Aluminium induced changes in the morphology of the quiescent centre, proximal meristem and growth region of the root of Zea mays

Treatment of the primary root with 8 mg dm-3 Al altered the pattern of cell growth so that with 48–h treatment, the root apex was no longer an organized, cytologically heterogeneous complex. An increase in mean cell volume was first observed with 2–h treatment, primarily in the cells of the quiescent centre where cell enlargement was associated with the removal of the constraint to quiescence by Al and in the mid-cortex 1–2 mm from the root tip where growth stimulation was associated with a departure from osmotic equilibrium. An initial increase in the osmotic potential of the root cell sap arising from Al treatment (1 h) was not maintained and subsequent decreases in the osmotic potential coincided with changes in the cell growth direction. Stress patterns arising from the anisotropic growth response of cortical cells with 20–h root exposure to Al were associated with the collapse of the conducting tissue of the stele and disintegration of the outer cells of the root. Advanced vacuolation of the cells of the root apex, first observed with 5–h treatment, was a feature of Al-stressed roots. Alteration to the nuclear structure in cells of the proximal meristem involving the degree of chromatin condensation and structure of the nucleolus was considered indicative of senescence. S. Afr. J. Bot. 1985, 51: 355–362 Behandeling van die primêre wortel met 8 mg dm−3 Al het die patroon van selgroei verander, sodat die wortelpunt na blootstelling van 48 h nie meer ‘n sitologies-georganiseerde geheel was nie. ‘n Toename in die gemiddelde selvolume is na blootstelling van 2 h waargeneem, hoofsaaklik in die selle van die rustende gebied, waar die vergroting van selle geassosieer is met die opheffing van die rustoestand, en in die sentrale korteks, 1–2 mm vanaf die wortelpunt, waar die aanvangsgroei gestimuleer is deur ‘n afwyking vanaf osmotiese ewewig. Die aanvanklike verhoging in die osmotiese potensiaal van die selsap, as gevolg van die Al-behandeling (1 h), is nie volgehou nie; die verlaging in osmotiese potensiaal het ooreengestem met veranderings in die rigting van selgroei. Spanningspatrone wat voortspruit uit die anisotropiese groeireaksie van die korteksselle na 20 h se blootstelling van die wortel aan Al, is geassosieer met die ineenstorting van die geleidingsweefsel van die stele en die disintegrasie van die wortels se epidermis. Gevorderde vakuolering van die wortelpuntselle wat vir die eerste keer opgemerk is met die 5 h-blootstelling is ‘n kenmerk van wortels wat aan Al blootgestel is. Veranderings in die kernstruktuur van die selle van die proksimale meristeem ten opsigte van die graad van chromatienkondensering in die struktuur van die nukleolus is beskou as aanduidings van veroudering. S.-Afr. Tydskr. Plantk. 1985, 51: 355–362