VACUOLE FORMATION IN THE ACTIVELY GROWING ROOT MERISTEM OF BARLEY (HORDEUM SATIVUM)

The subapical meristem of actively growing barley roots produces series of undifferentiated cells, some of which are devoid of vacuoles. At the beginning of their differentiation, the Golgi apparatus gives rise to vesicles and tubules which concentrate hydrolases, acid phosphatase being the typical representative of these enzymes. Some of these structures organize themselves as sequestration vacuoles. Then, the imprisoned fraction is destroyed by the process of autophagy after an alteration of the vacuolar internal membrane. These structures are identical to the “provacuolar apparatus” described by Marty in Euphorbia characias roots. Lytic processes which develop in autophagic vacuoles give rise to the first true meristematic vacuoles. Relations between dictyosomes, provacuoles and vacuoles, and their degree of exclusivity are discussed.