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匿名使用者 發問時間: 社會與文化語言 · 1 0 年前



Thus, in the absence of metabolic limitations, large decreases in gST under drought conditions will elicit proportionally greater decreases in photosynthesis than the same change in a C3 species. However, during prolonged or extreme drought, metabolic limitations to photosynthesis become more important than reduced gST (Lawlor, 2002; Ghannoum et al., 2003; Flexas et al., 2006). Decreased photosynthetic electron consumption is one important direct consequence of the drought-induced reduction in CO2 supply, causing a down-regulation of photosynthetic efficiency and increased requirement for additional electron sinks such as photorespiration and the Mehler reaction (Valentini et al., 1995; Cornic and Fresneau, 2002). Since the C4 pathway minimizes photorespiration (Osmond and Harris, 1971), drought is expected to reduce photochemical efficiency or increase alternative electron sinks to a greater extent than in C3 leaves. The South African grass Alloteropsis semialata was used as a model species for investigating the direct consequences of C4 pathway evolution on photosynthetic drought responses. A. semialata is unique in having C3 and C4 subspecies (Gibbs-Russell, 1983) and, used as a model species, thus avoids the confounding effects of phylogenetic distance usually encountered in C3/C4 comparisons. Preliminary analysis of the chloroplast DNA sequence ndhF suggests that the species is monophyletic, with a recent divergence between subspecies (DG Ibrahim, CP Osborne, TA Burke, unpublished data).

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  • 1 0 年前

    因此, 缺乏代謝限制的情況下, 與在一個C3 種類方面的相同的變化相比較,在在乾旱條件下的gST方面的大的減少將按比例引出在光合作用方面的更大的減少。 不過,在延長或者極端的乾旱期間,對光合作用的代謝限制變得比降低gST更重要(勞勒,2002; Ghannoum et al.,2003; Flexas et al.,2006)。 減少照片 合成電子消耗是乾旱引起的在CO2方面的削減的重要的直接的結果提供的一, 引起一次光合的效率的抑制對刺激的回應並且增加的另外的電子的要求象photorespiration 和Mehler 回應那樣下沉(Valentini et al., 1995 ; Cornic和Fresneau,2002)。 后來 al小路使photorespiration減到最小 (奧斯蒙德和哈裡斯, 1971 ) , 乾旱預計降低光化學效率或者增加其它電子下沉在相當程度上比在C3離開。 南非Alloteropsis semialata草地為在光合的乾旱回應上調查al小路演化的直接的結果被用作一個模型種類。 A. semial ata在有C3 和al亞種方面獨特(吉布玆-拉塞爾, 1983)和, 作為一個模型種類使用, 如此避免弄糊塗的通常在C3/C 4種比較遇到的phylogenetic 距離的效應。 Preli chloroplast脫氧核糖核酸順序ndhF的minary 分析建議物種是monophyletic, 由於在亞種之間的新近的分歧 (DG Ibrahim, CP奧斯本, TA巴爾克, 未發表過的數據)。

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