Influence of UV‐B radiation and putrescine on shoot and root growth of cucumber seedlings grown in nutrient solution

Abstract

Poinsett cucumber (Cucumis sativus L.) seedlings were grown in growth chambers in nutrient solution containing 0 or 500 μM putrescine (Put) and were exposed to 0.2 or 15 kJ‐m‐² day¹ of biologically effective UV‐B radiation to determine the comparative sensitivity of shoots and roots to increased UV‐B and the possible protective effect of polyamines. Shoot growth in UV‐B‐treated plants was reduced 48%, root growth 63%, total leaf area 38%, and specific leaf weight (SLW) 22%. This was in contrast to previous reports of increased SLW in cucumber plants grown in vermiculite or in a peat‐vermiculite mix. Putrescine treatment increased leaf area in the second and third leaf and total leaf area and Put also increased dry weight of shoots, but had no effect on dry weight of roots or on SLW. The Put treatment was ineffective in ameliorating UV‐B induced leaf chlorosis. This is the first report of greater sensitivity of roots to UV‐B radiation than of shoots in plants grown in solution culture. This could have significant consequences on marginal lands where root growth is already under limiting conditions.