Abstract:

Polyamine (PA) plays an important role in the regulation of senescence and stress-resistance of plants. It has been reported that PA accumulated, and the activities of PA-associated enzymes, involving polyamine oxidase (PAO), increased rapidly in leaves under drought stress. However, little is known about the effect of drought stress on PA metabolism of roots. In the present experiment, two wheat cultivar seedlings with different drought-resistances (Triticum aestivum L. cv. Jinmai 33 and Wenmai 8) under sand-cultivation were used to study the relationship between PA metabolism and drought-resistance. The results showed that the relative water content (RWC) of leaves declined gradually during drought stress (without water supply) compared with controls (with water supply during treatment), and the cv. Wenmai 8 (drought-resistant cultivar) could maintain more leaf RWC than cv. Jinmai 33 (drought-susceptible cultivar) after 48 h of drought stress. The PA (Put, Spd, Spm) content and PAO activity in roots and leaves of seedlings increased quickly during drought stress for 12 h. At this time, the contents of putrescine (Put), spermidine (Spd), spermine (Spm) in drought-treated seedlings of cv. Jinmai 33 were 86%, 69%, 50% higher than control in roots, and 71%, 18%, 11% higher in leaves, while in cv. Wenmai 8 these were 91%, 103%, 85% higher in roots, and 78%, 55%, 53% higher in leaves than control, respectively. The change of PAO activity between two cultivars differed, PAO activity in roots and leaves of drought treated seedlings were 47%, 40% in cv. Jinmai 33, and 26%, 10% in cv. Wenmai 8 higher than their control, respectively. Afterwards, the PA (Put, Spd, Spm) content and PAO activity in roots and leaves of seedlings in two cultivars all decreased, which PA did in a slower rate in cv. Wenmai 8. The Put content and PAO activity in roots and leaves of both cultivars, and the contents of Spd and Spm in cv. Jinmai 33 under drought stress, were significantly lower than their control, whereas the Spm and Spd contents in cv. Wenmai 8 were similar with control during drought stress for 48 h. The changing trends of PA content and PAO activity in roots and leaves were similar. A significant positive relationship in PA content and PAO activity was found between roots and leaves. It is suggested that the rapid accumulation of PA might be a signal responding to drought stress at first, and then the higher contents of Spm and Spd in roots and leaves could enhance drought-resistance in wheat seedlings.