Herppich Werner B, Midgley Guy F, Herppich Margaretha, Tüffers Arnd, Veste Maik, Von Willert Dieter J
W. B. Herppich (corresponding author, e-mail
Physiol Plant. 1998 Jan;102(1):148-154. doi: 10.1034/j.1399-3054.1998.1020119.x.
The ability of photosynthesis and CAM to acclimate to low (220 µmol m s ; LL) and relatively high (550 µmol m s ; HL) photosynthetic photon flux densities (PPFD) was investigated in the CAM-cycling species Delosperma tradescantioides by means of CO gas exchange and chlorophyll fluorescence analysis. Furthermore, the influence of short-term drought on malic acid accumulation and the activity of photosystem II (PSII) was studied to assess the possible interactions between drought and the prevailing PPFD in this species. HL plants showed features of sun versus shade acclimation relative to LL plants. Nocturnal malic acid accumulation (Δ-malate) and leaf water content also tended to be higher in HL plants. Irrespective of the PPFD during growth, the weak Δ-malate doubled within 3 days of drought. Despite largely restricted CO uptake, photosynthetic activity as estimated from fluorescence analysis declined only ca 5%. After 7 days of drought, when plants showed CAM-idling and Δ-malate had decreased again, potential carbon assimilation was still ca 84% of that in well-watered plants and remained relatively constant throughout the day. Decarboxylation of malic acid accounted for ca 23% of potential assimilation assuming total oxidation of a maximum portion of this organic acid. Drought did not affect predawn maximum photochemical efficiency (F /F ). Nonphotochemical quenching (qN) increased (24%) in response to desiccation and resulted in a more or less constant reduction state of PSII. This increase in qN resulted mainly from the change in its fast-relaxing component (qNF), while the slow component (qNS) was significant only at or above saturating PPFD in both HL and LL plants. The photon response characteristics of PSII, which differed between LL and HL plants, were unaffected by short-term drought. Photon harvesting and photon use were always adjusted to guarantee a low reduction state of PSII. Results suggest that in both LL and HL plants CAM-cycling may help to stabilize photosynthesis but to a large extent by other means than simply providing internally derived CO .
通过气体交换和叶绿素荧光分析，研究了景天酸代谢循环植物紫叶佛甲草（Delosperma tradescantioides）的光合作用和景天酸代谢（CAM）适应低光合光子通量密度（PPFD，220 μmol m⁻² s⁻¹；低光，LL）和相对高光合光子通量密度（PPFD，550 μmol m⁻² s⁻¹；高光，HL）的能力。此外，研究了短期干旱对苹果酸积累和光系统II（PSII）活性的影响，以评估该物种干旱与当前PPFD之间可能的相互作用。与LL植物相比，HL植物表现出阳生植物与阴生植物适应的特征。HL植物夜间苹果酸积累量（Δ-苹果酸）和叶片含水量也往往更高。无论生长期间的PPFD如何，干旱3天内，较弱的Δ-苹果酸增加了一倍。尽管二氧化碳吸收在很大程度上受到限制，但荧光分析估计的光合活性仅下降约5%。干旱7天后，当植物表现出CAM空转且Δ-苹果酸再次下降时，潜在碳同化仍约为充分浇水植物的84%，并且全天保持相对恒定。假设该有机酸最大部分完全氧化，苹果酸脱羧占潜在同化的约23%。干旱不影响黎明前最大光化学效率（Fv/Fm）。非光化学猝灭（qN）响应干燥而增加（24%），并导致PSII或多或少处于恒定的还原状态。qN的这种增加主要源于其快速弛豫成分（qNF）的变化，而慢成分（qNS）仅在HL和LL植物的饱和PPFD及以上时才显著。LL和HL植物之间不同的PSII光子响应特征不受短期干旱的影响。光子捕获和光子利用总是被调整以保证PSII处于低还原状态。结果表明，在LL和HL植物中，CAM循环可能有助于稳定光合作用，但在很大程度上是通过不同于简单提供内源性二氧化碳的其他方式。
