The bonds may be secured by an indenture by and between the company and a corporate trustee which may be any bank or other corporation having the power of a trust company or any trust company within or without this state. Such indenture may contain such provisions for protecting and enforcing the rights and remedies of the bondholders as may be reasonable and proper and not in violation of law, including covenants setting forth the duties of the company in relation to the exercise of its powers.