POLYAMINE MEDIATED MODIFICATIONS OF BEAN LEAF RESPONSE TO NITROGEN-DIOXIDE

This study of exogenous polyamine effects on NO2 sensitivity of bean was 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 nitrogen 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 nitrate 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 mass were demonstrated in greening leaves on plants treated with a combination of nitrate and spermidine, in secondary leaves on plants given either polyamine with or without nitrate, and in senescing primary leaves on plants treated with nitrate and spermine or nitrate and spermidine. These protective effects could not be consistently related to differential levels of total chlorophyll or total organic nitrogen induced by the treatments. It is suggested that polyamines applied to plants supplied with nitrate are able to ameliorate the injurious effects of NO2 on growth by restricting NO2 conversion to injurious products, and/or protecting tissues from injurious products.