Responses of greening bean seedling leaves to nitrogen dioxide and nutrient nitrate supply

Phaseolus vulgaris cv. Kinghorn Wax seedlings grown in darkness at 25 degrees C for 7 days with half strength Hoagland's nutrient solution containing no nitrogen, were transferred to lit continuous stirred tank reactors (CSTRs) in atmospheres containing 0 or 0.3 ppm NO(2) and irrigated with a nutrient solution containing 0 or 5 mm nitrate as sole nitrogen source and allowed to grow for a period of up to 5 days in a 14 h photoperiod. Exposure to NO(2) increased total Kjeldahl nitrogen in the leaves. Further, the exposure to NO(2) increased chlorophyll content from day 3 onwards and inhibited the leaf dry weight substantially on days 4 and 5. The primary leaves of the seedlings exposed to 0.3 ppm NO(2) and supplied with nitrate accumulated some nitrite after 5 days of exposure. Some of the seedlings were returned from CSTRs to growth chambers and allowed to grow for a further period of 5 days in a 14 h photoperiod without NO(2). The growth which developed after the NO(2) exposure growth period, as measured by fresh and dry weights of the leaves, was significantly less in NO(2)-exposed plants than in nitrate-grown plants. The experiments demonstrate that the leaves of greening seedlings are able to assimilate NO(2) and that a reduction in leaf dry weight by prolonged NO(2) exposure in the presence of nutrient nitrate can be associated with nitrite accumulation, and that NO(2) has a carry-over effect beyond the duration of NO(2) exposure. It is apparent that NO(2) induces some durable biochemical or cytological aberration in the presence of nutrient nitrate, which adversely affects subsequent leaf growth.