No abstract

Cultivation of Spirulina platensis in Zarrouk media containing 0–20 g l-1 glucose was studied in a photobioreactor for 30 days using a light intensity of 3 klux. Various parameters were measured to evaluate the enhancement of cell performance with glucose such as cell number, osmolarity, membrane stability, biomass productivity, doubling time, stress intensity, stress tolerance, chlorophyll, protein, carbohydrates, and lipid contents. Based on the results, we concluded that S. platensis is able to grow and produce some ingredients in Zarrouk media containing up to 20 g l-1 of glucose which is the first to be reported. The cell concentration of the mixotrophic cultures (80 cells per mm2) corresponded well to the sum of the autotrophic cell concentrations (50 cells per mm2), showing that the addition of carbohydrate positively effects on the microalgae growth. The continuous operation supplemented with 0.5 g l-1 of glucose (G0.5) led to the maximum cell concentration about 9.06 g l-1 wet and 1.32 g l-1 dry weights. The highest tolerance index, specific growth rate, biomass productivity, cell division, osmolarity and membrane stability index were respectively 102.5%, 0.15 d-1, 0.04 g l-1d-1, 0.26 div d-1, 0.87 osmol kg-1 and 93.8%, obtained in the same treatment. Chlorophyll (6.7 % in G0; 0.046 g l-1 in G0.5), protein (79.9 % and 0.884 g l-1 in G0.5), carbohydrates (55.5% in G20; 0.492 g l-1 in G6) and lipid (53.3% in G10; 0.636 g l-1 in G0) percentages and yields were mostly enhanced in the mixotrophic condition. This study indicated that mixotrophic growth of S. platensis is useful for commercial biomass production.

Plants respond to water deficit through several mechanisms. Among which, plant hormones play an important role in induction to abiotic stress tolerance. To bring this issue closer, an experiment was conducted to examine whether salicylic acid (SA) and gibberellic acid (GA3) exogenous applications through foliar spray could alleviate detrimental effects of water deficit on Persian petunia. Treatments consisted of water stress in three levels: 100% field capacity (F.C.) as control, 50, and 25% F.C linked with different concentrations of GA3 and SA sprayed at four levels (0, 100, 200 and 300 mg L–1). Results showed that the dry and fresh biomass, leaf area, photosynthetic pigments levels, relative water content (RWC) and the total number of flowers were significantly (P≤0.01) reduced in response to water deficit. However, free proline concentration and root-to-shoot ratio significantly increased in stressed plants. Plants subjected to severe water stress (25% F.C.), exhibit about 66% stomatal conductance rate lower than the plants grown at 100% F.C. The results showed that SA-treated plants exhibited reduced negative effect of water stress on most of the qualitative and quantitative attributes compared to control, while GA3 application had little impact on studied traits. Importantly, stomatal conductance and RWC were improved in water-stressed plants treated with SA. Moreover, SA-treated plants produced more flowers at all water deficit levels compared to GA3 sprayed plants. It can be concluded that Persian petunia plants respond to water deficit through adaptive changes at biochemical and morphological levels and that adverse effects of water deficit could be alleviated by exogenous application of SA.