, which requires bitcoins to pay the fee that keeps the network secure. But very little bitcoin is needed for any given asset transaction. Even if the issuance or transfer involves billions of dollars of value, only pennies worth of bitcoin are used. It’s like a postage stamp on an envelope full of assets.
They also say they are looking at Stellar, Ripple, Side Chains, and ethereum to move assets when they have proved their reliability.
There are other open financial networks being designed and tested, and the financial cloud will likely interoperate with them as they prove out their security models in the years ahead. Prominent examples include Stellar, Ripple, Side Chains, and ethereum.