POLYAMINE MEDIATED MODIFICATIONS OF BEAN LEAF RESPONSE TO NITROGEN-DIOXIDE

This study of exogenous polyamine effects on NO2 sensitivity of bean w as designed to elucidate relationships between spermine and spermidine , NO2 exposure and nitrogen nutrition, and their effects on leaves at different physiological stages. Green bean (Phaseolus vulgaris L. cv. Kinghorn Wax) seedlings were raised on nutrient solution without nitro gen either in the dark for 7 d or in a 14-h photoperiod for 14 d. The plants were then treated with nutrient solution containign 0 or 5 mM n itrate as nitrogen source and 100 mu M spermine or spermidine with our without nitrate, and exposed to 0.3 mu L L(-1) NO2 for 3 d in a 14 h photoperiod. Protective effects against NO2-induced loss of leaf dry m ass were demonstrated in greening leaves on plants treated with a comb ination of nitrate and spermidine, in secondary leaves on plants given either polyamine with or without nitrate, and in senescing primary le aves on plants treated with nitrate and spermine or nitrate and spermi dine. These protective effects could not be consistently related to di fferential levels of total chlorophyll or total organic nitrogen induc ed by the treatments. It is suggested that polyamines applied to plant s supplied with nitrate are able to ameliorate the injurious effects o f NO2 on growth by restricting NO2 conversion to injurious products, a nd/or protecting tissues from injurious products.