Abstract: Erjiufeng(EJF),a potassium-susceptible variety,and Yuanfengzao(YFZ),a potassium-tolerant variety,were used to study the effects of potassium deficiency on the photosynthetic rate and chlorophyll fluorescence parameters in rice seedlings.The net photosynthetic rate(Pn) and stomatal conductance(Gs) of the two varieties decreased significantly in the potassium deficient rice leaves.The content of the key enzyme of photosynthesis(Rubisco) was declined,whereas,the activity of the key enzyme of antioxidant-system(SOD) was increased in the potassium deficient rice leaves.The further study by chlorophyll fluorescence measurement showed that under potassium deficiency Fv/Fm,ФPSⅡ,qP and ETR were declined as time extended,indicating that the PSⅡ reaction center was damaged.Potassium deficiency also decreased the light-saturation points in both varieties.In that conditions,the light energy absorbed by PSⅡ was in excess of the need for assimilation,and a significant increase of NPQ in the stressed leaves of both varieties was detected,which indicated that the mechanism of thermal dissipation had been started to dissipate excessive light energy,and protected the plants from photoinhibition and photo-oxidation.Otherwise,it was also showed that YFZ was more tolerant to potassium deficiency compared with EJF,because YFZ could keep stronger photosynthetic ability with high resistance to(photoinhibition) under the potassium deficiency.Moreover,the photo-protection mechanism under potassium deficiency was also discussed.

Key words: rice, potassium deficiency, photosynthesis, chlorophyll fluorescence, enzyme activity, photoinhibition

摘要： 以钾敏感型品种二九丰和钾钝感型品种原丰早为材料，研究了缺钾对水稻光合和叶绿素荧光特性的影响以及光合防御机制，并对缺钾条件下的光合防御机制进行了讨论。在缺钾条件下，两品种的净光合速率(Pn)随气孔导度(Gs)的下降而下降；光合作用的关键酶Rubisco含量降低，而抗氧化酶系统的关键酶SOD活性显著上升。进一步的叶绿素荧光特性研究表明，随着钾胁迫时间的延长，缺钾水稻叶片中的 Fv/Fm、ФPSⅡ、qP及ETR均显著下降，说明PSⅡ反应中心受到伤害。缺钾也降低了水稻叶片的光饱和点，PSⅡ吸收的光能超过了光合作用所能利用的光能。缺钾叶片NPQ显著上升，说明钾胁迫下的水稻叶片通过启动热耗散机制耗散过剩的激发能，以减轻因PSⅡ吸收过多光能而引起的光抑制和光氧化从而保护光合机构免受伤害。从品种间的差异来看，原丰早在缺钾条件下，由于仍有较强的光合能力和抗光抑制能力，因此对缺钾有更强的耐性。

关键词: 水稻, 钾素缺乏, 光合作用, 叶绿素荧光, 酶活性, 光抑制