Summary• Expression and regulation of Arabidopsis metallothionein (MT) genes were investigated to examine the functions of MTs in plants.• To examine the tissue-specific expression of MT genes, GUS reporter gene activity driven by promoters of MT1a , MT2a , MT2b and MT3 was analysed in transgenic plants.• MT1a and MT2b are expressed in the phloem of all organs and are copper (Cu)-inducible; MT2a and MT3 , by contrast, are expressed predominantly in mesophyll cells and are also induced by Cu in young leaves and at root tips. Expression of MT genes is highly induced by Cu in trichomes and increases during senescence. Expression of MT4 genes is restricted to seeds.• We propose that plant MTs have distinct functions in heavy metal homeostasis, especially for Cu: MT1a and MT2b are involved in the distribution of Cu via the phloem, while MT2a and MT3 chaperone excess metals in mesophyll cells and root tips. These functional capabilities may allow MTs to play a role in mobilization of metal ions from senescing leaves and the sequestration of excess metal ions in trichomes.

Effects of day-length and GA₃ on flowering and endogenous hormone levels during flowering process of Rhynchostylis gigantea (Lindl.) Ridl. were studied. Three-year-old plants were grown under natural condition and short-day (10 h of light) combined with GA₃ at 0 and 3,000 ppm, for 3 months. The results revealed that short-day could induce flower faster than natural condition around two weeks. Short-day and natural condition had effects on stem height and bush width, while GA₃ had effects only on number of leaves per plant. ABA in leaf seemed to decreased in all treatments accept under NC-GA₃, there was a peak of ABA at 30 days. Furthermore, under SD, GA₃ seemed to decrease ABA in leaf. In shoot, ABA concentration was increased during 0-30 days in all treatments, after that GA₃ seemed to decrease ABA concentration under NC, while the ABA concentration kept constancy under SD. On the other hand, GA₃ seemed to boot t-ZR up in leaf under SD, but did not in shoot, where GA₃ seemed to drop t-ZR. The reducing ABA and increasing t-ZR in leaf and/ or shoot might be related to flower buds initiation and early flowering of R. gigantea, especially, under SD.

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