Histological evidence of morphogenesis from various explants of Jatropha curcas L.

Abstract

Jatropha curcas, a non-domesticated energy plant, has emerged as a source of biodiesel as it does not compete with the edible oil supplies. Realizing its importance, in vitro regeneration methods have been established to meet the demand of large scale supply of superior clones. However, no precise histological analysis has been conducted to document the in vitro morphogenesis in J. curcas. Here, we present a detailed histological description of the initiation of growth and morphogenesis from callus induced from immature cotyledon and embryonal axis of J. curcas. Microscopic observations revealed that the cells of sub-epidermis in immature cotyledon became meristematic and divided extensively to result in the formation of meristemoids within 3–4 weeks of culture. The meristemoid cells are compact, small, and exhibited densely stained cytoplasm compared to the loosely packed large non-meristematic cells. Presence of meristemoids in different developmental stages above the cambial zone, and the absence of vascular connection to the cotyledon explant led us to conclude that the origin of the meristemoids was adventitious in nature and regeneration is through organogenesis of morphogenic callus. On the other hand, callus derived from immature embryonal axis followed two types of regeneration—one type of shoot regeneration was via organogenesis while the second type was through multiplication of the pre-existing meristems. It was noticed that under similar experimental conditions, the process of organogenesis varied from explant to explant. The present study contributes to adequate knowledge and understanding the process of in vitro shoot morphogenesis in J. curcas.