The Response Of Poplar To Osmotic Stress And Salinity And The Relevance To Salt Tolerance

Poplar is one of the most important tree species for afforestation and virescence in the north of China. A in-depth study on poplar tolerance can help us to get a better understanding of their physiological mechanism of tolerance, improve drought and salt tolerance of poplar, thereby guiding work of tree breeding. We have found that significant difference on drought tolerance among poplars (Chen et al, 1996; Chen et al, 1997; Chen et al, 2002c), but systematic research on poplar's tolerance has not been done yet. To know ulteriorly the responses to ion and osmotic stress for different poplars and the relationship between the responses and tolerance, Populus euphratica Olive, Populus pupularis 35-44' (P. popularis) and P. × euramericana cv. I-214 (P. cv. Italica) were used in this experiment. They were examined with short time of low salt/osmotic and long time of high salt stress. During the treatment, relative growth rates of shoot height (RGR_h), gas exchange, ABA and CaM (ELISA) were measured respectively. In this study we investigated the response of poplar to osmotic stress and salinity and the relevance to salt tolerance. The results are followed. (i) under short low salt/osmotic stressa) NaCl and PEG treatment caused evident enhancement on Pn, Cs and TRN at 24 h except for Na~+ treatment, and Pn and Cs were decreased by 34% and 23% respectively with Na~+ treatment in P. euphratica. These results indicated that low salt/osmotic condition could induce resistance of Peuphratica, and Na~+ inhibited obviously the growth of P.euphratica.b) Leaf ABA content of P.euphratica increased gradually after the onset of PEG stress, and reached maximum at 4 h, and TRN also reduced significantly at 4 h. The reducation of TRN was more pronounced with Na~+ and NaCl treatment at 4 h. These results showed that the increase of ABA content could mainly result from the function of osmotic stress at the beginning of stress in P.euphratica. Furthermore, leaf ABA content of P.popularis didn't increase evidently until 24h under low salt/osmotic stress, which suggested P.euphraticawas more sensitive to soil salinity than P.popularis.c) At 1 h, leaf CaM content of P.euphratica enhanced markedly under salt/osmotic stress, but ABA didn't increase until 4 h. This implied there were other signals to induce increase of leaf CaM content at the beginning of stress in P.euphratica. On the other hand, leaf CaM content of P.popularis reduced at 24 h except for Na~+ and PEG treatment, which indicating that P.popularis had lower resistance under low salinity than P.euphratica, and the effect of Cl~- stress on P.popularis was more significant than that of Na~+ stress.d) Leaf ABA content of P.euphratica of which the roots were treated by Ca, CaM antagonists was increased by 51% and 82% respectively after 24 h salt/PEG treatment. Leaf CaM content of them also increased significantly. But Pn, Cs, TRN reduced markedly, and Pn reduced by 56% and 79% respectively. Leaf CaM content of P.popularis which the roots were treated by Ca, CaM antagonists rose greatly, however the changes of ABA content, Pn, Cs and TRN weren't significant after 24 h salt stress. We concluded that P.euphratica could response to salt/PEG stress, and synthesize ABA and CaM to regulate physiological change. In addition, the results implied CaM may work in stomatal close caused by ABA. (ii) under increasing high salinitya) Though RGRh of P.euphratica reduced, it was 94% of that of control plants on day 28 during the period of NaCl stress. On day 28, the reductions of RGRh were more pronounced in salinized plants of P.popularis and P. cv.Italica. At the same time, P.euphratica maintained a relatively higher Pn level, but Pn were reduced by 88%-92% in P.popularis and P. cv.Italica, which indicated that P.euphratica had higher salt tolerance than P.popularis and P. cv.Italica. And P.euphratica maintained higher TRN level, which was 96% of that of controls showing P.euphratica have strong capacity to absorb and transport water.b) Leaf ABA and CaM contents in P.euphratica significantly incr...