Modifications of photosynthetic activity and chioropiast morphology associated with in vitro trans-differentiation of Zinnia mesophyil cells into tracheary elements.

Abstract

Chioropiast morphology, chlorophyll dynamics and photosynthetic activity of Zinnia leaf mesophyil cells were studied during trans-differentiation into tracheary elements with the view of understanding the modification of these parameters in relation to TE differentiation. Size and the density (no. off chloropiasts/ cell) were drastically declined during the period from 48-72 hrs. off culture, which precisely overlaps with the initial deposition of wall hands, irrespective of light/ dark conditions. Distinct differences could be observed between nascent TEs and non-differentiating live cells in these events. Total photosynthetic activity was lost completely during the I s' 24 hrs. of culture, which coincided with de-differentiation of mesophyil cells, not necessarily be related to TE differentiation, but essentially to trans-differentiation. Both the PS I and PS II activity dropped rapidly between 48-72 hrs. of culture followed by complete loss of activity after 72 hrs (PS II) and 96 hrs (PS I), respectively. Total chlorophyll content was stable up to 48 hrs. and then declined sharply with a greater impact on chl-a content, as indicated by lowering chl-a:b ratio with time. There was no clear impact of light on these parameters except in the case of PS II activity where a faster rate of decline was observed in dark, right from the initiation of culture. As indicated by these findings, loss of PS activity and degradation of chioropiast structure of mesophyil cells are closely associated with the events of de-differentiation and secondary wall deposition, marking the arrest of metabolism in general, culminating cell death, accompanied with TE differentiation.