PHYSIOLOGICAL AND ANATOMICAL STUDIES ON CULTURING TISSUES OF PHASEOLUS VULGARIS PITTOLS VARYING IN AGE

Abstract

Explants from petioles of primary bean of varying ages (15, 21, 28, 35 and 42 days after sowing) were examined in callus tissue culture for their capacity for dedifferentiation and cell division activity in activity in relation to the hormonal status of the leaf and the anatomical structure of the petiole from which the explants were taken. Leaf area taken as growth parameter for primary bean leaves showed continuous increase up to the 3rd age then remained almost stable till the last age (yellowing). On the other hand, chlorophyll content taken as an indication for leaf development showed a similar pattern. Callus growth from the petiole explants of varying ages showed a similar trend to that of chlorophyll content of the leaf, yet the drop noticed occurred one week later at the 4th age. Explants of the last age (yellowing) showed late initiation of callus (70%) or complete failure of callus initiation (30%), parallel anatomical changes of the petiole revealed lignification of xylem parenchyma and transition of cambial cells into parenchyma starting from the 4th the 4th age. Meanwhile, activities of auxins and gibberellins in the primary leaf showed showed continuous decreasing tendency with increasing age together with the significant appearance of some inhibitors starting from the 4th age. On the other hand, cytokinins, activity increased to a maximum at the 3rd age then dropped to reach a minimum at the last age. The significance of these changes in view of the existence of irreversible processes during senescence that lead eventually to cellular death. is discussed.