Confusion about minimum Investment

Hi,

I am newbie in the world of investing.

I have few of the doubts as mentioned below.

Some of the mutual funds like franklin India Taxshield, ICICI Prudential tax plan have a minimum investment of rs 500.
Is this minimum investment amount is for one time or it has be invested through SIP? or in case I do not choose SIP at all, Can I invest rs 500 for in the beginning and make subsequent investment whenever I feel like anytime in the future?

Please help me clear this confusion.

Thanks in advance.