To elucidate the physiological responses of rice plants to the essential mineral silicon (Si), we assessed the effects of treatments with Si, nitrogen (NH4NO3; ammonium nitrate), and calcium (CaCl2; calcium chloride), independently or in combination on mineral uptake rates and levels of the hormones abscisic acid (ABA), gibberellin (GA1) and jasmonic acid (JA). We found that nitrogen and calcium uptake was inhibited by Si application. However, solo application of nitrogen or calcium did not affect Si uptake. Compared to the untreated plants, the application of Si, NH4NO3 or CaCl2 increased the endogenous hormone levels in treated plants. In particular, the concentrations of GA1 and JA increased significantly after the application of Si or NH4NO3. The level of GA1 observed after a treatment (solo or combine) with Si, and NH4NO3 was higher than that of the control. By contrast, independent application of CaCl2 or a combined treatment with Si and CaCl2 did not alter GA1 levels. The highest level of GA1 was present in plants given a combination treatment of Si and NH4NO3. This effect was observed at all time points (6 h, 12 h and 24 h). Endogenous JA contents were higher in all treatments than the control. In particular, a combination treatment with Si and NH4NO3 significantly increased the JA levels in plants compared to other treatments at all time points. A small increase in JA levels was observed after 6 h in plants given the CaCl2 treatment. However, JA levels did not differ between plants given a CaCl2 treatment and controls after 12 h or 24 h of exposure. We conclude that treatment with CaCl2 alone does not affect endogenous JA levels in the short term. Endogenous ABA contents did not show any differences among the various treatments.

The metabolism of [14~textrmC ] ~textrmGA12 in the Chinese yam (Dioscorea opposita Thunb. var. Tsukune) was examined to determine the identification of endogenous gibberellins. [14~textrmC ] ~textrmGA12 was metabolized to ~textrmGA53 , ~textrmGA44 , ~textrmGA19 , ~textrmGA20 , ~textrmGA1 , ~textrmGA8 , ~textrmGA15 , ~textrmGA24 , ~textrmGA9 , ~textrmGA36 and ~textrmGA4 . Radioactivity of GAs in non C-13 hydroxylation route was five-fold higher than that of early C-13 hydroxylation in analyzed GA-metabolites. Radioactivity of ~textrmGA4 was always four times higher than that of ~textrmGA1 at every feeding time. ~textrmGA1 radioactivity has always a lower level to below 200 DPM. The major pathway of endogenous GA metabolism in seedlings of the Chinese yam might be the non C-13 hydroxylation pathway.