Cellular differentiation in small clumps of Lotus corniculatus callus

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Abstract
Lotus callus cultures were studied in an attempt to determine, at the cellular and subcellular levels, what morphological changes precede and accompany differentiation. Small clumps of homogenized callus were plated onto a medium containing benzyladenine, which was known to induce differentiation in this system. Initially callus was yellowish and consisted of large, vacuolated cells with deposits of starch. Marked changes occurred in these cells; peripheral and endogenous meristematic areas were initiated giving rise to shoots and either groups of tracheary elements or roots, respectively. Roots developed within 5 days, while shoot apical meristems with leaf primorida formed by day 9. Many of the cells surrounding meristematic areas developed suberin lamellae in their walls, while others, both within and on the periphery of meristematic areas, accumulated phenolic substances. Cells within meristematic areas had large nuclei with prominent nucleoli, plastids with thylakoids but little or no starch, many mitochondria and dictyosomes. Morphological observations tend to support the view that physiological isolation of tissue may precede differentiation.