Ekelund N G
Mid Sweden University, Department of Applied Science, Härnösand, Sweden.
J Photochem Photobiol B. 2000 Mar;55(1):63-9. doi: 10.1016/s1011-1344(00)00029-4.
The effects of ultraviolet radiation (UV-A, 315-400 nm plus UV-B, 280-315 nm) on photosynthesis and 'light-enhanced dark respiration' (LEDR) in Euglena gracilis have been investigated by using light pulses (80 s) with increasing photon fluence rates of 59, 163, 600, 1180, 2080 and 3340 micromol m(-2) s(-1) and dark periods between the light pulses. LEDR is estimated as the maximum rate of oxygen consumption after a period of light minus the rate of oxygen consumption 30 s after the maximum rate. Without any exposure to UV radiation, the photosynthetic rate and LEDR increase with increasing photon fluence rate. After 20 and 40 min exposures to UV radiation, the photosynthetic rate and LEDR as functions of photon fluence rate are reduced. After a 20 min UV treatment respiration is greater than photosynthesis after the first light pulse of 59 micromol m(-2) s(-1) radiation, and especially at higher photon fluence rates photosynthesis is lower than the control values. The inhibitory effects of UV radiation on photosynthetic rate and LEDR are greater after a 40 min UV exposure than after a 20 min exposure. Only at 600 micromol m(-2) s(-1) is the rate of oxygen evolution greater than that of oxygen consumption after a 40 min UV treatment. Both photosynthetic rate and LEDR are inhibited by the photosynthetic inhibitor DCMU (10(-5) M) in a similar way, which indicates close regulatory interactions between photosynthesis and LEDR. Potassium cyanide (KCN) inhibits dark respiration more than it inhibits LEDR. Dark respiration is not affected to the same degree by UV radiation as are photosynthesis and LEDR.
通过使用光脉冲（80秒），并逐渐增加光子通量率至59、163、600、1180、2080和3340微摩尔·米⁻²·秒⁻¹，以及在光脉冲之间设置黑暗期，研究了紫外线辐射（UV-A，315 - 400纳米加上UV-B，280 - 315纳米）对纤细裸藻光合作用和“光增强暗呼吸”（LEDR）的影响。LEDR的估算方法是：一段时间光照后的最大耗氧率减去最大耗氧率后30秒的耗氧率。在未暴露于紫外线辐射的情况下，光合速率和LEDR随光子通量率的增加而增加。在暴露于紫外线辐射20分钟和40分钟后，作为光子通量率函数的光合速率和LEDR均降低。经过20分钟紫外线处理后，在59微摩尔·米⁻²·秒⁻¹辐射的第一个光脉冲后，呼吸作用大于光合作用，尤其是在较高光子通量率下，光合作用低于对照值。与20分钟暴露相比，40分钟紫外线暴露后，紫外线辐射对光合速率和LEDR的抑制作用更大。仅在40分钟紫外线处理后，在600微摩尔·米⁻²·秒⁻¹时氧气释放速率才大于氧气消耗速率。光合抑制剂DCMU（10⁻⁵M）以类似方式抑制光合速率和LEDR，这表明光合作用与LEDR之间存在密切的调节相互作用。氰化钾（KCN）对暗呼吸的抑制作用大于对LEDR的抑制作用。暗呼吸受紫外线辐射的影响程度与光合作用和LEDR不同。
