INFLUENCE OF UV-B RADIATION AND PUTRESCINE ON SHOOT AND ROOT-GROWTH OF CUCUMBER SEEDLINGS GROWN IN NUTRIENT SOLUTION

Poinsett cucumber (Cucumis sativus L.) seedlings were grown in growth chambers in nutrient solution containing 0 or 500 mu M putrescine (Put ) and were exposed to 0.2 or 15 kJ.m(-2).day(-1) of biologically effec tive UV-B radiation to determine the comparative sensitivity of shoots and roots to increased UVB and the possible protective effect of poly amines. Shoot growth in UV-B-treated plants was reduced 48%, root grow th 63%, total leaf area 38%, and specific leaf weight (SLW) 22%. This was in contrast to previous reports of increased SLW in cucumber plant s grown in vermiculite or in a peat-vermiculite mix. Putrescine treatm ent increased leaf area in the second and third leaf and total leaf ar ea and Put also increased dry weight of shoots, but had no effect on d ry weight of roots or on SLW. The Put treatment was ineffective in ame liorating UV-B induced leaf chlorosis. This is the first report of gre ater sensitivity of roots to UV-B radiation than of shoots in plants g rown in solution culture. This could have significant consequences on marginal lands where root growth is already under limiting conditions.