Comparative Growth, Morphology, and Anatomy of Easy- and Difficult-to-acclimatize Sea Oats (Uniola paniculata) Genotypes During In Vitro Culture and Ex Vitro Acclimatization

Growth and development of two sea oats (Uniola paniculata L.) genotypes with differing acclimatization capacities when transferred from in vitro to ex vitro greenhouse conditions were compared as a function of the duration of shoot multiplication and rooting stages. Anatomical and morphological development differed between genotypes in vitro. After 4, 8, and 12 weeks of Stage 11 culture, leaf length and shoot number were significantly greater for the easy-to-acclimatize genotype (EK 16-3) than the difficult-to-acclimatize genotype (EK 11-1). Shoot dry weights in both genotypes were greatest after 4 weeks culture. Browning and dying of tissue steadily increased with time. Shoot number per plantlet increased from Week 4 to 8 in both genotypes but decreased after 12 weeks. Once transferred to Stage III culture for 6 weeks, significant differences in root architecture and morphology were observed between the two genotypes. EK 16-3 plantlets developed short but numerous roots and "grass-like" leaves with fully expanded blades. Conversely, EK 11-1 plantlets developed few long roots and "lance-like" leaves, which were short, thick, and without expanded blades. Anatomical and morphological development during Stage III differed between culture duration and genotypes. Shoot and root dry weights of both genotypes increased during 3, 6, and 9 weeks of culture. Shoot dry weights of EK 16-3 plantlets were lower at 3 weeks but higher at 9 weeks than EK 11-1. Conversely, root dry weights were higher for EK 11-1 than for EK 16-3 plantlets throughout Stage III culture. Anatomical observations of EK 11-1 plantlets using light and electron microscopy correlated poor ex vitro acclimatization and poor survival with abnormal tissue organization, stomatal aperture blockage, and thylakoid membrane disruption.