"The iTunes Store, Mac App Store, App Store, and iBookstore services (“Services”) accept these forms of payment: credit cards issued by U.S. banks, payments through your PayPal account, iTunes Cards, iTunes Store Gift Certificates, Content Codes, and Allowance Account balances." - http://www.apple.com/legal/itunes/us/terms.html
Mac App Store: Frequently Asked Questions (FAQ) - http://support.apple.com/kb/HT4461
Can I use an iTunes Gift Card or Apple Store Gift Card to make purchases on the Mac App Store?
iTunes Gift Cards can be used to make purchases from the Mac App Store. Apple Store Gift Cards are redeemable in Apple retail stores, and may not be used on the Mac App Store.