Phytochrome Controlled Nyctinasty in Albizzia julibrissin. I. Anatomy and Fine Structure of the Pulvinule

Under appropriate experimental conditions, phytochrome controls leaflet closure in Albizzia by regulating differential turgor changes in motor cells of the pulvinule. Closure occurs when subepidermal dorsal cells expand and ventral cells become compressed; reopening involves the reverse changes. The internal cells surrounding the vascular core remain relatively unchanged during leaflet movement. Fine structural studies revealed several unusual features of the motor cells including: (1) fibrils oriented parallel to one another in the cytoplasmic matrix; (2) numerous spherosomes that appear to coalesce and enlarge to form vacuoles; and (3) a multivacuolate condition.