The Regulative Effects Of Exogenous ABA And Ca²⁺ On The Growth Of Poplar Cuttings

This paper was undertaken to study the regulative effects of the exogenous ABA and Ca²⁺ on photosynthesis, photosynthate transport and the related physiological indexes of Populus×euramericana cv.'Nanlin95'by indoor water culture and outdoor cutting, thereby to explore the regulative effect of exogenous ABA and Ca²⁺ on the growth of poplar cuttings. The results showed as follows:1. In a certain concentration range, the growth of water cultivated poplar seedlings would be improved with accession of Ca²⁺ into the nutrient solution, and the effects of Ca²⁺ at 0.1mmol/L were the most remarkable. In 0⁰.1mmol/L range, Ca²⁺ can not only enhanced Pn, chlorophyll content, root activity of water cultivated poplar seedlings, but also enhanced its SOD, POD activity and reduced the content of MDA, therefore promoted the metabolism of reactive oxygen species of water cultivated poplar seedlings to ensure poplar seedlings at a normal growth and development. When the Ca²⁺ concentration exceeded 0.1mmol/L, the growth of water cultivated poplar seedlings started to be inhibited; and when Ca²⁺ concentrations is as high as 10 and 50mmol/L, the water cultivated poplar seedlings survived only 60d and 30d respectively.2. Under the same ABA concentration stress, the relaxation effect of Ca²⁺ on water cultivated poplar seedlings was different. When ABA concentration was fixed, the relaxation effects of 0.1mmol/L and 2mmol/L Ca²⁺ on ABA stress were studied, the result showed that the Pn, chlorophyll content, root activity and the protective enzymes activities of poplar seedlings under ABA+Hoagland(2) treatment which containing 0.1mmol/L Ca²⁺ were higher than those under the ABA+Hoagland(1) treatments containing 2mmol/L Ca²⁺, and the content of MDA under ABA+Hoagland(2) treatment was less than that under the ABA+Hoagland(1) treatments, indicating that 0.1mmol/L Ca²⁺ could relax the ABA stress on water cultivated poplar seedlings more effectively than 2mmol/L Ca²⁺ did.3. The sink strength of'Nanlin95'cuttings would be improved somewhat by spraying Ca²⁺ of different concentration on leaves of poplar cuttings, and the optimum Ca²⁺ concentration was 20mg/L. In 0²0mg/L range, Ca²⁺ could effectively improve the Pn, chlorophyll and soluble protein content of poplar cuttings, promote its accumulation of soluble sugar and increase its sink strength of the stem, thereby promoted the transportation of photosynthate from leaves to stems of poplar; in this certain concentration range, Ca²⁺ would be able to regulate the activities of protective enzymes in leaves and stem of poplar cuttings and to reduce its MDA content, promoting the metabolism of reactive oxygen species accordingly; when Ca²⁺ concentration exceeded 20mg/L, all the indexes which is beneficial to the growth of poplar cuttings began to decline, and the promotion effects on the growth of poplar'Nanlin95'started weakening. In addition, spraying Ca²⁺ on poplar leaves can increase the contents of enogenous IAA, GA3 and ZR, the effect of 20mg/L was the most remarkable, however, there is no significant effect on the content of enogenous ABA.4. Spraying ABA on leaves of poplar'Nanlin95'cuttings could increase its sink strength effectively, which would facilitate photosynthate transport; the study of spraying ABA+Ca²⁺ on the leaves of poplar'Nanlin95'cuttings revealed that Ca²⁺ had an antagonistic effect on ABA. Low ABA concentration (0.1, 10mg/L) could promote Pn, accumulation and metabolism of sucrose in the leaves and stems of poplar cuttings and increase the sink strength of the stems to faciliate the transport of photosynthates. But high ABA concentration (100, 150mg/L) showed the opposite effect. With the treatment of ABA, chlorophyll content in poplar leaves and soluble protein content, SOD activity, and MDA content in leaves and stems of poplar cuttings dropped gradually. The POD activity under all the ABA treatments had no significant changes, with the exception of 0.1 mg/L ABA decreasing its activity. With the increasing of ABA concentration, the enogenous ABA content in leaves of poplar cuttings presented an gradually rising trend while the trend of GA3 content is quite different; enogenous IAA and ZR content in poplar leaves would increase under high ABA concentration and decrease under low ABA concentration. Moreover, the results also suggested that an antagonistic effect existed between ABA and Ca²⁺; ABA+Ca treatments could promote the growth of poplar cuttings much better compared with ABA treatments.