Abstract:

Objective: The study explored agarwood formation process of Aquilaria sinensis and physiological reaction by trunk-filling high-pressure carbon dioxide gas, with the aim to find available solution to induce agarwood formation by carbon dioxide and to understand the physiological mechanisms. Method: A randomized block design was used to deal with eleven-year-old trees. The inflating CO₂ was conducted at every 7 days (T1) and 15 days (T2) interval for three months. POD (peroxidase), SOD (superoxide dismutase) and CAT (catalase) activity and MDA (malonaldehyde) content were detected on the 30th, 60th, 90th, 120th,150th day after first inflating. The content of alcohol soluble extraction and agarotetrol, and the discoloration range of stem wood were determined in seven months and ten months after treatment. Result: 1) It was found that the stem-inflated CO₂ could speed up the transformation of starch granules in ray parenchyma cells and vessels. With the increase of induction time, the tylosis accumulated could completely blocked the ray cells and vessels in 10 months after T1 treatment. 2) Compared to CK1 and CK2, the discoloration ranges of stem xylem with CO₂ treatments was more longer. T1 treatment produced the maximal discoloration ranges of the longitudinal length of 26.45 cm, the horizontal width of 4.17 cm, and the radial length of 9.87 cm.3） The content of alcohol soluble extraction and agarotetrol gradually increased with T1 and T2 treatments, which were significantly higher than that of CK1 and CK2. 4) After 60 days under the T1 treatment, POD and CAT activity reached the peak value and then decreased slowly. However, POD activity was still higher than that of CK2. while the CAT activity had no significant difference with CK2 on the 150th days. SOD activity decreased in the first 90 days and then slowly increased. The content of MDA decreased firstly and dropped to the lowest value that dramatically lower than CK2 on the 90th day. On the 150th days, SOD activity and the content of MDA of T1 had no obvious difference compared with CK2. Conclusion: 1）Exogenous CO₂ could significantly promote conversion of starch in the xylem ray cell, which lead to more blockage with tylosis accumulating in vessel and ray parenchyma cell. 2) Exogenous CO₂ could induce the xylem discoloration, and the lengths in longitudinal, transverse and radial direction were all longer than the control. 3) Exogenous CO₂ could induce A. sinensis trees to form blocky agarwood with exquisite texture. The alcohol-soluble substances and agarotetrol contents was respectively 21.27% and 0.29% in the 10 months after the optimal treatment of T1, and was 1.42 and 2.11 times of that of CK1. 4) Exogenous CO₂ could activate the defense reaction of A. sinensis trees.

Key words: Aquilaria sinensis, carbon dioxide, trunk-filling, agarwood, alcohol soluble extraction