Department of Seed Research, D'Arrigo California, 21777 Harris Road, Salinas, CA 93908, USA.
Biosero Inc., 9560 Waples Street, San Diego, CA 92121, USA.
Ann Bot. 2023 Nov 25;132(4):869-879. doi: 10.1093/aob/mcad070.
The relative contributions of C3 photosynthesis and crassulacean acid metabolism (CAM) during the earliest stages of development were investigated to assess how much each might contribute to cactus pear (Opuntia ficus-indica) productivity.
The developmental progression of C3 photosynthesis and CAM was assessed in seedlings and daughter cladodes of mature plants by titratable acidity, δ13C isotopic values and diel gas exchange measurements.
Nocturnal acidification was observed in seedling cladodes and cotyledons at the earliest stages of development and became highly significant by 75 days of development. Seedling cotyledons showed mean δ13C values of -21.4 and -17.1 ‰ at 30 and 100 days of age, respectively. Seedling cladodes showed mean δ13C values of -19.4 and -14.5 ‰ at 30 and 100 days of age, respectively. These values are typical of CAM plants. Net CO2 assimilation was negative, then occurred in both the day and the night, with nighttime fixation becoming predominant once the primary cladode reached 5 cm in size. Emergent daughter cladodes growing on mature plants showed nocturnal titratable acidity at the earliest stages of development, which became significant when daughter cladodes were >2.5-5 cm in height. Emergent daughter cladodes showed mean δ13C values of -14.5 to -15.6 ‰, typical of CAM plants. CO2 assimilation studies revealed that net CO2 uptake was negative in daughter cladodes <12 cm in length, but then exhibited net positive CO2 assimilation in both the day and the night, with net nocturnal CO2 assimilation predominating once the daughter cladode grew larger.
Developing O. ficus-indica primary and daughter cladodes begin as respiring sink tissues that transition directly to performing CAM once net positive CO2 fixation is observed. Overall, these results demonstrate that CAM is the primary form of photosynthetic carbon assimilation for O. ficus-indica even at the earliest stages of seedling or daughter cladode development.
为了评估 C3 光合作用和景天酸代谢（CAM）在仙人掌梨（Opuntia ficus-indica）发育早期的相对贡献，研究了这两种途径的发育进程。
通过滴定酸度、δ13C 同位素值和昼夜气体交换测量来评估幼苗和成熟植株的子营养体的 C3 光合作用和 CAM 的发育进程。
在发育的最早阶段，幼苗营养体和子叶出现夜间酸化现象，在发育 75 天时变得非常显著。幼苗子叶在 30 天和 100 天时的平均 δ13C 值分别为-21.4 和-17.1‰。幼苗营养体在 30 天和 100 天时的平均 δ13C 值分别为-19.4 和-14.5‰。这些值是典型的 CAM 植物。净 CO2 同化为负值，然后在白天和夜间均发生，一旦初生营养体长到 5cm 大小，夜间固定作用占主导地位。在成熟植株上生长的新生子营养体在发育的最早阶段就出现夜间可滴定酸度，当子营养体高度>2.5-5cm 时变得显著。新生子营养体的平均 δ13C 值为-14.5 至-15.6‰，是典型的 CAM 植物。CO2 同化研究表明，长度<12cm 的子营养体的净 CO2 摄取为负值，但随后在白天和夜间均表现出净正 CO2 同化，一旦子营养体变大，净夜间 CO2 同化占主导地位。
发育中的 O. ficus-indica 初生和子营养体最初是作为呼吸的汇组织，一旦观察到净正 CO2 固定，它们就直接过渡到执行 CAM。总的来说，这些结果表明，即使在幼苗或子营养体发育的最早阶段，CAM 也是 O. ficus-indica 光合作用碳同化的主要形式。
