Photosynthesis and leaf structure of F1 hybrids between Cymbidium ensifolium (C3) and C. bicolor subsp. pubescens (CAM)

Abstract

Background and aims The introduction of crassulacean acid metabolism (CAM) into C3 crops has been considered as a means of improving water-use efficiency. In this study, we investigated photosynthetic and leaf structural traits in F1 hybrids between Cymbidium ensifolium (female C3 parent) and C. bicolor subsp. pubescens (male CAM parent) of the Orchidaceae. Methods Seven F1 hybrids produced through artificial pollination and in vitro culture were grown in a greenhouse with the parent plants. Structural, biochemical, and physiological traits involved in CAM in their leaves were investigated. Key results Cymbidium ensifolium accumulated very low levels of malate without diel fluctuation, whereas C. bicolor subsp. pubescens showed nocturnal accumulation and diurnal consumption of malate. The F1s also accumulated malate at night, but much less than C. bicolor subsp. pubescens. This feature was consistent with low nocturnal fixation of atmospheric CO2 in the F1s. δ 13C values of the F1s were intermediate between those of the parents. The leaf thickness was thicker in C. bicolor subsp. pubescens than in C. ensifolium, and those of the F1s were more similar to that of C. ensifolium. This was due to the difference in mesophyll cell size. The chloroplast coverage of mesophyll cell perimeter adjacent to intercellular air spaces of C. bicolor subsp. pubescens was lower than that of C. ensifolium, and those of the F1s were intermediate between them. Interestingly, one F1 had structural and physiological traits more similar to those of C. bicolor subsp. pubescens than the other F1s. Nevertheless, all F1s contained intermediate levels of phosphoenolpyruvate carboxylase but as much pyruvate,Pi dikinase as C. bicolor subsp. pubescens. Conclusions CAM traits were intricately inherited in the F1 hybrids, the level of CAM expression varied widely among F1 plants, and the CAM traits examined were not necessarily co-ordinately transmitted to the F1s.

Dissecting succulence: Crassulacean acid metabolism and hydraulic capacitance are independent adaptations in Clusia leaves

“…By fixing CO 2 at night, rather than during the day, CAM allows stomata to open when the atmosphere is cooler and more humid, which curtails transpirational water losses (Abraham et al, 2020; Winter et al, 2005). CAM requires large succulent chlorenchyma cells to provide sufficient space to store malic acid overnight (Barrera‐Zambrano et al, 2014; Males, 2018; Nelson et al, 2005; Töpfer et al, 2020; Yamaga‐Hatakeyama et al, 2022). However, succulence also performs a further, hydraulic function, by elevating bulk hydraulic capacitance (C FT ) (Borland et al, 2018; Ogburn & Edwards, 2012).…”

Predicting photosynthetic pathway from anatomy using machine learning

“…Recently, hybrids between species with different photosynthetic types have been used to study the relationships between CAM activity and anatomical traits. In both Yucca (Agavoideae, Asparagaceae; Heyduk et al, 2020) and Cymbidium (Epidendroideae, Orchidaceae; Yamaga-Hatakeyama et al, 2022), hybrids of C 3 9 CAM crosses possessed intermediate anatomical phenotypes and CAM activity. Within Yucca hybrid genotypes, however, the correlations between CAM activity and anatomy decreased in magnitude or disappeared entirely (Heyduk et al, 2020).…”

Predicting photosynthetic pathway from anatomy using machine learning

“…Recently, hybrids between species with different photosynthetic types have been used to study the relationships between CAM activity and anatomical traits. In both Yucca (Agavoideae, Asparagaceae) (Heyduk et al ., 2020) and Cymbidium (Orchidaceae) (Yamaga-Hatakeyama et al ., 2022), hybrids of C 3 x CAM crosses possessed intermediate anatomical phenotypes and CAM activity. Within Yucca hybrid genotypes, however, the correlations between CAM activity and anatomy decreased in magnitude or disappeared entirely (Heyduk et al ., 2020).…”