田间条件下棉花幼叶光合特性及光保护机制

doi:10.3724/SP.J.1258.2012.00662

摘要/Abstract

摘要：

通过比较棉花(Gossypium hirsutum)幼叶和完全展开叶气体交换参数及叶绿素荧光特性的差异, 探讨高光强下幼叶的光抑制程度及明确光保护机制间的协调机理。在田间自然条件下, 以棉花刚展平的幼嫩叶片(幼叶)和面积已达到最大的完全展开叶片为研究对象, 通过测定不同发育阶段叶片气体交换参数及叶绿素a荧光参数的变化, 并运用Dual-PAM100对不同发育阶段的叶片进行快速光响应曲线的拟合。结果表明: 幼叶和完全展开叶片在光合、荧光特性方面表现出明显的差异。与完全展开叶相比, 较低的叶绿素(Chl)含量和气孔导度(G_s)是幼叶较低净光合速率(P_n)的限制因素, 从而直接导致其光系统II (PSII)实际光化学效率(Φ_PSII)和光化学猝灭系数(q_P)的降低。在1800 μmol·m^-2·s^-1光强以下, 完全展开叶具有较强的围绕PSI循环的电子流(CEF), 有利于合成ATP, 是其具有较高光合能力的原因之一。相同光强下, 幼叶较低的光饱和点(LSP)更易受光抑制, 但其PSII原初光化学效率(F_v/F_m)的日变化幅度显著小于完全展开叶, 说明强光下幼叶通过类胡萝卜素(Car)猝灭单线态氧、光呼吸(P_r)、热耗散(NPQ)以及PSI-CEF等光保护机制能有效地耗散过剩的光能, 从而避免其光合机构发生光抑制。

关键词: 叶绿素荧光, 棉花, 气体交换, 完全展开叶, 光保护, 幼叶

Abstract:

Aims Differences of photosynthesis and chlorophyll fluorescence characteristics between flat young leaves (young leaves) and fully grown leaves (mature leaves) of cotton were compared to study the adaptation mechanisms of photoinhibition and photoprotection on young leaves under strong sunlight.

Methods We measured gas-exchange and chlorophyll fluorescence of young and mature leaves of cotton under field conditions and obtained rapid light curves with a Dual-PAM100 using an internal program.

Important findings There were significant differences between young and mature leaves in photosynthesis and fluorescence characteristics. Young leaves had lower chlorophyll content (Chl) and stomatal conductance (G_s), which accounted for lower net photosynthetic rate (P_n), which in turn resulted in lower actual photochemical efficiency (Φ_PSII) and photochemical quenching (q_P) in photosystem II (PSII). Below 1800 μmol·m^-2·s^-1, the higher cyclic electron flow (CEF) that was useful for composing ATP is one of the reasons for higher photosynthetic capacity in mature leaves. Lower light saturation point (LSP) was more susceptible to photoinhibition in young leaves under the same light; however, the magnitude of diurnal variation of its maximum photochemical efficiency of PSII (F_v/F_m) was significantly less than that of mature leaves. We suggest that photoprotective mechanisms, including direct quenching of reactive oxygen species by abundant carotenoids, photorespiration (P_r), non-photochemical quenching (NPQ) and the cyclic electron flow around PSI (PSI-CEF), can effectively dissipate the excess energy in young leaves to avoid photoinhibition under high irradiance.

Key words: chlorophyll fluorescence, cotton, gas-exchange, mature leaf, photoprotection, young leaf

李维, 张亚黎, 胡渊渊, 杨美森, 吴洁, 张旺锋. 田间条件下棉花幼叶光合特性及光保护机制. 植物生态学报, 2012, 36(7): 662-670. DOI: 10.3724/SP.J.1258.2012.00662

LI Wei, ZHANG Ya-Li, HU Yuan-Yuan, YANG Mei-Sen, WU Jie, ZHANG Wang-Feng. Research on the photoprotection and photosynthesis characteristics of young cotton leaves under field conditions. Chinese Journal of Plant Ecology, 2012, 36(7): 662-670. DOI: 10.3724/SP.J.1258.2012.00662

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https://www.plant-ecology.com/CN/Y2012/V36/I7/662

图/表 8

表1 棉花幼叶和完全展开叶光合色素含量、气体交换参数的变化(平均值±标准偏差)

Table 1 Changes of chlorophyll content and gas exchange parameter in young and mature leaves of cotton (mean ± SD)

