晴天条件下光、温变化对苹果绿色果皮原初光化学反应的影响

利用快速叶绿素荧光诱导动力学和光谱反射测定技术，研究了晴天条件下，光、温变化对苹果绿色果皮原初光化学反应的影响.结果表明：一天内，随着光、温的增强，金冠苹果果皮在12:00-14:00存在较严重的光抑制.O-J-I-P荧光诱导曲线在300 μs处的相对可变荧光（W_k）几乎没有变化，说明果皮PSⅡ的放氧复合体（OEC）的活性在一天当中没有受到强光和高温的伤害；但是果皮捕获的激子将电子传递到电子传递链中Q_A-下游电子受体的概率（Ψ_o）从8:00-12:00逐渐下降，说明金冠果皮PSⅡ反应中心受体侧的功能受到抑制.强光降低了果皮单位面积上有活性的反应中心（RC/CS）的数量，导致单位反应中心吸收的光能（ABS/RC）增加.果皮的光化学反应（TR_o/RC）不能完全利用所吸收的光能，使单位反应中心的热耗散（DI_o/RC）增加.伴随着光抑制的出现，苹果果皮叶黄素库的脱环化比例增加，表明强光下，果皮启动了叶黄素循环机制，来耗散过剩光能，以减轻过剩光能对光合机构的进一步伤害；一天中，光强和温度的增加均可加重果皮的光抑制程度，但光强对果皮的影响程度显著大于温度对果皮的影响.

Responses of primary photochemical reactions in apple fruit peel to the changes of incident PFD and air temperature in sunny days

Taking Malus domestica Borkh as test object,this paper studied the primary photochemical reactions and xanthophyll cycle in its fruit peel in response to the diurnal changes of incident photon flux density(PFD)and air temperature in sunny days.With the increase of PFD and air temperature in a daily cycle,a severe photo-inhibition of the primary photochemical reactions in M.domestica fruit peel occurred from 12:00 to 14:00.The relative variable fluorescence at 300 μs of chlorophyll a fluorescence transient(W_k)did not change significantly through the day,which indicated that the activity of oxygen evolving complex(OEC)was not damaged by strong light and high temperature.However,the efficiency that a trapped exciton moved an electron into the electron transport chain beyond Q_A~-(Ψ_o)was reduced from 12:00 to 14:00,indicating that the acceptor side of PS Ⅱ in apple fruit peel was damaged.Strong light decreased the density of PS Ⅱ reaction centers per excited cross-section(RC/CS),which induced the increase of the energy absorption per active reaction center(ABS/RC).However,the excited energy was not able to be efficiently used via photochemical reaction(TR_o/RC),resulting in an increase in non-photochemical energy dissipation per active reaction center(DI_o/RC).Along with the appearance of photo-inhibition,the de-epoxidation level of xanthophyll pigment pool(PRI)increased markedly,showing that the xanthophyll cycle in fruit peel was enhanced by strong light to dissipate excess excitation energy to prevent photosynthetic apparatus from further damage.Both strong light and high temperature enhancedthe photo-inhibition in apple fruit peel,and the effect of strong light was significantly more prominent than that of high temperature during a day.