Siraitia Grosvenorii Plantlets Grown Photoautotrophically In Response To Light Intensity And Photoperiod

Siraitia grosvenorii is a perennial vine native to southern China in Guangxi province.The fruit with medical and edible value was called "saint fruit in the east".Recently,the demands of S.grosvenorii were increased greatly and the traditional propagation method was not supplied enough for the demands.Plant tissue culture is an effective propagation method,but conventional micropropagation method using sugar-containing medium often associated with some problems such as poor plantlets with large callus mass on the root base,and the low survival during acclimatization.Photoautotrophic micropropagation(PA) using a sugar-free medium and leafy explants,in which plantlets utilize CO₂ in the air as the sole carbon source,has several advantages over photomixotrophic micropropagation(PM) on producing high quality plantlets.The objectives of this study were:(1) Find an alternative way to produce S.grosvenorii plantlets with good quality and high survival percentage by comparing the plantlets grown under photomixotrophic and photoautotrophic conditions.(2) Investigate the effects of light intensity and photoperiod on growth, photosynthetic ability of the photoautotrophic plantlets.(3) Investigate the effects of sucrose and NAA on callus formation.In the first experiment,S.grosvenorii plantlets were cultured in vitro for 26 days on sucrose- and hormone-free Murashige and Skoog(MS) medium with four levels of photosynthetic photon flux density (PPFD),namely 25,50,100 or 200μmol·m^-2·s^-1,and a CO₂ concentration of 1000μmol·mol^-1 in the culture room(i.e.PA treatments).The control treatment was a photomixotrophic culture using MS medium containing sucrose and NAA with a CO₂ concentration of 400μmol·mol^-1 in the culture room,and a PPFD of 25μmol·m^-2·s^-1.Compared to the control,the PA plantlet had a well-developed rooting system,better shoot, greater chlorophyll content and higher electron transport rate,and the ex vitro survival percentage was increased by 31%.The large callus masses were observed on the shoot bases of control plantlets,whereas calluses did not form on the shoot bases of PA plantlets grown in sucrose- and hormone-free medium.The stronger light intensities increased the fresh and dry weight of plantlets.A PPFD of 100μmol·m^-2·s^-1 was more suitable for the growth of S.grosvenorii plantlets.Therefore,photoautotrophic plantlets grown at high light intensities would be better suited to the intense irradiance found in sunlight.The second experiment was conducted with photoperiod of 8,12,16 and 24 h d^-1 at a PPFD of 50μmol·m^-2·s^-1.S.grosvenorii plantlets were cultured in vitro on MS medium for 26 days.The results showed that the longer photoperiod shorted the stem length and increased the fresh and dry weight of plantlets.The photopedod of 16 h d^-1 was more suitable for the growth of S.grosvenorii plantlets with high multiplication rate and great photosynthetic capacity.Based on the results of the first experiment,an experiment was conducted to investigate the effects of sucrose and NAA on callus formation.This experiment included two PM and two PA treatments.The PM plantlets were cultured on sucrose-containing medium with NAA or without NAA.The PA plantlets were cultured on sucrose-free medium with NAA or without NAA.The result suggested that NAA and a lesser extent sucrose caused callus formation and influenced the number of roots.NAA with the presence or absence of sucrose in the medium stimulated callus formation and produced more adventitious roots with less lateral branching.Plantlets grown on sucrose- and NAA-free medium had no callus and produced more vigorous adventitious roots with well-developed lateral branching.Clearly,both sucrose and NAA stimulated callus formation,and were unnecessary for root growth of S.grosvenorii under photoautotrophic conditions.