The result of a decrease in the risk-free rate of interest will increase put option prices and decrease call option prices.
A call option can be looked at as the right to delay a purchase. The higher the interest rate you can earn on the cash you will use to make that purchase, the greater the benefit of being able to delay that purchase.
A put option can be looked at as the right to delay a sale. The higher interest rate you can earn on the cash generated from that sale, the less desirable it is to delay that sale.