Abscisic Acid and the Regulation of Water Loss in Plantlets of Brassica oleracea L. var. botrytisRegenerated Through Apical Meristem Culture

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Abstract
Water loss was studied in regenerated plantlets of Brassica oleracea var. botrytis cv. Currawong derived through apical meristem culture. Hardening of plantlets was eliminated by a single application of a polyvinyl resin (S600) sprayed immediately after transplanting. Plantlets sprayed with S600 had higher cuticular resistances than unsprayed plantlets; this treatment had no effect on stomatal resistance. Leaves formed during the culture period showed very little wax formation and using marked leaves it was found that only reduced levels of wax formed on these leaves even after transplanting. New leaves formed after transplanting, showed typical wax formation compared to seed grown plants. Abscisic acid (ABA) at 10−4 M applied as a leaf spray to transplants did not cause a substantial increase in stomatal resistance in leaves which had been initiated during the culture period. Leaves of seed-grown plants as well as leaves of plantlets formed after transplanting did respond to a leaf spray of ABA at 10−4 M by a large increase in stomatal resistance. Relative concentrations of K, Na, Ca, P, S and Mg in guard cells were calculated for each leaf type by X-ray micro-probe analysis. K/Na values decreased in the order: seedling > leaves formed after transplanting > leaves intiated during culture. A high positive correlation was also found between K/Na and K/P for the three leaf types. K:Mg and K:Ca ratios for leaves formed during culture were low in comparison to the values obtained for leaves formed after transplanting and seedlings for which the values were similar.