叶型 Leaf type	叶绿素 Chl a + b (mg·dm^-2)	类胡萝卜素 Car (mg·dm^-2)	Car/Chl a + b	气孔导度 G_s (mol H₂O·m^-2·s^-1)	胞间CO₂浓度 C_i (μmol·mol^-1)	净光合速率 P_n (μmol CO₂·m^-2·s^-1)
YL	2.53 ± 0.07^b	0.41 ± 0.02^b	0.20 ± 0.01^a	0.45 ± 0.01^b	283.13 ± 0.23^a	21.09 ± 0.058 3^b
ML	4.3 ± 0.13^a	0.51 ± 0.05^a	0.15 + 0.01^b	0.64 ± 0.08^a	235.82 ± 1.17^b	37.61 ± 0.027 1^a

表2 棉花幼叶和完全展开叶中叶绿素荧光参数的比较(平均值±标准偏差) (PAR = 1957 μmol·m-2·s-1)

Table 2 Comparison of chlorophyll fluorescence parameters in young and mature leaves of cotton (mean ± SD) (PAR = 1957 μmol·m-2·s-1)

叶型 Leaf type	最大光化学效率 F_v/F_m	有效光化学效率 Φ_PSII	光化学猝灭系数 q_P	非光化学猝灭系数 NPQ
YL	0.812 ± 0.01^b	0.30 ± 0.02^b	0.52 ± 0.04^b	2.84 ± 0.03^a
ML	0.840 ± 0.05^a	0.35 ± 0.003^a	0.57 ± 0.01^a	2.15 ± 0.01^b

图1 棉花幼叶与完全展开叶的光合-光响应曲线(平均值±标准偏差)。PAR, 光合有效辐射; Pn, 净光合速率.

Fig. 1 Light response curves in young and mature leaves of cotton (mean ± SD). PAR, photosynthetic active radiation; Pn, net photosynthetic rate.

图2 棉花幼叶和完全展开叶Pn和PAR的日变化(平均值±标准偏差)。PAR, 光合有效辐射; Pn, 净光合速率。

Fig. 2 Diurnal variations of Pn and PAR in young and mature leaves of cotton (mean ± SD). PAR, photosynthetic active radiation; Pn, net photosynthetic rate.

图3 棉花幼叶和完全展开叶PSII最大光化学效率(Fv/Fm)的日变化(平均值±标准偏差)。

Fig. 3 Diurnal changes of maximum photochemical efficiency of PSII (Fv/Fm) in young and mature leaves of cotton (mean ± SD).

图4 1800 μmol·m-2·s-1光照下棉花幼叶和完全展开叶光呼吸(Pr)、光呼吸与总光合速率比例(Pr/Pm)的变化(平均值±标准偏差)。

Fig. 4 Variation of photorespiration (Pr) and ratio of photo- respiration/mass photosynthesis (Pr/Pm) in young and mature leaves of cotton under 1800 μmol·m-2·s-1 irradiance (mean ± SD).

图5 棉花幼叶和完全展开叶PSI和PSII中ETRs快速光响应曲线(平均值±标准偏差)。ETR(I)、ETR(II), 光系统I、光系统II电子传递速率; PAR, 光合有效辐射。

Fig. 5 Rapid light response curves of the ETRs around PSI and PSII in young and mature leaves of cotton (mean ± SD). ETR(I), ETR(II), apparent electron transport rate at PSI and PSII. PAR, photosynthetic active radiation.

图6 棉花幼叶和完全展开叶中PSII和PSI量子产量随光合有效辐射(PAR)升高的转化(平均值±标准偏差)。Y(I), 光系统I光化学量子产量; Y(II), 光系统II光化学量子产量; Y(ND), PSI中依赖于非光化学能力耗散的供体侧限制; Y(NA), PSI中依赖于非光化学能力耗散的受体侧限制; Y(NO), PSII中荧光和不依赖光的基础热耗散量子产量; Y(NPQ), PSII中ΔpH和叶黄素调节的热耗散量子产量。

Fig. 6 Conversion of quantum yields in PSII and PSI in young and mature leaves of cotton with increasing photosynthetic active radiation (PAR) (mean ± SD). Y(I), photochemical quantum yields in PSI; Y(II), photochemical quantum yields in PSII; Y(ND), quantum yield of non-photochemical energy dissipation in PSI due to donor side limitation; Y(NA), quantum yield of non-photochemical energy dissipation in PSI due to acceptor side limitation; Y(NO), quantum yield of fluorescence and light-independent constitution thermal dissipation; Y(NPQ), quantum yield of ΔpH-and xanthophyll-regulated thermal dissipation.

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