PECTINS IN NORMAL AND VITREOUS APPLE MICROPLANTS CULTURED IN LIQUID-MEDIUM

Normal apple microplants (Pyrus malus cv M26) were obtained when grown in a liquid medium with hydrolysed agar. The microplants became vitre ous when grown in a medium without hydrolysed agar. A comparison of th e two types of microplants over a 40-day culture period showed that th e pectic content of vitreous microplants increased over the first few days of the culture whereas the percentage of uronic acid decreased. B oth parameters might be early markers of vitrification phenomena. Chan ges in the pectic content, the percentage of uronic acid and in the as sociated ions occurred in both media but at an interval difference of several days. Besides, the pectins in the normal microplants showed re latively low and constant degrees of esterification over a period of t ime whereas esterification in pectins isolated from vitreous microplan t increased greatly between 15 and 25 days. So, the antivitrification action of hydrolysed agar might act through some effects on enzymes im plied in the pectic metabolism, namely pectin methylesterase and pecti n methyltransferase. Because it was also noted that hydrolysed agar in hibited the growth at the same time as it protected against vitrificat ion, physiological differences could not be conclusively linked to the morphological aspects. of the microplants.