Polygalacturonase (PG) in higher plants has been considered to be associated with ripening fruits although it is now known to be present in foliage and storage organs. We recently found very high levels of PG in some grass pollens (Plant Science 59, 57-62, 1989). This prompted an examination of other pollens for PG activity. All of the pollens analyzed contained PG but the range of activities was great. Eastern cottonwood pollen contained the most PG, with a level about 12 times higher than that usually found in ripe tomato fruit. Pollens from the other members of Populus were generally high in PG. Pollens from the oak family also contained very high PG, with the highest amount in white oak pollen. Pollens from pecan, English walnut, willows, birch and hickories contained moderate levels of PG. The lowest amounts of PG were found in pollens from beech, sycamore and conifers. The PG's from the two richest sources (eastern cottonwood and white oak pollens) were partially purified and characterized. Both enzymes were found to be exopolygalacturonases that require Ca2+ for activity. PG may be involved in some function related to pollination but an explanation for the wide range of activities indifferent pollen is not obvious.
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