Nitric oxide functions as a signal in ultraviolet-B induced inhibition of pea stems elongation

The effects of ultraviolet-B (UV-B) radiation on stem elongation growth, xyloglucan-degrading activity, the rate of nitric oxide (NO) release and nitric oxide synthase (NOS) activity were evaluated in stems of pea (Pisum sativum L.) seedlings during a 5 days growth period. UV-B radiation significantly induced NOS activity and promoted NO release subsequently inhibited xyloglucan-degrading activity which led to the inhibition of pea stems elongation. Similarly, exogenous NO donation to the rhizospheric zone of pea seedlings imitated the responses of stems to UV-B radiation. NOS inhibitor (LNNA) and NO scavenger (PTIO) had the opposite responses to UV-B radiation: decrease NO release, increase xyloglucan-degrading activity and stems elongation. The results indicated that reduction of stems length caused by UV-B radiation was possibly achieved through modification of the mechanical properties of cell wall polysaccharides, which was probably mediated by the change of xyloglucan-degrading activities in cell walls and NO might be as a signal regulating the xyloglucan-degrading activities in cell walls. In addition, the difference of NOS origin between graminaceous plants and dicots was discussed.