AN ENDO-1,4-BETA-GLUCANASE EXPRESSED AT HIGH-LEVELS IN RAPIDLY EXPANDING TISSUES

Plant developmental processes involving modifications to cell wall str ucture, such as cell expansion, organ abscission and fruit ripening, a re accompanied by increased enzyme activity and mRNA abundance of endo -l,4-beta-glucanases (EGases). An EGase cDNA clone, Ce14, isolated fro m tomato (Lycopersicon esculentum) has been shown to be identical to a tomato pistil-predominant EGase cDNA, TPP18. In addition to its previ ously reported expression during certain stages of early pistil develo pment, Ce14 mRNA was also detected at high levels in the growing zones of etiolated hypocotyls (about 2.5-fold less than in pistils) and in young expanding leaves (about 3.5-fold less than in pistils). The abun dance of Ce14 mRNA declined precipitously in older tissues as cells be came fully expanded, and was barely detectable in mature vegetative ti ssues. Ce14 mRNA abundance was also low in abscission zones, and did n ot increase as abscission progressed. In fruit, Ce14 mRNA was present at low levels during fruit expansion, but was essentially absent durin g subsequent fruit development and ripening. Treatment of etiolated hy pocotyls with ethylene or high concentrations of auxin sufficient to i nduce rapid lateral cell expansion and hypocotyl swelling also brought about an approximate doubling of Ce14 mRNA abundance, suggesting that Ce14 mRNA accumulation may be promoted directly or indirectly by ethy lene. Thus. accumulation of Ce14 mRNA was found to be correlated with rapid cell expansion in pistils, hypocotyls and leaves.