Abstract:

【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.

Key words: Betula platyphylla, BpGH3.5, mutant, precocious leaf senescence, characterization of photosynthetic