Perianths of 34 Dendrobium Sw. species and hybrids were examined to elucidate the roles of pigment distribution and shape of upper epidermal cells in determining color intensity, perception, and visual texture. Color intensity was determined by the spatial localization of anthocyanin in tissue layers, i.e., in the epidermal, subepidermal, and mesophyll layers, as well as by distribution of pigmented cells within the tissue layer. Anthocyanins were confined to the epidermal layer or subepidermal layer in flowers with low color intensity, whereas they were also in several layers of mesophyll in more intensely colored flowers. Striped patterns on the perianth were due to the restriction of pigment to cells surrounding the vascular bundles. Color perception is influenced by the presence or absence of carotenoids, which when present, were distributed in all cell layers. Anthocyanins in combination with carotenoids resulted in a variety of flower colors ranging from red, maroon, bronze to brown, depending on the relative location of the two pigments. Four types of epidermal cell shapes were identified in Dendrobium flowers: flat, dome, elongated dome, and papillate. Epidermal cell shape and cell packing in the mesophyll affected the visual texture. Petals and sepals with flat cells and a tightly packed mesophyll had a glossy texture, whereas dome cells and loosely packed mesophyll contributed a velvety texture. The labella in the majority of flowers examined had a complex epidermis with more than one epidermal cell shape, predominantly papillate epidermal cells.

No abstract

Both genome breeding (classical hybridisation) and molecular breeding approaches are used concurrently in our program for varietal development of Dendrobium and Anthurium as cut flowers and blooming potted plants. Two transgenic lines of anthurium 'Paradise Pink', engineered to produce the cecropinlike Shiva 1 lytic peptide, were able to significantly resist anthurium blight caused by Xanthomonas campestris pv. dieffenbachiae when compared to a standard resistant cultivar 'Kalapana'. However, disease severity could be significantly increased as well using the same transgene approach in a different genotype, 'Tropic Flame'. These lines were shown to be compatible with beneficial leaf-associated bacteria that can aid in suppressing blight, suggesting that use of GMO plants could be combined with beneficial bacteria to provide durable protection against anthurium blight disease. Blight resistance incorporated by hybridisation of A. andraeanum types with A. antioquiense also enhanced resistance, but the marketdesired heart-shaped spathe form was difficult to recover. Both gene and genome breeding for resistance occurred in a comparable time frame of less than 10 years. Dendrobium orchid breeding has benefit greatly from molecular tools in understanding genetic control of flower colour. A chemical survey of Dendrobium species and hybrids showed lavender cyanidin and peonidin to be the predominant anthocyanidin and orange pelargonidin to be rare. Our cloning and characterization of key anthocyanin biosynthetic genes such as of dihydroflavanol 4-reductase enables more productive hybridisation strategies to be implemented.

We studied the effect of NaCl salinity on the development of cellular photosynthesis using a green, photomixotrophic, cell-suspension culture of Alternanthera philoxeroides (Mart.) Griseb. For these cells, increasing the concentration of sucrose in the media produces a rapid drop in net photosynthetic rate, which recovers as sucrose is depleted from the media. This predictable recovery provides a simple system to examine cellular photosynthetic development. Cells, unadapted to high salinity, were transferred to nutrient media with 30 mM sucrose (Control) or nutrient media with 30 mM sucrose and 100 mM NaCl (Salt). A dramatic increase in the dark respiration rate of Control and Salt cells during the first 6 d of the experiment produced net oxygen consumption in the light. The high dark respiration rates during this period were accompanied by a decline in total Chl and the amounts of two photosynthetic proteins, the light harvesting Chl a/b binding protein of photosystem II (LHCP) and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco SSU). The dark respiration rate of Salt cells was greater than that of Control cells on days 4-8. After day 4, dark respiration rates decreased and net photosynthesis increased to stable values in both treatments at day 11 after media sucrose concentration reached a minimum. As dark respiration rates decreased and net photosynthetic rates increased, total Chl and the amounts of LHCP and rubisco SSU increased in both Control and Salt cells. The slower development of photosynthetic capacity in salt cells was correlated with a fresh weight that was 20% lower than that of control cells at the end of the experiment.

C0 2 assimilation and plant water status were measured in sand-culture-grown amputated coconut seedlings treated with three levels ofN, K, and CI and subjected to different soil water deficit conditions. Application of increased levels ofN and K enhanced the assimilation of C0 2 while individual and combined effects of N,K, and CI improved the water economy of coconut seedlings. Under the soil water deficit conditions, adequate supply ofN helped to maintain high leaf water potential by the accumulation of solutes like proline and sugars. Whereas, adequate supply of K and CI themselves acted as osmotica by increased accumulation of these nutrients in leaf tissues, although other solute concentrations such as those of sugars and proline were reduced. Our data show that maintenance of sufficient levels of N and K contribute to the growth of the coconut seedling through improved gaseous exchange, C0 2 assimilation and better partitioning of assimilated carbon into shoot and roots, potassium and C1 are further important for maintenance of water status of coconut seedlings by improved stomatal regulation, water uptake and osmotic adjustment of tissues under water deficit conditions.