Callus Induction and Plant Regeneration of Commercial Rice (Oryza sativa L.) Cultivars

Manipulation of agronomic traits at the cellular and molecular levels offers an efficient approach to enhance conventional breeding efforts for rice improvement. Plant regeneration protocols, required for biotechnological applications, have not yet been developed for a number of important rice cultivars. This study was conducted to establish a system for plant regeneration of elite rice cultivars adapted to the southern U.S.A. Callus was induced from dehusked grains of cultivars Alan, Katy, and LaGrue, on MS media containing 0.5, 2, and 4 mg L-1 2,4-D, with 0.5 mg L-1 kinetin or without kinetin. Plant regeneration was accomplished by transferring the callus to a hormone-free medium. Callus proliferation was influenced by 2,4-D, kinetin, and genotype in two-way interactions. The effects of these factors on embryogenesis and rhizogenesis was expressed in a three-way interaction. Depending upon the genotype up to 50% plant regeneration was obtained. In most cases treatments consisting of 0.5 to 2 mg L-1 2,4-D plus 0.5 mg L-1 kinetin produced the best callus proliferations with the highest embryogenic capacity. Regenerants grew to maturity in soil and produced viable seeds. The establishment of this regeneration system is essential for the development of a genetic transformation system for the aforementioned commercial rice cultivars

Special Issue on Date Palm Current Research II

Non peer reviewe

Silver ions disrupt K+ homeostasis and cellular integrity in intact barley (Hordeum vulgare L.) roots

The heavy metals silver, gold, and mercury can strongly inhibit aquaporin-mediated water flow across plant cell membranes, but critical examinations of their side effects are rare. Here, the short-lived radiotracer 42K is used to demonstrate that these metals, especially silver, profoundly change potassium homeostasis in roots of intact barley (Hordeum vulgare L.) plants, by altering unidirectional K+ fluxes. Doses as low as 5 μM AgNO3 rapidly reduced K+ influx to 5% that of controls, and brought about pronounced and immediate increases in K+ efflux, while higher doses of Au3+ and Hg2+ were required to produce similar responses. Reduced influx and enhanced efflux of K+ resulted in a net loss of >40% of root tissue K+ during a 15 min application of 500 μM AgNO3, comprising the entire cytosolic potassium pool and about a third of the vacuolar pool. Silver also brought about major losses of UV-absorbing compounds, total electrolytes, and NH4+. Co-application, with silver, of the channel blockers Cs+, TEA+, or Ca2+, did not affect the enhanced efflux, ruling out the involvement of outwardly rectifying ion channels. Taken together with an examination of propidium iodide staining under confocal microscopy, the results indicate that silver ions affect K+ homeostasis by directly inhibiting K+ influx at lower concentrations, and indirectly inhibiting K+ influx and enhancing K+ efflux, via membrane destruction, at higher concentrations. Ni2+, Cd2+, and Pb2+, three heavy metals not generally known to affect aquaporins, did not enhance K+ efflux or cause propidium iodide incorporation. The study reveals strong and previously unknown effects of major aquaporin inhibitors and recommends caution in their application