Cytokinin and its Physiological Effects

2.7. Cytokinin and its Physiological Effects

Cytokinins are derivatives characterized by an ability to induce cell division in tissue culture, and the most common cytokinin base in plants is zeatin. It is biosynthesized through the biochemical modification of adenine and transported from roots to shoots. The effects of cytokinins include cell division, morphogenesis, growth of lateral buds, leaf expansion, delay leaf senescence, enhancement of stomatal opening in some species, chloroplast development accumulation of chlorophyll and conversion of ethioplasts into chloroplasts Davies, 2004. A synthetic cytokinin N 1 -2-Chloro-4-pyridyl- N 3 -phenylurea CPPU is known to be effective for enhancing fruit enlargement by stimulating cell division andor cell expansion in many kinds of fruits including Actinidia deliciosa kiwifruit Iwahori et al., 1988; Lewis et al., 1996; Cruz-Castillo et al., 2002. Jo et al. 2003 reported that a single application of CPPU at the concentration of 16 mg l -1 15 days after pollination was effective for increasing the fruit size of a local selection. The effectiveness of CPPU application on fruit development of Actinidia deliciosa kiwifruit was largely influenced by the time of application and concentration Cruz-Castillo et al., 1999. Antognozzi et al. 1996 found that spraying application of CPPU 20 ppm on Actinidia deliciosa A. Chev. fruitlets inside the canopy 2 weeks after full bloom influenced fruit growth soon after treatment and yield per vine were about 25 higher than the control. The chlorophyll content was higher in CPPU treated fruits. During storage, the differences in carbohydrate content disappeared and treated fruits performed as well as control ones, maintaining good quality for up to 6 months. Cruz-Castillo et al. 2002 reported that the cytokinin-active compound, N 1 -2-chloro-4-pyridyl- N 3 -phenylurea CPPU, applied at different flowering dates, affected final „Hayward‟ kiwifruit size. Recent research conducted by Kim et al. 2006 showed that fruit size of hardy Kiwifruit was increased and fruit weight was doubled when CPPU was applied at concentration of 5-10 mg l -1 and at 10 days after petal fall DAPF. Although a significant reduction in the concentrations of total soluble solids TSS, titratable acids TA and ascorbic acid AsA in the CPPU-treated fruits 12 was recorded, the TSSTA ratio and AsA content per fruit increased by the treatment. CPPU application at petal fall induced abnormally protruding fruit tip.

2.8. Cobalt Sulphate CoSO