Studies on the improvement of calcium uptake into micropropagated potato

Various aspects of Ca2+ uptake into greenhouse-grown potato plants and micropropagated potato plantlets were examined, including the movement of Ca2+ into potato plants and tubers, identification of Ca-packing genotypes and assessment of the effect of improved medium Ca2+ level on different parameters such as plantlet growth, microtuber induction, yield and tissue Ca concentration. The effect of exogenous vitamin Ds and UV-elicited endogenous vitamin D synthesis on regulation of 45Ca 2+ uptake into plantlet shoots was also examined. Safranin dye was not as suitable as the tracer 45Ca2+ for monitoring translocation of Ca2+ into tubers. Uptake of Ca2+ into tubers occurred indirectly through the main basal roots and stolon roots and directly through tuber periderm. Liquid scintillation counting and flame atomic absorption spectrophotometry were used to screen six potato cultivars and two wild species for ability to take up Ca2+ from treatment solutions containing high or low Ca2+ levels. In vitro potato micropropagation, microtuberization, and tissue calcium concentration were compared for six cultivars when Murashige-Skoog basal medium Ca2+ level was increased from 3, to 5 or 15 mM. All aspects of growth including shoot dry weight, early microtuber induction, microtuber yield and tissue Ca concentration were improved when medium Ca2+ level was 15 mM. Cultivar Bintje was the most efficient genotype at accumulating Ca 2+ from treatment solutions or growth media containing high or low Ca2+ levels. Vitamin Ds improved 45Ca 2+ uptake into shoots of micropropagated potato plantlets and D 3 was more efficient in this regard than D2 or a combination of D3 and D2. Plantlets had increased 45Ca 2+ uptake when exposed to UV irradiation compared with the untreated control plantlets. Plantlets given a 24 hour interval in the dark after UV exposure had even greater 45Ca2+ uptake, suggesting that vitamin D, metabolites, specifically calcitriol (1, 25(OH)2-