黄瓜幼苗光合作用对高温胁迫的响应与适应

Response and adaptation of photosynthesis of cucumber seedlings to high temperature stress

以‘津优35号'黄瓜幼苗为试材,研究高温(HT:42℃/32℃)和亚高温(SHT:35℃/25℃)胁迫对黄瓜幼苗光合作用及生长量的影响.结果表明:高温、亚高温明显抑制幼苗生长.随着胁迫时间的延长,黄瓜幼苗叶片的光合速率(P_n)逐渐降低,胞间CO_2浓度(C_i)趋于升高,气孔导度(g_s)、蒸腾速率(T_r)、光呼吸速率(P_r)和暗呼吸速率(D_r)先上升后下降,高温、亚高温引起P_n降低的主要原因是非气孔限制.高温、亚高温可使黄瓜幼苗叶片的暗下光系统Ⅱ最大光化学效率(F_v/F_m)、光下实际光化学效率(Φ_(PSⅡ))、光化学猝灭系数(q_p)和电子传递效率(ETR)显著降低,初始荧光(F_o)和非化学猝灭系数(NPQ)逐渐升高.随着胁迫时间的延长,HT处理的RuBP羧化酶(RuBPCase)和Rubisco活化酶(RCA)活性及其mRNA表达量逐渐降低,而SHT处理的胁迫初期变化不大,3d后趋于降低;HT和SHT处理的景天庚酮糖-1,7-二磷酸酶(SBPase)和果糖-1,6-二磷酸醛缩酶(FBA)活性与mRNA表达均呈先升高后降低趋势.可见,适宜光强下短时亚高温处理黄瓜幼苗不会产生明显光抑制,高温胁迫会对其PSⅡ反应中心造成严重损伤;光合酶受高温胁迫诱导,但其诱导效应与温度升高幅度和高温持续时间有关.

Cucumber seedlings （ Cucumis sativus Jinyou 35） were used to study the effects of high temperature （I-IT： 42 ℃/32 ℃ ） and sub-high temperature （SI-IT： 35 ℃/25 ℃ ） on its photosyn- thesis and growth. The results showed that the growth of cucumber seedlings was dramatically inhibi- ted by the high and sub-high temperature stresses. The photosynthetic rate （Pn） was gradually re- duced, while intercellular CO2 concentration （Ci） was increased as heat stress lasted. Under heat stress, stomatal conductance （gs）, transpiration rate （Tr）, photorespiration rate （Pr） and dark respiration rate （Dr） showed a trend from rise to decline in cucumber seedlings, which implied that heat-induced decline of photosynthesis was mainly due to non-stomatal limitation. Maximal photo- chemical efficiency of PS Ⅱ in darkness （ Fv/Fm ）, actual photochemical efficiency （ ΦPSⅡ ）, pho- tochemical quenching （qp） and electron transport rate （ETR） were severely hampered, while ini- tial fluorescence （Fo） and non-chemical quenching （NPQ） were increased as a result of high and sub-high temperature stresses. Under extended high temperature stress, the activities of RuBP car- boxylase （RuBPCase） and Rubisco activase （RCA） as well as the mRNA abundance of Rubisco and RCA were in the trend of decrease, while they were reduced 3 days following the sub-high tem- perature treatment. The activities and mRNA expressions of sedoheptulose-1,7-bisphosphatase（SBPase） and fructose 1,6-bisphosphate aldolase （FBA） increased initially, but decreased after- wards under heat stress. Taken together, our data suggested that short-term sub-high temperature did not cause photoinhibition under optimal light conditions, however, high temperature led to se- vere damage to PS Ⅱ reaction center in cucumber duced by high temperature stress and the induction seedlings The photosynthetic enzymes were in- was affected by temperature and stress duration.