Relationship between auxins and cytokinins in the growth and organogenesis of Ocimum basilicum L. ‘Grecco a Palla’

Abstract

The in vitro development of a plant is controlled by factors that promote a series of plant responses, which interfere with tissue organogenesis and morphology. For plants of the family Lamiaceae, these factors remain unknown or poorly understood, hindering in vitro cultivation of these plants. The basil cultivar ‘Grecco a palla’ has attractive chemical properties for medicinal, pharmaceutical, and cosmetic industries; however, its production is limited due to the lack of appropriate cultivation conditions. Two types of explants of this species (nodal segments and stem apexes) were grown in culture media with auxin and cytokinin, and their development was followed for 60 days. During in vitro cultivation, both explants were subjected to higher concentrations of plant growth regulators (PGRs) produced only calluses, without induction of shoots. Small amounts of regulators favored hyperhydricity as nodal segments or stem apexes in the absence of PGRs produced plants with disturbances, including brittle, light green, and thick leaves. In this case, there was an increase in the cell layers of palisade parenchyma, which had large cell spaces and larger cells. This tissue also advanced to spongy parenchyma and compressed it. The stomatal density was low; however, the stomata were larger with additions mainly in the guard cells and the stomatic opening. Therefore, stem apexes in the absence of PGRs produced more vigorous plants, whereas nodal segments with low amounts of cytokinins and auxins developed a well-branched and abundant root system.