【目的】植物叶片早衰将影响作物产量和品质,研究叶片早衰机制对于培育耐早衰优良品种具有重要意义。【方法】以转BpGH3.5基因的白桦叶片早衰突变株(G4)、非转基因白桦(WT)及叶片正常的转基因白桦(G21)等为材料,测定其叶绿素含量、净光合速率(P_n)、气孔导度(G_s)、胞间CO₂浓度(C_i)、蒸腾速率(T_r)等光合指标,测定苗高的时序变化规律。【结果】叶片早衰突变影响了叶片叶绿素的合成及积累,突变株的叶绿素相对含量(SPAD)均值为36.08,相对两个对照株系分别下降7.34%、7.48%。叶片早衰突变影响了白桦光合呼吸作用。突变株的净光合速率、气孔导度、蒸腾速率分别为WT野生株系的67.54%、64.44%、64.93%,胞间CO₂浓度达到234.33 μmol/mol,显著高于G21对照株系( P<0.05)。突变株的当年高生长显著低于WT、G21 两个对照株系,当年高生长分别是WT、G21 两个对照株系的68.9%、85.0%。利用Logistic方程对3个参试株系当年苗高生长量的变化过程进行了拟合,其系数均高于0.98,同时,通过Logistic方程计算的生长参数揭示了早衰突变株高生长较两个对照株系低的原因是速生期苗高平均生长量(GR)、苗高日生长量的平均值(GD)等生长参数较低。【结论】转BpGH3.5基因的白桦发生了叶片早衰现象,使叶绿素提前降解,影响了光合呼吸作用,进而影响了苗高生长。

【Objective】 Knowing that precocious leaf senescence affects plant growth and wood quality, we aimed to understand the effect of precocious leaf senescence on photosynthesis and growth to reveal the mechanism underlying this phenomenon, and to create cultivars resistant to it. 【Method】 We used BpGH3.5 transgenic Betula platyphylla plants lines showing precocious leaf senescence (G4), non-transgenic B. platyphylla plants (WT), and transgenic plants with normal leaves (G21) to perform molecular analyses. Genetic transformation results were analyzed by quantitative gene expression. Moreover, experiments were performed to determine the chlorophyll content, the net photosynthetic rate ( P_n), the stomatal conductance (G_s), the intercellular carbon dioxide concentration (C_i), and the transpiration rate (T_r) for each plant. In addition, the seedling height was measured in a time series. Finally, a logistic model was used to perform fitting analysis and to judge the differences between growth parameters. 【Result】 The BpGH3.5 mutation affected both the synthesis and accumulation of chlorophyll in leaves. The average SPAD value of the mutant line was 36.08, which was 7.34% and 7.48% lower than that of the WT and the G21 plants, respectively. The B. platyphylla BpGH3.5 transgenic line G4 showed significant alterations in photosynthetic respiration values: net photosynthetic rate, stomatal conductance and transpiration rate in mutant lines were 67.54%, 64.44% and 64.93% compared with those from the WT line, respectively. The intercellular carbon dioxide concentration (234.33 μmol/mol) was significantly higher in G4 lines than in that G21 lines ( P < 0.05). Tree height current increment of BpGH3.5 transgenic line G4 was significantly lower than that from WT and G21 lines (representing the 68.9% and 85.0% of WT and G21, respectively). A Logistic model was used to fit tree height current increment of the three tested lines. All fitting coefficients were higher than 0.98. Moreover, calculated growth revealed that the height of the G4 mutant was lower than that of the two control lines, G21 and WT. This was due to a slow growth during the fast-growing period (GR) and a low daily growth rate in plant height (GD). 【Conclusion】 A mutation leading to precocious leaf senescence led to early degradation of chlorophyll in early leaf shedding. As a result, it affected the photosynthetic and respiration pathways, leading to a reduction in Betula platyphylla plant height.