Slow photosynthetic induction and low photosynthesis in Paphiopedilum armeniacum are related to its lack of guard cell chloroplast and peculiar stomatal anatomy.
Paphiopedilum and Cypripedium are close relatives in the subfamily Cypripedioideae. Cypripedium leaves contain guard cell chloroplasts, whereas Paphiopedilum do not. It is unclear whether the lack of guard cell chloroplasts affects photosynthetic induction, which is important for understory plants to utilize sunflecks. To understand the role of guard cell chloroplasts in photosynthetic induction of Paphiopedilum and Cypripedium, the stomatal anatomy and photosynthetic induction of Paphiopedilum armeniacum and Cypripedium flavum were investigated at different ratios of red to blue light. The highest stomatal opening and photosynthesis of intact leaves in P. armeniacum were induced by irradiance enriched with blue light. Its stomatal opening could be induced by red light 250 µmol m⁻² s⁻¹, but the magnitude of stomatal opening was lower than those at the other light qualities. However, the stomatal opening and photosynthesis of C. flavum were highly induced by mixed blue and red light rather than pure blue or red light. The two orchid species did not differ in stomatal density, but P. armeniacum had smaller stomatal size than C. flavum. The stomata of P. armeniacum were slightly sunken into the leaf epidermis, while C. flavum protruded above the leaf surface. The slower photosynthetic induction and lower photosynthetic rate of P. armeniacum than C. flavum were linked to the lack of guard cell chloroplasts and specific stomatal structure, which reflected an adaptation of Paphiopedilum to periodic water deficiency in limestone habitats. These results provide evidence for the morphological and physiological evolution of stomata relation for water conservation under natural selection.
Key Laboratory of Tropical Plant Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Yunnan 650223, China.
Shi-Bao
SB
Zhang
Zhi-Jie
ZJ
Guan
Wei
W
Chang
Hong
H
Hu
Qing
Q
Yin
Kun-Fang
KF
Cao
D000222:Adaptation, Physiological; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000528:radiation effects / Q000648:ultrastructure*; D008027:Light; D008856:Microscopy, Fluorescence; D029595:Orchidaceae / Q000502:physiology* / Q000528:radiation effects / Q000648:ultrastructure*; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects / Q000648:ultrastructure; D054046:Plant Stomata / Q000502:physiology / Q000528:radiation effects / Q000648:ultrastructure*; D011827:Radiation; D014867:Water / Q000378:metabolism
D002247:Carbon Isotopes; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide