THE EFFECT OF SEED SIZE ON IN VITRO SEED GERMINATION, SEEDLING GROWTH AND TISSUE CULTURE RESPONSE OF CALLUS FROM MATURE EMBRYOS OF WHEAT (TRITICUM SP.)
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Seeds are found in different sizes in nature. Heavy seeds with larger amounts of nutritive reserves in their endosperms or cotyledons have higher germination rate and seedlings show greater emergence and faster growth rates than light seed. In the current study, seeds of two wheat (Triticum sp.) cultivars were designated as heavy or light according to their 1000-seed weights. Heavy and light seeds of two wheat cultivars (Durum wheat (Triticum durum Desf.) cv. 'Cakmak 79' and bread wheat (Triticum aestivum L.) cv. 'Bezostaja 1') were compared regarding in vitro germination percentage, seedling growth, callus induction and shoot regeneration. Seeds were germinated in 100x10 mm Petri dishes between filter papers moistened with 5 ml of distilled water. Seed germination percentage was determined after 4 days, whereas root and seedling lengths, and seedling fresh and dry weights were recorded 8 days after culture initiation. Mature embryos were removed from sterilized seed. For callus induction, embryos were cultured on MS medium having 3 mg l(-1) 2,4-D in darkness for 14 days at 24 +/- 1 degrees C. For shoot regeneration, calli were transferred to hormone-free MS medium and incubated at 24 +/- 1 degrees C under cool white fluorescent light (27 mu mol m(-2) s(-1)) with a 16h light/8h dark photoperiod. The highest values with respect to callus induction and shoot regeneration were again obtained from large seeds. After rooting of regenerated shoots and plantlet recovery, rooted plantlets were transferred to soil in pots for obtaining mature plants. Six weeks after, width of flag leaf, plantlet height, root length and total chlorophyll content of flag leaf were recorded. Again in the stage of plantlet growth in soil, figures obtained in plantlets grown from heavy seeds-originated shoots were found more successful.