These specialized hyphae usually show negative gravitropism and positive phototropism allowing good spore dispersal. Light regulates three major plant processes&colon; photosynthesis, phototropism, and photoperiodism. Phototropins are photoreceptor proteins (more specifically, flavoproteins) that mediate phototropism responses in higher plants. This overturned a commonly held belief that carotene was the photoreceptor involved in phototropism. For example, phototropin is the blue light photoreceptor that controls phototropism. In plants and fungi, phototropism and gravitropism interact in a complex manner. Similar mechanisms occur in other tropic responses, such as phototropism. Both root tips and most stem tips exhibit positive phototropism to red light. Like phototropism, a thigmotropic response in stems requires light. Thus leading to the conclusion that two phases must be responsible for phototropism. Auxin participates in phototropism, geotropism, hydrotropism and other developmental changes. PIN3 and PIN7 proteins were thought to play a role in pulse-induced phototropism. There are several genes involved in plant phototropism including the "NPH1" and "NPL1" gene. "Dennstaedtia punctilobula" can exhibit varying degrees of phototropism. Together phytochromes and cryptochromes inhibit gravitropism in hypocotyls and contribute to phototropism.