为从能量平衡及分配的角度研究干旱胁迫下甘蔗(Saccharum officinarum)苗期光系统的运转状况, 进而为丰富不同甘蔗品种的抗旱性评价指标及实现对季节性干旱胁迫的快速诊断提供理论依据, 该研究通过对基于Lake模型的叶绿素荧光参数在不同入射光强下变化的动态分析, 研究光合电子传递链中能量平衡状态对不同水分梯度(40%、25%、10%、8%)的响应。结果表明: 两个供试品种(耐旱品种‘ROC22’和非耐旱品种‘ROC16’)的最大光能利用效率(Fv/Fm)、相对电子传递速率(rETR)、光系统II(PSII)量子效率(ΦII)和光化学猝灭(qL)均随着干旱胁迫程度的增加而下降, 可调节性能量耗散(ΦNPQ)和非调节性能量耗散(ΦNO)则随着干旱胁迫程度的增加而上升。除ΦNO之外的叶绿素荧光参数的变化幅度均随着光合有效辐射(PAR)的增加而增大。在干旱胁迫的前中期, 相对于‘ROC22’, ‘ROC16’的PSII反应中心能够维持较高的开放程度; 但‘ROC22’调节能量耗散的能力和对干旱胁迫的敏感程度均高于‘ROC16’, 说明较强的光保护能力是‘ROC22’的抗旱性高于‘ROC16’的主要原因之一。对干旱胁迫敏感且在不同PAR下较为稳定的ΦNO可作为甘蔗苗期抗旱性的快速诊断和评价指标。rETR对递增的PAR的响应表现为随着干旱胁迫程度的增加而提前出现峰值或下降趋势, 但是不同水分梯度下的rETR在PAR较低时并无显著差异, 表明干旱胁迫下光抑制现象的提早出现是造成光系统损伤的首要因素, 高光强对干旱胁迫信号起放大作用。
Aims Spring drought greatly limits the sugarcane (Saccharum officinarum) seedling growth in the southwest China. A major objective of this study is to investigate the change of the energy allocation in photosystem II (PSII) resulted from the stomatal and non-stomatal limit of photosynthesis under the drought stress condition. The study results can be used for drought resistant breeding and rapid drought stress diagnosis.
Methods Four levels (40%, 25%, 10% and 8%) of soil volumetric water content (VWC) have been chosen from natural drought treatments. The chlorophyll fluorescence parameters based on Lake-model were measured and analyzed with various levels of photosynthetically active radiation (PAR).
Important findings Results of the study in the enhanced drought stress for two tested cultivars (‘ROC22’ and ‘ROC16’) showed 1) decreased numbers in the maximum quantum use efficiency (Fv/Fm), the relative electron transport rate (rETR), the quantum efficiency of PSII (ΦII) and the photochemical quenching (qL) and 2) increased numbers in the down-regulated energy dissipation (ΦNPQ) and the non-light induced energy dissipation (ΦNO). There was no significant difference between the parameter qL of ‘ROC16’ and ‘ROC22’, except for the 8% level where the qL showed a sharp decline. The results indicated that the PSII of ‘ROC16’ remained a relatively high open fraction during the mild drought stress, but suffered severe damage in serious drought stress. The rising range of ΦNPQ for ‘ROC22’ were higher and more sensitive to drought stress than that of ‘ROC16’, which revealed a strong drought resistance resulted from strong photo-protective mechanism in‘ROC22’. The ΦNO was more sensitive to drought stress than Fv/Fm especially for non drought resistant variety, and remained high stability under different PAR. Therefore, ΦNO could be properly used as an indicator in drought stress diagnosis and resistance evaluation. Photo inhibition could be the initial factor leading to PSII damage and its signal had been amplified under high PAR related to photo inhibition since the appeared peak or decline of rETR related to increased PAR and its no significance at each water level and low PAR during drought stress.