Nitric Oxide Fumigation Research Articles

Expression of a nitric oxide degrading enzyme induces a senescence programme in Arabidopsis

Nitric oxide (NO) has been proposed to act as a factor delaying leaf senescence and fruit maturation in plants. Here we show that expression of a NO degrading dioxygenase (NOD) in Arabidopsis thaliana initiates a senescence-like phenotype, an effect that proved to be more pronounced in older than in younger leaves. This senescence phenotype was preceded by a massive switch in gene expression in which photosynthetic genes were down-regulated, whereas many senescence-associated genes (SAGs) and the 1-aminocyclopropane-1-carboxylic acid (ACC) synthase gene ACS6 involved in ethylene synthesis were up-regulated. External fumigation of NOD plants with NO as well as environmental conditions known to stimulate endogenous NO production attenuated the induced senescence programme. For instance, both high light conditions and nitrate feeding reduced the senescence phenotype and attenuated the down-regulation of photosynthetic genes as well as the up-regulation of SAGs. Treatment of plants with the cytokinin 6-benzylaminopurin (BAP) reduced the down-regulation of photosynthesis, although it had no consistent effect on SAG expression. Metabolic changes during NOD-induced senescence comprehended increases in salicylic acid (SA) levels, accumulation of the phytoalexin camalexin and elevation of leaf gamma-tocopherol contents, all of which occurred during natural senescence in Arabidopsis leaves as well. Moreover, NO fumigation delayed the senescence process induced by darkening individual Arabidopsis Columbia-0 (Col-0) leaves. Our data thus support the notion that NO acts as a negative regulator of leaf senescence.

The effect of nitric oxide fumigation at two CO2 concentrations on net photosynthesis and stomatal resistance of tomato (Lycopersicon lycopersicum L. cv. Abunda)

SUMMARYNet photosynthesis of 5‐week‐old tomato plants (Lycopersicon lycopersicum L. cv. Abunda), was measured in clean air or with NO fumigation, for five consecutive days under simulated winter glasshouse conditions: temperature 22 °C, VPD 04 kPa, irradiance 30 W m−2 and daylength 8–9 h. NO concentrations applied were 0 or 1 μl 1−1 in combination with CO, concentrations of 350 or 1000 μl −1.A reduction in net photosynthesis due to NO became apparent on the third day of measurement. On the fifth day this reduction was 38%, of the control at 350 μl −1 CO2 and 24%, at 1000 μl −1 CO2. The increase in photosynthesis due to CO, enrichment was initially 40%; this effect was strongly reduced after 5 d in the presence of NO. Plants did not recover in the dark after the daily fumigation treatment, the level to which photosynthesis was reduced at the end of the day being the level at which it started the next day. The decrease in photosynthesis could not be explained by an increased stomatal resistance, and the plants did not show visible symptoms of injury. Practical implications of the results are discussed.