559 Preferential Allocation and Inducible Calcium Sinks in Leaf Primordia of Dracaena sanderiana Hort. Sander ex M.T. Mast (Dracaenaceae)

Abstract

We induced preferential allocation of Ca to two calcium oxalate (CO) sinks in immature leaf tissues of D. sanderiana: subepidermal extracellular deposits and intracellular raphides. Allocation was affected by exogenous Ca levels. Two groups of rooted cuttings were termed Ca-deficient and non-deficient. The first group consisted of cuttings that had been deprived of Ca for 18 months, and, the second, cuttings rooted under standard horticultural conditions. All plants were grown in liquid medium supplemented with 100 ppm of potassium nitrate and subjected to 0, 3, or 7mm Ca from calcium acetate. The most striking feature of Ca-deficient plants grown in 0 mm Ca was the absence of intracellular raphides in the leaf primordia. The largest number of intracellular raphides developed in Ca-deficient plants grown in 7 mm Ca. The number of extracellular crystals in Ca-deficient plants grown in Ca-supplemented solutions versus non-supplemented were similar, but crystals were considerably smaller in non-supplemented plants. Total number of extracellular crystals per epidermal cell did not differ significantly between plants in all treatments. This implies that nucleation sites are pre-determined and finite in number. In contrast, the number of intracellular raphides was highly variable. In terms of Ca prioritization, the extracellular crystals took precedence over intracellular raphides, and this was most obvious in Ca-deficient plants. The significance of this research is that the extracellular crystals represent Ca sinks with limited induction capacity compared to intracellular Ca sinks. Plants with genetic predisposition for intracellular CO crystal formation may be able to respond favorably to root environments with low Ca levels compared to species with limited capacity for intracellular CO deposition. Intracellular CO crystals, therefore, play an integral role in plant nutrition as Ca storage sinks.