Effect of devernalization on the transition from vegetative to prefloral phase of the broccoli (Brassica oleracea var. italica cv. 'Fiesta') shoot meristem

Abstract

The morphological and histological changes which occur in the cold-induced apical meristem of broccoli (B. oleracea var. italica cv. ‘Fiesta’) during transition from the vegetative to the generative phase have been demonstrated in our previous investigations. Now, a light microscopic study on the micromorphological parameters of the tunica and corpus of the meristem was undertaken to ascertain their association with devernalisation. Changes in the apex of broccoli seedlings grown for 26 days at 24^oC, succeeded by 35 days of cold treatment (16^oC - vernalization) followed by 14 days of warm treatment (24^oC - devernalization), were studied and described. Microscopic analysis according to the new method of slide preparation showed cytohistological zonation and the spatial distribution of cells in the central and peripheral zones of the broccoli shoot meristem more precisely than possible hitherto. Comparison between subsequent stages of meristem reorganization after devernalization revealed variation in the structure of the apex during its transition to the evocation phase of flowering. The results of measurements show that the tunica width changes irregularly, increasing from its minimum value (112.39±5.78 μm) through the medium one to the maximum values (260.32±2.50), to decrease again, while its height increased and decreased sinusoidally from its minimum value (21.52±4.30μm) to the maximum one (76.98±7.44μm) and then decreasing again to the minimum value (21.52±4.30). The stratification of the tunica as well as its width and height revealed relatively low variation within the analyzed time. These structural traits correlated with cold/warm treatments may be further utilized in the broccoli breeding programme against developmental disturbances.