Stress-induced nitric oxide and adaptive plasticity in conifers

The excitable properties of conifer protoplasm consist of nitric oxide (NO) bursts that prime and prepare chemical messengers for the transmission of stressful environmental signals. NO in somatic and reproductive cells is produced in response to mechanical forces, gravity, wounding, changes in nutrition, hypoxia, drought, salinity, temperature shock, pollutants, and pathogen attack. NO arises primarily from nitrite via nitrite:nitric oxide reductase and nitrate reductase. It also arises from arginine N and oxygen via putative nitric oxide synthase activity. NO rapidly reacts with, oxygen species, hemes, thiols, and proteins to produce biochemical signals that directly and indirectly regulate enzymatic activity. The effects of NO depend on its location and concentration. Beneficial reactions counteract oxidative and nitrosative stresses, while damaging reactions, due to high levels of NO, cause oxidative and nitrosative damage, and cell death. NO contributes to structural and functional adaptive plasticity, and to the habituation of trees to their sites. The use of NO donors and traps, and enzyme inhibitors offers a new experimental approach and countermeasures to control stress signals throughout conifer life histories.