The Growth Pattern and Structure of Callus from the Red Alga Laurencia sp. (Rhodophyta, Ceramiales) Compared to Shoot Regeneration

Abstract

The occurrence of severa! forms of disorganized growth (filamentous, groups of cells and compact cell masses) has been reported in seaweed tissue culture as callus or callus-like, and in nature as galls, tumours or callus. Laurencia sp. formed callus in culture. To know whether callus or callus-like types of growth also occurred during regeneration, calluses were induced in explants, excised and cultivated separately. The growth pattern followed by these calluses and their main structural features, revealed by light and electron microscopy, were compared with those occurring on shoot regenerating explants in culture, and in wounded thallus regenerating in nature. Callus occurred as a compact cell mass at the proximal edge of the explants, bearing morphogenetic potential to regenerate shoots. The callus shared structural features with cells or group of cells from which shoots sprout in shoot-regenerating explants in culture. No callus, nor group of cells resembling callus, were seen in thallus regenerating in nature only shoot regeneration was observed.