Effects of GA3, BA, Thiamine and Ascorbic Acid on Some Morphological and Biochemical Characteristics of Periwinkle (Catharanthus roseus L.)

Catharanthus roseus (L.) belongs to Apocynaceae family is an important medicinal plant and also cultivated as an ornamental plant almost throughout the tropical and subtropical areas all over the world. Recently, the uses of natural substances are considered very helpful to improve plant growth and development. Application of plant growth regulators (PGRs) and vitamins are reported in many horticultural crops. Ascorbic acid is the most abundant antioxidant in plant which protects plant cells. This substance affects cell differentiation and growth. Now a day it is considered as a plant growth regulator. Thiamine or vitamin B1 is water soluble and one of the B complex vitamins. This study was conducted to investigate the effect of the ascorbic acid, thiamine, BA and GA on growth and biochemical parameters of periwinkle.
The experiment was perform as a completely randomized design with 5 replications at research greenhouse of Shahid Bahonar University of Kerman in 2014.The treatments used include spraying water (control), ascorbic acid 100 mg.l-1, gibberellic acid 100 mg.l-1, thiamine 100 mg.l-1, BA 200 mg. l-1 and combinations of two, three and four of them to determine the response of plants to these substances alone or in combination of them. When the seedlings become on 6-leavs stage, the first foliar spray was carried out. In other two steps was repeated with interval of 10 days. In this study, longevity of the flower, flower diameter, the number of lateral branches, branches length, fresh and dry weight, chlorophyll content and reduced sugars were measured. Chlorophyll content and reduced sugars were measured according to method of Somogy (1952) and Lichtenthder (1987), respectively.
The results showed that the effect of thiamine on the number of flowers was more pronounced than other substances. The lowest number of flowers per plant was found in plants treated with gibberellic acid. All growth promoter substances increased flower diameter. Combined application of BAwith gibberellic acid had more influence on this parameter than other treatments, and increase flower diameter about 25%. Ascorbic acid plays an important role in cell division, plasma membrane, proton pumps and enlargement cell. According to the theory of acidic growth, ascorbic acid weakens cell wall and increases cell enlargement. Among the applied treatments combination of banzyladenine, thiamine and ascorbic acid increased the number of lateral branches to 100%. Results showed that GA in all concentrations and combinations used in this experiment increased lateral branches length. Several reports in plants such as croton, hibiscus and pot marigold indicated that BA can increase the number of branches per plant. Therefore, BA is used to enhance branching and to reduce the total height of the plants. The highest fresh and dry weight were observed in plants treated with the combinations of BA, thiamine and ascorbic acid. Thiamine increased chlorophyll a content more than other substances. There was no significant difference between thiamine or thiamine combined with ascorbic acid treatment on chlorophyll b content. Thiamine in combinations with all the other treatments significantly improved carotenoids content compared to control. Chlorophyll plays a key role in plants for the absorption and utilization of light energy which used in photosynthesis. Therefore, effects of PGRs on chlorophyll biosynthesis or degradation influence directly on photosynthesis. Thiamine was reported that in some plants assist resynthesize of chlorophyll in plant without chlorophyll and increased growth and yield eventually. All the treatments significantly increased reducing sugar. Although all of the substances improved the amount of reducing sugar, the role of thiamine was more dramatic compared to other treatments. The greatest amount of reducing sugar 85.3 mg. g-1 fresh weight was observed in the combination of BA, thiamine and ascorbic acid. Thiamine is an essential part of the biosynthesis of pyrophosphate thiamine coenzyme which has an important role in carbohydrate metabolism. Application of vitamin c it was reported the increased soluble sugar in Chinese hibiscus.
Periwinkle is a bedding plant that the number of flowers and lateral branches is very important. BA with thiamine and ascorbic acid combination has the best effects on these traits and improved growth condition of it. On the other hand, application of gibberellic acid, either simple or combined with other materials, due to the excessive increase in plant height, led to the bending of the plant.